Acid-labile ester monomer having spirocyclic structure, polymer, resist composition, and patterning process

An acid-labile ester monomer having a spirocyclic structure, represented by the general formula (2) or (3):

• wherein X is a divalent group which forms a substituted or unsubstituted cyclopentane, cyclohexane or norbornane ring with the carbon atom to which it is attached, R1 is hydrogen, fluorine, methyl or trifluoromethyl, R2 is hydrogen or a straight, branched or cyclic C1-C10 monovalent hydrocarbon group, R3 and R4 are each independently hydrogen or a straight, branched or cyclic C1-C10 monovalent hydrocarbon group, or R3 and R4, taken together, stand for a divalent group which forms a substituted or unsubstituted cyclopentane or cyclohexane ring with the carbon atom to which they are attached, R5 is hydrogen or methyl, n is 1 or 2, and p is 0 or 1.