Hemiacetal compound, polymer, resist composition, and patterning process

1. A polymer comprising recurring units of at least one type selected from the general formulae (2a) to (2d):

wherein R 1 is hydrogen, methyl or trifluoromethyl, R 2 is methyl, R 3 and R 4 are each independently hydrogen or a straight, branched or cyclic, C 1 -C 15 monovalent hydrocarbon group in which any constituent —CH 2 — may be replaced by —O— or —C(═O)—, X 1 is a straight, branched or cyclic, C 1 -C 15 divalent hydrocarbon group in which a constituent —CH 2 — may be replaced by —O— or —C(═O)—, X 2 is —CH 2 — or —O—, the ring ZZ designates a non-aromatic mono- or polycyclic ring of 4 to 20 carbon atoms having a hemiacetal structure, k 1 is 0 or 1, and k 2 is an integer of 0 to 3.

2. The polymer of claim 1 , further comprising recurring units of at least one type selected from the general formulae (4A) to (4E):

wherein R 1 is as defined above, XA is an acid labile group, XB and XC are each independently a single bond or a straight or branched, C 1 -C 4 divalent hydrocarbon group, XD is a straight, branched or cyclic, C 1 -C 16 di- to pentavalent aliphatic hydrocarbon group in which a constituent —CH 2 — may be replaced by —O— or —C(═O)—, XE is an acid labile group, YA is a substituent group of lactone, sultone or carbonate structure, ZA is hydrogen, a C 1 -C 15 fluoroalkyl group or a C 1 -C 15 fluoroalcohol-containing group, k 1A is an integer of 1 to 3, and k 1B is an integer of 1 to 4.

3. The polymer of claim 1 , further comprising recurring units of at least one type selected from sulfonium salt units (f1) to (f3) represented by the following general formula:

wherein R 112 is hydrogen or methyl; R 113 is a single bond, phenylene, —O—R 122 —, or —C(═O)—Z 22 —R 122 —, Z 22 is oxygen or NH, R 122 is a straight C 1 -C 6 or branched or cyclic C 3 -C 6 alkylene group, C 2 -C 6 alkenylene group or phenylene group, which may contain a carbonyl (—CO—), ester (—COO—), ether (—O—), or hydroxyl moiety; L is a single bond or —Z 33 —C(═O)—O—, Z 33 is a straight C 1 -C 20 or branched or cyclic C 3 -C 20 divalent hydrocarbon group which may be substituted with or separated by a heteroatom, Z 11 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R 123 — or —C(═O)—Z 44 —R 123 —, Z 44 is oxygen or NH, R 123 is a straight C 1 -C 6 or branched or cyclic C 3 -C 6 alkylene group, C 2 -C 6 alkenylene group or phenylene group, which may contain a carbonyl, ester, ether, or hydroxyl moiety; M − is a non-nucleophilic counter ion; R 114 , R 115 , R 116 , R 117 , R 118 , R 119 , R 120 , and R 121 are each independently a straight C 1 -C 20 or branched or cyclic C 3 -C 20 hydrocarbon group which may be substituted with or separated by a heteroatom.

4. A resist composition comprising a base resin containing the polymer of claim 3 , and an organic solvent.

5. A resist composition comprising a base resin containing the polymer of claim 1 , an acid generator, and an organic solvent.

6. The polymer of claim 1 wherein the ring ZZ is a non-aromatic mono- or polycyclic ring selected from the group consisting of the following formulae:

wherein R 2 and R 3 are as defined above.

7. A polymer comprising recurring units of at least one type selected from the general formulae (2c) and (2d):

wherein R 1 is hydrogen, methyl or trifluoromethyl, R 2 to R 4 are each independently a straight, branched or cyclic, C 1 -C 15 monovalent hydrocarbon group in which any constituent —CH 2 — may be replaced by —O— or —C(═O)—, X 1 is a straight, branched or cyclic, C 1 -C 15 divalent hydrocarbon group in which a constituent —CH 2 — may be replaced by —O— or —C(═O)—, X 2 is —CH 2 — or —O—, the ring ZZ designates a non-aromatic mono- or polycyclic ring of 4 to 20 carbon atoms having a hemiacetal structure, k 1 is 0 or 1, and k 2 is an integer of 0 to 3.

8. The polymer of claim 7 , further comprising recurring units of at least one type selected from the general formulae (4A) to (4E):

wherein R 1 is as defined above, XA is an acid labile group, XB and XC are each independently a single bond or a straight or branched, C 1 -C 4 divalent hydrocarbon group, XD is a straight, branched or cyclic, C 1 -C 16 di- to pentavalent aliphatic hydrocarbon group in which a constituent —CH 2 — may be replaced by —O— or —C(═O)—, XE is an acid labile group, YA is a substituent group of lactone, sultone or carbonate structure, ZA is hydrogen, a C 1 -C 15 fluoroalkyl group or a C 1 -C 15 fluoroalcohol-containing group, k 1A is an integer of 1 to 3, and k 1B is an integer of 1 to 4.

9. The polymer of claim 7 , further comprising recurring units of at least one type selected from sulfonium salt units (f1) to (f3) represented by the following general formula:

wherein R 112 is hydrogen or methyl; R 113 is a single bond, phenylene, —O—R 122 —, or —C(═O)—Z 22 —R 122 —, Z 22 is oxygen or NH, R 122 is a straight C 1 -C 6 or branched or cyclic C 3 -C 6 alkylene group, C 2 -C 6 alkenylene group or phenylene group, which may contain a carbonyl (—CO—), ester (—COO—), ether (—O—), or hydroxyl moiety; L is a single bond or —Z 33 —C(═O)—O—, Z 33 is a straight C 1 -C 20 or branched or cyclic C 3 -C 20 divalent hydrocarbon group which may be substituted with or separated by a heteroatom, Z 11 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R 123 — or —C(═O)—Z 44 —R 123 —, Z 44 is oxygen or NH, R 123 is a straight C 1 -C 6 or branched or cyclic C 3 -C 6 alkylene group, C 2 -C 6 alkenylene group or phenylene group, which may contain a carbonyl, ester, ether, or hydroxyl moiety; M − is a non-nucleophilic counter ion; R 114 , R 115 , R 116 , R 117 , R 118 , R 119 , R 120 , and R 121 are each independently a straight C 1 -C 20 or branched or cyclic C 3 -C 20 hydrocarbon group which may be substituted with or separated by a heteroatom.

10. A resist composition comprising a base resin containing the polymer of claim 9 , and an organic solvent.

11. A resist composition comprising a base resin containing the polymer of claim 7 , an acid generator, and an organic solvent.