Preparation and properties of Si‐containing copolymer for near‐UV resist. I. Poly(N‐(4‐hydroxyphenyl) maleimidealt‐p‐trimethylisilylstyrene)

Abstract

AbstractA new negative near‐UV photoresist consisting of poly(N‐(4‐hydroxyphenyl) maleimidealt‐p‐trimethylisilylstyrene) (PHMS) and a naphthoquinonediazide ester was developed. PHMS was synthesized by solution free‐radical polymerization of the comonomers with azobisisobutyronitrile (AIBN) in 1,4‐dioxane at 60°C. The preparation of PHMS in terms of reaction time, thermal initiator, and solvent was evaluated; and a series of different molecular weight copolymers were prepared. PHMS was 1: 1 in composition and was predominantly alternating. These copolymers dissolved in a wide range of solvents (including 5% tetramethylammonium hydroxide). The thermal properties of these copolymers were investigated by DSC and TGA. The chain‐stiffening effect of the maleimide group played an important role in effecting high thermal resistance. Near‐UV exposure was carried out using a Canon PLA‐501F contact printer. High resolution negative images were obtained which had resistance to thermal deformation at 330°C and above. The developed patterns exhibited good adhesion to the silicon substrates without the use of an adhesion promoter. The lithographic applications of a bilayer photoresist system in which the prepared resist was used as the top imaging layer were examined. It is supposed that if PHMS was used as a binder for a diazonaphthoquions sulfonate (NDS) photochemically, positive images would be obtained; however, on the contrary, negative images were observed. It is proposed that photocrosslinking occurred in the PHMS main chain.