Papers

AVS1997 Session TF+VM-TuA: Hard Coatings - II

Tuesday, October 21, 1997 2:00 PM in Room B3/4

Tuesday Afternoon

Start	Invited?	Item
2:00 PM		TF+VM-TuA-1 Amorphous Hydrogenated Carbon Nitride Films Deposited via an Expanding Thermal Plasma at High Growth Rates A. de Graaf, J.L. Longueville, M.C.M. van de Sanden, D.C. Schram (Eindhoven University of Technology, The Netherlands); E.H.A. Dekempeneer (VITO, Belgium) An expanding thermal plasma of argon and nitrogen in which acetylene is injected, was used to deposit amorphous hydrogenated carbon nitride (a-C:N:H) films. Without an external bias high growth rates (up to 37 nm/s) were achieved on both glass and silicon samples. The growth rate and refractive index of the films were studied in situ with HeNe-ellipsometry. The growth rate increases with increasing acetylene flow and does not show a distinct dependence on the nitrogen flow. The refractive index of the a-C:N:H films is lower than for a-C:H films deposited under the same conditions, but without addition of nitrogen. Fourier transform infrared (FTIR) absorption spectroscopy was used to investigate the different C-N bondings. The infrared absorption of the stretching mode of the C triple bond with N (at 2216 cm^-1) shows an increase with increasing nitrogen concentration in the plasma, indicating an increase in polymerisation. Evaluation of the chemical composition was achieved by Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA). The amount of nitrogen in the film decreases with an increasing hydrogen content in the film. This suggests that nitrogen and hydrogen are in competition during formation of the film. The microhardness and Young's modulus were determined by nano-indentation measurements. The hardness lies in the range 1.95-9.41 GPa, whereas the Young's modulus varies from 54.2 to 94.0 GPa. Both quantities show a strong increase with increasing acetylene flow, and a decrease on addition of nitrogen. This is attributed to the increasing polymerisation of the film with increasing nitrogen incorporation.
2:20 PM		TF+VM-TuA-2 Effect of Substrate Biasing on the Properties and Stuctures of Hydrogen-free Amorphous Carbon Thin Films by Rf Magnetron Sputtering J.-Y. Kim (Seoul National University, Korea); H.M. Cho, H.K. Yang, J.C. Park (Korea Electronics Technology Institute, Korea); Y.J. Kim (Kyonggi University, Korea); H.J. Kim (Seoul National University, Korea) Amorphous carbon films have been widely investigated for various applications including protective coating on magnetic and optical disks and wear-resistant coating on mechanical parts, because of their unique properties such as high hardness, good wear resistance, excellent chemical inertness, high electrical resistance, lack of magnetic response, and optical transparency in the infrared region. The physical properties and bonding structures of amorphous carbon films are known to be changed with their deposition methods and process conditions. Low substrate temperature and the existence of high energy carbon species are known to be essential for the deposition of high quality tetrahedral amorphous carbon f ilms. Therefore, in sputtering system they can be deposited at room temperature only by biasing of substrate, which is able to produce energetic ions. But in case of dc substrate biasing, the bias effect decreases with sputtering time because the film deposited on substrate has high electrical resistivity. High quality thick amorphous carbon films can be more easily obtained by rf substrate biasing, but rf substrate biasing effect on the properties of amorphous carbon films have not been systematically studied yet. In this study, amorphous carbon thin films were deposited on Si(100) and Corning 7059 glass using graphite target by an r.f. magnetron sputtering system. D.c. or r.f. bias was applied to the substrate during deposition. Dependence of the film properties and structures on deposition conditions, especially applied substrate bias, was investigated. The hardness, resistivity and intrinsic stress of carbon films increased with a bias voltage, whereas their surface roughness was rather improved. The sp²/sp³ bonding ratio of the films was also affected by the applied bias.
2:40 PM		TF+VM-TuA-3 Growth of CN_x Multilayers by Unbalanced Dual Cathode Reactive Magnetron Sputtering from C and B₄C Targets T. Berlind, M.P. Johansson, N. Hellgren, L. Hultman, J.-E. Sundgren (Linkoping University, Sweden) A newly developed controllably unbalanced dual cathode reactive magnetron sputtering system have been used for deposition of CN_x/BN:C multilayers from C (graphite) and B₄C targets. The two 3 inch magnetrons were unbalanced of type II and were designed to have opposing magnetic poles. An additional magnetic field in the vicinity of the substrate, from an in-situ magnetic coil, was applied supporting the outer poles of the magnetron with B₄C target during its deposition time. Previous studies have shown that magnetron sputtered CN (30 at% N) and BN:C (10 at% C) films can be made very hard and at the same time highly elastic. The application of multilayer structures of these materials lends additional possibilities for the tayloring of mechanical properties. Deposition conditions for a given mechanical properties condition, however, are known to be different for CN_x and BN:C. In this study, CN_x/BN:C multilayers were deposited in an Ar/N₂ discharge. Prior to deposition of multilayers, homogeneous CN_x and BN:C films were grown in order to optimize the deposition process. It was found that CN_x and BN:C layers could be deposited sequentially in a fixed gas mixture of 60% Ar and 40% N₂, substrate temperatures of 300 C and substrates held at floating potential (8-12 V and 25-28 V, respectively). Operation of the magnetic coil during growth of BN:C layers resulted in a 5-fold increase of the ion-flux for growth as compared to CN_x layers. Based on these results, CN_x/BN multilayers were deposited with a range of periodicities from 2.5 nm to 10 nm with a total film thickness of 0.5 µm on Si (001) and cemented carbide substrates. As-deposited films were analysed with respect to its structure, composition, and mechanical properties by TEM, AES, XRD, and nanoindentation studies. Films exhibited elastic recoveries of 80-90% (10 mN load). Low-angle XRD of the 10-nm-period multilayer showed 2-order satellite reflections.
3:00 PM		TF+VM-TuA-4 Synthesis and Characterization of CN_x/TiB₂ Multilayers M.L. Wu, Y.W. Chung, M.S. Wong (Northwestern University); W.D. Sproul (Sputtered Films, Inc.) We demonstrated in previous studies that it is possible to stabilize the formation of some crystalline carbon-nitrogen phase by using TiN(111) or ZrN(111) as the growth template. In this talk, we will provide additional evidence from electron diffraction and electron energy loss spectroscopy that this crystalline carbon-nitrogen phase is likely beta-C₃N₄. The maximum hardness of these multilayer coatings is in the 50 GPa regime. The hardness can be improved further by using TiB₂ (0001) as the growth template for two reasons. First, TiB₂ (0001) is lattice-matched to beta-C₃N₄ (0001). Second, TiB₂ is about twice as hard as ZrN (40 vs 20 GPa), when deposited under proper substrate bias and working pressure conditions. This talk presents some preliminary results demonstrating the high hardness of this new CN_x /TiB₂ multilayer system when deposited under ambient substrate temperatures.
3:20 PM		TF+VM-TuA-5 Properties and Microstructure of DLC/DLC:Me Multilayers Prepared by Cathodic Arc Deposition M.P. Delplancke-Ogletree (Universite Libre de Bruxelles, Belgium); O.R. Monteiro (Lawrence Berkeley National Lab & Univ. of California, Berkeley) The great interest in the use of amorphous C-films as a coating material for a variety of applications is justified by the superior wear resistance and hardness, chemical stability, and very low friction coefficient characteristics of these coatings. Unfortunately DLC films have high levels of internal stresses originated during the growth process, and the stress is directly correlated with the hardness. We try to reduce the internal stresses while conserving the good surface mechanical properties of the DLC films by preparing multilayers. We have used cathodic arc deposition to prepare DLC/DLC:Me, where Me is a refractory metal. During the deposition, a repetitively pulsed bias voltage was applied to the substrate in order to improve the adhesion to the substrate and between the individual layers. Multilayers with different periodicities were synthesized and the nature of the metal was varied. These multilayers were characterized in terms of fundamental properties (chemistry and microstructure) and functional properties (hardness, and friction coefficients).
3:40 PM		TF+VM-TuA-6 A Study of the Chemical Structure of Carbon Nitride Thin Films B.C. Holloway, M.A. Kelly, P. Pianetta (Stanford University); D.K. Shuh (Lawrence Berkeley National Laboratory); S. Hagstrom (Stanford University) Carbon nitride thin films have been deposited with a magnetron sputter system. In-vacuo and ex-situ Near Edge X-ray Absorption Fine Structure (NEXAFS) measurements show that the films have predominately sp and sp² bonding, with little sp³ bonding present. Ex-situ X-ray Photoelectron Spectroscopy (XPS) results show that there are multiple bonding states for both the carbon and nitrogen; however, it will be demonstrated that XPS is not a sufficient means of identifying sp³ to sp² bonding ratios. Nanoindentation results suggest that the films are extremely elastic, and that traditional means of calculating hardness and Young's modulus are not applicable. Parametric studies of the changes in the mechanical properties and chemical structure with variations of the substrate temperature and chamber pressure will also be presented.
4:00 PM		TF+VM-TuA-7 Synthesis and Mechanical Properties of Ultra-Thin Carbon Nitride Films B. Zhou (Northwestern University); W.C. Chan (Hong Kong City University); Y.W. Chung (Northwestern University) Carbon nitride films with thickness in the 3-4 nm range are being explored as overcoats for future hard disk systems. Using a single-cathode magnetron sputtering system, we explore the hardness, surface roughness and lubricant-wetting properties of carbon nitride thin films as a function of process parameters (substrate bias, magnetron power density, working pressure and nitrogen partial pressure). The possible existence of pinholes was explored using several techniques, including Auger electron spectroscopy, corrosion current and capacitance measurements.