THE MODELING OF RESISTANCE CHANGES IN THE EARLY PHASE OF ELECTROMIGRATION

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 fol lowed by a more or less linear increase (less than 1%) for a considera ble period of time. Ultimately, breakdown will occur preceded by an er ratic behavior of the resistance. This paper reviews existing models f or these early changes. It reviews the importance of a generation term for vacancies separate from a divergence of flux term in the explanat ion of small resistance changes in these models and proposes an altern ative view that explains the linear behavior of the resistance change and can also incorporate a variety of initial changes depending on ini tial mechanical stress conditions. In this model it is assumed that el ectron wind can create vacancies in the grain boundary regions that ar e further redistributed because of the electrical current. In this cre ation process less mobile damage is created, that contributes to the s cattering of electrons and thus increases the resistance. (C) 1998 Els evier Science Ltd.