A high resolution 248 nm bilayer resist

Bilayer thin film imaging is one approach to extend 248 nM optical lithography to 150 nm regime and beyond. In this paper, we report our progress in the development of a positive-tone bilayer resist system consisting of a thin silicon containing imaging layer (270 nm thick with 11 wt% silicon) over a recently developed crosslinked polymeric underlayer (700-1000 nm thick). The chemically amplified imaging layer resist is based on a novel dual-functional silicon containing monomer, tris(trimethylsilyl)silylethyl methacrylate, which in addition to providing etch resistance, also functions as the acid sensitive functionality. The stabilization of beta-silyl carbocation by silicon allows this moiety to serve as an acid sensitive protecting group. Thus high silicon content and high resist contrast are achieved simultaneously. Lithographic evaluation of the bilayer resist with a 0.63 NA and a 0.68 NA 248 MI exposure tool has demonstrated resolution down to 125 nm equal line/space features with a dose latitude of 16% and depth of focus (DOF) of 0.6 um (0.68NA, annular illumination, attenuated phase shift mask). The dose latitude and DOF for 150 nm equal line/space features are 22% and 1.2 um (0.6NA, annular illumination, attenuated phase shift mask), respectively. Finally, residue-free, ultra-high aspect ratio (>10:1) resist features have been obtained by O-2 or O-2/SO2 reactive ion etching (RIE) using a high-density plasma etch system. The resist design, deprotection chemistry, lithographic and etch characteristics of the top layer, as well as the design of the new underlayer, will be discussed.