Papers

ICMCTF1999 Session D2-2: Synthesis and Characterization of Diamond and Related Materials

Tuesday, April 13, 1999 8:30 AM in Room Forum/Senate/Committee

Tuesday Morning

Start	Invited?	Item
8:30 AM		D2-2-1 Effects of D.C. Bias Voltage on the Formation of Interfacial Layer of Diamond on Silicon by MPECVD Synthesis X.J. Guo, S.L. Sung (National Tsing Hua University, R.O.C.); K.P. Huang (Naitonal Chung Hsing University, R.O.C.); F.R. Chen (National Chung Hsing University, R.O.C.); H.C. Shih (National Tsing Hua University, R.O.C.) To grow highly oriented diamond film, the d.c. bias pre-treatment is crucial, since the initial orientation of the diamond nuclei controls the subsequent growth of the diamond film. It is well-known that an amorphous interlayer with silicon carbide particles imbedded predominantly formed between the substrate Si and the diamond nuclei during the bias stage. Thus the control and elimination of these interfacial layers are essential to the achievement of direct epitaxy of diamond on Si. Samples prepared by MPECVD with various bias voltages and CH₄/H₂ ratios were investigated by HRTEM and SEM as well as Raman spectroscopy. Experimental results show that colored rings, which were formed during bias stage on the Si substrate, correspond to amorphous layers of different thickness. Diamonds nucleate subsequently on these amorphous layers. The nucleation density is found to be a function of bias voltage with fixed bias time. Also, the amounts of interfacial silicon carbide show similar results. For higer CH₄/H₂ ratios and more negative bias voltage, the spatial distributions of the nuclei are more even and uniform morphologically. All Raman spectra show similar trends, but with broadened diamond and graphite peaks. Detailed analysis of HRTEM results and microstructural evolution, etc. will be discussed in this paper.
8:50 AM		D2-2-2 Formation of Intermetallic Cobalt-Phases in the Near Surface Region of Cemented Carbides R. Cremer, R. Mertens, D. Neuschütz (RWTH Aachen, LTH, Germany); O. Lemmer, M. Frank, T. Leyendecker (CemeCon, Germany) Due to the negative influence of cobalt upon a number of CVD deposition processes, 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 of e.g. diamond films. 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 could be the formation of chemically inactive Co containing intermetallic phases. The present paper focusses on the formation of intermetallic phases in the near surface region of pure Co substrates and cemented carbides. Especially the influence of boron and aluminum upon the formation of B-Co and Al-Co phases is investigated. Phase analysis was performed by grazing incidence X-ray diffraction and electron probe microanalysis. The suitability of the process for the CVD deposition of diamond films on cemented carbide was investigated by WDX element mappings and SEM. The analysis revealed that the formation of intermetallic Co-phases is an attractive alternative to the etching of cemented carbide substrates before the deposition of diamond films.
9:10 AM		D2-2-3 Improvements in the Properties and Structure of Diamond Films Deposited by Pulsed Bias Enhanced Hot Filament Chemical Vapour Deposition W. Ahmed, I.U. Hassan, C.A. Rego, N. Ali (Manchester Metropolitan University, United Kingdom) For many industrial applications the surface properties of diamond films are of critical importance. Standard methods of sample pre-treatment are inadequate due to poor reproducibility and lack of control. For practical applications homogeneous films with low defect density over large areas are required. Bias enhanced nucleation has been investigated as a possible solution to these problems. The optimum cw biased enhanced nucleation conditions for the subsequent growth of diamond were a substrate temperature of 1100 K; a methane and hydrogen ratio of 3%; a pressure of 20 Torr, a bias voltage of -250 V and a bias time of 60 minutes. In this paper we also describe a process for enhancing the nucleation density of diamond films on (100) silicon substrates using a pulsed DC biased enhanced HFCVD process in the range of -50 to -300V. The nucleation and subsequent growth of diamond were characterised by using scanning electron microscopy, surface profilometry and Raman spectroscopy. The effects of duty cycle on the nucleation density, surface roughness, structure and growth rate are presented. The film uniformity and surface roughness were considerably improved producing highly textured diamond. Columnar growth was inhibited.
9:30 AM		D2-2-4 Microwave Plasma Chemical Vapor Deposition of Diamond Films And Fabrication of Diamond Film for Micro Electro Mechanical Systems (MEMS) A.A. Shaik, H.A. Naseem, W.D. Brown (University of Arkansas) Diamond Films are attractive for both electronic and mechanical applications because of their excellent hardness, strength, chemical and thermal stability, thermal conductivity etc. Diamond films were deposited on 3-inch diameter p-type<100> oriented silicon substrates using a Wavemat Inc. microwave plasma disk reactor (MPDR). The wafers were first cleaned and then seeded with 4nm diamond powder. A dry abrasive seeding technique was used that is simple and gives higher nucleation density compared to other seeding techniques. The smaller size of diamond powder used (4nm) gave higher nucleation density. The process parameters were power of 3500 Watts, pressure of 60 Torr and methane concentration of 1%. The substrate temperature is kept above 800 degree celsius. A study was done on the effects due to variation of deposition condition in which methane was introduced simultaneously with hydrogen instead of introducing after the chamber pressure reached a desired value. The deposited films were characterized using SEM, XRD, AFM and Raman. The XRD results of the films deposited under the changed deposition conditions show some graphitic and silicon carbide phases along with diamond. The AFM results show extremely smooth film in some regions. This behavior is under investigation. Also selective deposition of diamond is done in order to create Diamond diaphragm, cantilevers etc for MEMS applications.
9:50 AM		D2-2-5 Mechanism of Intrinsic Stress Generation in High Quality CVD Diamond Films I.I. Vlasov, V.G. Ralchenko (General Physics Institute, Russia); D.N. Zakharov, N.D. Zakharov (Institute of Crystallography, Russia) The origin of intrinsic stress in diamond films grown by chemical vapor deposition (CVD) in microwave plasma was studied by co-operative use of micro-Raman spectroscopy and transmission electron microscopy (TEM). The films from 50 µm to 1000 µm in thickness were analysed. "High quality" of these films means absence of amorphous carbon within the sensitivity of the Raman measurements, 2.8-3.0 cm ^-1 Raman diamond linewidth in unstressed regions at 1.0 cm ^-1 spectral resolution, and relatively large (up to 2.5 µm x 6.7 µm) defect-free areas observed with TEM. Samples of "black" diamond were also examined for comparison purposes. TEM analysis showed that the main defect of the films is twins and microtwin lamella starting from the boundary between the grains and ending inside the grain. Formation of the defect is explained as a way of the observed stress relaxation. Characteristic sizes of spreading the twinning regions achieve a few microns the same as for stress regions. Surface and bulk micro-Raman mapping of the high quality films revealed existence of strong stressed regions located in the vicinity of grain boundaries. Characteristic lateral sizes of the regions were of a few microns, in dependence on film thickness. The model of incoherent interfaces in coalescent crystallites is proposed for explanation of the stress generation
10:30 AM		D2-2-7 Low Temperature Selective Deposition of Diamond Film T.-G. Kim (Miryang National University, South Korea); S.-H. Kim (Silla University, South Korea) Diamond films were selectively deposited at low temperature (~773 K) on the glass substrates in a microwave plasma-enhanced chemical vapor deposition (MPECVD) system. We could achieve the low temperature deposition via the remote plasma from the substrate, with low microwave power (500 W) and low pressure (20 mTorr) during the reaction. For the selective deposition, we treated the glass substrate using carbon-based materials before inserting it into the reactor. The pretreatment was carried out as a stripe-type by spreading or drawing the carbon-based materials onto the glass substrate. The selectivity and the characteristics of the films were investigated as functions of materials and methods used in the pretreatment. The enhancement of the selectivity and the diamond quality could be correlated with the ratio of the carbon component in the materials. Finally, we could suggest the best materials and method for achieving the low temperature selective deposition of the diamond film via the pretreatment technique based on the carbon-based materials.
10:50 AM		D2-2-8 Comparison of FTIR-Emission Spectra From Diamond and Diamond-like Films M. Farhan, V. Ayres, T. Al-Hindi (Michigan State University) In this work, the infrared intrinisic and defect signatures of diamond and diamond-like films are investigated and compared. The primary experimental technique used is FTIR-Emission spectroscopy. The traditional method of obtaining the infrared spectra is through absorption spectroscopy. However, infrared absorption measurements require careful polishing of the film surface, which is difficult for thin films of diamond material. Emission spectroscopy yields the same information as absorption spectroscopy. In emission measurements, the heated sample is itself the infrared light source. The collected light is a product of the gray-body emission and emitted light characteristic of the vibrational states of the sample. The emission technique circumvents the need for polished surfaces and is ideal for in-situ characterization as it exploits the high temperature growth conditions of CVD reactors and is completely non-intrusive. These investgations are undertaken with the goals of (1) developing comparative knowledge of the signatures of diamond and diamond-like materials, with and without additives such as nitrogen, (2)determinging the limitations of the FTIR-emission technique by comparison of the IR results with alternate techniques and with theory, and (3)developing a diagnostic which can ultimately be used for in-situ characterization of CVD diaomnd and diamond-like film growth.
11:10 AM		D2-2-9 High Rate Deposition of Diamond Like Carbon Film by Magnetically Enhanced Plasma CVD System Z. Sun, X. Shi, E. Liu (Nanyang Technological University, Singapore) A magnetically enhanced plasma chemical vapor deposition (MEPCVD) system has been developed for deposition of DLC film without deterioration of film quality. A perpendicular magnetic field (B) to the electric field was applied in the RF capacitively coupled plasma enhanced (PE) CVD system. A significantly higher levels of ionization are achieved in MEPCVD system, result in much lower self-bias voltage and higher deposition rate. The deposition rate of DLC film can be increased about one order in magnitude (B at 200 Gauss) by MEPCVD, comparing with non-magnetic field case. The properties of the DLC film deposited by MEPCVD system were also improved, there is a higher hardness and Young's modulus, and lower surface roughness, comparing with that of the DLC film deposited by conventional PECVD system.
11:30 AM		D2-2-10 The Structural and Emission Characteristics of Unhydrogenated Amorphous Carbon Film by Pulsed Laser Deposition H.H. Park, H.S. Jung, S.Y. Lee, S.S. Pang (Yonsei University, Korea) Unhydrogenated amorphous carbon films have been deposited on Si (100) by pulsed laser deposition (PLD) using 355 §¬ (Nd:YAG) laser. The emission can be turn on at 6.3 V/µm and 2 §Ë of emission current was obtained at 7 V/µm in case of as-deposited DLC film. In order to investigate the effect of thermal treatment on the I-V characteristics of carbon films, post-anneal treatment was carried at 500 °C under vacuum. The switch-on voltage increased with the post-annealing treatment ,this result was discussed in relation to the variation of other properties of amorphous carbon film. Changes in the properties of DLC films with various annealing temperatures were also examined by X-ray diffractometer, Raman spectroscopy, atomic force microscopy, photoluminescence and four-point probe measurement. With annealing the degradation of emission behavior was observed. after 300 °C was sufficient to observe the degradation. In contrast, other properties were not significantly changed with annealing treatment at 300 ¡É except the results of energy loss spectra. Although post-annealing treatment can modify the sp²/sp³ ratio in surface as well as bulk of film, but the annealing effect seems to be intensified on the surface than the bulk of amorphous carbon film.
11:50 AM		D2-2-11 Measurement of Elastic Properties of Diamond-like Carbon Films S.-J. Cho, K.-R. Lee, K.Y. Eun (Korea Institute of Science and Technology, Korea); Y. Kim (Chonnam National University, Korea) Elastic properties of diamond-like carbon (DLC) films were measured by a simple method using DLC bridges which are free from mechanical constraint of substrate. The DLC films were deposited on Si wafer by C₆H₆ r.f. glow discharge at the deposition pressure 1.33 Pa. Because of the high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement by removing the constraint of the substrate. By measuring the amplitude with known bridge length, we could determine the strain of the film which ocurred by stress relaxation. Combined with independent stress measurement by laser reflection method, this methode allows calculation of the biaxial elastic modulus, E/(1-ν), where E is the elastic modulus and ν Poisson's ratio of the DLC film. The biaxial elastic modulus increased from 10 to 158GPa as the negative self bias voltage increased from 100 to 550V. This result was in good aggreement with the elasic modulus measured by vibrational resonance method. The limitation of the present bridge method was also discussed.