Study of Electromigration-Induced Resistance and Resistance Decay in A1 Thin Film Conductors

Using an AC Bridge technique, the resistance of thin film (5000A thick) Al and (2000A thick)Al/5% Cu conductor stripes were monitored during high direct current density (1 X 106 A/cm2) stressing. The resistance was found to increase approximately linearly with time during stressing, which in this experiment was for periods of at least three hours, after which the current was turned off and the resistance continued to be monitored. The rate of the resistance increase was found to be thermally activated, but with an activation energy which varied considerably from sample to sample. Following stressing, an exponential decay in the resistance was observed which took place over a period of several hours. The decay appears to be characterized by more than one Characteristic thermally activated decay time (tau). The results are explained in terms of a model where electromigration induced vacancy supersaturations precipitate into defects and their subsequent decay.