ICMCTF2003 Session B6: Plasma Assisted CVD, Thermochemical Treatments and Duplex Technology

Tuesday, April 29, 2003 8:30 AM in Room Town & Country

Tuesday Morning

Start	Invited?	Item
8:30 AM	Invited	B6-1 Thermochemical Treatments with Added Corrosion Protection and Wear Protection J. Crummenauer, J. Vetter (Metaplas Ionon, Germany) Numerous advantages over traditional thermochemical treatments are achieved with combinations of different traditional methods or with duplex treatments such as nitriding and hard coating. A big step towards excellent corrosion protection using plasma processes is done by the development of the IONIT OX process and plant technology. Comparing to other processes the results are superior and have led to a wide range of applications especially for series parts in the automotive industry. The IONIT technology with controlled oxidation process enabled conventional nitriding processes such as gas nitriding and gas nitrocarburizing to be combined with the plasma nitriding process for the first time ever. The patented IONIT OX process represents a combination of the following thermal processes; gas nitrocarburizing, plasma activation (plasma nitrocarburizing) and oxidation. The processes technology is explained. Comparison between IONIT OX and classical processes such as gas nitrocarburizing and oxidation and plasma nitrocarburizing and oxidation are discussed. The combination of nitriding and physical vapour deposition (PVD) - another example for the application-oriented optimisation - offers the possibility to improve the functional properties of tools and machine parts compared to single treatments. Duplex treatments have been investigated for various applications, mostly for increasing the wear resistance of tools. But also machine parts and series parts for the automotive industry are very promising candidates for the combination of plasma nitriding and PVD. Examples for thermochemical treatments with added corrosion protection and wear protection are given which demonstrate the wide range of potential applications.
9:10 AM		B6-3 Plasma Post Oxidation of Nitrocarburized Hot Work Steel Samples M. Zlatanovic (Faculty of Electrical Enigneering, Yugoslavia); N. Popovic, Z. Bogdanov (Nucelar Science Institut Vinca, Yugoslavia); S. Zlatanovic (University San Diego) A post oxidation process applied to nitrided and nitrocarburized parts made of plain carbon steel was found to be very effective against wear and corrosion of surface layer and also environmentally clean compared to some galvanic and similar surface protection techniques. An attempt was made to develop a combined plasma nitrocarburizing and plasma oxidation process that can be applied for surface treatment of hot work steel substrates. Pulse glow discharge at 5 kHz and 95% duty cycle with various content of hydrogen, nitrogen, carbon and oxygen was used in experiments to form a nitrocarburized zone with superficial oxide layer onto samples made of steel grades H11 and H13 quenched and tempered to the hardness of 49 ± 1 HRC. Nitrocarburizing was performed at 520°C followed by half an hour plasma oxidation at 500°C. The surface structures were analyzed by the optical microscopy, SEM and XRD, while Vickers microhardness test was used for measuring the surface microhardness and microhardness distribution over the samples cross section. Some samples were salt bath nitrided in an industrial equipment in which a high quality monophase epsilon zone very effective against mechanical wear was formed. Both salt bath and plasma nitrocarburized samples were post oxidized using pulse plasma processing. The XRD analyses revealed the existence of a superficial oxide layer onto epsilon underlayer beneath with traces of a γ zone in the case of plasma nitrocarburized samples. The oxygen concentration gradient at the oxide-nitride interface, the growth, structure and thickness of the oxide layer, the micropores concentrations and the type of the oxide phase (Fe₃O4, Fe₂O₃, or FeO) can be controlled by post oxidation process parameters. It was demonstrated that the ε phase with magnetite overlayer can successfully be formed onto diffusion zone of nitrocarburized hot work steel samples and industrial components in order to enhance wear and corrosion resistance.
9:30 AM		B6-4 Growth of SiO₂ Films by using Indigenously Developed TEOS-System for Microelectronics Applications A. Mahajan, L.S. Patil, D.K. Gautam (North Maharashtra University, India) The silicon dioxide (SiO₂) films have been grown by indigenously developed Plasma Enhanced Chemical Vapor Deposited (PECVD) system using liquid tetraethoxysilane (TEOS) as a source of Si instead of hazardous silane gas. The PECVD grown Silicon Dioxide (SiO₂) films found to be most useful as a final passivation layer (and also other purposes) in microelectronic applications as PECVD is the most promising low temperature (much less than the melting point of the underlying metal, Al, layer), fast deposition technique for dielectric films. Excellent thickness uniformity within the substrate and substrate-to-substrate has been observed for these SiO₂ films. We present in this paper, the effect of variation in the RF power on the properties of the deposited SiO₂ films, at constant chamber pressure of 133 Pa. However, the other process parameters like substrate temperature, TEOS bubbler temperature, inter-electrode spacing, and process time are kept at their optimized constant values of 300°C, 45°C, 7cm and 5 minutes respectively. The Ellipsometric observations (using Ellipsometer Philips SD-1000) for refractive index (R. I.), stress of the SiO₂ film and uniformities of film thickness and R I, have also been reported. The films have also been etched with standard enchants and reasonable etch rate has been observed. The effect of RF power variation on the film stress has also been studied in addition to the uniformity of R.I. and film thickness. The absorption spectra of the deposited SiO₂ films have also been taken by Fourier transform infrared (using FTIR Shimadzu-8400) spectroscopy and the spectra observed to be qualitatively same for the SiO₂ films deposited at different RF powers.
9:50 AM		B6-5 Enhanced Corrosion Resistance with Plasma Thermochemical Treatments V.H. Baggio-Scheid (Centro Tecnico Aeroespacial, Brazil); B.C. Ferreira, M.A.S. Oliveira (Instituto Tecnologico de Aeronautica, Brazil) Plasma thermochemical treatments are environmentally harmless technologies, which have been employed to improve corrosion and wear resistance, as well as to increase surface hardness and fatigue strength of engineering steels. In this work we investigate the corrosion behavior of plasma nitriding, nitrocarburizing and nitrocarburizing plus post-oxidation on AISI 1010 and 1020 mild steels. The samples were treated at temperatures varying from 673 up to 873 K. The influence of the treatment time, ranging from 10 up to 60 minutes, and gas concentration on the corrosion resistance was also investigated. The structure and phase composition were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion resistance was evaluated by salt-spray fog, electrochemical and mass loss in acid solution tests. Anodic current densities of plasma treated samples were 500-fold lower than that of galvanized samples. An improvement in the corrosion resistance was observed with increasing temperature and nitrogen concentration. However, the interesting result is that the more effective protection against corrosion was achieved in the first 15-30 minutes of treatment. Based on our results, the optimum plasma parameters towards improvements in corrosion resistance are proposed.
10:10 AM		B6-6 TaN Diffusion Barriers by Chemical-enhanced Physical Vapor Deposition (CEPVD) D.N. Ruzic, Ning Li, J.P. Allain (University of Illinois, Urbana-Champaign) Ta and TaN films deposited by physical vapor deposition (PVD) or ionized PVD (iPVD) are widely used as conducting diffusion barrier layers in ultra-large scale integrated (ULSI) devices to prevent migration of Cu into adjacent dielectrics. While PVD films lack the highly conformal sidewall coverage of chemical vapor deposition (CVD) or metalorganic CVD (MOCVD), they offer high density and low resistivity desired for optimum barrier performance. Since the parameter space of PVD is quite different from CVD, getting the best attributes of both methods is problematic. We describe a novel process called chemically-enhanced physical vapor deposition (CEPVD) that, by the addition of a proper amount of precursor in the vicinity of the substrate, has the potential to deposit films with PVD quality and CVD step coverage. A Ta target is sputtered in a magnetron system with the Ta-containing metal-organic precursor vapor, TBTDET, in combination with a reactive (N2) carrier gas and an RF-powered secondary ionization plasma. In this preliminary experiment, planar films were deposited on silicon wafers at different pressures, RF incident powers, substrate temperatures and bias voltages. The ionized metal deposition conveys significant energy to the surface through bombardment, promoting film adhesion and generating films of stable crystallographic orientation. In addition the ion bombardment enhances the impurity volatilization and reduces the substrate temperature needed for chemical decomposition. Deposition rate and ionization fraction are measured using a gridded energy analyzer and a quartz crystal microbalance (QCM). Surface morphology are visualized using SEM and AFM; film composition and microstructure are characterized by XPS and XRD, respectively. Resistivity is evaluated by a four-point probe. Extension of the method to patterned structures is also discussed.
10:30 AM	Invited	B6-7 Characterization of Industrial Scale Cascade Arc Assisted CVD Technology V. Gorokhovsky (Arcomac Surface Engineering, LLC.) Cascade arc plasma assisted CVD (CACVD) technology is based on an innovative reactor design which utilizes the properties of a linear-arc plasma column¹. While operating in the same pressure ranging from 10 Pa up to atmospheric pressure, the CACVD reactor overcomes the disadvantages of conventional Arc Torch CVD reactors by creating a homogeneous, concentrated plasma column in a cylindrical or rectangular reaction chamber with a length of 1 m or more. In a high temperature CACVD process the temperature of substrates is affected by the balance between energy flow from the plasma column, radiative losses and heat removal through cooling of the substrate holders and reactor wall. The voltage- current characteristics of Ar-H₂-CH₄ cascade arc in relation to thermal balance of substrates to be coated and deposition rate of polycrystalline diamond coatings will be discussed. Direct measurements of the substrate temperature vs. incoming energy flow from arc plasma allow to estimate the thermal balance of the substrates. Composite powder variable conductance insulation has been developed to control substrate temperature during deposition of polycrystalline diamond coatings in CACVD reactor. Approximately 1000 cylindrical substrates 2 mm dia x 20 mm long can be mounted and coated simultaneously in the industrial tubular CACVD reactor with 1m long reaction zone. The morphology and composition of CVD diamond coatings were assessed using Micro-Raman spectroscopy and scanning electron microscopy. A comparison of characteristics of films deposited on Mo, W, and stainless steel substrates is also presented. Another application of CACVD technology are coatings deposited on substrates suspended in the arc plasma, e.g. tungsten on synthetic diamond powder. The characterization of tungsten coated diamond powders will be discussed. ¹V.Gorokhovsky, U.S.Patent No. 5,587,207.
11:10 AM		B6-9 Design and Test of Duplex Coatings J.-D. Kamminga, R. Hoy (Netherlands Institute for Metals Research, The Netherlands); G.C.A.M. Janssen (Delft University of Technology, The Netherlands) The optimum coated tool for a given application, combines good properties of coating and substrate. In order to design such a tool, knowledge of the separate contributions of coating and substrate properties to the performance of the tool is essential. Different properties are important for the coating and the substrate. In sliding contacts for example, the hard coating provides a low friction coefficient and good abrasive wear properties, whereas for the substrate a high load carrying capacity is required. Duplex coatings consisting of a surface hardened steel substrate covered with a hard ceramic coating, combine low friction, good abrasive wear resistance and high load carrying capacity. In previous work duplex coatings consisting of a nitrided steel substrate covered with a sputter deposited CrN layer deposited in a single step process, without intermediate polishing treatment, have been discussed. Good adhesion of CrN layer on the nitrided steel substrate was obtained, and both the scratch and impact wear resistance proved to be very well¹. The present work concerns series of duplex coatings deposited using different nitriding conditions with on top a CrN layer that was the same for all specimens. The scratch test, which provides a suitable model system for specimens in sliding contact, has been used to investigate the mechanical properties of the duplex coatings. The performance of the duplex coatings is discussed in view of the stress field induced by the scratch tip and the coating and substrate properties/microstructures. The optimisation of the properties of coating and substrate for optimum performance in a given application is discussed. ¹Presented at the 8^th Int. Conf. on Plasma Surface Engineering (PSE 2002) Garmisch-Partenkirchen, and submitted to Surface and Coatings Technology.
11:30 AM		B6-10 Microstructures and Tribological Behaviours of Plasma Nitrided and Nitrocarburized Aisi 5140 Steel A. Alsaran, M. Karakan, F. Bulbul, Ayhan Celik, I. Efeoglu (Ataturk University, Turkey) The structural, mechanical and tribological properties of plasma nitrided and nitrocarburized AISI 5140 steel were characterized using X-Ray diffraction, SEM, microhardness tester and pin-on-disk tribotester. It was observed that the compound layer thickness and surface roughness obtained after plasma nitrocarburizing are higher than that of plasma nitriding. The thick compound layer decreased friction coefficient. However, it was found that the brittle compound layer caused an increasing wear rate due to the fracture of the compound layer with hard abrasive particles formation during wear.
11:50 AM		B6-11 Characterization of Large-area CVD Diamond Wafers Deposited by the Single-cathode DC PACVD Process W.-S. Lee, Y.-J. Baik (Korea Institute of Science and Technology, Korea); K.-W. Chae (Precision Diamond Tech. Inc., Korea) The free-standing diamond wafers were fabricated by the single-cathode DC PACVD with the diode type electrode configuration. The wafers with various diameters ranging from 5 inch to 8 inch were fabricated and characterized. Methane-hydrogen gas mixture was used as the precursor gas. The methane content in hydrogen was 3~9% by volume. The chamber pressure was 100~130 torr. The averaged substrate temperature was varied within the range of 1100~1250°C as measured by the optical pyrometer. The power density was around 0.3~0.4kW/cm². The averaged thickness of the wafers were in the range of 500~1000µm. The characterization was focused on the wafer-scale uniformity. The thermal property was characterized by the converging thermal wave technique. The crystal quality was analyzed by the macro-Raman spectroscopy. The thickness was measured by the thickness gauge. The surface microstructures were analyzed by SEM. At the optimized deposition conditions, the deviation of thickness and the thermal conductivity could be reduced below 10% of the respective averaged values.The distribution of FWHM of Raman diamond peak over the wafer surface also showed excellent uniformity.