Effects of the Ar and He dilution gas mixture ratio on the hardness of a-C:H films synthesized by atmospheric pressure plasma enhanced chemical vapor deposition

Abstract

Hydrogenated amorphous carbon (a-C:H) films synthesized by atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) possess a low hardness because of the large amount of incorporated hydrogen. To increase the hardness of these a-C:H films, detachment of the hydrogen is accomplished using Ar ion bombardment during the deposition process. Herein, a-C:H films were deposited by AP-PECVD and the effects of varying the dilution gas mixing ratio of Ar and He on the hardness of the a-C:H films were investigated. As the Ar ratio in the mixture gas increased from 0% to 20%, the hardness of the films increased from 0.8 to 2.7 GPa. Furthermore, as the Ar ratio increased, the metastable He atoms in the plasma decreased, the intensity of the CHx peaks related to the hydrogen decreased, and the surface roughness of the films increased. These results imply that Ar ion bombardment at the film surface occurred and was caused by the Penning effect of metastable He and Ar atoms. The hardness of the a-C:H films synthesized by AP-PECVD was increased by the dilution of Ar and He gases because the hydrogen content of the films was decreased via the Ar ions generated by the Ar and He mixture gases.