content_image/915078.jpg content_image/915079.jpg content_image/915080.jpg content_image/915081.jpg
Herein RA is hydrogen or methyl; X$^{1 }$is a single bond or ester group; X 2 is a C$_{1 }$-C$_{12 }$ straight, branched or cyclic alkylene group or CcC$_{10 }$ arylene group, any methylene moiety in the alkylene group may be substituted by an ether moiety, ester moiety or lactone ring-containing moiety, at least one hydro› gen in the group X 2 is substituted by iodine; X 3 is a single bond, ether group, ester group or C$_{1 }$-C$_{12 }$straight, branched or cyclic alkylene group, any methylene moiety in the alkylene group may be substituted by an ether or ester moiety; Rf$^{1 }$to R:t4 are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf 1 to Rf4 is fluorine or trifluoromethyl, Rf 1 and Rf 2 may bond together to form a carbonyl group; R 1 to Rf4 are each independently a C$_{1}$-C$_{12 }$ straight, branched or cyclic alkyl group, C$_{2}$ -C$_{12 }$ straight, branched or cyclic alkenyl group, C$_{2}$-C$_{12 }$straight, branched or cyclic alkynyl group, C$_{6}$-C$_{20 }$ aryl group, C$_{1 }$-C$_{2 }$ aralkyl group, or C$_{7}$-C$_{12 }$ aryloxyalkyl group, in which at least one hydrogen may be substituted by hydroxyl, carboxyl, halo› gen, oxo, cyano, amide, nitro, sultone, sulfone or sulfonium salt-containing moiety, and in which any methylene moiety may be substituted by an ether, ester, carbonyl, carbonate or sulfonate moiety, and R$^{1 }$and R 2 may bond together to form a ring with the sulfur atom to which they are attached. 

[0013] Preferably the recurring units having formulae (al) and (a2) are represented by the formulae (al-1) and (a2-1), respectively. 

<img src='content_image/915078.jpg'>

<img src='content_image/915079.jpg'>

Herein RA, R$^{1 }$to R 5 , Rf4 to Rf4, andX $^{1 }$are as defined above; R 6 is a C$_{1 }$-C$_{4 }$ straight, branched or cyclic alkyl group, halogen atom exclusive of iodine, hydroxyl group. C$_{1 }$-C$_{4 }$ straight, branched or cyclic alkoxy group, or C$_{2}$-C$_{5 }$ straight, branched or cyclic alkoxycarbonyl group, mis an integer of 1 to 4, and n is an integer of Oto 3. 

[0014] The resist composition may further comprise an organic solvent. 

[0015] In a preferred embodiment, the polymer further comprises recurring units having to the formula (bl) or (b2). 

<img src='content_image/915080.jpg'>

<img src='content_image/915081.jpg'>

Herein RA is independently hydrogen or methyl; Y 1 is a single bond, phenylene group, naphthylene group, or a C$_{1 }$-C$_{12 }$ linking group containing an ester moiety and/or lactone ring; Y 2 is a single bond or ester group; R$^{11 }$and R 12 are each independently an acid labile group; R$^{13 }$is halogen, trifluoromethyl, cyano, C$_{1 }$-C$_{6 }$ straight, branched or cyclic alkyl or alkoxy group, or C$_{2}$-C$_{7 }$ straight, branched or cyclic acyl, acyloxy or alkoxycarbonyl group; R$^{14 }$is a single bond or C$_{1 }$-C$_{6 }$ straight or branched alkylene group in which at least one carbon atom may be substituted by an ether or ester moiety, p is 1 or 2, and q is an integer of O to 4. 

[0016] The resist composition may further comprise a dissolution inhibitor, the resist composition being a chemi› cally amplified positive tone resist composition. 

[0017] In one embodiment, the polymer is free of an acid labile group. The resist composition may further comprise a crosslinker, the resist composition being a chemically ampli› fied negative tone resist composition. 

[0018] The resist composition may further comprise a surfactant. 

[0019] In another aspect, the invention provides a process for forming a pattern comprising the steps of applying the resist composition defined above onto a substrate, baking to form a resist film, exposing the resist film to high-energy radiation, and developing the exposed film in a developer. 

[0020] In a preferred embodiment, the high-energy radia› tion is ArF excimer laser radiation of wavelength 193 nm, KrF excimer laser radiation of wavelength 248 nm, EB or EUV of wavelength 3 to 15 nm. 

[0021] A resist material containing a polymer comprising recurring units derived from a sulfonium or iodonium salt having a polymerizable unsaturated bond and containing iodine in the linker between the polymerizable unsaturated bond and a fluorosulfonic acid has the advantage of reduced acid diffusion because of the high atomic weight of iodine. This prevents resolution from declining due to blur by acid diffusion and enables to reduce LWR and improve CDU. 

## Advantageous Effects of Invention 

