Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography

Abstract

A bilayer resist system, consisting of hydrogen silsesquioxane (HSQ) as negative tone electron (e)-beam resist top coat and hard baked novolak resist as bottom coat, has been investigated for its ability to yield high aspect ratio nanoscale structures. For comparison, single layer HSQ (hard mask) has been investigated for its resolution, contrast, and process latitude. In single layer HSQ, dense lines and spaces (1:1) have been resolved down to 20 nm and single lines have been obtained with widths less than 15 nm. Processing conditions which result in higher contrasts in HSQ also result in higher horizontal contrasts, i.e., in poorer process latitudes; this effect has previously been observed for other negative tone e-beam resists as well. In the bilayer combination, HSQ allows nanoscale structures with an aspect ratio exceeding 15 to be etched in hard baked novolak resist. Single lines with 800 nm height and 40 nm width, semidense lines and spaces (1:2) with 155 nm height and 25 nm width, and dense lines and spaces (1:1) with 130 nm height and 40 nm width have been patterned in this bilayer system. Both the single layer HSQ and the HSQ/novolak bilayer system appear to be suitable as e-beam resists for research on nanoscale gates in complementary metal–oxide–semiconductor (CMOS) and other devices.