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exposed to EUV through a patterned mask. The resist film was baked (PEB) on a hotplate at the temperature shown in Table 2 for 60 seconds and developed in a 2.38 wt % TMAH aqueous solution for 30 seconds to form a hole pattern having a size of 23 nm and a pitch of 46 nm. 

The resist pattern was evaluated under CD-SEM (CG- 5000, Hitachi High-Technologies Corp.). The exposure dose that provides a hole pattern having a size of 23 nm is reported as sensitivity. The size of 50 holes at that dose was measured, from which a size variation (3a) was computed and reported as CDU. 

The resist composition is shown in Table 2 together with the sensitivity and CDU of EUV lithography. 

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It is demonstrated in Tables 1 and 2 that resist composi› tions comprising an iodonium salt having formula (A) within the scope of the invention offer a satisfactory reso› lution and improved LWR and CDU. 

Japanese Patent Application No. 2017-052391 1s mcor- porated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teach› ings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

The invention claimed is: 

1. A resist composition comprising a base polymer, an acid generator and a quencher containing an iodonium salt having the formula (A): 

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wherein R 1 is a hydroxyl group, C$_{1}$-C$_{6 }$ straight, branched or cyclic alkyl or alkoxy group, C$_{2}$-C$_{6 }$ straight, branched or cyclic acyloxy group, fluorine, chlorine, bromine, amino, -NR$^{5}$-C(=O)-R 6 , or-NR $^{5}$----C (=O)-O-R 6 , R 5 is hydrogen or a C$_{1}$-C$_{6 }$ straight, branched or cyclic alkyl group, R 6 is a C$_{1 }$-C$_{6 }$ straight, branched or cyclic alkyl group or C$_{2}$ -C$_{8 }$ straight, branched or cyclic alkenyl group; X$^{1 }$is a single bond or a ( q+ 1 )-valent C$_{1 }$-C$_{20 }$linking group which may contain at least one moiety selected from ether, carbonyl, ester, amide, sultone, lactam, carbonate, halogen, hydroxyl and carboxyl; X 2 is an ether, ester or amide group; R 2 and R 3 are each independently trifluoromethyl or a CcC$_{10 }$ aryl, C$_{2}$ -C$_{6 }$ alkenyl or C$_{2}$-C$_{6 }$ alkynyl group in 

