Sulfonium salt monomer, polymer, chemically amplified resist composition, and pattern forming process

Abstract

A polymer comprising repeat units derived from a sulfonium salt consisting of a carboxylate anion having a styrene or vinylnaphthalene structure as a polymerizable group and iodine and a sulfonium cation having pentafluorosulfanyl and hydrocarbyloxycarbonyl groups is useful as a polymer-bound quencher. A resist composition comprising the polymer exhibits a high solvent solubility, high sensitivity and high contrast and forms a small-size pattern having satisfactory lithography properties such as EL, LWR, CDU and DOF as well as collapse resistance and etching resistance.