Depth Distribution Functions of Secondary Electron Production and Emission

Abstract

  As fundamental importance to SEM observation of specimen surface, secondary electron generation and emission processes have been studied by a Monte Carlo method. The simulation is based on a discrete description of cascade secondary electron production. The Monte Carlo model combines the use of Mott’s cross section for electron elastic scattering and of Penn’s dielectric function for electron inelastic scattering. Two models of dielectric function, i.e. the single pole approximation and the full Penn algorithm, are shown to give energy distribution and yield of secondary electrons in agreement with experimental results for non-free electron materials and free electron metals, respectively. We use a constructive solid geometry modeling to describe sample 3D geometry and a Gaussian function to describe random surface roughness. The technique is efficient and powerful in a simulation of SEM images of secondary electrons and backscattered electrons for a quite complex geometry of nanostructures. Finally we present the depth distribution functions for secondary electron generation and emission. Their dependences on primary energy and atomic numbers are analyzed. Furthermore, we shall also discuss a general issue of depth distribution function for rough surfaces.