Protective carbon films deposited by dc-bias facing targets sputtering with microscopic ultraflatness and strong sp3 coordination

Abstract

Carbon thin films were deposited on hard disks as protective layers by facing targets sputtering (FTS), and their characteristics were evaluated to determine whether they would be suitable protective layers for thin-film magnetic recording media. The performance and lifetime of a hard disk drive (HDD) are intimately related to the head-disk interface. Increase in performance due to reduction of the flying height and magnetic spacing, and longer product lifetime are related to the properties of protective layers covering the surfaces of hard disks. Currently, such layers are generally sputtered amorphous carbon films, whose characteristics are strongly dependent on various sputtering conditions such as the argon gas pressure, substrate temperature, and dc and rf bias voltages. In this study, the dependence of the characteristics of carbon films on the dc bias voltage of the FTS was investigated, and the characteristics were also compared with those obtained without a dc bias voltage supply. The carbon films were deposited at an argon gas pressure of 0.2 mTorr and a substrate temperature of 25 °C as room temperature, with several dc bias voltages and also without any bias voltage. There have been no reports to date of the successful use of such low gas pressures to realize excellent protective layers. The properties of the films were characterized by Raman spectroscopy, and the results were compared with previously reported ones obtained in different sputtering conditions at high argon pressures. Carbon films deposited, without plasma damage, by FTS, with dc bias voltage at argon gas pressures as low as 0.2 mTorr, showed a large population of sp3 coordination, columnless morphology, and a microscopically flat surface. These are better properties than those obtained with no dc bias voltage, and may lead to an intrinsically excellent protective layer for hard disks.