Resistance oscillations induced by DC electromigration

Abstract

Abrupt changes in resistance (ACRs) such as steps and oscillations are frequently observed during DC electromigration testing of Al interconnections. ACRs are observed in a interconnection which width is as large as the mean Al grain size. Investigations are concentrated to these resistance oscillations, and it is revealed that there are two types in resistance oscillations; downward spikes and upward spikes. These spikes are further classified into quasi-periodic ones and random ones. Investigations on the current density dependence and locality and non-locality strongly suggest that origins of the upward spikes and the downward spikes are quite different. The downward spikes are local phenomena which occur within a range of several μm, while the upward spikes are non-local phenomena which occurs in a range extending to more than several thousands μm. A frequency of the downward spikes drastically increases with an increase in the current density, on the other hand, an amplitude increased drastically in the case of the upward spikes. It is most likely that the downward spikes correspond to the alternation of annihilation and formation of a single void, and a modeling based on the current detour effect around a high-resistance region such as a vacancy cluster well explains the current density dependence of the frequency. The mechanisms of the upward spikes are remained to be clarified, however, one possible mechanism may relate to pulsating of stress of the interconnection due to dislocation dynamics such as climb, generation and annihilation.