New deep-ultraviolet positive photoresists .2. Copolymers of p-trimethylsilylstyrenes and acrylics

o-Nitrobenzyl cholate has been widely used as the photoactive component in dissolution inhibition of deep-UV photoresist of poly(methylmethacrylate-co-methacrylic acid) [poly(MMA-co-MAA)]. We wished to promote this system in a bilayer resist application, so we used the copolymers containing silicon instead of poly(MMA-co-MAA). Poly(p-trimethylsily-alpha-methylstyrene-co-methacrylic acid), (PTMSMSMAA, I), poly(p-trimethylsilyl-alpha-methylstyrene-co-acrylic acid), (PTMSMSAA, II), poly(p-trimethylsilylstyrene-co-methacrylic acid), (PTMSSMAA, III), and poly(p-trimethylsilylstyrene-co-acrylic acid), (PTMSSAA, IV) were synthesized by solution-free radical polymerization of trimethylsilylstyrenic monomers (TMSMS and TMSS) with comonomers (MAA and AA). The preparation of the copolymers in terms of reaction time, thermal initiator, solvent, and the feed mol ratio of reactants was evaluated. The thermal properties of these copolymers were investigated with the differential scanning calorimeter and by thermogravimetric analysis. The chain-stiffening effects of the cr-methylstyrene and styrene groups were responsible for high thermal stabilities. The developed patterns exhibited good adhesion to the silicon substrates without the use of any adhesion promoter. The resolution of the resists was at least 0.8 mu m and exhibited an oxygen plasma etching rate of 1:15 compared with hard-baked HPR-204. (C) 1997 American Vacuum Society.