Pulsed magnetron sputtering system with rotating graphite cathode for diamond-like carbon films deposition

Extended cylindrical magnetron sputtering system with rotating 600-mm long and 90-mm diameter graphite cathode and pulsed power supply voltage generator were developed and fabricated. Time-dependent Langmuir probe characteristics together with deposited carbon film thickness data were acquired in various positions of the probe and witness samples relatively the cathode. It was shown that ratio of ions flux to carbon atom flux for pulsed magnetron discharge mode was equal to Phi(i)/Phi(C) = 0.2 and did no depend on the discharge current in the range I-d = 10 - 60 A since both the plasma density and the film deposition rate were found approximately proportional to the discharge current. In spite of this fact carbon film structure was found to be strongly dependent on the discharge current. Grain size increased from 100 nm at I-d = 10 - 20 A to 500 nm at I-d = 40 - 60 A. To deposit fine-grained hard nanocrystalline or amorphous carbon coating current regime with I-d = 20 A was chosen. Pulsed negative substrate bias voltage (tau = 40 mus, U-b = 0.5-10 kV) synchronized with magnetron discharge pulses. Pulsed bias voltage of U-b = 3.4 kV was shown to be optimum for a hard carbon film deposition. Lower voltages were not sufficient for amorphization of a growing graphite film, while higher voltages led to excessive ion bombardment and effects of recrystalization and graphitization.