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However, it has only a little influence on performance improvement. There is a desire to have a quencher for further improving contrast. 

Patent Document 4 discloses an amine quencher which reduces its basicity through a mechanism that an acid labile group is eliminated under the action of acid, and lactam is then formed. Due to the mechanism that basicity is reduced under the action of acid, acid diffusion is controlled by high basicity in the unexposed region where the amount of acid generated is minimal, whereas acid diffusion is promoted due to reduced basicity of the quencher in the overexposed region where the amount of acid generated is large. This expands the difference in acid amount between the exposed and unex› posed regions, from which an improvement in contrast is expected. However, the contrast enhancing effect is low since deprotection reaction of the base polymer and deprotection reaction of the quencher and ensuing lactam-forming reaction take place simultaneously in parallel. If the deprotection reac› tion of the quencher is slower than the deprotection reaction of the base polymer, the contrast enhancing effect is lower. There is a desire to have a quencher capable of further contrast improvement. 

Patent Document 1: JP-A 2001-194776 

Patent Document 2: JP-A 2002-226470 

Patent Document 3: JP-A 2002-363148 

Patent Document 4: JP-A 2012-137729 (US 20120141938) 

Non-Patent Document 1: SPIE Vol. 5039 pl (2003) 

Non-Patent Document 2: SPIE Vol. 6520 p65203L-1 (2007) 

Non-Patent Document 3: SPIE Vol. 7639 p76390W (2010) 

A blend of an onium salt of a-non-fluorinated sulfonic acid or carboxylic acid with an onium salt of a-fluorinated sul› fonic acid, imidic acid or methidic acid is effective for reduc› ing LWR, but suffers from a low dissolution contrast. An amine compound quencher provides a high dissolution con› trast, but is less effective for reducing LWR. There is a desire to have a quencher which offers a high dissolution contrast and reduced LWR. 

An object of the invention is to provide a resist composition 45 which exhibits a high dissolution contrast and reduced LWR independent of whether it is positive or negative working; and a pattern forming process using the same. 

The inventors have found that a resist composition com› prising a sulfonium or iodonium salt of a carboxylic acid having an acid-reactive group of specific structure is used to form a photoresist film having a high contrast and minimal LWR. 

In one aspect, the invention provides a resist composition comprising a base polymer and a sulfonium salt having the general formula (1 )-1 or a iodonium salt having the general formula (1)-2. 

## CITATION LIST 

## DISCLOSURE OF INVENTION 

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Herein R 1 is hydrogen, or a straight, branched or cyclic C$_{1 }$-C$_{30 }$ alkyl, CcC$_{30 }$ aryl, C$_{7}$ -C$_{30 }$ aralkyl, C$_{2}$ -C$_{30 }$ alkenyl, C$_{2}$-C$_{10 }$ alkynyl, or C$_{4}$ -C$_{12 }$heterocyclic-bearing group, or a combination of such groups, which group may contain a hydroxyl, mercapto, carboxyl, ether, thio ether, ester, sulfonic acid ester, sulfonyl, lactone ring, carbonyl, cyano, nitro, halo› gen, trifluoromethyl, amide, imide, sulfonamide, carbonate, sulfide, -N=CR---0-, -N=CR-S-, or N-O› N=moiety, or R $^{1 }$may be an acid labile group; R is hydrogen, mercapto, hydroxyl or C$_{4}$ -C$_{3 }$ alkyl, or may bond with the nitrogen atom in formula (1) to form a ring; R $^{2 }$and R$^{3 }$each are hydrogen, a straight or branched C$_{1 }$-C$_{4 }$ alkyl group or C$_{2}$-C$_{4 }$ alkenyl group, or R$^{2 }$andR$^{3 }$may bond together to form a ring with the carbon atom to which they are attached; R 4 , Rs and R 6 are each independently a straight, branched or cyclic C$_{1 }$-C$_{12 }$alkyl, alkenyl, oxoalkyl or oxoalkenyl group, CcC$_{20 }$ aryl, C$_{7}$-C$_{12 }$aralkyl or aryloxoalkyl group, in which at least one hydrogen atom may be substituted by an ether, ester, carbonyl, carbonate, hydroxyl, carboxyl, halogen, cyano, amide, nitro, sultone, sulfonic acid ester, sulfone moiety, or sulfonium salt-containing substituent, R 4 and Rs may bond together to form a ring with the sulfur atom to which they are attached; R$^{7 }$and R$^{8 }$each are a C$_{6}$-C$_{20 }$aryl group which may contain a straight, branched or cyclic C$_{1 }$-C$_{10 }$alkyl or alkoxy moiety, and m is an integer of 2 to 8. 

The resist composition may further comprise an acid gen› erator capable of generating a sulfonic acid, imidic acid or methidic acid. 

In a preferred embodiment, the base polymer comprises recurring units (al) derived from (meth)acrylate, styrenecar› boxylic acid or vinylnaphthalenecarboxylic acid having an acid labile group substituted thereon, or recurring units (a2) derived from hydroxystyrene having an acid labile group substituted thereon, as represented by the general formula (2): 

wherein R 9 and R 11 are each independently hydrogen or methyl, Xis a single bond, a C$_{1}$-C$_{12 }$linking group having an ester moiety or lactone ring, phenylene group or naphthylene group, Y is a single bond or ester group, and R $^{10 }$and R $^{12 }$are each independently an acid labile group. 

The resist composition may further comprise an organic solvent, the resist composition being a chemically amplified positive resist composition. Further a dissolution inhibitor may be added. 

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-continued 

