The effects of a Ta barrier layer upon the electromigration and stress migration of Cu films were investigated. The Ta barrier layer enhanced both the (111) texture and the median grain size of the annealed Cu films. At 225C, the electromigration mean-time-to-failure (225C-MTF) of Ta/Cu/Ta multi-layer interconnects was about 2 times longer than that of Cu monolayer interconnects. After 500 thermal cycles, the 225C-MTF of Ta/Cu/Ta multi-layer interconnects did not change and was about 3 times longer than that of Cu monolayer interconnects. The activation energy, Ea, for electromigration of Ta/Cu/Ta multi-layer interconnects was 0.77eV, which was higher than that of Cu monolayer interconnects (0.65eV). Since the Ta/Cu/Ta specimen had an enhanced crystallographic texture and a larger grain size, it had both a higher electromigration
endurance and thermal stress resistance than Cu. However, the measured mean-time-to-failure was shorter than that predicted by an equation proposed by Vaidya and Sinha. The shorter mean-time-to-failure and lower Ea values for the Ta/Cu/Ta multiplayer, as compared with the predicted ones, were due to the weak Ta/Cu interface. A lifetime of 100 years was predicted for Ta/Cu/Ta multi-layer interconnects with and without 500 thermal cycle stress.

Effect of the Tantalum Barrier Layer on the Electromigration and Stress Migration Resistance of Physical-Vapor-Deposited Copper Interconnect. Y.L.Chin, B.S.Chiou, W.F.Wu: Japanese Journal of Applied Physics - 1, 2002, 41[5A], 3057-64