The nitrided ultrathin SiO2 films using a remote nitrogen plasma source were investigated by high-resolution x-ray photoelectron spectroscopy. At the low nitridation temperature of 500 degreesC, the nitrogen is effectively incorporated in 15 Angstrom SiO2 film. The chemical shifts of the N Is peaks show that the quantity of the second-nearest neighbors of oxygen atoms and N-O bonds influences the difference of the peak shift depending on the nitridation temperature and post-annealing in ultrahigh vacuum. The peak intensity changes of the N Is peak at the different take-off angles indicate that the nitridation dominantly occurs at the interfacial region as the nitridation temperature increases, which suggests that the highly incorporated nitrogen at the surface region can be accomplished even with a low temperature nitridation process using a remote nitrogen plasma source. The defect formation due to the nitrogen incorporation resulted in a negative shift of the capacitance-voltage curve, and the difference is increased as the nitridation temperature is elevated.