Synthesis and lithographic performance of poly(1,4-dioxaspiro[4.7] dodecane-2-methyl methacrylate)

Abstract

This study treats ketal-protected polymer which is available to be used as photoresist material whose main characteristic is polarity change. The ketal group of the polymer hydrolyzes under acid catalysis to give two hydroxy groups and a ketone. The ketal-type polymer is insoluble in an aqueous developer, while the hydrolyzed products are soluble. Poly(1,4-dioxaspiro[4.7]dodecane-2-methyl methacrylate) (DDMMA) was synthesized and evaluated for photoresist. The glass transition temperature and decomposition temperature of the polymer were 160.9℃ and 220℃. The absorbance was $0.0148㎛^{-1}$ at 248 nm and $0.0758㎛^{-1}$ at 193 nm. In this study, for enhancing the solubility in conventional TMAH solution, we copolymerized DDMMA and t-butylcholyl methacrylate (TBCMA), cholate based material with carboxylic acid when exposed and baked. The glass transition temperature of this polymer were 166.7℃. The absorbance was $0.017㎛^{-1}$ at 248 nm and $0.095㎛^{-1}$ at 193 nm. The resist composed of DDMMA and TBCMA and photoacid generator gave 0.6㎛ line/space patterns when relative humidity was over 70%.