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16. A resist composition comprising a base polymer and a sulfonium or iodonium salt having the formula (A): 

wherein R $^{1 }$is a straight, branched or cyclic C$_{1 }$-C$_{24 }$ alkylene group which may contain, an alkoxy, ether, ester, sulfonic acid ester moiety, double bond, triple bond or aromatic moiety, 

A+ is a sulfonium cation having the formula (B) or iodonium cation having the formula (C): 

wherein R 2 , R 3 and R 4 are each independently a straight, branched or cyclic C$_{1 }$-C$_{12 }$ alkyl or oxoalkyl group, a straight, branched or cyclic C$_{2}$-C$_{12 }$ alkenyl or oxoalkenyl group, C$_{6}$-C$_{20 }$ aryl group, or C$_{7}$ -C$_{12 }$ aralkyl or aryloxoalk~l group, in which at least one hydrogen of at least one of R , R $^{3 }$and R 4 is 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 50 which at least one hydrogen may be substituted by a straight, branched or cyclic C$_{1 }$-C$_{10 }$ alkyl or alkoxy moiety, 

wherein the base polymer comprises recurring units of at least one type selected from the formulae (fl) to (f3): 

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wherein R 51 , R $^{55 }$and R $^{59 }$each are hydrogen or methyl, R 52 is a single bond, phenylene, ---0- R 63 -, or ----C(=0)-Y 1 -R 63 -, Y $^{1 }$is ---0- or-NH-, R 63 is a straight, branched or cyclic C$_{1 }$-C$_{6 }$ alkylene or alkenylene group which may contain a carbonyl, ester, ether or hydroxyl moiety, or phenylene group, 

Rs3 Rs4 Rs6 Rs7 Rss R6o R61 and R62 are each i~depe~dently a ~traight, br~ch~d or cyclic C$_{1 }$-C$_{12 }$ alkyl group which may contain a carbonyl, ester or ether moiety, or a CcC$_{12 }$ aryl group, C$_{7}$ -C$_{20 }$ aralkyl group or mercaptophenyl group, 

A 1 is a single bond, -A$^{0}$----C(=0)-0-, -A$^{0}$-0- or -A$^{0}$-0----C(=0)-, A 0 is a straight, branched or cyclic C$_{1 }$-C$_{12 }$ alkylene group which may contain a carbonyl, ester or ether moiety, 

A 2 is hydrogen or trifluoromethyl, 

Z 1 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, ---O-R 64 -, or ----C(=0)› Z2 -R 6 4-, Z 2 is -0- or -NH-, R $^{64 }$is a straight, branched or cyclic C$_{1 }$-C$_{6 }$ alkylene or alkenylene group which may contain a carbonyl, ester, ether or hydroxyl moiety, or phenylene, fluorinated phenylene or trifluo› romethyl-substituted phenylene group, 

M- is a non-nucleophilic counter ion, and fl, f2 and f3 are numbers in the range: 0sfls0.5, 0sf2s0.5, 0sf3s0.5, and 0<fl+f2+f3s0.5, and 

the sulfonium or iodonium cation is selected from the group consisting of the following formulae: 

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