Substrate effects correction in Auger electron spectrometry and electron probe microanalysis of thin films

This paper reviews a method of correcting EPMA (electron probe microanalysis) and AES (Auger electron spectroscopy) signals from thin films for variations in substrate composition. In developing the fundamental expressions for the intensity of an Auger peak, it is usually assumed that the excitation (core level ionization) rate is constant with depth, at least within the detection volume for AES. The same assumption applies in EPMA when the detected element only exists within a very thin coating, i.e. the ionization function ϕ(ρz) can be replaced by its surface value ϕ(0). Analytical expressions for this surface excitation from backscattered electrons and X-ray (or Auger) signal were experimentally tested. The main advantage of this approach is that it does not require local knowledge of the substrate composition and it can be applied for all incidence angles during analysis by EPMA or AES. This method was successfully applied to linescans in AES, and thickness maps in EPMA. Moreover, an iterative algorithm for concentration determination in EPMA was also carried out. It is based on classical hyperbolic iteration used in EPMA and AES, but differs in using the proposed analytical expressions instead of ZAF (atomic number (Z), X-ray absorption (A), and secondary fluorescence correction (F)) or global ϕ(ρz) methods.