Simple Modeling and Characterization of Stress Migration Phenomena in Cu Interconnects

Many observations of stress-induced voids beneath vias in wide Cu lines have been performed to analyze stress migration phenomena. Most of the voids that caused fatal failures of circuits accompanied grain boundaries in the lower lines. Finite element method calculations were performed to obtain the stress distribution around a via sandwiched between wide upper and lower lines. Based on these results, a void growth model for the Cu stress migration phenomena has been proposed by applying the Hull and Rimmer theory. This model takes two diffusion paths, such as a grain boundary and a barrier/Cu interface, into consideration. Compared with experimental results, the proposed model successfully explained the mean time to failure dependence on the temperature and geometrical parameters of Cu interconnects.