SiO2 / Si Interface Structures and Reliability Characteristics

This paper shows that a structural transition layer of exists at an interface prepared by thermal oxidation of Si. Using a newly developed grazing‐incidence x‐ray diffraction of synchrotron radiation, the transition layer density is found to be lower than the immediate bulk density , and its thickness is approximately 7 nm. Electrical properties of the films are examined by using Fowler‐Nordheim tunneling electrons which are injected from the polycrystalline silicon gate electrode into the film. The injected charge‐to‐breakdown ( Qbd ) rapidly degrades when the film thickness decreases below approximately 7 nm due to dielectric breakdown in the transition layer. Based on theoretical analysis, the mechanism of the dielectric breakdown in the transition layer is proposed to be Si‐Si bond formations via hypervalent Si atoms and a replacement reaction of an oxygen atom with an electron. Introduction of nitrogen atoms into the transition layer improves the Qbd degradation of thin films, because the Si‐Si bond formation is suppressed by stress relaxation in the transition layer.