Positive resist composition and patterning process

1. A positive resist composition comprising a base polymer comprising recurring units (a) having the structure of an ammonium salt of a sulfonamide having an iodized aromatic ring and recurring units of at least one type selected from recurring units (b1) having a carboxyl group substituted with an acid labile group and recurring units (b2) having a phenolic hydroxyl group substituted with an acid labile group,

wherein the recurring units (a) have the formula (a):

wherein m is an integer of 1 to 5, n is an integer of 0 to 3, 1≤m+n≤5, p is 1 or 2, q is 1 or 2,

R A is hydrogen or methyl,

X 1A is a single bond, ester bond or amide bond,

X 1B is a single bond or a C 1 -C 20 (p+1)-valent hydrocarbon group which may contain an ether bond, carbonyl moiety, ester bond, amide bond, sultone moiety, lactam moiety, carbonate bond, halogen, hydroxyl moiety or carboxyl moiety,

R 1 , R 2 and R 3 are each independently hydrogen, a C 1 -C 12 alkyl group, C 2 -C 12 alkenyl group, C 6 -C 12 aryl group, or C 7 -C 12 aralkyl group, R 1 and R 2 , or R 1 and X 1B may bond together to form a ring with the nitrogen atom to which they are attached, the ring may contain oxygen, sulfur, nitrogen or a double bond,

R 4 is a hydroxyl group, optionally halogenated C 1 -C 6 saturated hydrocarbyl group, optionally halogenated C 1 -C 6 saturated hydrocarbyloxy group, optionally halogenated C 2 -C 7 saturated hydrocarbylcarbonyloxy group, optionally halogenated C 2 -C 7 saturated hydrocarbyloxycarbonyl group, optionally halogenated C 1 -C 4 saturated hydrocarbylsulfonyloxy group, fluorine, chlorine, bromine, amino, nitro, cyano, —N(R 4A )—C(═O)—R 4B , or —N(R 4A )—C(═O)—O—R 4B , R 4A is hydrogen or a C 1 -C 6 saturated hydrocarbyl group, R 4B is a C 1 -C 6 saturated hydrocarbyl group, C 2 -C 8 unsaturated aliphatic hydrocarbyl group, C 6 -C 14 aryl group or C 7 -C 15 aralkyl group,

R 5 is a C 1 -C 10 (q+1)-valent hydrocarbon group,

R 6 is a C 1 -C 6 fluorinated saturated hydrocarbyl group or C 6 -C 10 fluorinated aryl group, and

L 1 is a single bond, ether bond, carbonyl group, ester bond, amide bond, carbonate bond, or C 1 -C 20 hydrocarbylene group, the hydrocarbylene group may contain an ether bond, carbonyl moiety, ester bond, amide bond, sultone ring, lactam ring, carbonate bond, halogen, hydroxyl moiety or carboxyl moiety.

2. The resist composition of claim 1 wherein the recurring units (b1) have the formula (b1) and the recurring units (b2) have the formula (b2):

wherein R A is each independently hydrogen or methyl,

Y 1 is a single bond, phenylene, naphthylene, or a C 1 -C 12 linking group containing an ester bond and/or lactone ring,

Y 2 is a single bond or ester bond,

Y 3 is a single bond, ether bond or ester bond,

R 11 and R 12 each are an acid labile group, R 13 is a C 1 -C 6 saturated hydrocarbyl group, C 1 -C 6 saturated hydrocarbyloxy group, C 2 -C 6 saturated hydrocarbylcarbonyl group, C 2 -C 6 saturated hydrocarbylcarbonyloxy group, C 2 -C 6 saturated hydrocarbyloxycarbonyl group, halogen, nitro group, or cyano group,

R 14 is a single bond or a C 1 -C 6 saturated hydrocarbylene group in which some carbon may be replaced by an ether bond or ester bond,

a is 1 or 2, b is an integer of 0 to 4, and 1≤a+b≤5.

3. The resist composition of claim 1 wherein the base polymer further comprises recurring units of at least one type selected from recurring units having the formulae (d1) to (d3):

wherein R A is hydrogen or methyl,

Z 1 is a single bond, or a C 1 -C 6 aliphatic hydrocarbylene group, phenylene group, naphthylene group, or a C 7 -C 18 group obtained by combining the foregoing, or —O—Z 11 —, —C(═O)—O—Z 11 — or —C(═O)—NH—Z 11 —, Z 11 is a C 1 -C 6 aliphatic hydrocarbylene group, phenylene group, naphthylene group, or a C 7 -C 18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety,

Z 2 is a single bond or ester bond,

Z 3 is a single bond, —Z 31 —C(═O)—O—, —Z 31 —O—, or —Z 31 —O—C(═O)—, Z 31 is a C 1 -C 12 hydrocarbylene group, phenylene group or a C 7 -C 18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond, bromine or iodine,

Z 4 is methylene, 2,2,2-trifluoro-1,1-ethanediyl or carbonyl,

Z 5 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene group, —O—Z 51 —, —C(═O)—O—Z 51 — or —C(═O)—NH—Z 51 —, Z 51 is a C 1 -C 6 aliphatic hydrocarbylene group, phenylene group, fluorinated phenylene group, or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety,

R 21 to R 28 are each independently a C 1 -C 20 hydrocarbyl group which may contain a heteroatom, a pair of R 23 and R 24 or R 26 and R 27 may bond together to form a ring with the sulfur atom to which they are attached, and

M − is a non-nucleophilic counter ion.

4. The resist composition of claim 1 , further comprising an acid generator capable of generating a sulfonic acid, sulfone imide or sulfone methide.

5. The resist composition of claim 1 , further comprising an organic solvent.

6. The resist composition of claim 1 , further comprising a dissolution inhibitor.

7. The resist composition of claim 1 , further comprising a surfactant.

8. A pattern forming process comprising the steps of applying the positive resist composition of claim 1 to form a resist film on a substrate, exposing the resist film to high-energy radiation, and developing the exposed resist film in a developer.

9. The process of claim 8 wherein the high-energy radiation is ArF excimer laser of wavelength 193 nm or KrF excimer laser of wavelength 248 nm.

10. The process of claim 8 wherein the high-energy radiation is EB or EUV of wavelength 3 to 15 nm.

11. The resist composition of claim 1 wherein L 1 is an ether bond, carbonyl group, ester bond, amide bond or carbonate bond.

12. The resist composition of claim 1 wherein R 5 is a C 2 -C 10 (q+1)-valent hydrocarbon group.