Electromigration Resistance of Fine-Line Al for VLSI Applications

The electromigration lifetimes were determined for an as-yet unexplored combination of long lines (up to 3cm.) and narrow linewidths (down to 1 ¿m) of evaporated and magnetron sputter-source deposited Al-Cu-Si films. The lifetimes for the sputtered films were found to be significantly smaller than those for e-beam evaporated films. The latter displayed an unusually large improvement in the lifetime for finer linewidths (1.5 and l¿m). Failure modes were analyzed and correlations made with a new microstructural parameter incorporating the film grain-size, its sigma and the degree of preferred orientation.