Polymerizable anion-containing sulfonium salt and polymer, resist composition, and patterning process

1. A sulfonium salt having the general formula (1):

wherein R 1 is hydrogen, fluorine, methyl or trifluoromethyl, R 2 , R 3 and R 4 are each independently a substituted or unsubstituted, straight or branched C 1 -C 10 alkyl, alkenyl or oxoalkyl group or a substituted or unsubstituted C 6 -C 18 aryl, aralkyl or aryloxoalkyl group, or at least two of R 2 , R 3 and R 4 may bond together to form a ring with the sulfur atom to which they are attached, A is a divalent C 1 -C 20 organic group which may contain a heteroatom, and n is 0 or 1.

2. A polymer capable of generating a sulfonic acid in response to high-energy radiation or heat, the sulfonic acid comprising recurring units of the general formula (1a):

wherein R 1 is hydrogen, fluorine, methyl or trifluoromethyl, A is a divalent C 1 -C 20 organic group which may contain a heteroatom, and n is 0 or 1.

3. A polymer comprising recurring units of the general formula (1b):

wherein R 1 is hydrogen, fluorine, methyl or trifluoromethyl, R 2 , R 3 and R 4 are each independently a substituted or unsubstituted, straight or branched C 1 -C 10 alkyl, alkenyl or oxoalkyl group or a substituted or unsubstituted C 6 -C 18 aryl, aralkyl or aryloxoalkyl group, or at least two of R 2 , R 3 and R 4 may bond together to form a ring with the sulfur atom to which they are attached, A is a divalent C 1 -C 20 organic group which may contain a heteroatom, and n is 0 or 1.

4. The polymer of claim 3 , further comprising recurring units of at least one type selected from the general formulae (2) to (6):

wherein R 1 is as defined above, R 5 and R 6 are each independently hydrogen or hydroxyl, X is an acid labile group, Y is a substituent group having lactone structure, Z is hydrogen, C 1 -C 15 fluoroalkyl or C 1 -C 15 fluoroalcohol-containing substituent group, N is an integer of 0 to 2, R 7 is hydrogen or C 1 -C 10 alkyl, B is a single bond or a divalent C 1 -C 10 organic group which may have oxygen substituted thereon, a is an integer of 0 to 3, and b is an integer of 1 to 3.

5. The polymer of claim 3 , further comprising recurring units of at least one type selected from the general formulae (7) to (11):

wherein R 1 and X are as defined above, and G is oxygen or carbonyloxy (—C(═O)O—).

6. A resist composition comprising the polymer of claim 3 as a base resin.

7. The resist composition of claim 6 , further comprising a surfactant which is insoluble in water and soluble in an alkaline developer.

8. A pattern forming process comprising the steps of:

applying the resist composition of claim 6 onto a substrate to form a coating,

heat treating the coating and exposing it to high-energy radiation through a photomask,

optionally heat treating the exposed coating and developing it with a developer.

9. A pattern forming process comprising the steps of:

applying the resist composition of claim 6 onto a substrate to form a resist coating,

heat treating the resist coating,

applying onto the resist coating a protective coating which is insoluble in water and soluble in an alkaline developer,

exposing the coated substrate to high-energy radiation from a projection lens through a photomask while holding water between the substrate and the projection lens,

optionally heat treating the exposed coating and developing it with a developer.

10. A pattern forming process comprising the steps of applying the resist composition of claim 6 onto a substrate to form a coating, heat treating the coating, imagewise writing with an electron beam, heat treating the coating, and developing it with a developer.

11. A resist composition comprising the polymer of claim 3 and a polymer free of recurring units of formula (1b) as a base resin.