Monte Carlo simulations of electron transport in solids: applications to electron backscattering from surfaces

We report results of Monte Carlo simulations to investigate the effects of backscattered electrons in scanning Auger microscopy (SAM) on the radial distributions of emitted Auger electrons. We considered the emission of copper M3VV and L3VV Auger electrons from a thin Cu overlayer on a substrate of silicon or g-old for primary electrons with energies of 5 and 10 keV that were normally incident on the sample. The Cu layer was assumed to be sufficiently thin that there were no changes in the angular and energy distributions of primary and backscattered electrons passing through the overlayer. We report values of the information radius, r(a)(p), from which a selected percentage P of the emitted Auger electron intensity originates. Values of found here range from 119 angstrom (Cu L3M45M45 Auger transition, Eo = 5 keV, Au substrate, P = 80) to 6757 angstrom (Cu M3VV Auger transition, E-0 = 10 keV Si substrate, P = 95). For the same substrate, primary energy, and chosen value of P, values of r(a)(P) are larger for Auger electrons from the Cu M3VV Auger transition than for the Cu L3M45M45 Auger transition. In addition, values of r(a)(p) increase with primary energy and are larger for the Si substrate than the Au substrate. The values of r(a)(p) are generally much larger than the radius of the primary beam (assumed to be 50 angstrom here) on account of inner-shell ionizations by backscattered electrons. We also report values of the mean escape radius, < r >, that range from 82.5 angstrom (Cu L3M45M45 Auger transition, E-0 = 5 keV, Au substrate) to 1169 angstrom (Cu M3VV Auger transition, E-0 = 10 keV. Si substrate). Knowledge of r(a)(p) and < r > is important in the analysis of fine features in SAM because appreciable Auger signal can be collected from the nearby region as well as from the feature of interest. Finally, we report Monte Carlo simulations of Auger line scans across the edge of a thin Cu overlayer on a Si or Au substrate. The shapes of the line scans depended only weakly on the Cu Auger transition, although the differences were more pronounced for the Si than the An substrate. On account of backscattered electrons, the lateral distance corresponding to signal variations of 25% and 75% of the maximum intensity in a line scan varied from 53.6 angstrom (Cu L3M45M45 transition, E-0 = 5 keV, Si substrate) to 75.1 angstrom (Cu M3VV transition, E-0 = 10 keV, Au substrate). (c) 2004 Elsevier B.V. All rights reserved.