Extension of 248-nm optical lithography: a thin film imaging approach

Abstract

A negative-tone bilayer thin film imaged (TFI) resist has been developed for extension of 248 nm optical lithography to sub-150 nm regime. The bilayer TFI resist system consists of a thin (0.2 um) silicon containing top imaging layer and a thick (0.7 - 0.8 um) highly absorbing organic underlayer. The chemically amplified negative-tone top layer resist comprises of three major components: an aqueous base soluble silicon containing polymer, poly(hydroxybenzylsilsesquioxane); a crosslinking agent; and a photoacid generator. The highly absorptive underlayer is a hard baked novolak resist or a DUV ARC. Imaging of the top layer resist has shown resolutions down to 137.5 nm for line/space features and 130 nm for isolated features with 248 nm exposure tools and chrome on glass masks. The O<SUB>2</SUB> reactive ion etch (RIE) selectively of the top layers versus a novolak underlayer is more than 25:1 as a result of the high silicon content in the silicon containing polymer. Furthermore, residue-free and nearly vertical wall profile image transfer to the underlayer has been achieved with RIE. Application of the negative-tone bilayer resist to 150 nm Gbit DRAM critical level lithography has been demonstrated. Resist line edge roughness is also discussed.