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[0179] Of the other PAGs, those compounds having an anion of formula (3A’) or (3D) are especially preferred because of reduced acid diffusion and high solubility in resist solvent, and those compounds having an anion of formula ( 4’) are especially preferred because of minimized acid diffusion. 

[0180] When the resist composition contains the other PAG (D), an appropriate amount of the PAG added is 0.1 to 40 parts, more preferably 0.5 to 20 parts by weight per 80 parts by weight of the base resin (B). As long as the amount of component (D) is in the range, good resolution is achiev› able and the risk of foreign particles being formed after development or during stripping of resist film is avoided. The other PAG may be used alone or in admixture as component (D). 

(E) Quencher 

[0181] The resist composition may further include (E) a quencher or acid diffusion controlling agent. As used herein, the "quencher" refers to a compound capable of trapping the acid generated by the PAG in the resist film to prevent the acid from diffusing to the unexposed region thereof for thereby forming the desired pattern. 

[0182] Typical of the quencher (E) are onium salts having the formulae (5) and (6). 

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[0183] In formula (5), Rq is hydrogen or a C$_{1 }$-C$_{40 }$mon› ovalent hydrocarbon group which may contain a heteroa› tom, exclusive of the group wherein hydrogen bonded to the carbon atom at a-position relative to the sulfa group is substituted by fluorine or fluoroalkyl. In formula (6), Rq 2 is hydrogen or a C$_{1 }$-C$_{40 }$monovalent hydrocarbon group which may contain a heteroatom. The monovalent hydrocarbon groups may be straight, branched or cyclic and examples thereof are as exemplified above for R$^{112 }$in formula (3A’). 

[0184] Examples of the monovalent hydrocarbon group Rq 1 include methyl, ethyl, propyl, isopropyl, n-butyl, sec› butyl, tert-butyl, n-pentyl, tert-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, nor› bornyl, oxanorbomyl, tricyclo[5.2.l.0 2 • $^{6}$]decanyl, adaman› tyl, phenyl, naphthyl, and anthracenyl. In these groups, some hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and a moiety containing a heteroatom such as oxygen, sulfur or nitrogen may intervene between carbon atoms, so that the group may contain a hydroxyl moiety, cyano moiety, car› bonyl moiety, ether bond, ester bond, sulfonic acid ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride, or haloalkyl moiety. Examples of the monovalent hydrocarbon group Rq 2 include fluoroalkyl groups such as trifluoromethyl and trifluoroethyl and fluoroaryl groups such as pentafluorophenyl and 4-trifluoromethylphenyl as well as the substituents exemplified above for Rq 1 . 

[0185] Examples of the anion in the onium salt having formula (5) are shown below, but not limited thereto. 

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