Synthesis and Characterization of Some Acrylate Copolymers and their Evaluation as Aqueous Developable Photoresists

Abstract

In the recent past, it has been found that the use of onium salts as acid-generating species has improved the performance of photoresists, particularly for microelectronic applications. However, little research has been dedicated to the use of these photo-initiators in aqueous-developable resists. This work describes the synthesis and characterization of some water-soluble polymers and investigates the feasibility of employing one of the onium salts in the formulation of a resist polymer for use in aqueous conditions. The ability of this onium salt to photo-initiate the cationic polymerization of epoxies residues was exploited using water-soluble copolymers, containing glycidyl methacrylate (GMA). The comonomers included methacrylic acid. Various copolymers were prepared by radical copolymerization typically in methyl ethyl ketone. It was found that the copolymer containing 85 mol.% of GMA unit in feed was soluble in aqueous base and crosslinked in the presence of photogenerated acid caused by acid-initiated ring opening polymerization of the pendant epoxide groups. A good pattern with reasonable resolution was attained by exposure to a UV lamp with λ = 365 nm light followed by a post exposure bake at 80° C for 1 min.