Effects of Mg additions on the electromigration behavior of Al thin film conductors

Aluminum thin film conductors containing Mg alloying additions have been tested for electromigration failure by formation of electrically open circuits. The test conditions were either 2 × 10⁶ A/cm² or 4 × 10⁶ A/cm² for the current density, and either 175 or 225°C for the temperature. The median lifetimes were found to increase with increasing Mg concentrations up to the highest concentration tested, about 6%. With polycrystalline films the maximum increase in lifetime resulting from Mg additions corresponds to a factor of about 100, as compared to pure Al films. This is about equal to previously reported results obtained with Cu additions. The increase in lifetime has been shown to result from a decrease in the rate of grain boundary diffusion for the Al atoms. Magnesium atoms diffuse at approximately the same rate as Al atoms. Thus the mechanism of failure formation in Al films containing Mg is thought to be different than in Al-Cu films, where Cu atoms diffuse faster than Al atoms and failure ensues upon local Cu depletion.