Degradation and breakdown of thin silicon dioxide films under dynamic electrical stress

Thin oxide MOS capacitors have been subjected to dynamic voltage stresses of different characteristics (shape, amplitude and frequency) in order to analyze the transient response and the degradation of the oxide as a function of the stress parameters. The current transients observed in dynamic voltage stresses have been interpreted in terms of the charging/discharging of interface and bulk traps. As for the oxide degradation, the experimental data has been interpreted in terms of a phenomenological model previously developed for dc stresses. According to this model, the current evolution in voltage stresses is assumed to be related to the oxide wearout. The evolution of the current during bipolar voltage stresses shows the existence of two different regimes, the degradation being much faster at low frequencies than at high frequencies. In both regimes, the frequency dependence is not significant, and the change from one regime to the other takes place at a threshold frequency which depends on the oxide field. These trends are also observed in time-to-breakdown versus frequency data, thus suggesting a strong correlation between degradation and breakdown in dynamic stresses. The experimental results are discussed in terms of microscopic degradation models