Electron beam lithography and dimensional metrology for fin and nanowire devices on Ge, SiGe and GeOI substrates

Abstract

Until now there is no systematic study on the effect of the substrate type on the hydrogen silsesquioxane (HSQ) electron beam lithography (EBL) patterning process. We investigate arrays of line structures with varying width and spacing, starting at 10 nm, exposed at varying dose, and developed by salty NaOH and TMAH developers on group IV semiconductor substrates. We demonstrate that the HSQ EBL process on Ge is much more limited in achieving the smallest obtainable features, having optimal uniformity and fidelity, in comparison to Si. Monte-Carlo simulations of the e-beam/substrate interactions for “pure” Si and Ge substrates, and varying content Ge/Si epitaxial layers on Si, suggest that the limitations seen are directly linked to back-scattered electron (BSE) generation. As predicted by the simulations and shown experimentally, improved fidelity and resolution of the features can be achieved by minimizing the (BSE) generation coming from the Ge contribution in the substartes. Finally, from a metrology perspective, it is demonstrated that although line patterns may appear resolved in SEM images, the variation in the brightness across neighbouring lines is a key parameter in understanding the resist clearance between lines, that will affect the next etching step for pattern transfer onto the underlying substrate. These results are important for patterning high-density line structures and nano-device engineering as required for realising state-of-the art laterally stacked group IV multi-channel field effect transistors (FETs).