Large-area Diamond Research Articles

Preparation of 4-inch Ir/YSZ/Si(001) substrates for the large-area deposition of single-crystal diamond

Diamond/Ir/YSZ/Si(001) is currently the most promising multilayer structure for the future realisation of large-area diamond single crystals. A decisive key is the preparation of the iridium layers on silicon. It is shown in this work that high quality iridium films with mosaic spread below 0.2° can be grown on oxide buffer layers with a mosaic spread higher than 1°. An averaging process during the coalescence of the iridium islands provides a plausible mechanism for this phenomenon. The oxide buffer and the iridium overlayers can be grown homogeneously on 4-inch wafers in a similar quality as for 1 × 1 cm 2 samples. Bias enhanced nucleation followed by 40 h growth on the large-area Ir/YSZ/Si(001) wafers yields diamond films with a mosaicity of 0.16° (tilt) and 0.34° (twist). For a further increase of the area of heteroepitaxial diamond nucleation the homogeneity of the plasma discharge has to be improved.

Study of the Thermal and Intrinsic Stress of Large Area Diamond Film Prepared by HFCVD

High residual stress that includes thermal and intrinsic stress is an obstacle to the further application of chemical vapor deposited diamond thick film. In this paper, CVD diamond thick film was deposited on silicon substrate by hot filament chemical vapor deposited (HFCVD) system. The finite element analysis (FEA) simulation and experimental research were carried out on the thermal and intrinsic stress of large area diamond thick film. The FEA model is set up to investigate the distribution and magnitude of thermal stress. The intrinsic stress is studied by X-Ray diffraction “sin2ψ” method. The thermal stress and intrinsic stress are both compression stress. Simulation results show the discontinuous sharp of the diamond film result in the stress concentration and low cooling velocity is a good way to reduce thermal stress. The intrinsic stress is correlative with the microstructure and non-diamond component of diamond film. The origin of the intrinsic stress is discussed in detail in this paper.

Investigation of Technology and Analysis of Residual Stress in Large Area Diamond Films

We investigated the residual stress in diamond films grown on molybdenum substrates as a function of different places in the same large sample. The diamond film wafers of Ф60 mm diameter were deposited at 900°C by high power DC arc plasma jet CVD method using a gas mixture of methane (1.8% vol.) and hydrogen ( 90% vol.). The grain sizes, obtained from the top view scanning electron microscopy (SEM) images, were found to become larger from center to the border in the same sample, and the x-ray diffraction indicated that the intensity of characteristic spectroscopy in same diamond film was changed from (220) to (111) with the increases of (311). Profile curves presented the appreciable difference of surface texture from center to edge. The film had 4.3GPa of residual compressive stress. Examination of the Raman spectra of the film revealed that residual stress in the film of up to approximately 0.70GPa, and the Raman spectroscopy shifts from 1332.99cm-1 at the center to 1331.17cm-1 at the border, which means the stress mode changed from compressive to tensile. These demonstrated a significant inhomogeneity of stress in diamond films. The differences have been attributed partly to high temperature inhomogeneity arc jet during growth and morphological aspects of the film growth. The relationships between stress and methane concentration, and substrate temperature are discussed in detail.

Evaluation research of polishing methods for large area diamond films produced by chemical vapor deposition

The current study compared several polishing techniques of chemical vapor deposition (CVD) diamond films. Although research on various diamond polishing techniques has been carried for years, some issues still need to be examined in order to facilitate application on large areas in a cost-efficient manner. In the present work, microwave plasma enhanced chemical vapor deposition (CVD) was used to obtain diamond films with full width half magnitude (FWHM) less than 10 wavenumbers at 1332 cm − 1 Raman peak. The diamond films were processed through mechanical polishing, chemical-assisted mechanical polishing, thermo-chemical polishing, excimer laser ablation, and catalytic reaction assisted grinding. A profilometer, an atomic force microscope, and a scanning electron microscope have been used to evaluate the surface morphology of diamond films before and after polishing. The results obtained by using the above mentioned techniques were analyzed and compared.

Diamond cone arrays with controlled morphologies formed by self-organized selective ions sputtering

Controlled preparation of nanoscale materials and the underlying mechanisms are essential issues nowadays. Here, we report a significant subtractive formation process of large-area diamond conical nanostructure arrays using a hot filament chemical vapor deposition (HFCVD) system with negative biasing of the substrates, and the etching effect of energetic ions on the formation of diamond cone arrays with controlled morphology has been studied in detail. It shows that methylic ions dominantly contribute to diamond cone formation based on a neutral-ion charge exchange collision model. The self-organized selective sputtering process of as-formed hillock bottoms on a roughened surface by low energetic ions plays a key role for the formation and development of diamond cones. The cone morphologies under various experimental parameters are systematically studied, and they nicely confirm and supplement the as-established cone formation mechanism.

The effect of the substrate position on microwave plasma chemical vapor deposition of diamond films

The study is made on synthesizing diamond films using microwave plasma chemical vapor deposition (MPCVD) method, the kinetic energy uniformity of particles just above substrate surface are found to be improved as the substrate moved toward the plasma core. However, the deposition of non-diamond carbons will form if the substrate is placed close enough to the plasma core. It shows that the diamond characteristic qualities of the diamond film can be significantly promoted by adequately adjusting the working distance. A large area diamond film with consistent diamond qualities over various surface regions can thus be successfully synthesized using lower power plasma.

Enhanced electron emission from diamond film deposited on pre-seeded Si substrate with nanosized diamond power

Diamond film was synthesized by microwave plasma chemical vapor deposition (MWPCVD) method. The deposition process of diamond film on 4-in. pre-seeded mirror polished silicon wafer was divided into four steps: (a) seeding nano-diamond powder on Si surface; (b) annealing for increasing the adsorbed strength between diamond powder and substrate; (c) diamond film growth; (d) bombarding with H + ion for decreasing film stress and obtaining planar field emission from diamond film with large area. Scanning electron microscopy (SEM), Raman spectroscopy and stress measurement system were used to characterize the structure and property of diamond film. The electron emission from large area diamond film on seeded substrate was described and compared with that from diamond film deposited on Si substrate scratched by diamond powder. The results suggested that low-field electron emission and high emission current could be obtained from diamond film deposited on seeded substrate due to the reduction of interface energy barrier for electron tunneling. A threshold field of 3.0 V/μm and emission current density of 1 mA/cm 2 at 30 V/μm were achieved.

Technology of polycrystalline diamond thin films for microsystems applications

Large area and uniform polycrystalline diamond (poly-C) thin films, with a thickness of approximately 1μm, were grown and patterned on 4in. oxidized Si wafers using IC compatible processes for microsystems applications. Uniform and reproducible seeding with a density of 2×1010∕cm2 was achieved by spinning diamond powder loaded water on 4in. wafers. Gas mixture of 1.5% methane in hydrogen was used in MPCVD system for diamond film growth with optimized pressure and microwave power. Thickness variation of less than 20% was achieved on the 4in. area using 43Torr pressure and 2.8kW microwave power. Electron cyclotron resonance (ECR)-assisted microwave plasma reactive ion etch was carried out using SF6∕O2∕Ar gases to pattern the diamond films with an etch rate around 80nm∕min and less than 10% variation in etch rate over a 4in. area.

IBIC imaging of intra-crystallite charge transport in CVD diamond at reduced temperature

We present high resolution maps of charge collection efficiency in polycrystalline CVD diamond film, acquired using ion beam induced charge imaging with a 2 MeV He 2+ microbeam. By measuring the charge collection efficiency in a coplanar electrode device, it is possible to observe the spatial variations in charge drift length within a single large-area diamond crystallite. The measured charge collection efficiency within the crystallite increases with bias voltage, with no saturation observed at voltages up to −250 V, corresponding to an average bulk electric field of 2.5 V/μm. When cooling the device from 297 K to 200 K, the maximum charge collection efficiency decreases from 70% to 13% due to a reduction in charge carrier lifetime. This data gives an insight into the role of relatively shallow traps present within diamond crystallites, which tend to limit the charge drift length in CVD diamond radiation detectors at room temperature.

Microcrystalline CVD-diamond samples as storage media for ultraviolet images

Photocathode structures have been fabricated by means of thin microcrystalline CVD-diamond samples. Owing to the presence of structural defects in the material, metastable phenomena related to the existence of trap states within the diamond bandgap can be observed. Such effects are mainly reflected in the increase of the subgap photoemission sensitivity of the diamond film after an exposure under over bandgap ultraviolet photons (λ<225 nm). This fact suggests the use of diamond as storage medium for ultraviolet images. The possible structure of an image sensor for UV-radiation based on large area diamond film on silicon has been proposed and tested.

A study on nano-nucleation and interface of diamond film prepared by hot filament assisted with radio frequency plasma

We have combined radio frequency (RF) plasma with hot filament (HF) chemical vapor deposition (CVD) together to investigate diamond growth. By modifying the conventional RF apparatus and tungsten arrangement in RF system, we systematically investigated the process of nucleation, interlayer formation and growth by atom force microscopy (AFM), X-ray diffraction (XRD) and Raman spectra. The experimental results showed that at low substrate temperature, nano-crystal diamond and other non-diamond carbons formed. The interface between the film and the substrate contained four components: SiC, tungsten (W), W/WC or W 2C, W–δ-WB and W/Si 2W. High-quality diamond film can only be prepared at T s>700 °C by RF+HF-CVD and the contamination from tungsten filaments has been remarkably reduced by pre-heating the filament in CH 4+H 2 atmosphere and placing it as near the upper electrode as possible. Furthermore, large area diamond film can be easily synthesized by HF+RF-CVD method, which has more advantages than other methods.

Precise patterning of diamond films for MEMS application

To apply diamond films in microelectromechanical systems (MEMS), it is necessary to develop suitable techniques to pattern diamond films in micrometer scale. In this paper, three different techniques capable of precise patterning diamond films will be demonstrated. One is to selectively grow diamond films in the desired region by pre-improving the diamond nucleation density in the said region using DC bias-enhanced microwave plasma chemical vapor deposition (MPCVD). Another technique is to selectively grow diamond films in the desired region by seeding the given region using diamond-powder-mixed photoresist. The third technique is to selectively etch large-area diamond film by an oxygen-ion beam under an Al mask. Several diamond-film patterns with a feature size of a few micrometers were successfully fabricated, and some technical problems encountered in the techniques are discussed.

NUMERICAL PREDICTION OF THE INFLUENCE OF PROCESS PARAMETERS ON LARGE AREA DIAMOND DEPOSITION BY DC ARCJET WITH ARC ROOTS ROTATING AND OPERATING AT GAS RECYCLING MODE

A computer model have been set up for simulation of the flow and temperature field, and the radial distribution of atomic hydrogen and active carbonaceous species over a large area substrate surface for a new type dc arc plasma torch with rotating arc roots and operating at gas recycling mode A gas recycling radio of 90% was assumed. In numerical calculation of plasma chemistry, the Thermal-Calc program and a powerful thermodynamic database were employed. Numerical calculations to the computer model were performed using boundary conditions close to the experimental setup for large area diamond films deposition. The results showed that the flow and temperature field over substrate surface of Φ60-100mm were smooth and uniform. Calculations were also made with plasma of the same geometry but no arc roots rotation. It was clearly demonstrated that the design of rotating arc roots was advantageous for high quality uniform deposition of large area diamond films. Theoretical predictions on growth rate and film quality as well as their radial uniformity, and the influence of process parameters on large area diamond deposition were discussed in detail based on the spatial distribution of atomic hydrogen and the carbonaceous species in the plasma over the substrate surface obtained from thermodynamic calculations of plasma chemistry, and were compared with experimental observations.

Generation of pulsed direct-current plasma above 100 torr for large area diamond deposition

A high-temperature, large-size plasma was successfully generated at a pressure above 100 torr using a pulsed direct current (DC) electric power for the application of wafer-scale diamond thick film growth. A diode type electrode configuration was used, with a Mo disk of 13 cm in diameter as a cathode and a W disk of 10 cm in diameter as a substrate. By adjusting the pulse condition and maintaining the cathode temperature between 1000°C and 1100°C, the arc between the electrodes was suppressed completely and the plasma was maintained very stably for over 100 h. Above and below this cathode temperature range, solid carbon was deposited on the cathode, which induced either the arc or non-uniformity of plasma state. A diamond wafer with a thickness up to 1 mm was successfully grown using this plasma of methane and hydrogen mixed gas. The plasma characteristics were analyzed using an optical emission spectroscopy.

Neutron irradiation studies on window materials for EC wave systems

Fast neutron irradiation experiments are reported to study tolerable fluence levels of the primary window of electron cyclotron (EC) wave systems near the torus. Model discs of CVD diamond grades (30/40 mm diameter) were irradiated to fluences between 10 20 and 10 22 n/m 2 ( E>0.1 MeV). For a torus window demonstrator, a large area diamond disc of (106 mm diameter) was irradiated to 0.9.×10 21 n/m 2. Mechanical strength tests were performed with specimens (11 mm diameter) cut from medium size diamond discs (62 mm diameter). In contrast to dielectric and mechanical properties, the most sensitive material parameter is thermal conductivity for which at 10 −4 dpa a significant reduction by about a factor of 2 has to be accounted for. Comparative dielectric measurements for Quartz discs and special silica glass grades (Infrasil, KU1) showed that loss in quartz stayed at the tan δ-level of 10 −4 at least up to 10 22 n/m 2; loss in the unirradiated KU1 glass reached the 10 −3 level.

Diamond for high-density optical recording

The feasibility of optical recording by irradiating diamond with energetic ion beams has been investigated. The radiation damage in the exposed target areas provides sufficient optical contrast to the unexposed parts as to distinguish analog or digital patterns by visible light. The physical properties of the radiation effects have been studied by a variety of experimental techniques, including optical transmission and luminescence, photo-thermal deflection spectroscopy, infrared and Raman spectroscopy, and ion beam channeling in conjunction with atomic force measurements. The important result is that permanent data storage in diamond is possible with high pixel densities. A unique feature of diamond, irradiated up to and beyond a critical ion fluence, is the thermal phase transformation to its allotropic form of graphite. This feature can be used to enhance optical contrast at sub-amorphization irradiation levels. Estimates on the pixel density of data recording in diamond are presented and the necessity of developing large-area diamond wafers of high optical quality is emphasized.

Novel technique for hetero-epitaxial diamond film growth on cubic boron nitride from iron carbide at high temperature and high pressure

Cubic boron nitride (c-BN) crystals about 0.1–0.3 mmin dimension were treated with iron carbide powders (high purity 99%) with size of 80–100 mesh at a high temperature of 1620 K and a high pressure of 5.2 GPa. It was found that hetero-epitaxial diamond films have been grown on the c-BN from iron carbide. The formation of dia-mond films on the cubic boron nitride can be confirmed by laser Raman spectra, face scan of elements and reflective high-energy electron diffraction. It was suggested that diamond films could be epitaxially formed on the c-BN through decomposition of iron carbide. This approach provides a possible and very effective way to realize hetero-epitaxial growth of homogeneous and large-area diamond films on c-BN, which is different from the conventional technique using a chemical vapor deposition method.

Deposition of large area high quality diamond wafers with high growth rate by DC arc plasma jet

We have successfully developed a system for deposition of large area diamond films by a DC arc plasma jet operated in gas recycling mode. In the present paper, the influence of substrate temperature, methane concentration, flow rate of feeding gas and the input power of the jet for diamond film deposition is presented. Deposition of a large area of uniform thickness high quality diamond wafer of Φ65 mm in diameter at a growth rate of 15 μm/h is reported. The thickness of the wafer is 0.7 mm and the thermal conductivity can be 18.1 W/cm K.

Effect of Oxygen Component in Magneto-Active Microwave CH4/He Plasma on Large-Area Diamond Nucleation over Si

Nucleation-enhanced pretreatments have been studied for large-area diamond growth on Si (100) substrates using magneto-active microwave plasma chemical vapor deposition (CVD) at low pressures below 10 Pa. In this study, an optimal CO2 composition in the CH4/He plasma used for the pretreatment was mainly examined for the case of a low substrate temperature of ∼600°C. A two-hour subsequent growth using a CH4[5 sccm]/CO2[10 sccm]/H2[85 sccm] gas mixture after the pretreatment resulted in <100>-oriented growth of diamond Particles with a high density (∼109/cm2) on Si substrates pretreated at CO2 concentrations of 1–2%. On the other hand, at CO2 concentrations higher than these, the carbon films deposited during the pretreatment were less dense and were almost completely etched off after a 10-min treatment using the growth plasma. It was found that quadrupole mass spectra, optical emission spectra and Raman scattering spectra changed substantially when CO2 beyond 3.8% was added to the source gas.

Large area diamond films growth in multi-filament chemical vapor deposition

Large area diamond film growths were carried out on Si wafer 40 mm in diameter using multi-filament chemical vapor deposition (CVD). For the purpose of increasing the utilization ratio of reactive gases and gas flow velocity a conduit and gas centralizing cavity were used during deposition. Deposited films were characterized by scanning electron microscope (SEM) and Raman spectroscopy. Thickness variations across the substrate were measured. The experimental results show that high quality diamond films were deposited all over the substrate surface. The film quality and growth rate are uniform across the substrate surface. Due to the introduction of conduit and gas-centralizing cavity the growth rate is rather high and is about 2 μm h −1.