Abstract Carbon nitride films were deposited on a Si (100) wafer by an inductively coupled plasma assisted chemical vapor deposition (ICP-CVD) at room temperature. A mixture of N 2 and C 2H 2 were used as the precursor. Additional r.f. power (13.56 MHz) was applied to the substrate with various negative self bias voltages ( V self=0 to −60 V), and the effect of the substrate bias on the structure and properties of the films was investigated. The composition and chemical bonding of the films were analyzed by Raman spectroscopy, Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The surface roughness of films was investigated by atomic force microscopy (AFM). It was found that nitrogen content of films were in the range of 13.5–21.4 at.%, decreased with increasing bias voltage. As the bias voltage was increased, the deposition rate decreased due to resputtering and the substrate temperature increased as a result of the energetic ions. The film hardness increased with increasing bias voltage up to 30 GPa at −60 V. The results from Raman and XPS analyses showed that the amount of sp 3 C C or sp 3 C N bonds increased with increasing bias voltage, while the number of the C H, N H and sp 2 C N bonds decreased.