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[0088] In formulae (dl) to (d3), RA is each independently hydrogen or methyl. Z 1 is a single bond, phenylene, -O-Z 11 , ----C(=0)-0-Z 11 - or ----C(=0)-NH› Z11-, wherein Z 11 is a C$_{1}$-C$_{6 }$ alkanediyl group, C$_{2}$-C$_{6 }$ alkenediyl group, or phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety. z 2 A is a single bond or ester bond. zw is a single bond or a C$_{1 }$-C$_{12 }$ divalent group which may contain an ester bond, ether bond, lactone ring, bromine or iodine. Z 3 is a single bond, methylene, ethylene, phenylene, fluorinated phe› nylene, ---O-Z 31 -, ----C(=0)-0-Z 31 - or -C(=0)-NH-Z 31 -, wherein Z $^{31 }$is a C$_{1}$-C$_{6 }$ alkanediyl group, C$_{2}$-C$_{6 }$ alkenediyl group, or phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety. 

[0089] In formula (d2), Rf$^{1 }$to R:t4 are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf 1 to R:t4 being fluorine. Preferably at least one of Rf $^{3 }$and R:t4 is fluorine, most preferably both RF and R:t4 are fluorine. 21 28 

[0090] In formulae (dl) to (d3), R to R are each independently a C$_{1 }$-C$_{20 }$ monovalent hydrocarbon group which may contain a heteroatom, any two of R 23 , R $^{24 }$and R$^{25 }$or any two of R 26 , R $^{27 }$and R$^{28 }$may bond together to form a ring with the sulfur atom to which they are attached. The monovalent hydrocarbon group may be straight, branched or cyclic and examples thereof include C$_{1 }$-C$_{12 }$ alkyl, CcC$_{12 }$ aryl, and C$_{7}$-C$_{20 }$ aralkyl groups. In these groups, some or all hydrogen may be substituted by C$_{1 }$-C$_{10 }$ alkyl, halogen, trifluoromethyl, cyano, nitro, hydroxyl, mer› capto, C$_{1 }$-C$_{10 }$ alkoxy, C$_{2}$-C$_{10 }$ alkoxycarbonyl, or C$_{2}$-C$_{10 }$ acyloxy moiety, or some carbon may be replaced by a carbonyl moiety, ether bond or ester bond. 

[0091] Examples of the sulfonium cation in formula (d2) or ( d3) are as will be later exemplified for the cation of the sulfonium salt having formula (1-1). 

[0092] In formula (dl), M- is a non-nucleophilic counter ion. Examples of the non-nucleophilic counter ion include halide ions such as chloride and bromide ions; fluoroalkyl› sulfonate ions such as triflate, 1, 1, 1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such as mesylate and butanesulfonate; imide ions such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfo› nyl)imide and bis(perfluorobutylsulfonyl)imide; methide 

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ions such as tris(trifluoromethylsulfonyl)methide and tris (perfluoroethylsulfonyl)methide. 

[0093] Also included are sulfonate ions having fluorine substituted at a-position as represented by the formula ( dl-1) and sulfonate ions having fluorine substituted at a-position and trifluoromethyl at ~-position as represented by the formula (dl-2). 

[0094] In formula (dl-1), R 31 is hydrogen, or a C$_{1}$-C$_{20 }$ alkyl group, C$_{2}$-C$_{20 }$ alkenyl group, or C$_{6}$-C$_{20 }$ aryl group, which may contain an ether bond, ester bond, carbonyl moiety, lactone ring, or fluorine atom. The alkyl and alkenyl groups may be straight, branched or cyclic. 

[0095] In formula ( dl-2), R 32 is hydrogen, or a C$_{1 }$-C$_{30 }$ alkyl group, C$_{2}$-C$_{30 }$ acyl group, C$_{2}$-C$_{20 }$ alkenyl group, C$_{6}$-C$_{20 }$ aryl group or C$_{6}$-C$_{20 }$ aryloxy group, which may contain an ether bond, ester bond, carbonyl moiety or lactone ring. The alkyl, acyl and alkenyl groups may be straight, branched or cyclic. 

[0096] Examples of the monomer from which recurring unit ( dl) is derived are shown below, but not limited thereto. RA and M- are as defined above. 

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