Amorphous silicon oxynitride, a-SiOxNy, layers were prepared by nitridation of 7-nm thick thermally grown silicon dioxide, a-SiO2, layers on n-type crystalline Si substrates, in NH3 plasma with different temperatures (T-P = 300-500 degreesC). The compositional and structural properties for the a-SiOxNy layers were examined using current-voltage (I-V), capacitance-voltage (C-V), electron spin resonance (ESR), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy and Fourier transform infrared measurements. We found a strong correlation between the change in the ESR spin density and that in the C-V characteristics with varying T-P. These results were interpreted as indicating a change in the compressive strain. The I-V characteristics showed that the breakdown strength monotonically decreased with increasing T-P. In the distribution of the constituent atoms, the AES profiles were roughly independent of T-P. The changes in the 800 and 1070 cm(-1) IR absorption bands were also examined based on those in the compressive strain, as well as a proposal for interpreting the ESR and C-V results. (C) 2003 Elsevier Ltd. All rights reserved.