Synthesis and characterization of novel copolymers of carboxyphenylmaleimide and Methacrylates with trimethylsiloxy groups for Deep-UV photoresists

N-(4-Carboxyphenyl) maleimide (CPMI), with high thermal stability structure, was synthesized from maleic anhydride and p-aminobenzoic acid. Free-radical copolymerization of CPMI and three comonomers (M-1, M-2, and M-3) bearing a trimethylsiloxy group was performed at 60degreesC in the presence of azobisisobutyronitrile as an initiator in 1,4-dioxane. Two different processes were adopted to prepare resists using these copolymers. The first one was to mix the dissolution inhibitor, o-nitrobenzyl cholate, into the new copolymers. The second approach was to react the new copolymers with o-nitrobenzyl bromide using 1,8-diazabicyclo[5.4.0]undeca-7-ene in dimethylformamide. The cyclic maleimide group was responsible for the high thermal stability. After irradiation by a deep-ultraviolet light and development with aqueous Na2CO3 (0.01 wt %), the developed patterns showed positive images and exhibited good adhesion to the silicon wafer without the use of any adhesion promoter. The resolution of the resists was at least 0.8 mum and the most effective factor for improving the etching selectivity was to increase the silicon content. We found that suitable amounts of silicon (about 14%) can drastically lower the etching rates of organic polymers; that is, an oxygen-plasma etching rate of 1 : 7.92 compared with hard-baked HPR-204. (C) Wiley Periodicals, Inc.