Two-step deposition using O-2/He or N-2/He intermediate plasma treatment was studied to improve the characteristics of SiO2/Si interfaces. Under this method plasma damage on the Si surface could be minimized and the interface characteristics such as intermediate oxidation states, causing P-b center, and V-fb shift could be improved. In the case of the intermediate plasma treatment on 6 nm 1st oxide. the improvement of the interface characteristics was best. N-2/He plasma intermediate treatment showed better interface characteristics than O-2/He plasma treatment. The number of Si atoms (N-SiOx) in the sub-oxide region was decreased by approximately 27% after N-2/He plasma intermediate treatment compared with the sample without plasma treatment. Also, the transition layer thickness was decreased to 1.34 monolayers. P-b center density decreased from 4.7 X 10(12)/eV cm(2) to 2.29 X 10(11)/eV cm(2) due to nitrogen incorporation in the transition region. The moderate nitrogen incorporation near the SiO2/Si interface reduced the V-fb shift due to the decrease in the fixed oxide charge.