Secondary ion species from plasma-enhanced chemical vapor deposited (PECVD) SiO2 films have been investigated using time-of-light secondary ion mass spectrometry (TOF-SIMS). Comparative studies of PECVD SiO2 films prepared using a mixture of SiH4/N2O reaction gas at 400 degrees C with thermally oxidized SiO2 films grown at 900 degrees C were carried out in the mid-range mass spectra from 95 to 165 amu. Small amounts of ion species containing nitrogen atoms, including Si2O2N+, Si3O2N+ and Si3O3N+ , were detected in the SiO2 bulk from the PECVD SiO2 films. Furthermore, large amounts of Si3O2N+ and Si2O3N were found at the interface between silicon and the SiO2 films. Depth analysis showed that the intensity peak shapes of these ion species containing nitrogen atoms at the interface were closely coincident with those of Si3O3+ corrected by subtracting the influence of the SiO2 matrix. The variation in the spectra of these ion species clearly indicates that two types of structures of oxynitride exist for the PECVD SiO2 films in the SiO2 bulk films and at the interface. These are likely produced by the reaction of reactive gas with SiO2 and silicon surfaces where dangling bonds of silicon may exist in the different form. (c) 2008 Elsevier B.V. All rights reserved.