Ultrathin SiON films with different nitrogen profiles grown by the plasma-enhanced CVD method and the rapid thermal nitridation (RTN) of SiO2 with an NO gas have been analyzed by high-resolution angle-resolved photoelectron spectroscopy using bright synchrotron radiation to investigate interfacial chemistry and in-depth distribution of nitrogen atoms based on the second nearest nei-hbor effect of N 1s chemical shift. It is found that the CVD-deposited SiON film has a three-layer structure consisting of homogeneously-distributed N atoms in the [Si-Si3-xNx](3)N chemical state, N atoms in the (Si-Si-3-O-x(x))(3)N chemical state of about two monolayers, and the top SiO2 layer. In contrast, N atoms in the NO-RTN SiON film exist at the SiON/Si interface as a double layer consisting of the [Si-Si3-xNx](3)N lower layer and the (Si-Si3-xO3)(3)N upper layer with the concentration of 3.9 x 10(14) and 1.7 x 10(14) cm(-2), respectively, based on the N 1s chemical shift of about 0.6 eV. (C) 2003 Elsevier Science B.V. All rights reserved.