Enhanced Flatband Voltage Recovery in Hardened Thin MOS Capacitors

The short-term recovery of hardened pyrogenic SiO2 MOS capacitors exposed to pulsed electron-beam irradiation was studied as a function of oxide thickness between 200 and 1000 Å. Two sets of samples were studied: one set grown to a single thickness and then etched back to various thicknesses, and the other set grown for different lengths of time to varying thicknesses. In both cases, the recovery time was observed to vary approximately as the fourth power of oxide thickness. This anomalous superlinear dependence of recovery time on the SiO2 thickness agrees with the predictions of the stochastic model of hole transport based on a continuous-time random walk. Combining the highly field activated character of hole transport in SiO2 with the thickness dependence reported here demonstrates that very significant gains in the short-term recovery speed can be made by reducing the oxide thickness and/or increasing the oxide field.