Charge trapping mechanism under dynamic stress and its effect on failure time [gate oxides]

The aim of this work was to investigate the effect of dynamic versus DC voltage stress applied to thin oxides. A longer lifetime was observed under pulsed stress at high electric fields. When increasing the frequency, we noticed an increment of lifetime and a different trapped charge location, regardless of the stress polarity. To detect the charge trapping evolution under pulsed stress, we used a new experimental procedure. Fast transitory phenomena detected using this technique are interpreted as charging and discharging of positive traps located in the anodic region. The consequent reduction of the effective positive charge allows us to explain the lifetime enhancement and the charge trapping evolution. We also compared the behaviour under pulsed stress of oxides grown in dry or steam environments. The lifetime increase is more relevant in dry oxides showing a correlation between the interface quality and the oxide reliability in dynamic mode