Heterogene Interdiffusion von nanokristallinen Cu/Co/Au-Schichten

Abstract

The interdiffusion of Cu/Au-thin films is investigated using several analytical and microscopical methods of high resolution. The main part of the experiments was carried out by means of the tomographic atomprobe (TAP). With this method a chemical analysis on a nm-scale is possible in three dimensions. This work presents the first results of thin film interdiffusion in the system Cu/Au that are obtained by the TAP.It is shown that the specific specimen preparation, which is required for atomprobe investigations, results in a nanocrystalline microstructure of the thin films. This corresponds to a high density of grain boundaries and triple junctions, both of which serve as fast diffusion paths for atomic transport. In this way initial interdiffusion leads to a complex three-dimensional reaction pattern. Its complexity is further increased by the migration of grain boundaries during grain boundary diffusion (DIGM).This work includes the first complete nanoanalys is of a triple junction that was enriched by an interdiffusion process. In this way it is possible to evaluate the diffusion coefficients of the triple junction and its neighbored grain boundaries. It was found that the diffusion coefficient of the triple junction exceeds that of the grain boundaries by four orders of magnitude.By the introduction of a diffusion barrier, which consists of a thin Co-layer, the interdiffusion of the Cu- and the Au-layer is slowed down and can therefore be investigated at higher temperatures. Hereby, diffusion is no longer restricted to grain boundaries and triple junctions since volume diffusion inside the grains is activated. In this way the complex reaction pattern is replaced by a homogenous mixing inside the single layers.