Synthesis of copolymers with diazo groups and their application as DUV resists

Abstract

Photobleachable deep UV resists were designed by introducing diazoketo groups in polymer side chains. The diazoketo groups undergo the Wolff rearrangement upon irradiation in the deep UV, affording ketenes that react with water to provide base soluble photoproducts. There is no necessity for the post exposure bake step that is the cause of acid diffusion. The polymers were synthesized by radical copolymerization of methyl 5-norbornenyl-2-diazo-3-oxopropionate, norbornene, and maleic anhydride. The weight average molecular weights of the copolymers were in the range of 5,090-5,120 and polydispersities were1.95-2.29. Weight loss of the polymers occurred at 130℃ in the TGA analysis. After irradiation, the absorbances of the polymers were decreased by 68-74 % at 248 nm and 41-76 % at 193 nm. Dry etch resistance of the polymers to $CF_4$ -reactive ion etching is comparable to that of poly(4-hydroxystyrene). The resist formulated with these materials showed 0.6 mm line and space patterns at a dose of 60mJㆍ$cm^{-2}$ using a mercury-xenon lamp in a contact printing mode and a standard developer. A new monomer, ethyl 2-diazo-4-methyl-3-oxo-pent-4-enoate (EDMOP), was made through diazo transfer reaction of p-tosyl azide with ethyl 4-methyl-3-oxo-pent-4-enoate. The polymers were obtained from radical polymerization of EDMOP, adamantly methacrylate, and hydroxy styrene. The number average molecular weights of polymers were 3,000-6,000 and the polydispersity was found between 1.43 and 2.07. The $T_gs$ of polymers were observed at 150℃. The dry-etching rate of the poly(EDMOP-co-HS) was 1.32. The resist formulated with poly(EDMOP-co-HS) gave 0.8㎛ patterns. 2-(2-Diazo-3-oxo-butyryloxy)-ethyl methacrylate (DOBEMA) was prepared via diazo transfer reaction of p-tosyl azide with 2-(methacryloyloxy)ethyl acetoacetate. Copolymers of DOBEMA, 2-hydroxyethyl methacrylate, methacrylic acid, methylmethacrylate, methacrylisobutyl-POSS, and γ -butyrolacton-2-yl methacrylate with variou...