Electron detrapping characteristics in positive bias temperature stressed n-channel metal-oxide-semiconductor field-effect transistors with ultrathin HfSiON gate dielectrics

Electrons trapped in the HfSiON gate dielectrics of n-channel metal-oxide-semiconductor field-effect transistors induced by positive bias temperature stress start to decay when the stress is interrupted or an opposite (recovery) voltage is applied. The decay begins with a quick detrapping within tens of nanoseconds followed by a slow detrapping. The quick detrapping depends on the recovery voltage and the trapping history, whereas the slow detrapping obeys approximately a logarithmic dependence on time with an almost identical slope before saturation. The observed detrapping behavior can be explained by a spatial and/or energetic distribution of trapped electrons in the HfSiON film. The device degradation under various dynamic stresses is found to be almost independent of frequency ranging from 0.001to1MHz, while it is slightly enhanced at 10MHz, probably due to insufficient recovery at the recovering half cycle.