Backscattering effect in quantitative AES sputter depth profiling of multilayers

AES sputter depth profiles of multilayers with constituents of very different backscattering factors show characteristic distortions in the shape of the intensity–depth profiles. These distortions are quantified by introducing an extension of the local effective backscattering factor concept developed in an earlier paper in the mixing-roughness-information depth (MRI) model for profile quantification. The extension is based on a linear superposition of two newly defined parameters, the effective backscattering factors for each interface that are diminished with distance from the respective interface by another characteristic parameter, the mean effective backscattering decay length. As shown for a Ni/C multilayer structure of six alternating layers of Ni (38 nm) and C (25 nm) on a Si substrate, AES intensity depth profiles calculated with the presented modification of the MRI model, yield an excellent agreement with the measured profile after some adjustment of the initial mean effective backscattering decay lengths and, sometimes, after a slight change of the backscattering factors given by the Ichimura–Shimizu relations. The backscattering effect is studied as a function of the single layer thickness. A critical layer thickness can be determined, below which the backscattering influence becomes negligible for typical AES depth profiling results. Copyright © 2007 John Wiley & Sons, Ltd.