Growth Mechanism and Prevention Measure of Stress-Induced Voids in Copper Interconnects

We studied stress-induced voiding under via-holes in copper interconnects. The internal stress developed in copper interconnects was analyzed by using a finite-element method. The intrinsic stress of the construction materials was measured to analyze the internal stress. We investigated the relationship between the analyzed copper-line stress under the via-hole and the increase in electrical resistance of copper-interconnect-structure test samples. By comparing the results, it was found that the resistance due to the growth of stress-induced voids increases with the increase in the copper-line stress and in the stress gradient. Furthermore, molecular dynamics simulations showed that both the stress and stress gradient activate copper-atom diffusion, which is a dominant factor in void growth. Therefore, the reduction of the copper-line stress and stress gradient is important in suppressing the growth of stress-induced voids.