Unambiguous identification of the NBTI recovery mechanism using ultra-fast temperature changes

We study temperature and bias dependence of VTH and interface states recovery after NBTI (Negative Bias Temperature Instability) stress. By making use of in situ heated test structures, we are able to change the temperature quickly and reliably at any stage of the experiment while keeping the device bias conditions untouched. This tool enables us on the one hand (i) to bring identically processed devices to the same degradation level, by stressing them under the same bias and temperature conditions, and on the other hand (ii) to vary the temperature in a defined way during recovery. Additionally we also study the influence of gate bias switches at constant temperature. Out of those experiments we have discovered that recovery acceleration can be observed either by increasing the temperature or by switching the gate bias for a short period of time towards accumulation. Since Charge Pumping (CP) measurements before stress and after recovery indicate that interface states cannot be made responsible for this acceleration, we suggest the neutralization of NBTI induced positive oxide traps to be the dominant recovery mechanism. However, if this is the case, we have to consider inelastic phonon-assisted tunneling in order to explain the temperature acceleration at fixed gate bias.