Resist composition and patterning process

1. A resist composition comprising a base polymer and a salt, the salt consisting of an anion derived from a carboxylic acid having an iodized or brominated hydrocarbyl group exclusive of iodized or brominated aromatic ring and a cation derived from a 2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane, biguanide or phosphazene compound wherein the salt has the formula (A):

wherein m and n are each independently 1, 2 or 3,

X B1 is iodine or bromine,

X 1 is a single bond, ether bond, ester bond, amide bond, carbonyl group or carbonate group,

X 2 is a single bond or a C 1 -C 20 (m+1)-valent hydrocarbon group which may contain a heteroatom other than iodine and bromine,

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

A + is a cation having the formula (A)-1, (A)-2 or (A)-3:

wherein R 11 to R 13 are each independently a C 1 -C 24 hydrocarbyl group which may contain a heteroatom,

R 14 to R 21 are each independently hydrogen or a C 1 -C 24 hydrocarbyl group which may contain a heteroatom, a pair of R 14 and R 15 , R 15 and R 16 , R 16 and R 17 , R 17 and R 18 , R 18 and R 19 , R 19 and R 20 , or R 20 and R 21 may bond together to form a ring with the nitrogen atom to which they are attached, or the nitrogen atoms to which they are attached and intervening carbon atom, the ring optionally containing an ether bond,

R 22 to R 29 are each independently hydrogen or a C 1 -C 24 hydrocarbyl group which may contain a heteroatom, a pair of R 22 and R 23 , R 23 and R 24 , R 24 and R 25 , R 25 and R 26 , R 26 and R 27 , or R 27 and R 28 may bond together to form a ring with the nitrogen atom to which they are attached, or the nitrogen atoms to which they are attached and intervening phosphorus atom, a pair of R 22 and R 23 , R 24 and R 25 , R 26 and R 27 , or R 28 and R 29 may bond together to form a group having the formula (A)-3-1, and R 23 may be a group having the formula (A)-3-2 when R 22 is hydrogen,

wherein R 30 to R 39 are each independently hydrogen or a C 1 -C 24 hydrocarbyl group which may contain a heteroatom, a pair of R 30 and R 31 , R 31 and R 32 , R 32 and R 33 , R 33 and R 34 , R 34 and R 35 , R 36 and R 37 , or R 38 and R 39 may bond together to form a ring with the nitrogen atom to which they are attached, or the nitrogen atoms to which they are attached and intervening phosphorus atom, a pair of R 30 and R 31 , R 32 and R 33 , or R 34 and R 35 may bond together to form a group having the formula (A)-3-1,

the broken line designates a valence bond.

2. The resist composition of claim 1 , further comprising an acid generator capable of generating a sulfonic acid, sulfonimide or sulfonmethide.

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, R 41 and R 42 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.

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

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

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

7. 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, —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 51 to R 58 are each independently a C 1 -C 20 hydrocarbyl group which may contain a heteroatom, any two of R 53 , R 54 and R 55 or any two of R 56 , R 57 and R 58 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.

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

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

10. The resist composition of claim 1 wherein R 1 is a C 1 -C 20 (n+1)-valent straight or branched aliphatic hydrocarbon group which may contain at least one moiety selected from the group consisting of fluorine, chlorine, hydroxyl, carboxyl, C 6 -C 12 aryl, ether bond, ester bond, carbonyl, amide bond, carbonate, urethane bond, and urea bond, when X BI is bromine.

11. A process for forming a pattern comprising the steps of applying the resist composition of claim 1 to form a resist film on a substrate, 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 nm.

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