It was noted that, while electromigration eventually caused macroscopic damage in the form of voids and hillocks, the earliest stages of the process (where the stress in individual micron-sized grains was still building up) was largely unexplored. By using synchrotron-based X-ray micro-diffraction during an in situ electromigration experiment, an early pre-failure mode of plastic deformation was discovered which involved preferential dislocation generation and the motion and formation of a sub-grain structure within the individual grains of a passivated Al (Cu) interconnect. This behavior occurred long before macroscopic damage (hillocks, voids) was observed.

Early Stage of Plastic Deformation in Thin Films Undergoing Electromigration. B.C.Valek, N.Tamura, R.Spolenak, W.A.Caldwell, A.A.MacDowell, R.S.Celestre, H.A.Padmore, J.C.Bravman, B.W.Batterman, W.D.Nix, J.R.Patel: Journal of Applied Physics, 2003, 94[6], 3757-61