Oxynitride films grown on preoxidized (100) silicon surfaces in a nitric oxide (NO) ambient at 950 °C have been investigated using x‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), and cross‐sectional transmission electron microscopy (XTEM). Compared to N2O oxynitride, NO oxynitride exhibits very different surface chemistry, interface properties, and growth mechanisms. The etch back of NO and N2O oxynitride films allows control of sample thickness for the XPS measurements. NO oxynitride has the interfacial nitrogen (Nint) 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 Si2=N—O bonds. Furthermore, the NO oxynitride surface roughness as determined by AFM is lower than that of the Si/SiO2 interface. © 1995 American Institute of Physics.