The X-ray reflectivity measurements were used for the analyses of the SiC and SiN thin layers. Density, roughness and the thickness were determined for searching materials. The calculations and simulations were carried out using the WinGixa software. The obtained results show that the studied layers are non-homogenous and there are consist of “sub-layers” rich in Si-C, Si-N, SI-O phases. Moreover, the presence of the main amorphous phase was observed in all searching samples.