Resist composition, patterning process, and barium, cesium and cerium salts

1. A resist composition comprising a base resin comprising recurring units containing an acid labile group and a salt,

wherein the salt is a barium salt having the formula (2), a cesium salt having the formula (3) or a cerium salt having the formula (4):

wherein R 6 is a C 4 -C 20 straight, branched or cyclic alkyl, alkenyl or alkynyl group or C 6 -C 20 aryl group, which may contain halogen, ether, thiol, ester, carbonate, carbonyl, amide, amino, azide, carbamate, nitro, cyano, hydroxyl, carboxyl, sulfo, sulfonic acid ester, sultone moiety, lactone ring or lactam ring.

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

wherein R 2 and R 4 are each independently hydrogen or methyl, R 3 and R 5 each are an acid labile group, Y 1 is a single bond, a C 1 -C 12 linking group having at least one of ester moiety, lactone ring, phenylene moiety and naphthylene moiety, a phenylene group, or a naphthylene group, Y 2 is a single bond, ester group or amide group, a1 and a2 are numbers in the range: 0≤a1≤0.9, 0≤a2≤0.9, and 0<a1+a2<1.

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), (b2) and (b3):

wherein R 101 , R 105 , and R 110 each are hydrogen or methyl, R 102 is a single bond, phenylene, —O—R 114 —, or —C(═O)—Y—R 114 —, Y is —O— or —NH—, R 114 is a straight, branched or cyclic C 1 -C 6 alkylene group, phenylene group or straight, branched or cyclic C 3 -C 10 alkenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety, R 103 , R 104 , R 107 , R 108 , R 109 , R 111 , R 112 , and R 113 are each independently a straight, branched or cyclic C 1 -C 12 alkyl group which may contain a carbonyl, ester or ether moiety, or a C 6 -C 12 aryl, C 7 -C 20 aralkyl, or mercaptophenyl group which may contain a straight, branched or cyclic C 1 -C 10 alkyl, halogen, trifluoromethyl, cyano, nitro, hydroxyl, alkoxy, alkoxycarbonyl or acyloxy moiety, R 106 is hydrogen or trifluoromethyl, Z 1 is a single bond or —C(═O)—Z 3 —R 115 —, Z 2 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R 115 — or —C(═O)—Z 3 —R 115 —, Z 3 is —O— or —NH—, R 115 is a straight, branched or cyclic C 1 -C 6 alkylene group, phenylene group or straight, branched or cyclic C 1 -C 6 alkenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety, a pair of R 103 and R 104 , R 107 and R 108 , R 107 and R 109 , R 108 and R 109 , R 111 and R 112 , R 111 and R 113 , or R 112 and R 113 may bond directly or via a methylene moiety or ether bond to form a ring with the sulfur atom to which they are attached, Q − is a non-nucleophilic counter ion, b1, b2 and b3 are numbers in the range: 0≤b1≤0.5, 0≤b2≤0.5, 0≤b3≤0.5, and 0<b1+b2+b3≤0.5.

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

5. The resist composition of claim 1 , further comprising an acid generator, the composition being a chemically amplified positive resist composition.

6. The resist composition of claim 1 , further comprising at least one component selected from among an organic solvent, a dissolution inhibitor, a basic compound, and a surfactant.

7. The resist composition of claim 1 wherein the salt is in an amount of 0.01 to 100 parts per 100 parts by weight of the base resin.

8. A pattern forming process comprising the steps of coating the resist composition of claim 1 onto a substrate, baking, exposing the resulting resist film to high-energy radiation, and developing with a developer.

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

10. The process of claim 8 wherein the high-energy radiation is EB at an accelerating voltage of 1 to 150 kV.

11. The process of claim 9 wherein in the step of exposing the resist film to high-energy radiation, the surface of the substrate underneath the resist film is electrically charged positive.

12. A barium salt having the formula (2), a cesium salt having the formula (3) or a cerium salt having the formula (4):

wherein R 6 is a C 4 -C 20 straight, branched or cyclic alkyl, alkenyl or alkynyl group or C 6 -C 20 aryl group, which may contain halogen, ether, thiol, ester, carbonate, carbonyl, amide, amino, azide, carbamate, nitro, cyano, hydroxyl, carboxyl, sulfo, sulfonic acid ester, sultone moiety, lactone ring or lactam ring.