The modeling of resistance changes in the early phase of electromigration

Abstract

Sensitive measurements of the evolution of the resistance of aluminum based metallisation stripes that have been electrically stressed with large current densities show a rather unpredictable initial change followed by a more or less linear increase (less than 1%) for a considerable period of time. Ultimately, breakdown will occur preceded by an erratic behavior of the resistance. This paper reviews existing models for these early changes. It reviews the importance of a generation term for vacancies separate from a divergence of flux term in the explanation of small resistance changes in these models and proposes an alternative view that explains the linear behavior of the resistance change and can also incorporate a variety of initial changes depending on initial mechanical stress conditions. In this model it is assumed that electron wind can create vacancies in the grain boundary regions that are further redistributed because of the electrical current. In this creation process less mobile damage is created, that contributes to the scattering of electrons and thus increases the resistance.