Combined depth profile analysis with SNMS, SIMS and XPS: Preferential sputtering and oxygen transport in binary metal oxide multilayer systems

Depth profile measurements of binary metal oxide multilayer systems have been performed by combined SIMS, SNMS and XPS. The combination of data about the particle fluxes and thus the bulk stoichiometry by SNMS, the ionic fluxes by SIMS, and the surface composition and the oxidation state of the metals by XPS provides a detailed insight into the mechanism of preferential sputtering in these systems. We present results on the systems Al2O3/TiO2 and SiO2/HfO2. The signal behaviour at the interfaces cannot be explained by preferential sputtering alone, but must include an oxygen transport mechanism due to chemical driving forces. By comparison of these systems with four other multilayer systems, we have developed a model of combined preferential sputtering and oxygen transport which accounts for the experimental results. The investigated systems can be classified according to their metal/oxygen sputter yield ratio, the degree of preferential sputtering, and the heat of formation of the oxide.