Resist composition and patterning process

1. A resist composition comprising a base polymer and a quencher, the quencher containing an onium salt having the formula (A):

wherein m is an integer of 1 to 5, n is an integer of 0 to 4, m+n is from 1 to 5, k is 1 or 2,

R 1 is hydrogen, hydroxyl, optionally halogen-substituted C 1 -C 6 saturated hydrocarbyl group, optionally halogen-substituted C 1 -C 6 saturated hydrocarbyloxy group, optionally halogen-substituted C 2 -C 7 saturated hydrocarbylcarbonyloxy group, optionally halogen-substituted C 2 -C 7 saturated hydrocarbyloxycarbonyl group, optionally halogen-substituted C 1 -C 4 saturated hydrocarbylsulfonyloxy group, fluorine, chlorine, bromine, amino, nitro, cyano, —NR 1A —C(═O)—R 1B , or —NR 1A —C(═O)—O—R 1B , some or all of the hydrogen atoms in the saturated hydrocarbyl, saturated hydrocarbyloxy, saturated hydrocarbylcarbonyloxy, saturated hydrocarbyloxycarbonyl and saturated hydrocarbylsulfonyloxy groups may be substituted by halogen, R 1A is hydrogen or a C 1 -C 6 saturated hydrocarbyl group, R 1B is a C 1 -C 6 saturated hydrocarbyl, C 2 -C 8 unsaturated aliphatic hydrocarbyl, C 6 -C 14 aryl or C 7 -C 15 aralkyl group,

R 2 is a C 1 -C 10 (k+1)-valent hydrocarbon group,

R 3 is a C 1 -C 6 fluorinated saturated hydrocarbyl group or C 6 -C 10 fluorinated aryl group,

X 1 is a single bond, ether bond, carbonyl group, ester bond, amide bond, carbonate bond or C 1 -C 20 hydrocarbylene group, the hydrocarbylene group may contain an ether bond, carbonyl moiety, ester bond, amide bond, sultone ring, lactam ring, carbonate bond, halogen, hydroxyl moiety or carboxyl moiety,

M + is a sulfonium cation having the formula (Aa), iodonium cation having the formula (Ab), or ammonium cation having the formula (Ac):

wherein R a1 to R a3 are each independently halogen or a C 1 -C 20 hydrocarbyl group which may contain a heteroatom, R a1 and R a2 may bond together to form a ring with the sulfur atom to which they are attached,

R a4 and R a5 are each independently halogen or a C 1 -C 20 hydrocarbyl group which may contain a heteroatom,

R a6 to R a9 are each independently hydrogen or a C 1 -C 24 hydrocarbyl group which may contain at least one moiety selected from halogen, hydroxyl moiety, carboxyl moiety, ether bond, ester bond, thiol moiety, thioester bond, thionoester bond, dithioester bond, amino moiety, nitro moiety, sulfone moiety, and ferrocenyl moiety, R a6 and R a7 may bond together to form a ring with the nitrogen atom to which they are attached, a pair of R a6 and R a7 and a pair of R a8 and R a9 each may bond together to form a spiro-ring with the nitrogen atom to which they are attached, R a8 and R a9 , taken together, may form ═C(R a10 )(R a11 ), R a10 and R a11 are each independently hydrogen or a C 1 -C 16 hydrocarbyl group, R a6 and R a10 may bond together to form a ring with the carbon and nitrogen atoms to which they are attached, the ring may contain a double bond, oxygen, sulfur or nitrogen.

2. The resist composition of claim 1 wherein m is an integer of 2 to 4.

3. The resist composition of claim 1 , further comprising an acid generator capable of generating a sulfonic acid, imide acid or methide acid.

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

5. 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, Y 1 is a single bond, phenylene group, naphthylene group, or C 1 -C 12 linking group containing at least one moiety selected from ester bond and lactone ring, Y 2 is a single bond or ester bond, Y 3 is a single bond, ether bond or ester bond, R 11 and R 12 each are an acid labile group, R 13 is fluorine, trifluoromethyl, cyano or C 1 -C 6 saturated hydrocarbyl group, R 14 is a single bond or C 1 -C 6 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, and a+b is from 1 to 5.

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

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

8. The resist composition of claim 7 which is a chemically amplified negative resist composition.

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

wherein R A is each independently hydrogen or methyl,

Z 1 is a single bond, a C 1 -C 6 aliphatic hydrocarbylene group, phenylene group, naphthylene group, or C 7 -C 18 group obtained by combining the foregoing, or —O—Z 11 —, —C(═O)—O—Z 11 — or —C(═O)—NH—Z 11 —, Z 11 is a C 1 -C 6 aliphatic hydrocarbylene group, phenylene group, naphthylene group, or C 7 -C 18 group obtained by combining the foregoing, which may contain a carbonyl, ester bond, ether bond or hydroxyl moiety,

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 saturated hydrocarbylene group which may contain a carbonyl moiety, 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 aliphatic hydrocarbylene group, phenylene group, fluorinated phenylene group, or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety,

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

R HF is hydrogen or trifluoromethyl, and

M − is a non-nucleophilic counter ion.

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

11. The resist composition of claim 1 wherein X 1 is an ether bond, carbonyl group, ester bond, amide bond, or carbonate bond.

12. A process for forming a pattern comprising the steps of applying the resist composition of claim 1 onto a substrate to form a resist film thereon, 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.