Characterization of the silicon nitride-thermal oxide interface in ONO structures by ELS, XPS, ellipsometry, and numerical simulation [SONOS EEPROM]

Using electron energy loss spectroscopy (ELS), XPS, and ellipsometry measurements, large amount of Si-Si bonds at Si₃N₄/thermal SiO₂ interface are identified. Abnormally large value of refractive index (n=2.1) in the Si ₃N₄/SiO₂ interface layer was obtained. The effective width of Si-rich interfacial layer is estimated to be about 5-10 Å. The excess silicon at Si₃N₄/SiO₂ interface was created by replacing nitrogen with oxygen during the oxidation of Si₃N ₄. The abnormally large electron capturing at Si₃N ₄/SiO₂ interface observed previously and the accumulation of positive charge at top interface of nitrided oxide under ionizing irradiation are explained with the existence of Si-Si bonds at Si₃N₄/SiO₂ interface