Effect of Nitrogen on the Frequency Dependence of Dynamic NBTI-Induced Threshold-Voltage Shift of the Ultrathin Oxynitride Gate P-MOSFET

The dynamic negative-bias-temperature-instability- induced threshold-voltage shift |DeltaV_t| of p-MOSFETs employing ultrathin decoupled-plasma- and thermal-nitrided SiO₂ gate dielectrics is studied as a function of gate frequency. The dependence of |DeltaV_t| on the gate frequency under unipolar stress is observed to become weaker for p-MOSFETs having higher nitrogen concentrations in the gate oxide. Evidence shows that reduced frequency dependence results from a greater lock-in of |DeltaV_t|, mainly due to an increased generation of recovery-resistant deep-level hole traps in the heavily nitrided gate p-MOSFET.