Resist composition and patterning process

A pattern forming process comprising the steps of coating a positive resist composition onto a substrate, baking to form a resist film, exposing the resist film to high-energy radiation, and developing the exposed resist film in a developer,

• wherein the high-energy radiation is EB or EUV,
• wherein the positive resist composition comprises a base resin containing a polymer comprising recurring units (a) having the formula (a), recurring units (b1) having a carboxyl group whose hydrogen is substituted by an acid labile group andior recurring, units (b2) having a phenolic hydroxyl group whose hydrogen is substituted by an acid labile group and recurring units of at least one type selected from recurring units having the formulae (d1), (d2) and (d3) as an acid generator, and an organic solvent, the polymer having a weight, average molecular weight of 1,000 to 500,000,
• wherein RA is hydrogen or methyl, R1 is hydrogen or C1-C4 straight or branched alkyl, and R2 is a single bond or methylene,
• wherein RA is each independently hydrogen or methyl, R11 is a single bond, phenylene group, —O—R21—, or —C(═O)—Z1—R21—, Z1 is —O—or —NH—, R21 is a C1-C6straight, 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, Rf1 to Rf4 are each independently fluorine, hydrogen or trifluoromethyl, at least one of Rf1 to Rf4 being fluorine, R12 to R19 are each independently a C1-C12 straight, branched or cyclic alkyl group which may contain a carbonyl, ester or ether moiety, C6-C12 aryl group, C7-C20 aralkyl group, or mercaptophenyl group, Y1 is a single bond or a C1-C12 linking group which may contain an ester, ether moiety or lactone ring, Y2 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R22—, or —C(═O)—Z2—R22—, Z2 is —O— or —NH—, R22 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, and M− is a non-nucleophilic counter ion.