Papers

ICMCTF2002 Session B2-1: CVD Hard Coatings and Technologies

Wednesday, April 24, 2002 1:30 PM in Room Golden West

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		B2-1-1 Carbon Nanotubes by Chemical Vapor Deposition M. Meyyappan (NASA Ames Research Center) Carbon nanotubes(CNTs) have been receiving much attention recently due to their unique electronic and extraordinary mecahnical propoerties. Chemical vapor deposition(CVD) is emerging as a viable technique to grow CNTs on patterned substrates for applications in nanoelectronics and sensor development. The growth is promoted by transition metal catalysts at temperatures above 700°C. Typically a hydrocarbon feedstock is used to grow nanotubes at atmospheric pressure. In this presentation, results will be presented for growth of single-walled and multi-walled nanotubes as a function of temperature, flow rates and catalyst preparation procedures. Characterization resuts using SEM, HRTEM, Raman spectroscopy and EDX will be presented. Currently understanding of the growth phenomena is lacking. Complementary modeling and diagnostics will also be discussed to understand the species responsible for growth. We have recently investigated a plasma procedure also to grow CNTs which produces vertically-aligned nanotubes. A brief discussion on applications will also be provided.
2:10 PM		B2-1-3 Doped CVD Al₂O₃ Coatings for High Performance Cutting Tools M. Kathrein, W. Schintlmeister, W. Wallgram, U. Schleinkofer (Plansee Tizit AG, Reutte, Austria) Today, high performance applications of cemented carbide cutting tool inserts demand coatings with enhanced wear resistance. Chemical vapour deposited (CVD) coatings based on Ti(C,N) and Al₂O₃ are the systems of choice for these applications. The influence of experimental variables on process stability and Al₂O₃ modification and structure was investigated. General deposition characteristics of Al₂O₃ as a function of doping combinations, generated by additional gases (TiCl₄, BCl₃, H₂S), and deposition temperature are reported. The Al₂O₃ coatings were deposited in the temperature range of 930 – 1030°C at normal pressure. Doping element concentrations and distribution were investigated by secondary ion mass spectrometry, energy-dispersive X-ray spectra and scanning transmission electron microscopy. Microstrain and substructure were evaluated by high temperature X-ray diffraction analysis and discussed in consideration of doping element type and concentration, deposition temperature and phase stability in the application temperature range of 800 - 1100°C. The effect of doping elements and deposition temperature on deposition rates are discussed. Productionscale aspects concerning deposition process stability and enhancements of performance results of different Al₂O₃-coated tools are outlined.
2:30 PM		B2-1-4 Role of H₂ in Deposition of CN_x Layers by PE-HF-CVD D. Dumitriu (Swiss Federal Institute of Technology Lausanne (E.P.F.L.), Switzerland); P.E. Schmid (Ecole Polytechnique Fédérale de Lausanne, Switzerland); A. Karimi (Swiss Federal Institute of Technology Lausanne (E.P.F.L.), Switzerland) CN_x layers were deposited by plasma enhanced (PE) hot filament (HF) chemical vapour deposition (CVD) with dimethylamine (DA) or trichloroethylene (TCE) and ammonia (NH₃) precursors using N₂ or N₂+H₂ mixtures as background gas.We have shown that for the different gas composition, appropriate substrate temperature must be used to deposit continuous and adherent CN_x layers. Films prepared with H₂ are delaminated during deposition because of differential thermal expansion. To improve adhesion, the temperature of the substrate was decreased down to 400^OC for depositions using DA/N₂+H₂ , and down to room temperature for TCE+NH₃/N₂+H₂ mixtures. Depositions rates were found to decrease with increasing H₂ content into the gas phase. The microstructure and morphology of the films were characterized by microscopy techniques (SEM, TEM, STM, AFM), the nature of chemical bonding was investigated by FT-IR and Raman spectroscopy, while mechanical properties were investigated by nanoindentation. The chemical composition of the films was analyzed by RBS. H₂ acts as an etching agent during depositions of CN_x films. Using H₂ results in an increased sp³ bonds content and compact films, as well as an increased N content (up to 25at%). Hardness of CN_x layers was improved when H₂ was added to the gas mixture. A nitrogenated DLC structure was found to be approached for films prepared with N₂+H₂ mixtures as background gas, while films prepared without H₂ are mainly graphitic.
2:50 PM		B2-1-5 Stress Distribution in Diamond Films Grown on Cemented WC-Co Dental Burs Using Modified Hot-filament CVD N. Ali (University of Aveiro, Portugal); H. Sein, W. Ahmed (Manchester Metropolitan University, United Kingdom); J. Gracio (University of Aveiro, Portugal) A vertical filament hot-filament chemical vapour deposition (HFCVD) system has been used to deposit diamond films onto dental burs. The as-grown films were found to be polycrystalline and displayed good coverage. Micro-Raman spectroscopy was used to characterise the stress distribution in the deposited films. Raman spectra were taken at different positions along the cutting parts of the dental bur. Raman diamond peak shifts from the 1332 cm^-1 value were used to calculate the stress. The distribution of stress along and across the diamond coating was evaluated. It was found that the stress across the coating remained constant. However, the stress along the coating displayed interesting characteristics. The stress at the back, in the middle and at the tip of the bur was calculated to be -1.7, -2.3 and -3.4GPa in compression, respectively. The temperature of the bur was found to be different at different positions during diamond CVD. The temperature of the bur at the back of the cutting area; at the middle of the bur; and at the tip of the bur was found to be 842°C, 908°C and 952°C, respectively. It was found that the stress in the films was a function of the thermal distribution at the cutting regions. SEM analysis was used to characterise the as-grown films for morphology and crystallinity.
3:10 PM		B2-1-6 Deposition of Alumina Hard Coatings by Bipolar Mid Frequency PECVD O. Kyrylov, R. Cremer, D. Neuschütz (LTH, RWTH Aachen, Germany) Pulsed and mid frequency plasma sources are gaining increased attention for the deposition of ceramic hard coatings by PVD as well as PECVD. Especially bipolar techniques allow the deposition of insulating layers under stable plasma conditions. In this paper, the deposition of alumina films on the molybdenum based superalloy TZM and on steel substrates from gaseous mixtures of AlCl₃, N₂, H₂ and Ar in a bipolar mid frequency glow discharge at temperatures from 500 °C up to 650 °C is reported. Special attention was paid to the correlation between plasma characteristics and film properties. The measurements revealed that the structure as well as the properties of the resulting coatings were significantly influenced by the characteristics of the power supply. Increasing plasma power densities led to the deposition of films with higher crystallinity and a change in structure from amorphous Al₂O₃ to γ- and finally α-Al₂O₃. Depending on the gas composition and plasma parameters, alumina films with high hardness and good adhesion were deposited. Optimized coatings exhibited good corrosion and oxidation resistance, thus proving the suitability of these coatings for the protection of dies during the semi solid processing of steel.
3:30 PM		B2-1-7 Iridium Coatings Grown by Metal-Organic Chemical Vapor Deposition in a Hot Wall CVD Reactor. F. Maury (CNRS/INPT, Ensiacet, France); F. Senocq (CNRS, France) It is generally easier to deposit uniform coatings on relatively large size and or complex shape pieces using isothermal rather than cold wall CVD reactor. After a review of the state of the art of Ir CVD processes aiming the selection of the starting chemical system, iridium thin films were deposited on tungsten substrates in a horizontal hot wall MOCVD reactor by thermal decomposition of Ir(COD)CpMe either in presence of H₂ or O₂. The growth was carried out under reduced pressure and low temperature (300-400 °C). The CVD process using hydrogen was found more difficult to control in this reactor configuration than the one with oxygen. The purity, the microstructure, the growth rate and the thickness uniformity depend on the deposition conditions. Oxygen avoids carbon incorporation in the layers and enhances significantly the growth rate. However a co-deposition of Ir and IrO₂ was observed using a too large excess of O₂. Polycrystalline, compact, untextured and pure Ir coatings were deposited with a satisfactory thickness uniformity over a length of about 15 centimeters and with a typical thickness of 1-2 µm. These coatings have attractive properties to be used as oxidation barriers at high temperature. Optimal deposition conditions were found using the trends predicted by a kinetic model of the growth rate along the CVD reactor. A good thickness uniformity along the reactor requires a very short residence time of the reactive species. As a result, a poor yield is found for this CVD process. This strongly affects economical requirements of this process whose the cost essentially depends on the molecular precursor.
3:50 PM		B2-1-8 Kinetic and Diffusion Barrier Properties of Metallorganic Chemical Vapor Deposited Niobium Nitride Films For Cu Metallization C.W. Wu, W.C. Gau, J.C. Hu (National Tsing Hua University, Taiwan, ROC); T.C. Chang (National Sun Yat-Sen University, Taiwan, ROC); C.H. Chen, C.J. Chu (Nanmat Technology Co., LTD., Taiwan, ROC); L.J. Chen (National Tsing Hua University, Taiwan, ROC) Amorphous NbN_x films were deposited by metallorganic chemical vapor deposited (MOCVD) using ethylimidotris(diethylamido)niobium(V) [Nb=NEt(NEt₂)₃] source with and without NH₃ at various temperatures. The gas-phase reaction mechanism of the compounds was monitored by in situ Fourier transform infrared spectroscopy. In the MOCVD system, the precursor was introduced to reaction chamber by a bubbler with Ar as a carrier gas. Both deposition temperature and resistivity of the film was found to decrease drastically upon the addition of NH₃. The activation energy for the surface reaction was measured to be 0.82 eV in the temperature range of 500- 600°C and decreased to 0.23 eV by adding 20 sccm NH₃ in the temperature range of 300 - 400°C. The NbN_x films was found to be amorphous by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Concentration-depth analysis was carried out by Auger electron spectroscopy (AES). The concentration of C in films was reduced significantly and the concentration ratio of N to Nb was varied from 1.67 to 1.10 by using NH₃ as a reactant gas. From XRD spectra analysis of as-deposited and annealed Cu/NbN/Si samples, niobium silicide was found to form at an annealing temperature of 600°C, but copper silicide was not yet formed. The results suggest that the barrier failure mechanism in NbN_x is the diffusion of Cu through the barrier layer rather than the formation of silicide with barrier metals.