Off-state stress degradation mechanism on advanced p-MOSFETs

Deep insights into the Off-State Stress (OSS) degradation mechanism on p-MOSFETs with High-K/Metal Gate technology are presented in this paper. Large subthreshold slope degradation, or positive Vth shift is observed in high, or low Vth devices, where both phenomena impact the off current degradation. The OSS degradation mechanism in pMOS is generated by (1) hot carrier generation close to the drain junction by impact ionization, then (2) hot electron injection into the oxide bulk defects, and (3) Si/oxide interface degradation. Both TCAD simulations and measurement with VGate-to-Drain modulation demonstrate the mechanism. The Vth shift in OSS is toward an opposite direction compared to CHC or BTI, which suggest a means to restore the Vth to the initial value after the OSS degradation.