Nano- and micrometer-scale thin-film-interconnection failure theory and simulation and metallization lifetime prediction, Part 2: Polycrystalline-line degradation and bulk failure

Abstract

The degradation and bulk failure of a polycrystalline interconnect line caused by vacancy electromigration along grain boundaries and vacancy-cluster nucleation at triple points in the bulk conductor are investigated within the general theory of the electromigration-induced degradation and failure of thin-film on-chip interconnect lines, presented in Part 1 [1]. The general equations are tailored to deal with vacancy electromigration, mechanical-stress generation, and void nucleation at triple points. Appropriate boundaryvalue problems are formulated, and numerical methods and procedures to solve them are developed and implemented in software. Computer simulations are performed to identify a pattern of electromigration failure at triple points. On this basis, (1) interconnect lifetime is investigated over wide ranges of variation of material, structural, geometric, and operating parameters, and (2) the current-density and temperature dependence—of the mechanical stress, vacancy concentration, and level of vacancy supersaturation at a triple point, and of void radius and time to nucleation-is examined and explained. The simulation results are found to agree well with previous experiments. This investigation could be seen as a natural continuation of our study of electromigration failures developed by multilevel-metallization systems as a result of interconnect failure near via junctions or at open ends [1]. Together they cover most mechanisms of electromigration failure suffered by metallization systems.