Monomer, polymer, resist composition, and patterning process

1. A monomer having the formula (1a) or (1b):

wherein R 1 to R 3 are each independently a C 1 -C 6 straight, branched or cyclic monovalent hydrocarbon group, R 1 and R 2 may bond together to form an alicyclic group with the carbon atom to which they are attached, R a is hydrogen, methyl or trifluoromethyl, X a is a C 1 -C 10 alkylene group, X b is a C 1 -C 10 straight, branched or cyclic (k 1 +1)-valent hydrocarbon group in which any constituent —CH 2 — moiety may be replaced by —O— or —C(═O)—, with the proviso that X b is exclusive of a group that forms the O—X b bond in the formula which is dissociable under the action of acid, X c is a single bond, methylene or ethylidene, X d is a single bond, methylene or ethylidene, Z a is an atomic group necessary to form a C 3 -C 10 alicyclic group with the carbon atom to which it is attached, A is a polymerizable functional group, and k 1 is 1 or 2.

2. The monomer of claim 1 wherein A is acryloyl or methacryloyl.

3. A polymer comprising recurring units containing as pendant a group having the formula (2a) and/or a group having the formula (2b):

wherein R 1 to R 3 are each independently a C 1 -C 6 straight, branched or cyclic monovalent hydrocarbon group, R 1 and R 2 may bond together to form an alicyclic group with the carbon atom to which they are attached, R 4 is hydrogen, methyl or trifluoromethyl, X a is a C 1 -C 10 alkylene group, X b is a C 1 -C 10 straight, branched or cyclic (k 1 +1)-valent hydrocarbon group in which any constituent —CH 2 — moiety may be replaced by —O— or —C(═O)—, with the proviso that X b is exclusive of a group that forms the O—X b bond in the formula which is dissociable under the action of acid, X c is a single bond, methylene or ethylidene, X d is a single bond, methylene or ethylidene, Z a is an atomic group necessary to form a C 3 -C 10 alicyclic group with the carbon atom to which it is attached, and k 1 is 1 or 2.

4. The polymer of claim 3 wherein the recurring units have the formulae (2aa) or (2bb):

wherein R 1 to R 3 , R a , X a to X d , Z a and k 1 are as defined above, R 4 is hydrogen or methyl.

5. The polymer of claim 3 , further comprising recurring units of at least one type selected from recurring units having the formulae (3) to (5):

wherein R 4 is hydrogen or methyl,

R 5 and R 6 are each independently a C 1 -C 6 straight, branched or cyclic monovalent hydrocarbon group, R 5 and R 6 may bond together to form an alicyclic group with the carbon atom to which they are attached,

R 7 is a C 1 -C 6 straight, branched or cyclic monovalent hydrocarbon group,

R 8 and R 9 are each independently a C 1 -C 6 straight, branched or cyclic monovalent hydrocarbon group, R 8 and R 9 may bond together to form an alicyclic group with the carbon atom to which they are attached,

X 1 and X 2 are each independently a single bond, methylene or ethylidene,

X 3 is a C 1 -C 20 straight, branched or cyclic divalent hydrocarbon group in which any constituent —CH 2 — moiety may be replaced by —O— or —C(═O)—,

Z b is a C 1 -C 9 straight, branched or cyclic aliphatic hydrocarbon group,

Z c is an atomic group necessary to form a C 2 -C 10 alicyclic group with the carbon atom to which it is attached,

Z d is a C 1 -C 20 straight, branched or cyclic aliphatic hydrocarbon group in which any constituent —CH 2 — moiety may be replaced by —O— or —C(═O)—,

with the proviso that Z b is exclusive of a group that forms the O—Z b bond in formula (3) which is dissociable under the action of acid, when X 1 is a single bond, and Z d is exclusive of a group that forms the O—Z d bond in formula (5) which is dissociable under the action of acid,

the total number of carbon atoms in X 1 , Z b , R 5 and R 6 is 5 to 12, the total number of carbon atoms in X 2 , Z c and R 7 is 5 to 12, k 2 is 0 or 1, k 3 is an integer of 2 to 4.

6. The polymer of claim 3 , further comprising recurring units of at least one type selected from recurring units having the formulae (A) to (D):

wherein R 4 is hydrogen or methyl, Z A is a C 1 -C 20 fluoroalcohol-containing group, exclusive of a structure undergoing a polarity switch under the action of acid, Z B is a C 1 -C 20 phenolic hydroxyl-containing group, Z C is a C 1 -C 20 carboxyl-containing group, Z D is a substituent group having a lactone structure, sultone structure, carbonate structure, cyclic ether structure, acid anhydride structure, alcoholic hydroxyl, alkoxycarbonyl, sulfonamide or carbamoyl moiety, X 4 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, naphthylene, —O—R 01 —, or —C(═O)—Z X —R 01 —, Z X is —O— or —NH—, and R 01 is a C 1 -C 6 straight, branched or cyclic alkylene, C 2 -C 6 straight, branched or cyclic alkenylene, phenylene or naphthylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety.

7. The polymer of claim 3 , further comprising recurring units of at least one type selected from recurring units having the formulae (f1) to (f5):

wherein R 11 is each independently hydrogen or methyl, R 12 is a single bond, phenylene, —O—R 25 —, or —C(═O)—Z 22 —R 25 —, Z 22 is —O— or —NH—, R 25 is a C 1 -C 6 straight, branched or cyclic alkylene group, C 2 -C 6 straight, branched or cyclic 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 C 1 -C 20 straight, branched or cyclic divalent hydrocarbon group which may contain a heteroatom, Z 11 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R 26 —, or —C(═O)—Z 44 —R 25 —, Z 44 is oxygen or NH, R 26 is a C 1 -C 6 straight, branched or cyclic alkylene group, C 2 -C 6 straight, branched or cyclic alkenylene group or phenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety, M − is a non-nucleophilic counter ion, R 13 to R 24 are each independently a C 1 -C 20 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom, R 13 and R 14 may bond together to form a ring with the sulfur atom to which they are attached, any two or more of R 15 , R 16 and R 17 or any two or more of R 18 , R 19 and R 20 may bond together to form a ring with the sulfur atom to which they are attached.

8. The polymer of claim 3 , further comprising recurring units of at least one type selected from recurring units having the formulae (X-1) to (X-4):

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

9. A resist composition comprising a base resin, an acid generator, and an organic solvent, the base resin comprising the polymer of claim 3 .

10. A pattern forming process comprising the steps of applying the resist composition of claim 9 onto a substrate, baking to form a resist film, exposing the resist film to high-energy radiation to define exposed and unexposed regions, baking, and developing the exposed resist film in a developer to form a pattern.

11. The pattern forming process of claim 10 wherein the developing step uses an alkaline developer in which the unexposed region of resist film is dissolved and the exposed region of resist film is not dissolved, for forming a negative tone pattern.