Valence-band tunneling enhanced hot carrier degradation in ultrathin oxide nMOSFETs

Enhanced hot carrier degradation with stress V/sub g/ in the valence-band tunneling regime is observed. This degradation is attributed to channel hole creation by valence-band electron tunneling. The created holes provide for Auger recombination with electrons in the channel and thus increase hot electron energy. The valence-band tunneling enhanced hot carrier degradation becomes more serious as gate oxide thickness is reduced. In ultrathin gate oxide nMOSFETs, our result shows that the valence-band tunneling enhanced degradation, as opposed to max. I/sub b/ stress induced degradation, exhibits positive dependence on substrate bias. This phenomenon may cause a severe reliability issue in positively biased substrate or floating substrate devices.