Resist composition and patterning process

1. A resist composition comprising a base polymer, a quencher, and a sulfonium salt having the formula (A-1) or an iodonium salt having the formula (A-2):

wherein R 1 is a hydroxyl group, carboxyl group, fluorine, chlorine, bromine, amino group, or a straight, branched or cyclic C 1 -C 20 alkyl, C 1 -C 20 alkoxy, C 2 -C 20 alkoxycarbonyl or C 2 -C 20 acyloxy group which may contain fluorine, chlorine, bromine, hydroxyl, amino or alkoxy moiety, or —NR 9 —C(═O)—R 10 or —NR 9 —C(═O)—O—R′°, R 9 is hydrogen, or a straight, branched or cyclic C 1 -C 6 alkyl group, R 10 is a straight, branched or cyclic C 1 -C 16 alkyl, straight, branched or cyclic C 2 -C 16 alkenyl, or C 6 -C 12 aryl group which may contain halogen, hydroxyl, alkoxy, acyl or acyloxy moiety,

R 2 is a single bond, or a divalent C 1 -C 20 linking group which may contain oxygen, sulfur or nitrogen,

R f is fluorine or trifluoromethyl,

R 3 , R 4 and R 5 are each independently fluorine, chlorine, bromine, iodine, C 1 -C 12 straight, branched or cyclic alkyl group, C 2 -C 12 straight, branched or cyclic alkenyl group, C 6 -C 20 aryl group, or C 7 -C 12 aralkyl or aryloxyalkyl group, at least one hydrogen in the foregoing groups being optionally substituted by hydroxyl, carboxyl, halogen, oxo, cyano, amide, nitro, sultone, sulfone, or sulfonium salt-containing moiety, or at least one carbon in the foregoing groups being optionally substituted by an ether, ester, carbonyl, carbonate or sulfonate moiety, or R 3 and R 4 may bond together to form a ring with the sulfur atom to which they are attached,

R 6 and R 7 are each independently trifluoromethyl, a C 6 -C 10 aryl group, C 2 -C 6 alkenyl group, or C 2 -C 6 alkynyl group, at least one hydrogen in the foregoing groups being optionally substituted by a halogen, trifluoromethyl, C 1 -C 10 straight, branched or cyclic alkyl or alkoxy, hydroxyl, carboxyl, alkoxycarbonyl, nitro or cyano moiety,

m is an integer of 1 to 5, n is an integer of 0 to 3, and p is an integer of 1 to 4.

2. The resist composition of claim 1 , further comprising an organic solvent.

3. The resist composition of claim 1 wherein the base polymer comprises recurring units having the formula (a1) or recurring units having the formula (a2):

wherein R A is each independently hydrogen or methyl, X 1 is a single bond, phenylene group, naphthylene group, or C 1 -C 12 linking group containing an ester moiety and/or lactone ring, X 2 is a single bond or ester group, R 11 and R 12 each are an acid labile group, R 13 is fluorine, trifluoromethyl, cyano, C 1 -C 6 straight, branched or cyclic alkyl or alkoxy group, or C 2 -C 7 straight, branched or cyclic acyl, acyloxy or alkoxycarbonyl group, R 14 is a single bond or a C 1 -C 6 straight or branched alkylene group in which at least one carbon may be substituted by an ether or ester moiety, q is 1 or 2, and r is an integer of 0 to 4.

4. The resist composition of claim 3 , further comprising a dissolution inhibitor.

5. The resist composition of claim 3 which is a chemically amplified positive resist composition.

6. The resist composition of claim 1 wherein the base polymer is free of an acid labile group.

7. The resist composition of claim 6 , further comprising a crosslinker.

8. The resist composition of claim 6 which is a chemically amplified negative resist composition.

9. The resist composition of claim 1 , further comprising a surfactant.

10. The resist composition of claim 1 wherein the base polymer further comprises recurring units of at least one type selected from the formulae (f1) to (f3):

wherein R A is each independently hydrogen or methyl,

Z 1 is a single bond, phenylene group, —O—Z 12 — or —C(═O)—Z 11 -Z 12 —, Z 11 is —O— or —NH—, Z 12 is a C 1 -C 6 straight, branched or cyclic alkylene group, C 2 -C 6 straight, branched or cyclic alkenylene group or phenylene group, which may contain a carbonyl, ester, ether or hydroxy moiety,

R 31 to R 38 are each independently a C 1 -C 12 straight, branched or cyclic alkyl group which may contain a carbonyl, ester or ether moiety, or a C 6 -C 12 aryl group or C 7 -C 20 aralkyl group, in which at least one hydrogen may be substituted by a C 1 -C 10 straight, branched or cyclic alkyl moiety, halogen, trifluoromethyl, cyano, nitro, hydroxyl, mercapto, C 1 -C 10 straight, branched or cyclic alkoxy moiety, C 2 -C 10 straight, branched or cyclic alkoxycarbonyl moiety, or C 2 -C 10 straight, branched or cyclic acyloxy moiety, any two of R 33 , R 34 and R 35 , or any two of R 36 , R 37 and R 38 may bond together to form a ring with the sulfur atom to which they are attached,

Z 2 is a single bond, —Z 21 —C(═O)—O—, —Z 21 —O— or —Z 21 —O—C(═O)—, Z 21 is a C 1 -C 12 straight, branched or cyclic alkylene group which may contain a carbonyl, ester or ether moiety,

A is hydrogen or trifluoromethyl,

Z 3 is a single bond, methylene group, ethylene group, phenylene group, fluorinated phenylene group, —O—Z 32 —, or —C(═O)—Z 31 -Z 32 —, Z 31 is —O— or —NH—, Z 32 is a C 1 -C 6 straight, branched or cyclic alkylene group, a phenylene, fluorinated phenylene or trifluoromethyl-substituted phenylene group, or C 2 -C 6 straight, branched or cyclic alkenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety, and

M − is a non-nucleophilic counter ion.

11. A process for forming a pattern comprising the steps of applying the resist composition of claim 1 onto a substrate, baking to form a resist film, exposing the resist film to high-energy radiation, and developing the exposed film in a developer.

12. The process of claim 11 wherein the high-energy radiation is ArF excimer laser radiation of wavelength 193 nm or KrF excimer laser radiation of wavelength 248 nm.

13. The process of claim 11 wherein the high-energy radiation is electron beam or extreme ultraviolet radiation of wavelength 3 to 15 nm.