Recently, both electrical and material properties of lanthanum oxide (La2O3) have been found to significantly improve with a trace amount of nitrogen doping. This work conducted a detailed investigation on the nitrogen incorporation at the La2O3/Si interface by using X-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements. The process-dependent chemical bonding structures of Si, O, and La atoms at the interface were studied in detail. For samples annealed at 500 degrees C and above, the interfacial metallic La-Si bonds were converted into La-N bonds, and some Si-O bonds were found at the interface. These effects resulted in a significant reduction in the interface trap density. The bulk properties of La2O3 were also improved with the proposed technique as a result of the filling of oxygen vacancies with nitrogen atoms.