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

Abstract

In recent experiments, the formation of lamellar features within an Al film was observed when deposited on a thin Sn layer. The present study investigates the influence of the deposition rate of the Al film on the lamella thickness to gain insight into the mechanism of lamella formation.Al–Sn–Al sandwich layers were prepared in HV by magnetron sputtering at 180 °C substrate temperature on natively oxidized Si wafers. Al and Sn were sequentially sputtered from a 100-mm diameter DC magnetron target. The samples consisted of an Al base layer (400 nm), a Sn interlayer (10 nm) and an Al capping layer (400 nm). The base layer and the Sn interlayer were deposited at a rate of 0.4 and 0.1 nm s−1, respectively. The deposition rate for the capping layer was varied between 0.1 and 0.8 nm s−1.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.