The authors synthesized carbon nitride films on chromium steel substrate under various conditions by unbalanced magnetron sputtering method. As a result of changing the flow rate of N2 gas and Ar gas during deposition, it was found that the film thickness and the amount of nitrogen inside the film increased with the increase in nitrogen gas. Further, in the plasma during synthesis, an increase in CN emitting species could be also confirmed by the increase in gas flow rate. In addition, when the substrate bias voltage was-100 V or less, it was found that the film thickness decreased and the chemical bonding state changed, but the hardness of the film was constant at 10 to 15 GPa. However, when the substrate bias voltage was not applied, the film hardness was constant at 6 to 10 GPa. The nitrogen concentration in the films was 25atom% at the maximum. As a result of a friction test, the friction coefficient of a carbon nitride film was equal to or less than that of a DLC film under machine oil condition.

Carbon nitride films are anticipated for application as hard films in various fields. The authors synthesized a carbon nitride film using unbalanced magnetron sputtering (UBM) while changing the pulse period of sputtering and negative bias voltage. Both the pulse period and the substrate bias voltage affect the synthesized carbon nitride films' surface morphology. At all negative bias voltages, the film thickness decreases in the pulse period of 40-65 μs, but it increases at pulse periods of 65 μs or more. The sputtering rate is considered to decrease because carbon nitride is generated on the carbon target surface in pulse periods of 40-65 μs. The film hardness is influenced strongly by the substrate negative bias voltage. It becomes higher as the substrate negative bias voltage is lower. The substrate bias voltage and the pulse period also influence the N/C concentration ratio, the chemical bonding state, and the film structure of the carbon nitride films. These results are thought to be attributable to changes in the deposition process caused by application of negative bias voltage and sputtering of carbon nitride formed on the carbon target.