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 which best incorporates these variations is the effective atomic diffusivity D eff 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, D eff values must vary significantly along the interconnect, and that such variations are enough to yield encouraging simulations of resistance variations under bidirectional stress.