The deposition process of carbon coating by plasma CVD was studied for the development of a high-density magnetic disk with an ultra thin overcoat of about 4nm thickness. A hot filament discharge system was installed to disk production equipment for the simultaneous deposition of a carbon thin coating on both sides of the disk. The hot filament high-density plasma, in a low-pressure atmosphere of 0.5Pa, was found to be more advantageous, compared with other CVD sources, such as radio frequency plasma, in deposition of the hard carbon thin coating on a negatively biased substrate with ion incidence to the sample. Ion impinging on the substrate was evaluated by calculating its contribution ratio, roughly, from growth rate and bias current density, then examined in relation to the hardness of the carbon thin coatings. In conclusion, hot filament plasma, as a stable CVD source, enables the deposition of the hard carbon overcoat at over 10GPa at the rate of about 1 nm/s, by generating high-density plasma in a low-pressure atmosphere.
