EPMA SPUTTER DEPTH PROFILING, PART-I - THEORY AND EVALUATION

Electron probe x-ray microanalysis is capable of the sensitive detecti on and the reliable quantification of small (partial)mass coverages on a submicron scale. To improve depth profiling so as to give reasonabl e depth resolution, the technique can be combined with a sputtering pr ocess. This paper presents theoretical aspects concerning the experime nt of EPMA sputter depth profiling and the evaluation of the measured data. By means of a Monte-Carlo-Simulation program sputter-intensity p rofiles for multilayered systems can be calculated. It is shown that t he calculated intensity-sputter profiles provide more information abou t elemental depth distributions than those obtained by the more common EPMA-method of electron beam energy variation. For optimising the new technique, its sensitivity to the measuring parameters and the materi al's composition and structure is studied. As a result, at low electro n beam energies the calculated profiles of intensity versus sputtered depth correspond approximately to the elemental-depth profiles. At rel atively high energies the sensitivity is reduced but, due to the chara cteristic features in the intensity profiles such as kinks at sharp in terfaces, there is sufficient information (although convoluted by the excitation volume) for structure determination. For reconstructing ele mental-depth distributions from intensity-sputter profiles an algorith m based on maximum entropy analysis is developed. The algorithm is tes ted using calculated x-ray data from a well-characterised multilayer s tructure and the data are overlaid by statistical noise. Then elementa l-depth profiles can be determined quantitatively with regard to both composition and depth coordinate.