Deposition of high-durability protective layers with a composite structure of DLC and GLC by facing-targets sputtering

An amorphous carbon film is currently used for the protective layer for overcoating the surface of the recording layer of a hard disk. In this study, the film was deposited by faring-targets sputtering (FTS), which can discharge at a lower argon gas pressure than other sputtering, such as dc magnetron sputtering, because the plasma is sufficiently confined by a magnetic field applied perpendicular to both of the target planes. As a result, the layers can be deposited without plasma damage. Thus, very smooth and uniform thin films can be obtained. The dependence of the structure and properties of carbon layers on various sputtering conditions such as the argon gas pressure, dc and rf bias voltages, and substrate temperature at room temperature, compared with the previous report, was investigated when layers with a thickness of 500 Å were deposited by FTS on glass and Al/Ni-P substrates. The surface appearances of the layers were observed by FE-SEM, and their structures were characterized by Raman spectroscopy. All the carbon films in this study revealed both diamondlike carbon (DLC: D) and graphitelike carbon (GLC: G) structures. The ratio of the integral intensity of the D peak to that of the G peak, I(D)/I(G), was measured by Raman spectroscopy. As a result, it was found that the ratio I(D)/I(G) was significantly dependent on the sputtering conditions and was well correlated with the surface appearance. The films with very low surface roughness had I(D)/I(G) ratios in the range of 196-1.99. This seems to indicate that the fine DLC grains are isolated and distributed with almost equal spacing in the homogeneous GLC matrix, occupying twice the area of the GLC structure. The films appear to have a composite structure of strong DLC and GLC