Negative resist composition and pattern forming process

A chemically amplified negative resist composition comprising a polymer as a base resin comprising recurring units (a) of the general formula (1), recurring units of at least one type selected from the group consisting of a vinylnaphthalene (b1), indene (b2), acenaphthylene (b3), chromone (b4), coumarin (b5), norbornadiene (b6), and vinylcarbazole (b7), as represented by the general formula (2), and recurring units (d1), (d2) or (d3) having a sulfonium salt as represented by the following general formula (3), the polymer having a weight average molecular weight of 1,000 to 500,000, and an organic solvent,

• wherein R1 is hydrogen or methyl, X is a single bond or —C(═O)—O—R4—, R2 is a single bond or C1-C4 alkylene group, R3 is a linear C2-C8 alkylene group, R4 is a single bond or C1-C4 alkylene group,
• wherein R5 is hydrogen or methyl, m is an integer of 0 to 2, n is an integer of 0 to 5, R110 to R116 are each independently hydrogen, C1-C30 alkyl, partially or entirely halo-substituted alkyl (the alkyl and halo-substituted alkyl optionally having an alkyl-substituted or unsubstituted hydroxyl or carboxyl group), hydroxyl, C1-C4 alkoxy, acyl, acyloxy, alkoxycarbonyl, C6-C10 aryl, halogen, or 1,1,1,3,3,3-hexafluoro-2-propanol group, Y is a single bond, —O—, —S—, —C(═O)—O—R6—, or —C(═O)—NH—R6—, R6 is a single bond or C1-C4 alkylene group, X0 is methylene, oxygen or sulfur atom;
• b1 to b7 are numbers in the range:
• 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0, 0≦b4<1.0, 0≦b5<1.0, 0≦b6<1.0, 0≦b7<1.0, 0<b1+b2+b3+b4+b5+b6+b7<1.0, 0<a<1.0, and 0<a+b1+b2+b3+b4+b5+b6+b7<1.0,
• wherein R20, R24, and R28 each are hydrogen or methyl, R21 is a single bond, phenylene, —O—R—, or —C(═O)—Y0—R—, Y0 is oxygen or NH, R is a straight, branched or cyclic C1-C6 alkylene group, alkenylene group or phenylene group, which may contain a carbonyl, ester, ether, or hydroxyl moiety, R22, R23, 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 moiety, a C6-C12 aryl group, a C7-C20 aralkyl group, or a thiophenyl group, Z0 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R32—, or —C(═O)—Z1—R32—, wherein Z1 is oxygen or NH, and R32 is a straight, branched or cyclic C1-C6 alkylene group, alkenylene group or phenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety, M− is a non-nucleophilic counter ion, and 0≦d1≦0.35, 0≦d2≦0.35, 0≦d3≦0.35, and 0<d1+d2+d3≦0.35.