Electromigration, aluminum

A failure mechanism in semiconductor devices. Due to momentum exchange between the current-carrying electrons and the host metal lattice, aluminum ions can drift in the direction of the electron current. In the presence of flux divergent sites, this drift induces a stress gradient that at steady state is proportional to the current density. In sufficiently long conductors and at high current densities, the stress will increase to the point where voids will form in regions of tensile stress that subsequently grow to the point of failure. It is also possible that at locations of high compressive stress extrusions and hillocks can form that can cause failure of the protective passivation or induce short circuits. (Reference JEP122F)