Nucleation and growth mechanism of diamond during hot-filament chemical vapour deposition

High-resolution transmission electron microscopy (HRTEM) was employed to study the nucleation and subsequent growth mechanism of crystalline diamond grown on copper TEM grids by the hot-filament chemical vapour deposition process. The HRTEM revealed direct evidence for the formation of a diamond-like amorphous carbon layer 8–14 nm thick, in which small diamond microcrystallites about 2–5 nm across were embedded. These diamond microcrystallites were formed as a result of direct transformation of the diamond-like carbon into diamond. Large diamond crystallites were observed to grow from these microcrystallites. The diamond surface was found to be non-uniform. It is envisaged that the diamond microcrystallites present in the amorphous, diamond-like carbon layer provide nucleation sites on which the large diamond crystallites grew. A mechanism of diamond growth has been proposed, based on the experimental findings, and is consistent with available theoretical models and numerous experimental observations reported in the literature.     

Effect of reaction pressure on the nucleation behaviour of diamond synthesized by hot-filament chemical vapour deposition

Synthetic diamond particles were deposited on a Si (1 0 0) substrate using a hot-filament chemical-vapour-deposition method in order to study the effect of the reaction pressure on the nucleation behaviour. The reaction pressure was controlled, as an experimental variable, from 2 to 50 torr under the following conditions: a filament temperature of 2200 °C, a substrate temperature of 850 °C, a total flow rate of 200 s.c.c.m. and a methane concentration of 0.8 vol%. Diamond deposits on the Si wafer were characterized by micro-Raman spectroscopy, scanning electron microscopy (SEM) and optical microscopy.The maximum nucleation density of diamond particles on the unscratched Si substrate is shown at the reaction pressure of 5 torr. These phenomena can be explained by the competition effect between -SiC formation, which increases the diamond nucleation density, and atomic-hydrogen etching which decreases the nucleation sites.A new fabrication method for a high-quality diamond film without any surface pretreatments is introduced using a combination process between diamond nucleation at low pressure (5 torr) and growth at high pressure (30 torr).     

The nature of stresses in hot-filament chemical vapour deposited diamond thin films on WC substrates

The nature of film stresses in hot-filament chemical vapour deposited (HFCVD) diamond thin films on tungsten carbide substrates, is reported. Commercial WC substrates were subjected to various surface treatments. Subsequently, they were coated with a diamond film and examined for stresses using X-ray diffraction. All but one of the stress measurements indicated various levels of compressive stresses in the film and at the film–substrate interface. These stresses are compared with those obtained by other researchers. Intrinsic film stresses were also computed for diamond films and found to be tensile. WC drills, of 0.125 in. diameter, were also diamond coated and the stress levels measured along drill flanks and flutes. Significant variations were found in these stresses, and the results were analysed from a film–substrate adhesion perspective.     

Structure of diamond and diamond like carbon thin films grown by hot-filament chemical vapour deposition technique

Micro-crystalline diamond (MCD) and diamond like carbon (DLC) thin films were deposited on silicon (100) substrates by hot-filament CVD process using a mixture of CH₄ and H₂ gases at substrate temperature between 400–800°C. The microstructure of the films were studied by X-ray diffraction and scanning electron microscopy. The low temperature deposited films were found to have a mixture of amorphous and crystalline phases. At high temperatures (> 750°C) only crystalline diamond phase was obtained. Scanning electron micrographs showed faceted microcrystals of sizes up to 2μm with fairly uniform size distribution. The structure of DLC films was studied by spectroscopic ellipsometry technique. An estimate of the amount of carbon bonds existing insp ² andsp ³ form was obtained by a specially developed modelling technique. The typical values ofsp ³/sp ² ratio in our films are between 1·88–8·02. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Magnetic and cytotoxic properties of hot-filament chemical vapour deposited diamond

Microcrystalline (MCD) and nanocrystalline (NCD) magnetic diamond samples were produced by hot-filament chemical vapour deposition (HFCVD) on AISI 316 substrates. Energy Dispersive X-ray Spectroscopy (EDS) measurements indicated the presence of Fe, Cr and Ni in the MCD and NCD samples, and all samples showed similar magnetisation properties. Cell viability tests were realised using Vero cells, a type of fibroblastic cell line. Polystyrene was used as a negative control for toxicity (NCT). The cells were cultured under standard cell culture conditions. The proliferation indicated that these magnetic diamond samples were not cytotoxic.     

The effect of pretreatment in a fluidized bed upon diamond synthesis on particles by chemical vapour deposition

Diamond synthesis was carried out on non-diamond particles (single- and poly-crystal silicon, quartz and SiC) by microwave plasma-enhanced chemical vapour deposition. Fine diamond particles were deposited on the non-diamond particle surface. The particle deposition density on the untreated particle substrates was strongly dependent on the surface characteristics of the particle substrates. The value ranged from 10–10⁵ mm^–2 for each particle. Particle substrates were pretreated in a gas-solid fluidized bed, and these were then used for the deposition of diamond. The pretreatment of the surface of the particle substrate in the fluidized bed greatly enhanced the nucleation of diamond. A deposition density of about 10⁷ mm^–2 was obtained on single-crystal silicon particles pretreated for 15 h. The effectiveness of the fluidized bed pretreatment on the deposition density was observed to be appreciable for the four kinds of particle examined.     

等离子热丝化学气相沉积金刚石膜工艺参数研究

采用等离子热丝化学气相沉积(PHFCVD)装置进行了金刚石薄膜的制备实验。实验条件为：氢气流量为200sccm,甲烷流量为2～12sccm,基体温度为700～900℃,偏压为0～400V,真空室压力为4kPa。通过实验得出了甲烷含量、基体温度和偏压对沉积金刚石膜的影响,并运用扫描电子显微镜(SEM)、原子力显微镜(AFM)和X射线衍射(XRD)等测试方法对金刚石薄膜进行了观察分析。     

The effects of oxygen on diamond synthesis by hot-filament chemical vapor deposition

The effects of oxygen addition on the synthesis of diamond are extensively studied by using the hot-filament chemical vapor deposition (HFCVD) method, in which it is simple and easy to control the deposition parameters independently. Diamond films are deposited on silicon wafers under the conditions of substrate temperature 530–950 C; total reaction pressure 700–8000 Pa; and methane concentration 0.4–2.4% in both CH₄–H₂ and CH₄–H₂–O₂ systems.At deposition conditions of low substrate temperature, high CH₄ concentration or high total pressure, soot-like carbon and/or graphite are deposited without oxygen addition. When even a small amount of oxygen (about 0.6%) is added, well-faceted diamond films are observed in scanning electron microscopy micrographs and a sharp diamond peak in the Raman spectra appears. The range of deposition parameters for high-quality diamond syntheses are extended by oxygen addition (low substrate temperature, high methane concentration and high reaction pressure).     

The effective chemical vapour deposition rate of diamond

The effective chemical vapour deposition (CVD) rate of diamond, defined as the total thickness of diamond or as the mass of diamond deposited per unit time, may be increased by orders of magnitude by increasing the substrate area per unit volume. To obtain these high deposition rates, novel substrate designs are proposed that exploit three-dimensional arrays of small diameter wires or fibres. The analysis suggests that the increased diamond output should be achieved with no increase in the net gas flow or power consumption, which could lead to the more economic production of solid diamond shapes and of composites containing continuous or short diamond fibres, or particulate diamond. Estimates for the cost of CVD diamond made by the fibre array technique are compared with reported current and predicted costs for CVD diamond and estimates for the cost of CVD SiC.     

Atmospheric pressure chemical vapour deposition of 3C-SiC for silicon thin-film solar cells on various substrates

The production of crystalline silicon thin-film solar cells on cost effective ceramic substrates depends on a highly reliable diffusion barrier to separate the light absorbing layers from the substrate. Ideally this intermediate layer should be deposited with cost effective techniques, be conductive and should feature optical confinement. Furthermore the intermediate layer should withstand high temperatures and harsh chemical environments like they occur during solar cell processing. Especially stability against oxidizing solvents like HNO3 or inactivity during e.g., oxide removing steps with HF is required. Crystalline silicon carbide (c-SiC) deposited by atmospheric pressure chemical vapour deposition (APCVD) can match all those requirements and additionally fits the thermal properties of crystalline silicon. The c-SiC intermediate layer is deposited from methyltrichlorosilane (MTS) and H2 at 1100 degrees C. Under these conditions, growth of solely cubic 3C-SiC could be observed by X-ray diffraction measurements. Use of such intermediate layers during high temperature steps prevents diffusion of transition metals, originating from the substrates, into active silicon layers. Doping of these 3C-SiC layers with nitrogen results in specific resistivity of less than 100 ohms cm. The different potentially cost-effective substrates are made from graphite, crystalline silicon, sintered silicon carbide and sintered zircon (ZrSiO4). Surface properties of the coated substrates were investigated, explaining changes in surface roughness and influences on the solar cell processing.     

Plasma-enhanced chemical vapour deposition of AlN coatings on graphite substrates

Graphite substrates have been covered with aluminium nitride (AlN) layers prepared by plasma-enhanced chemical vapour deposition from AlBr₃-N₂-H₂-Ar gas mixtures. The glow discharge (frequency, 13.56 MHz; power, 50–500 W) was generated by an r.f. induction coil. The graphite substrate mounted on a grounded graphite susceptor was inductively heated up to a temperature in the range 200–800 °C. The mass of the deposit per square centimetre was determined as a function of reaction time, total gas pressure, substrate temperature, r.f. power, gas flow velocity and AlBr₃ concentration. The morphology of the AlN layers was examined by scanning electron microscopy. Fine-grained polycrystalline AlN films were grown at 700 °C under a total pressure below 10 Torr. Translucent polycrystalline AlN films having a 〈001〉 preferred orientation were deposited at a total pressure in the range 10–40 Torr.     

Growth of diamond thin films by chemical vapour deposition

Deposition of diamond thin films on non-diamond substrates at low pressures (<760 torr) and low temperatures (<2000°C) by chemical vapour deposition (CVD) has been the subject of intense research in the last few years. The structural and the electrical properties of CVD diamond films grown on p-type 〈111〉 and high-resistivity (>100 kΩ-cm) 〈100〉 oriented silicon substrates by hot filament chemical vapour deposition technique are described in this review paper.     

Microstructures of diamond films deposited on (100) silicon wafer by microwave plasma-enhanced chemical vapour deposition

Diamond films were deposited on (1 0 0) silicon wafer by microwave plasma-enhanced chemical vapour deposition. The microstructural changes of the diamond films were studied in relation to the pre-treatment of the silicon substrate, the methane concentration and the substrate temperature. The ultrasonic method for the pre-treatment of the silicon substrate increased the nucleation density, resulting in the deposition of small diamond particles. The surface morphology changed from the close-packed (1 1 1) to the (1 0 0) plane with increase in the methane concentration due to the decreased adatom mobility. The morphology also changed from (1 1 1) to (1 0 0) planes with substrate temperature, due to the effect of the increased chemical species. The change in the crystallinity with deposition time was also investigated.     

Diamond chemical vapour deposition on seeded cemented tungsten carbide substrates

Diamond particles were deposited onto seeded cemented tungsten carbide (WC-Co) substrates using conventional hot-filament chemical vapour deposition (HFCVD) and time-modulated CVD (TMCVD) processes. The substrates were pre-seeded ultrasonically with diamond particles of different grit sizes. In this investigation, we employ timed methane (CH₄) gas modulations, which are an integral part of our TMCVD process in order to enhance diamond nucleation density. During diamond deposition using the conventional HFCVD process, methane gas flow was maintained constant. The total hydrogen flow into the reactor during TMCVD process was higher than in the HFCVD process. Hydrogen etching can be expectedly more prominent in the TMCVD process than in HFCVD of diamond particles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that a proper selection of the diamond grit size for seeding using ultrasounds can lead to enhancement in the nucleation density values of about two orders of magnitude (10⁷ to 10⁹ cm^− 2). The TMCVD process using the different seeded substrates can result in high nucleation density values of up to 10¹⁰ cm^− 2.     

Nucleation and growth study of copper thin films on different substrates and wetting layers by metal-organic chemical vapour deposition

Chemical vapour deposition of copper thin films on different diffusion barrier/adhesion promoter layers have been studied. Copper thin films were grown in low pressure CVD reactor, using Cu(dpm)₂ as precursor and argon as carrier gas. Growth rates, film adhesion to the substrate, and surface morphology were studied in detail. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Stability of low pressure chemical vapour deposition amorphous silicon

The study of the influence of phosphorous doping and hydrogen content on transport properties and thermally induced metastability of low pressure chemical vapour deposition a-Si is reported. Introduction of hydrogen causes change of dominant carrier transport mechanism at room temperature. The thermally induced metastability was observed in both unhydrogenated and hydrogenated P-doped a-Si films. In this paper we report our studies on the effect of the thermally induced metastability in unhydrogenated and hydrogenated films of LPCVD a-Si, as a function of phosphorous concentration.