Papers

ICMCTF2000 Session D2-2: Synthesis and Characterization of Diamond and Related Materials

Thursday, April 13, 2000 1:30 PM in Room Royal Palm Salon 4-6

Thursday Afternoon

Start	Invited?	Item
1:30 PM		D2-2-1 Nanocrystalline Silicon Carbide Films Deposited by ECRCVD M.B. Yu, A. Rusli, S.F. Yoon, J. Cui, K. Chew, J. Ahn, Q. Zhang (Nanyang Technological University, Republic of Singapore) Silicon carbide (SiC) is one of the wide gap semiconductors and has been actively studied for applications in blue light emitting diode (LED). However, due to its indirect gap, the quantum efficiency of the device is very low. Therefore, enhancement of the luminescence intensity is strongly desired. Currently, research on Si based emission materials has focused on the quantum confinement effect of nanocrystalline Si grain embedded in a matrix of Si nitride or oxide that could result in strong visible light emission. If nanocrystalline SiC films could be similarly fabricated, it is possible to obtain high efficiency short wavelength emission. Towards this objective, we have investigated the growth of nanocrystalline SiC films using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique. The samples were deposited in an ultra-high vacuum ECR-CVD equipment. It was found that under the deposition conditions of strong hydrogen dilution and high microwave power, SiC films embedded with smaller grain crystals could be obtained. This is evident from the high resolution TEM picture, where nanometer crystalline grains can be clearly seen. The result is interesting and significant in view of the depositions being carried out at room temperature. Fourier transform infrared absorption spectrum of the film revealed an obvious absorption peak at 817 cm^-1 which is related to the TO phonons of Si-C bonds. Other structural characterizations have also confirmed the successful fabrication of SiC nanocrystallites embedded in an amorphous SiC matrix. Very strong visible light photoluminescence was obtained at room temperature. This is promising for application in large area flat panel displays.
2:10 PM		D2-2-3 Effects of the Addition of Helium on the Synthesis of Diamond Films V. Baranauskas, H.J. Ceragioli, A.C. Peterlevitz, M.C. Tosin, S.F. Durrant (Faculdade de Engenharia Eletrica e Computacao, Universidade Estadual de Campinas, Brazil) In this work we present experimental results of CVD diamond growth in ethanol vapor with the substitution of hydrogen by helium in concentrations varying from 0 % to 99 % vol.. Hydrogen dilution has been widely employed with success in the diamond synthesis process. However, atomic hydrogen is a good thermal conductor and is therefore one of the main factors in substrate heating, which impedes the independent control of the deposition temperature. Since helium is not dissociated by the filament, the substitution of hydrogen by helium minimizes the loss of energy by the filament. Also, since helium has a much smaller thermal conductivity than atomic hydrogen this allows the lowering of the substrate temperature and increases control of the process. Helium also produces a larger mean free path for the carbon radicals formed at the filament allowing them to reach the substrate without recombining. Morphological data obtained by scanning electron microscopy and optical characterization by micro-photoluminescence and micro-Raman spectroscopy will be discussed.
2:30 PM		D2-2-4 Optimization of Process Parameters in Hot Filament Chemical Vapor Deposition of Diamond and Carbon Nitride Thin Films K. Elshot, J.S. Kapat, D. Zhou (University of Central Florida) Hot Filament Chemical Vapor Deposition (HFCVD) has become a widely used technique for the manufacturing of diamond film and similar hard coatings. Advantages of this method are its simplicity, ease in controlling the reaction parameters, and its ability to produce high quality large area films. Deposition of diamond and carbon nitride films on a silicon substrate by HFCVD process is the focus of this paper. The favorable tribological and/or thermal properties of diamond and CN thin films are the main reasons behind this interest in these two thin films. Thin film coatings that can act as tribological coatings or as heat spreaders are quite important in proper functioning of meso-scale silicon-based engineering systems. This paper concentrates on optimization of process parameters in hot filament assisted chemical vapor deposition of diamond and carbon nitride thin films, and numerical simulation is used as the main tool for this optimization process. Computational results are verified against experimental results for some of the cases of diamond deposition. Simulation of HFCVD using computational fluid dynamics software is a cost-effective and reliable method of predicting optimal conditions for thin film deposition. In this study, a numerical model using a commercial computation fluid dynamics code, CFD-ACE, has been developed for analyzing chemically reacting flow, mass and heat transport and reactions in HFCVD of diamond and CN thin films on a silicon substrate. The HFCVD system model consists of a vacuum-sealed stainless steel cylindrical reaction chamber with a single tungsten wire filament. The silicon substrate is only passively heated by the filament. Calculations are performed for different temperatures, pressures, substrate-to-filament distances, and different compositions of the reacting gas mixtures of precursor and carrier gases.
2:50 PM		D2-2-5 Influence of Different Physical Factors on Microstructure and Properties of Magnetron Sputtered a-C Films A.A. Onoprienko, L.R. Shaginyan, V.F. Britun, V.P. Smyrnov (Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Ukraine) Amorphous carbon (a-C) films were deposited by d. c. magnetron sputtering of graphite target in argon plasma. As substrates were polished wafers of Si (111) single crystals, Si-Ti-Al-O ceramics, and cleavages of NaCl (100) single crystals. Film microstructure was examined by Raman spectroscopy, transmission electron microscopy, and electron diffraction. Film resistivity was calculated through the measurements at room temperature the film thickness and the resistance parallel and perpendicular to substrate surface. Film thickness was measured with an optical interferometer and calculated from electron-probe microanalysis measurements. Influence of substrate temperature and d. c. negative bias voltage on film resistivity and microstructure has been studied. It was shown that a-C films deposited without ion bombardment reveal prominent resistivity anisotropy depending on substrate temperature during deposition, whereas ion bombardment results in change of film texture relative to substrate surface. The mechanism of film structure formation based on predominantly sp² bonding of carbon atoms, and relationship between film structure and properties are discussed.
3:30 PM		D2-2-7 Synthesis and Characterization of Pulsed-laser Deposited Amorphous Carbon Films V.I. Merkulov, D.H. Lowndes, G.E. Jellison, Jr., L.R. Baylor, A.A. Puretzky, D.B. Geohegan (Oak Ridge National Laboratory) Amorphous carbon films with variable amount of tetrahedral, sp³ bonding (up to ~ 75%) were synthesized by ArF (193nm) pulsed laser deposition. Kinetic energy of C ions was measured in-situ using an ion probe and correlated with the properties of the resultant C films. It is found that films with the most diamond-like properties are obtained at the C ion kinetic energy of ~ 90 eV, as determined by electron energy loss spectroscopy and spectroscopic ellipsometry measurements. Film properties are found to be uniform within a 12-15° angle from the plume centerline. Atomic force microscopy measurements show that the deposited films are extremely smooth, with rms roughness of only ~ 1-2 Å over distances of several hundred nm. Finally, field emission measurements carried out using a scanning point probe reveal that smooth, undoped C films do not appear to be good electron emitters, regardless of their sp³ content.
3:50 PM		D2-2-8 Chemical Vapour Deposition of Diamond Films from CH/H2/N2 Mixtures - Experiment and Modelling W. Ahmed, C.A. Rego, A. Afzal (Manchester Metropolitan University, United Kingdom) In recent years there has been considerable interest in the addition of nitrogen to the standard precursor gas mixture of methane and hydrogen and its influence on the properties of the diamond films deposited by Chemical Vapour Deposition (CVD). The addition of nitrogen results in changes in the surface roughness, structure, growth rate, morphology and the electrical and optical properties of the films. Good quality films have been deposited using 1% methane in hydrogen in a hot filament CVD system with a varying nitrogen addition of between 50-5000ppm. Scanning electron microscopy, Raman and x-ray diffraction has been used to characterise the film structure and surface roughness. It was found that the growth rate, phase purity, resistivity are optimum at about 200ppm nitrogen addition with further addition degrading gradually all the film properties when the structure is disrupted. In order to explain the results obtained during deposition the gas phase was sampled using a mass spectrometer to identify stable intermediates in the gas mixture near the surface of the wafer. In order to understand the gas phase chemistry occurring and presence of various intermediates such as CN,CH₃, and CH₂ near the surface region the system was modelled using a SENKIN and CHEMKIN package into which thermodynamic and kinetic data was incorporated. Although the modelling work gives some indication regarding the possible reaction mechanisms it far from satisfactory for nitrogen doped films. Much more detailed and accurate measurements of the environment near the wafer surface are required to provide further insight into mechanisms responsible for diamond growth in the presence of nitrogen.
4:10 PM		D2-2-9 Effect of Substrate Biasing on Magnetoplasmadynamic Accelerator Assisted Synthesis of Diamond J.J. Blandino (Jet Propulsion Laboratory); D.G. Goodwin (California Institute of Technology) A direct current, self-field, magnetoplasmadynamic (MPD) accelerator operating in the 10 - 20 kW power range is used to synthesize diamond film on a molybdenum substrate. In these experiments, a subatmospheric hydrogen/argon discharge (5 - 10 Torr) is used with methane as a carbon precursor. Results of a study of film growth as a function of substrate biasing are presented. Optical emission spectroscopy of the near substrate plume provide a qualitative indication of the presence of atomic hydrogen as well as atomic and molecular carbon. Results are also presented with respect to film quality and surface morphology evaluated using micro-Raman and SEM analysis.
4:30 PM		D2-2-10 Deposition of Undoped and Doped Textured Diamond Layers K. Bartsch, B. Arnold, S. Oswald, D. Schläfer, S. Waidmann, A. Leonhardt (Institut für Festkörper- und Werkstofforschung Dresden, Germany); L. Sümmchen (Technische Universität Dresden, Germany) Undoped biaxially oriented diamond films were deposited from CH₄-H₂ gas mixtures onto (100)-silicon substrates using the microwave (MW) plasma process combined with bias enhanced nucleation. The influence of some parameters of the nucleation step (voltage, time, MW power) on the seed density and the film orientation was investigated and a process window was claimed for biaxial growth. For the azimutal angular spread of {111} pole density a FWHM-value of 9 degree was achieved. The polar alignment depends on the thickness of layer and can be improved by its enhancement. [110]-oriented layers with fiber texture were also deposited by changing the growth conditions. Further investigations concerning in-situ doping of oriented layers were performed and the influence of gas phase doping on the layer growth was studied. As doping agents tri-methylborate(p-doping) and tri-n-butylphosphin(n-doping), resp., were used. Both for p-doping and n-doping a loss of the biaxial orientation was observed with increasing dopant concentration in the gas phase. The layers were characterized regarding structure, sp³/sp² content, and dopant concentration by XRD, TEM, EELS, SIMS, and Raman spectroscopy. It was confirmed by EELS measurements that at high B-concentration in the gas phase the sp³/sp² ratio of the layers increases, even if the layer structure gets more and more disordered in case of the biaxially oriented layers. At n- doping a low addition of the phosphorus compound during the bias nucleation step already results in a drastic decrease of the diamond Raman peak at 1332 cm^-1. A phorphorus addition only during the growth step had no remarkable influence on the Raman spectrum for a rather large concentration range. Further characterization results will be presented and some efforts to characterize the electrical conductivity of the layers by Hall measurements will be discussed.
4:50 PM		D2-2-11 Adherent Diamond Coatings on Stainless Steel Substrates using Multilayers 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) Stainless steel has great number of potential applications waiting to be exploited once diamond could be successfully deposited onto it. The major problem encountered with diamond on steel synthesis is the poor adhesion. This is mainly due to two reasons. Firstly, the iron present in steel is a strong carbon-dissolving element. During deposition the carbon swiftly diffuses into the steel substrate, leaving behind no carbon or diamond-like residues which are required for diamond nucleation. Secondly, steel has a thermal expansion coefficient value which greatly differs from the thermal expansion coefficient value corresponding to diamond. This causes large residual stresses in the diamond film, which has a negative effect on the adhesion. However, a number of attempts have been made to enhance the nucleation and adhesion on steel substrates with limited success. In this paper we use multilayers of Au/Cr to improve the nucleation and adhesion of CVD diamond films on stainless steel substrates. Gold (Au) interlayer being a non-carbide forming material acts as the base layer, which prevents the diffusion of carbon into the steel. The chromium (Cr) interlayer is classed as a fairly strong carbide forming material which enhances diamond nucleation. Diamond coatings have been deposited onto steel by hot-filament chemical vapour deposition (HFCVD) process. Methods such as micro-indentation methods, peel-off tests and scratch tests have been used to measure the adhesion. The results show that the Au/Cr interlayer is most effective in enhancing the adhesion between diamond and steel. Pull-off tests show that the adhesion between diamond and steel is better than 13 MPa. Micro-indentation results reveal that the adhesion between steel and diamond is equivalent to the adhesion between diamond and single crystal silicon.
5:10 PM		D2-2-12 Effects on the Deposition and Mechanical Properties of Diamond-like Carbon Film Using Different Inert Gases in Methane Plasma Z. Sun, C.L. Lin, YL Lee, X. Shi, J.R. Shi, B.K. Tay (Nanyang Technological University, Singapore) Diamond-like carbon (DLC) films using various inert gases, He, Ne, Ar/methane mixture were deposited by magnetically enhanced plasma chemical vapor deposition. The deposition rates and mechanical properties in terms of stress, hardness and Young's modulus of the DLC films under various substrate bias voltage and inert-gas/methane ratio were studied. At a fixed inert-gas/methane ratio (10%), the deposition rates and mechanical properties of the DLC film were enhanced by adding the inert gases in methane plasma, compared with that of the DLC film deposited only using methane plasma. At a fixed substrate bias voltage (250 V), with increasing the inert-gas/methane ratio, the deposition rate, stress, hardness and Young's modulus increased, and reached maximum at a certain inert-gas/methane ratio (30% for deposition rate, 20% for mechanical properties), then decreased. The magnitude of the effect was found as Ne, Ar and He, which was proposed due to the optimum balance in the ionization potential and atomic mass of the inert-gas.