Resist composition, patterning process, and barium salt

1. A resist composition comprising a base resin comprising recurring units having an acid labile group, and a metal salt of sulfonic acid having the formula (1):

wherein X is each independently iodine or bromine,

R 1 is hydroxy, C 1 -C 20 alkyl, C 1 -C 20 alkoxy, C 2 -C 20 acyloxy, fluorine, chlorine, amino, —NR 2 —C(═O)—R 3 , or —NR 2 —C(═O)—O—R 3 , at least one hydrogen on the alkyl, alkoxy or acyloxy group may be substituted by fluorine, chlorine, bromine, iodine, hydroxyl, amino or a C 1 -C 6 alkoxy moiety,

R 2 is a C 1 -C 6 alkyl group,

R 3 is a C 1 -C 16 alkyl, C 2 -C 16 alkenyl or C 6 -C 12 aryl group in which at least one hydrogen may be substituted by a halogen, hydroxyl, C 1 -C 6 alkoxy, C 2 -C 6 acyl or C 2 -C 6 acyloxy moiety,

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

M q+ is a sodium, magnesium, potassium, calcium, rubidium, strontium, yttrium, cesium, barium or cerium ion,

m is an integer of 2 to 5, n is an integer of 0 to 3, m+n is 2 to 5, p is an integer of 1 to 3, and q is an integer of 1 to 3.

2. The resist composition of claim 1 wherein the recurring units having an acid labile group have the formula (a1) or (a2):

wherein R A is each independently hydrogen or methyl, R 11 and R 12 each are an acid labile group, Y 1 is a single bond or a C 1 -C 15 linking group containing an ester bond, lactone ring, phenylene or naphthylene moiety, and Y 2 is a single bond, ester bond or amide bond.

3. The resist composition of claim 1 wherein the base resin further comprises recurring units of at least one type selected from the formulae (b1) to (b3):

wherein R A is each independently hydrogen or methyl,

Z 1 is a single bond, phenylene group, —O—Z 11 —, —C(═O)—O—Z 11 —, or —C(═O)—NH—Z 11 —,

Z 2 is a single bond, —C(═O)—O—Z 11 —, or —C(═O)—NH—Z 11 —,

Z 3 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—Z 11 —, —C(═O)—O—Z 11 —, or —C(═O)—NH—Z 11 —,

Z 11 is a C 1 -C 6 alkanediyl group, phenylene group, or C 2 -C 10 alkenediyl group, which may contain a carbonyl, ester bond, ether bond or hydroxyl moiety,

R 21 to R 28 are each independently a C 1 -C 22 monovalent hydrocarbon group which may contain a heteroatom, a pair of R 21 and R 22 may bond together to form a ring with the sulfur atom to which they are attached, any two of R 23 , R 24 and R 25 or any two of R 26 , R 27 and R 28 may bond together to form a ring with the sulfur atom to which they are attached,

A is hydrogen or trifluoromethyl, and

Q − is a non-nucleophilic counter ion.

4. The resist composition of claim 3 wherein the base resin comprises recurring units of formula (b2).

5. The resist composition of claim 1 which is a chemically amplified positive resist composition.

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

7. The resist composition of claim 1 , further comprising an acid generator.

8. The resist composition of claim 1 , further comprising a quencher.

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

10. A process for forming a pattern comprising the steps of applying the resist composition of claim 1 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.

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

12. The process of claim 10 wherein the high-energy radiation is EB emitted at an accelerating voltage of 1 to 150 kV.

13. The process of claim 11 wherein during the exposure step, the surface of the substrate underlying the resist film is electrically chained positive.

14. A barium salt having the formula (2):

wherein R 1 is hydroxy, C 1 -C 20 alkyl, C 1 -C 20 alkoxy, C 2 -C 20 acyloxy, fluorine, chlorine, amino, —NR 2 —C(═O)—R 3 , or —NR 2 —C(═O)—O—R 3 , at least one hydrogen on the alkyl, alkoxy or acyloxy group may be substituted by fluorine, chlorine, bromine, iodine, hydroxyl, amino or a C 1 -C 6 alkoxy moiety,

R 2 is a C 1 -C 6 alkyl group,

R 3 is a C 1 -C 16 alkyl, C 2 -C 16 alkenyl or C 1 -C 12 aryl group in which at least one hydrogen may be substituted by a halogen, hydroxyl, C 1 -C 6 alkoxy, C 2 -C 6 acyl or C 2 -C 6 acyloxy moiety,

L′ is a single bond, or a C 1 -C 12 alkanediyl, C 2 -C 12 alkenediyl or C 6 -C 10 arylene group which may contain an ether bond, carbonyl, ester bond,

m is an integer of 2 to 5, n is an integer of 0 to 3, m+n is 2 to 5.