ICMCTF2003 Session B3: CVD Coatings and Technologies

Tuesday, April 29, 2003 1:30 PM in Room Town & Country

Tuesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	B3-1 Multiscale Modeling of CVD Film Growth A. Dollet (CNRS, IMP-Perpignan, France) Understanding and modeling the mechanisms that govern film growth from the vapor phase is a very promising route towards the prediction of film microstructure and properties. Since Chemical Vapor Deposition involves a large number of complex and coupled processes over a wide range of space and time scales, a multiscale approach must be used to model the whole deposition process. In the present work, some general ideas on multiscale computer simulation of deposition processes are first given. A multiscale self-consistent modeling of 3C-SiC growth on 3C-SiC(100) substrates from C₃H₈/SiH₄/H₂ mixtures is then presented, based on a strong coupling between a macroscale transport model (reactor) and an atomic scale Kinetic Monte Carlo model (film growth). It is found that the most important depositing species are SiH₂, CH₃ and C₂H₂, and that film roughness at an atomic scale increases with increasing film thickness. The role played by the various chemical species during the early stages of growth is also enlightened. Finally, the interest of our self-consistent approach is discussed in the light of previous multiscale modeling works, mainly devoted to the growth of CVD carbon-based materials (diamond, ...).
2:10 PM		B3-3 Characterization of Chemical Vapor Deposited HfN Multilayer Coatings on Cemented Carbide Cutting Tools M.H. Staia (Central University of Venezuela); D. Bhat (University of Arkansas); E.S. Puchi-Cabrera (Universidad Central de Venezuela); J. Bost (Stellram/Metalworking Products) Hard coatings on cutting tools have been shown to provide significantly enhanced abrasive wear resistance and tool life in aggressive machining conditions. At the same time, demands for higher productivity have pushed the need for faster machining speeds, leading to tool failure due to thermal cracking. Multilayer coatings have been used extensively to address the problem of combined wear and thermal cracking behavior. Preliminary studies of various multilayer coating combinations in the machining of steels and cast irons showed that multilayer coating designs containing hafnium nitride (HfN) exhibited improved resistance to the observed failure modes. The present study was, therefore, undertaken to evaluate the tribological behavior of HfN-based multilayer-coated tools used for milling. In this paper, we report the initial results of the wear behavior of multilayer HfN coatings in the laboratory friction and wear tests at room temperature against WC as tribological pair. As part of the characterization of the mechanical properties of the coatings, Vickers microindentation tests were also carried out employing loads in the range of 0.01-10 N, in order to evaluate the composite hardness of the coating-substrate systems. Information regarding the absolute hardness of the HfN monolayer film has been obtained employing a model recently developed by one of the authors. This information is then used in order to determine the properties of the TiCN films present in the multilayer coating. It has also been found that the wear rate of multilayer HfN coatings is an order of magnitude lower than that for a single-layer coating. The results are discussed in the context of the composite hardness and the effect of multilayers on the overall wear behavior of the coatings.
2:30 PM		B3-4 Characterization of CVD Titanium Nitride Films Deposited as Diffusion Barriers for the Integration of Low-k Dielectric Methylsilsequiazane W.C. Gau, C.W. Wu (National Tsing Hua University, Taiwan, ROC); T.C. Chang (National Sun Yat-Sen University, Taiwan, ROC); P.T. Liu (National Nano Device Laboratories, Taiwan, ROC); C.J. Chu, C.H. Chen (Nanmat Technology Co., LTD., Taiwan, ROC); L.J. Chen (National Tsing Hua University, Taiwan, R.O.C.) Ti_xC_yN_z thin films are used as diffusion barriers between a copper interconnect layer and a silicon oxide dielectric. Annealing and plasma treatment, by modifying the film microstructure, was utilized to improve the film barrier property. In the present study, metal organic chemical vapor deposition (MOCVD) Ti_xC_yN_z films were deposited using tetrakis-dimethylamino-titanium (TDMAT) and NH₃ as a reaction gas at temperatures from 325 to 400°C with multi-layers Ar/ NH₃ plasma treatment. Effect of annealing and the subsequently performed Ar/NH₃ plasma treatment on the microstructure, composition, and electrical properties of these films were studied. Ti_xC_yN_z barrier films were found to be nano-crystalline. Rapidly thermal annealing and furnace annealing was found to decrease the reisitivity drastically after annealing above 500°C, by reducing the concentration of carbon and inducing the grain growth.<200> texture was found to increase. By multi-layer plasma treatment, the resistivity of Ti_xC_yN_z thin films decreased from 960 to 548 µΩ -cm and the concentration of oxygen in barrier films are also decreased. The plasma treatment can also slightly remove the organic residue and induce crystallization at the surface of the as-deposited nano-crystalline Ti_xC_yN_z films. Inter-diffusions in the Cu/CVD-TiN/SiO₂ and Cu/CVD-TiN/Methylsilsequiazane (MSZ) multilayer structures on silicon wafer after annealing in furnace at 500-800°C have also investigated. With thermal annealing in N₂ ambient for 30 min, Cu/CVD-TiN/Methylsilsequiazane (MSZ) structure was found to be metallurgically stable up to 650°C.
2:50 PM		B3-5 Thermal Stability and Tribological Properties of TiAlN/VN Nano-Scaled Multilayered Coatings D.B. Lewis, P.Eh. Hovsepian, Q. Luo, W.-D. Münz (Sheffield Hallam University, United Kingdom) Nano-scaled multilayered TiAlYN/CrN/VN coatings have been grown on stainless steel and M2 hss substrates at U_B =-85 V in an industrial, four target, Hauzer HTC 1000 coater using combined cathodic steered arc etching/unbalanced magnetron sputtering. Nano-scaled multilayered TiAlN/VN coatings exhibit at room temperature low coefficients of friction, f = 0.4 to 0.5 and low sliding wear coefficients 1.2 x 10^-17 m³ nm^-1. However, at temperatures above 630^oC the VN component in the multilayer is completely oxidised to V₂O₅ and at temperatures above 670^oC, the V₂O₅ starts to melt. High temperature ball on disk tests (Al₂O₃ ball) performed at 670^oC has shown that coefficient of friction decreases rapidly from f =0.6 to f =0.2 as a result of melting of the V₂O₅ formed in the wear track. After a short period of time, typically 60 minutes the friction coefficient, f increases to 0.8 (the value of steel) as a result of complete loss of the coating from the wear track and complete failure of the coating. In this work the elements Y and Cr have been incorporated into the TiAlN/VN based coating to avoid melting. X-ray diffraction has been used to investigate the effects of incorporation of Cr and Y on texture evolution (using texture parameter P), development of residual stress (sin²ψ method) and superlattice period whilst the phase composition of the oxides present was investigated by glancing angle XRD. The composition of the coating was determined using Energy Dispersive X-ray analysis The Cr content of the coating increases from 6 at % to 24 at % as the power on the single Cr target is increased from 2 to 9 kW and in parallel incorporation of Cr into the superlattice architecture leads to the development of a {110} texture (P=2.3), the TiAlN/VN coating deposited under the similar conditions developed a {100} texture (P=2.6). Increasing the power from the Cr target from 2 to 9 kW resulted in an increase in the intensity of the {110} texture from P = 2.3 to P = 4.6. In parallel the superlattice period increased almost linearly from 3.5 nm to 5.0 nm, whilst the Cr content of the coating increased from 6 at % to 24 at %. The residual stress varied between -4.7 GPa and -6.3 GPa. The maximum value of residual stress and Knoop hardness (HK_0.025 = 3800) was observed when the superlattice period was 4.4 nm. Incorporation of Y and Cr into TiAlN/VN coatings has resulted to a substantial improvement in the oxidation resistance of the coating, the coating still being intact at temperatures up to 800^o C. In these coatings the lower melting point V₂O₅ was not present; the major oxide phase was identified as the higher melting point CrVO₄ phase.
3:10 PM		B3-6 Diamond CVD on Fine-Grained WC-10%Co using a New Growth Regime N. Ali, G. Cabral (University of Aveiro, Portugal); W. Ahmed (Manchester Metropolitan University, United Kingdom); J. Gracio (University of Aveiro, Portugal) Generally, diamond growth onto WC-Co is difficult to accomplish. The difficulties encountered during diamond CVD are well documented. In this paper, we implement our newly developed process, known as time-modulated CVD (TMCVD), to enhance the nucleation density and the coating adhesion of diamond films deposited onto fine-grained WC-10%Co substrates. This grade of hard metal is used in manufacturing microdrills and dental tools. Generally, as the WC grain size decreases and the cobalt concentration increases, the diamond CVD process becomes more difficult. The TMCVD process pulses methane, at different flows, for modulated deposition times. This regime of film growth is different from the conventional one, where methane gas is flowed into the vacuum reactor at a constant rate throughout the entire deposition process. Our results show that the high/low methane pulses give rise to the generation of nanocrystalline diamond layers. The key feature of TMCVD is that is promotes secondary nucleation during high methane pulses. As a result of the increased number of nucleation processes occurring during TMCVD, primary and secondary nucleation, the overall nucleation density of the diamond crystallites increases significantly. Furthermore, it was found that the time-modulated films displayed better coating adhesion, mainly due to the increased mechanical interlock at the film/substrate interface. The nucleation density and the morphologies of the as-grown films were characterised using SEM. The films were characterised for adhesion using conventional Rockwell C indentation test methods. The lateral cracks appearing on both the coatings and the substrate after the indentation loadings have been discussed in some detail.
3:30 PM		B3-7 TEM Investigation of CVD Alumina Multilayers: Influence of Process Parameters on the Microstructure M. Halvarsson (Chalmers University of Technology and Goteborg University, Sweden); S. Ruppi (Seco Tools AB, Sweden) Alpha, kappa and gamma alumina can be produced by Chemical Vapour Deposition (CVD) in a reproducable way. The phase content and microstructure of the alumina layers are influenced by the process parameters and intermediate layers used. In order to make detailed investigations TEM analysis has to be used in addition to OM and SEM. However, the TEM investigations are relatively time consuming. A way to reduce time for specimen preparation is to study multilayer coatings with different process parameters in each layer. In this way, the influence of a number of process parameters and intermediate layers can be investigated in one cross section TEM specimen. The specimens will be examined using a number of techniques including SAED, CBED, EDX and HREM. Special attention will be given to the interfaces between the different layers. The aim is to relate different microstructural features, such as grain size, grain shape, defect density, grain orientations etc, to the CVD process parameters.
3:50 PM		B3-8 Titanium- and Silicon-based Ceramic Coatings by Chemical Vapor Deposition in a Fluidized Bed Reactor C. Colominas, J. Perez-Mariano (GEM-IQS, Spain); A. Sanjurjo, K.H. Lau (SRI International); S. Borros (GEM-IQS, Spain) Ceramic coatings are widely used for wear-resistant applications, like cutting-tools or engine parts. They also serve as a corrosion protection for metals, diffusion barriers in microelectronics, tribological coatings in biomaterials and coatings on glasses for decoration. The aim of this work is to study the chemical vapor deposition process in a fluidized bed reactor (FBR-CVD) applied to the obtention of ceramic coatings, in particular titanium nitride (TiN) and silicon nitride (Si₃N₄). First, thin films of silicon or titanium were obtained from a mixture of gases (Ar,H₂ and HCl) and a single bed of silicon or titanium particles, respectively. Thermodynamical calculations were performed to estimate the optimal working conditions. With this information, various deposition times and temperatures were used to tune the deposition process. The films were characterised by means of scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. The coated samples were also tested for corrosion resistance by electrochemical impedance spectroscopy and cyclic voltammetry. For the deposition of nitride layers a double regime bed was used, which consisted of an underlying fixed bed of particles -Si or Ti- and an upper fluidized bed of small-sized alumina (Al₂O₃) particles. The influence of deposition time and temperature was also studied, and the same characterization and corrosion tests than for the metal thin films were performed, together with microhardness measurements. Our results show that FBR-CVD is a suitable method to obtain metal and ceramic thin films under controlled conditions. This technique is a promising method for the synthesis of more complex multilayer coatings for specific applications.