Abstract
The distributions of activation energies for electromigration damage in Al and Al-4%Cu thin-film interconnects were determined using temperature-ramp resistance analysis to characterize electromigration. The activation energies for the pure aluminum conductors are well represented by a normal distribution. It is noted that the normality of the distribution of activation energies can account for the log-normal distribution of failure times that has been observed. On the other hand, the population of activation energies for the Al-4%Cu conductors is composed of three subpopulations, each of which is well represented by a normal distribution. This deviation from the results obtained for the Al samples can account for variations from log normality that have been observed in failure time distributions, for aluminum-alloy interconnects. It is proposed that the origin of the subpopulations is the affect of copper on the grain-boundary transport of aluminum.