Positive-tone silylated, dry-developed, deep ultraviolet resist with 0.2 μm resolution

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This paper describes the development of a surface-imaging process for a positive-tone silylated, dry-developed bilayer resist which has 0.2 μm resolution and an aspect ratio of 4.5 using deep-UV (248 nm) exposure. The many processing variables such as thermal treatment parameters, silylation conditions, and etching conditions were examined to determine their effects on lithographic performance in terms of resolution, feature size linearity, focus latitude, and sensitivity. Critical to the success of the process are: the bilayer structure which restricts diffusion of the Si, the use of a disilane reagent to increase the Si content of the masking layer, limiting migration of photogenerated acid by the appropriate choice of softbake and post-exposure bake temperatures, initial etching with an Ar/Cl2 mixture to remove the thin layer of silylated resist in the exposed areas, and employing CO2 instead of O2 as the etching gas to eliminate lateral etching of the features. With this process we have obtained good critical dimension linearity down to 0.25 μm for bright-field and dark-field lines and spaces as well as isolated lines and isolated spaces. The dose required is ∼75 mJ/cm2 and the dose latitude is ±6%. Focus latitude is at least ±0.4 μm. We also observe no environmental effects on sensitivity or resolution.