The mechanisms of electromigration, i.e. mass transport induced by high electric current, were studied in thin AlSi₁Cu_0.5 interconnects using in situ experiments in a Scanning Electron Microscope (SEM). The influence of grain boundaries as important paths of diffusion could be shown because the initial grain structure was recorded in detail by an orientation mapping with high lateral resolution over the whole interconnect. That was done by the Electron Back Scatter Diffraction technique in the SEM. The role of grain boundaries with high misorientation angles and of large blocking grains was investigated in detail by comparison of the localised damages with the corresponding part of orientation map. The formation of fatal voids was found to take place at the end of a large blocking grain followed by a high angle grain boundary directed parallel to the current flow. Hillocks were seen to be formed at such grain boundary triple junctions where a high flux divergence occurs due to different misorientation angles of the joined grain boundaries, and due to their direction with respect to the current flow. Additionally an increased content of the alloying element Cu was found in some of the hillocks.

Keywords: electromigration, SEM, in situ, EBSD, grain orientation, grain boundary diffusion

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