Ultimate Depth Resolution and Profile Reconstruction in Sputter Profiling with AES and SIMS

摘要

New developments in quantitative sputter depth profiling during the past tenyears are reviewed, with special emphasis on the experimental achievement ofultrahigh depth resolution (below 2 nm for sputtered depths larger than 10 nm).In this region, the depth resolution function generally is asymmetric(i.e.non-Gaussian) and it is governed by the three fundamental parameters:atomic mixing length, roughness and information depth. The so calledmxing-roughness-information depth (MRI)-model and its application to thequantitative reconstruction of the in-depth distribution of composition, with atypical accuracy of one monolayer and better, is demonstrated for SIMS and AESdepth profiles. Based on the combination of the above three parameters, theultimate depth resolution is predicted to be about 0.7-1.0 nm. Up to now,values of 1.4-1.6 nm have been reported, and the use of low energy molecularions, e.g. by using sulfur hexafluoride as sputtering gas, has recently pushedthe mixing length down to 0.4-0.6 nm. However, particularly in depth profilingof multilayers, it can be shown that minimizing the rouhgness parameter,including the straggling of the mixing length, is most important for theachievement of the ultimate depth resolution.