US 10,620,533 B2  3  4  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.  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).  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)  CITATION LIST  DISCLOSURE OF INVENTION  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  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).  (A)  (B)  R3  I  R $^{2}$-s+-R4  (C)  R $^{5}$-I+-R6  (al)  (a2)  ~  y  ORl4  (fl) 