2nd-derivative Auger electron spectra analyses and time-of-flight secondary ion mass spectroscopy depth profiles are employed for analyzing quantitatively chemical compositions in ultra-thin oxide-nitride-oxide (ONO) stacked films. Tunnel oxide of 2.3 nm is grown on silicon substrate in nitrogen-diluted oxygen ambient. Nitride of 5.7 nin is immediately deposited on the tunnel oxide by a low-pressure chemical vapor deposition. Blocking oxide is subsequently grown by oxidizing the oxide-nitride structure in a wet 02 ambient. Some chemical mixing occurs during the ONO formation. That is, the tunnel oxide formed on the silicon substrate changes into SiO1.11N0.67 by nitrogen substitution. Oxygen diffuses into the nitride layer, and converts some of the nitride layer into SiO1.11N0.67 during wet oxidation. We think the SiON and Si2NO species exist near the tunnel oxide-nitride and the nitride-blocking oxide interfaces are segments of the Si2N2O. These are evidence of dangling bonds as unstable chemical species which may act as charge traps in the oxide-nitride interfaces. (C) 2007 Elsevier B.V. All rights reserved.