Synthesis and characterization of novel copolymers with the trimethylsilyl group for deep-UV photoresists

N-(4-Acetoxyphenyl) maleimide (APMI) and three kinds of comonomers bearing a trimethylsilyl group were copolymerized at 60degreesC in the presence of azobisisobutyronitrile (AIBN) as an initiator in 1,4-dioxane to obtain the three IP, IIP, and IIIP copolymers. These copolymers were removed from the acetoxy group in a transesterification process into new IVP, VP, and VIP copolymers with a pendant hydroxyl group. Two modified processes were adopted to prepare photoresists using these copolymers. The first process involved mixing the dissolution inhibitor, o-nitrobenzyl cholate, with the new copolymers. Second, o-nitrobenzyl cholate was introduced into the copolymers using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in dimethylformamide (DMF). The cyclic maleimide structure is responsible for the high thermal stability of these copolymers. After irradiation using deep-UV light and development with aqueous Na2CO3 (0.01 wt %), the developed patterns showed positive images and exhibited good adhesion to the silicon wafer without using any adhesion promoter. The resolution of these resists was at least 0.8 mum and an oxygen-plasma etching rate was 1/5.3 to that of hard-baked HPR-204. (C) 2002 John Wiley Sons, Inc.