Copolymers and radiation-sensitive resin composition

PROBLEM TO BE SOLVED: To provide a radiation-sensitive resin composition which is excellent in resolving power and LEF resistance as a chemically amplified photoresist responding to far-ultraviolet radiation represented by KrF excimer laser, ArF excimer laser and F 2 excimer laser, and a copolymer which can be used for the radiation-sensitive resin composition. SOLUTION: The copolymer contains a repeating unit (I) represented by formula (1), a repeating unit (II), a repeating unit (III) represented by formula (4) and a repeating unit (IV) represented by formula (5), wherein the repeating unit (II) is obtained through cleavage of carbon-carbon double bonds in a monomer which has at least one bivalent group represented by formula (2) or (3), which is broken down by an action of an acid, and at least two polymerizable carbon-carbon double bonds which are connected to each other via the bivalent group. COPYRIGHT: (C)2006,JPO&NCIPI