BackgroundA plausible approach for mitigating the mask 3-D (M3D) effects observed in extreme ultraviolet (EUV) lithography is to replace the existing mask absorber with alternative materials. Absorbers with a high EUV extinction coefficient k allow for lower best focus variation (BFV) through pitch and reduced telecentricity errors (TCEs).AimWe aim to evaluate Ta-Co alloys as potential high-k mask absorbers from material suitability and imaging standpoints.ApproachWe study the film morphology, surface composition, and stability of Ta-Co alloys in mask cleaning solutions and a hydrogen environment as present in the EUV scanner to assess the material suitability from an experimental aspect. Optical constants for three selected compositions, viz., TaCo, Ta2Co, and TaCo3, were determined from EUV angle-dependent reflectivity measurements. Next, utilizing rigorous simulation software, the imaging performance of Ta-Co alloys is evaluated and compared with the reference absorber. The recommended absorber thickness for Ta-Co alloy absorbers is based upon normalized image log slope (NILS) enhancement, threshold to size, and balancing of diffraction order amplitudes. A 10 nm line and space pattern with a pitch of 20 nm and 14 nm square contact holes with a pitch of 28 nm are used for the simulation study using high numerical aperture 0.55 EUV lithography process settings. The primary imaging metrics for through pitch evaluation include NILS, TCE, and BFV.ResultsThe Ta-Co alloys exhibit a higher EUV extinction coefficient k compared with the currently used Ta-based absorber. TaCo and Ta2Co demonstrate smooth surfaces and are stable in a hydrogen environment and in mask-cleaning solutions.ConclusionTa-Co alloys allow for a reduction in M3D effects at a lower absorber thickness compared with a 60 nm Ta-based reference absorber.
This conference presentation was prepared for Photomask Japan 2022: XXVIII Symposium on Photomask and Next-Generation Lithography Mask Technology, 2022.
Performance demands for many devices has driven feature dimensions to reduce to sub nm scale. Whilst new, and complex combinations of materials have increased the importance of interface effects at the atomic scale. Many of the macro-market dynamics such as Internet of Everything, increased volume in data traffic and energy efficiency require III-V based devices eg GaN, SiC. The combination of new materials and dimensions means that new etch solutions are required to achieve the accuracy and low damage needed for optimized device results. Low damage etching of AlGaN, GaN and SiN layers were studied using the PlasmaPro100 Cobra300 system from Oxford Instruments Plasma Technology, configured with ICP-RIE, RIE and ALE plasma etching modes. These techniques were used to etch shallow depths of between 5 and 100 nm in both SiN, AlGaN and GaN substrates and the resultant etched surface layer quality was measured using Atomic Force Microscopsy (AFM). ALE of SiN and GaN showed etch rates of 2.5 nm/min and 2 nm/min respectively. Using a conventional ICP-RIE process a GaN etch rate of 50 nm/min with a selectivity to AlGaN of 25:1 was achieved.
To demonstrate the possibility of using electron beam-induced deposition (EBID) masks for sub-10 nm pattern transfer into silicon, first experiments were carried out by using 20- to 40-nm EBID masks, which were etched by different chemistries. It is experimentally verified that recipes based on hydrogen bromide, chlorine, and boron trichloride can selectively etch silicon when using 20- to 40-nm masks made by EBID. We observed an enhancement of the height ratio, i.e., the ratio of the height of structures before and after etching, up to a factor of 3.5 when using chlorine chemistry. To demonstrate the pattern transfer of sub-10 nm structures, further experiments were carried out using 8- to 20-nm EBID masks in combination with hydrogen bromide, chlorine, and fluorine chemistries. Fluorine chemistry provided the best results in terms of surface smoothness and height ratio. In this case, 7.4-nm lines were successfully transferred into silicon, resulting in 14.3-nm-wide lines with a height ratio of ∼5.
To demonstrate the possibility of using EBID masks for sub-10 nm pattern transfer into silicon, first experiments were carried out by using 20-40 nm EBID masks, that were etched by different chemistries. It is experimentally verified that recipes based on hydrogen bromide, chlorine and boron trichloride can selectively etch silicon when using 20-40 nm masks made by EBID. We observed an enhancement of the height ratio, i.e. the ratio of the height of structures before and after etching, up to a factor of 3.5 when using the chlorine chemistry. To demonstrate the pattern transfer of sub-10 nm structures, further experiments were carried out using 8-20 nm EBID masks in combination with hydrogen bromide, chlorine and fluorine chemistries. Fluorine chemistry provided the best results in terms of surface smoothness and height ratio. In this case, 7.4 nm lines were successfully transferred into silicon, resulting in 14.3 nm wide lines with a height ratio of approximately 5.
Electron beam writing remains one of the reference pattern generation techniques, and plasma etching continues to underpin pattern transfer. We report a systematic study of the plasma etch resistance of several e-beam resists, both negative and positive as well as classical and Chemically Amplified Resists: HSQ[1,2] (Dow Corning), PMMA[3] (Allresist GmbH), AR-P6200 (Allresist GmbH), ZEP520 (Zeon Corporation), CAN028 (TOK), CAP164 (TOK), and an additional pCAR (non-disclosed provider). Their behaviour under plasma exposure to various nano-scale plasma etch chemistries was examined (SF6/C4F8 ICP silicon etch, CHF3/Ar RIE SiO2 etch, Cl2/O2 RIE and ICP chrome etch, and HBr ICP silicon etch). Samples of each resist type were etched simultaneously to provide a direct comparison of their etch resistance. Resist thicknesses (and hence resist erosion rates) were measured by spectroscopic ellipsometer in order to provide the highest accuracy for the resist comparison. Etch selectivities (substrate:mask etch rate ratio) are given, with recommendations for the optimum resist choice for each type of etch chemistry. Silicon etch profiles are also presented, along with the exposure and etch conditions to obtain the most vertical nano-scale pattern transfer. We identify one resist that gave an unusually high selectivity for chlorinated and brominated etches which could enable pattern transfer below 10nm without an additional hard mask. In this case the resist itself acts as a hard mask. We also highlight the differing effects of fluorine and bromine-based Silicon etch chemistries on resist profile evolution and hence etch fidelity.
New processes using HBr chemistry have been developed for etching InP and related materials using photoresist as a
mask in a high ion density inductively coupled plasma system. An etch rate of above 1 micron/min, a selectivity of 14:1
with vertical profile, and smooth etched surface have been achieved. The effects of ICP power, table temperature,
chamber pressure and DC bias on etching rate, selectivity, etched profile and surface morphology will be discussed in
this paper.
Plasma Enhanced Chemical Vapour Deposition (PECVD) was used in the development of silica layers for use in planar waveguide applications. The addition of GeH4 to silica was used to control the refractive index of core layers with index differences core-clad in the range of 0.2%-1.3%. High rate SiO2 and Ge-doped SiO2 films have been deposited on to 4” Si <100> wafers. The ‘as deposited’ and ‘annealed’ film properties have been compared, including film uniformity, RI, RI uniformity and stress have been compared. Ge-doped SiO2 films up to 10 um thickness have been deposited and annealed for the above study. Refractive index uniformity of ± 0.0002 was achieved after annealing for 4” silicon wafers. The core layers were shown to be capable of producing optical losses of <0.1dB/cm when incorporated into a typical waveguide design.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.