We studied two-step deposition with an O-2/He intermediate plasma treatment to improve the SiO2/Si interface characteristics. Using this method, we can minimize the plasma damage on the Si surface and improve the interface characteristics such as intermediate oxidation states, interface trap density D-it, and V-fb shift. The interface characteristics were improved with the intermediate plasma treatment after a 6 nm first oxide deposition. The number of Si atoms (N-SiOx) in the suboxide region, compared with the sample without plasma treatment, was decreased 14.7% and a sixfold ring structure became dominant. Interface trap density was decreased from 1.65 X 10(11)/eV cm(2) to 6.87 X 10(10)/eV cm(2) by the oxygen incorporation in the transition region. The moderate oxygen incorporation near the SiO2/Si interface reduced the V-fb shift due to the decrease of the fixed oxide charge.