Copper Versus Magnesium as an Alloying Element in Aluminum Interconnects: Effects on Electromigration

It is well known that the addition of Cu improves the electromigration resistance of Al conductor lines. However, the underlying mechanisms are not entirely understood. As Mg has also been found to have a beneficial effect, a thorough comparison between these two alloying elements may result in new insights. In this work, we present results of drift velocity experiments on Al-2wt%Cu and A1-3wt%Mg, where the edge drift was measured in-situ as a function of temperature. Additionally, the concentration profile of either alloying element was measured as a function of testing time using an electron probe micro-analysis technique. For both alloys an incubation time for stripe drift was observed. The activation energies of edge drift after this depletion were determined to be 0.83 eV and 1.01 eV for Al-Cu and Al-Mg, respectively. Both activation energies seem to agree with the activation energy of electromigration of the alloying element rather than the activation energy of drift in pure Al, which was determined separately to be 0.5 eV.