The effect of residual stress on vacancy transportation in Cu interconnection due to electromigration

The effect of residual stress on vacancy transportation in Cu interconnection due to electromigration was investigated. An equation of vacancy transportation caused by electromigration coupled with residual stress was proposed. The distribution of vacancy concentration was derived using the computer aided simulation. The hydrostatic stress was calculated by an elastic-plastic finite elemental method. Behavior of vacancy transportation was found to be dominated by the competitive relationship between residual stress and electrical stress in interconnection. When the residual stress dominantes, vacancy concentrates around the maximum hydrostatic stress region, such as elastic-plastic boundary. On the other hand, when electrical stress is dominant, vacancy do not concentrate around the maximum hydrostatic stress region, but moves from the cathode end to the anode end. These results are in good agreement with the in-situ experimental results conducted in our previous paper. Based on the result mentioned above, various failure modes in LSI interconnection cased by electromigration are predictable by using the proposed equation.