Microstructural evolution in passivated Al films on Si substrates during thermal cycling Original Research Article

In situ and post-mortem transmission electron microscopy (TEM) observations of thermally cycled Al thin films have been made to identify and characterize the deformation mechanisms that govern the thermo-mechanical response of these films. The early stages of thermal cycling were associated with grain growth, untangling and motion of low angle boundaries and the absorption of dislocations into the metal/oxide interfaces. Comparison with wafer curvature experiments indicate that mechanical saturation is related to the generation of large, relatively clean, columnar grains and that the presence of the capping layer slows the rate at which the as-deposited structure is transformed to this state. The formation of large, defect-free grains facilitated the observation of dislocation sources, the motion of threading dislocations across the Al films, and the interaction of these dislocations with local obstacles and grain boundaries. However, the density and velocity of dislocations were too low to account for the thermal strains being imposed during thermal cycling, and no misfit dislocations were observed at the metal/oxide interfaces. These latter findings point to the possible influence of diffusion-related processes.