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.
The influence of the tilt angle of a sample in front of a cylindrical mirror analyzer (CMA) on AES depth profiles is calculated with the conventional mixing-roughness-information (MRI) depth model and an extended MRI model. While the conventional model works with an average electron escape depth value, the extended model takes into account the intensity from different segments along the azimuth angle corresponding to different escape depth values before summing up for the total, measured intensity. The deviation between both approaches is generally less than 4%, even for the worst case at 47.7°tilt angle. The shape of the profile is slightly different for both approaches. Because, for a CMA with coaxial gun, the sample tilt angle varies as the electron beam incidence angle, the influence of the latter has to be additionally taken into account for quantification of AES. In reasonable agreement with experimental results it is shown that above 45°the Auger peak intensity of Cu (914 eV) increases up to about a factor of two for an incidence angle of 85°.
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