Mechanisms for very long electromigration lifetime in dual-damascene Cu interconnections

Electromigration in 0.27 mum wide Cu damascene interconnections has been investigated. The results show that the electromigration time to failure of Cu interconnections is greatly influenced by the thickness of the metal liner at the contact between the via and underlying line. A remarkably long lifetime was achieved when a 3 nm thick liner (at the via/metal line interface) was used, since the abrupt mass flux divergence at this interface normally seen is greatly diminished. Voids were found in the regions where there was no electric field and on the bamboo Cu grain structure. Void formation is explained by the effect of a vacancy wind. (C) 2001 American Institute of Physics.