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

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Abstract
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 ((sigma) ), 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.

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