The evolution of the mechanical stressed which resulted from electromigration in polycrystalline thin-film interconnects was simulated as a function of the current density; assuming zero-stress boundary conditions. A polygranular cluster region was introduced into lines with otherwise bamboo microstructures, and resulted in a pair of atomic flux divergence sites and a tensile-compressive stress dipole. The atomic diffusivity in the tensile stress region was higher than that in the compressive stress region, thus leading to more rapid electromigration, so that the tensile stress was initially slightly larger than the compressive stress in the dipole. However, the tensile stress eventually fell to a small value while the compressive peak in the cluster increased to above its initial value; due to a stress build-up at the end of the cluster. The maximum compressive stress, for a given line, which resulted from electromigration was larger than the maximum tensile stress. Increasing the current density led to an increasing difference in the maximum compressive and tensile stresses.

The Effects of the Stress Dependence of Atomic Diffusivity on Stress due to Electromigration Y.J.Park, C.V.Thompson: Journal of Applied Physics, 1997, 82[9], 4277-81