Film characteristics of thin oxynitride dielectrics grown in nitrous oxide (N2O) and nitric oxide (NO) gas ambients at 950 degrees C were investigated by secondary ion mass spectrometry, x-ray photoelectron spectroscopy, atomic force microscopy (AFM), and cross-sectional transmission electron microscopy. Compared to N2O oxynitride, NO oxynitride exhibits very different surface chemistry, interface properties, and growth phenomena. NO oxynitride has the N-int sharply peaked on the Si substrate side of the interface, while it is broad and on the dielectric side of the interface for the N2O oxynitride. The N (1s) XPS results reveal a clear distinction between N2O oxynitride and NO oxynitride. Near the Si/dielectric interface the NO oxynitride shows primarily Si=N bonds, while the N2O films showed a N (1s) binding energy peak that is in between that of Si=N bonds and Si=N-O bonds. Further, the NO oxynitride surface roughness as determined by AFM is lower than that of the Si/SiO2 interface. The film characteristics of N2O and NO oxynitrides after reoxidation in O-2 ambient are different. An anomalous increase in N-int content and a decrease in oxygen content of these oxynitrides were observed as a result of reoxidation in oxygen ambient. These results are explained on the basis of changes in matrix composition of reoxidized oxynitride films.