Characterization of SiO2 Dielectric Breakdown for Reliability Simulation

Breakdown statistical distributions of thin oxide MOS capacitors are analyzed to reveal the limitations of accelerated procedures for reliability simulations at circuit level. The detailed analysis of the breakdown distributions corresponding to different stress voltages shows the presence of three modes of breakdown, associated with different kinds of defects. These breakdown modes control the shape of the distributions at different oxide field ranges. The mean values of time-to-breakdown, charge-to-breakdown, and energy-to-breakdown and their dependence on oxide field are found to be directly related to the mode dominating the distribution. Since the shape of the breakdown distribution changes with stress voltage, an accelerated testing procedure must provide a way to extrapolate to operation conditions not only the mean value, but also the shape of the distributions. Our results indicate that different physical mechanisms cause the breakdown at low and high fields. Consequently, the acceleration conditions have to be low enough to avoid different breakdown mechanisms in the accelerated and normal operation field ranges. The importance of localized latent defects is also demonstrated. These defects, which require a certain stress time (roughly independent of stress conditions) to cause the oxide failure, dominate the low-probability tail of the breakdown distribution and determine the failure rate of complex IC's. In addition to the intrinsic breakdown model, the latent-defect-related tails have to be also correctly accounted for in reliability simulators. © 1993 IEEE