Automatic beam focusing in the 2nd generation PBW line at sub-10 nm line resolution

Proton beam writing (PBW) has the ability to fabricate high aspect ratio 3D micro/nano-structures with precise edges, smooth and straight side-walls. The newly developed 2nd generation PBW line has a high lens demagnification and is equipped with a superior quality resolution standard, which results in a spatial beam resolution down to 19 nm × 30 nm (van Kan et al., 2012). Fine lithographic hydrogen silsesquioxane (HSQ) patterns featuring 19 nm line width and 60 nm spacing have been fabricated using the 2nd generation PBW line (Yao et al., 2014). In those experiments, beam focusing was done by manually adjusting the currents of the magnetic quadrupole lens power supplies to achieve a small beam spot size. Here we present an automatic focusing program which can focus a 2 MeV proton beam down to 9.3 nm × 32 nm in less than 10 min.