Quantitative Auger electron spectroscopy in thin film depth profiling

Abstract

Auger Electron Spectroscopy (AES) analyzes the very first atomic layers with a characteristic intensity which exponentially decreases with depth from the surface. Therefore, any quantification strongly depends on the in depth distribution of composition within these first few monolayers. During depth profiling by ion sputtering, the surface composition is changed due to many phenomena such as ion beam induced atomic mixing and surface roughening, radiation enhanced diffusion, preferential sputtering and segregation. Even if the last ones can be neglected, the most fundamental effects of atomic mixing and ion beam induced roughening lead to a significant deviation between the measured profile and the AES depth profile that is predicted by the usual quantification method assuming an ideal layer by layer sputtering behavior. The difference depends mainly on the ratio of the Auger electron information depth and the mixing zone length and on the elemental distribution within these regions. Taking into account these dependencies in an appropriate model of the three parameters mixing length, roughness and information depth (M,R,I), the measured AES depth profiles can be calculated with high accuracy in the atomic monolayer regime. As demonstrated for GaAs AIAs multilayers, this model enables an accurate description of the depth resolution function as well as the conversion of the sputtering time in a depth scale which are the key issues for reconstruction of the original depth distribution profile.