Amorphous hydrogenated silicon carbide (a-SiC:H) thin films were treated in a capacity coupled r.f. discharge plasma jet working in nitrogen. The samples, with a carbon content in the range of 30%-50%, were deposited onto Si(100) wafers by plasma enhanced chemical vapor deposition. The capacity coupled r.f. discharge (less than 100 W) is generated in flowing nitrogen or ammonia in a small distance (1-2 mm) gap, at medium pressure (3-25 torr). The gap is limited by a planar (40 mm diameter) electrode and a nozzle (1-2 mm) opening. Plasma expands as a bright nitrogen plasma jet in a larger vacuumed vessel. The sample’s holder (which can be heated) was placed downstream the nozzle at several centimeters distance, being exposed to the plasma beam. In this way the samples (a-SiC:H) were irradiated. Various techniques, such as X-ray diffraction, X-ray photoelectron spectroscopy, Fourier infrared transmission spectroscopy measurements, spectroscopic ellipsometry and microhardness measurements were used to characterize the induced composition evolution towards Si-C-N (SiC-SiN-CN) mixtures.