Establishment of coating technology of superhard carbon nitrides films based on the measurement of the surface reaction probabilities.

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Mechanically hard amorphous carbon nitride (α-CN_x) films were prepared by applying a combination of the 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. In order to obtain the mechanical hardness, following two experiments were made.[1]The first was the deposition with suppressing temperature rise of the substrate during the application of the RF bias voltage by circulating cooling water inside the substrate stage. When the substrate was cooled, the maximum hardness of the film was 17.5 GPa under the condition of -V_<RF>=30 V, being 【approximately equal】2 times higher than that prepared without cooling. From the IR spectra of the films, three-dimensional C-N network structure was observed. This result suggested that the substrate cooling is effective for maintaining the sp^3-hybridized bonding in the films and, consequently, for suppressing the relaxation of the internal stress of the film.[2]The second experiment was the pursed operation of the RF bias voltage in the range of -V_<RF>=40-100 V. Film formation became possible in this high -V_<RF> region by this operation, although films were not formed due to severe sputtering when this voltage was applied continuously. As a result of measurement of the microhardness, it was in the case that t_<on>/t_<off>【greater than or equal】7/3 to exceed maximum hardness, 17.5 GPa, obtained by applying continuous RF bias. Hardness of the films formed under the condition of T=1000 s was higher than that formed under T=100 s. The maximum hardness of the film was 46.1 GPa, being obtained under the condition of T=1000 s, -V_<RF>=100 V, and t_<on>/t_<off>=8/2. Under the condition of t_<on>/t_<off>=9/1, the films were not deposited. Therefore, the optimum condition of t_<on>/t_<off> lies between 8/2 and 9/1