Plasma-Developable Electron-Beam Resists

Abstract

Plasma-developable positive and negative resists with a high etching rate ratio between exposed and unexposed areas have been developed for electron-beam lithography. The negative resist systems are composed of radiation-degradation polymers such as poly-alkylmethacrylate and low molecular weight phenylsilane compounds such as triphenylsilane and diphenylsilandiol. Electron-beam exposure induces the formation of nonvolatile silicone compounds through chemical reaction between decomposition products of polyalkylmethacrylate and added silicone compound. The negative resist patterns are obtained by RIE 0₂ plasma development after removing the added silicone compound from unexposed areas by a relief treatment. Since the surface of the exposed area is covered with a plasma resistant layer produced from the nonvolatile silicone compound, the etching rate ratio between exposed and unexposed area is very high. The sensitivity of these resist systems depends on the glass transition temperature (Tg) of polyalkylmethacrylate and species of silicone compound. The range of sensitivity is 7 to 70 μC/cm² and the resolution is better than 1.0 μm. These resist systems are applicable to bi-level or tri-level resist processes, and high aspect ratio patterns are obtainable. The positive resist systems comprise crosslinking polymers such as chloromethylatedpoly-styrene and the same silicone compounds. Positive resist patterns are obtained by electron-beam exposure and subsequent RIE 0₂ plasma development. Electron-beam exposure reduces resist film thickness by a few percent as a result of the crosslinking of polymer, then, the added silicone compound is separated as minute particles from uniformly mixed resist film. The exposed areas show less resistance to RIE 0₂ plasma than unexposed areas. The sensitivity of the typical resist system is about 60 μC/cm², and resolution is 0.4 μm for 1.0 μm original resist film thickness.