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[0085] The compound having the anion of formula (3D) has a sufficient acid strength to cleave acid labile groups in the base polymer because it is free of fluorine at a-position of sulfa group, but has two trifluoromethyl groups at ~-po› sition. Thus the compound is a useful PAG. 

[0086] Also compounds having the formula ( 4) are useful as the PAG. 

[0087] In formula ( 4), R 201 and R$^{202 }$are each indepen› dently a C$_{1 }$-C$_{30 }$ straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom. R $^{203 }$is a C$_{1 }$-C$_{30 }$ straight, branched or cyclic divalent hydrocarbon group which may contain a heteroatom. 201 

[0088] Any two ofR , R $^{202 }$and R$^{203 }$may bond together to form a ring with the sulfur atom to which they are attached. LA is a single bond, ether bond or a straight, branched or cyclic C$_{1 }$-C$_{20 }$ divalent hydrocarbon group which may contain a heteroatom. XA, XB, Xe and xn are each independently hydrogen, fluorine or trifluoromethyl, with the proviso that at least one of XA, XB, Xe and xn is fluorine or trifluoromethyl, and k is an integer of Oto 3. 

[0089] Suitable monovalent hydrocarbon groups include methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, t-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclo› pentyl, cyclohexyl, 2-ethylhexyl, cyclopentylmethyl, cyclo› pentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclo› hexylethyl, cyclohexylbutyl, norbomyl, oxanorbornyl, tricyclo[5.2. l .0 2 • $^{6}$]decanyl, adamantyl, phenyl, naphthyl and anthracenyl. Also included are the foregoing groups in which some hydrogen is replaced by a radical containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, or in which some carbon is replaced by a radical containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxyl, cyano, carbonyl, ether, ester, sulfonic acid ester, carbonate, lactone ring, sultone ring, carboxylic acid anhydride or haloalkyl radical. 

[0090] Suitable divalent hydrocarbon groups include lin› ear alkane diyl groups such as methylene, ethylene, propane- 1,3-diyl; butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane- 1, 10-diyl, undecane-1, 11-diyl, dodecane-1, 12-diyl, tride› cane-1, 13-diy 1, tetradecane-1, 14-diy 1, pentadecane-1, 15- diy l, hexadecane-1,16-diyl, heptadecane-1,17-diyl; 

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