Electromigration of Gold Metallization

This study investigates the electromigration performance of gold metallization with vias of different sizes and shapes. Electromigration lifetime was limited by void formation which scaled directly with via size, especially those with square vias, where the fatal void formed in the via at the interface of the feeder metal. This dependence saturates for larger vias once the failure mode switches to voiding through the thickness of the tested metal at the cathode line-end. The highest lifetimes were measured for line-only structures where failure was observed at the grain boundaries. Further, non-square vias can be mapped to an equivalent square via size to enable electromigration design rule formulation. Also, the activation energy and current-density exponent as seen in Black’s Law were measured to be 0.41eV and n = 2.14, respectively, on structures with vias, which indicates low temperature dependence and void-nucleation limited failure. (Abstract)