Interface structure of ultrathin oxide prepared by N₂O oxidation

With X-ray photoelectron spectroscopy (XPS) measurements, we found in the N₂O-grown oxide that the nitrogen incorporation should involve the NO or N reaction with the Si-Si bond and P_b at the interface. Consequently, nitrogen content is very low and accumulated mainly at the interface. In addition, we found that the nitrogen atoms at the interface exist in the form of Si-N bonding and the interface oxynitride layer is a mixture of SiO₂ and Si₃ N₄ clusters. This structure will result in several undesirable effects. It will give rise to the permittivity and bandgap fluctuations at the interface and hence induced gigantic surface potential fluctuation and mobility degradation in the channel of MOS devices. This bonding structure also explains the interface trap generation during the electrical stressing. The sources of trap generation are attributed to the Si-Si bonds, P_b centers, and nitride-related defects due to the over-constrained silicon atoms in the Si₃N₄ clusters at the interface.