Impact of field enhancement on TDDB lifetimes of Cu/Low-k test structures

Small area finger test structures were designed to isolate and study the physical failure analysis of Cu/low-k system. This paper aims to study the impact of field enhancement and area scaling through the comparison of dielectric breakdown lifetime of the finger test structures and conventional comb structure. It was found that the lifetime extracted from finger tests structures does not scale to comb structure by the Poisson area scaling law. Discrepancy is believed to have arisen due to the difference in field enhancement caused by the difference in shapes. Finite element modelling (FEM) simulation was performed using physical images to affirm this field enhancement effect. Finger test structure was found to suffer from a higher field enhancement compared to the comb structure, hence supporting the experimental results where extrapolation of lifetime from comb structure to small area over-estimates the lifetime.