Resist composition and patterning process using the same

A resist composition comprising:

• an organic solvent;
• an acid generator, and
• a base resin comprising a polymer compound having one or more repeating units selected from repeating units a1 to a5 shown by the following general formulae (2-1) to (2-5), the polymer compound having a weight average molecular weight ranging from 1,000 to 500,000,
• wherein R1 and R3 to R5 represent a linear, branched, or cyclic alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms;
• R2 represents a linear, branched, or cyclic alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 3 to 4 carbon atoms;
• R6 represents a hydroxyl group or an alkoxy group or an acyloxy group having 1 to 6 carbon atoms;
• and “m” represents 1 or 2;
• X1 to X5 represent a single bond or —C(═O)—O—R12— where R12 represents a linear, branched, or cyclic alkylene group having 1 to 10 carbon atoms and optionally containing an ester group, an ether group, or a lactone ring;
• R7 to R11 represent a hydrogen atom or a methyl group;
• a1 to a5 satisfy 0≤a1<0.2, 0≤a2<0.2, 0≤a3<0.2, 0≤a4<0.2, 0≤a5<0.2, and 0<a1+a2+a3+a4+a5<0.2.