Lamellar growth in sputter-deposited aluminum-tin-aluminum sandwich layers

Cross-sectional transmission electron microscopy (X-TEM) shows that, with increasing deposition rate of the capping layer, the lamella thickness slightly decreases. This is in contradiction to a previously formulated hypothesis of lamella growth which predicted an increase of lamella thickness with increasing deposition rate. On the other hand, contact mode atomic force microscopy (AFM) as well as X-TEM show a significant decrease of the Al grain size in the polycrystalline capping layer with increasing deposition rate. If the resulting higher grain boundary density is taken into account, the experimentally observed lamella thicknesses can reasonably be described by a model combining the diffusion of Sn along the Al grain boundaries and the oxidation of Sn on the growth surface.