US Patent 8048610 Sulfonium salt-containing polymer, resist composition, and patterning process

A polymer comprising recurring units having formulae (1), (2) and (3) is provided as well as a chemically amplified resist composition comprising the same. R1 is H, F, CH3 or CF3, Rf is H, F, CF3 or C2F5, A is an optionally fluorine or oxygen-substituted divalent organic group, R2, R3 and R4 are alkyl, alkenyl, oxoalkyl, aryl, aralkyl or aryloxoalkyl, or may form a ring with the sulfur atom, N=0-2, R8 is H or alkyl, B is a single bond or optionally oxygen-substituted divalent organic group, a=0-3, b=1-3, and X is an acid labile group. The polymer generates a strong sulfonic acid which provides for effective cleavage of acid labile groups in a chemically amplified resist composition.