Phenolic hydroxyl group-containing copolymer and radiation-sensitive resin composition

A phenolic hydroxyl group-containing copolymer consisting essentially of a recurring unit which is hydrolyzed with an acid after anionic-copolymerizing a monomer of the following formula_(1) and a recurring unit which is hydrolyzed with an acid after anionic-copolymerizing a monomer of the following formula (2), wherein an acid-labile group of the monomer of the formula_(1) is hydrolyzed completely, and an acid-labile group of the monomer of the formula_(2) is hydrolyzed partially,

• wherein R1 represents a hydrogen atom or a methyl group, and R2 and R3 represent saturated hydrocarbon groups having 1-4 carbon atoms or bond together to form a cyclic ether having 3-7 carbon atoms,
• wherein R1′ represents a hydrogen atom or a methyl group, and R4, R5, and R6 represent saturated hydrocarbon groups having 1-4 carbon atoms.

A phenolic hydroxyl group-containing copolymer comprising a recurring unit which is hydrolyzed with an acid after copolymerizing a monomer of the following formula_(1) and a recurring unit which is hydrolyzed with the acid after copolymerizing a monomer of the following formula (2),

• wherein a polystyrene-reduced weight average molecular weight of the copolymer is not less than 500 and not more than 2,000,
• wherein R1 represents a hydrogen atom or a methyl group, and R2 and R3 represent saturated hydrocarbon groups having 1-4 carbon atoms or bond together to form a cyclic ether having 3-7 carbon atoms,
• wherein R1′ represents a hydrogen atom or a methyl group, and R4, R5, and R6 represent saturated hydrocarbon groups having 1-4 carbon atoms.