Ultimate depth resolution and profile reconstruction in sputter profiling with AES and SIMS

Abstract

New developments in quantitative sputter depth profiling during the past 10 years are reviewed, with special emphasis on the experimental achievement of ultrahigh depth resolution (<2 nm for sputtered depths of >10 nm). In this region, the depth resolution function generally is asymmetric (i.e. non-Gaussian) and it is governed by three fundamental parameters: atomic mixing length, roughness and information depth. The so-called mixing–roughness–information depth (MRI) model and its application to quantitative reconstruction of the in-depth distribution of composition, with a typical accuracy of one monolayer and better, is demonstrated for SIMS and AES depth profiles. Based on the combination of the above three parameters, the ultimate depth resolution is predicted to be ∼0.7–1.0 nm. Up to now, values of 1.4–1.6 nm have been reported and the use of low-energy molecular ions, e.g. by using sulphur hexafluoride as sputtering gas, has recently pushed the mixing length down to 0.4–0.6 nm. However, particularly for the depth profiling of multilayers, it can be shown that minimizing the roughness parameter, including straggling of the mixing length, is most important to achieve the ultimate depth resolution. Copyright © 2000 John Wiley & Sons, Ltd.