Significant large-scale modifications of the surface of Al-Si conductors was observed, due to electromigration in wide lines under low-stress conditions. After electromigration stressing, the Al layers exhibited local damage due to thinning. The mechanism which underlay this damage caused substantial metal transport. Thinning was observed in various alloys (Al-Si, Al-Cu, Al-Si-V, Al-Si-V-Pd), with various under-layers (SiO2, W-Ti), as a function of temperature and current density, in structures with or without passivation. The results showed that thinning was a general phenomenon. An activation energy of about 0.5eV was deduced for the temperature dependence of a combined mechanism of concurrent thinning plus voiding in Al-1%Si. It was shown that diffusion at the Al/oxide interface was most likely to play an important role in the damage mechanism; even under stress conditions where grain boundary diffusion was thought to predominate. The results also showed that alloying of the Al with Pd could reduce the effects of thinning damage.

R.A.Augur, R.A.M.Wolters, W.Schmidt, A.G.Dirks, S.Kordic: Journal of Applied Physics, 1996, 79[6], 3003-10