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1 November 2007 Bimetallic thermal resists potential for double-exposure immersion lithography and grayscale photomasks
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Abstract
Double exposure/patterning is considered the best candidate for extending 195nm optical lithography below 40nm resolution. However, double exposure techniques require a resist where the exposures do not add linearly to produce the final result. A class of negative thermal resists that show this effect are bimetallic thin-films consisting of Bi/In or Sn/In. The films are bi-layered structured until sufficiently heated by a laser exposure pulse (7 mJ/sq. cm for 4 nsec). Experiments with interference lithography at 266nm in air demonstrated that Bi/In resists have a resolution limit <42nm, the exposure system limit. As a first investigation into the resist's potential for immersion lithography, the response of bimetallic resists to immersion lithography was examined. The Sn/In film used demonstrated successful development as thermal resist for immersion exposures and the power level required to convert the film was only slightly higher than the level required for exposing the film in air. Bimetallic films have demonstrated transmittances <0.1% when unexposed and >60% when highly exposed to an Argon laser, enabling their application as grayscale photomasks. However, direct laser-writing of the photomasks causes fine variations in their transparency due to the laser beam's Gaussian power profile. To correct this problem, a beam-shaping mask was designed to manipulate the power profile of the laser. To help measure mask transparency at a resolution suitable for characterizing a photomask, two photodiode sensors were added to the writing system. The profiling ability offered by the modified system allows the use of test structures 100x smaller then previously required.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
James M. Dykes, Calin Plesa, Chinheng Choo, and Glenn H. Chapman "Bimetallic thermal resists potential for double-exposure immersion lithography and grayscale photomasks", Proc. SPIE 6730, Photomask Technology 2007, 673040 (1 November 2007); https://doi.org/10.1117/12.746990
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