Resist composition and patterning process

1. A resist composition comprising

an ammonium salt and fluorine-containing polymer comprising repeat units AU having an ammonium salt structure containing a sulfonamide anion containing fluorine, but not iodine and bromine, a phenoxide anion containing fluorine, but not iodine and bromine, or an enolate anion of β-diketone containing fluorine, but not iodine and bromine, and repeat units of at least one type selected from repeat units FU-1 having a trifluoromethylalcohol group which may be substituted with an acid labile group and repeat units FU-2 having a fluorinated hydrocarbyl group, and

a base polymer comprising repeat units of at least one type selected from repeat 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 moiety, ester bond, ether bond or hydroxy moiety,

Z 2 is a single bond or ester bond,

Z 3 is a single bond, —Z 31 —C(═O)—O—, —Z 31 —O— or —Z 31 —O—C(═O)—, Z 31 is a C 1 -C 12 hydrocarbylene group, phenylene group, or C 7 -C 18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond, iodine or bromine,

Z 4 is a methylene, 2,2,2-trifluoro-1,1-ethanediyl or carbonyl group,

Z 5 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene group, —O—Z 51 —, —C(═O)—O—Z 51 —, or —C(═O)—NH—Z 51 —, Z 51 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 hydroxy 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, and

M − is a non-nucleophilic counter ion.

2. The resist composition of claim 1 wherein the repeat unit AU has the formula (AU), the repeat unit FU-1 has the formula (FU-1), and the repeat unit FU-2 has the formula (FU-2):

wherein n 1 is 1 or 2, n 2 is a positive number in the range: 0<n 2 /n 1 ≤1, n 3 is 1 or 2,

R A is each independently hydrogen or methyl,

X 1A is a single bond, phenylene group, ester bond or amide bond,

X 1B is a single bond or a C 1 -C 20 (n 1 +1)-valent hydrocarbon group which may contain an ether bond, carbonyl moiety, ester bond, amide bond, sultone ring, lactam ring, carbonate bond, halogen, hydroxy moiety or carboxy moiety,

X 2A is a single bond, phenylene, —O—, —C(═O)—O— or —C(═O)—NH—,

X 2B is a C 1 -C 12 (n 3 +1)-valent saturated hydrocarbon group or (n 3 +1)-valent aromatic hydrocarbon group, which may contain fluorine, hydroxy moiety, ester bond or ether bond,

X 3 is a single bond, phenylene, —O—, —C(═O)—O—X 31 —X 32 — or —C(═O)—NH—X 31 —X 32 —, X 31 is a single bond or C 1 -C 4 alkanediyl group, X 32 is a single bond, ester bond, ether bond or sulfonamide bond,

R 1 , R 2 and R 3 are each independently hydrogen, a C 1 -C 12 alkyl group, C 2 -C 12 alkenyl group, C 6 -C 12 aryl group or C 7 -C 12 aralkyl group, a pair of R 1 and R 2 or R 1 and X 1B may bond together to form a ring with the nitrogen atom to which they are attached, the ring may contain oxygen, sulfur, nitrogen or a double bond,

R 4 is a single bond, ester bond, or a C 1 -C 12 saturated hydrocarbylene group in which some or all of the hydrogen atoms may be substituted by fluorine and some carbon may be replaced by an ester bond or ether bond,

R 5 is hydrogen, fluorine, methyl, trifluoromethyl or difluoromethyl, a pair of R 5 and R 6 may bond together to form a ring with the carbon atom to which they are attached, the ring may contain an ether bond, fluorine or trifluoromethyl,

R 6 is hydrogen or an acid labile group,

R 7 is a C 1 -C 20 hydrocarbyl group which is substituted with at least one fluorine, and in which some carbon may be replaced by an ester bond or ether bond, and

X − is a sulfonamide anion containing fluorine, but not iodine and bromine, a phenoxide anion containing fluorine, but not iodine and bromine, or an enolate anion of β-diketone containing fluorine, but not iodine and bromine.

3. The resist composition of claim 1 wherein 0.001 to 20 parts by weight of the ammonium salt and fluorine-containing polymer is present per 100 parts by weight of the base polymer.

4. A resist composition comprising

an ammonium salt and fluorine-containing polymer comprising repeat units AU having an ammonium salt structure containing a sulfonamide anion containing fluorine, but not iodine and bromine, a phenoxide anion containing fluorine, but not iodine and bromine, or an enolate anion of β-diketone containing fluorine, but not iodine and bromine, and repeat units of at least one type selected from repeat units FU-1 having a trifluoromethylalcohol group which may be substituted with an acid labile group and repeat units FU-2 having a fluorinated hydrocarbyl group,

a base polymer, and

an acid generator capable of generating a sulfonic acid, imide acid or methide acid.

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

6. The resist composition of claim 1 wherein the base polymer comprises repeat units having the formula (a1) or repeat 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, R 13 is fluorine, trifluoromethyl, a C 1 -C 5 saturated hydrocarbyl group or C 1 -C 5 saturated hydrocarbyloxy group, Y 1 is a single bond, phenylene group, naphthylene group, or C 1 -C 12 divalent linking group containing at least one moiety selected from ester bond and lactone ring, Y 2 is a single bond or ester bond, and a is an integer of 0 to 4.

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

8. The resist composition of claim 1 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 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 nm.

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