Polymer, resist composition, and patterning process

A resist composition comprising (A1) a polymer comprising repeat units of the general formulae (1a), (2) and (3), (B) a polymer having a lactone ring and/or maleic anhydride-derived structure which becomes soluble in an alkaline developer under the action of an acid, (C) a compound capable of generating an acid upon exposure to high-energy radiation, and (D) an organic solvent, wherein the amount of polymer (A1) is 0.5 to 10 parts by weight per 100 parts by weight of polymer (B),

• wherein R1 is hydrogen, fluorine, or straight or branched C1-C4 alkyl or fluoroalkyl, R2a and R2b are hydrogen or straight, branched or cyclic C1-C10 alkyl, R3a and R3b are hydrogen or straight, branched or cyclic C1-C6 alkyl, R3c is straight, branched or cyclic C1-C10 alkyl, R4a and R4b are hydrogen or straight, branched or cyclic C1-C10 alkyl, R5 is hydrogen, straight, branched or cyclic C1-C10 alkyl, or an acid labile group, R6 is an acid labile group, R2a and R2b, and R4a and R4b may bond together to form a non-aromatic ring of 1 to 20 carbon atoms with the carbon atom to which they are attached, m is an integer of 1 to 6, a1, a2 and a3 are numbers satisfying 0.4≦a1≦0.9, 0≦a2≦0.6, 0≦a3≦0.6, 0<a2+a3≦0.6 and 0<a1+a2+a3≦1.