Electron Trap Transformation Under Positive-Bias Temperature Stressing

Electron detrapping in the TiN/HfO2 gate n-MOSFET under dynamic positive-bias temperature instability (PBTI) is examined. Similar to hole detrapping under dynamic negative-bias temperature instability (NBTI), electron detrapping per relaxation cycle is a constant under a low oxide stress field (similar to 5.5 MV/cm), independent of the number of times the transistor is stressed and relaxed, and it progressively decreases with the number of stress/relaxation cycles at a higher oxide stress field (similar to 7 MV/cm). Analysis shows that the decrease is due to a portion of the electron trap states being transformed into deeper levels, thereby increasing the emission time of the trapped electrons. However, unlike hole detrapping, the decrease in electron detrapping is not accompanied by a correlated increase in the stress-induced leakage current, and it can be reversed with a moderate negative gate voltage. These differences from NBTI suggest that distinct defects are active under PBTI.