Impact of via interactions and metal slotting on stress induced voiding

Stress induced voiding was investigated for a 0.13 mum Cu/low-k interconnect process. The focus of our study was on the ldquohumprdquo failure mode using a statistical approach to both the design of the vehicle and the data analysis. The time-to-failure (TTF) was studied with respect to geometrical aspects of the lower metal level, insertion of a dummy via, via arrays and metal slotting for long via chains. It is found that insertion of dummy vias increased the reliability, through reduction in the probability for void nucleation and a reduction in void growth rate. The lifetime improvement is attributed to a stress modification in the interconnect. The stress modification can effect vias far from the local ldquodiffusive volumerdquo during void growth, indicating possible new approaches for redundant electrical or dummy via placement. Insertion of metal slots close to the electrically active via act as a diffusive barrier, and slots located elsewhere can modify the stress in the interconnect to improve via lifetime.