Chemically amplified resist composition and pattern forming process

1. A chemically amplified resist composition comprising (A) a sulfonium salt having the general formula (1) and (B) a polymer comprising recurring units having the general formula (U-1), which is decomposed under the action of acid to increase its solubility in alkaline developer,

wherein R 11 and R 22 are each independently a branched or cyclic C 3 -C 20 monovalent hydrocarbon group which may be substituted with or separated by a heteroatom, R 33 and R 01 are each independently hydrogen, or a straight C 1 -C 20 or branched or cyclic C 3 -C 20 monovalent hydrocarbon group which may be substituted with or separated by a heteroatom, k is an integer of 0 to 4, or R 11 , R 22 , R 33 and R 01 may bond together to form a ring with the carbon atoms to which they are attached and the carbon atom or atoms therebetween, m is 0 or 1, R 101 , R 102 and R 103 are each independently a straight C 1 -C 20 or branched or cyclic C 3 -C 20 monovalent hydrocarbon group which may be substituted with or separated by a heteroatom, or any two or more of R 101 , R 102 and R 103 may bond together to form a ring with the sulfur atom,

wherein q is 0 or 1, r is an integer of 0 to 2, R 1 is hydrogen, fluorine, methyl or trifluoromethyl, R 2 is each independently hydrogen or C 1 -C 6 alkyl, B 1 is a single bond or C 1 -C 10 alkylene which may contain an ether bond, a is an integer satisfying a≦5+2r−b, and b is an integer of 1 to 3.

2. The resist composition of claim 1 wherein component (A) is selected from the following sulfonium salts (A-30) to (A-44).

3. The resist composition of claim 1 , further comprising an acid generator capable of generating at least one acid selected from sulfonic acids, imidic acids, and methide acids, upon exposure to high-energy radiation.

4. The resist composition of claim 1 wherein the polymer further comprises recurring units having the general formula (U-2):

wherein s is 0 or 1, t is an integer of 0 to 2, R 1 , R 2 , and B 1 are as defined above, c is an integer satisfying c≦5+2t−e, d is 0 or 1, e is an integer of 1 to 3, X is an acid labile group when e is 1 or X is hydrogen or an acid labile group when e is 2 or 3, at least one X being an acid labile group.

5. The resist composition of claim 1 wherein the polymer further comprises recurring units having the general formula (U-3) and/or (U-4):

wherein f is an integer of 0 to 6, R 3 is each independently hydrogen, an optionally halo-substituted C 1 -C 6 alkyl or primary or secondary alkoxy group, or an optionally halo-substituted C 1 -C 7 alkylcarbonyloxy group, g is an integer of 0 to 4, and R 4 is each independently hydrogen, an optionally halo-substituted C 1 -C 6 alkyl or primary or secondary alkoxy group, or an optionally halo-substituted C 1 -C 7 alkylcarbonyloxy group.

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

7. The resist composition of claim 1 which is subject to ArF, KrF, EB, EUV or X-ray lithography.

8. A pattern forming process comprising the steps of applying the chemically amplified resist composition of claim 1 onto a processable substrate to form a resist film, exposing patternwise the resist film to high-energy radiation, and developing the exposed resist film in an alkaline developer to form a resist pattern.

9. The pattern forming process of claim 8 wherein the processable substrate has the outermost surface of a chromium-containing material.

10. The pattern forming process of claim 8 wherein the processable substrate is a photomask blank.