Dependence of electromigration caused by different mechanisms on current densities in VLSI interconnects

In this paper, we have studied electromigration (EM) behavior under different current densities experimentally and theoretically. Our experimental results have shown that the dependence of median-time-to-failure on current density is not the same in different regimes of current densities. Both the theoretical analysis and observation of SEM showed that mechanisms causing EM failure in different regimes are different. In the low current density regime EM failure is caused by microstructural changes, while in the high current density regime it is microstructural changes caused by a temperature gradient. We have developed a model to describe the dependence. The calculated results are consistent with experiments.