Application of Cathodic Arc Deposited Amorphous Hard Carbon Films to the Head/Disk Tribology
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Mat. Res. Soc. Symp. Proc. Vol. 517 ©1998 Materials Research Society
process of cathodic arc deposited amorphous hard carbon, describe the study of the mechanical, tribological, tribochemical, and corrosion-related properties of these films, and report on a number of applications to the head/disk interface tribology. NEW DEVELOPMENTS IN CATHODIC ARC DEPOSITION Cathodic arc deposition is based on the production of a plasma by a cathodic arc discharge on a graphite cathode in case of amorphous carbon deposition. The cathodic arc discharge is a highcurrent (typically 100-200A), low voltage (typically 20V) discharge which forms the plasma in a fast sequence of microexplosions on the cathode. The explosive character leads to a fully ionized plasma which is beneficial for the deposition since the ion energy which is the most important factor for obtaining high sp 3 content films can be easily influenced by substrate biasing. It also leads to the formation of micron-size particles (solid for graphite cathodes, liquid for metal cathodes) which can be detrimental for the film formation since the particles can be embedded in the film or cause other film defects such as pinholes. Cathodic arcs and cathodic arc deposition are described in great detail in [4]. Over the last decades research was concentrated on the optimization of the deposition conditions to form films with the highest sp 3 content and the lowest macroparticle content. It was found that the ion energy and substrate temperature are the main parameters that determine the sp3 content with a maximum value of 85% obtained at ion energies around 100 eV [5-7] and substrates at room temperature or lower [8]. While the establishment of these parameters was relatively easy, the problem of macroparticle contamination has been severe. Attempts to filter the plasma using bent magnetic fields have been successful for applications such as the deposition of high quality titanium nitride thin films, but carbon has been a problem because the particles are solid and multiply reflected from filter walls. Straight filters [9] and filters with bending angles of 20 degrees [10], 45 degrees [II], and 90 degrees [12] were tested, and only a system consisting of two connected 90 degrees filters in the shape of an "S"could produce films which are acceptable for the application to the disk drive industry [13]. This S-filter has only a low efficiency and the larger part of the plasma produced in the source is lost, but due to the high plasma production rate of the cathodic arc discharge (the ion current is about 10% of the total arc current and therefore in the order of 10 A) and the low film thicknesses required for head/disk applications the deposition rate can be in the range of 1 nm/s and sufficient for industrial applications. At the moment there are cathodic arc sources available on the market which are equipped with 45 degrees and 90 degrees filters, and it can be expected that sources with better filters will be available soon. PROPERTIES OF CATHODIC ARC AMORPHOUS HARD CARBON IN
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