The study of diffusion of copper in thin films of silver and AgAl alloys as a function of increasing aluminium concentration

Abstract

The diffusion of copper through electron-beam-evaporated silver and AgAl alloy thin films of four different compositions (5.8, 9.2, 15.8 and 18.2 at % Al) has been studied by monitoring the electrical resistance with time in the temperature range 343–543 K. The aim of this work is to determine the extent to which the presence of aluminium affects copper diffusion through silver thin films. It is found that the activation energy Q and the pre-exponential factor D 0 determined from the Arrhenius plot decrease in the aluminium content in the alloy film but as a whole the diffusion coefficient increases with increasing aluminium content in the temperature range of interest. Transmission electron microscopy and thin film X-ray diffraction studies with 9.2 and 18.2 at.% Al alloy films indicate that the microstructures and corresponding selected-area diffraction pattern vary as a function of aluminium content. With the addition of aluminium, copper reacts to form Al 2 Cu (θ phase) precipitates even at room temperature. Precipitation probably occurs along the grain boundaries of copper and along the alloy-Cu interface, thereby reducing grain growth, but, on annealing such films, this retarding effect of the precipitates on the grain growth is removed. The cause of enhancement of diffusion coefficient with increased aluminium content is attributed to the fact that the concentration gradient and accompanying stress gradient at the interface and grain boundaries produce dislocations.