Resist composition and patterning process

1. A resist composition comprising a base polymer and a sulfonium salt having the formula (A-1) or iodonium salt having the formula (A-2):

wherein X 1 is a single bond, ether group, ester group, amide group, or a C 1 -C 6 straight, branched or cyclic alkylene group having an ether or ester moiety,

R 1 is hydroxyl, carboxyl, alkoxycarbonyl, fluorine, chlorine, amino or nitro group, or R 1 is a straight, branched or cyclic C 1 -C 20 alkyl, straight, branched or cyclic C 1 -C 20 alkoxy or straight, branched or cyclic C 2 -C 20 acyloxy group wherein the alkyl, alkoxy or acyloxy may contain fluorine, chlorine, bromine, hydroxyl, amino or alkoxy moiety, or R 1 is —NR 8 —C(═O)—R 9 or —NR 8 —C(═O) 13 O—R 9 wherein R 8 is hydrogen, or a straight, branched or cyclic C 1 -C 6 alkyl group which may contain a halogen, hydroxy, alkoxy, acyl or acyloxy moiety, R 9 is a straight, branched or cyclic C 1 -C 16 alkyl or straight, branched or cyclic C 2 -C 16 alkenyl group, or C 6 -C 12 aryl group, in which R 9 may contain a halogen, hydroxy, alkoxy, acyl or acyloxy moiety,

R 2 is a single bond or a C 1 -C 20 divalent linking group when r=1, or a C 1 -C 20 tri- or tetravalent linking group when r=2 or 3, the linking group optionally containing an oxygen, sulfur or nitrogen atom,

Rf 1 and Rf 2 are each independently hydrogen, fluorine or trifluoromethyl, or Rf 1 and Rf 2 , taken together, may form a carbonyl group, Rf 3 and Rf 4 are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf 3 to RF 4 being fluorine or trifluoromethyl,

R 3 , R 4 , R 5 , R 6 , and R 7 are each independently a C 1 -C 12 straight, branched or cyclic alkyl group, C 2 -C 12 straight, branched or cyclic alkenyl group, C 2 -C 12 straight, branched or cyclic alkynyl group, C 6 -C 20 aryl group, C 7 -C 12 aralkyl group or C 7 -C 12 aryloxyalkyl group, in R 3 , R 4 , R 5 , R 6 , and R 7 at least one hydrogen may be substituted by a hydroxy, carboxy, oxo, halogen, cyano, amide, nitro, sultone, sulfone or sulfonium salt-containing moiety, or in R 3 , R 4 , R 5 , R 6 , and R 7 least one carbon atom may be substituted by an ether, ester, carbonyl, carbonate or sulfonic acid ester moiety, wherein R 3 and R 4 may bond together to form a ring with the sulfur atom to which they are attached,

p is an integer of 1 to 5, q is an integer of 0 to 4, and r is an integer of 1 to 3.

2. The resist composition of claim 1 wherein p is an integer of 2 to 5.

3. The resist composition of claim 1 , further comprising a quencher.

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 an ester moiety and/or lactone ring, Y 2 is a single bond or ester group, R 11 and R 12 each are 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 alkoxycaibonyl group, R 14 is a single bond or 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, s is 1 or 2, and t is an integer of 0 to 4.

6. The resist composition of claim 5 , further comprising a dissolution inhibitor.

7. The resist composition of claim 5 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 , further comprising a crosslinker.

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

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

12. The resist composition of claim 1 wherein the base polymer comprises recurring units of at least one selected from the consisting of formula (f1), formula (f2) and formula (f3):

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, in which Z 1 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 R 31 to R 38 are each independently a C 6 -C 12 aryl group or a C 7 -C 20 aralkyl group, and in R 33 to R 38 at least one hydrogen may be substituted by a C 1 -C 10 straight, branched or cyclic alkyl group, halogen, trifluoromethyl, cyano, nitro, hydroxyl, mercapto, C 1 -C 10 straight, branched or cyclic alkoxy group, C 2 -C 10 straight, branched or cyclic alkoxycarbonyl group, or C 2 -C 10 straight, branched or cyclic acyloxy group, any two of R 33 , R 34 and R 35 or any two of R 36 , R 37 and R 38 may bond together to form a ring with the sulfur atom to which they are attached;

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 straight, branched or cyclic alkylene group which may contain a carbonyl, ester or ether moiety,

A is hydrogen or trifluoromethyl,

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 C 1 -C 6 straight, branched or cyclic alkylene group, phenylene group, fluorinated phenylene group, trifluoromethyl-substituted phenylene group, or C 2 -C 6 straight, branched or cyclic alkenylene group, in which Z 3 may contain a carbonyl, ester, ether or hydroxy moiety, and

M − is a non-nucleophilic counter ion.

13. 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.

14. The process of claim 13 wherein the high-energy radiation is ArF excimer laser radiation of wavelength 193 nm or KrF excimer laser radiation of wavelength 248 nm.

15. The process of claim 13 wherein the high-energy radiation is electron beam or extreme ultraviolet radiation of wavelength 3 to 15 nm.