Deposition of Diamond-Like Carbon Film and Mass Spectrometry Measurement in CH4/O2 RF Plasma

Abstract

The deposition of diamondlike carbon (DLC) film and the measurements of ionic species by means of mass spectrometry were carried out in a CH4/N2 RF (13.56 MHz) plasma at 0.1 Torr. The film deposition rate greatly depended on both CH4/N2 composition ratio and RF power input. It was decreased monotonically as CH4 content decreased in the plasma and then rapidly diminished to negligible amounts at a critical CH4 content, which became large for higher RF power. The rate increased with increasing RF power, reaching a maximum value in 40% CH4 plasma. The predominant ionic products in CH4/N2 plasma were NH+ 4 and CH4N+ ions, which were produced by reactions of hydrocarbon ions, such as CH+ 3, CH+ 2, CH+ 5, and C2H+ 5 with NH3 molecules in the plasma. It was speculated that the production of NH+ 4 ion induced the decrease of C2H+ 5 ion density in the plasma, which caused a reduction in higher hydrocarbon ions densities and, accordingly, in film deposition rate. The N+ 2 ion sputtering also plays a major role in a reduction of film deposition rate for relatively large RF powers. The incorporation of nitrogen atoms into the bonding network of the DLC film deposited was greatly suppressed at present gas pressure conditions.