The requirement for a much finer line width circuits on semiconductors needs new developers such as supercritical fluid to prevent the collapse of the photoresist micro-patterns. The copolymers contain t-butyl methacrylate having an acid-cleavable t-butyl group and supercritical fluid $CO_2$ soluble perfluorinated decyl methacrylate segments. The supercritical fluid $CO_2$-philic properties of the photoresist changed to supercritical fluid $CO_2$-phobic properties after the deprotection reaction by exposure, which made the exposed resist insoluble in the supercritical fluid $CO_2$ developer. The synthesized copolymers containing more than 30% of perfluorinated decyl methacrylate were found to be soluble in supercritical fluid $CO_2$. The variation of film thickness before and after exposure was largest when the mole ratio of perfluorinated decyl methacrylate in the copolymer was 30%.