The kinetics of θ-phase (Al2Cu) precipitation in passivated bamboo Al-0.2at%Cu segments was studied in situ in a scanning electron microscope during electromigration. The electrical current was used to reversibly transport Cu back and forth along the segment and allowed for a systematic study of Cu diffusion and precipitate nucleation, growth, and dissolution. The observations allowed an independent determination of diffusion with and without an electric current and showed that both interface and lattice diffusion were important in Cu precipitation in bamboo segments. It was also found that a substantial supersaturation of Cu was required to nucleate the θ-phase. A simple model for electromigration-induced motion of Cu could be used to explain the data and predicts that an interconnect with Cu both in solution and in periodically spaced precipitates would have optimal reliability.

Electromigration-Induced Cu Motion and Precipitation in Bamboo Al-Cu Interconnects. C.Witt, C.A.Volkert, E.Arzt: Acta Materialia, 2003, 51[1], 49-60