Electron effective attenuation lengths for applications in Auger-electron spectroscopy and x-ray photoelectron spectroscopy

The electron effective attenuation length (EAL) can be defined for the measurement of overlayer film thicknesses (the most common application) and for the measurement of the depth of a thin marker layer by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). For each of these applications, a local EAL can be defined for a narrow range of thicknesses or depths and a practical EAL can be defined for specified larger ranges of thicknesses or depths. We show the results of illustrative calculations of these different EALs for XPS of Si 2p(3/2) photoelectrons with Mg Kalpha x-rays, and point out situations where numerical differences occur. We compare practical EALs (with the overlayer film definition) for Si 2s, Si 2p(3/2), An 4s and Aut 4f(7/2) photoelectrons that were obtained from Monte Carlo simulations and from an analytical expression derived from solution of the Boltzmann equation within the transport approximation. The average of the percentage deviations between the EALs from the two approaches for various overlayer thicknesses and emission angles was 5.28%. This average percentage deviation was considered to be acceptably small and justifies the use of the more approximate analytical expression in calculations of practical EALs for the measurement of overlayer thicknesses by AES and XPS. This computational approach is much faster than Monte Carlo simulations. We report calculations of practical EALs for the principal photoelectron and Auger electron lines of Si, Cu, Ag and W. For overlayer thicknesses of practical relevance, the practical EALs do not change appreciably with film thickness for electron emission angles (with respect to the surface normal) of <60degrees. Under these conditions, average practical EALs can be used to determine overlayer film thicknesses. For emission angles of >60degrees, the practical EALs generally change rapidly with film thickness and emission angle and, for these conditions, an EAL should be determined for the particular conditions. We have compared our practical EALs for photoelectron and Auger electron lines of Si, Cut, Ag and W with similar EALs derived from Monte Carlo simulations by Cumpson and Seah. At an emission angle of 45degrees, we find a root-mean-square deviation of 1.6% between the EALs from the two approaches. Published in 2002 John Wiley Sons, Ltd.