Bilevel high resolution photolithographic technique for use with wafers with stepped and/or reflecting surfaces

Abstract
We have investigated the feasibility of a two-level scheme to obtain steep profile, thick resist, and high resolution patterns over stepped and/or reflecting surfaces. The two-level scheme provides an alternative to a recently developed three-level approach. The negative photosensitive inorganic resist Ag2Se/GeSe is formed on top of a thick polymer layer, which is not photo-sensitive. High resolution patterns are produced in a 0.3 μm thick, pinhole-free, inorganic resist layer using a commercial projection printer. The pattern is transferred to the polymer layer by oxygen reactive ion etching using the inorganic resist pattern as the mask against etching. Vertical-walled 0.8 μm lines and spaces are obtained in a 2.5-μm-thick polymer. The high absorbance of light by the Se–Ge layer (2.5×105cm−1 at 400 nm) eliminates standing wave effects associated with reflection from the surface.