Hydrogen silsesquioxane bilayer resist process for low-voltage electron beam lithography

Namatsu, van Delft, and others have reported printing exceptionally small features using high voltage (>50kV) electron beam exposure of hydrogen silsesquioxane (HSQ). They also reported that HSQ has very high exposure dose requirements (~2000(mu) C/cm2 at 100kV). We have explored the utility of HSQ as a resist for low-voltage electron beam lithography. Because low energy electrons have a very limited penetration depth, a thin film imaging technique must be employed in conjunction with anisotropic oxygen reactive ion etching to generate the high aspect-ratio features required to provide adequate etch resistance for subsequent image transfer steps. HSQ's exceptionally low oxygen plasma etch rate makes it an excellent top layer for a bilayer process of this sort. High resolution, high aspect ratio images were printed with this system using 1kV electrons with an imaging dose of less than 60 (mu) C/cm2. The resulting features have very smooth sidewalls. Monte Carlo simulations have been performed for the exposure process and compared to experimental results.