Monte Carlo Simulations of Electron Transport in Solids: Applications to Electron Backscattering From Surfaces

Published

April 1, 2005

Author(s)

Aleksander Jablonski, Cedric J. Powell

Abstract

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 gold for primary electrons with energies of 5 keV 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^P_a, from which a selected percentage P of the emitted Auger-electron intensity originates. Values of r^P_a found here range from 119 (Cu L₃M₄₅M₄₅ Auger transition,E₀ = 5 keV, Au substrate, P = 80) to 6757 (Cu M₃VV Auger transition, E₀ =10 keV, Si substrate, P = 95). For the same substrate, primary energy, and chosen value of P, values of r^P_a are larger for Auger electrons from the Cu M₃VV Auger transition than for the Cu L₃M₄₅M₄₅ Auger transition. In addition, values of r^P_a increase with primary energy and are larger for the Si substrate than the Au substrate. The values of r^P_a are generally much larger than the radius of the primary beam (assumed to be 50 here) on account of inner-shell ionizations by backscattered electrons. We also report values of the mean escape radius, , that range from 82.5 (Cu L₃M₄₅M₄₅ Auger transition, E₀ = 5 keV, Au substrate) to 1169 (Cu M₃VV Auger transition,E₀ =10 keV, Si substrate). Knowledge of r ^P_a and 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 Carl 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 Au 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 (Cu L₃M₄₅M₄₅ transition, E₀ keV, Si substrate) to 75.1 (Cu M₃VV transition, E₀ = 10 keV, Au substrate).

Citation

Applied Surface Science

Volume

242

Pub Type

Journals

Keywords

analysis area, Auger electron spectroscopy, backscattered electrons, copper, gold, information radius, mean escape radius, Monte Carlo simulations, silicon

Citation

Jablonski, A. and Powell, C. (2005), Monte Carlo Simulations of Electron Transport in Solids: Applications to Electron Backscattering From Surfaces, Applied Surface Science (Accessed April 26, 2024)