Measurements of the range of secondary electrons in low-Z materials
Previously, calculations of the resolution of SEM secondary electron images due to the escape depth of these electrons utilized Monte-Carlo calculations to simulate the “edge brightness effects” seen in high resolution magnification images obtained with small probe sizes (e.g.,). Similar Monte-Carlo calculations have been made to try to deduce the energy dissipation profiles in PMMA due to secondary electrons. We are trying to develop a simple analytical model which might allow us to get a better feel for the salient features with which the secondary electrons limit the pattern size in microfabrication and spatial resolution in the SEM.For our initial measurements, we have fabricated the structure shown in figure 1. The thickness of both the PMMA and Si substrate are less than one mean free path for inelastic scattering (of 100 keV electrons) thick. A 10 Å diameter beam of convergence angle of 15 mrad is incident normal to the sample surface.