High-Temperature Reverse-Bias Stressing of Thin Gate Oxides in Power Transistors

Abstract

High-temperature reverse-bias (HTRB) and Fowler-Nordheim (FN) stresses were applied to assess the reliability of n-channel U-shaped trench-gated metal-oxide-Si field-effect transistors (N-UMOSFETs) of ~0.5 microns trench width and ~1 micron channel length. The HTRB causes degradations in the threshold voltage and drain leakage of the N-UMOSFET. The degradation is observed when the HTRB is applied in a humid ambient and is attributed to the generation, by the stress, of hydrogen protons (H+s) in the gate oxide. It is concluded that HTRB gives rise to negative-bias temperature instability (NBTI) in a parasitic P-channel MOSFET structure occurring in the trench base of the N-UMOSFET. The NBTI is promoted by the degraded condition of the gate oxide at the trench base as observed by charge pumping and SEM following FN stress of the N-UMOSFET.