Mark topography for alignment and registration in projection electron lithography

We have studied two mark geometries for possible use in a projection e-beam lithography system using SCALPEL (SCattering with Angular Limitation in Projection Electron Lithography). These are V-grooves and vertically etched geometries - pedestals or trenches. We report results of measurements of backscattered electron (BSE) contrast from topographic marks of varying size and as a function of energy up to 100 kV. The marks were fabricated on silicon wafers. The measurements were taken both in a scanning electron microscope and in an experimental SCALPEL machine operating in focused probe mode. The V-grooves ranged from 1.0 to 30 μm wide. The vertical etched features ranged from 2 to 30 μm wide and 0.6 and 50 μm depth. The results depended not only on the feature width and depth, but also on whether the features were isolated or in line and space patterns. Using a BSE ratio of 1.05 as a criterion for acceptable contrast from an alignment mark, V-grooves and vertical etched features had acceptable contrast with exception of the smallest and shallowest features for both geometries.