The SiO2/Si interfaces of the 2 nm thick dry oxide using rapid thermal oxidation and wet oxide using H2O formed by catalysis of Pt were investigated in order to understand the difference between the two oxides relevant to the device reliability using various methods. The interstitial defects at the interfacial region were detected using medium energy of ion scattering spectroscopy in the sample of dry oxidation, but not in the wet oxidation., The interfacial roughness and the interstitial defects strongly depended on the oxidation process, although the interfacial strain differs very little between the dry and wet oxidation processes. The results of high resolution x-ray photoelectron spectroscopy using a synchrotron radiation source clearly provided the difference of the defects between two oxides. The scanning tunneling microscope image of the SiO2 layers subjected to hot electron injection from the tip showed that wet oxide had superior quasi-breakdown characteristics to dry oxide. Time-dependent dielectric breakdown of the SiO2 layer also depended on the oxidation process, indicating that the interface roughness and the defects critically affect the reliability of the gate oxide. Thus the wet oxidized SiO2 film is found to, be more stable against the dielectric breakdown than the dry oxidized sample. (C) 2003 American Vacuum Society.