Resist composition and patterning process

1. A resist composition comprising a quencher containing a sulfonium salt having the formula (1):

wherein R 1 and R 2 are each independently a single bond or a C 1 -C 20 divalent aliphatic hydrocarbon group which may contain an ether bond, ester bond or hydroxyl,

L 1 is an ester bond, ether bond or amide bond,

L 2 and L 3 are each independently a single bond, ester bond, ether bond or amide bond,

R 3 is hydroxyl, carboxyl, nitro, cyano, fluorine, chlorine, bromine, amino, or a C 1 -C 20 alkyl, C 1 -C 20 alkoxy, C 2 -C 20 acyloxy, C 2 -C 20 alkoxycarbonyl or C 1 -C 4 alkylsulfonyloxy group, which may contain fluorine, chlorine, bromine, hydroxyl or amino, or —NR 3A —C(═O)—R 3B or —NR 3A —C(═O)—O—R 3B , wherein R 3A is hydrogen or a C 1 -C 6 alkyl group which may contain halogen, hydroxyl, C 1 -C 10 alkoxy, C 2 -C 10 acyl or C 2 -C 10 acyloxy, R 3B is a C 1 -C 16 alkyl, C 2 -C 16 alkenyl or C 6 -C 12 aryl group, which may contain halogen, hydroxyl, C 1 -C 10 alkoxy, C 2 -C 10 acyl or C 2 -C 10 acyloxy,

R 4 is hydroxyl, carboxyl, nitro, cyano, fluorine, chlorine, bromine, iodine, amino, or a C 1 -C 20 alkyl, C 1 -C 20 alkoxy, C 2 -C 20 acyloxy, C 2 -C 20 alkoxycarbonyl or C 1 -C 4 alkylsulfonyloxy group, which may contain fluorine, chlorine, bromine, iodine, hydroxyl, amino or ether bond,

R 5 is a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, in case of r=1, two R 5 may be the same or different and may bond together to form a ring with the sulfur atom to which they are attached,

X − is a carboxylic acid anion, amic acid anion, fluorine-free sulfonic acid anion or halide ion,

m is an integer of 1 to 5, n is an integer of 0 to 3, the sum of m+n is 1 to 5, p is 0 or 1, q is an integer of 0 to 4, and r is an integer of 1 to 3.

2. The resist composition of claim 1 wherein m is an integer of 2 to 5.

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

4. The resist composition of claim 1 , further comprising an acid generator capable of generating a fluorosulfonic acid, fluoroimidic acid or fluoromethide acid.

5. The resist composition of claim 1 , further comprising a base polymer.

6. The resist composition of claim 5 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, Y 1 is a single bond, phenylene group, naphthylene group, or C 1 -C 12 linking group containing an ester bond or lactone ring, Y 2 is a single bond or ester bond, R 11 and R 12 each are an acid labile group, R 13 is fluorine, trifluoromethyl, cyano, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, C 2 -C 7 acyl, C 2 -C 7 acyloxy, or C 2 -C 7 alkoxycarbonyl group, R 4 is a single bond or a C 1 -C 6 straight or branched alkanediyl group in which some carbon may be replaced by an ether bond or ester bond, a is 1 or 2, b is an integer of 0 to 4, the sum of a+b is 1 to 5.

7. The resist composition of claim 6 which is a chemically amplified positive resist composition.

8. The resist composition of claim 5 wherein the base polymer is free of an acid labile group.

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

10. The resist composition of claim 5 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 11 —, —C(═O)—O—Z 11 — or —C(═O)—NH—Z 11 —, Z 11 is a C 1 -C 6 alkanediyl group, C 2 -C 6 alkenediyl group, or phenylene group, which may contain carbonyl, ester bond, ether bond or hydroxyl,

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 alkanediyl group which may contain carbonyl, ester bond or ether bond,

Z 3 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—Z 31 —, —C(═O)—O—Z 31 — or —C(═O)—NH—Z 31 —, Z 31 is a C 1 -C 6 alkanediyl group, C 2 -C 6 alkenediyl group, phenylene group, fluorinated phenylene group, or trifluoromethyl-substituted phenylene group, which may contain carbonyl, ester bond, ether bond or hydroxyl,

R 21 to R 28 are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, any two of R 23 , R 24 and R 25 or any two of R 26 , R 27 and R 28 may bond together to form a ring with the sulfur atom to which they are attached,

A is hydrogen or trifluoromethyl, and

M − is a non-nucleophilic counter ion.

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

12. 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 resist film in a developer.

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

14. The process of claim 12 wherein the high-energy radiation is EB or EUV of wavelength 3 to 15 nm.

15. The resist composition of claim 1 wherein the carboxylic acid anion is selected from the group consisting of the following formulae: