Study of void formation kinetics in Cu interconnects using local sense structures

A test structure that allows the study of void formation kinetics during electromigration is proposed and characterized. Compared to a standard single-via electromigration test structure voltage-senses are placed near the via. This allows monitoring resistance changes before final void formation, while the void formation process is not affected. Part of the samples show single void formation, while for other samples, multiple voids are formed. For the single void case, a model is proposed to calculate void-depth as a function of time. Initially, voids grow faster and this growth slows down towards the end of the void formation process. Estimated velocities during void formation are in the same order of magnitude compared to literature results of drift velocities during void growth. Cases where multiple voids are formed show that voids which initially form further away from the via stop growing upon formation of a void closer to the via.