Deposition of mechanically hard amorphous carbon nitride films from decomposition of BrCN. Effects of substrate cooling and pulsed rf-bias voltage

Mechanically hard amorphous carbon nitride films were formed by applying a combination of radio frequency (RF) bias voltage to the substrate and the chemical vapor deposition process using the decomposition reaction of BrCN with the microwave discharge flow of Ar. Cooling water was circulated inside the substrate stage. The maximum hardness was (17 ± 1) GPa for the film prepared under the negative RF bias voltage, −V_RF, of 30 V. This hardness was nearly twice that of the film prepared without cooling, suggesting that substrate cooling was effective for suppressing the relaxation of the internal stress of the film due to the temperature rise during the application of the RF bias voltage. Under the continuous operation of the RF bias voltage, films cannot be formed for −V_RF > 40 V because of the sputtering by the bombardment of energetic Ar⁺. Then, the RF bias voltage was applied with a pulsed operation. By using this operation films were prepared in the range of −V_RF = 40-100 V. The hardness, (36 ± 10) GPa, was obtained for the film obtained under the conditions of −V_RF = 100 V, the pulse period of 1000 s, and the pulse-on time of 800 s. The observed hardness scattered largely for the different observation points within this film; a single observation point in that film showed the maximum hardness of 46 GPa. According to the IR spectra of the films, the three-dimensional C-N network structure was developed.