Optimization of via contact test structure for electro-migration

The effects of via contact test structure on electromigration (EM) lifetime were investigated. We model the median-time-to-failure (MTF) and log-normal dispersion of the failure time (σ) of via contacts with consideration to stress-induced backflow effect and Al drift velocity. The MTF and σ are described as a function of the critical length and the length between vias of via contact test structure and increase as the length between vias approaches the critical length. Also, MTF and σ depend on stress current density in accelerated EM test. We propose an optimized via contact test structure and accelerated conditions for the accurate extrapolation of EM lifetime of multilevel interconnects