Diamond-Like-Carbon Beschichtung auf flachen Substraten mittels gepulster, plasmaunterstützter Abscheidung aus der Gasphase

Abstract

Silicon doped Diamond-Like-Carbon layers where deposited on 360x500mm chromium steel plates with a bipolar pulsed PACVD deposition process and were investigated. Up to five samples on one plate were deposited and analysed afterwards. In this respect special attention was paid to hardness, thickness of the layer, layer composition and possible changes caused by the position on the sample plate. With an installed bypass the gas was inserted from the top or the bottom of the vessel. The gas consisted of hydrogen, argon, methane, HMDSO and for some samples tetrafluoromethane. The temperature was set between 280°C and 320°C. The voltage was set up to 450V. The setting was discharged with a pulse of reversed polarity and 20 microseconds duration after 20 pulses with a length of 200 microseconds. Between pulses was always a pause of 200 microseconds. The mean deposition ratio was about 0,01µm/min and hardness values of up to 2000HV were reached. The current density was very temperature dependent and settled in between 0,6A/m2 and 2,7A/m2. The measurement of temperature showed strong variation inside the vessel but by controlling of different heat zones a temperature difference was restricted to a maximum of 5°C. The deposition ratio was mostly constant during an increment of temperature. The current density increased strongly with higher temperature and this resulted in an increase of the hardness of the layers. During a deposition process the current density decreased over time but a reduction of the ratio of negative and positive pulses could be used against this effect. In a later analysis of the layers the content of carbon, oxygen and silicone were determined and reached values of about 62% (C), 13% (O) and 24% (Si). The top and the bottom samples of the plate during the same deposition showed a gradient in silicone content. The samples at the bottom edge contained up to a total of 2% (atomic percentage) less silicone. The part of carbon was accordingly higher. This effect seems to be caused by a reduction of silicone in the gas during the gas flow, because an introduction of the gas from the other side resulted in an inversion of the effect. Doping with fluorine was achieved without problems as well. Deposition on a plate with dimensions of 360x500mm was achieved successfully as well. Defects only occurred rarely on the surface.