Serrated cathode dissolution under high current density: Morphology and root cause

Excessive cathode dissolution due to high current densities is investigated. Such excessive dissolution is one of the key electromigration-induced degradation processes in micro systems, and exhibits a distinctive serrated morphology. In this study, Cu cathode and Cu anode connected with Sn is stressed at a 4.5 × 10⁴ A/cm² current density for time as long as 1500 h. Careful sequential micro polishing is able to establish for the first time that the serrated cathode interface in fact is the expression of rod-like indentations in three-dimensional morphology. This unique morphology supports the proposition that fast Cu diffusion through Cu₆Sn₅ grain boundaries is the root cause for this excessive dissolution.