Photoacid generators have formula (1) wherein R.sup.1 and R.sup.2 are alkyl, or R.sup.1 and R.sup.2, taken together, may form a C.sub.4 C.sub.6 ring structure with sulfur, R is hydrogen or alkyl, R' is hydrogen, alkyl, alkoxyl or nitro, n is 1 to 6, and Y.sup.- is alkylsulfonate, arylsulfonate, bisalkylsulfonylimide or trisalkylsulfonylmethide. Chemically amplified resist compositions comprising the same have improved resolution, thermal stability, storage stability and minimized line edge roughness ##STR00001##