ICMCTF2000 Session D2: Synthesis and Characterization of Diamond and Related Materials

Thursday, April 13, 2000 8:30 AM in Room Royal Palm Salon 4-6

Thursday Morning

Start	Invited?	Item
8:30 AM		D2-1 Improved Diamond Layer Deposition by Formation of Intermetallic Cobalt-phases in the Near Surface Region of Cemented Carbides R. Cremer, D. Neuschütz (LTH, RWTH Aachen, Germany); T. Leyendecker, O. Lemmer, M. Frank, J. Gussone (CemeCon GmbH, Germany) Due to the negative influence of cobalt upon diamond deposition, the cobalt-based binder phase in cemented carbide substrates has to be removed in the near surface region in an etching step prior to deposition. The removal of the Co-binder phase may weaken the near surface region resulting in a decrease of performance of the coated cemented carbide tool. An alternative to the selective etching of the cobalt binder phase is the formation of chemically inactive Co containing intermetallic phases ¹. Based on a previous study ¹, the paper focusses on the formation of intermetallic Co-B phases in the near surface region of cemented carbides. In a boronizing step, cemented carbide insert tips were treated in BCl₃-H₂ mixtures. The formation of Co-B phases was determined by grazing incidence X-ray diffraction. The suitability of the process for the CVD deposition of diamond films on cemented carbides was investigated by elemental mappings and SEM as well as wear tests. The analysis revealed that the formation of intermetallic Co-phases improves the performance of diamond coated cemented carbides significantly as compared to conventionally etched substrates. ¹ 1. R. Cremer, R. Mertens, D.Neuschütz, O. Lemmer, M. Frank, T. Leyendecker, presented at the 26th ICMCTF, 1999, to be published in Thin Solid Films
8:50 AM		D2-2 Characterization of Diamond-like Carbon Coatings Deposited by Plasma Assisted Chemical Vapor Deposition G. Ceccone, F. Bertelli (European Commission Joint Research Centre, Italy); P Leray (European Commission,Joint Research Centre, Italy); S. Vernoli, F. Rossi (European Commission Joint Research Centre, Italy); F. Marabelli (University of Pavia, Italy) Diamond-like carbon coatings have been deposited on Si(100) polished wafers and stainless steels (AISI316) by capacitively coupled plasma assisted chemical vapor deposition (PACVD) method,by using CH₄, Ar/CH₄ and N₂/CH₄ gas mixtures. A typical deposition rate of 2-6µm/hr has been obtained when using 1250W RF power and 500 volt substrate negative bias voltage. The plasma characteristics have been assessed using Langmuir probe and Optical Emission Spectrometry (OES). The coatings have been characterized by means of Raman and FTIR Spectroscopy, SEM/EDX, AES, EELS and XRD. The coating mechanical properties have been investigated by nanoindentation. Correlation between the plasma parameters and the coating properties are presented anddiscussed. Topics requiring further investigation are also identified.
9:10 AM		D2-3 An Amorphous Hydrocarbon Diamond-like Polymer as Precursor for Diamond Growth Z. Sun (Nanyang Technological University, Singapore); Y. Sun (New York University); S.R. Wilson (Consultant) A diamond-like polymer, poly(phenlycarbyne), was synthesized by reductive condensation of tricholorotoluene monomer with an ultrasonically-generated NaK alloy emulsion in tetrahydrofuran under an inert atmosphere. The polymer consists of a randomly constructed rigid network of tetrahedral polycarbyne units in which each carbyne carbon forms three C-C bonds to the network and one to a substituent structure of the polymer, which was analyzed by nuclei magnetic resonance (NMR), X-ray photo spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The polymer is easily soluble in organic solvents to form a solution which can be applied to various substrates and forms films with large area. By simple heat-treatment process, this amorphous polymer can transform into diamond crystals at low temperatures (600 ° C), and structure of the diamond crystals was confirmed by micro-Raman spectroscopy. The correlation of thermal gravimetric analysis (TGA) and differential thermal analysis (DTA), FTIR and Raman spectra of polymer provides important information on the process of phase transformation.
9:30 AM	Invited	D2-4 Effects of Ion-bombardment During CVD Diamond Nucleation and Growth C.-P. Klages, X. Jiang (Fraunhofer Institute for Surface Engineering and Thin Films, Germany) Bias-induced ion bombardment of substrates is now an established technique for the nucleation of diamond from the gas phase during metastable diamond growth. The effects of continuous or intermittent ion bombardment during diamond film growth on the other hand have only recently started to gain interest: Preliminary investigations indicate that the combination of CVD diamond growth from neutral species (hydrogen atoms and methyl radicals) with the simultaneous bombardment of the growth surface by energetic particles of variable energies can provide a wide range of modifications of the diamond phase and furthermore the film properties. Recently it was demonstrated that hydrogen ion bombardment during the diamond CVD can enormously modify the growth leading to a fine crystalline, fully (001) textured film morphology, independent of the type of growth substrates. In this report the modification of diamond film growth by ion bombardment of different energy ranges at different substrate temperature in microwave plasma chemical vapour deposition will be presented. The films structure were studied by SEM, and Raman spectrometry. Film stress was in situ characterised by using the bending beam method.
10:30 AM		D2-7 The Effect of Residual Stress on Raman Peak Shift of Tetrahedral Amorphous Carbon Prepared by Filtered Vacuum Arc Deposition J.K. Shin, K.-R. Lee, K.Y. Eun (Korea Institute of Science and Technology, Korea) Although Raman spectroscopy has been considered as a useful analysis tool for the structure identification of carbon films, ambiguity and controversy in Raman analysis of tetrahedral amorphous carbon (ta-C) films still remain. In conventional hydrogenated amorphous carbon (a-C:H) films, the G-peak position in Raman spectra moves to higher wave number with increasing content of graphitic components. However, inconsistent results were reported in ta-C films. In the present work, hydrogen-free, hard amorphous carbon films prepared by a filtered cathodic arc method with different stress levels were investigated using Raman spectroscopy. The effects of residual stress on Raman spectra were quantitatively investigated by comparing the Raman spectra of stressed films with those of the unstressed ones. The unstressed free-hang of the films were obtained by removing mechanical constraint of Si substrate using an anisotropic etching technique. The origin of ambiguity and controversy in Raman analysis of highly stressed ta-C films were proved to be due to the residual stress. We observed that the G-peak position moves by +4.1cm^-1 per GPa. By considering the residual stress effect, the Raman behavior of stress-free amorphous carbon films was essentially identical to that of a-C:H films. The results were discussed in terms of the origins of Raman peaks of carbon materials.
10:50 AM	Invited	D2-8 Homoepitaxial Diamond Growth with Sulfur-doping by Microwave Plasma-assisted Chemical Vapor deposition M. Nishitani-Gamo (Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), Japan); E. Yasu (Kubota Corporation, Japan); C. Xiao, Y. Zhang, Y. Kikuchi, I. Sakaguchi, Y. Sato (Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), Japan); T. Ando (Core Research for Evolutional Science and technology (CREST), Japan Science and Technology Corporation (JST), and National Institute for Research in Inorganic Materials (NIRIM), Japan) We have investigated the effect of H₂S addition to the chemical vapor epitaxy of diamond crystals. The small amount of H₂S affects the homoepitaxial diamond growth quality to be increased. The effect of sulfur was similar to that of oxygen. However, excess H₂S caused to decrease the crystal quality. The grown homoepitaxial diamond films were characterized by confocal Raman spectroscopy (CRS), optical differential interference contrast micrography (ODICM), scanning electron micrography (SEM), reflection high energy electron diffraction (RHEED), and cathode luminescence Spectroscopy (CL). The homoepitaxially grown diamond (100) films with 50ppm H₂S at 830^oC showed a very good crystal quality. CRS indicated a sharp Raman peak at 1332cm^-1 with 2.8 cm^-1 of full-width at half-maximum (FWHM). We distinguished the Raman signals of the homoepitaxial films from those of the substrate diamond by using ¹³C substrate diamond and confocal optics. The RHEED showed a very clear and sharp Kikuchi patterns, and ODICM and SEM showed the homoepitaxial surface was very flat and smooth. CL spectrum at 83K indicated a sharp peak of free exciton at 235 nm. These results suggest the homoepitaxial diamond quality is very good. The sulfur incorporation was observed by secondary ion mass spectrometry (SIMS) and particle induced X-ray emission spectroscopy (PIXE). While oxygen incorporation was never observed in diamond crystals, a small amount of sulfur could be incorporated. The sulfur was successfully doped into homoepitaxial diamond (100) films, which exhibit n-type conduction by Hall effect measurements in the temperature range of 250-550K. The mobility of electrons at room temperature was 597 cm² V^-1 s^-1. The mobility decreased with increasing measurement temperature. The ionization energy of 0.38~0.40eV was determined by measuring the carrier concentration as a function of temperature.
11:30 AM		D2-10 Optimising Diamond Nucleation via Combined Surface Pretreatment N. Ali, W. Ahmed (Manchester Metropolitan University, United Kingdom); Q.H. Fan (University of Aviero, Portugal); I.U. Hassan, C.A. Rego (Manchester Metropolitan University, United Kingdom) Pre-treatment of substrate surfaces prior to diamond deposition is essential in optimising the nucleation density. Several pre-treatments such as surface polishing using various abrasives and substrate biasing have been investigated. In this study we describe the effects of these pre-treatments on the nucleation density and the film properties of diamond deposited on copper. The results show that combined surface polishing with diamond powder and biasing the substrate gives a higher nucleation density than the two treatments applied individually. It was found that an increase of 70% in the nucleation density was observed when the surfaces were polished with diamond paste and then negatively biased. Copper surfaces polished with diamond powder and then biased gave the highest nucleation density although the percentage increase with biasing was the greatest with diamond paste. After negatively biasing the substrate for 30 minutes, broad D- and G-bands of microcrystalline graphite were present in the Raman spectrum, which completely disappeared with subsequent diamond growth. It was found that the carbon precursor to diamond growth, formed during the biasing stage was preferentially etched when exposed to hydrogen plasma. This suggests that the deposited material at this stage consists of a carbon network etchable by the hydrogen plasma, such as amorphous carbon (sp2 or sp3 bonded) and microcrystalline graphite. It was also found that higher emission currents yield a much increased nucleation density.
11:50 AM		D2-11 Review of Modified Direct Current Plasma Assisted Chemical Vapor Deposition Method (DC PACVD) for Wafer Scale Free Standing Diamond Film Y.-J. Baik, J.-K. Lee, W.-S. Lee, K.Y. Eun (Korea Institute of Science and Technology, Korea) Basic concept and experimental results of recently developed modified DC PACVD methods were reviewed. Basically DC PACVD method could produce free standing wafer at low prices due to its simple geometry and operation, but it has not been realized because of instability of plasma. Recently, methods maintaining stable plasma were established either by using thermodynamic analysis and multi-cathode geometry or by using pulse-powered cathode, which were used to diamond wafer fabrication. Both stabilizing methods were very successful to produce 4” diameter 1 mm thick diamond wafer very economically and competitively. Since the plasma was close to thermal equilibrium, growth rate and crystallinity were very high, similar to those obtainable using arc-jet CVD. Compared to other competitive methods, these methods were scalable more easily. Deposition behavior and characteristics, such as thermal conductivity, of diamond wafers were also discussed.
12:10 PM		D2-12 Studies on Nano-crystalline Diamond Films Deposited by CVD of Camphor: an Eco-friendly Precursor Material S. Chaudhuri, K. Chakrabarti, A.K. Pal (Indian Association for the Cultivation of Science, India) Camphor, which is a low cost eco-friendly material containing three methyl groups, was found to be suitable for diamond deposition at low substrate temperature. Nanocrystalline diamond films were deposited by chemical vapour deposition (CVD) of camphor (C ₁₀ H ₁₆ O) and hydrogen (~75 vol.%) on glass (at 523-623 K) and quartz/Si substrates (at 523-713 K). The roughness of the films were determined by AFM and optical reflectance measurements, which indicated that the films had low values of surface roughness (~17 nm on quartz). IR studies of the films deposited on Si substrate indicated the films to be transparent in the IR region. Optical properties of the films deposited on quartz (fused silica) and glass (Corning) substrates were studied. The films had high band gap (~4.8 eV). Absorption coefficient (alfa) of the diamond films were recorded by a spectrophotometer. The absorption data (alfa / alfa ₀ versus wavelength, alfa ₀ = value of alfa at the band gap) of the diamond films in the below band gap region were recorded to estimate the strain (2-12x10 ^-3), stress (1.9-8.4 GPa) and hardness (47-62 GPa) by a theoretical curve fitting procedure, which is a non-destructive method for studying the mechanical properties of thin films. The FTIR studies of the films did not show prominent absorption around 2900 cm ^-1),. The Raman spectra of the films indicated a sharp peak ( with FWHM ~ 8 cm ^-1), ) at 1337 cm ^-1), corresponding to the presence of high stress in the nano-diamond films.