Medium- to high-pressure plasma deposition of hydrogenated amorphous carbon films by dielectric barrier discharge

In this study, we evaluated and compared the surface roughness, structure and mechanical properties of hydrogenated amorphous carbon (a-C:H) films prepared by a CH4-dielectric barrier discharge (DBD) plasma at medium (100-500 Pa) and atmospheric (1.0x10(5) Pa) pressure. The effects of power frequency, deposition pressure and Pd value (the product of CH, pressure P, and discharge gas spacing d) on film quality were analyzed and the electrical characteristics of the discharge were discussed. The objective of this study was to explore whether hard a-C:H films with smooth surfaces can be deposited by the technique at medium and higher pressures: The quality of deposited films was mainly determined by the power frequency and Pd value. Increasing the power frequency from 50 Hz to 1.4 kHz causes an obvious increase of deposition rate and film hardness. The higher substrate temperature produced at 20 kHz power frequency leads to the transition from hard diamondlike to soft graphite-like film characteristics. The glow-like DBD plasma produced at smaller Pd value (typically 0.26 Pa.m) contributes to the formation of hard a-C:H films with smooth surfaces. The atmospheric DBD plasma at higher Pd value leads to the deposition of a soft polymer-like a-C:H film with rough surface. It appears to be difficult to prepare hard a-C:H films with smooth surfaces at higher pressure (>10(4) Pa) by reducing the gas spacing due to the formation of a large electric field in the dielectric. In this paper we also review the DBD-induced a-C:H film deposition technique.