Post-irradiation dopant passivation in MOS capacitors exposed to high doses of x-rays

We study post-irradiation dopant passivation in p-type silicon metal-oxide-semiconductor capacitors exposed to high doses of low-energy x-rays. The passivation presents a logarithmic temporal behaviour which can be detected within less than one hour and continues to evolve for several thousand hours after irradiation. The time delay between irradiation and passivation increases with radiation dose and a change in the anneal curve slope of oxide charge is associated with the onset of passivation. These observations are discussed in terms of tunnelling electrons from the silicon substrate, which may interact with traps in the oxide and trigger the passivation by releasing hydrogen-related species.