Si/SiH/CNx and Si/SiC/CNx film structures have been obtained in a two step procedure: a-Si:H and a-SiC:H thin films have been deposited by PECVD from CH4/SiH4 precursors; CNx films have been prepared by exposing the previous obtained samples to a RF plasma beam discharge generated in nitrogen with graphite electrodes. Several samples were submitted to KrF laser irradiation and treated at various incident laser fluences. The samples have been investigated by in depth X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Chemical and structural modifications are induced by the treatments. The promotion of Si-C bonds and the build-up of an intermediate SiCN layer at the a-Si:H/CNx and a-SiC:H/CNx interfaces are proven.