Resist composition and pattern forming process

1 . A resist composition comprising

(I) an acid compound having the formula (A):

wherein R 1 is fluorine, hydroxy or a C 1 -C 20 hydrocarbyl group which may contain a heteroatom, Rf 1 and Rf 2 are each independently fluorine or trifluoromethyl,

(II) an acid generator having the formula (1):

Ar 1 —I + —Ar 2 (X a n− ) 1/n   (1)

wherein Ar 1 and Ar 2 are each independently a C 6 -C 18 aryl group which may contain a heteroatom, Xa n− is an n-valent anion of strong acid, and n is an integer of at least 1 and/or

(III) a photo-decomposable quencher having the formula (2):

Ar 3 —I + —Ar 4 (X q m− ) 1/m   (2)

wherein Ar 3 and Ar 4 are each independently a C 6 -C 18 aryl group which may contain a heteroatom, Xq m− is an m-valent anion of weak acid, and m is an integer of at least 1, and

(IV) a base polymer adapted to change its dissolution rate in a developer under the action of an acid.

2 . A resist composition comprising

(I) an acid compound having the formula (A):

wherein R 1 is fluorine, hydroxy or a C 1 -C 20 hydrocarbyl group which may contain a heteroatom, Rf 1 and Rf 2 are each independently fluorine or trifluoromethyl, and

(IV′) a base polymer adapted to change its dissolution rate in a developer under the action of an acid and comprising repeat units having the formula (b1):

wherein R A is hydrogen or methyl,

Y 1 is a single bond or ester bond,

Y 2 is a single bond or a C 1 -C 20 hydrocarbylene group which may contain at least one moiety selected from an ester bond, ether bond, lactone ring, amide bond, sultone ring and iodine,

Y 3 is a single bond, ether bond or ester bond,

Rf 11 to Rf 14 are each independently hydrogen, fluorine or trifluoromethyl, at least one thereof being fluorine or trifluoromethyl, and

Ar 5 and Ar 6 are each independently a C 6 -C 18 aryl group which may contain a heteroatom.

3 . The resist composition of claim 2 , further comprising (III) a photo-decomposable quencher having the formula (2):

Ar 3 —I + —Ar 4 (X q m− ) 1/m   (2)

wherein Ar 3 and Ar 4 are each independently a C 6 -C 18 aryl group which may contain a heteroatom, Xq m− is an m-valent anion of weak acid, and m is an integer of at least 1.

4 . The resist composition of claim 1 wherein the acid compound having formula (A) has any one of the formulae (A-1) to (A-3):

wherein R 1A is hydrogen or a C 1 -C 20 hydrocarbyl group which may contain a heteroatom, R 2 and R 3 are each independently hydrogen or a C 1 -C 20 hydrocarbyl group, R 2 and R 3 may bond together to form a ring with the carbon atom to which they are attached, and L is a single bond, ether bond or ester bond.

5 . The resist composition of claim 1 wherein the base polymer comprises repeat units having the formula (a):

wherein R A is hydrogen or methyl,

X 1 is a single bond, ester bond, amide bond, or a C 1 -C 12 divalent linking group containing at least one moiety selected from phenylene, naphthylene, ester bond, ether bond, lactone ring, and amide bond,

R 11 is hydrogen, fluorine, or a C 1 -C 6 saturated hydrocarbyl group, R 11 and X 1 may bond together to form a ring with the carbon atoms on the aromatic ring to which they are attached,

p is 1 or 2, q is an integer of 0 to 4, p+q is from 1 to 5, and r is 0 or 1.

6 . The resist composition of claim 1 wherein the base polymer comprises repeat units having a structural site which is decomposed to generate an acid upon exposure to actinic ray or radiation.

7 . The resist composition of claim 6 wherein the repeat units having a structural site which is decomposed to generate an acid upon exposure to actinic ray or radiation have the formula (b2):

wherein R A is hydrogen or methyl,

Y 1 is a single bond or ester bond,

Y 2 is a single bond or a C 1 -C 20 hydrocarbylene group which may contain at least one moiety selected from an ester bond, ether bond, lactone ring, amide bond, sultone ring and iodine,

Y 3 is a single bond, ether bond or ester bond,

Rf 11 to Rf 14 are each independently hydrogen, fluorine or trifluoromethyl, at least one thereof being fluorine or trifluoromethyl,

R 21 to R 23 are each independently a C 1 -C 20 hydrocarbyl group which may contain a heteroatom, R 21 and R 22 may bond together to form a ring with the sulfur atom to which they are attached.

8 . The resist composition of claim 1 wherein the base polymer further comprises repeat units (c) having a carboxy group whose hydrogen is substituted by an acid labile group.

9 . The resist composition of claim 8 wherein the repeat units (c) have the formula (c):

wherein R A is hydrogen or methyl,

Z 1 is a single bond, phenylene group, naphthylene group, or a C 1 -C 12 linking group containing at least one moiety selected from an ester bond, ether bond and lactone ring, and

R AL is an acid labile group.

10 . The resist composition of claim 1 wherein the base polymer is free of repeat units substituted with an acid labile group.

11 . The resist composition of claim 10 , further comprising a crosslinker.

12 . A pattern forming process comprising the steps of (i) applying the resist composition of claim 1 onto a substrate to form a resist film thereon, (ii) exposing the resist film to high-energy radiation, and (iii) developing the exposed resist film in a developer.