Formation of diamond-like carbon thin films using barrier-type surface discharge plasma under atmospheric pressure

Abstract

We studied the deposition of diamond-like carbon (DLC) thin films using barrier-type surface discharge plasma under atmospheric pressure. The main radicals generated by the barrier-type surface discharge using H2, CH4, and He as the plasma gases were Hα, Hβ, and CH. The emission intensities increased as the ratio of CH4 in the mixed gas decreased, and the mixed gas ratios of 2% CH4, 18% H2, 80% He were appropriate for the generation of the barrier-type surface discharge. The gas flow rate and applied voltage required to achieve a suitable plasma state for deposition of the DLC films varied depending on the polarity of the applied pulse. When a negative pulse is used, homogenous films can be obtained on the silicon wafer under the entire hole of the electrode; however, the deposition rate becomes very low in the range of 1.8–5.8 nm/min because the surface streamer plasma is very weak. On the other hand, using a bipolar and a positive pulse, a relatively high deposition rate in the range of 10–30 nm/min can be achieved on the silicon wafer under the central part of the electrode, although the thickness of the DLC films becomes nonuniform at the edge part of the electrode. The appropriate conditions of the DLC film deposition in this study were the pulse voltages of 6–8 kV and a gas flow rate of 1500 mL/min when using bipolar- and positive-pulse voltages. The relatively hard DLC films (6–8 GPa) were obtained under these conditions.