In structure studies performed using the Grazing Incident X-ray Diffraction Geometry (GIXD) for different incident angles it was indicated that the Si-N layers are non-homogenous and their structure depends on the penetration depth. The layers close to substrate (α = 2, 1°) show the presence of the Si3N4, SiO2, SiO2, SiC phases and an amorphous Si-N phase as well. The layers near the surface (α = 0.5; 0.25; 0.15°) are poorer in Si-N phases. There are only observed the presence of the Si3N4 and SiO2 phases. The obtained results confirm the non-homogenity of layers.