Investigation of Affecting Factors on the Hardness of Fluorine-Containing Amorphous Carbon Film Coated by Pulsed-Plasma Ablation

Hardness control of fluorine-containing diamondlike carbon (F-DLC) film deposited by pulsed-plasma ablation (PPA) of polytetrafluoroethylene (PTFE) was investigated. During coating, one substrate was set at a downstream position (front position) in the direction of plasma acceleration from a PTFE block, whereas another substrate was set at a side position in the direction perpendicular to the plasma acceleration from the PTFE. A typical Raman spectrum of diamondlike carbon, including D and G peaks due to sp² carbons, was observed only from the front substrate; on the other hand, such a spectrum was not clearly seen from the side substrate. The hardness of F-DLC was 5.7 GPa at the front position, whereas it was 0.4 GPa at the side position. These results indicated that the bombardment of accelerated plasma to the front substrate played an essential role to increase the film hardness. In order to further increase the hardness of F-DLC film with PPA, H₂O addition to the chamber during coating was attempted. The hardness of F-DLC was increased up to 10.4 GPa at a chamber pressure of 5 10^-4 torr obtained by H₂O addition to the base pressure less than 0.4 10^-4 torr.