APPROACHING THE LIMITS OF HIGH-RESOLUTION DEPTH PROFILING

Depth profiling by ion sputtering in combination with surface analysis methods such as AES, XPS, ISS and SIMS is commonly applied to characterize thin films and interfaces with high depth resolution. Frequently, degradation of the depth resolution is observed due to changes of surface topography and composition of the sample during sputtering. Recent progress in sputter profiling of bilayers, multilayers and delta marker profiles of different materials and with different methods has revealed a more detailed knowledge about the limiting factors which impede the attainment of high resolution. In many cases, ion bombardment induced surface topography has been shown to be considerably reduced when using sample rotation during depth profiling. The depth resolution is mainly governed by the altered layer generated during sputtering and depends on ion beam characteristics (ion mass, ion energy and angle of incidence) as well as on thermochemical and atomic transport properties of the sample components. Under favorable conditions, the physical limits of depth resolution of the order of a few atomic monolayers can be approached. Comparison of theoretical modelling of depth profiles with experimental data in many cases allows an estimation of the resolution function and enables deconvolution of the measured profile. The predictability of the depth resolution function for given materials and experimental conditions mainly depends on a detailed understanding of the physico-chemical processes during ion sputtering.