Theory of Electromigration Failure in Polycrystalline Metal Films

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Electromigration failure of polycrystalline aluminum interconnects is one of the primary failure mechanisms limiting the reliability of integrated circuits. In this research, Monte Carlo simulations and analytical studies will be made of a model of electromigration failure in polycrystalline metal thin films based on percolation theory. The dependence of the average film lifetime and the distributions of lifetimes on the temperature and degree of structural disorder will be investigated. An empirical distribution for the film lifetime which is commonly employed in engineering applications will be compared to the Monte Carlo results, providing a test of this distribution for much lower failure rates than is possible experimentally. A theory of the failure kinetics will be constructed which is based on recent advances in the theory of irreversible processes in random media. As time permits, these ideas will be applied to the related problem of fatigue-induced fracture in inhomogeneous brittle materials. %%% As integrated circuits become smaller and smaller, the problem of how to connect elements within these circuits, and the circuits themselves to the outside world, becomes more critical. As these connections, or interconnects, become smaller, the probability that circuit failure may occur in the interconnect increases. Thus, an understanding of the underlying mechanisms and of the probability for interconnect failure are important for predicting lifetimes of devices. This grant is using an unconventional approach to look at this difficult problem. Percolation theory looks at conducting systems such as interconnects from a general point of view. It is not as concerned about the underlying physical details as with the more global aspects of the problem. The research proposed here will use percolation theory for the first time to try to make predictions of interconnect lifetimes and determine general parameters which affect interconnect failure.