Resist composition and patterning process

A resist composition comprising a base resin containing a polymer comprising recurring units having the formula (a):

• wherein RA is hydrogen or methyl, R1 is an acid labile group, R2 is a C1-C6 straight, branched or cyclic alkyl group or halogen other than bromine, X1 is a single bond, phenylene group, or a C1-C12 straight, branched or cyclic alkylene group which may contain an ester moiety or lactone ring, X2 is —O—, —O—CH2— or —NH—, m is an integer of 1 to 4, and n is an integer of 0 to 3, and
• recurring units of at least one type selected from the formulae (d1) to (d3):
• wherein RA is each independently hydrogen or methyl,
• Z1 is a single bond, phenylene group, —O—Z12—, or —C(═O)—Z11-Z12—, Z11 is —O— or —NH—, Z12 is a C1-C6 straight, branched or cyclic alkylene group, C2-C6 straight, branched or cyclic alkenylene group, or phenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety,
• R31 to R38 are each independently a C1-C12 straight, branched or cyclic alkyl group which may contain a carbonyl, ester or ether moiety, or a C6-C12 aryl group or C7-C20 aralkyl group, in which at least one hydrogen may be substituted by a C1-C10 straight, branched or cyclic alkyl moiety, halogen, trifluoromethyl, cyano, nitro, hydroxyl, mercapto, C1-C10 straight, branched or cyclic alkoxy moiety, C2-C10 straight, branched or cyclic alkoxycarbonyl moiety, or C2-C10 straight, branched or cyclic acyloxy moiety,
• Z2 is a single bond, a C1-C12 straight, branched or cyclic alkylene group or C2-C12 straight, branched or cyclic alkenylene group which may contain an ether moiety, ester moiety or lactone ring, or C6-C10 arylene group,
• Z3 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—Z32—, or —C(═O)—Z31-Z32—, Z31 is —O— or —NH—, Z32 is a straight, branched or cyclic C1-C12 alkylene or C2-C12 alkenylene group which may contain a carbonyl, ester or ether moiety, or phenylene group, in which at least one hydrogen atom may be substituted by fluorine or hydroxyl, and
• M− is a non-nucleophilic counter ion.