Deposition of diamond-like carbon films by a hollow cathode multi-jet rf plasma system

Diamond-like carbon (DLC) films were deposited on silicon and polycarbonate substrates with diameters up to 5 inches. Deposition temperatures and negative rf-bias were 60°C and 250–450 V, respectively. The central part of the deposition system is a novel scaleable 13.56 MHz rf hollow cathode multi-jet plasma source operating typically at 400 W and a pressure of 100 Pa. He was used as carrier gas in the primary hollow cathode discharge with a standard flow of 400 sccm. Downstream from a second gas distribution level close to the primary plasma outlet, methane (CH4) and acetylene (C2H2) serving as the carbon supply were effectively dissociated and activated. The measured maximum ion concentrations depend on the systems operation mode. When powering the substrate holder only, up to 4.7×1010 cm−3 ions were measured. Simultaneous operation of the hollow cathode plasma source and powering of the substrate holder, however, increases the ion density up to 2×1011 cm−3. As expected, high ion concentrations yield high deposition rates with 70–80 and 160–200 nm min−1 for methane and acetylene (stationary deposition mode), respectively. The DLC films were characterized by micro-Raman spectroscopy, ellipsometry and microhardness measurements. It was found that even in the stationary deposition mode, film thickness variations across a 5-inch wafer did not exceed ±3.5%. The highest deposition rate and best film quality were obtained at a substrate holder bias of −350 to −420 V. Methane-derived films showed refractive indices ranging from 2.1 to 2.3 at 632 nm and a Vickers microhardness of up to 30 GPa.