We investigated defect generation in silicon carbon nitride (SiCN) dielectric films subjected to ultraviolet (UV) lights with two different photon energies at room temperature using electron spin resonance (ESR) and electrical measurements. A buildup of negative charge occurred and paramagnetic defects were generated by exposing the SiCN films to 4.9-eV UV illumination. However, a photon energy of 3.4 eV was insufficient to generate the negative charge and paramagnetic defects. The characteristics of the UV-induced ESR signals suggest that the generated paramagnetic defects are neutral silicon dangling bond centers. On the other hand, in the SiCN-SiO(2) stacked film subjected to 4.9-eV UV illumination, no net negative charge accumulated although a large number of paramagnetic defects were generated. This indicates that the generation of paramagnetic defects and the buildup of negative charge are based on different mechanisms. We discussed a consistent picture to explain these phenomena. (C) 2009 Elsevier B.V. All rights reserved.