Relationship between x-ray-produced holes and interface states in metal-oxide-semiconductor capacitors

Metal-silicon dioxide-silicon capacitors were irradiated with soft x rays to 40 krads (SiO2) with different biases (−3 to +12 V) at 83 K. The number of interface states generated after samples were warmed was found to bear a linear relation with the flatband voltage shift measured before warm up. A one-to-one relationship was observed between the number of interface states generated in the central 0.7-eV portion of the Si band gap during a one year storage at room temperature and the number of holes that moved to the Si–SiO2 interface during warm up. Annihilation of the x-ray-generated holes by photoinjection of electrons before warm up prevented the generation of interface states. Both experiments support a cause-and-effect relationship between holes in the oxide and interface states generated in the metal-oxide semiconductor structure.