PII: S0040-6090Ž03.00283-9 Solid state diffusion of Sn in polycrystalline Al films

The formation of a wetting layer of Sn and the Stranski–Krastanov growth of Sn on a polycrystalline Al film surface has been proved recently. In the present experiments the influence of Sn on the structure evolution of Al films has been analyzed in detail. The films were prepared in HV by magnetron sputtering at 180 8C substrate temperature on Si wafers covered by the native oxide. 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) and were investigated by analytical and high resolution X-TEM, AFM and scanning AES. If the Sn-interlayer is oxidized, no effect on the growth of the Al-capping layer is observable. If, on the other hand, the Sn-interlayer is prevented from oxidation grain growth is promoted in the Al-capping layer as confirmed by X-TEM and AFM. The capping layer contains intragranular line-like features roughly parallel to the substrate plane. Microanalysis shows the presence of Sn in the capping layer and indicates that Sn is associated with these linear features. The promotion of grain growth in the capping layer can be attributed to the permanent transport of Sn to the growth front via grain boundaries which was confirmed by dynamic scanning AES-measurements. The linear intragranular feature formation is explained by the oxidation of Sn on the free surface due to the residual oxygen present in the background gas