Iodonium salt, resist composition, and pattern forming process

A resist composition comprising

• a quencher comprising an iodonium salt having the formula (1), and
• a base resin consisting of recurring units having the formula (a) and recurring units having the formula (b) and optionally recurring units of at least one type selected from recurring units having the formulae (c1) to (c4):
• wherein Rf1 and Rf2 are each independently hydrogen, fluorine, or a C1-C4 straight or branched monovalent hydrocarbon group which may contain fluorine, at least one of Rf1 and Rf2 being fluorine or a C1-C4 straight or branched monovalent hydrocarbon group which may contain fluorine,
• Ar1 and Ar2 are each independently a C6-C40 aryl group which may contain a heteroatom, or Ar1 and Ar2 may bond together to form a ring with the iodine atom to which they are attached, and
• wherein RA is hydrogen, fluorine, methyl or trifluoromethyl, ZA is a single bond, phenylene, naphthylene or (backbone)-C(═O)—O—Z′—, Z′ is a C1-C10 alkanediyl group which may contain a hydroxyl moiety, ether bond, ester bond or lactone ring, or phenylene or naphthylene, XA is an acid labile group, and YA is hydrogen or a polar group containing at least one structure selected from the group consisting of hydroxyl, cyano, carbonyl, carboxyl, ether bond, ester bond, sulfonic acid ester bond, carbonate bond, lactone ring, sultone ring and carboxylic anhydride,
• wherein RA is hydrogen, fluorine, methyl or trifluoromethyl,
• L1 is a single bond, phenylene, —O-L11-, —C(═O)—O-L11- or —C(═O)—NH-L11-, L11 is a C1-C20 alkanediyl group, C2-C20 alkenediyl group or phenylene group, which may contain a heteroatom,
• L2 and L3 are each independently a single bond or a C1-C20 divalent hydrocarbon group which may contain a heteroatom,
• L4 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O-L41-, —C(═O)—O-L41- or —C(═O)—NH-L41-, L41 is an optionally substituted phenylene group,
• R11 to R21 are each independently a C1-C20 monovalent hydrocarbon group which may contain a heteroatom, any two of L1, R11 and R12 may bond together to form a ring with the sulfur atom to which they are attached, any two of R13, R14 and R15, any two of R16, R17 and R18, or any two of R19, R20 and R21 may bond together to form a ring with the sulfur atom to which they are attached,
• Xc− is a non-nucleophilic counter ion,
• A1 is hydrogen or trifluoromethyl,
• n1 is 0 or 1, n1 is 0 when L2 is a single bond, n2 is 0 or 1, n2 is 0 when L3 is a single bond.