Resist composition and patterning process

A resist composition comprising

• an iodized base polymer, and
• at least one quencher selected from the group consisting of a sulfonium or ammonium salt of iodized benzene ring-containing carboxylic acid, a sulfonium or ammonium salt of iodized benzene ring-containing N-carbonylsulfonamide, and an iodized benzene ring-containing ammonium salt,
• wherein the sulfonium or ammonium salt of iodized benzene ring-containing carboxylic acid, the sulfonium or ammonium salt of iodized benzene ring-containing N-carbonylsulfonamide, and the iodized benzene ring-containing ammonium salt have the following formulae (A)-1, (A)-2 and (A)-4, respectively,
• wherein R1 is hydroxyl, fluorine, chlorine, bromine, amino, nitro, cyano, or a C1-C6 alkyl group, C1-C6 alkoxy group, C2-C6 acyloxy group or C1-C4 alkylsulfonyloxy group, which may be substituted with halogen, or —NR1A—C(═O)—R1B or —NR1A—C(═O)—O—R1B, R1A is hydrogen or a C1-C6 alkyl group, R1B is a C1-C6 alkyl group or C2-C8 alkenyl group,
• R2 is a single bond or a C1-C20 divalent linking group which may contain ether bond, carbonyl moiety, ester bond, amide bond, sultone moiety, lactam moiety, carbonate moiety, halogen, hydroxyl moiety or carboxyl moiety,
• R3 is a C1-C10 alkyl group or C6-C10 aryl group, which may be substituted with amino, nitro, cyano, C1-C12 alkyl, C1-C12 alkoxy, C2-C12 alkoxycarbonyl, C2-C12 acyl, C2-C12 acyloxy, hydroxyl or halogen,
• R4 is a C1-C20 divalent hydrocarbon group which may contain an ester bond or ether bond,
• R5 is hydrogen, nitro, or a C1-C20 monovalent hydrocarbon group which may contain hydroxyl, carboxyl, ether bond, ester bond, thiol, nitro, cyano or amino, with the proviso that in case of p=1, groups R5 may bond together to form a ring with the nitrogen atom to which they are attached, the ring optionally containing a double bond, oxygen, sulfur or nitrogen,
• m is an integer of 1 to 5, n is an integer of 0 to 4, meeting 1≤m+n≤5, p is 1, 2 or 3, q is 1 or 2,
• Aq− is a carboxylate anion, fluorine-free sulfonimide anion, sulfonamide anion, or halide ion,
• X+ is a sulfonium cation having the formula (Aa) or ammonium cation having the formula (Ab):
• wherein R6, R7 and R8 are each independently fluorine, chlorine, bromine, iodine, or a C1-C20 monovalent hydrocarbon group which may contain a heteroatom, R6 and R7 may bond together to form a ring with the sulfur atom to which they are attached,
• R9 to R12 are each independently hydrogen or a C1-C24 monovalent hydrocarbon group which may contain halogen, hydroxyl, carboxyl, thiol, ether bond, ester bond, thioester bond, thionoester bond, dithioester bond, amino, nitro, sulfone or ferrocenyl, R9 and R10 may bond together to form a ring, R9 and R10 taken together may form ═C(R9A)(R10A), R9A and R10A are each independently hydrogen or a C1-C16 monovalent hydrocarbon group, R9A and R10A may bond together to form a ring with the carbon and nitrogen atoms to which they are attached, the ring optionally containing a double bond, oxygen, sulfur or nitrogen,
• wherein the iodized base polymer comprises recurring units having the formula (a1) or recurring units having the formula (a2):
• wherein RA is each independently hydrogen or methyl, R21 is a single bond or methylene, R22 is hydrogen or a C1-C4 alkyl group, X1 is a single bond, ether bond, ester bond, amide bond, —C(═O)—O—R23—, phenylene, -Ph-C(═O)—O—R24—, or -Ph-R25—O—C(═O)—R26—, wherein Ph stands for phenyl, R23 is a C1-C10 alkanediyl group which may contain an ether bond or ester bond, R24, R25 and R26 are each independently a single bond or a C1-C6 straight or branched alkanediyl group, a is an integer of 1 to 5, b is an integer of 1 to 4, meeting 1≤a+b≤5.