Band alignment of SiO2/Si structure formed with nitric acid vapor below 500 deg C

A relatively thick (i.e., 9 nm) SiO2 layer can be formed by oxidation of Si with nitric acid (HNO3) vapor below 500 deg C. In spite of the low temperature formation, the leakage current density flowing through the SiO2 layer is considerably low, and it follows the Fowler-Nordheim mechanism. From the Fowler-Nordheim plots, the conduction band offset energy at the SiO2/Si interface is determined to be 2.57 and 2.21 eV for HNO3 vapor oxidation at 500 and 350 deg C, respectively. From X-ray photoelectron spectroscopy measurements, the valence band offset energy is estimated to be 4.80 and 4.48 eV, respectively, for 500 and 350 deg C oxidation. The band-gap energy of the SiO2 layer formed at 500 deg C (8.39 eV) is 0.68 eV larger than that formed at 350 deg C. The higher band-gap energy for 500 deg C oxidation is mainly attributable to the higher atomic density of the SiO2 layer of 2.46 X 1022/cm3. Another reason may be the absence of SiO2 trap-states.