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This report studies the electromigration performance of W-plug via structures under the reservoir effect. The lifetime improvement factor M was observed to be a weak function of the stressing current and approximately equal to 2. A Simple model is included in the report to explain this observation. The model also predicts the most effective reservoir length for electromigration lifetime improvement.

The temperature-composition phase diagram of the Ni-Cr system was calculated using a first-principles approach based on a statistical-mechanical approximation for the configurational entropy and a tigh-binding method for electronic structure calculations. A self-consistent tight-binding Hamiltonian with only d-electrons was implemented by imposing a condition of zero charge transfer. Hamiltonian parameters were taken from the results of first-principles band-structure calculations. The effects of self-consistent d-electron numbers for pure Ni and Cr on the phase diagram and thermochemical properties were also investigated.