Formation and properties of amorphous hydrogenated carbon films with low hydrogen concentration

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In order to determine the optimum properties of hard a-C:H films suitable for protective use in fusion wall, thermal erosion behavior of hard a-C:H films prepared by ECR plasma deposition from the mixture of CHィイD24ィエD2 and Ar were measured. When these films were heated with raising the substrate temperature under vacuum, they released Ar, large amount of HィイD22ィエD2 and slight amount of hydrocarbon but the thickness of the films did not decrease. After they were heated up to 800 ℃, almost all HィイD22ィエD2 was released and micro-Vickers-hardness of them decreased but they were still hard. Namely, heat-treatment of hard a-C:H films gives semi-hard a-C:H films with low hydrogen concentration. The addition of Ar to the source methane gas causes the films formed to have smooth surface. However, if the hardness of original hard a-C:H film is much higher than that of silicon substrate, there gives rise to many craters on the surface owing to the Ar gas effusion by heat-treatment under vacuum. The pore size of very hard a-C:H films is considered to be small enough to prevent the effusion of incorporated gasses but the effusion of gases destroy the film textures. The cleaning procedure of silicon substrate is effective to prevent the peering of films during heat-treatment. The proper hardness of a-C:H films for protective use in fusion wall is considered to be that of silicon substrate.