Photolithography is a key component of the industry's ability to continue to shrink devices according to Moore's Law, and any improvements immediately translate into large economic benefits for the industry. The relative contribution of the wetware, i.e., the photoresists and other chemicals used in the photolithography step, vs. the contribution of the exposure tool development is investigated by expressing the resist performance improvement as a numerical aperture (NA). Using this equivalent NA concept, it is shown that the contribution from resist improvements has historically outpaced that from stepper NA improvements. However, R&D expenditures for hardware and wetware have consistently been at greatly different levels. While part of that difference is probably intrinsic in the cost structure of the respective development efforts, it is suggested that the relative amount of spending on resist R&D has historically not been at a level that optimizes the overall return for the industry.

Spatially addressable immobilization of biomolecules and cells on patterned surfaces and microfabricated topographies has gained momentum in recent years. One major driving force behind this new impetus was the emergence of combinatorial DNA, protein and -soon- cell-based chips. The recent advances in New Generation Lithographies (NGL) as members with full rights in the panoply of microlithography techniques, automatically opened enormously large opportunities for microlithography engineering in the area of microarrays, which can be now seen as patterned chips. Despite all of these developments and related -yet to be fulfilled- opportunities, many other remained almost entirely unexplored. For instance, the intrinsic capability of the microlithographic materials -resists- to manipulate the surface properties via exposure to light has not been used for the patterning of biomolecules or cells. Also, other areas of classical microlithographic expertise, e.g. yield management, registration and alignment, and resolution enhancement are in many senses undiscovered by the bio-techniques for biomolecular and cellular patterning. This contribution will explore these hidden opportunities review the state of the art of biomolecular and cellular patterning through the glasses of a microlithographic engineer and it will explore the future areas where microlithography can contribute with the highest scientific, technical and commercial return-on-investment.

Our primary platform for 157 nm positive resists is built on a copolymer of t-butyl 2-trifluoromethylacrylate (TBTFMA) and norbornene bearing hexafluoroisopropanol (NBHFA) as an acid group, which is prepared by radical copolymerization. The radical copolymerization of 2-trifluoromethylacrylic monomers with norbornene derivatives has been found through reactivity ratio determination and in situ ¹H NMR analysis of kinetics to deviate from the terminal model but to follow the penultimate model. These copolymers typically contain >50 mol% TBTFMA, are lipophilic, and fail to provide good imaging due to poor wettability. Blending a homopolymer of NBHFA (optical density (OD)=1.7/micrometers at 157 nm) into the copolymers (OD=2.5-2.7/micrometers ) increases the hydrophilicity and reduces OD to 2.2-2.0/micrometers , providing high resolution images. Another platform we have identified is a copolymer of TBTFMA with vinyl ethers, which can be prepared by using a common radical initiator. Some of the vinyl ether copolymers are also homogeneously miscible with the NBHFA homopolymer and thus their OD and aqueous base development can be improved by blending.

Lithography with 157 nm fluorine lasers is rapidly emerging as the next evolutionary step in optical lithography and is clearly seen as the likely successor to 193 nm lithography. In fact, it may become the technology of choice for the sub-100-nm node features. The photoresists used for this technology will be required to be extendable to less than 70 nm. As has been demonstrated with the transition to shorter wavelengths in the past, the photoresist materials that were developed for the longer wavelength applications are too absorbent for practical use as high-resolution single layer resist with 157 nm radiation. This high absorbency will force the coated resist thicknesses to be well under 100 nm. Fluorine containing polymers have been demonstrated to be more transparent in this spectral region than pure hydrocarbon polymers. We have developed and evaluated a number of unique 4-hexafluoroisopropanol styrene based polymer systems which we previously termed FESCAP resists and have developed new acetal partially blocked 4-hexafluoroisopropanol styrene based copolymers. These resists can have absorbencies of under 3 micrometers ^-1 at 157 nm which could allow imaging to thicknesses of 150 nm. Our recent resist designs are shown to have imaging capability down to 70 nm with a 0.60 NA microstepper.

Several fluoro-substituted polymers consisting of acid cleavable methacryoic or cinnamic acid tert.-butyl ester compounds copolymerized with maleic acid anhydride derivatives were synthesized by radical copolymerization. Vacuum ultraviolet transmission measurements of the samples reveal absorbances down to 5micrometers ^-1 despite of the strongly absorbing anhydride moiety which serves as silylation anchor for the application of the Chemical Amplification of Resist Lines (CARL) process, one of the promising approaches for sub-90nm pattern fabrication. Some of the samples exhibit resolutions down to 110nm dense at 157nm exposure using an alternating phase shift mask. The feasibility of the CARL principle including the silylation reaction after development has been demonstrated with selected fluorinated polymer samples.

This paper describes characterization and lithographic results for one class of low absorbance fluoropolymers that were developed for use in 157 nm lithography. We discuss basic resist properties such as absorbance, hydrophobicity, thickness, resolution and profile for dense 1:1 and semi- dense 1:1.5-10 L/S features, reflection control and plasma etching resistance as a function of composition. Lithographic results were obtained on two types of substrates, silicon and SiON hardmask anti-reflectant. The results on the anti-reflectant were compared to those obtained from simulations using PROLITH. Some of the conclusions of this investigation are: Lower absorbance resists have higher hydrophobicity and better resolution; Resists with high hydrophobicity have very poor adhesion on SiOn, but have very good adhesion on Si and organic anti-reflectants; Only inorganic anti-reflectants have sufficient absorption to provide very low reflectance in <30nm thick films; 100 nm 1:1 L/S resolution is attained in 205 nm thick resist on Si at a resist absorption of 2.2/micrometers . The profile is tapered due to absorption; Adhesion to SiON has been achieved by polymer modification.

The synthesis and characterization of several new fluoropolymers designed for use in the formulation of photoresists for exposure at 157 nm will be described. The design of these resist platforms is based on learning from previously reported fluorine-containing materials. We have continued to explore anionic polymerizations, free radical polymerizations, metal-catalyzed addition polymerizations and metal-catalyzed copolymerizations with carbon monoxide in theses studies. The monomers were characterized by vacuum-UV (VUV) spectrometry and polymers characterized by variable angle spectroscopic ellipsometry (VASE). Resist formulations based on these polymers were exposed at the 157 nm wavelength to produce high-resolution images. The synthesis and structures of these new materials and the details of their processing will be presented.

Fluorocarbon based polymers have been identified as promising resist candidates for 157nm material design because of their relatively high transparency at this wavelength. This paper reports our recent progress toward developing 157nm resist materials based on transparent dissolution inhibitors. These 2 component resist systems have been prepared and preliminary imaging studies at 157nm are described. Several new approaches to incorporating these transparent monomers into functional polymers have been investigated and are described. The lithographic performance of some of these polymers is discussed.

Novel fluoropolymers having partially fluorinated monocyclic (5-membered and 6-membered ring) structure have been synthesized with radical cyclo-polymerization, which have C- F bond in the polymer main chain and also possess fluorocontaining acidic alcohol group. These polymers have excellent transparency lower than 1.0 μm^-1 at 157nm wave length. The number-average molecular weight (Mn) of the polymers is 4000 to 20000, the glass transition temperature (Tg) is 130 to 155 °C and the decomposition temperature (Td) is about 400 °C. Copolymerization reaction with the other monomers (ex. fluoroolefins,(meth)acrylates and vinyl esters) were also examined. The introduction of protecting group (ex. methoxylmethly, and t-butoxycarbonyl group) to alcohol units of the polymer can be applied before or after polymerization reaction. We also evaluated fundamental resist performances. These have excellent transparency of 0.5 to 1.5 μm^-1, good solubility in the standard alkaline solution (0.26N N-tetramethylammonium hydroxide aqueous solution) and relatively high sensitivities below than 10mJ/cm². The imaging results of the above fluoropolymer based positive- working resists are presented. Under 100-nm line and space pattern are delineated in 200-nm thick film by using the phase shift mask.

Hexafluoroisopropyl alcohol-functionalized acrylate monomers and their (co)polymers were prepared as photoresist platforms for 157 nm imaging. In order to balance transparency with other desirable traits such as etch resistance, we developed several copolymer systems. One is using 2-methyl adamantyl methacrylate as a comonomer, and the copolymer system showed better dissolution contrast compared to the copolymer with tetrahydropyranyl methacrylate without sacrificing transparency. To further improve the absorption properties at 157 nm, monomers having (alpha) -trifluoromethyl group were prepared and polymerized in anionic mechanism. The product polymer was unexpectedly transparent at 157 nm (A = 1.6 micrometers ^-1) in spite that all the monomers contain carbonyl group. The second system is the copolymer with p-t-butoxy-tetrafluorostyrene. p-Hydroxy-tetrafluorostyrene and p-t-butoxy-tetrafluorostyrene were polymerized radically using AIBN in good yield, and the two resulting polymers showed distinctive solubility differences in aqueous base solution. Finally, this paper describes the synthesis of new monomers having fluorine (e.g CF₃- group) in the vicinity of the double bond to improve transparency at 157 nm. Due to the lower electron density of the double bond, these monomers can be copolymerized with electron-rich vinyl monomers using radical initiators.

The design of 157 nm photoresists is a daunting task since air, water, and most organic compounds are opaque at this wavelength. Spectroscopic studies1 led to the observation that fluorinated hydrocarbons and siloxanes offer the best hope for the transparency that is necessary for the design of an effective 157nm photoresist, and these classes of materials have quickly become the prominent platforms for a variety of research activities in this field. There have been a number of authors that have suggested that negative resists have unique attributes for specific device applications. Numerous authors have discussed negative photoresists over the years. There are many uses for such materials at various levels in a semiconductor device. One such use is with complementary phase shift mask thus eliminating the need for a second exposure step. This paper reports our recent progress toward developing a negative 157nm resist materials based on fluoropolymers with crosslinkers that are transparent at 157nm. The authors will report on the synthesis of the polymers used in this work along with the crosslinkers and other additives used in the formulation of the photoresist. Imaging experiments at practical film thicknesses at 157nm with binary and strong phase shifting masks will be shown demonstrating imaging capabilities. Spectroscopic data demonstrating chemical mechanisms and material absorbance will be shown along with other process related information.

The copolymerization reaction between methyl cyanoacrylate (MCA) and a variety of cycloolefins (CO) was investigated. Cycololefin/cyanoacrylate (COCA) copolymers were obtained in good yields and with lithographically interesting molecular weights for all cycoolefins studied. Anionic MCA homopolymerization could be largely suppressed using acetic acid. Based on NMR data, the copolymerization may tend to a 1:1 CO:MCA incorporation ratio but further work with better suppression of the anionic component is needed to confirm this. Lithographic tests on copolymers of appropriately substituted norbornenes and MCA showed semi-dense and isolated line performance down to 90 nm.

The present paper describes a novel class of norbornene- based copolymers containing 7,7-dimethyloxepan-2-one acid labile groups. Poly(3-(bicyclo[2.2.1]hept-5-en-2- ylhydroxymethyl)-7,7-dimethyloxepan-2-one-co-5-((2- decahydronaphth-yl)oxycarbonyl)-norbornene-co-5-norbornene- 2-carboxxylic acid-co-maleic anhydride) was synthesized and evaluated as a potential chemically amplified resist for ArF lithography. The 7,7-dimethyloxepan-2-one group of the matrix polymer was readily cleaved and the carboxylic acid functionality was formed by acid-catalyzed ring-opening reaction in the exposed region after post-exposure bake. 0.12micrometers line and space patterns were obtained at a dose of 10 mJ cm^-2 with a conventional developer, 2.38 wt% tetramethylammonium hydroxide aqueous solution, using an ArF excimer laser stepper.

We have investigated new photoresist materials based on modified cycloolefin-maleic anhydride resin for 193nm lithography. Compared to COMA resin, the new resin offers several good properties such as UV transmittance, taper in pattern profile, PED stability and storage stability. The resist using the new resin showed good lithographic performances on ArF exposure tool. So, we obtained good hole patterns below 90nm with condition of exposure: PAS 5500/900 full field scanner, resist thickness: 320nm, development: 2.38% TMAH, for 40sec., Illumination: 0.61NA, conventional SOB: 110 degree(s)C/90sec, PEB:130 degree(s)C/90sec, on BARC. In this paper we will report on the properties of new polymer and will show the contact hole pattern that demonstrate progress in these areas.

A high performance 193 nm resist has been developed from a novel hybrid copolymer based on a cycloolefin-maleic anhydride and methacrylate (COMA/Methacrylate) polymer system. A variety of copolymers have been synthesized from t-butyl norbornene carboxylate (BNC), t-butyl tetracyclo [4.4.0.1.^2,61^7,10]dodec-8-ene-3-carboxylate (BTCDC), and 5-[2-trifluoromethyl-2,1,1-trifluoro-2-hydroxypropyl]-2- norbornene (F1) with different types of methacrylate monomers and maleic anhydride (MA). The effect of the monomers and the ratio of monomers in the copolymer on lithographic performance and etch rate has been studied. Lithographic evaluation of some of these polymers has shown resolution down to 80 nm using conventional 193 nm illumination and standard development conditions, particularly for semi and fully isolated lines. This paper will report the chemistry of the polymer platform and relative advantages of having certain monomers in terms of lithographic performance and line edge roughness.

Crown ether derivatives are composed of multi-ethyleneoxy units and have an electron rich cavity that can accommodate a proton. We have broadly investigated the effect of lone pair electrons of accumulated oxygen. First, we studied whether these crown compounds can control acid diffusion or not. Second, we synthesized monomers containing cyclic multi-ethyleneoxy units and studied their effect in polymers. Finally, we compared them with amines. Crown either, 18-crown-6, has a proper cavity to capture a proton by hydrogen bonding and actually had enough basicity to control acid diffusion. These studies show that crown ether derivatives can replace amines as a bases to restrain acid diffusion.

ArF lithography is the current ramp-up technology for next generation devices. However, some manufacturing issues still remain when considering the resist design for the most advanced processes. Several polymer platforms have been proposed, among them, Methacrylate, CycloOlefin-alt Maleic Anhydride, and even pure Cyclo-Olefin. More recently, Vinyl-Ether Maleic Anhydride (VEMA) polymers have demonstrated potential in terms of both lithographic properties and etch capabilities. In this paper, the evaluation of some advanced samples of VEMA resists for 120nm and sub-120 nm gate applications will be discussed. The various criteria investigated for this study were; focus and exposure latitude for 120 and 100 nm lines (1/1.5 L/S to isolated lines), Iso-Dense bias, Line End Shortening (LES), Line Edge Roughness (LER), masking linearity, BARC compatibility, sensitivity to PEB temperature and electron beam, and finally etch resistance. Additionally some process optimizations were tested in order to minimize Iso-Dense Bias and the LER of the resists (See figure 1). In fact, this latter parameter has been a major focus of this work in improving the VEMA resist chemistry since its introduction and preparing it for device manufacture. The results obtained when varying parameters such as resist formulation, development conditions will be reported and so will demonstrate the current maturity of the most advanced VEMA samples.

We have studied 193 nm contact hole resists in view of resist components, process conditions and optical settings. Sidewall roughness was improved by optimizing photoacid generators. Side lobes were eliminated by applying higher post exposure bake temperature or modification of polymers. The influence of optical settings, types of masks and mask bias was discussed with simulation and lithographic results and guidelines for better resolution and iso-dense bias were proposed. The optimized formulation, AZAX1050P has a high resolution combined with a large depth of focus and an iso- dense overlap window (130 nm(NA=0.63) DOF 0.38micrometers Exposure latitude 10%).

As resist feature sizes have decreased and the performance demands on chemically amplified photoresists have increased the role of the photoacid generator (PAG) in determining overall resist performance has become increasingly apparent. Over the past 20 years a variety of different types of PAG's have been introduced as researchers have sought to optimize properties such as acid strength, acid volatility, diffusion length, wavelength response, solubility etc. PAGs that produce very strong organic acids are widely used, in part because of requirements for high photospeed resists. Most of these acid generators are based on perfluoroalkyl sulfonic acid based onium salts. In an effort to identify and characterize alternative PAGs we have investigated the performance of a variety of photoacid generators that are not based on sulfonic acids. In this report we will describe the relative reactivities of these PAGs under a variety of exposure wavelengths and processing conditions including acid diffusion proprieties and photospeed measurements.

The lithographic performance of a new class of onium type photo acid generators (PAGs) developed by 3M Company has been evaluated using standard hybrid/acetal and ESCAP type DUV (248 nm) photoresist formulations. The new PAGs produce perfluoroalkyl sulfonylimides or sulfonylmethides with superacidic properties matching or exceeding the acid strength of commonly known perfluoroalkyl sulfonic acids, such as trifluoromethane sulfonic acid. The direct comparison of near commercial photoresist formulations containing onium perfluoroalkyl sulfonates with identical materials using equimolar amounts of the new PAGs revealed that the new 3M PAGs give rise to almost identical lithographic properties, such as resolution, DOF, and exposure latitude. In addition, secondary properties such as photoresist stability, delay stability, or line edge roughness are almost equivalent, and thus the new PAGs are considered as suitable candidates used for the manufacturing of high volume production photoresists.

The advent of 193nm lithography has stimulated the search for novel photocid generators (PAGs) with increased transparency at 193nm. This need for more transparency stems from the use of phenyl groups in the classic 248nm PAGs, such as triphenylsulfonium salts. Unfortunately for 193nm resist development, the phenyl group is highly absorbing at that wavelength, thereby severely restricting the PAG formulation space. It has not yet been pointed out, however, that photoacid generation efficiency has also become more important for 193nm systems. The reason is that 193 polymers cannot sensitize the PAG, as is the case for 248nm phenolic systems, i.e. the light absorbed by the polymer does not contribute to acid generation. Furthermore, the photoacid generation efficiency of sulfonium PAGs drops considerably when going from 248nm to 193nm. Thus, the ability to quantify the photoefficiency of a new PAG quickly becomes key to successful new 193nm PAG development. While there are many ways to determine the quantum yield of photoacid generation ((Phi) ) of PAGs, they are usually time and labor-intensive. Therefore, in the first part of this paper, we describe the P-parameter as a fast, simple and more practical way than the quantum yield, (Phi) to characterize the photoefficiency of a PAG. Results for a number of sulfonium PAGs at both 248 and 193nm are determined this way, and the observed trends are discussed. In the second part of this work we investigate how lithographic performance is impacted by those two parameters. A transparency/efficiency matrix of nine PAGs is evaluated in a 193nm standard resist formulation. The results indicate that the PAGs with a combination of high efficiency and transparency yield the best lithographic results, underlining the importance of efficiency as a key parameter in 193nm PAG design.

Fluoropolymers are key materials for single-layer resists in 157-nm lithography. We investigated main-chain fluorinated polymers and found that the incorporation of fluorine atoms into polymer backbones such as that in tetrafluoroethylene and monocyclic monomers reduced their absorption coefficients to less than 1 micrometers ^-1 at 157 nm, while side-chain fluorinated polymers had absorption coefficients of 2 to 3 micrometers ^-1. The main-chain fluorinated polymers also showed good solubility in a standard alkaline developer and their dry-etching resistance was comparable to that of a ArF resist. Prototype positive-tone resists had good sensitivities of less than 10 mJ/cm², and they exhibited fine imaging resolution with 80-nm dense patterns. The resists can be used to obtain 300-nm-thick films.

We designed platforms for a 157-nm resist polymer that have both high transparency and high etch resistance. We measured the etching rate of various fluoropolymers under the conditions of poly etch and oxide etch processes. Most of the fluoropolymers showed good correlation with an etching rate ratio and a value of (N_C-N_O-N_F) / N_T (N_T, N_C, N_O, and N_F was the number of total atoms, carbon, oxygen, and fluorine atom in a monomer unit, respectively). This index, (N_C-N_O-N_F) / N_T was named IERF (index for etch resistance of fluoropolymers). It became easy to design a fluoropolymer that has high etch resistance using this index. Moreover, the acrylic polymer that has a particular kind of fluorinated alicyclic compound in its side chain was not in the above-mentioned correlation, however, it was found to have higher etch resistance. Base upon these results, two platforms were built, one of the copolymer type with polyacrylate (PA) and polystyrene (PS), the other of the copolymer type with PA and polycycloolefin (PC). Resists belonging to the two platforms were made and a high resolution of 85 nm or less was obtained by using the Microstepper (NA0.6, (sigma) 0.3, alternating phase shift mask). These resists showed a slightly higher etch resistance as compared with a COMA (cycloolefin-maleic anhydride) type resist with comparatively high etch resistance even during the ArF resist.

To accomplish minimizing feature size to sub 70nm, 157nm photolithography becomes a strong candidate as a new lithographic technology. However, there is a strong need for new photoresists, which are transparent to 157nm light sources. To have a transparency for 157nm light source, fluorinated organic polymers are studied intensively. As a result, there are some of polymers that have absorbance of 2/micrometers . However, in spite of this low absorbance of 2micrometers , resist profile simulation tells us bulk slope problems. TO obtain more than 85 degree of resist pattern profile, the absorbance of resist must be 1.2micrometers . The absorbance of 1.2micrometers is very difficult target to accomplish. To overcome this light absorption problem, we have developed amine gradient resist process (AGRP) which gives an amine gradient in photoresist and can make a vertical profile though the resist has poor transparency to light source. By adding chromophore that absorbs 193nm wavelength, we made model ArF resists of which absorbances were from 1.2micrometers to 4micrometers . By patterning experiment using these model resists and 193nm scanner, we could confirm that the resist absorbance should be lower than 1.2micrometers to obtain vertical profile pattern at the resist thickness of 150nm. But if we use AGRP, the absorbance of 2.5micrometers will be enough value for the vertical profile pattern. So we could conclude that by combining 157nm resists and amine gradient process, resist absorbance problem in 157nm photolithography could be solved. We also studied for the resist properties that were suitable for AGRP.

We describe and evaluate three kinds of pattern transfer processes that are suitable for 157-nm lithography. These transfer processes are 1) a hard mask (HM) process using SiO as a HM material, 2) a HM process using an organic bottom anti-reflecting coating (BARC)/SiN structure, and 3) a bi- layer process using a silicon-containing resist and an organic film as the bottom layer. In all of these processes, the underlayer fo the resist acts as an anti-reflecting layer. For the HM processes, we patterned a newly developed fluorine-containing resist using a 157-nm microstepper, and transferred the resist patterns to the hard mask by reactive ion etching (RIE) with minimal critical dimension shift. Using the HM pattern, we then fabricated a 65nm Wsi/poly-Si gate pattern using a high-NA microstepper (NA=0.85). With the bi-layer process, we transferred a 60nm 1:1 lines and spaces pattern of a newly developed silicon-containing resist to a 300nm-thick organic film by RIE. The fabrication of a 65nm 1:1 gate pattern and 60nm 1:1 organic film patten clearly demonstrated that 157-nm lithography is the best candidate for fabricating sub-70nm node devices.

A fabrication technique recently developed at Georgia Institute of Technology involving thermally sacrificial polymeric materials allows for fabrication of microfluidic devices with greater degrees of functionality (i.e., fully integrated, complex, multi-level fluidic systems with functional valves, pumping systems, and other micro- electromechanical system [MEMS] components). In this method, thermally sacrificial polymers are coated onto a substrate and patterned into the shape of the desired channels and devices. These polymeric structures are then over-coated with a permanent structural material such as an inorganic glass or polymer. These steps can be repeated to produce complex, three-dimensional systems. Once the device build-up is complete, the structure is heated to a temperature at which the sacrificial polymer slowly decomposes, thus leaving behind the desired open-channeled structures. This process was first developed using functionalized polynorbornenes that decompose at temperatures in the range of 425 degree(s)C. In order to make this approach compatible with a wider range of substrates and structural materials, polymers with lower decomposition temperatures were desired. Polycarbonates were identified as a class of polymers with the desired lower decomposition temperatures (200- 300 degree(s)C). A disadvantage of commercially available polycarbonates, like poly (propylene carbonate), is that they have low glass transition temperatures (T_gapproximately equals 40 degree(s)C). This introduces several problems, including pattern deformation at elevated processing temperatures. Also, a significant number of process steps are required to pattern the channel structures using simple polymer materials. Therefore, this paper will describe recent results of work on photodefinable polycarbonates with improved thermal properties. Utilizing a polymer that can be patterned directly by conventional lithography greatly simplifies the fabrication process and eliminates the need for the plasma etch steps required in the original process. Results of the synthesis and characterization of polycarbonates patterned with the use of a photoacid generator, thus exploiting the acid-catalyzed thermolysis of polycarbonates, will be presented.

Alkaline soluble maleimide based tetrapolymers which were prepared by free radical copolymerization are found to be suitable for use as non-imaginable resists in multilevel photolithographic processing. These materials offer widely variable undercut rates because of the ability to vary the composition during free radical polymerization and show little or no scumming when used in lift-off resist. This new polymer system may also be used as the base soluble resin in a photoresist formulation or a base soluble antiflective coating composition as well as used in making lift-off resists.

An ever increasing need exists for thick resist layers in the processing of MEMS and for advanced packaging. Applications in the MEMS field include bulk micromachining, surface micromachining, and the actual creating of active device structures. For advanced packaging, the applications are in redistribution and passivation layers, and micromolds for metal bumps. The various applications can require resist layer thicknesses up to and exceeding 1000 micrometers . In order to properly achieve these thicknesses, appropriate coating materials were developed by manufacturers. These materials include AZ P4620, Shipley SPR220, AZ PLP100XT, JSR THB 611P, and SU-8. Finally, equipment was developed to handle these materials, in the form of specialized coating equipment and contact/proximity aligners.

Low-k₁ imaging, high-NA optics, pattern collapse, and the absorption of resist materials in 157-nm and EUV lithographies are driving down the thickness of the photoresist layer in integrated circuit fabrication processes. Although devices and test structures have been successfully fabricated with resist films thinner than 160 nm on various levels, the fabrication of working devices with high yield using ultrathin resist (UTR) integrations on multiple device layers has yet to be demonstrated. In the present work, gates have been patterned with 140-nm thick resist films with 10-15 defects per wafer, none of which are specific to the UTR process. Similar UTR gates were also patterned over 80-nm steps with no defects associated with the topography. The UTR NMOS transistors in this work have 10 pA/micrometers leakage and 400 (mu) A/micrometers drive currents, but the PMOS transistors do not perform as well. The line-edge roughness (LER) is 5-8 nm 3(sigma) depending upon exposure mask (binary vs. PSM) and substrate. Etching into 100 nm of crystalline Si reduces the LER to 4-7 nm 3(sigma) . The power spectral densities of the roughness have a Lorentzian shape, and most of the roughness occurs over length scales larger than 100 nm. Contact chains with electrical characteristics comparable to standard processes were fabricated with 120-nm thick resist films. Polysilicon as thick as 150 nm was etched successfully with 80-nm thick resist films and hardmasks.

The lithographic performance of a single layer 193nm resist platform, Sumitomo PAR707, was evaluated for 100nm node patterns for thicknesses ranging from 313nm to 60nm. We first demonstrated that the standard resist formulation could not be used for sub-200nm thicknesses because of unacceptable line edge roughness (LER). We then evaluated the influence of the concentration of photo acid generator (PAG) in the resist formulation of LER over the thickness range of 313nm to 60nm. High PAG loading was found to decrease LER significantly for sub-200nm thicknesses. Using the optimal formulation for minimal LER for a given thickness, process latitudes for 100nm node patterns were determined. The overall dose-focus latitudes were found to remain very close for all thicknesses, with slightly larger latitude for thicker imaging layers.

Investigations of the dissolution behavior of the IBM V2 193 nm methacrylate photoresist polymer and its formulations using the recently developed impedance quartz-crystal microbalance methodology unequivocally confirm the presence of an interfacial gel layer during dissolution. All aspects of V2 dissolution behavior are strong functions of resist formulation, developer concentration, and resist film thermal history. The dissolution process is characterized by (a) a complex gel layer evolution regime; (b) a steady-state dissolution regime; and (c) a final gel layer decay regime upon depletion of solid resist film. The gel layer evolution regime exhibits a linear increase in mass and development of a lossy film component (interfacial gel) associated with developer uptake. The transition from this regime to the steady-state dissolution regime is accompanied by reproducible correlated excursions in frequency shift and film resistance measurements. The steady-state dissolution regime exhibits a linear decrease in mass and fairly constant gel-layer; upon depletion of the solid resist film, the gel layer decays. Absolute and relative metrics for phenomena occurring in these regimes can be extracted from the dissolution data and are useful for analyzing the influences of formulation components on dissolution and gelation behaviors. Formulation components explored include a photoacid generator, bis(t-butylphenyliodonium) perfluorobutanesulfonate, and common dissolution modifiers, t-butyl lithocholate and lithocholic acid. Film thermal history impacts dissolution phenomena strongly and appears to reflect both polymer annealing and residual solvent evaporation effects.

The use of chemically amplified photoresists for the fabrication of sub-100 nm features will require spatial control with nanometer level resolution. To reach this goal, a detailed understanding of the complex reaction-diffusion mechanisms at these length scales is needed and will require high spatial resolution measurements. In particular, few experimental methods can directly measure the spatial evolution of the deprotection reaction front and correlate it with the developed structure. In this work, we demonstrate the complementary use of neutron (NR) and x-ray (XR) reflectometry to measure the reaction front profile with nanometer resolution. Using a bilayer geometry with a lower deuterium-substituted poly(tert-butoxycarboxystyrene) (d-PBOCSt) layer and an upper poly(hydroxystyrene) (PHOSt) layer loaded with a photoacid generator (PAG), we directly measure the spatial evolution of the reaction front. We show that the reaction front profile is broader than the initial interface after a post-exposure bake and the compositional profile changes upon development in an aqueous base solution. We also directly correlate the final developed structure with the reaction front profile. The spatial detail enabled by this general methodology can be used to differentiate between and evaluate quantitatively reaction-diffusion models.

Water is known to play a key role in the solubility switching reaction of novolac-diazonaphthoquinone photoresists and certain chemically amplified resists. In order to quantitatively study these effects, an environmental chamber was built in which the % RH could be controlled while the extent of acid catalyzed deprotection was monitored during the post exposure bake by reflectance FTIR spectroscopy. The extent of acid catalyzed deprotection of tBOC, KRS-XE, UV6, and a tBOC-poly(hydroxystyrene) copolymer have been measured as a function of time over a range of 0-60 % RH. For tBOC, the deprotection reaction rate was found to slow considerably as the %RH was increased. Also, the relative film shrinkage varied considerably with varying % RH. Several possible mechanisms for the dependence of the reaction rate and thickness loss on % RH were investigated. For KRS-XE, the deprotection reaction kinetics were found to increase as the % RH was increased, which was an expected trend. For UV6 and the tBOC-PHOST copolymer, no change in deprotection reaction rate was observed with changes in %RH.

Surface properties of photo resist lines are of particular interest in future semiconductor applications. Current hot topics as pattern collapse (PC) and line edge roughness (LER) are closely related to surface properties of the resist. The surface origin on PC and LER based on the interaction of the rinse liquid with the resist and the interaction between the resist surface and the developer, respectively. In this paper we present a characterization of a reference surface prepared by an open frame exposure. Utilizing scanning force microscopy (SFM) the surface topography is analyzed. From the SFM images vertical structures (root mean square roughness) as well as lateral structures (most prominent in-plane lengths) are extracted. Advancing and receding contact angles were measured to characterize changes in hydrophilic/hydrophobic surface properties of the photo resist after development. With increasing thickness loss of the initial film the surface roughness and the most prominent in-plane length scales increase while the contact angle decreases. An analogy of the prepared surfaces with phase separated structures is presented.

Using Small Angle Neutron Scattering (SANS), we present the first quantitative measurements of the 3-dimensional conformation of macromolecules in thin polymer films of D < R_G,Bulk, where D is the film thickness and R_G,Bulk is the bulk radius of gyration. For D approximately equals 0.5 R_G,Bulk, the molecular size along the film normal is less than 0.5 R_G,Bulk, while relatively small changes are observed parallel to the surface. The observed changes in molecular size agree with predictions of molecular dynamics simulations of polymers confined in thin films, resulting from increased molecular orientation rather than chain distortion. Segregation of molecular centers of mass to the film center facilitates molecular packing while minimizing chain distortion. Estimates of length scales relating to the onset of chain distortion and chain orientation in thin film resists are D approximately equals 0.1 R_G,Bulk and D approximately equals N_(sigma ) respectively, where D is the film thickness, N is the number of chain segments, and (sigma) is the persistence length.

We have extended the recent work on high numerical aperture (NA) effects in novolac photoresists to investigate the influences of s- and p-polarization at Brewster's angle on the final developable image of a chemically amplified (CA) resist. Using our interferometric lithography tool, resist films (Shipley UVII-HS) were exposed using either s- or p-polarization at both Brewster's angle (146 nm pitch), and at a small angle of incidence (400 nm pitch), where polarization effects are considered negligible. Cleaved and decorated samples were analyzed with a scanning electron microscope (SEM) which provides a measure of the spatial distribution of energy deposition in the film convolved with the image transformation that occurs during PEB. The experimental images were compared to simulated latent images using a PEB model that mimics UVII-HS behavior and a more simplified model, a blurred acid image. Our results indicate that the degraded aerial image contrast at high NA caused by the absence of an antireflection coating (ARC) leads to complex developable images. This degraded contrast can increase line-edge roughness, and affect critical dimension variation. This work reveals the need to understand the details of resist response to high NA aerial images to predict structures, and the importance of a well-designed ARC to maintain control over image formation.

The effect of aerial image contrast upon line edge roughness (LER) of four different commercial resists-UV210, SEPR-463, Apex-E, and UVII-HS-is examined via scanning electron microscopy (SEM) and atomic force microscopy (AFM). Image contrast is varied by exposing both a detailed foreground pattern and a large open area background pattern on the same wafer location. Contrast varies from 0.37 to 1.0. In the case of UV210, LER measured via AFM is 2.55 nm at 1.0 contrast, 2.16 nm at 0.54 contrast, and 3.6 nm at 0.37. Results from other resists follow this trend, wherein no consistent correlation between LER and aerial image contrast can be drawn. SEM measurements also demonstrate no significant correlation between LER and image contrast in any resist type.

Lithographic performance is controlled by both the projected aerial image and the photoresist process. It is usually easier to calculate the output of the optical system than to construct an accurate predictive model for the photoresist process. This point, coupled with the trend toward extremely high contrast photoresists where the resist starts to act like an ideal image threshold detector, means that aerial images alone are increasingly useful for predicting performance. In this work, discrepancies between resist processes with finite imaging contrast, and aerial image predictions are explored. The method used is to construct several lithographic problems (various line and hole patterns with high NA lenses) and to directly calculate differences for important responses such as exposure latitude, dense:isolated bias, and isofocal curvature. The expected performance range for resist processes can be found with a simulation program and systematically varied resist models, producing hundreds of trial cases. The results show that the resist process predictions deviate from the aerial image predictions in a consistent way; interpretable as a resist vector whose magnitude varies depending on the details of the resist process, but whose direction does not vary much. Knowledge of the vector provides a route for extrapolating aerial image calculations to what actually prints on the wafer. Physical explanations based on finite dissolution contrast and non-zero diffusion are offered. Where possible, experimental data is used to support the arguments.

A mesoscale computer simulation for positive tone chemically amplified resists is reported. The simulation is based upon detailed models of resist function, and the required simulation inputs are fundamental quantities that can be measured independently of lithographic performance. These input parameters include resist formulation variables such as polymer molecular weight, photoacid generator loading, and activation energy of the deprotection reaction, as well as processing variables such as temperature and duration of bake steps and developer concentration. The simulation can model all major resist processing steps: spincoat and post apply bake, exposure, post exposure bake, dissolution, and drying. The general approach involves representing the photoresist film on a three dimensional lattice. Some lattice sites represent acid or solvent molecules and other lattice sites are strung together to form polymer chains. Each lattice cell is considered individually during the simulation, and each behaves in a manner consistent with its chemical identity. The mesoscale nature of the model allows investigation of stochastic effects that lead to line edge roughness, such as shot noise during exposure and the finite size of resist molecules. The model is based upon extensive experimental studies, and has now yielded results that are qualitatively correct for all major lithographic processing steps.

An extended 248nm lithography process with alternating phase-shift masks (PSMs) and etch-trimming techniques has produced 50nm gate critical dimensions (CDs). Well-controlled CD uniformity and line-end edge roughness (LER) are also demonstrated in this work. The primary factor in the improvement of through-pitch proximity bias was phase shifter width. With optimum shifter width, where pitches are greater than 600 nm, a through-pitch proximity bias of less than 10 nm can be obtained. Photoresist also has a significant role in implementing alternating PSMs, requiring high activation energy and suitable thickness. Soft-bake and post-bake temperatures were determined to enlarge the depth-of-focus (DOF). The forbidden pitch effect was enhanced to constrain the common process window after optical proximity correction (OPC) had been implemented. However, proximity bias can be kept constant with changeable diffusion length due to the through-pitch CD profiles, all isolated like. Improvement of through-focus CD at the forbidden pitch was examined by optimizing diffusion length; the common process window can be improved by 25%. All process results, including line-end roughness, DOF, exposure latitude, well-controlled CD uniformity, and through-pitch proximity bias, showed that 248 nm photolithography with alternating phase shifting mask could meet the requirements of 100nm node application.

As 193 nm resist moves into production with minimum feature sizes approaching 100nm, bilayer resist is being evaluated more closely for certain applications. Our polymer design has been evolving to meet tighter outgassing requirements. Optical density, etch resistance and dissolution behavior are other considerations. The protecting group used in our 248 nm bilayer is not useful for 193 nm lithography because of the high optical density contribution from Si-Si linkage. Silicon was incorporated into a COMA platform for the first generation polymer. Maleic anhydride is used to modulate dissolution characteristics. The first generation 193 nm bilayer was optimized to print 120 nm L/S patterns with an attenuated PSM on a 0.6 NA Nikon S302. We will describe next generation platforms that address silicon outgassing concern. The lithographic performance of these resists was evaluated on a 0.6 NA Nikon S302 with a dark field mask. Results for 280nm pitch (1:1 L/S) and 245 nm pitch (105 nm L, 140 nm S) lithography are presented. Also shown is result for a 245 nm pitch (1:1 L/S) and 210 nm pitch (1:1 L/S) on a 0.75 NA ASML PAS 5500/1100. Outgassing data generated at MIT Lincoln Laboratory will be discussed.

Carbon dioxide (CO₂) based microlithography (dry microlithography) represents an immense opportunity for the semiconductor industry to keep pace with Moore's Law while reducing its environmental impact. Currently, rinsing <130nm developed images with supercritical CO₂ is the only method which can prevent image collapse at this resolution. In this article, we will discuss CO₂'s ability to improve lithographic performance as we demonstrate its potential to replace the most solvent intensive steps of the microlithography process; spin coating, developing, and stripping. During these steps, semiconductor manufacturers produce vast amounts of organic and aqueous waste, which are detrimental to our ecosystem. However, before CO₂ can replace conventional solvents, photoresist systems must be designed and synthesized to be compatible with CO₂. These photoresists must be soluble in liquid CO₂ to insure that uniform thin-films can be produced by spin coating while maintaining characteristics of conventional resist systems such as low absorbance, high sensitivity, solubility contrast, good resolution, and etch resistance. Using our CO₂ compatible resist system, we will show the ability of CO₂ to spin coat uniform thin-films which (after exposing and PEB) can be developed using scCO₂ to produce lithography features that may be stripped in CO₂. Thus, revealing the enormous potential of CO₂ to provide the microlithography industry an opportunity to escape its water and organic solvent dependence.

A dissolution rate monitor (DRM) was successfully constructed to study the behavior of thin photoresist films undergoing the dissolution process in supercritical carbon dioxide (SCCO₂). The DRM is based on the principles of interferometry but requires special modifications to the processing vessel to allow for the passage of transmitted and reflected He-Ne laser light. Dissolution rates obtained agree well with independent profilometric measurements of film thickness loss. We found that for block and random copolymers of THPMA-F7MA, dissolution rates vary with film thickness, slowing down considerably towards the silicon surface. This behavior was also observed in TBMA-F7MA random copolymers.

Recently, there is significant interest in using chemically amplified (CA) resists for electron beam (E-Beam) applications including mask making, direct write, and projection printing. CA resists provide superior lithographic performance in comparison to traditional non CA E-beam resists in particular high contrast, resolution, and sensitivity. Due to the electron scattering effect and the image collapse problem, thinner imaging layer is desirable. Sufficient etch selectivity is needed to compensate reduced resist thickness. Therefore, there is a need to have a high etch resistant resist system which can survive Cr etch (Cl₂/O₂RIE etchant) process in mask making. For device making, the thin film bilayer approach needs a resist that can withstand O₂ etch for image transfer to the underlayer. We have found Si-O containing polymer has the etch characteristics for both applications. In the first approach, using a blend of KRS-XE and silsesquioxane polymer, we have been able to resolve resist images down to 50nm with etch rate 20% slower than conventional novolak I- line resist systems. In the second approach, we have investigated the copolymer of vinyl phenol and acrylate siloxy silane systems. Superior litho performance and etch properties have been observed. In this presentation, we will discuss the chemistry, the miscibility in blends, etch characteristics and lithographic performance of these resist systems.

Over the years for enhanced resolution, electron beam exposure tools have migrated to higher accelerating potentials. High kV exposure requires faster resist to offset the loss of absorbed radiation. In addition, in order to maintain throughput in mask writing tools, photoresist sensitivities of the order of 5(mu) C/cm² at 50 kV are needed and likewise 5 (mu) C/cm² at 100 kV for projection exposure tools. To meet this sensitivity requirement there is a keen interest in using chemically amplified resists (CAR). The CAR resists offer additional benefits such as high contrast, improved resolution, larger process windows, and dry resistance. This study is focused on enhancing the sensitivity of a low activation ketal protected polyhydroxystyrene. One such resist, which has been reported previously, is insensitive to the post apply bake temperature and does not require a post exposure bake. To enhance the resolution, process latitudes, and chemical contrast, base quenchers are usually added to limit the diffusion of the acid after exposure. To improve the sensitivity of the formulation, the effect of the acid generator (AGX), type of base, base concentrations and ratios in combination with the polymer protection level has been studied. Yields of acid formed were measured by titration and NMR. It was also found that both the AGX and base has an inhibition effect on dissolution. By increasing the among of AGX and decreasing the polymer protection level, the sensitivity of the formulation was improved while maintaining the resist contrast, resolution, vacuum stability, and bake latitudes. In addition, the sensitivity of the resist can be altered by quantity and type of added base. We have also investigated the effect of Pk_a of the base on the sensitivity, and process exposure latitude. The ionic onium acid generators or non ionic hydroxyimides provide adequate acid when coupled with adjusted concentrations of base to achieve 5 (mu) C/cm² at 100 kV.

The goal of this work was to develop a resist material for high-keV (>=10 keV) electron beam patterning with: (1) high sensitivity (~10 (mu) C/cm² 50 keV), (2) high contrast, and (3) etch resistance comparable to current optical resists. In this work, an approach was desired that used multi-component resist design to (1) decouple sensitivity from etch performance and to improve resist contrast but (2) avoided environmental stability problems. Therefore, a resist design first proposed by researchers at IBM in the late 1980s that uses an electron beam sensitive polymeric dissolution inhibitor (poly (2-methyl-1-pentene co 2-ethoxyethyl-methallyl ether sulfone)) in conjunction with novolac resins was explored in this work. Significant advancements have been made in high performance novolac resins used for advanced I-line resist materials since the original work performed at IBM. Thus, one of the primary reasons for reinvestigating this resist design is to evaluate the performance of resists formulated using polysulfone dissolution inhibitors in conjunction with such advanced novolac resins. In this work, the basic lithographic performance of sulfone-novolac system (SNS) resists formulated using modern novolac resins was evaluated and optimized by varying the resist film preparation and development conditions.

Fluorinated dissolution inhibitors (DIs) for 157 nm lithography were designed and synthesized as part of an ongoing study on the structure/property relationships of photoresist additives. The problem of volatilization of small DI candidates was observed from matrices such as poly(methyl methacrylate) (PMMA) and poly(hexafluorohydroxy-isopropyl styrene) (PHFHIPS) during post-apply bake cycles using Fourier Transform Infrared Spectroscopy (FT-IR). To avoid this problem, low volatility fluorinated inhibitors were designed and synthesized. Three fluorinated DIs, perfluorosuberic acid bis-(2,2,2,-trifluoro-1-phenyl-1-trifluoromethyl-ethyl) ester (PFSE1), perfluorosuberic acid bis-[1-(4-trifluoromethyl-phenyl)-ethyl] ester (PFSE2) and a fluorinated phenylmethanediol diester (FPMD1), largely remained in a PHFHIPS film during the post-apply bake. The dissolution behavior of the two fluorinated diesters was studied and found to slow down the dissolution rate of PHFHIPS with inhibition factors of 1.9 and 1.6, respectively. The absorbance of PHFHIPS films containing 10 wt% of the diester inhibitors is 3.6 AU/micron compared with an absorbance of 3.3 AU/micron for the polymer itself. The absorbance of 10% FPMD1 in PHFHIPS was measured as 3.5 AU/micron compared with an absorbance of 3.4 AU/micron for the polymer itself. Thus, the non-volatility and transparency of the fluorinated inhibitors at 157 nm as well as their ability to reduce the development rate of fluorinated polymers make them suitable for use in a 157 nm resist system.

The reactive ion etch (RIE) properties of fluorine funtionalized polymers in which fluorine atoms were incorporated in the main chain were examined. There was a tendency that the etching rates of these polymers were higher as lower the fluorine contents. The existing four models such as the Ohnishi model, the Kunz model, the Ohfuji model and the Kishimura model were applied to explain the correlation between the etching rates and the polymer compositions or structures, but the errors were too large to explain the relationship. A new model has developed to explain the effect of the fluorine incorporation to the dry etch resistance. The model assumed that there would be a correlation between the number of main chain fluorine atoms and the dry etch resistance, and the main chain fluorine incorporation would increase the dry etch resistance. The model could explain the dry etch resistance of the main chain fluorine incorporated polymers with adequate accuracy.

Various polymer structures for 157-nm lithography have been vigorously developed for post 193-nm lithography. Polymers with a fluorinated main chain can improve high transparency at the 157-nm wavelength; conversely, norbornene copolymers with fluoride pendant groups do not achieve so high transparency at the 157-nm wavelength. We have developed a novel 157-nm chemically amplified resist. It is composed of a fluorinated monocyclic main-chain polymer, which shows high transparency and can be used for single layer resists. This new resist is referred to as a Small Absorbance Fluorine contAining ResIst (SAFARI). The SAFARI resist exhibited high-resolution patterns of 65-nm line and space patterns using a 0.85 NA microstepper, good sensitivity of 4 mJ/cm², and high transparency when applied to 250-nm film thickness.

We have designed and synthesized a number of unique polymer systems composed of acrylate and styrene even though it had moderate transparency. Our first model of 157nm photoresist was based on a (alpha) trifluoromethylacrylate and styrene bearing a pendent hexafluoroisopropanol with pentafluoroisopropyl t-butyl carbonate (PFITBC) as the transparent enhancer and acid labile compound. PFITBC was obtained from perfluorinated enolate with di-t-butyl carbonate with high yield. All of the absorbance of our system ranged over 3.0~3.4micrometers ^-1 for base resin, which corresponded to a resist thickness of 110~125 nm at the optical density of 0.4. We have formulated several resists based on these polymers and these formulations have shown high resolution and contrast at 248 nm. We were able to obtain 240nm 1:1 image when exposed at 248 nm by a Nikon stepper with 0.45NA. To overcome the weak etch resistance with thin thickness film, we investigated the vapor phase silylation treatment (SILYAL) in which the treated pattern was more persistent against the O₂ plasma and turned to smoother surface. DMSMDA with Bi(DMA)MS of 30-40 wt% showed not only good control resist flow but also the improvement of line-edge roughness. Our results suggested that a facile approach to fluorine incorporated resin with SILYAL process can accelerate the 157nm lithography.

In future lithography the 157 nm wavelength is expected to succeed the 193 nm wavelength in 2004. So an early CARL resist for sub 100 nm resolution was developed at Infineon Technologies within the German BMBF project Laserbasierte Ultraprazisionstechnik - 157 nm Lithographie. Common 248 and 193 nm resist materials have a high absorbance (7- 12 μm^-1) A main challenge at this short exposure wavelength is the development of a transparent base polymer or the imaging has to be done alternatively with ultra thin films. In contrast to a high transparency of the polymer a high quantum yield for the photo chemicals is required. CARL is a bilayer resist system developed by Siemens/Infineon Technologies. A modified CARL version is presented here for exposures at 157 nm, consisting of a silicon free top resist (Si free CARL) as thin imaging layer. A separate silylation step of the structured top resist after exposure and wet development provides a high etch resistance in the dry development step and allows imaging of ultra-thin films with a film thickness of ca. 50 nm. An oxygen plasma is taken to transfer these top resist structures into the up to 300 nm thick underlying Novolac type bottom resist. In dry development. The bottom resist itself provides high etch resistance also for aggressive substrate etch processes.

The data presented is from resist materials exposed on the 157-nm Microstepper at SEMATECH. Photoresist suppliers provided the first samples of materials in early 2001. During the remainder of 2001, several improved formulations were supplied and tested. Over the last year, the lithographic performance of thick chemistries has improved, but exposure latitude is still inferior compared to Ultra Thin Resist (UTR) samples. Recently, more transparent samples have appeared demonstrating performance that is close to that of UTRs in terms of processing latitudes. Although sub 100-nm imaging has been shown, limited 70-nm performance with the alternating PSM indicates that significant progress still has to be made before the resists are capable of the targeted 70-nm node with a high NA tool.

A survey of fluorine-containing aromatic polymers, with and without base soluble functionality, was conducted to determine their potential utility in 157 nm lithography. The focus was toward the design and evaluation of fluorine- containing polymers that closely paralleled the ESCAP matrix resins now successfully used in 248 nm photoresists. New 4- hydroxytetrafluorostyrene (HTFS) based homo-, co- and ter- polymers were prepared and evaluated for their potential utility at 157 nm resists. Significant advances were made toward reducing absorbance with fluorine substitution and monomer variation. The polymers form good films, have acceptable thermal stability and show good dry etch resistance with promising potential in thin film resist applications. The synthesis and pertinent characteristics of the new polymer systems as well as preliminary oxide etch results on representative polymers are discussed.

It is expected that ArF lithography will be introduced for device manufacturing for sub-100 nm nodes, as high NA ArF step and scan systems (NA=0.75) become available. We previously reported on a platform, based on a vinyl ether- maleic anhydride (VEMA) alternating polymer system. This platform demonstrated both good resolution and high dry etch resistance in comparison to other platforms based on acrylate and cyclic-olefin-maleic anhydride (COMA) polymer systems. The VEMA platform has been continuously improved to meet the increasing requirements, such as resolution, depth of focus (DOF) iso-dense bias, and post-etch roughness for real device manufacturing. This VEMA system is being implemented for sub-100 nm device with high NA (NA=0.75) ArF exposure systems. In this paper, recent experimental results are reviewed.

A three-component positive working resist composed of an acrylate polymer, vinyl ether cross-linker, and photoacid generator was evaluated for vacuum UV lithography. The vinyl ether cross-linker using tricyclodecyl group of alicyclic compound has a high transparency. This resist system shows a relatively high sensitivity and has a good profiling by irradiation using 193 nm light from an ArF excimer laser. Moreover, we found that these cross-linking type resists have advantages with respect to its resist properties such as the acid diffusion and the dry etching resistance.

Several molecular resist materials were synthesized for 193 nm photoresists. They include cholate derivatives as dendrimer cores and ester groups as peripheral parts. Cholate derivatives provide etch resistance and peripheral parts give coatability and acid-labile polarity change. They were synthesized using an acetal-protected anhydride derivative of 2,2-bis(hydroxymethyl)proponic acid as an acylating reagent. These dendrimer materials were grown to the 1st generation. t-Butoxy esters are attached to the end of peripheral parts for positive-tone resists. These molecular resist materials were coated well to the silicon wafer and show good sensitivity and etch resistance.

Along with the trend of reducing the critical dimension in photolithography, exposure wavelength has been shortened from 248nm to 193nm. Resin structures of resist including their chemical characteristics have been altered from PHS to acrylate polymer. On the other hand, 2.38wt% TMAH developer solution is widely used, which was optimized at the time of 436nm resist process. However, since the resist backbone and chemical characteristics of 193nm resist are different from that of 436nm resist. So, TMAH concentration of 2.38wt% is not necessarily the best value for 193nm process and may even worsen the process latitude. Therefore, we have studied improvement of the process latitude such as CD uniformity, pattern defect, and dissolution mechanism of 193nm resist in developer solution, by applying Diluted Developer Solution (DDS) on 193nm resist process.

To accomplish minimizing feature size to sub 100nm, new light sources for photolithography are emerging, such as ArF((lambda) =193nm), F₂((lambda) =157nm), and EUV(extremely Ultraviolet, (lambda) =13nm). Among these lithography technologies, ArF lithography will be used for 100nm and sub 100nm lithography. Past few years, ArF resist development has been the key issue for the success of ArF lithography. Now the resist problems are solved clearly and it is time to start on logic and DRAM real device fabrication using ArF lithography. In this study we will show all the resist process for 100nm real DRAM using ArF resist. For critical layers with no etching problems (Striation, PR Deformation etc.), the acrylate type resist was used. While the other critical layers, such as oxide layers, the COMA type resist was adapted to avoid the etching problem. Furthermore, we have optimized resist process and etching conditions, along with additional E-beam curing was minimized (only 2~3 layer is required) for the real device production. In case of contact hole patterns, the 110nm contact hole could be obtained successfully without additional process sch as RFP(Resist Flow Process) or RELACS(Resolution Enhancement Lithography Assisted by Chemical Shrink), leading to a good patterning and etching performance applicable to even below 100nm node tech.

For the fabrication of IC devices, the patterning of C/H (contact holes) is essential but very difficult in comparison with L/S (lines and spaces). 193nm lithography following KrF lithography is expected to play a main role in 0.1micrometers technology node. However, many lithographers have reported various troubles such as poor profiles, resist shrinkage, and pattern edge roughness due to inherent flaws of ArF resist materials. In this study, we noticed such complex issues relating to patterning C/H and evaluated two resists (acrylate, ROMA), which are promising materials among ArF resists, at the condition of various baking temperatures of the soft bake and the post exposure bake. And then we investigated lithographic capability (resolution limit, exposure latitude, depth of focus, and CD uniformity) at the optimum bake conditions. Besides, the resist flow properties were estimated on both resists, respectively. Throughout experimentals, we were able to observe ArF resist properties for bake conditions and find optimum temperatures to improve several issues occurred on C/H pattern. Thus we directly achieved 0.12~0.10 micrometers C/H and also decade- nanometer C/H by applying the resist flow process.

We have investigated the requirements for resist materials in via-first dual damascene copper processes. We first patterned vias on a dielectric stack, and then, after via etching and stripping, we formed metal trench patterns using KrF/ArF lithography. A bottom anti-reflective coating (BARC) was used to fill the vias prior to the resist coating in order to protect the bottom of the vias during the trench etching. Trench patterns were formed on the BARC using chemically amplified resists. We found that resists with lower transparency and a lower maximum development rate (Rmax) were not developed in the vias on the partially filled BARC. When the trench patterns were etched with resist residue in the vias, severe fence defects were observed around the via openings at the bottom of the trenches. These defects cannot be removed by dry or wet stripping. Complete removal of the resists in the vias prevented the formation of fences. Simulation of the resist profile showed the use of resists with high transparency and a high Rmax prevented the accumulation of resist residue in the vias. A KrF resist formulated with higher transparency and a higher Rmax was completely developed even in the vias, so that trench patterns without the fences were formed after trench etching.

We studied the effect of ArF resist shrinkage under electron bombardment during ebeam metrology and also the effect of resist shrinkage on the after etch CD. The traditional approach is to reduce the electron energy and dose to minimize resist shrinkage, often at the cost of reduced precision and image quality. We found that resist trimming by high-density plasma etcher (ion density about 10¹²cm^-3) can improve the stability of resist under ebeam. Exposed to beams of 600V and 300V accelerating voltage, fresh photoresist CD shrinkage was reduced by ~70% and ~50% after resist trimming in the etcher. The effect of resist trimming is similar to that of e-beam curing. More interestingly, after etch and clean of the wafer, no difference in average CD value was found between area exposed to ebeam measurement and area that were not measured. This suggests that the resist trimming step in the normal etching process may overwhelm resist shrinkage effect caused by ebeam metrology. The implication is that the key selection criteria for stable ebeam metrology on ArF resist is a beam that produces consistent shrinkage, not minimum average shrinkage.

Electron beam (e-beam) curing techniques are known to improve etch and CD-SEM stability of 248 and 193nm resists. The effects of three different e-beam curing processes (standard, LT and ESC) on the methacrylate and hybrid type 193nm resists were studied with respect to resin chemistry changes, resist film shrinkage, pattern profiles, etch rates, and CD SEM stability. Both methacrylate and hybrid type 193nm resists lose carbonyl groups from the resins, with possibly a reduction in the free volume leading to improved etch resistance/selectivity. Methacrylate resist films shrink ca. 22-24% and hybrid resist films shrink ca. 23-27%. The LT process shrinks the least compared to the ESC and standard process. The ESC and LT processes were found to stabilize the patterns uniformly compared to the standard process. Etch rate, selectivity and resist surface roughness after etch of both methacrylate and hybrid resists were improved using the e-beam curing process. E-beam curing drastically reduces the CD SEM shrinkage (from ca. 15% to 2- 5%); however, considerable shrinkage occurs during the curing process itself.

We have developed novel acrylic copolymers for ArF photoresist which have more etching durability than usual. The excellent one of those copolymers in handling contains 8- or 9- methacryloyloxy-4-oxatricyclo[5.2.1.0^2,6]decan-3-one (OTDMA) and (gamma) ,(gamma) -dimethyl-(alpha) -methylene-(gamma) -butyrolac tone (DMMB). OTDMA is a new methacrylic ester monomer having a lactone unit with bridged structure. DMMB introduces a lactone structure to the main chain of acrylic copolymers. It was suggested that the solubility of monomers depends on the hindrance of their polar group, and the role of the hydrophilic monomers has been discussed from the standpoint of the position of their hydrophilic parts.

A mixture of high Mw fractionated novolac resin and 2EAdMA (2-ethyl-2-adamantyle methacrylate)/HST (hydroxy styrene) copolymer brought about high resolution almost comparative to simple 2EAdMA/HST copolymer. Dry etching resistance was higher than 2EAdMA/HST copolymer. A mixture of unfractionated novolac resin and 2EAdMA/HST copolymer showed low resolution. Discrimination curve was measured by DRM on each case. Dissolution contrast of fractionated mixture was almost same as unfractionated one. Dissolution characteristics cannot tell the difference of resolution between fractionated and unfractionated novolac mixture.

We prepared ter-polymer of hydroxystyrene, tert-butyl acrylate and 4-(3-cyano-1,5-di-tert-butyl carbonyl pentyl styrene) (P(HS-TBA-CBPS)) and discussed a characteristic of prepared polymer. As TBA, newly introduced monomer increases, contrast of resist is improved. And the prepared polymer was blended with poly(4-hydroxystyrene-co-4-(1-ethylethoxystyrene)) (EE-PHS). The synergic effect on a resist performance in KrF lithography by the combination of high and low activation energy system was shown. A resist using blending polymer was shown a good performance on resolution and LER(Line Edge Roughness) than resist using polymer separately. Based on the results, it was found that high performance KrF resist could be obtained by optimization of polymer blending.

Various derivatives of modified poly(4-hydoxystyrene-co-4-(1-ethylethoxystyrene))(M-EEPHS) were synthesized by insertion of third monomer unit such as styrene, 4-acetoxystyrene, 4-methoxycarbonyloxystyrene, tertbutoxycarbonyloxystyrene, tert-butyl acrylate, and 4-(1-cyclohexylethoxy)styrene. Their dissolution rate behavior was investigated with different blocking level. From the average dissolution rate of M-EEPHS in a 2.38wt% TMAH solution as a function of the total protection%, hydrophobicity was proven as more influential factor for the dissolution inhibition rather than hydrogen bonding by ester or carbonate functionality in a blocking group. To study structural effect on KRF lithographic performance, resists containing M-EEPHS were formulated and testified. Defects that are found in EEPHS based resist, such as LER (Line Edge Roughness) and top surface erosion at defocus can be solved by incorporation of carbornate, bulky acetal functionality or dissolution inhibition group. When hybrid system, which contained both M-EEPHS and poly[4-hydroxystyrene-co-tert-butyl acrylate-co-4-(3-cyano-1,5-di-tert-butyl carbonyl pentyl styrene)](P(HS-TBA-CBPS)) as an annealing type resin, were compared with the lithographic results of single polymeric system (M-EEPHS only), their performances were directly projected to those of blends of high activation type and low activation type resin.

The present paper demonstrates the applicability of thermal flow resist to print sub-0.1micrometers contact holes using 248nm lithography. With the thermal flow resist, 200nm contact holes were defined by KrF lithography system. Then following one step thermal flow resulted in down to 70nm contact holes with vertical sidewall profile. The main feature of the thermal flow resist is one step process having the linear dependency of flow rate on baking temperature. As the results, thermal flow resists pattern shrinkage controlled by post development baking temperature. Resist flowing occurred post development temperature was higher than Tg. Baking temperature was not the dominant factor from the contact hole shrinkage size curve. The thermal flow process using the thermal flow resist is a promising candidate for the fabrication of gigabit devices.

Satellite spots defects of size less than 1um are being experienced with UV series positive deep-UV photo resists at Chartered and it is believed to be formed as a result of the insoluble resist residue remaining on the BARC after the developing process. Though these defects reported are by far cosmetic defects that are not transferred after etch, we expect the results presented here to be significant and applicable to smaller geometries and to 12-inch wafer fabs. Figure 1 shows a typical satellite spots defect found in the open area where there are no resist patterns after the developing process. The spinning cycle of the developing process is thought to make the aqueous resist-developer dissolution adhere to the surface of the BARC in a satellite-like formation. In a small geometry on a patterned wafer under microgravity environment, the Marangoni convection occurs in the thin resist-developer dissolution during developing causing the micro dry spots in the dissolution under the spreading developer. The high surface tension of the deep-UV resists is believed to make it more difficult to remove after the hard bake process. The probabilistic model for the mechanism of resist-developer dissolution provides a theoretical backing to the resolution of satellite spots defect and it adequately accounts for the dissolution behavior of poly (hydroxystyrene) (PHS). Different developing recipes ranging from DI-water pre-wet, developer pre-wet, to high spin speed during DIW rinse were being investigated to find out the effectiveness in removing satellite spots. The combination of extended DIW rinse time, without resorting to high spin speed or high acceleration, and double developer puddling programs produce the lowest counts with the TMAH developer. Considerable defect density improvement after the developing process can be realized using the above control methodology. Although no significant yield improvement can be achieved at the present 0.25micrometers technology in Chartered, we believe that the results presented here will become significant as the Company moves towards smaller geometries.

In a photolithography process, it is vital to control Critical Dimension (CD) within wafer. In the current process, although parameters are controlled during post-exposure bake (PEB) and development, only film thickness is checked before exposure for the CD control. However, as the fine patterning by using chemically amplified resist (CAR) has progressed, CD control within wafer has been affected by very small changes of protecting groups; distribution of additives (PAG, quencher etc.) concentrations, and solvent concentrations, thus it has become more important to control film compositions = film properties before exposure. Following by CD variations within wafer caused by air flow in Post applied Bake (PAB) chamber, we examined evaluation methods of KrF resist film properties and made various evaluations of unexposed film after PAB. This paper describes correlation between CD and PAG, quencher, and solvent concentration; consideration of CD variations mechanism based on the correlation data; and problems when shifting to the next generation process.

The current work was done jointly between Institute of Microelectronics, Singapore and Tokuyama Corporation, Japan. Here the patterning performance of four different developers was evaluated. Three of these were with surfactant and one was without surfactant. The parameters evaluated were resist thickness loss, resist contrast, process windows such as depth of focus and exposure latitudes, across wafer critical dimension (CD) uniformity, and post pattern defect density. Feature sizes of 180 nm and 150 nm were evaluated for litho process latitudes. CD uniformity was also evaluated for 180 nm and 150 nm geometries. The resist loss was found to be minimum for developer A which was without surfactant. The depth of focus and exposure latitude of smaller geometry (150nm lines) in general showed better values for developers with surfactants. Developer solutions with surfactant also gave better across wafer CD uniformity for smaller geometries (150nm). Post pattern defects were found to be least with developer C that which contained nonionic type of surfactant and cationic one. Defects were highest for developer B which contained nonionic type of surfactant. The addition of optimum surfactant to developer has potential for reducing defects to lower levels and achieves better across wafer CD uniformity for smaller geometries.

One of the major problems for DUV resists is linewidth change owing to Post Exposure Delay (PED) and PEB conditions. In this work, the influence of PED and PEB baking conditions have been investigated based on the measured linewidth, i.e., critical dimension (CD). Our previously established model has been employed to describe the linewidth for various resists and process conditions. Based on our analyzed results, the process flow of wafer can be modified to improve the throughput, and still retain the CD stability and resist profile control.

Airborne amine control history for DUV lithography dates back to early 1990's. Environmentally stable resist coupled with air filter system was successfully adopted to cope with the issue. Today's trend toward extending KrF lithography lifetime further, however, demands a hard-to-achieve goal in CD control budget. Small CD change which was acceptable several years ago can no longer be tolerated in current critical technology node. We came to know that CD changes in a different manner for delay time depending on the amine concentration, pattern size, shape, and density. At very low amine concentration, delay time dependency is strongly governed by the chemical composition of the resist material. Relaxation of such dependency could be fulfilled by tuning resist bake condition.

Ultrathin ESCAP resists have been examined for logic applications in our paper. Lithographic studies have been carried out with these resists at the thickness of 60, 120 and 400 nm for contacts, and at the thickness of 250 vs 400nm for gate layer applications. A clear relationship between optimization of resist profile and film thickness through design of inhibited resists is shown. As the resist thickness is reduced to the UTR regime, more significantly inhibited resists are necessary. This effect is shown through the low R_min values for XP1335 and the extreme surface inhibition built into the resist film. The benefits of UTR resists are multiple: larger overall process windows particularly with respect to exposure latitude, profile optimization through inhibition, and reduced pattern collapse effects. We can see dramatic differences in dissolution properties and solvent distribution below 120nm film thickness for the UTRs in this study. We attribute most of these differences due to solvent distribution effects which are more severe as the resist is thinned. It is well known from previous studies, that photogenerated acid and volatilized base profiles may be also affected by solvent depletion. There also is no dramatic change in photospeed as resist thickness is reduced.

Several contact hole shrinking techniques have been discussed in the literature recently. Two notable techniques; Resolution Enhancement Lithography Assisted by Chemical Shrink (RELACSTM) and Resist Flow Process (RFP) were investigated in conjunction with several commercially available high activation energy chemically amplified materials and one bilayer material. During the course of this study the unique set of advantages along with the inconveniences associated with each technique were explored. It was not only the lithographic attributes of each technique that were of interest, but also characteristics that would effect manufacturability. To that end, experiments were designed so that standard statistical techniques could be employed at the data analysis stage. The attributes of interest were the amount and control of shrinkage, nested and isolated feature bias, process window comparisons, and line edge roughness. It will be shown how several of theses attributes are directly related to manufacturing issues such as lot-to-lot repeatability and linewidth variations across the wafer.

Traditionally, the stable-state temperature uniformity of resist post-exposure bake (PEB) units is considered major contributor to within wafer critical dimension (CD) uniformity. However, it has been realized that continued improvements in CD uniformity requires across-the-wafer temperature uniformity for the entire PEB cycle. The wafer temperature uniformity of the PEB heating and chilling cycle contribution to CD uniformity has been characterized in detail. When a silicon wafer is first placed on a traditional hot plate the within wafer temperature variance can be several degrees Celsius before the wafer reaches equilibrium at the set-point temperature target. A completely new hot plate design has been conceptualized and produced to attain thermal uniformity of the process wafer for the entire PEB cycle. This new PEB hot plate design was modeled after thermal transfer principle of a heat pipe to attain across-the-wafer uniformity during wafer heating and stable-state PEB. The new PEB plate design also allows to quickly change the PEB process temperature set-point up or down. Characterization has been completed to detail the importance of this new PEB plate design in attaining within wafer CD uniformity on single-digit nanometer level for KrF and ArF photolithography resist processing on track equipment.

With the shrunken device rule below 130nm, the patterning of smaller contact hole with enough process margin is required for mass production. Therefore, shrinking technology using thermal reflow process has been applied for smaller contact hole formation. In this paper, we have investigated the effects of chemical characteristics such as molecular weight, blocking ratio of resin, cross-linker amount and solvent type with its composition to reflow process of resist and found the optimized chemical composition for reflow process applicable condition. And several process conditions like resist coating thickness and multi-step thermal reflow method have been also evaluated to stabilize the pattern profile and improve CD uniformity after reflow process. From the experiment results, it was confirmed that the effect of crosslinker in resist to reflow properties such as reflow temperature and reflow rate were very critical and it controlled the pattern profile during reflow processing. And also, it showed stable CD uniformity and improved resist properties for top loss, film shrinkage and etch selectivity. The application of lower coating thickness of resist induced symmetric pattern profile even at edge with wider process margin. The introduction of two-step baking method for reflow process showed uniform CD value, also. It is believed that the application of resist containing crosslinker and optimized process conditions for smaller contact hole patterning is necessary for the mass production with a design rule below 130nm.

A material and process development of a tri-level resist system is carried out to introduce the resist system into 130nm and 110nm device fabrication. The tri-level resist system consists of organic films as a bottom layer, spin-on- glass (SOG) as a middle layer and DUV photoresists as a top imaging layer. A wettability and an acidity of the SOG film are adjusted depending on the type of resist materials to obtain a desirable resist profile. The anti-reflective performance of the tri-level resist system is evaluated along with the lithographic performance. A light reflection (reflectivity) in the DUV photoresist film is reduced less than 0.5% for both KrF resist and ArF resist by choosing the nominal thickness of the SOG film and the bottom layer. A conventional DNQ-Novolak type MUV resist is used for the bottom layer in the KrF tri-level resist system. The MUV resist is thermally cured to avoid mixing with the SOG and to increase the optical density at 248nm wavelength. A newly developed spin-on-carbon film is used for the bottom layer in the ArF tri-level resist system. The spin-on-carbon has an excellent dry etch resistance because of its high carbon content (>90%). The dry etch rates of the MUV resist and the spin-on-carbon for CF4/O2/Ar etch chemistry (SiN RIE condition) are 372nm/min and 287nm/min respectively. A pattern transfer using the tri-level resist system is demonstrated for both L/S and hole structures.

A loading effect in particular is accounting for an increasing percentage of factors responsible for CD variations. A multi-puddle method in development process therefore is considered a solution of this problem. However, the method consumes large amounts of developer solution. In this paper, we have studied the influence of loading effect on CD and evaluated several development methods to minimize the influence. In this paper, we evaluated the correlation between the width of exposed area and CD in the device area. Based on this result, we estimated the diffusion range of dissolution products. We also found another phenomenon that CD uniformity within a wafer became worse when each pattern was surrounded by an unexposed area. A novel development method we have evaluated in this study is as follows: (1) perform a puddle formation normally; (2) after a short static development, spin off developer solution from the puddle; and (3) after the puddle is decreased in volume, perform a rather long static development. This new method proved to have the capability of minimizing the influence of dissolution products.

We can print the contact hole pattern beyond the optical resolution limit using resist flow process. But its application has not strong point for the layer having various kinds of contact hole size and duty ratio according to x-axis or y-axis. Nevertheless, for the mass production of sub-150nm design rule device with KrF lithography using resist flow process, moderate shrink bias of below 40nm is required because the CD uniformity gets worse as the shrink bias gets larger by the influence of the hotplate dependency. We developed novel technology of shrinking contact hole using chemically amplified resist. It is generally known that the chemically amplified resist have t- top profile or larger line width when it has too much post exposure delay time at high amine concentration. Using this phenomenon, we intentionally treated amine of hexamethyl disilazane between exposure step and post exposure bake step, so we got smaller contact hole. Pattern profile of contact holes obtained by CONPEAT(CONtact hole resolution enhancement by Post Exposure Amine Treatment) process was fine. The contact size was 190nm with normal process and it was shrunk to 150nm using CONPEAT process. In this paper, we report the novel contact hole shrinkage technology of CONPEAT process. Its process feasibility was studied considering pattern fidelity, shrink bias and CD uniformity. We also introduce the experimental results of super contact hole shrinkage process using both contact hole shrinkage technology of CONPEAT process and resist flow process simultaneously.

Recently we have developed new class of non-ionic oxime sulfonate PAG. The compounds generate various kinds of sulfonic acids, such as n-propane, n-octane, camphor and p-toluene sulfonic acid under Deep-UV exposure and are applicable for chemically amplified (CA) photoresists. The application-relevant properties of the compounds such as solubility in propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, ethyl 3-ethoxypropionate, and 2-heptanone, UV absorption, thermal stability with or without poly(4-hydroxystyrene) (PHS), storage stability in a neat form or in PGMEA solution with or without additives, sensitivity in a model resist formulation, dissolution inhibition efficiency during the development process and volatility were evaluated. The compounds exhibit good solubility in PGMEA, high sensitivity in positive tone CA resist formulations, with Deep-UV exposure, and no significant volatility. Especially it was found that the compounds are superior in terms of thermal stability and storage stability, i.e., high thermal stability up to 188 degree(s)C in a phenolic matrix, and no change during storage in PGMEA at 60 degree(s)C for 5 months.

A novel filtration technique was developed and implemented to study the effect of CUNO Zeta Plus filtration on metal removal from a number of photoresist chemical systems. To obtain consistent metal removal performance, it was found that it was necessary to remove extraneous contaminants from the filtration system prior to actual filtration. A rinse-up protocol was developed and followed for the filtration system and filter medium. The EC and 40Q grades of Zeta Plus were employed in single stage as well as serial multi-stage filtration to remove metal ions from a wide range of microlithography process chemicals. The metal concentration was determined by Atomic Absorption Spectrometry for the influent and effluent samples before and after Zeta Plus filtration. The results showed 90% or greater reduction of the metal levels after single pass filtration. Three photoresist solvents were selected as examples to demonstrate the metal removal performance of Zeta Plus filtration.

A new class of ionic photo-acid generators (PAGs) useful in chemically amplified photoresist formulations has been developed. The new PAGs are salts comprising a photoactive cation and a fluoroorganic sulfonylimide or sulfonylmethide anion. These highly delocalized, nitrogen- and carbon-centered anions are extremely nonbasic and weakly coordinating. Correspondingly, their conjugate acids are powerful superacids. The imide and methide acids produced by photolysis of the corresponding ionic PAGs are highly active in initiating the cationic polymerization of various organic monomers (as in negative resists) and have been shown to catalyze the deprotection of acid-sensitive organic functional groups (as in high activation energy, positive resists) with good photospeeds. The unique balance of reactivity and physical properties provided by the imide and methide anions suggests that they may be useful alternatives to, or replacements for, the organic or inorganic anions commonly employed in existing ionic PAG formulations (e.g., perfluoroalkanesulfonate anions and MF6- anions, where M is Sb, As or P). A family of ionic PAGs based upon these new anions and their combinations with diaryliodonium or triarylsulfonium cations has recently been made available by 3M as experimental products for lithographic evaluations in positive and negative photoresists. In this report we will describe the characterization of these PAGs, including melting points, thermal stabilities, UV extinction coefficients, solubilities and photo-acid volatilities. Potential advantages of these new PAGs in positive and negative photoresist applications will also be presented.

Novel organic PAGs have been prepared in order to improve line edge roughness (LER) of 248nm and 193nm resists. From careful design of PAG, transparent, highly diffusive PAG was successfully prepared. New PAGs have increased hydrophilicity in cationic portion of PAG(photoacid generator.).

A positive working molecular photoresist based on (beta) -cyclodextrin ((beta) -CD) and its inclusion complex ((beta) -CD-IC) has been developed. Cyclodextrin is one of the most important host molecules in supramolecular systems. 1-Adamantanecarboxylic acid (Ad-COOH) is employed as a guest molecule to increase the dry etch resistance. (beta) -CD and (beta) -CD-IC were protected with t-BOC to control the dissolution rate with various feed ratios of di-t-butyl dicarbonate. The t-BOC protecting ratio turns out about 34 mol% which corresponds to the protection of primary hydroxyl groups on the upper rim of (beta) -CD. The t-BOC-protected (beta) -CD has low absorbances at 248 and 193 nm, and good film forming property. Using t-BOC-protected (beta) -CD and (beta) -CD-IC, submicron patterns were delineated when it was exposed to a KrF stepper and developed with a 2.38 wt% aqueous TMAH solution.

A newly developed, high resolution negative i-line resist product family, is introduced in this paper. Variation in resist film absorption provides optimum inverted sidewall slopes adequate for most metal lift-off applications. Resist resolution below 0.3micrometers is demonstrated. The capability of further resolution enhancement with the use of a simple shrink process is also demonstrated.

Hydrogels have gained general acceptance as biocompatible materials and are the basis of many promising applications in tissue engineering, drug release formulations and biosensors. Polymer processing techniques that can generate miniature hydrogel microstructures are not only critical as scaffolds for tissue re-growth but also very effective for increasing the efficiency of drug delivery and biosensors. Our approach is to use both optical and soft lithographic methods to microfabricate hydrogels. In this paper, we describe a photolithographic process to pattern hydrogel materials and analyze factors influencing sensitivity and lateral resolution. The model system we are investigating is based on 2-hydroxyethyl methacrylate (HEMA), which is well known for its non-toxicity and its widespread use in the contact lens industry.

In view of the fact that little analysis of the mechanism for the achievement of high resolution or a high aspect ratio in the thick-film resist process has been performed, we study development properties with respect to differences between the development methods employed for pattern formation using thick-film resist. This study identifies the most effective development method for thick-film resist and reports the mechanism of development. For this investigation, we use a development rate measurement system, a mask aligner, and lithography simulator to examine the dipping development method, the step puddle development method, the vibration development method, and the reverse development method. We employ a thick-film positive resist composed of diazo-naphthoquinone (DNQ) and Novolak resin, which is coated on a silicon substrate to a thickness of 24 micrometers . After pre-baking, the coated substrate is placed in a vacuum dessicator to remove water, followed by immersion in deionized water for a fixed period. A mask pattern is transferred to the resist coated substrate with a Mask Aligner Q4000 made by Quintel Corporation, and then the rate of development is measured. A laser microscope analysis of the result indicates that the step puddle development method gives the highest pattern resolution and sharpness, followed by the vibration development method, the dipping development method, and lastly the reverse development method. The mechanisms of the development are studied by comparing the development contrast and the energy of activation involved in each development method, and by conducting resist pattern simulations. The results indicate that the factors responsible for retarding the progression of the development process and causing a degradation of pattern profile and resolution are development inhibition due to N₂ released from inside the resist during the development process, and due to products that are dissolved in the development solution.

In our paper, we discuss implications currently relevant to 300mm resist processing in lithography. The large size of the wafers, and therefore the large volume of machine modules and media within these modules, demand tighter specifications and a careful re-consideration of design. Firstly, we investigated a novel resist development process based on a new developer dispense nozzle. The CD uniformity across the 300mm wafer thus achieved is compared to a common process. Based on this, we are able to make a preliminary recommendation for the photoresist development technology required for future, high-end semiconductor device manufacturing. Resist thickness fluctuations around the edge area of a silicon wafer typically occur if high spin speeds are applied during the photoresist coating process. 300mm coating processes are particularly prone to the occurrence of such spin marks as the operating range of applicable spin speeds is lower in comparison to processes applied to wafers of lower diameters. We show in our example how such local resist thickness fluctuations impact the product yield. Finally, a special type of micromasking defect was found to be particularly relevant to 300mm lithography layers. This doughnut-type defect detracts the yield of the semiconductor product. The defect has a distinct physical appearance and is precipitated onto the wafer as a hollow resin sphere. This defect has not yet been observed on our 200mm reference process. The occurrence of the defect directly depends on the matching of the air flows entering and leaving the 300mm coater cup. The mechanism of formation involves the presence of a photoresist-solvent aerosol.

The development process is very important in determining the resist resolution of lithography. Polymer dissolution during development was studied based on resonance frequency and impedance measured by the quartz crystal microbalance (QCM) method. A transmission-line analysis of QCM data was then carried out. The dissolution characteristics were also evaluated from the standpoint of molecular structures and polymer acidity measured by potentiometric titration. Fluoropolymers showed dissolution characteristics which reflect large fluorine effects in addition to acidity effects. The fluorine effects retarded the dissolution rates and formed a swelling layer. Poly(methacrylate)s had a complicated swelling behavior during development owing to the hydrophobic components in the polymers. The fluorine and hydrophobic effects rather than polymer acidity play the dominant role in forming the swelling layer during development.

The phenolic polymer is assumed to be transferred, via intermediate gel state, from the resin to the developer solution. A mechanism for the development of phenolic polymer is proposed to derive a development rate equation considering gel layer formation. In the previous paper, new model using the concept of gel layer made it possible to provide a theoretical interpretation for experimental data of dissolution behavior, for example the dependence of the dissolution rate of phenolic polymer on the aqueous base concentration and molecular weight of resin. Following the previous paper, the dependence of the dissolution rate on the size of the base cation can be explained by taking the diffusion of base through the gel layer into account.

To clarify the origin of the roughness generated on resist surface, we investigated the effects of molecular weight of resist, exposure dose, and developer molecular size on surface roughness by atomic force microscope observations of surface morphology of electron-beam exposed surface after development. Surface roughness is strongly influenced by the polymer aggregates appearing on the exposed resist surface after exposure and development. As the molecular weight becomes higher, surface roughness becomes larger because the aggregate size increases. On the other hand, at higher exposure doses, surface roughness gradually decreases because the number of aggregates on the surface decreases. This indicates that appearance of the aggregates due to aggregate extraction development is suppressed at higher doses. As the developer molecules become smaller, fewer aggregates appear on the surface and the surface roughness becomes small. This also indicates that the aggregate extraction development can be suppressed with small developer molecules. These results can be explained by considering the relationship between the size of free volume holes in the aggregates and the developer molecular size.

As the emphasis on critical dimension (CD) control in sub-micron lithography becomes more important, the mechanism of the development process and the different contributing factors will need to be further explored by equipment manufacturers. It was observed that the use of reticles with smaller exposed area ratio (EAR) have different affects on CD uniformity. To gain better control of CDs, we examined several of the contributing factors in the development process. Some significant factors are the affects of EAR and the affects of the rapid concentration changes of tetrametylammonium hydroxide (TMAH) surrounding the resist patterns that appears to slow the reaction rates of the developer. Using several chemically amplified resists (positive) and reticles with varying EAR, we determined that there are two phases (First Term & Second Term) of the development process. Within each term, there are significantly important processes taking place in and around the resist patterns. In the First Term, the importance is on proper amount of equally distributed developer on the wafer surrounding the resist patterns. In the Second Term, there is a rapid change to CD's meaning a greater possibility of control. Once determining the two terms of the development process, different concentrations of TMAH were experimented with to examine the mechanism of the resist dissolution movement. After observing the movement on the surface of the wafer, we believe that the resist dissolution moves within the puddle of the developer impeding the reaction rate for proper CD formation. By controlling the impeding affects of the dissolved resist in the Second Term, we believe that CD uniformity can be greatly improved.

We have used ellipsometry to study the glass transition temperature (T_g) of thin films (thicknesses 4-300 nm) of monodisperse polystyrene (PS-M), polydisperse polystyrene (PS-P), and a Shipley photoresist base polymer (SBP) with and without photoacid generator (PAG) on silicon substrates. For films less than 40 nm thick, T_g values decreased with respect to their bulk values for PS-M and SBP films. Films containing PAG exhibited further reduction of T_g values as predicted by the Fox equation to within experimental error.

In a chemically amplified resist the exposure energy is used to generate a catalytic species, which promotes a solubility-switching reaction during a post exposure processing step. Using an absorbed photon to generate a catalyst, instead of using it to directly cause a solubility-switching photochemical reaction, allows for much lower exposure doses to be used for patterning since the catalytic species can eventually promote multiple solubility-switching events instead of just one. Some level of catalyst mobility is necessary to achieve the amplification effect as the catalyst must move from reaction site to reaction site, but any catalyst mobility creates the possibility of movement from exposed regions into unexposed regions causing image blur or line width spreading. As the catalyst diffuses in the resist, it promotes chemical reactions; these chemical reactions complicate analyses of catalyst diffusion by changing the chemical environment of the diffusant. Thus, the material properties of the surrounding resin are changing, sometimes drastically, as the catalyst diffuses. In addition to simple changes in material type, the chemical reaction also generates a transient material state as reaction by-products either remain in the resist film or desorb. The variation in lifetime of this transient state is another factor that must be considered in a full analysis. This work reports a method to separate reaction effects from catalyst diffusion effects. Acid diffusion in polymers which are close structural analogues to poly(4-t-butyloxycarbonyloxystrene) (TBOCST), while being unreactive to diffusing acidic molecules, was studied. Specifically, the diffusion properties of photogenerated perfluorobutanesulfonic acid in the unreactive TBOCST analogues poly(4-isopropyloxycarbonyloxystyrene) and poly(4-neopentyloxycarbonyloxysytrene) are reported. Measuring and understanding diffusion in these analogue polymers provides insight into the more complicated, and more important, reaction-diffusion processes of TBOCST.

In this work an automate optimization routine is used to modify modeling parameters for a chemically amplified photoresist, with the goal of minimizing the error observed between lithography simulation and experimental results. It is shown that a basic tuning procedure modifying, optimizing only CD measurement offset and acid generation efficiency, improves the fit significantly. Further improvements can be made by optimization of the diffusion-deprotection kinetic parameters, in combination with the two aforementioned values. It is shown further improvement is observed if the actual temperature profile experienced in the postexposure bake process is considered and the temperature dependence of both the diffusion and the deprotection processes are optimized. This parameter values that result in this improvement infer a temporal offset in the start, and finish, of deprotection and acid diffusion.

The kinetic processes occurring during postexposure bake (PEB) were studied for different Shipley photoresists as a function of bake temperature with the aim of developing models to accurately simulate the observed temperature dependent responses. S7 193nm photoresist based on a high activation energy methacrylate platform and SL4000 248 nm photoresist based on a low activation energy acetal platform were investigated. Deprotection rate constants, K_amp, were measured directly by IR spectroscopy. K_amp was independent of PEB temperature for SL4000 and followed standard Arrhenius behavior for S7. Activation energies of deprotection determined from measurements of K_amp were 13.4 and 0.82 kcal/mol for S7 and SL4000, respectively, and of the same order of magnitude as the corresponding pseudo- Arrhenius activation energies, 10.3 and 3.2 kcal/mol, respectively, determined from E₀ clearing doses as a matching experimental and simulated CDs of isolated lines as a function of PEB time and temperature. However, values of D could not be unambiguously determined because a finite bulk acid loss rate constant was required to accurately simulate the observed CD changes at high PEB temperature. The need for a blk acid loss rate constant at high bake temperatures suggests that the effects of base diffusion are significant under these conditions. CD changes in SL4000 were best simulated with a 1st order model, where the imaging chemistry occurs solely during the exposure step as in DNQ/Novolac photoresists.

Various resist develop models have been suggested to express the phenomena from the pioneering work of Dill's model in 1975 to the recent Shipley's enhanced notch model. The statistical Monte Carlo method can be applied to the process such as development and post exposure bake. The motions of developer during development process were traced by using this method. We have considered that the surface edge roughness of the resist depends on the weight percentage of protected and de-protected polymer in the resist. The results are well agreed with other papers. This study can be helpful for the developing of new photoresist and developer that can be used to pattern the device features smaller than 100 nm.

A sequential double exposure technique for characterizing resist materials suggested by the authors is demonstrated experimentally at 248nm lithography. This technique is verified to improve two-dimension pattern and line end shortening. A new PEB parameter extraction method based on the double exposed technique is applied to UV210 and APEX-E and the first round results have been obtained. With the help of the new methodology, Fickean and non-Fickean diffusions are evaluated.

The design of 157nm photoresist is a daunting task since air, water, and most organic compounds are opaque at this wavelength. Spectroscopic studies led to the observation that fluorinated hydrocarbons improve the transparency of 157nm resist materials rather dramatically. These fluorinated resists have quickly become the prominent material platform for a variety of research activities. Regardless of wavelength, developing a practical photoresist material is always challenging; the added difficulties associated with 157nm radiation complicates the overall design problem and severely limits the choice of material classes to work with. This paper will discuss our 157nm simulation and parameter extraction efforts that have been completed over the past few months at International SEMATECH. During the past year we have developed the methodologies and practical test methods that are needed to study the lithographic behavior of 157nm resist systems. Our work is based on procedures in the open literature and augmented by internal research.

The Mask Error Enhancement Factor (MEEF) is an important consideration for determining the best mask bias used in conjunction with Optical Proximity Corrections (OPC). Reducing MEEF, increasing process window, and minimizing through pitch proximity bias are all factors that need to be addressed when optimizing OPC and illumination. These simulations determine the interaction between isofocal bias with the sign (positive or negative) and the magnitude of the mask bias that reduces the MEEF for 130nm lines/spaces in DUV resist. Ideally, bias applied in this manner minimizes the through pitch print bias, thereby increasing the overlap of the individual process windows, and hence the common process window. Incorporating the current technique of varying mask bias through pitch to minimize MEEF and increase common process latitude, we correlate the isofocal bias to the sign of the mask bias for optimal MEEF reduction.

A vapor phase silylation process after wet development allows a patterned resist film to have etch resistance similar to that of bi-layer resist. In our study, the mixture of dimethylsilyldimethylamine(DMSDMA) and bis(dimethylamino)methylsilane(B(DMA)MS) was used as a silylation agent. DMSDMA was an effective silylation agent providing silicon compound quickly into resist film and also, had a role of improving the line edge roughness (LER) of resist pattern profile. Bi(DMA)MS, was added as a cross linker to prevent the resist flow due to the drop of glass transition temperature(Tg) of the resist film during silylation. Thermally stable silylated resist pattern was baked at 160 degree(s)C in order to control critical dimension(CD) bias generated by volume expansion during silylation, without desilylation arising at the typical silylation process using DMSMA.

Top Surface Imaging (TSI) is a well-established technique to improve resolution for optical, ultraviolet (UV) and e-beam lithography. The Positive Resist Image by Dry Etching (PRIME) process is a high resolution single layer lithography system incorporating electron beam exposure, silylation and dry development. In this paper, modeling of nanostructures down to 30nm using PRIME with 0.5micrometers thick Shipley SPR505A resist are presented. The simulated profiles have been found to correlate closely with the published experimental data. Moreover, the liquid-phase silylation process step in PRIME has been experimentally characterised using FT-IR spectroscopy, UV spectroscopy, SIM spectrometry as well as cross-sectional SEM and TEM. The impact of different silylating agents on SPR505A is presented for both the UV exposed and e-beam crosslinked regions of the resist. Results show that an e-beam dose of 50(mu) C/cm² at 30KeV is sufficient to crosslink the resist and prevent silylation. The silylation contrast using Hexamethylcyclotrisilazane (HMCTS) was found to be the highest (11:1) in comparison with other two silylating agents. It was found that the silicon incorporation in SPR505A resist follows Case II diffusion mechanisms.

As exposure wavelengths continue to decrease, the use of conventional single layer resist (SLR) materials is becoming increasingly more difficult. Since most organic materials absorb at wavelengths below 200 nm, it becomes problematic to create polymers with sufficient transparency to serve as SLR resins. This paper is focused on a novel approach to top surface imaging, termed surface monolayer initiated polymerization (SMIP), in which a reactive monolayer is exposed and patterned. This pattern is subsequently amplified by surface polymerization to produce patterned polymeric features that can serve as an etch barrier. In particular, the reactive monolayer is exposed to patterned radiation (UV, x-ray, e-beam, etc.) that deactivates the monolayer in the exposed areas. The substrate is then heated or exposed to radiation in the presence of a monomer, resulting in activation of the monolayer in the unexposed areas and polymerization of patterned polymer structures. Thus, in this type of process the imaging properties of the monolayer system and the etch resistance of the polymer film formed are completely decoupled. This paper focuses on recent results intended for characterizing the exposure kinetics of a radical initiator compound, 4,4'-Azobis-(4-cyanopentanoic acid-(3'-chlorodimethylsilyl) allylic ester), used as a SMIP monolayer. X-ray photoelectron spectroscopy (XPS) has been used to measure the kinetics of the DUV (248 nm) exposure reaction in this monolayer. Examples of simple patterning tests using this approach are also presented.

A novel negative-tone bilayer scheme has been developed using organometallic imaging materials in conjunction with organic planarizing layers. Precursor films containing the radiation sensitive organometallics are spin coated and converted to a metal oxide through electron beam exposure to form an etch mask for pattern transfer. After exposure, the unexposed regions are washed away using an appropriate developer solution and the etch mask pattern is transferred through the organic planarizing layer by an oxygen reactive ion etch (RIE). In this work, a multicomponent organometallic precursor Ba(Sr,Ti) [Ba(2-ethylhexanote), Sr(2-ethylhexanote), Ti(IV)(diisopropoxide) (bisacetylacetonate)] is evaluated as a possible imaging material for bilayer lithography applications. The sensitivity of the 1:1:2 (molar ratio of metals) Ba(Sr,Ti) precursor was found to be 56.5 (mu) C/cm² with a contrast of 16.1 at 10keV accelerating potential. In order to enhance the sensitivity, partial conversion of the precursor to the metal oxide prior to electron beam exposure through thermal baking was investigated. It was found that a 30 second thermal bake at 150 degree(s)C enhanced the sensivity to 23.3 (mu) C/cm² but decreased the contrast to 4.2. Also, blanket etch studies on exposed samples found that the remaining organic ligands in the precursor are further converted to the metal oxide upon exposure to the O₂ plasma causing shrinkage of the etch mask. After shrinkage, the precursor offers excellent etch selectivity as compared to hard baked novolac. This bilayer process is demonstrated by printing 200 nm line and space patterns using electron beam patterning.

Previous generations of Bottom Anti-Reflective Coatings (BARCs) have had excellent optical properties but the etch performance for these BARC's were only 30% faster than the photoresist at best. A novel BARC chemistry has increased the capability of the photolithography process; this new chemistry has the capability to change etch and optical properties by the BARC bake process. This paper will present the bake process changes required to modify both etch characteristics and optical properties. Etch characteristics that were measured were bulk etch rate and etch selectivity to photoresist. Index of refraction and the absorption coefficients were measured for optical properties. Photolithography results focusing on Acetal and Hybrid photoresist types will be presented with specific attention to critical dimension control and focus latitude shifts, if any, associated with these BARC bake process changes.

This series of studies focuses on the fundamental fluid properties of several commercially available bottom anti- reflective coatings (BARCs). A goniometer was used to complete pendant drop analysis and dynamic contact angle measurement for two similar varieties (A-1 and A-2) of a 248nm BARC and another, competing variety (B-1) of a 248nm BARC. The pendant drop analysis shows that the liquid surface tension of the three BARCs is identical. The contact angle analysis was performed on SiON, low k dielectric, and F-based oxide type layers. Contact angle analysis shows that B-1 wets the least quickly, A-1 wets the most rapidly, and A-2 wets at an intermediate rate. All three wet quickly, A-1 and A-2 completely wet the surface, and B-1 nearly does. The surface type does not seem to affect the wetting rate, despite a real difference in the chemistry of the surface, as shown by the different surface energies of the materials. A Newman-type polymer-spreading model is proposed for the BARC spreading and shown to offer reasonable explanation of the wetting process. Three wafers, one for each BARC, were coated with resist and BARC and then stripped. The stripping process appears to have no major effect on the SiON and F- based oxide surfaces. However, the stripping process modifies the low k dielectric surface in an unknown way, making it more hydrophilic, which causes A-1 and A-2 BARCs to spread less well. Three wafers, one for each BARC, were subjected to a 20 degree(s)C/minute bake over the temperature range 50-220 degree(s)C in a mass spectrometer. The analysis shows that A-1 BARC exhibits the most outgassing, that A-2 BARC exhibits an intermediate level of outgassing and that the B-1 exhibits the least level of outgassing. In general, the B-1 peaked at substantially lower levels. The analysis shows that water vapor forms the largest component of the evolved gas. A-1 BARC causes the most water outgassing. The A-2 BARC, being substantially more viscous than the A-1 BARC, coats much thicker. The thickness is related to the spin speed by an inverse power relationship, where the power is -0.419.

Semiconductor companies have been successful in introducing new process technology generations every two years. In order to maintain this accelerated pace, 157nm technology is schedule to be introduced in late 2003. Although there are still several obstacles to achieving this goal, there has been considerable progress in the 157nm program. The solution to 157nm technology is however, not complete without an antireflective coating. This paper describes in detail the various design considerations for an antireflective layer for 157nm lithography. These considerations involve a) multilayer system vs. single layer, b) optical constants, c) screening of chromophore, d) etch rate, and e) lithography. This paper will show the optical constants necessary to maintain less than 2% reflectance for single layer systems (1st and 2nd min) and bilayer systems (3rd and 4th min). Additionally, it will demonstrate that it is possible to control k value of the antireflective layer in the range of 0.2 to 0.5. It will be shown that materials with both high k value and etch selectivity >1 can be designed for 1st min single layer applications. Lastly, resist profiles were generated using currently available 157nm photoresist and a commercial BARC.

The need for constant reduction in critical dimensions (CD) of integrated circuits to make them faster has been the driving force for next generation lithography. Currently KrF (248nm) is the shortest wavelength of light being used by IC manufacturers to mass produce devices. If the semiconductor industry continues at the same pace of packing more information on a chip, shorter wavelength (193nm) (ArF Excimer laser) will soon be introduced in production. Shorter wavelengths mean larger swing ratios, CD variations, reflective notching and standing waves due to sharp increase in reflectivity. Therefore some mechanism to reduce reflectivity becomes increasingly important at shorter wavelengths. Bottom antireflective coatings (BARCs) will play an important role in this endeavor. This paper discusses the chemistry and performance of two new spin-on organic 193nm BARCs (ARC 27 and ARC 28) optimized for their use at 1st reflectivity minimum thickness (30-40nm). The optical values of ARC 27 (n= 1.7, k= 0.56) measured by ellipsometer at 193nm give 0% reflectivity at the 1st reflectivity minimum with the optimum thickness of the BARC being 30nm. Lithographic studies with 193nm photoresist show good performance down to 90nm with isolated line (PAR705) and 100nm with dense line photoresist (PAR710,718). The optical properties of ARC 28 are 1.53 and 0.54 and a nominal thickness of 40nm on silicon is recommended to achieve 0% reflectivity. It shows good resolution at 110nm L/S and broad photoresist compatibility.

In the recent ITRS roadmap, the ArF lithography combining with resolution enhancement techniques have great potential to lead IC technologies to the generation less than 100nm. The problems of critical dimension control caused by highly reflective substrates are far more serious in the ArF regime than in the longer wavelengths. It is therefore important to find a high performance antireflective coating layer working in this spectral regime. For increasing resolution of optical lithography, expose systems with high numerical aperture (NA) are essential. The efficiency of conventional single layer BARC structure will degrade as the incident angle increased. It is due to the reflectance at resist/BARC interface increased in high incident angle regimes. Here we demonstrate a multi-layer bottom antireflective coating (BARC) layer for high NA ArF lithography. The multi-layer antireflective structure is composed of conventional SiON films. In a multi-layer BARC, the extinction coefficient of each BARC layer is gradually increased layer by layer, an dis the highest at the bottom. By adding an optimized structure, the reflectance can be remained less than 2% at resist/silicon substrate interface as the incident angle from 0 to 60 degrees (i.e. NA ~ 0.85). The swing effect in the resist is also shown significantly reduced. It also has a great potential to be used as BARC layer on other highly reflectance substrate such as copper, aluminum silicon (Al-Si), poly-silicon, tungsten silicide (W-Si), which are commonly used in IC processes.

There are considerable interests in the application of KrF lithographic process to achieve the beyond 0.13 micrometers resolution pattern. Decreasing in KrF resist thickness for high resolution in the lithographic process needs improvements of Bottom Anti-Reflective Coating (BARC) physical properties such as high etch selectivity and low reflectivity in thin KrF BARC film (350 ~ 400 Angstroms). It is known that the real and imaginary refractive indices of BARC are changed by film density and absorbance. Our research group have studied two different chromophore classes (BM1 and BM2) of functional groups that are highly absorptive at 248 nm and achieve high etch selectivity. Also, we have evaluated the effects of polymer structure on BARC in terms of refractive index changes and film density.

To have excellent compatibility with ArF resists is the goal in development of bottom antireflective coatings (B.A.R.C.) for 193nm lithographic application. We need to be able to adjust chemical compatibility and optical properties of ArF B.A.R.C. to accommodate various film stacks. We need to deliver ArF B.A.R.C. materials with excellent coating uniformity, long shelf life and ultra-low defect level. In the meantime, we also need to improve etch rate of the ArF B.A.R.C.s for shorter etch time. In this paper, we will focus on our recent efforts to optimize the organic ArF B.A.R.C.s' compatibility with ArF resists in the areas mentioned above.

Full and/or partial filling of 193 nm antireflective materials in contact holes is required for dual damascene applications. One of the major challenges for via filling is to minimize various fill bias associated with via size, via pitches and wafer size to an acceptable level. Toward this aim, various formulations were prepared and tested on different types of wafers using different processing conditions. It has been found that both the properties of the filling materials (e.g., molecular weights, glass transition temperatures, etc.) and processing conditions (e.g., spinning speed, dispense modes, baking temperatures, etc.) affect the filling behaviors. This paper presents our recent progress in the development of 193 nm B.A.R.C. materials designed for the dual damascene process. Through screening of the B.A.R.C. materials and optimization of the processing parameters, we have successfully developed two types of B.A.R.C. materials, namely, AZ EXP ArF-2P1 and AZ EXP ArF-2P5A, both of which show good filling performance.

Due to miniaturization of semiconductor devices, ArF (193nm) lithography is likely expected to be used for sub 100nm regime. For sub 100nm devices, high NA (>=0.70) exposure tools and various strong off-axis illumination (OAI) conditions should be used. But unlike KrF (248nm) lithography, resist pattern collapse becomes one of the most serious problems in ArF lithography. In order to solve pattern collapse problem, thin resist process is generally introduced but its poor etch resistance is an obstacle for being applied in real production process. Due to this reason, new kinds of organic BARC materials are investigated and optimized to avoid pattern collapse. As mentioned, the most important issue in ArF organic BARC is believed to be the pattern collapse problem. A number of organic BARCs were made by varying polymer, cross-linker, thermal acid generator, and additive. We tried to analyze the key factor in terms of pattern collapse. This paper is to compare the various elements of the organic BARC formulation and to discuss what brings and causes pattern collapse.

The aggressive scaling in critical dimensions, coupled with the increasing use of subresolution features in optical proximity correction (OPC), dictates that maskwriters should have at their disposal electron beam resists capable of printing 100-nm OPC features on 280-nm design rule masks (70-nm features on the wafer). There is a need to survey commercial chemically amplified resists for use as mask making resists, and for completeness, such a survey would require that each resist be compared with an optimized resist process. To accomplish this task in a acceptable time period we have chosen to perform electron beam lithography modeling to quickly identify the resist process combinations that will lead to superior resist performance. We have used the technique of combining electron beam resist modeling with lithography to screen chemically amplified resists for use in electron beam mask making. This was accomplished by comparing experimentally determined resist sensitivities and profiles with those predicted from ProBeam /3D lithography modeling software.

The goal of this work was to develop a resist material for high-keV (>=10 keV) electron beam patterning with: (1) high sensitivity (~10 (mu) C/cm² 50 keV), (2) high contrast, and (3) etch resistance comparable to current optical resists. In this work, an approach was desired that (1) used multi-component resist design to decouple sensitivity and etch performance and improve contrast but (2) avoided environmental stability problems. Therefore, a resist design first proposed by researchers at IBM in the late 1980s that uses an electron beam sensitive polymeric dissolution inhibitor (poly (2-methyl-1-pentene co 2-ethoxyethyl-methallyl ether sulfone)) in conjunction with novolac resins was explored in this work. In this paper, the fundamental behavior of the polysulfone dissolution inhibitor upon exposure to e-beam and heat was studied. This behavior establishes the processing window for the polysulfone dissolution inhibitor. The thermal stability of polysulfone was studied using TGA, FTIR, and mass spectrometry. The results show that accelerated decomposition of polysulfone occurs above 150 degree(s)C. Polysulfone decomposition upon exposure to e-beam was studied using (1) ellipsometry, (2) quartz crystal microbalance methods, and (3) FTIR. The results of this study show that polysulfone is highly sensitive to electron beam exposure and most of it decomposes at a very low nominal e-beam dose.

Sub 100 nm T-gate structures have been produced using a tri- level resist stack modified from previously published results utilizing ZEP7000A, PMGI and ZEP520A positive e-beam resists. The new resist stack replaces the top resist with the more sensitive ZEP7000A from Zeon Chemical. The does sensitivity of the ZEP1000A is an order of magnitude higher than the ZEP520A. This difference provides the flexibility to create T-gate structures with larger top cross-sectional dimensions, which increase the transconductance. The technique can also be used to create other novel structures such as gamma-gates and small air bridges, by varying the dose on the different parts of a feature design to achieve the desired three-dimensional resist structure.

In this study, it is investigated how chemical modifications of a given resist platform can induce improvements in e-beam lithographic performances. Molecular weight (Mw) as well as photo-acid generator (PAG) modifications will act as fine tuners for Sumitomo NEB-33 negative resist to match specific applications: preparation of advanced CMOS R&D architecture (highly resolving resists needed) and fast patterning for production environment (highly sensitive resists needed).

Namatsu, van Delft, and others have reported printing exceptionally small features using high voltage (>50kV) electron beam exposure of hydrogen silsesquioxane (HSQ). They also reported that HSQ has very high exposure dose requirements (~2000(mu) C/cm² at 100kV). We have explored the utility of HSQ as a resist for low-voltage electron beam lithography. Because low energy electrons have a very limited penetration depth, a thin film imaging technique must be employed in conjunction with anisotropic oxygen reactive ion etching to generate the high aspect-ratio features required to provide adequate etch resistance for subsequent image transfer steps. HSQ's exceptionally low oxygen plasma etch rate makes it an excellent top layer for a bilayer process of this sort. High resolution, high aspect ratio images were printed with this system using 1kV electrons with an imaging dose of less than 60 (mu) C/cm². The resulting features have very smooth sidewalls. Monte Carlo simulations have been performed for the exposure process and compared to experimental results.

The most common resist used for LIGA applications with deep X-ray lithography is PMMA. It achieves very good resolution of the mask structures with a typical resist thickness from 200 micrometers to 2 mm. The resist system employed here is crosslinked on the substrate after preparation, and this can lead to problems with internal stresses and resist cracking. To optimize the resist performance, a design of experiments procedure was implemented. Design of experiments assists the determination of optimized process parameters through the use of statistical procedures. The principal components of the PMMA resist employed in the optimization procedure were PMMA, adhesion promoter, crosslinker, initiator and accelerator. The PMMA type employed was kept constant and the concentrations of adhesion promoter, crosslinker, initiator and accelerator were altered following a design of experiments methodology. At first 18 resists compositions were prepared and irradiated to determine preliminary exposure behavior. A selection was made from this composition on the basis of the performance, and then these resist composition were irradiated with standard test structures. This determined the performance of the resist to stress, its inherent stability and the inherent resolution that can be achieved. A smaller parameter set was then implemented in the final optimization of the resist. A design of experiments procedure has assisted the optimization of the PMMA resist for LIGA application with deep X-ray lithography. The results obtained demonstrate the effectiveness of the procedure in quickly attaining resist compositions suitable for deep X-ray lithography.

EUV lithography is perhaps the most promising of the NGL technologies for sub-100nm resolution. To address needs in this area, we have designed and synthesized several types of organoelement resists using only low absorbing elements, including H, C, Si and B. One category is based on silicon-containing block and random polymers. They show high transparency according to theoretical simulations and have high oxygen reactive ion etch resistances compared to Novolac resins. In a preliminary study, we were able to image these polymers to 180 nm line/space patterns using EUV exposure. A second type of EUV transparent resist platform involves boron-containing polymers. Carborane carboxylic acid was attached to a copolymer backbone to introduce boron atoms with controlled attachment level. It was found that incorporation of a small amount of B provides remarkably high oxygen etch resistance.

The widespread adoption of advanced packaging techniques is primarily driven by electrical device performance and chip form factor considerations. Flip chip packaging is currently growing at a 27% compound annual rate and it is expected that by 2005 over 60% of all 300 mm wafers will be bumped. To ensure optimal productivity and cost of ownership it is imperative to provide lithographic materials that are optimized for these applications. Flip chip packaging frequently uses one or more redistribution levels to increase the number of pads that can be bumped in the minimum form factor. The redistribution level requires a photosensitive dielectric material to be used as a permanent insulating layer. The mechanical, electrical and lithographic properties of the material for this level are all important. This study will characterize a novel photosensitive siloxane material (Shin-Etsu SINRT Photoresist) for the use in the redistribution layer. Siloxanes are a good choice for redistribution because of their excellent physical properties, ease of processing and relatively low curing temperatures. The lithographic performance of SINR photoresist has been optimized using a broad band 1X stepper to control critical dimensions (CD). This study evaluates process capability at multiple exposure wavelengths and post exposure bake (PEB) conditions. Cross sectional SEM analysis, process linearity, Bossung plots and process windows are used to establish the lithographic capabilities. Material modifications also were investigated to control the photoresist sidewall angles.

We discuss a new dry lithographic process using only carbon dioxide (CO2) as a solvent. Novel CO2 soluble photoresists were synthesized based on random copolymers of poly(1,1-dihydroperfluorooctyl)methacrylate 2-tetrahyrdopyranyl methacrylate. Photoresist spin casting, development, and stripping were all carried out in either liquid or supercritical CO₂. We investigate such parameters as resist sensitivity, contrast, and resolution. The contrast of these resists has been evaluated using 248 nm exposures, and promising test images have been formed.

Incorporating fullerene into DNQ novolak resist provides a 60 percent reduction in the ECR plasma etch rate in a hydrogen/argon plasma. The reduction in plasma etch rate was also accompanied by a 5 degree(s)C increase in the pattern flow temperature. Plasma etch resistance was added to the photoresist after pattern exposure. Fullerene incorporation was accomplished by pattern development in a C₆₀ /tetra-methyl ammonium hydroxide (TMAH) solution.

Bilayer Bi/In thin films form thermal resists with many new microfabrication and micromachining applications due to their changed physical, chemical and optical characteristics after the laser exposures. Wavelength invariance has been shown from the results of both experiment and Airy Summation optical modeling. The modeling projects bimetallic resist sensitivity to be nearly constant at about ~7 mJ/cm² from 248 to 13.4 nm and is still very sensitive at 1 nm in X-ray range. Two kinds of acid solutions were effective in developing the exposed films by removing the unexposed area. Both nitric acid mixture (HNO₃:CH₃COOH:H₂O=1:3:6) and hydrochloride acid mixture (HCl:H₂O₂:H₂O=1:1:48) give etching selectivity of exposed to unexposed area of larger than 60:1. The etch rate of unexposed area is about 2.6 nm/sec. The Bi/In resist can be stripped away by an RCA2 clean. Bi/In resist was successfully used as a mask layer for KOH anisotropic silicon etching process. Due to the unusual conductive property of its exposed and developed films, Bi/In has demonstrated that it can be used as a direct laser write electroplating resist material. Copper and nickel plating was carried out on developed Bi/In layers on various substrates such as Si wafers, glass slides, wet-oxidized wafers. Large optical transmission changes (OD>3.5 before exposure and OD<0.3 after exposure at I-line) indicate that Bi/In can be used as a direct-write photomask material.

Polyacrylate derivative was first developed as raw material for ArF resist and it was selected the first candidate in spite of some defects. Cycloolefin-maleic anhydride polymer[COMA] and other polymers were therefore given opportunity. The resist based on COMA shows a good dry-etch resistance compared with that based on acrylate polymer. However, the pattern profile of the resist formulated by using COMA has some defects such as taper and low resolution because of transmittance issue of the polymer. In order to solve the issue, we have developed a new polymer [It was named ROMA Resin]. The new polymer has good physical properties such as UV transmittance, stability during storage and moderate glass transition temperature. We also found that the pattern profile of the resist formulated by using the polymer shows good results in terms of pattern profile, CD SEM slimming and PED stability.

The greatly compressed resist development cycle and the explosion of the number of resists at a specific lithographic wavelength have necessitated a hastened pace in developing high-performance resists. Traditionally, high- performance chemically amplified resists have been developed by copolymerization of monomers with various functionalities to achieve the desired properties. This approach, while immensely successful, however suffers from long lead times to deliver successful products to the markplace. In this paper, we report a more rapid approach to developing high- performance chemically amplified resists by blending different polymers with complementary properties. As a model system, a 248nm negative-tone bilayer resist has been demonstrated based on acid catalyzed cross-linking of blends of silicon-containing polymers with a non-silicon-containing polymer. The silicon-containing polymers and the non- silicon-containing polymer used were poly(p- hydroxybenzylsilesquioxane-co-p-methoxybenzylsilsesquioxane) (PHBS/MBS), poly(p-hydroxyphenylethylsilesquioxane-co-t- butylsilsesquioxane)(PHPES/BS) and poly(p- hydroxystyrene)(PHS), respectively. The resist based on this simple polymer blend approach has achieved lithographic performance comparable to that based on more elaborate copolymers that require time-consuming synthetic optimization. Differential scanning calorimetry (DSC), quartz crystal microbalance (QCM), and atomic force microscopy (AFM) were employed to probe the properties of the polymer blends and the resist. DSC results suggested that PHBS/MSB and PHS are miscible throughout the entire composition range. Addition of the phenolic polymer into the silicon-containing polymer dramatically improves the lithographic performance of the bilayer resist. This improvement in lithographic performance is attributed to the enhancement of thermal properties (i.e. glass transition temperature), the modulation of dissolution properties, and more cross-linkable sites for the acid catalyzed cross-linking. O₂ RIE etch selectivity of the blends vs. and organic underlayer increases with increasing concentration of the silicon-containing polymer in the blends. The present approach could also be applied to developing other high-performance resists more swiftly at other lithographic wavelengths.

Contact lithography for the 100nm generation is a difficult challenge with current layer 193nm resist processes. The SIA roadmap lists the contact hole size for 100 nm lithography as 115 nm. Even with next generation very high NA (>0.7) 193nm exposure tools, early results indicate that these contact hole sizes can not be obtained with standard processing techniques. Therefore, we have investigated the feasibility of using resist reflow to obtain small contact hole sizes.

In this study we determined the dimension dependent onset of pattern collapse for different 193 and 157nm resist platforms, and explored production relevant techniques to suppress pattern collapse. Test structures were designed and implemented to generate well-defined capillary forces on beams of resist during drying. X-ray and 193nm (using alternating phase shifting masks) lithography were used to print test structures and patterns of dense lines with critical dimensions as small as 100 nm. The collapse behavior was quantified in terms of the critical aspect ratio for collapse as a function of the spacing between structures. The resist platforms exhibited different collapse behavior at line widths of greater than 150 nm, but at line widths of 100 nm and less, all of the resist structures collapsed with aspect ratios greater than 3. A principal conclusion from this work is that changes in resist chemistry or formulation alone will not be sufficient to solve the collapse problem at the 100 nm node and below. The most effective strategy to suppress the resist collapse is to reduce the capillary forces that act on the structures during drying. For 193 nm resists, collapse behavior was quantified for a number of surfactants that were added to the rinse liquid. We demonstrate that with a simple modification of the final rinse and drying process, we could increase the critical aspect ratio from 4.2 to 5.2 at a spacing of 110 nm for a champion resist. This means, for example, that we can image 110 nm dense lines with the surfactant rinse at a thickness of 575 nm whereas without surfactant we were limited to 460 nm. The results are interpreted in terms of the contact angles of rinse liquids on the resists and their respective surface tensions.

The material make-up of photoresists span a wide polarity range and chemistry. Resists contain reactive components which are photochemically triggered to convert and condense to forms that result in a solubility change. When designing a cleaning process, a knowledge of the resist chemistry is fundamental. A DNQ/novolak system may follow a simple dissolution model under normal conditions. However, when the same resist is sent through a dry etch process, crosslinking and metallic impregnation occurs to form a residue that is insoluble by simple dissolution. The same applies for negative-tone resists, where bonds must be broken and a high chemical interaction is needed to facilitate solvent penetration. Negative resists of different chemistry, such as the benzoin/acrylic, trazine/novolak, and azide/isoprene, must be addressed separately for specific polarity and reactant requirements. When dissolving and removing these crosslinked systems, benefits in formulated chemistries such as GenSolveTM and GenCleanTM are immediately observed. Once the chemistry is identified, conditions can be optimized with process design using temperature, agitation, and rinsing to achieve a robust process with a wide process latitude.

We analyzed nano-lithography process with using plasma graft polymerized styrene resist and spin coated polystyrene resist in order to find problems and limit of downsizing of the lithography pattern. The ESCA measurement of the interface between the resist and the substrate revealed the chemical structure. Plasma grafted styrene had a chemical bond to the silicon substrate. But spin coated polystyrene was observed that the film condensed without the chemical bond to the substrate. For the spin coated polystyrene film at a thickness of 1nm, ESCA measurement showed a simple peak of carbon and silicon, but showed new chemical shift after Ar ion or E-beam treatment. These results suggested that utilization of the chemical bond between polystyrene and Si will realize single molecular lithography. In this work, we also discussed the mechanism of pattern resolution comparing polystyrene at 2000 and 800 of a molecular weight.