Evaluation of siloxane and polyhedral silsesquioxane copolymers for 157 nm lithography

Siloxane and silsesquioxane copolymers have been synthesized and first evaluated as potential components of 157 nm resist materials. In block copolymers of dimethylsiloxane and tert-butyl methacrylate negative imaging chemistry dominates at 157 nm, due to the presence of the siloxane component, although positive imaging in aqueous base developers via chemical amplification was obtained at longer wavelengths (248. nm). The same behavior is observed in graft copolymers of dimethylsiloxane and tert-butyl methacrylate. On the other hand, random copolymers of polymerizable polyhedral oligomeric silsesquioxane monomers with various acrylates, including partially fluorinated, can be used as components of resist formulations that provide positive imaging at 157 nm, aqueous base development, and physicochemical properties which resemble those of conventional poly (meth)acrylates. Pattern transfer properties depend on the selection of the silsesquioxane component. Polymers containing 30% or higher w/w ethyl-substituted silsesquioxane cages provide the necessary etch resistance as well as low surface roughness to oxygen plasma at 100 nm film thickness, allowing bilayer 157 nm lithography, even without further absorbance optimization. (C) 2002 American Vacuum Society.