Direct observation of electromigration-induced surface atomic steps in Cu lines by in situ transmission electron microscopy

Surface atomic steps in unpassivated copper lines under electromigration (EM) have been directly observed in ultrahigh vacuum by in situ transmission electron microscopy (in situ TEM). The combination of {111} planes and ⟨110⟩ directions for crystalline Cu were found to be the most favored EM paths. The in situ TEM study of EM-induced evolution of Cu surface structures provides a sound basis for understanding the dependence of EM-induced atomic migration mechanism on crystal orientation of crystalline Cu. The understanding shall lead to the effective strategy of using appropriate passivation layer to suppress the electromigration.