Patent ID: 8597867

Claim:
A lactone-containing copolymer [I] which is a resin insoluble or scarcely soluble in alkali, but becomes alkali-soluble by the action of an acid, has a recurring unit shown by the following formula (1), a recurring unit shown by the following formula (2), and a recurring unit shown by the following formula (3), and has a polystyrene-reduced weight average molecular weight determined by gel permeation chromatography (GPC) of 1,000 to 100,000, wherein R 1 represents a hydrogen atom, methyl group, trifluoromethyl group, or hydroxymethyl group and m and m′ are independently an integer of 1 to 3, wherein R 2 represents a hydrogen atom, methyl group, trifluoromethyl group, or hydroxymethyl group, and wherein R 3 represents a hydrogen atom, methyl group, trifluoromethyl group, or hydroxymethyl group, and R 4 indicates a linear or branched alkyl group having 1 to 4 carbon atoms, and n is 1.