Diamond-like carbon film deposition by a 13.56 MHz hollow cathode RF-RF system using different precursor gases

Diamond-like carbon films (DLC) were deposited in a novel 13.56 MHz RF-RF system (Plasma Consult GmbH PlasCon HCD-System) at a substrate temperature of 60 degreesC. Typically, a radiofrequency (RF) power of 400 W was used for plasma generation by a hollow cathode discharge plasma source (HCD). The substrate holder was also RF powered and had a negative DC self bias voltage in the range of 200-600 V. Both HCD and the RF-substrate holder are run with synchronized RF-power generators and automated impedance matching units. The carrier gas He was introduced into the primary hollow cathode discharge at a flow rate of typical 400 seem. Methane and acetylene were used as a carbon source at flow rates between 15 and 100 seem. An ion concentration of up to 2 X 10(11) cm(-3) was measured in the plasma with a HCD and RF bias on. Without the HCD an ion concentration of approximately 5 X 10(10) cm(-3) was achieved. Higher ion concentration had a positive influence on the deposition process and allowed to achieve a higher deposition rate. In the stationary mode deposition rates of 70-80 nm min(-1) with methane as a precursor gas and 180-260 mn min(-1) with acetylene as a precursor gas were measured. The films were investigated by micro-Raman spectroscopy, FTIR, ellipsometry and microhardness measurements. It was found that even in the stationary mode deposition the film thickness variations across a 5" Si-wafer were lower than +/-3.5%. The acetylene based DLC films have a refractive index of 2.1-2.15 at wavelength of 632 mn. The refractive index of DLC films, deposited with methane as a precursor, was between 2.2 and 2.3. Vickers microhardness of these films of up to 30 GPa were achieved. (C) 2001 Elsevier Science B.V. All rights reserved.