Electromigration and current-carrying implications for aluminum-based metallurgy with tungsten stud-via interconnections

The electromigration behavior of Ti-AlCu-Ti metallurgy is presented in this work. For single-level structures in the absence of tungsten (W) stud interconnections, a greater-than-100x lifetime improvement over AlCu is measured. The metal linewidth strongly affects the median time to failure, T50, and standard deviation, sigma (a), of the lognormal distribution. For two-level W stud chains, a 50x degradation in lifetime as compared to single-level structures is measured. The lifetime of these W stud chains depends on the Ti-AlCu-Ti current density rather than the stud current density. The "reservoir effect", in which the electromigration lifetime of Ti-AlCu-Ti stripes depends strongly on W studs near the electron source end of the stripes, is a direct result of W acting as a diffusion barrier. The lifetime of W stud chains with Ti-AlCu-Ti metallurgy is longer for 2.0% copper than for 0.5% copper.