Resist composition and patterning process

1. A resist composition comprising a base polymer and a quencher, the quencher being an ammonium salt consisting of an ammonium cation having an iodine-substituted aromatic ring bonded to the nitrogen atom via a C 1 -C 20 hydrocarbylene group which may contain at least one moiety selected from ester bond and ether bond and a carboxylate anion having an iodine or bromine-substituted hydrocarbyl group which does not contain an iodine or bromine-substituted aromatic ring.

2. The resist composition of claim 1 wherein the ammonium salt has the formula (A):

wherein m is an integer of 1 to 5, n is an integer of 0 to 4, 1≤m+n≤5, p 1 is 1, 2 or 3, p 2 is 1 or 2, q 1 is 1, 2 or 3, and q 2 is 1, 2 or 3,

X 1 is a C 1 -C 20 (p 2 +1)-valent hydrocarbon group which may contain at least moiety selected from ester bond and ether bond,

R 1 is hydroxyl, C 1 -C 6 saturated hydrocarbyl group, C 1 -C 6 saturated hydrocarbyloxy group, C 2 -C 6 saturated hydrocarbylcarbonyloxy group, fluorine, chlorine, bromine, amino group, —NR 1A —C(═O)—R 1B , or NR 1A —C(═O)—O—R 1B , 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 12 aryl or C 7 -C 13 aralkyl group,

R 2 is hydrogen, nitro, or a C 1 -C 20 hydrocarbyl group which may contain at least one moiety selected from hydroxyl, carboxyl, thiol, ether bond, ester bond, nitro, cyano, halogen and amino moiety, in case of p 1 =1 or 2, two R 2 may bond together to form a ring with the nitrogen atom to which they are attached, the ring optionally containing a double bond, oxygen, sulfur or nitrogen, or R 2 and X 1 may bond together to form a ring with the nitrogen atom to which they are attached, the ring optionally containing a double bond, oxygen, sulfur or nitrogen,

X BI is iodine or bromine,

X 2 is a single bond, ether bond, ester bond, amide bond, carbonyl group or carbonate group,

X 3 is a single bond or a C 1 -C 20 (q 1 +1)-valent hydrocarbon group which may contain a heteroatom exclusive of iodine and bromine,

R 3 is a C 1 -C 20 (q 2 +1)-valent aliphatic hydrocarbon group which may contain at least one moiety selected from fluorine, chlorine, hydroxyl, carboxyl, C 6 -C 12 aryl, ether bond, ester bond, carbonyl, amide bond, carbonate, urethane bond, and urea bond.

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, R 11 and R 12 each are an acid labile group, 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, and Y 2 is a single bond or ester bond.

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, phenylene group, —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 or phenylene group, 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 a C 1 -C 20 hydrocarbyl 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 1 is hydrogen or trifluoromethyl, and

M − is a non-nucleophilic counter ion.

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

11. 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.

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 m.

13. The process of claim 11 wherein the high-energy radiation is EB or EUV of wavelength 3 to 15 nm.