Characterization of Anodic Oxide Layers by Sputter Profiling with AES and XPS

Abstract

The chemical characterization of thin films can be accomplished by the combination of a surface analysis technique such as Auger electron spectroscopy (AES) or X-ray induced photoelectron spectroscopy (XPS) with ion sputtering1, 2. The high in-depth resolution3 of the electron spectroscopies of the order of 1 nm together with the gradual, slow erosion of the surface by the impinging primary ion beam is advantageous for the determination of composition profiles. Although AES spectra contain chemical information, XPS is ideally suited to obtain the chemical bond characteristics of an element in a compound by observation of the chemical shift of the respective elemental peaks4. On the other hand, AES generally gives better depth resolution than XPS because of the smaller analysis spot with respect to the sputtered area1, 2, 5. A combination of both techniques should reveal the elemental composition profile with optimum depth resolution (AES) and a chemical bonding profile (XPS). However, besides the many possible pitfalls due to incorrect experimental arrangement as discussed elsewhere1, 6, there is a fundamental limitation in obtaining the true profile: the change of elemental composition and chemical bonds induced by the interaction of the primary ion beam with the sample. The principal result of this effect is an atomic mixing of the first few surface layers7 with subsequent formation of new chemical bonds and a depletion of the elements which are preferentially sputtered.