Diamond Deposition Process Research Articles

Two-dimensional modeling of diamond growth by microwave plasma activated chemical vapor deposition: Effects of pressure, absorbed power and the beneficial role of nitrogen on diamond growth

A two-dimensional (2D(r, z)) self-consistent model developed and validated in previous studies of diamond deposition processes in microwave (MW) plasma activated chemical vapor deposition reactors is applied in a systematic study of ways in which the gas pressure (over the range p = 75–350 Torr) and absorbed power (P = 1–3 kW) affect the plasma parameters, species distributions and diamond deposition processes from a gas mixture (1%CH4/H2 with 60 ppm added N2) at substrate temperatures (Ts = 1073 and 1323 K) and diameters (ds = 32–100 mm). A more limited set of process conditions for a 0.006%N2/4%CH4/H2 gas mixture and Ts = 1038–1153 K are investigated also. The study traces variations in the global distributions of electron concentration, electron and gas temperature, absorbed power density, key species concentrations and the hydrocarbon interconversion reactions, with particular focus on the radial profiles of CH3 radical and H atom concentrations just above the substrate and on predicted diamond growth rates, G(r). The results and the trends revealed when varying p and P should help guide future optimizations of deposition regimes. The absorbed power density is shown to exhibit quite steep gradients in both the radial (r) and axial (z) directions. This, and the finding of significant power absorption beyond the glowing plasma region, limits the utility of the oft-quoted ‘averaged power density’ as a parameter. The modeling also highlights the essential 2D character of the hydrocarbon interconversion and diffusion transfer processes, which challenges the applicability of any 1D modeling of such MW plasmas. Trace additions of N2 to a MW plasma activated CH4/H2 gas mixture have negligible effect on the plasma parameters or chemistry yet are known to boost the diamond growth rate. A semi-empirical expression for G(r) is developed further to explicitly include the effects of added N2 and a new mechanistic picture presented to account for the observed N-induced enhancements in G. This picture invokes stable moieties such as that formed by CH2 insertion into a CN dimer bond on the 2 × 1 reconstructed (100) diamond surface as ‘anchor’ sites that enable shorter CH2 surface migration lengths and more step-edges for irreversible incorporation of such migrating groups on the growing diamond surface.

Effects of TiMoTa nano-crystalline interlayer on nucleation, adhesion and tribological behaviors of diamond coating

To investigate the influence of the transition layer on diamond nucleation and growth, the TiMoTa multi-alloy interlayers were firstly prepared on WC-6%Co cemented carbide by double glow plasma surface alloying technique, and diamond was then deposited using microwave plasma chemical vapor deposition system. The thickness of the TiMoTa interlayers increased from 1.2 μm to 2.7 μm with the deposition temperature increasing from 800 to 900 °C. Due to the formation of nano-crystalline structure and hard phase, the as-prepared TiMoTa interlayer exhibited high micro-hardness. In the diamond deposition process, the nano-carbide particles preferentially formed at the TiMoTa interlayers can effectively prevent the further diffusion of C, so the surface carbon concentration rapidly accumulates to the critical value required for the nucleation and growth of diamond microcrystals. Finally, a microscale wear-resistant diamond coating with good adhesion was grown on the transition layer, the crack propagation radius of the diamond coating is ∼162 μm, and can reach Hf 2–3 grade. Therefore, our prepared TiMoTa nano-crystalline interlayer provides a new path for the development of a high-quality diamond coating with good adhesion on cemented carbide.

Diamond encapsulated silicon optical fibers synthesized by chemical vapor deposition

Semiconductor optical fibers encapsulated in a protective diamond coating can theoretically lead to immense power handling capabilities and infrared functionality. Here, silicon optical fibers are grown using high pressure chemical vapor deposition before being coated by 50 μm–300 μm of diamond by microwave plasma-assisted chemical vapor deposition. This coating extends conformally around the fiber cross section with diamond crystallites in the film on the order of several micrometers. Complete coating of high-quality diamond around the fiber is indicated by scanning electron microscopy and Raman measurements. The encapsulated silicon fibers are durable enough to survive the diamond deposition process, as demonstrated by their ability to guide infrared light.

Deposition of Boron-Doped Thin CVD Diamond Films from Methane-Triethyl Borate-Hydrogen Gas Mixture

Boron-doped diamond is a promising semiconductor material that can be used as a sensor and in power electronics. Currently, researchers have obtained thin boron-doped diamond layers due to low film growth rates (2–10 μm/h), with polycrystalline diamond growth on the front and edge planes of thicker crystals, inhomogeneous properties in the growing crystal’s volume, and the presence of different structural defects. One way to reduce structural imperfection is the specification of optimal synthesis conditions, as well as surface etching, to remove diamond polycrystals. Etching can be carried out using various gas compositions, but this operation is conducted with the interruption of the diamond deposition process; therefore, inhomogeneity in the diamond structure appears. The solution to this problem is etching in the process of diamond deposition. To realize this in the present work, we used triethyl borate as a boron-containing substance in the process of boron-doped diamond chemical vapor deposition. Due to the oxygen atoms in the triethyl borate molecule, it became possible to carry out an experiment on simultaneous boron-doped diamond deposition and growing surface etching without the requirement of process interruption for other operations. As a result of the experiments, we obtain highly boron-doped monocrystalline diamond layers with a thickness of about 8 μm and a boron content of 2.9%. Defects in the form of diamond polycrystals were not detected on the surface and around the periphery of the plate.

Cutting performance of tungsten carbide tools coated with diamond thin films after etching for various times

In this study, diamond thin films were deposited on tungsten carbide tools using surface-wave plasma-enhanced chemical vapor deposition (SWP-CVD). To eliminate the adverse effects of cobalt on the diamond deposition process, the cobalt was removed from the surface of the tools by etching with Murakami’s reagent for various times (30, 60, and 120 min). The cutting performance of the untreated and the diamond-coated WC tools was examined by performing cutting test on carbon fiber-reinforced plastic (CFRP). The results showed that all the diamond-coated tools exhibited great improvement on the durability and wear resistance compared to the uncoated one. In addition, the diamond-coated tool lift time is found to be proportional to the etching time. An increase more than twofold has been achieved when the etch time was increased from 30 min to 120 min.

Influence of Laser Vibrational Excitations of Ethylene Molecules in Laser-Assisted Combustion Diamond Synthesis

ABSTRACTLaser-induced vibrational excitation of ethylene molecules was integrated to the CVD diamond deposition process for an in-depth understanding of the energy coupling path in chemical reactions and an alternative method to enhance the diamond deposition. On- and off-resonance excitations of ethylene molecules were achieved via tuning the incident laser wavelengths centered at 10.532 µm. With the same amount of laser power absorbed, the chemical reaction is highly accelerated with on-resonance vibrational excitation whereas energy coupling with off-resonance excitations was less efficient in influencing the combustion process. The diamond deposition rate was enhanced by a factor of 5.7 accompanied with an improvement of diamond quality index with the on-resonance excitation at 10.532 μm. The measured flame temperature demonstrated that the resonant vibrational excitation was an efficient route for coupling energy into the reactant molecules and steering the combustion process.

Spatial characterization of H 2 :CH 4 dissociation level in microwave ECR plasma source by fibre-optic OES

Spatially resolved optical emission spectroscopy (SR-OES) was used to investigate microwave activated H2/Ar/CH4 plasma under conditions of the electron cyclotron resonance (ECR). The chemistry and composition of the gas phase were studied using self-designed fibre-optic system with echelle type spectrometer during CVD deposition of polycrystalline diamond. One-dimensional intensity profiles of the main species were collected along the vertical axis of chamber. The dominant species in the flux, originating from excited hydrogen and hydrocarbons, were identified as H, H+, CH and CH+; they are crucial for the diamond deposition process. The effect of ECR on the spatial distribution of H2 and CH4 dissociation profiles was studied in depth. The influence of processing parameters (gas flow rates, input power, pressure and magnetic field level) on species excitation as a function of the distance above substrate was asessed. The obtained data can be used for the ECR system optimization.

Hydrodynamics effects in high power density microwave plasma diamond growth reactors

Most of the time, the hydrodynamics effects in plasma modelling, used to describe CVD diamond deposition processes operating at a moderate pressure and gas flow (assisted by microwave plasma or by a hot filament), are neglected. As a matter of fact, the transport of the reactive species in such reactors is mainly controlled by diffusion. However, when working at very high power densities (high pressure and microwave power), it has been observed that the growth rates are a function of the gas inlet and outlet setup, which is the opposite of what is generally reported in the literature when working at lower pressures. We report here both a 2D axisymmetrical and a full 3D description of the hydrodynamic flow in PECVD diamond deposition reactors. The consequent increased complexity of the fluid modelling required some compromise by simplifying the plasma description and reducing the chemical kinetic scheme. In this paper, we describe a new thermochemical fluid model, emphasizing its hydrodynamic formulation (relevant for the high-pressure conditions described here) and detailing its differences with our previous plasma models. We also present a series of comparisons, both to pre-existing calculations and to experimental results, which show that the thermochemical fluid model properly reproduces the plasma behaviour and allows us to study hydrodynamics effects.

Acid Pretreatment of WC-Co Prior to CVD Diamond Coating

Pretreatment on tungsten carbide (WC-Co) surface is critical for obtaining perfectly adherent diamond coatings by chemical vapor deposition (CVD). The carbide surface should have high roughness to facilitate diamond nucleation and adhesion. The presence of cobalt—common binder for tungsten carbide—on the surface to be coated should be made minimum since it has negative influence on the diamond deposition process. In this study, surface pretreatment on tungsten carbide using sulfuric acid was evaluated in terms of the resulted cobalt removal and the surface roughening. The variables included were acid concentration, reaction temperature, and reaction time. The resulted surface roughness was 29% higher than initial, averaged at 1.07 µm. The acid pretreatment was also found effective in eliminating surface cobalt.

Recent Advances in the Deposition of Diamond Coatings on Co-Cemented Tungsten Carbides

Co-cemented tungsten carbides, namely, hard metals are largely used to manufacture high wear resistant components in several manufacturing segments. Coating hard metals with superhard materials like diamond is of utmost interest as it can further extend their useful lifespan. The deposition of diamond coatings onto WC-Co can be extremely complicated as a result of poor adhesion. This can be essentially ascribed to (i) the mismatch in thermal expansion coefficients between diamond and WC-Co, at the typical high temperatures inside the chemical vapour deposition (CVD) chamber, generates large residual stresses at the interface; (ii) the role of surface Co inside the WC-Co matrix during diamond CVD, which promotes carbon dissolution and diffusion. The present investigation reviews the techniques by which Co-cemented tungsten carbides can be treated to make them prone to receive diamond coatings by CVD. Further, it proposes interesting ecofriendly and sustainable alternatives to further improve the diamond deposition process as well as the overall performance of the coated hard metals.

High-Rate Diamond Deposition by Combustion Flame Method Using Twin Acetylene/Oxygen Gas Welding Torch

To develop a high-rate diamond deposition process using combustion flame method, diamond deposition equipment with twin acetylene/oxygen welding torch was manufactured, and diamond deposition by using this equipment was carried out. 304 Stainless steel plates and molybdenum plates were used as substrates. The diamond deposition was conducted under the following conditions: oxygen flow rate: 1.25 SLM, acetylene/oxygen flow ratio: 1.15, and diamond deposition temperature: around 1473 K. Consequently, diamonds could be deposited even on the stainless steel substrate, and diamond deposition rate was promoted by using twin torch equipment. Besides, the diamond/molybdenum hybrid coating using diamonds deposited by twin torch equipment have the same wear-resistant property as that using diamonds by the single torch equipment. From these results, this technique was thought to have high potential for high-rate diamond deposition in combustion flame method.

On the Plasma Chemistry of CH4H2Ar System Relevant to Diamond Deposition Process by Plasma Enhanced Chemical Vapor Deposition

AbstractDiamond films are extensively deposited using plasma enhanced chemical vapor deposition (PECVD). In this work, the most important non‐neutral plasma surface processes, which are needed to analyze the deposition mechanism of diamond films from plasma gas phase, are considered. Moreover, the role of ionic species, which is mostly neglected in deposition investigations, has been considered. To analyze the diamond deposition process, we use the reaction probability algorithm for different surface phenomena. Then, using different methods like Motz and Wise modified relation, the reaction probability is transformed to the mass action kinetic rate constant. Our results lead to the calculation of rate coefficients for non‐neutral gas‐surface reactions that take place during the diamond deposition from plasma in CH4H2Ar system.

ENHANCED NUCLEATION AND SMOOTHNESS OF NANOCRYSTALLINE DIAMOND FILMS VIA W-C GRADIENT INTERLAYER

CVD diamond coating was deposited on to 13%wt. Co -containing tungsten cemented carbide surfaces using a hot filament chemical vapor deposition (HFCVD) to improve wear properties and performance of WC -13% wt . Co . Prior to the deposition of the diamond films, a W - C gradient intermediate layer had been sputtered on WC -13% wt . Co . The surface and cross-section morphology, phase transformation, and grain size distribution of the samples were investigated by means of field emission scanning electron microscope (SEM), X-ray diffractometer (XRD), and atomic force microscope (AFM), respectively. The results show that W - C gradient intermediate layers can effectively reduce the diffusion of Co in cemented carbide substrates during diamond deposition process, resulting high nucleation density and ultra smooth nanocrystalline diamond films.

Optical emission study of a doped diamond deposition process by plasma enhanced chemical vapor deposition

Standard H2∕CH4∕B2H6 plasmas (99% of H2 and 1% of CH4, with 0–100ppm of B2H6 added) used for doped diamond film growth are studied by optical emission spectroscopy in order to gain a better understanding of the influence of boron species on the gas phase chemistry. Only two boron species are detected under our experimental conditions (9∕15∕23Wcm−3 average microwave power density values), and the emission spectra used for studies reported here are B(S1∕22−P1∕2,3∕202) and BH[AΠ1-XΣ+1(0,0)]. Variations of their respective emission intensities as a function of the ratio B∕C, the boron to carbon ratio in the gas mixture, are reported. We confirmed that the plasma parameters (Tg, Te, and ne) are not affected by the introduction of diborane, and the number densities of B atoms and BH radical species were estimated from experimental measurements. The results are compared to those obtained from a zero-dimensional chemical kinetic model where two groups of reactions are considered: (1) BHx+H↔BHx−1+H2 (x=1–3) by analogy with the well-known equilibrium CHx+H set of reactions, which occurs, in particular, in diamond deposition reactors; and (2) from conventional organic chemistry, the set of reactions involving boron species: BHx+C2H2 (x=0–1). The results clearly show that the model based on hydrogen and boron hydrides reactions alone is not consistent with the experimental results, while it is so when taking into account both sets of reactions. Once an upper limit for the boron species number densities has been estimated, axial profiles are calculated on the basis of the plasma model results obtained previously in Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions, and significant differences in trends for different boron species are found. At the plasma-to-substrate boundary, [BH] and [B] drop off in contrast to [BH2], which shows little decrease, and [BH3], which shows little increase, in this region.

Direct deposition of polycrystalline diamond onto steel substrates

The excellent characteristics of diamond such as its high wear resistance and chemical inertness raise the possibility to improve the performance and life time of industrial steel components by the deposition of a protective diamond coating. Therefore, we have investigated the direct deposition of diamond onto tool and stainless steel substrates by means of hot-filament-assisted chemical vapor deposition. Our growth studies show that, without any pretreatment procedure, the formation of interlayers consisting of a mixture of graphite, amorphous carbon and iron carbides prior to diamond film growth is unavoidable. For the tool steel substrates, ballas type diamond with large quantities of graphite is formed. For the stainless steel, the carbon in-diffusion leads to lesser amounts of graphite. However, as a result of the competitive growth of non-diamond phases, the obtained diamond films are still not continuous. The differences in graphitization effects of iron between both types of steel are explained by the differences in generation and decomposition of the metastable cementite (Fe 3C) phase. Our results are discussed with the outcomes of recent works on multiple-stage diamond deposition processes and the application of diffusion barrier layers to overcome the above-mentioned problems.

20403 燃焼炎法によるダイヤモンド合成領域の大面積化の検討(材料加工(1))

In this study, to develop large and uniform diamond deposition process using combustion flame method, diamond deposition on one dimensionally traversing Mo substrate and investigation of diamond partile appearance variation depended on deposition position were conducted. Consequently, difference of the appearance between particles of center and edge of the deposition area, which was shown in the case of fixed substrate, was existed even in case of traversing substrate. However, there was no difference of the appearance among particles deposited on the area located on the same locus of the combustion flame, that is, one dimensionally uniform diamond deposition area could be formed by traversing substrate.

Nanocrystalline diamond resonator array for RF signal processing

Two-dimensional arrays of weakly coupled radio frequency (RF) nanomechanical resonators were designed and fabricated in 50–150 nm thick nanocrystalline diamond films using electron beam lithography and dry etch techniques. We present a novel resonator design that allows us to reduce fabrication tolerances and to confine the frequency spread of individual resonators within ∼ 0.6% over the entire modal frequency range up to 100 MHz. Due to an optimized plasma enhanced chemical vapor deposition (PECVD) nanocrystalline diamond deposition process, high quality factors ( Q > 8000) have been demonstrated for particular modes of vibrations in single nanomechanical resonators. 2D arrays of coupled resonators exhibit an acoustic band, formed by the splitting of the individual resonant modes. The propagation of a wide-band signal within the array has been demonstrated using a high magnification optical imaging setup with two independently controlled scanning lasers. In order to alleviate various sources of disorder in resonator arrays and to demonstrate their potential for RF signal processing, nanomechanical resonator fabrication techniques and resonator designs will be detailed and compared in this manuscript.

CVD Diamond Coatings for Machining

Machining of modern materials requires high performance tools. More than 60% of metal cutting tools used are coated to limit abrasive wear. As the harder material known to man, diamond and consequently Chemical Vapour Deposited (CVD) diamond coatings allow to increase performances of tungsten carbide tools, i.e. tool life, machined surface quality, and to decrease costs. However, CVD diamond coated tools quality is very dependent on the surface preparation as much as the fabrication process parameters. This paper aims to discuss the influence of pretreatments before deposition, and thermal stresses induced by the cooling operation. Diamond deposition process is described emphasizing the role of every step and its function. Some numerical simulations of the residual stresses at the interface are presented, enlightening that tool geometry is an important factor while using a coating, and that tools must be designed for the diamond coating.

Formation of microcrystalline diamond using a low-pressure inductively coupled plasma assisted by thermal decomposition of di- t-alkyl peroxide

Microcrystalline diamond has been successfully synthesized in a low-pressure inductively coupled plasma using di- t-alkyl peroxide. Di- t-alkyl peroxides are thermally decomposed into acetones and methyl radicals, which presumably serve as precursors for the formation of diamond on the silicon substrate at 943 K and 993 K. The deposits on the substrate were examined by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. It was found that the deposits contained a microcrystalline diamond phase even at a low pressure of 11 Pa. Diamond formation over a large area in low-pressure plasmas has been demonstrated by the present novel diamond deposition process using di- t-alkyl peroxide thermally decomposed as a feed gas.

Diamond films grown by millimeter wave plasma-assisted CVD reactor

Polycrystalline diamond films are deposited in a novel MPACVD reactor based on 10 kW gyrotron operating at frequency 30 GHz. The influence of increasing the operating frequency of microwaves in CVD reactor that exceeds the conventionally used frequency 2.45 GHz on diamond deposition process is discussed. Polycrystalline diamond films are grown on silicon substrates with 60–90 mm diameter. The growth rate of diamond films, their quality and morphology at wide variation of process parameters (gas pressure, substrate temperature, microwave power, methane and argon concentrations) in gas mixture Ar / H 2 / CH 4 are investigated. High growth rates up to 9 μm/h are obtained. The results of the diamond growth in 2.45 and 30 GHz MPACVD reactors are compared. The growth rate of diamond films in the 30 GHz reactor is shown to be 5 times greater than the growth rate in the 2.45 GHz reactor under identical process parameters.