Concentration profiling using x-ray reflectivity: Application to Cu-Al interfaces

Abstract

Synchrotron radiation measurements were made using glancing-angle x-ray reflectivity to study Cu-Al thin-film interfaces. The reflectivity data contains information about film morphology, and its sensitivity to the concentration of an element can be improved by measuring above and below an absorption edge. An analysis routine for the reflectivity data was developed to extract a model of the concentration profile and roughness. The results are compared from Cu-Al interfaces prepared in an ultrahigh vacuum environment, with and without exposure to oxygen before Al deposition. The reactions caused by thermal annealing at temperatures ranging from 65 to 160 °C are also studied. Density profiles of the two samples after various anneals indicate that there are different levels of mixing at the interface, and the tendency to reach a similar level after high-temperature (140–160 °C) anneals. The low levels of reaction observed in this work are difficult to detect by other techniques, such as Rutherford backscattering spectroscopy. In view of the simplicity and the sensitivity of the glancing-angle x-ray reflectivity technique, it can be generalized to other thin-film systems.