Sulfonium salt, polymer, resist composition, and patterning process
A polymer comprising recurring units derived from a sulfonium salt of specific structure having a polymerizable group is coated to form a resist film which is amenable to precise micropatterning because of improved LWR, CDU and resolution.
1. A sulfonium salt comprising an anion having the formula (1a) and a sulfonium cation having the formula (1b) or (1C):
wherein R is a C 1 -C 20 straight, branched or cyclic monovalent hydrocarbon group containing at least one iodine atom, Rf 1 and Rf 2 are each independently hydrogen, fluorine or trifluoromethyl, n is an integer of 0 to 5, and L 1 is a single bond, or a divalent group containing an ether bond, thioether bond, ester bond, sulfonic acid ester bond, carbonate bond or carbamate bond,
wherein A is an organic group having a polymerizable group, R 1 , R 2 and R 3 are each independently a halogen, nitro, cyano, or C 1 -C 20 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, where a plurality of groups R 1 , R 2 or R 3 are included, two adjacent groups R 1 , R 2 or R 3 may bond together to form a ring with the carbon atoms to which they are attached, X is a single bond, or —O—, —NH—, —S—, —SO—, —SO 2 —, —CO— or —CH 2 —, p is an integer of 0 to 4, q and r are each independently an integer of 0 to 5, q′ and r′ are each independently an integer of 0 to 4.
2. The sulfonium salt of claim 1 wherein the sulfonium cation has the formula (1b-1) or (1c-1):
wherein R 1 , R 2 , R 3 , X, p, q, r, q′ and r′ are as defined above, L 2 is a C 1 -C 20 straight, branched or cyclic divalent hydrocarbon group which may contain a heteroatom, and R A is each independently hydrogen or methyl.
3. The sulfonium salt of claim 1 wherein the anion has the formula (1a-1):
wherein Rf 1 , Rf 2 , L 1 and n are as defined above, R 4 is a C 1 -C 20 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, s is an integer of 1 to 5, t is an integer of 0 to 4, and 1≤s+t≤5.
4. The sulfonium salt of claim 3 wherein the anion has the formula (1a-2):
wherein R 4 , s and t are as defined above, L 3 is a C 1 -C 20 straight, branched or cyclic divalent hydrocarbon group which may contain a heteroatom, u and v are each independently 0 or 1.
5. The sulfonium salt of claim 1 wherein R is a C 1 -C 20 straight, branched or cyclic monovalent hydrocarbon group containing at least two iodine atoms.
6. The sulfonium salt of claim 1 wherein R is a C 6 -C 20 aryl group containing at least one iodine atom.