Synthesis of Ultrathin Ta-C Films by Twist-Filtered Cathodic Arc Carbon Plasmas
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Synthesis of Ultrathin ta-C Films by Twist-Filtered Cathodic Arc Carbon Plasmas André Anders1 and Ashok V. Kulkarni2 Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 2 Read-Rite Corporation, 44100 Osgood Road, Fremont, California 94539 1
ABSTRACT The application of cathodic-arc-deposited films has been very slow due to the infamous macroparticle problem. We report about the application of the open Twist Filter as the key component to an advanced filtered cathodic arc system. Ultrathin tetrahedral amorphous carbon (ta-C) films have been deposited on 6 inch wafers. Film properties have been investigated with respect to application in the magnetic data storage industry. Films can be deposited in a reproducible manner where film thickness control relies on arc pulse counting once deposition rates have been calibrated. Films of 3 nm thickness have been deposited that passed acid and Battelle corrosion tests. Monte Carlo Simulation of energetic carbon deposition shows the formation of an intermixed transition layer of about 1 nm. The simulation indicates that because the displacement energy of carbon is not smaller than of magnetic materials, films thinner than 2 nm are either not high in sp3 content or represent a carbidic phase. INTRODUCTION Diamondlike films are characterized by an outstanding combination of advantageous properties: they can be very hard, tough, super-smooth, chemically inert, well adherent to the substrate, and compatible with lubricants. They can be deposited fast, efficiently, at low cost, and on room temperature substrates. The various deposition methods result in a variety of diamondlike films. Widely used is hydrogenated diamondlike carbon (DLC or a-C:H), nitrogendoped amorphous carbon (a-C:N) or amorphous carbon nitride (CNx) [1-3], hydrogenated carbon nitride (CHxNy), non-hydrogenated amorphous carbon (a-C), silicon-doped amorphous carbon (a-C:Si) or silicon carbide (SiC) [4], and metal-doped amorphous carbon (a-C:Me) [5]. Amorphous carbon films (a-C) often have a very high percentage of tetrahedral (sp3) bonding and therefore they are referred to as tetrahedral amorphous carbon (ta-C). Ultrathin (< 5 nm) hard carbon films are being used as protective overcoats on hard disks and read-write heads. The tribological properties of the head-disk interface are not only mechanical but also chemical in nature: the overcoat is required to protect the magnetic layer against wear and corrosion [6, 7]. As the areal density (of information stored) increases at a breathtaking rate of about 100% per year [8], the “magnetic spacing” between the magnetic layer of the disk and read/write sensor of the head must decrease. The magnetic spacing includes magnetically dead layers, carbon overcoats, lubrication, pole tip recession, and the fly height. Thinner overcoats allow the head to be closer to the disk, and hence, the size of individual bits to be smaller. Areal densities of 70 Gbit/in2 have recently been demonstrated in the laboratory, and the industry is working towa
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