Time-dependent evolution of SiO2/Si interface traps after repeated radiation damage

The post-irradiation evolution of the interface traps in metal/SiO2/Si (MOS) capacitors after repeated x-ray irradiation has been investigated. The results indicate that, immediately after the first irradiation, a characteristic peak (peak-1) in the energy distribution of the interface traps above midgap appears, which subsequently decreases with time in storage at 75 °C. Accompanying this decrease is the formation and growth of a second peak (peak-2) below midgap. Evidence will be presented which suggests that this is due to an interfacial defect transformation process. Measurements done after repeated irradiation-storage cycles indicate that peak-2 is not generated directly by the x-ray irradiation; rather, the existence of peak-1 is a necessary condition for the formation of peak-2 through the defect transformation process. There is also evidence that only a portion (although a significant portion) of peak-1 defect undergoes the transformation process.