Diffusivity variation in electromigration failure

Electromigration driven void dynamics plays an important role in the reliability of copper interconnects; a proper understanding of which is made more difficult due to local variations in line microstructure. In simulations, the parameter incorporating these variations best is the effective atomic diffusivity Deff which is sensitive to grain size and orientation, interface layer thickness, etc. We examine a number of experimental results and conclude that, to explain observations using current theoretical models, Deff values must vary significantly along the interconnect, and that such variations are enough to yield encouraging simulations of resistance variations under bidirectional stress.