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

Electromigration in 0.27 mum wide Cu damascene interconnections has been in vestigated. The results show that the electromigration time to failure of C u interconnections is greatly influenced by the thickness of the metal line r at the contact between the via and underlying line. A remarkably long lif etime 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 normall y seen is greatly diminished. Voids were found in the regions where there w as no electric field and on the bamboo Cu grain structure. Void formation i s explained by the effect of a vacancy wind. (C) 2001 American Institute of Physics.