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serving as acid pairs with an anion, the hopping of proton is reduced as the size of anion becomes larger. 

Another component that is expected effective for mitigat› ing the influence of PPD is a quencher. Conventional quenchers were developed for the purpose of suppressing acid diffusion during PEB at high temperature for thereby enhancing the contrast of deprotection reaction. For miti› gating the influence of PPD, it is desired from a different viewpoint to develop a quencher capable of suppressing acid diffusion at room temperature. 

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 2015-090382 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 p76390 W (2010) 

Desired are quenchers capable of suppressing acid diffu› sion at room temperature, providing a high dissolution contrast, and reducing edge roughness (LWR) rather than such quenchers as amine quenchers, sulfonium and iodo› nium salts of sulfonic acid and carboxylic acid. 

An object of the invention is to provide a resist compo› sition which exhibits a high dissolution contrast, a reduced LWR, and no dimensional changes on PPD, independent of whether it is of positive tone or negative tone; and a pattern forming process using the same. 

The inventors have found that using a sulfonium or iodonium salt of sulfonic acid containing a morpholino group as the quencher, a resist film having a reduced L WR, a high dissolution contrast, and no dimensional changes on PPD is obtainable. 

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

Herein R 1 is a straight, branched or cyclic C$_{1 }$-C$_{24 }$alkylene group which may contain a hydroxyl, alkoxy, ether, ester, sulfonic acid ester moiety, halogen atom, double bond, triple bond or aromatic moiety. A+ is a sulfonium cation having the formula (B) or iodonium cation having the formula (C). 

Herein R 2 , R 3 and R 4 are each independently a straight, 65 branched or cyclic C$_{1 }$-C$_{12 }$ alkyl or oxoalkyl group, a straight, branched or cyclic C$_{2}$-C$_{12 }$ alkenyl or oxoalkenyl 

## CITATION LIST 

## DISCLOSURE OF INVENTION 

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group, CcC$_{20 }$ aryl group, or C$_{7}$ -C$_{12 }$aralkyl or aryloxoalkyl group, in which at least one hydrogen may be substituted by a substituent containing an ether, ester, carbonyl, carbonate, hydroxyl, carboxyl, halogen, cyano, amide, nitro, sultone, sulfonic acid ester, sulfone, thiol moiety or sulfonium salt, or R 2 and R 3 may bond together to form a ring with the sulfur atom to which they are attached; R 5 and R 6 are each independently a CcC$_{20 }$ aryl group in which at least one hydrogen may be substituted by a straight, branched or cyclic C$_{1 }$-C$_{10 }$alkyl or alkoxy moiety. 

The resist composition may further comprise an acid generator capable of generating sulfonic acid, imide acid or methide acid, and an organic solvent. 

In a preferred embodiment, the base polymer comprises recurring units having the formula (al) or recurring units having the formula (a2). 

Herein R 1 and R 13 are each independently hydrogen or methyl, R$^{12 }$and R$^{14 }$are each independently an acid labile group, X is a single bond, ester group, phenylene group, naphthylene group or a C$_{1 }$-C$_{12 }$ linking group containing lactone ring, and Y is a single bond or ester group. 

The resist composition may further comprise a dissolution inhibitor. 

Typically the resist composition is a chemically amplified positive resist composition. 

In another preferred embodiment, the resist composition is a chemically amplified negative resist composition; the base polymer is free of an acid labile group; and the resist composition may further comprise a crosslinker. 

In a preferred embodiment, the base polymer comprises recurring units of at least one type selected from the for› mulae (fl) to (f3). 

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