Positive resist composition and patterning process

A positive resist composition comprising as the base resin a polymer comprising;

• recurring units (a) of the general formula (2), selected from (meth)acrylic acid and derivatives thereof, styrenecarboxylic acid, and vinylnaphthalenecarboxylic acid,
• wherein R1 and R2 each are hydrogen, a C1—C4 alkyl, alkoxy, alkanoyl or alkoxycarbonyl group, hydroxyl, C6-C10 aryl group, halogen, or cyano group, R is hydrogen, a straight, branched or cyclic C1-C12 alkyl group which may have an oxygen or sulfur atom, C2-C12 alkenyl group, or C2-C12 alkynyl group, or C6-C10 aryl group, R3 to R6 are hydrogen or a pair of R3 and R4, R4 and R5, or R5 and R6 may bond together to form a benzene ring, m and n each are an integer of 1 to 4, R7 is hydrogen or methyl, X1 is a single bond, —C(═O)—O—R8—, phenylene or naphthylene, and R8 is a straight, branched of cyclic C1-C10 alkylene group which may have an ester, ether or lactone group;
• recurring units (b) having a phenolic hydroxyl group selected from units (b1 ) and (b8) represented by the general formula (3):
• wherein R9 is each independently hydrogen or methyl, X2 is —C(═O)—O—R10—, X3 is a single bond or —C(═O)—O—R10—, X4 and X5 each are —C(═O)—O—R10—, R10 is a single bond or a straight, branched or cyclic C1-C10 alkylene group, Y1 and Y2 each are methylene or ethylene, A is methylene, oxygen or sulfur, and p is 1 or 2;
• and
• recurring units selected from sulfonium salts (d2) and (d3) represented by the general formula (5):
• wherein R24 and R28 each are hydrogen or methyl, R25, R26, R27, R29, R30, and R31 are each independently a straight, branched or cyclic C1-C12 alkyl group which may contain a carbonyl, ester or ether group, or C6-C12 aryl group, C7-C20 aralkyl group, or thiophenyl group, Z0 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R32—, or —C(═O)—Z1—R32—, Z1 is oxygen or NH, R32 is a straight, branched or cyclic C1-C6 alkylene group, phenylene group or alkenylene group, which may contain a carbonyl, ester, ether or hydroxyl group,
• molar fractions “a” and “b” of the respective units being in the range:
• 0<a<1.0, 0<b<1.0, and 0.05≦a+b<1.0, and molar fractions d2 and d3 are in the range:
• 0≦d2≦0.3, 0≦d3≦0.3, and 0<d2+d3≦0.3,
• said polymer having a weight average molecular weight of 1,000 to 500,000.