US Patent 8039198 Sulfonium salt-containing polymer, resist composition, and patterning process

A polymer comprising recurring units of a sulfonium salt represented by formula (1) is provided as well as a chemically amplified resist composition comprising the same. R1 is H, F, methyl or trifluoromethyl, R2 to R4 are C1-C10 alkyl or alkoxy, R5 is C1-C30 alkyl or C6-C14 aryl, k, m and n are 0 to 3. The recurring units generate a sulfonic acid upon exposure to high-energy radiation so as to facilitate effective scission of acid labile groups in the resist composition. The resist composition exhibits excellent resolution and a pattern finish with minimal LER.