A copolymer is provided which exhibits improved resolution, sensitivity, and exposure latitude and excels in pattern collapse margin. The copolymer contains a recurring unit which is hydrolyzed completely an acid-labile group with an acid after copolymerizing a monomer of the following formula(1) and a recurring unit which is hydrolyzed partially acid-labile group with an acid after copolymerizing a monomer of the following formula (2), wherein R.sup.1 represents a hydrogen atom or a methyl group, and R.sup.2 and R.sup.3 represent saturated hydrocarbon groups having 1-4 carbon atoms or bond together to form a cyclic ether having 3-7 carbon atoms, wherein R.sup.1' represents a hydrogen atom or a methyl group, and R.sup.4, R.sup.5, and R.sup.6 represent saturated hydrocarbon groups having 1-4 carbon atoms.