Electron spin resonance study of low-kappa insulating layers reveals that from a defect perspective these materials resemble oxygen-rich silicon dioxide matrices. The layers fabricated using porogen technology also contain a considerable amount of residual carbon in the form of clusters. Furthermore, ion sputtering damage generates additional defects provisionally identified as dangling bonds in the silicon oxycarbide clusters. The density of these defects is found to increase with increasing porosity of the low-kappa insulator. Nevertheless, a lower defect density may be attained if using a porogen-free self-assembly technology. (C) 2011 Elsevier B.V. All rights reserved.