The traditional scaling of feature sizes to ever smaller dimensions which has driven the semiconductor industry for 30 years is being challenged by physical and cost limits. As we approach the development of the l8Onm generation, we have a quite different technology scenario facing us than we have seen in the past. The approaches being contemplated can be summarized in order of utility as: 1. Extensions of existing patterning methods 2. Non-lithography patterning approaches 3. Extensions of the optical projection/reduction approach 4. New beam techniques 5. Probe techniques I will review the challenges in each of these categories and indicate where serious development efforts are needed to sustain technology scaling into the ULSI generations

I propose to discuss three topics that bear on the relations between industrial research labs and research universities. There are powerful forces of change at work on both of these parties; how we think about these changes, and how we react to them, will have a definite effect on the future course of university-industry relations.

The designed optical system, which included an illumination optics and an imaging optics, consists of only one grazing-incidence mirror and a two-aspheric-mirror optics with a synchrotron radiation (SR) as a light-source. The illumination optics provides uniform illumination and high-collection efficiency of radiation from the SR. Since there are only four bounces in this system, including the reflective-mask bounce, this optical system has higher throughput. A throughput of 20-30 wafers/hour is predicted with the designed optics. A one- quarter-size prototype of the designed imaging optics was constructed with the numerical aperture of 0.1 and the magnification of 1/5. The efficiency of 60 percent (obtaining dose per estimated one) was obtained with AZ-PN 100 resist in the experiment. A minimum pattern of 0.12-micrometers lines and spaces was printed on a 0.15-micrometers -thick layer of AZ-PN 100 resist.

Experiments concerning silicon oxide deposition using a focused ion beam were carried out in order to apply silicon oxide as insulator in integrated circuit modification. Silicon oxide film was formed using a 25-keV gallium focused ion beam with a mixed gas of 1.3.5.7- tetramethylcyclotetrasiloxane and oxygen. The deposited film consisted of mainly silicon and oxygen, which was analyzed by micro-Auger electron spectroscopy. It also contained 5 percent gallium, but carbon content was below noise level. The ratio of silicon to oxygen was 1 to 2. It was found that carbon content depended on oxygen used as deposition source gas. The resistivities of the eight deposited silicon oxide films were measured. The resistivities wer 28-79 M(Omega) cm at 5 volts and these values did not change significantly even after the samples were left in a room for three months. It was determined that it will be possible to use deposited silicon oxide for integrated circuit modification.

A laboratory extreme ultraviolet ltihography tool (EUVL) has been assembled at Sandia National Laboratories. Its major components include a Schwarzschild camera with 0.1 micrometers resolution integrated with a laser plasma source and a magnetically levitated stage. Other subsystems are a grazing-incidence optical system to maintain focus, and a through-the- lens Moire alignment system for overlay. This exposure tool is being used to study integration issues for EUVL. Experiments have been performed to characterize the alignment system's performance. The measured sensitivity of the alignment system is 25 nm 3(sigma) .

Short-period GaAs quantum wire (QWR) array was grown by metalorganic chemical vapor deposition on submicron gratings. And a new lithography technique to fabricate submicron current-blocking layer on the short-period QWR array without any external masks was developed. The methods include the followings. The photoresist was coated on the nonplanar top of the laser diode structure. The photoresist stripes were designed to remain over each QWR with a flood exposure and a develop technique. The GaAs contact layers on the parts of the (111)A and all the (100) top quantum wells were removed by employing the photoresist remaining on the top valley as masks. The submicron current-blocking layer was produced all over the regions except QWR's, by sputtering SiO₂ film followed by lift-off and metal evaporation. It must help a majority of current pass into QWR active region.

General theoretical schemes have been detailed for the designing of the ion projection lithography systems, using the results of preceding theoretical investigations. The designing is on the basis of simulation modeling by splitting off critical conditions and using known regularity of formation optical characteristics. The initial step of an investigation begins with the search of optimum configuration with respect to distortion as the most critical parameter. It is finding a corresponding configuration given reduction in the best way. Introduction of some additional degrees of freedom in two lenses projector makes tuning to required magnification coefficient possible. Then the problem of paraxiality for a system whole is solved. Large attention is given to research of the different collateral phenomena. Accounting all potential sources of perturbations is used for an individual tolerances. The contrast function is calculated for the required resolution.

Constantly growing chip areas, scaling down of pattern sizes, proximity corrections, OPC etc. gives rise to an expansion of layout data. The methods of our JENOPTIK universal exposure systems outlined in this paper serve the purpose of drastically reducing the enormous data volumes. ZBA e-beam systems are capable of processing repeated subpatterns down to runtime format. The ZBA-subpatterns may have any complexity and can be positioned randomly or as an array. Subpatterns are exploded by a fast specific hardware in the very last moment of exposure. Using such repetitive structures, data preprocessing, data transfer and data exposure times are considerably reduced. A suitable data preprocessor is described to provide detecting and saving of substructures.

We have developed a technique based on use of a novel e-beam detector to enhance pattern placement accuracy of high-performance e-beam tools in the patterning of membrane masks. The detector consists of a reverse biased Schottky diode whose area coincides with that of the membrane, and which is placed immediately behind the membrane/-absorber/resist multilayer. An accurately patterned absorber overlayer covers the detector surface. The overlayer absorbs a fraction of the incident electrons, modulating the detector signal as the beam passes over the membrane. We have studied and modeled the performance of prototype detectors covered with 16 micrometers period gratings over an incident energy range of 5-50 keV. The combination of Schottky diode and patterned overlayer has been used to improve electron scattering models. We have observed excellent SNR with a 40 nC/cm² dose at 50 kV, and spatial resolution better than 0.1 micrometers of a beam transmitted through a membrane. More accurate position information can be obtained by taking a Fourier transform of the diode current waveform created as the incident beam traverses several grating periods. In a poor operating environment, we have observed phase accuracy in 100 micrometers fields of +/- 4 degrees. We have developed an algorithm capable of processing pattern-based data sets at high speeds and low information storage requirements. This technique can be easily implemented with little overhead and little modification of existing systems.

A new electron beam (EB) mask writing system based on both the Hitachi HL-700MIII and HL-800D systems is developed. The target of the system is a 0.25 micrometers design rule in semiconductor mass-production. To improve critical dimensions (CD) to better than 0.03 micrometers , an acceleration voltage of 50 kV is used with a variable shaped beam method. Further, EB proximity correction using a pattern area density map which is the same as that of HL-800D has been adopted for the improvement of pattern width linearities. This correction system, which consists of hardware only, covers the entire mask area. In the mechanical system, continuously moving stage with constant velocity and three-axis active vibration- isolation are used to improve positioning accuracy to better than 0.04 micrometers . In addition, a new mask handling system in which a robot carries the mask realizes automatic transportation without human assistance. Some experiments to evaluate the new system have been performed. In particular, the characteristics of masks written with an EB accelerated to 50 kV have been investigated. The results of CD pattern uniformity for a 1 micrometers line pattern over the entire mask area are better that 0.025 micrometers . In addition, pattern linearity using EB proximity correction is within +/- 0.03 micrometers . A stitching accuracy of 0.037 micrometers is obtained.

Two new positive tone, chemically amplified, DUV resists from Shipley, XP-9525 and XP- 9549Q (UV III) have been investigated for use as direct write e-beam resists. Both of these materials have shown extremely high resolution capabilities while maintaining excellent sensitivity to e-beam exposure. Sub-0.20 micrometers line and space gratings were resolved in UV III, and 0.10 micrometers gratings were resolved in XP-9525. A formal design of experiment was created and used as a framework to develop a process for UV III which would optimize several resultant responses including: exposure latitude, edge roughness, and sensitivity. This paper will discuss the process development of these resists, and detail their performance characteristics. Effects relating to post-exposure bake delay will also be considered due to the susceptibility of many chemically amplified resists to airborne contaminants. UV III exhibited much greater stability than XP-9525, and was able to maintain precise linewidth control after 4 hours of delay, making it acceptable for use in a normal process environment. In contrast, XP-9525 exhibited severe T-topping after post-exposure bake delays of only 15 minutes, a condition which can only be solved using additional processing steps and/or environmental controls.

The critical dimension uniformity required in the fabrication of photomasks for 1 gigabit DRAMs will be more stringent that 20 nm in terms of 3 sigma. High-voltage variable-shaped e-beam (VSB) writing is advantageous because of its high resolution, linewidth stability, and throughput performance. However, stitching errors in VSB writing have been a critical problem in the fabrication of advanced photomasks. In this paper, an improved method to calibrate the size of a VSB shot and reduce shot stitching errors is proposed. The accuracy of the calibration method depends on that of the linewidth measurement system, and shot-size calibration with an accuracy of +/- 10 nm can be achieved using existing measurement systems. The positioning accuracy of VSB shots was enhanced by a multiple pass exposure scheme. With these procedures applied to a 50 kV VSB system, the linewidth variation of a photomask in a local area such as a square region of 200 micrometers X 200 micrometers was reduced to less than 20 nm.

In this paper we explore the pattern density dependent contrast which results from the non- Gaussian nature of the energy deposition profile in exposed resist. A long, spatially extended tail on the actual beam energy deposition profile degrades exposure contrast over that which is predicted by two-Gaussian models. As most background dose equalization schemes, such as GHOST, depend critically on the two-Gaussian model for their success, these schemes cannot correct for background dose variation caused by these long tails. This paper shows that this effect can lead to significant degradation of critical dimension control. A strategy to minimize this degradation based on test structure evaluation is proposed.

We have studied two mark geometries for possible use in a projection e-beam lithography system using SCALPEL (scattering with angular limitation in projection electron lithography). These are V-grooves and vertically etched geometries, pedestals or trenches. We report results of measurements of backscattered electron (BSE) contrast form topographic marks of varying size and as a function of energy up to 100 kV. The marks were fabricated on silicon wafers. The measurements were taken both in a scanning electron microscope and in an experimental SCALPEL machine operating in focused probe mode. The V-grooves ranged from 1.0 to 30 micrometers wide. The vertical etched features ranged from 2 to 30 micrometers wide and 0.6 and 50 micrometers depth. The results depended not only on the feature width and depth, but also on whether the features were isolated or in line and space patterns. Using a BSE ratio of 1.05 as a criterion for acceptable contrast from an alignment mark, V-grooves and vertical etched features had acceptable contrast with exception of the smallest and shallowest features for both geometries.

Both e-beam and optical proximity effects are still a major barrier in the transfer of an ULSI design from the CAD station to the printed result on wafer. Optical proximity effect correction (OPC) is shown to be a strong tool to improve the printing latitudes for i-line lithography of 0.35 micrometers feature sizes and below, but leads to fractal geometries around 0.1 micrometers (corresponding to 0.5 micrometers on a 5x reticle). This quantum leap in required minimum linewidth on the mask may urge mask makers to apply e-beam proximity effect correction (PEC), even more than a decrease in the reticle magnification from 5x to 4x (and further) would. For raster scan e-beams, which are typically used in mask making, correction by dose variation is not practical. Hence, PEC for these systems must be tackled by modifying the geometry of the design, in a way similar to OPC techniques. Both corrections must compromise between the accuracy achieved, which is dominated by the selected (correction and exposure) grid size, and the resulting throughput loss, caused by the use of a smaller grid size. Sigma-C now introduces a new algorithm, which enables the proximity effect correction by shape variation. It is included into CAPROX and supports hierarchy in the same manner as the other postprocessing operations. The exposure of the shape corrected pattern on a raster scan machine requires only one beam pass, whereas dose variation would require one pass for each dose. Exposures were made at IMEC and at Compugraphics. The first results on Leica EBMF10.5 and MEBES III are promising. The pure shape correction increases the line width uniformity and opens the process window for critical dimensions below 1 micrometers . Performance measurements show that the 64 Mb DRAM is a job of a few hours.

This paper reports the initial results and experimental approach method on three-dimensional simulation and modeling of electron beam lithography in the 0.2micrometers line and space patterns. We studied the electron scattering distribution in the resist, the energy distribution of patterns and the developement mechanism for profile formation. The simplified string model of three-dimensions is used to remove the pattern exposed by direct writing. Development rate is experimentally decided as the dependency of dose, development time, and resisit characteristics in the solvents to delineate 0.2micrometers /0.3micrometers line and space patterns for negative and positive resist. As a result, we obtained the optimum resist profile of 0.2micrometers line and space patterns with various forms as the variance of exposure energy and develop time. Also, we can see the proximity effects in generating pattern. These results agree with actual process for deep sub-micron patterns.

Grating-pitch accuracy is studied from minimum pitch variation point of view. The pitches of the gratings delineated at the focus range from -50micrometers to +50micrometers and stitching errors between subfields are evaluated using an EB machine which features a long distance between the deflector and the wafer stage. The grating pitch variation is realized by using a deflection amplitude control. It is confirmed that errors of the pitches due to defocus are less than 0.05 nm, and the deviations from nominal setting of the pitch are also less than 0.1 nm when the pitches are varied from -6 percent to +6 percent at 0.1 percent step.

The mix-and-match method is an effective method to meet the requirements of minimizing the exposure time and the feature size, in which only the critical gate layer is exposed by electron beam lithography system, and the other ones by conventional g-line stepper. The negative type chemically amplified resist SAL601, made by Shipley, has been used for gate fabrication. The optimum conditions for the electron beam lithography including mark dimension, resist process and etching process have been investigated. The accelerating voltage and the beam current were fixed to be 40 kV and 0.25 nA, respectively. The mark of the electron beam lithography has the trench cross shape of 0.5 micrometers in depth, 20 micrometers in length and 3 micrometers in width. The sensitivity of SAL601 resist has been 20 (mu) C/cm² for 0.1 micrometers patterning at 40 kV accelerating voltage. The polysilicon gate was etched by electron cyclotron resonance with SiO₂ thin mask in HBr/O₂ gas, for the appropriate anisotropy of etching and for the polysilicon-to-oxide selectivity of HBr/O₂ gas plasma. The well defined profile of polysilicon gate with 0.1 micrometers width has been obtained successfully.

The Microlithographic Mask Development Center (MMD) was established as the X-ray mask manufacturing facility at the IBM Microelectronics Division semiconductor fabricator in Essex Junction, Vermont. This center, in operation for over two years, produces high yielding, defect-free X-ray masks for competitive logic and memory products at 250nm groundrules and below. The MMD is a complete mask facility that manufactures silicon membrane mask blanks in the NIST format and finished masks with electroplated gold X-ray absorber. Mask patterning, with dimensions as small as 180 nm, is accomplished using IBM-built variable shaped spot e-beam systems. Masks are routinely inspected and repaired using state-of-the-art equipment: two KLA SEM Specs for defect inspection, a Leica LMS 2000 for image placement characterization, an Amray 2040c for image dimension characterization and a Micrion 8000 XMR for defect repair. This facility maintains a baseline mask process with daily production of 250nm, 32Mb SRAM line monitor masks for the continuous improvement of mask quality and processes. Development masks are produced for several semiconductor manufacturers including IBM, Motorola, Loral, and Sanders. Masks for 64Mb and 256Mb DRAM (IBM) and advanced logic/SRAM (IBM and Motorola) designs have also been delivered. This paper describes the MMD facility and its technical capabilities. Key manufacturing metrics such as mask turnaround time, parametric yield learning and defect reduction activities are highlighted. The challenges associated with improved mask quality, sub-180nm mask fabrication, and the transition to refractory metal absorber are discussed.

This paper presents results of using silicon carbide (SiC) and silicon-rich silicon nitride (SiN_x) as membrane for X-ray masks in technology of X-ray lithography. Microcrystalline silicon carbide film was deposited on silicon substrate by electron synchrotron resonance plasma-enhanced chemical vapor deposition at 300 degrees C utilizing a SiH₄/CH₄/H₂/Ar gas mixture. Low tensile stress film which is suitable as X-ray membrane can be achieved by annealing after silicon carbide film deposition. The microwave power over 800 watts and the gas ratio (Methane:Silane) larger than 1.5 are needed for the stoichiometry of SiC film. On the other hand, we deposited silicon-rich silicon nitride film on silicon substrate by low pressure chemical vapor deposition at 850 degrees C to 900 degrees C. In order to get low tensile stress film, different gas flow ratios (Dichlorosilane:Ammonia) were tested. The increased gas flow ratio (Dichlorosilane:Ammonia) and the increased deposition temperature are related to the decrease of tensile stress of film. Roughness, uniformity, optical transmittance and soft X-ray transmission of both films are reported. The absorption bands of both films were measured by FTIR spectroscopy. The surface morphology was monitored by AFM. The photon transmission of both films was measured in the range of 400 to 800 nm for visible light and 800 to 1600 ev photon energy for SR soft X-ray transmission was conducted at the Synchrotron Radiation Research Center, Hsinchu, Taiwan. The deposition rate of both films are 13 nm/min and 40 nm/min for silicon nitride and silicon carbide, respectively.

A continuing trend in X-ray lithography is the requirement for high accuracy masks. Image placement, or the ability to pattern images in the correct locations, is one of the most critical requirements. It is driven by a number of parameters, including the electron-beam lithography system and precision of the metrology system. Also, because the X-ray mask substrate consists of a thin membrane, it is very susceptible to the stresses of the resist film, absorber material, and plating base. An extensive analysis of the contributors to image placement was performed to determine the relative contribution of each. This analysis highlighted those contributors which caused the largest distortions and which, therefore, presented the most opportunities for improvement. Several changes were then implemented which resulted in a 50 percent overall improvement to placement of the X-ray mask images. The experimental design and detailed results are discussed.

We present the design and preliminary experimental results on a novel x-ray mask inspection tool based on a transmission x-ray secondary electron conversion microscope (TXsecM). The x-ray beam transmitted through the mask impinges onto a high quantum yield photoemissive cathode located at the plane where the wafer will be placed in the stepper. The cathode converts photons into low energy secondary electrons with narrow bandwidth, and the electrons are then imaged by a specially designed low voltage electrostatic lens column with 1200X magnification. Therefore, the micrographs thus obtained represent an accurate map of the x-ray radiation on the resist in an actual production exposure. TXsecM is an ideal tool for x-ray mask inspection as well as image formation analysis in real time. The design goal is to achieve 20nm spatial resolution.

The applicability of synchrotron radiation (SR) lithography to fabricate a giga bit scale dynamic random access memory (DRAM) cell array structure with minimum feature size of 0.14micrometers is demonstrated. Four lithography levels, isolation, transfer gate, bit line and storage node, were exposed by SR lithography. Exposure was carried out at Mitsubishi SR lithography facility using Canon x-ray stepper XFPA with a new negative tone resist and home-made x-ray mask set for each exposure level. These masks were composed of 2micrometers SiC membrane and 0.5micrometers W-Ti absorber. To minimize the mask-induced distortion, we applied the various techniques to the x-ray mask fabrication, changing the mask fabrication process flow, step annealing and electron beam multiple writing, and as the result, the pattern placement accuracy between two exposure level masks was about 50nm. Exposure latitude was about 22 percent for 0.15micrometers line and space pattern at the proximity gap of 30micrometers , and the critical dimension deviation for 0.14micrometers transfer gate pattern was 0.014micrometers at the almost same position in the mask in spite of the replication on the real DRAM topographic structure. The overlay accuracy was about 80nm for 20 X 20mm2 area. These results show SR lithography is the promising technique for giga bit level device fabrication.

X-ray exposures performed at IBM's Advanced Lithography Facility (ALF) in Hopewell Junction, New York has led to the ability to routinely print sub 250nm discrete devices in photoresist. When fully processed, the resulting electrical channel length for these devices is below 150nm leading to average switching delays of 35 picoseconds. Sub 150nm devices with resulting electrical channel lengths of 100nm have also been made producing switching delays of 20 picoseconds, which are among the fastest reported in CMOS technology. In addition to the discrete devices, fully functional 0.25um 64Kb SRAMs were fabricated with an approximate 40 percent chip yield on the best wafer. Recent improvements in the overall lithographic process have enabled the gate line to be printed at sub 125nm. The resulting electrical channel is below 100nm. Device performance is expected to be faster at these smaller dimensions. The results obtained are based on several lots of 200mm wafers processed with the use of mix and match (x-ray to optical) steppers. The results can be viewed as current x-ray lithography in ALF.

Simple geometric considerations suggest that the interface between a photoresist and a wafer surface will be increasingly important in semiconductor lithography as critical dimensions in X-ray and other lithographies drop below 0.25 micrometers . A sensitive, qualitative adhesion test, indentation debonding, was used to compare directly the adhesion of a photoresist to a silicon native oxide throughout various wafer preparation procedures prior to exposure. It is argued and shown that hexamethyldisilazane (HMDS), a commonly used primer, is unlikely to be the optimal choice at feature dimensions below 0.25 micrometers . Application of HMDS left solely methyl groups at the surface of the wafer allowing only for Van der Waals forces for interactions with the polymer. This actually weakened the potential for chemical bonding between the resist and the wafer, in agreement with others. It is also shown that the bonding sites available at the surface of the native oxide varied with cleaning preparation of the wafer and with time of storage between the final cleaning step and lithography. HMDS was not adept at covering the variable native oxide, and this may have allowed for contaminant species such as water or aqueous bases to more easily compete with the polymer for surface sites. A monomolecular layer of organotrimethoxysilane was found to be superior at normalizing the variability of the substrate and also offered the ability to design the functional moieties of the monolayer preferentially to interact with the resist backbone. If designed properly, the increased interaction of the monolayer primer with the polymer can be enhanced while concurrently decreasing the potential for interference from competing monomeric contaminants such as water or aqueous developers. This improves both mechanical and lithographic adhesion.

The use of the X-ray lithography to produce blazed diffractive optical elements (DOEs) is described. The proposed method allows one to make highly efficient blazed DOE with a deep phase profile (ten wavelengths and more) using a single X-ray mask with a binary transmission pattern. Unlike the well-known multilevel DOEs, blazed ones do not involve fabrication and aligning of a set of masks. DOEs with a profile depth of 10 micrometers and more and zone sizes of down to 1 micrometers can be obtained due to the short wavelength and high penetrability of X- rays. The first experimental samples of blazed DOEs with a 10 micrometers -height profile (lenses and gratings) were fabricated by X-ray lithography with synchrotron radiation using the X-ray masks, prepared in accordance with the pulse-width modulation algorithm. Diffraction efficiency for lenses was measured for white light. It is higher than 80 percent for the central part of the lenses (inside a 10 mm diameter) and about 60 percent for an area of 20 mm diameter.

The X-ray lithography with synchrotron radiation at the VEPP-3 storage ring was applied for fabrication of polymer microstructures with submicron sizes of elements and with rather high aspect ratio (up to 20). The microstructures are the regular microporous membranes with pores of 0.3-0.5 micrometers in diameter arranged with a 1 micrometers spacing. The membranes were fabricated on a base of 2.5, 3, 6 and 10 micrometers thick mylar films. In contrast to the commercial track membranes with random pore locations, the regular membranes have no dispersion of pore sizes caused by confluence of adjoining pores. The fabricated membranes have a porosity of 10-20 percent and this value can be increased up to 50 percent and higher by using an X-ray mask with an appropriate pattern. The results of the membrane examination by different techniques are presented. Possible improvements of the membrane parameters and some potential applications of the membranes are discussed as well.

Spherical pinch and vacuum spark have been pursued by Advanced Laser and Fusion Technology, Inc. for a number of years as candidates for point radiation source needed in microlithography. In the spherical pinch electrical energy is used to generate spherical imploding shock waves that compress a performed plasma into small (diameter < 1.0 mm) radiation source. The temperature of the central plasma can be high enough for emission of broadband radiation from the UV to the soft X-ray region of the spectrum. In the vacuum spark a small capacitor (a few nF) is discharged through two properly shaped electrodes in a vacuum. During the discharge 'hot spots' (minute high temperature plasmas) are formed in the vicinity of the anode and intense pulsed soft X-rays can be generated around the characteristic lines of the electrode materials. High rep-rate operation of the vacuum spark is necessary to provide sufficient dosage for microlithography.

As a synchrotron or excimer-laser alternative, this paper presents transition radiation as a soft x-ray source for step and scan lithography. This source offers high brightness, collimation, modest operating vacuum, ideal spectral characteristics and moderate cost. The x-ray radiation is emitted in a forward cone in the 0.5-1.8 keV range and generated by electron beams with moderate energies between 25-100 MeV. The radiator target consists of many thin metal foils of beryllium, which are separated by a vacuum. The target output power wavelength can be optimized for highest photoresist sensitivity, window transmission and minimal spurious exposure. For collimation, ellipsoidal-grazing-angle optics or capillary optics increase the mask/wafer image plane into a finite-line image. As in synchrotron systems, the line is then scanned for dose uniformity. For a 70-MeV 400-(mu) A-average-current electron beam, the total x-ray power delivered through the 1-micrometers Si window and 1-micrometers Si substrate to the photoresist in the photon energy in the desired bandwidth (0.5 to 1.8 keV) is 16 mW in a 22-mm X 32-mm area. With a 1-mJ/cm² resist (required for EUV-lithography), the exposure time would be 440 mS.

A hot and dense plasma produced from a laser-irradiated gas puff target, created by pulsed injection of gas with a solenoid valve, offers the possibility to realize a debrisless x-ray point source for the x-ray lithography applications. This paper reports experimental investigations on the x-ray generation in 1-keV photon-energy range from a high-pressure gas puff xenon target irradiated with a laser pulse of 1-ns duration at intensities of about 10¹³ Wcm^-2. X-ray output in this range for the gas puff xenon target, estimated from the measurements made using the semiconductor detectors, was higher than x-ray output for a solid tellurium or iron target measured for the same conditions.

The effects of exposure damage with an electron beam of 20 to 50 kV acceleration voltage on silicon nitride film prepared by LPCVD system have been investigated. It is shown that the optical and mechanical properties of this material are modified and may potentially limit the use as a membrane in an x-ray mask structure for the high density memory devices of GDRAM level. Especially, the optical transmission of films exposed by electron beam with the acceleration voltage of 50 kV and the dosage of 900 (mu) C/cm² degraded about 17 percent in the wavelength range of 633 +/- 10 nm. The differences in mechanical deflection on the membrane area of 800 X 800 micrometers ² area which was, before and after, exposed by electron beam of acceleration voltage of 20 kV - 50 kV were shown about 500 angstrom to 100 angstrom. It was measured by the (alpha) -step (Tencor 200) with the stylus force of 19.6 dyne. The distortion of SiN X-ray mask membrane with alignment window was investigated by interferometric phase mapping.

When residual or uncorrected leveling/tilt errors are present at a wafer site, during exposure, gap accuracy and repeatability can not be determined from overall field size measurements in the x and y directions. In such cases, gap is a function of wafer/site plane leveling or tilt in the exposure column. For a given field size, gap is determined by the tilt angle, or conversely, for a given site tilt angle, gap, is a function of field size. As a result, four measurements are needed, at each site, to determine both the actual site position and orientation during exposure, and the corrections required to reduce the magnification errors and field distortions to acceptable levels.

Electron beam direct writing is used to structure resist over topographical surfaces of technological layers. By using accelerating voltages of 2.5 kV and 20 kV different shapes of the resist profiles after wet deveopment are found. Applying Monte-Carlo methods to simulate the travelling of electrons in matter and using a cell-removal-algorithm to calculate the following wet development an agreement between experimental and simulated resist profiles is achieved to understand this behavior.

We have developed new enhanced inspection techniques for small hole defect and half-tone defect in x-ray masks with the printed wafer inspection method. As the inspection sensitivity depends on the signal quality from the inspection sample as well as the performance of the inspection system, we focused on improving the signal quality from the resist pattern by selecting a better x-ray exposure condition. To inspect small hole defects in x-ray mask, we fabricated dot patterns with high contrast signal by printing with negative resist, and succeeded in detecting them accurately. For half-tone defects in x-ray mask, we induced larger defects than original ones by varying the x-ray exposure dosage from the standard, and succeeded in detecting them accurately. These techniques are being applied to the defect inspection process to make a defect-free x-ray mask.

Conventional resist application techniques are based on spinning a resist layer onto a mechanically dominating substrate. As thicker imaging layers are required, the integrity of the resist/substrate system is influenced by the resist thickness. The traditional LIGA approach is to form a PMMA resist sheet on the substrate by casting using a press. This method causes high stresses in the resist and at the resist/substrate interface. Another method consists of gluing or bonding a PMMA sheet with subsequent machining to a desired thickness. The stresses can be high enough to cause the resist to crack and/or separate from the substrate. In this paper, alternative and improved techniques are presented. One of these is a modified multiple coating spin-on method, suitable for producing PMMA resist thickness of 60-80 micrometers . The other method is based on bonding a solid PMMA sheet of desired thickness using an appropriate solvent. These techniques produce uniform PMMA layers with thicknesses ranging from 5 micrometers to 1500 micrometers and above. A mechanical cleaving test was used to estimate the resist/substrate bond strength and characterize the bonding solvents. Issues such as radiation swelling and thickness losses associated with latent image formation in PMMA are addressed.

This paper reports on electron beam lithography for super low noise HEMT (high electron mobility transistor)s. For the optimization of the electron beam lithography for the HEMTs, the SPACING (spacing between the footprint and the head patterns) and the dosage for the head and the footprint to define 0.1 micrometers T-shaped gates with wide head at 30 kV acceleration voltage were investigated by experiment and Monte Carlo simulation. We also compared the single exposure method with dose split method. The footprint of 1 pixel line is to be 0.1 micrometers and the head size to be larger that 1 micrometers when the dosage of the footprint is 700 (mu) C/cm², the SPACING is 3 pixels and the head dosage is 60 (mu) C/cm². Using this optimized technique, a T-shaped gate of 0.1 micrometers level with a high ratio of gate head size to footprint, larger than 10, was obtained, and a AlGaAs/InGaAs/GaAs pseudomorphic HEMT with 0.13 micrometers T-shaped gate was successfully fabricated. The HEMT device exhibited very low noise figures of 0.34 dB and 0.49 dB at 12 GHz and 18 GHz, respectively.

This paper focuses on the process latitude for achieving 100-500 nm dimensions in SAL-601 e-beam resist. Si wafers were coated with 140 nm of resist and lithographically exposed with a JEOL JBX-5DII e-beam lithography system, operated at 50 kV and a probe standard deviation, (sigma) , of approximately 10 nm. Post exposure bake (PEB) conditions were 105 degrees C for 1, 3, and 10 min. and 110 degrees C for 1 min. The measured backscatter coefficient was 0.51, in agreement with out Monte Carlo simulation results. Resist thickness measurements showed a factor of 2 variation in sensitivity with PEB conditions but no change in contrast. The measured linespread functions for isolated lines could be fit to single Gaussians with (sigma) of 27-33 nm, depending of the PEB conditions. The measured widths of the linespread functions were more than a factor of 2 larger than predicted by the Monte Carlo simulation. The PEB condition of 105 degrees C for 1 min. showed slightly better dose latitude than the other PEB conditions for fabricating gaps between pads. Still the process latitude became acutely narrow in patterning 100 nm gaps. For 20 micrometers pads the dose latitude was less than 3 percent. There was no single dose that could produce a gap of less than 250 nm in a tower pattern with pad widths of 0.5 to 20 micrometers . The results are compared to calculated dose profiles that incorporate both measured linespread functions and those generated by a Monte Carlo code.

A process for the fabrication of surface acoustic wave (SAW) devices with line widths of 250 nm and less, based on x-ray lithography using a laser-plasma source has been developed. The x-ray lithography process is based on keV x-ray emission from Cu plasma produced by 15 Hz, 50 ps, 248 nm KrF excimer laser pulses. The full structure of a 2 GHz surface acoustic wave filter with interdigital transducers in a split-electrode geometry has been manufactured. The devices require patterning a 150 nm thick aluminum layer on a LiNbO₃ substrate with electrodes 250 nm wide. The manufacturing process has two main steps: x-ray mask fabrication employing e-beam lithography and x-ray lithography to obtain the final device. The x-ray masks are fabricated on 1 micrometers thick membranes of Si₂N₄. The line patterns on the masks are written into PMMA resist using a scanning electron microscope which has been interfaced to a personal computer equipped to control the x and y scan voltages. The opaque regions of the x-ray mask are then formed by electroplating fine grain gold into the open spaces in the etched PMMA. The mask and sample are mounted in an exposure cassette with a fixed spacer of 10 micrometers separating them. The sample consists of a LiNbO₃ substrate coated with Shipley XP90104C x-ray resist which has been previously characterized. The x-ray patterning is carried out in an exposure chamber with flowing helium background gas in order to minimize debris deposition on the filters. After etching the x-ray resist, the final patterns are produced using metallization and a standard lift-off technique. The SAW filters are then bonded and packaged onto impedance matching striplines. The resultant devices are tested using Scalar Network Analyzers. The final devices produced had a center frequency of 1.93 GHz with a bandwidth of 98 MHz, close to the expected performance of our simple design.

Scanning probe microscopes are promising tools for fabrication of nanometer size structures (nanolithography) since the use of near field interactions avoids problems associated with conventional lithography techniques, like the restriction of the limit of minimum structure sizes by wavelengths, or diffraction phenomena. Several applications of scanning probe microscopes to nanolithography are reported, and even though these instruments have been successfully used for sub-micron lithography, their application is limited to selected surfaces, materials, and low thicknesses of the resist layers. A new technique combining both extremely high resolution and the ability of 'exposing' conventional e-beam resists is lithography with a scanning force microscope in liquid environment. The substrate with the resist is placed in development liquid, and the microscope tip is scanned in direct contact with the surface leading to a local solution of the resist restricted to the small contact area between tip and surface. First experiments had been carried out leading to minimal structure sizes in conventional e-beam resists of 94 nm line width, and to maximum areas of approximately 20 micrometers by 20 micrometers .

Simple measurements techniques for evaluation of x-ray lithography sources are presented in this paper. Experimental results obtained with this simple method in a point source x-ray system consisting of a Cu target irradiated by a Nd:glass laser agree with complete calculations performed taking into account the spectrum from the x-ray source measured with calibrated crystal and CCD detectors.