Polymerization of N-(tert-butyldimethylsilyloxy)maleimide and applications of the polymers as resist materials

Abstract

A new silicon-containing maleimide monomer, N-(tert-butyldimethylsilyloxy) maleimide (SiOMI) has been synthesized. SiOMI was radically copolymerized with styrene derivatives (XSt) to obtain alternating copolymers, P(SiOMI/XSt), in high conversions. The copolymers have high glass transition temperatures above 190 degrees C, and the tert-butyldimethylsilyloxy groups are thermally stable up to 300 degrees C. The SiOMI units in the copolymers were converted into N-hydroxymaleimide (HOMI) units by acidolytic deprotection of the tert-butyldimethylsilyloxy protecting groups. The facile deprotection of the side-chain tert-butyldimethylsilyloxy groups from the protected copolymers provided a significant change in solubility of the polymers due to the large polarity change. Submicron positive-tone images were obtained from the copolymers containing an onium salt as a photoacid generator by irradiation with electron beam and development with alkaline solutions. The polymer films also showed very high oxygen plasma etch resistance compared with novolac resins. The silicon-containing maleimide polymers were found to have required properties, such as good alkaline solubility after deprotection, superior adhesion, low optical density, high thermal stability with high T-g, and high plasma etch resistance for applications as deep ultraviolet and electron beam resist materials. (C) 1997 John Wiley & Sons, Inc.