Polarity dependence of FN stress induced degradation on NMOSFETs with polysilicon gate and HfSiON gate dielectrics

Polarity dependent FN stress induced degradation was observed on NMOSFETs having a polysilicon gate and HfSiON gate dielectric. Positive bias stress (substrate injection) showed more degradation on the bulk region of high-k at the near valence band edge region and low-voltage stress induced leakage current behavior was observed around the flatband voltage. Negative bias stress (gate injection) degraded a wider energy range and in a lower energy band region than positive stress. Therefore, the gate injection case caused worse degradation in terms of interface state density and subthreshold swing than the substrate injection case.