DIFFUSION AT THE AL AL OXIDE INTERFACE DURING ELECTROMIGRATION IN WIDE LINES/

Significant large-scale modification of the surface of Al-Si conductor s was observed, due to electromigration in wide lines and under low st ress conditions. After electromigration stressing the Al layers showed local thickness variations, i.e., damage by thinning. The mechanism u nderlying this damage causes substantial metal transport. Nevertheless , damage by thinning has received little attention in the past. Thinni ng was observed: (1) in a number of different alloys (Al-Si, Al-Cu, Al -Si-V, and Al-Si-V-Pd), (2) with a number of different underlayers [Si O2, W-Ti (no vacuum break after Al deposition) and W-Ti (oxidized surf ace before Al deposition)], (3) over an extended temperature range, (4 ) over a range of current density, and (5) in structures with and with out passivation. The results show that thinning is a general phenomeno n. An activation energy of approximately 0.5 eV was determined for the temperature dependence of a combined mechanism of concurrent thinning plus voiding in Al99S1. Several alternatives are examined to explain the observations, namely mass movement along dislocations, Al bulk dif fusion, and diffusion at the interface between the Al and its oxide. I t is shown that diffusion at the Al/Al oxide interface most probably p lays an important role in the damage mechanism, even under stress cond itions where grain boundary diffusion is traditionally thought to domi nate. Results also showed that alloying of Al with Pd can reduce the e ffects of damage by thinning. (C) 1996 American Institute of Physics.