Resist composition and patterning process

1. A resist composition comprising a base resin containing a polymer comprising recurring units having the formula (a):

wherein R A is hydrogen or methyl, R 1 is an acid labile group, R 2 is a C 1 -C 6 straight, branched or cyclic alkyl group or halogen other than bromine, X 1 is a single bond, phenylene group, or a C 1 -C 12 straight, branched or cyclic alkylene group which may contain an ester moiety or lactone ring, X 2 is —O—, —O—CH 2 — or —NH—, m is an integer of 1 to 4, and n is an integer of 0 to 3, and

recurring units of at least one type selected from the formulae (d1) to (d3):

wherein R A is each independently hydrogen or methyl,

Z 1 is a single bond, phenylene group, —O—Z 12 —, or —C(═O)—Z 11 -Z 12 —, Z 11 is —O— or —NH—, Z 12 is a C 1 -C 6 straight, branched or cyclic alkylene group, C 2 -C 6 straight, branched or cyclic alkenylene group, or phenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety,

R 31 to R 38 are each independently a C 1 -C 12 straight, branched or cyclic alkyl group which may contain a carbonyl, ester or ether moiety, or a C 6 -C 12 aryl group or C 7 -C 20 aralkyl group, in which at least one hydrogen may be substituted by a C 1 -C 10 straight, branched or cyclic alkyl moiety, halogen, trifluoromethyl, cyano, nitro, hydroxyl, mercapto, C 1 -C 10 straight, branched or cyclic alkoxy moiety, C 2 -C 10 straight, branched or cyclic alkoxycarbonyl moiety, or C 2 -C 10 straight, branched or cyclic acyloxy moiety,

Z 2 is a single bond, a C 1 -C 12 straight, branched or cyclic alkylene group or C 2 -C 12 straight, branched or cyclic alkenylene group which may contain an ether moiety, ester moiety or lactone ring, or C 6 -C 10 arylene group,

Z 3 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—Z 32 —, or —C(═O)—Z 31 -Z 32 —, Z 31 is —O— or —NH—, Z 32 is a straight, branched or cyclic C 1 -C 12 alkylene or C 2 -C 12 alkenylene group which may contain a carbonyl, ester or ether moiety, or phenylene group, in which at least one hydrogen atom may be substituted by fluorine or hydroxyl, and

M − is a non-nucleophilic counter ion.

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

3. The resist composition of claim 1 wherein the polymer further comprises recurring units having a group capable of polarity switch under the action of acid.

4. The resist composition of claim 3 wherein the polarity switch under the action of acid takes place by elimination reaction.

5. The resist composition of claim 3 wherein the recurring units having a group capable of polarity switch under the action of acid have the formula (b1) or (b2):

wherein R A is each independently hydrogen or methyl, R 11 and R 12 are each independently an acid labile group, R 13 is fluorine, trifluoromethyl, cyano, a C 1 -C 6 straight, branched or cyclic alkyl or alkoxy group, or a C 2 -C 7 straight, branched or cyclic acyl, acyloxy or alkoxycarbonyl group, R 14 is a single bond or a C 1 -C 6 straight or branched alkylene group in which at least one carbon atom may be substituted by an ether or ester moiety, p is 1 or 2, q is an integer of 0 to 4, Y 1 is a single bond, phenylene group, naphthylene group, or a C 1 -C 12 linking group which may contain an ester moiety, ether moiety or lactone ring, and Y 2 is a single bond, —C(═O)—O— or —C(═O)—NH—.

6. The resist composition of claim 1 wherein the polymer further comprises recurring units having an adhesive group selected from among hydroxyl, carboxyl, lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether, ester, sulfonic acid ester, cyano, amide, and —O—C(═O)-G- wherein G is —S— or —NH—.

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

8. The resist composition of claim 1 , further comprising an acid generator.

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

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, baking to form a resist film, exposing the resist film to high-energy radiation, and developing the exposed film in a developer.

12. The process of claim 11 wherein the high-energy radiation is i-line, KrF excimer laser, ArF excimer laser, EB or EUV of wavelength 3 to 15 nm.

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

14. The resist composition of claim 1 , further comprising an acid generator.

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

16. A resist composition comprising a base resin containing a polymer comprising recurring units having the formula (a), and a quencher which is an onium salt of sulfonic acid which is not fluorinated at α-position as represented by the formula (4) or carboxylic acid as represented by the formula (5):

wherein R A is hydrogen or methyl, R 1 is an acid labile group, R 2 is a C 1 -C 6 straight, branched or cyclic alkyl group or halogen other than bromine, X 1 is a single bond, phenylene group, or a C 1 -C 12 straight, branched or cyclic alkylene group which may contain an ester moiety or lactone ring, X 2 is —O—, —O—CH 2 — or —NH—, m is an integer of 1 to 4, and n is an integer of 0 to 3,

wherein R 501 , R 502 and R 503 are each independently hydrogen, halogen exclusive of fluorine, or a C 1 -C 40 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, any two of R 501 , R 502 and R 503 may bond together to form a ring with the carbon atom to which they are attached, R 504 is a C 1 -C 40 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, and M + is an onium cation.

17. The resist composition of claim 16 wherein the quencher is a sulfonium salt of sulfonic acid having the following formula (4′) or sulfonium salt of carboxylic acid having the following formula (5′):

wherein R 551 , R 552 and R 553 are each independently a C 1 -C 20 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, any two or more of R 551 , R 552 and R 553 may bond together to form a ring with the atom to which they are attached and intervening atoms, R 554 is a C 1 -C 40 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, R 555 and R 556 are each independently hydrogen or trifluoromethyl, R 557 and R 558 are each independently hydrogen, fluorine or trifluoromethyl, R 559 is hydrogen, hydroxyl, a C 1 -C 35 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, or optionally substituted C 6 -C 30 aryl group, the subscript j is an integer of 1 to 3, and z 1 , z 2 and z 3 are each independently an integer of 0 to 5.

18. The resist composition of claim 16 wherein the recurring units having a group capable of polarity switch under the action of acid have the formula (b1) or (b2):

wherein R A is each independently hydrogen or methyl, R 11 and R 12 are each independently an acid labile group, R 13 is fluorine, trifluoromethyl, cyano, a C 1 -C 6 straight, branched or cyclic alkyl or alkoxy group, or a C 2 -C 7 straight, branched or cyclic acyl, acyloxy or alkoxycarbonyl group, R 14 is a single bond or a C 1 -C 6 straight or branched alkylene group in which at least one carbon atom may be substituted by an ether or ester moiety, p is 1 or 2, q is an integer of 0 to 4, Y 1 is a single bond, phenylene group, naphthylene group, or a C 1 -C 12 linking group which may contain an ester moiety, ether moiety or lactone ring, and Y 2 is a single bond, —C(═O)—O— or —C(═O)—NH—.

19. The resist composition of claim 16 wherein the polymer further comprises recurring units having an adhesive group selected from among hydroxyl, carboxyl, lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether, ester, sulfonic acid ester, cyano, amide, and —O—C(═O)-G- wherein G is —S— or —NH—.