Study of electromigration damage in Al interconnect lines inside a SEM

The mechanisms of electromigration, i.e. mass transport induced by high ele ctric current, were studied in thin AlSi1Cu0.5 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 init ial grain structure was recorded in detail by an orientation mapping with h igh lateral resolution over the whole inter-connect. That was done by the E lectron Back Scatter Diffraction technique in the SEM. The role of grain bo undaries with high misorientation angles and of large blocking grains was i nvestigated in detail by comparison of the localised damages with the corre sponding 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 g rain boundary directed parallel to the current flow. Hillocks were seen to be formed at such grain boundary triple junctions where a high flux diverge nce occurs due to different misorientation angles of the joined grain bound aries, and due to their direction with respect to the current flow. Additio nally an increased content of the alloying element Cu was found in some of the hillocks.