We investigated the abnormal degradation of high-voltage p-type MOSFET (HV pMOSFET) under negative AC gate bias stress. In HV pMOSFET with n+ polycrystalline silicon (poly-Si) gate, the abnormal degradation occurs after the gradual degradation during negative AC stress. The abnormal degradation is suppressed by changing the gate material from n+ poly-Si to p+ poly-Si, and it is caused by hot holes produced by the impact ionization near the surface when electrons move from the gate toward the gate oxide. We suggest a possible mechanism to explain the improvement of degradation by using p+ poly-Si as a gate material.

We investigated hot hole-induced degradation in HV pMOSFETs. When the electric field between gate and channel is negatively higher than 6 MV/cm, an additional shift of sub-threshold swing leads to the shift of threshold voltage due to Fowler-Nordheim (FN) tunneling from the gate to the substrate. Hot hole is generated under highly-negative gate voltage near the surface, and accelerate the degradation. We observe that hot hole-induced degradation has a dependency of operation conditions and gate materials, and is suppressed under particular conditions. In this work, we studied the mechanism of hot hole-induced degradation qualitatively and discussed an improvement of this phenomenon by TCAD simulation and a variety of experimental results on the characteristics of electron and hole trap as function of gate materials.