High Quality Diamond Films Research Articles

Low-Temperature Deposition of Diamond Films by MPCVD with Graphite Paste Additive

Modern integrated circuits (ICs) take advantage of three-dimensional (3D) nanostructures in devices and interconnects to achieve high-speed and ultra-low-power performance. The choice of electrical insulation materials with excellent dielectric strength, electrical resistivity, strong mechanical strength, and high thermal conductivity becomes critical. Diamond possesses these properties and is recently recognized as a promising dielectric material for the fabrication of advanced ICs, which are sensitive to detrimental high-temperature processes. Therefore, a high-rate low-temperature deposition technique for large-grain, high-quality diamond films of the thickness of a few tens to a few hundred nanometers is desirable. The diamond growth rate by microwave plasma chemical vapor deposition (MPCVD) decreases rapidly with lowering substrate temperature. In addition, the thermal conductivity of non-diamond carbon is much lower than that of diamond. Furthermore, a small-grain diamond film suffers from poor thermal conductivity due to frequent phonon scattering at grain boundaries. This paper reports a novel MPCVD process aiming at high growth rate, large grain size, and high sp3/sp2 ratio for diamond films deposited on silicon. Graphite paste containing nanoscale graphite and oxy-hydrocarbon binder and solvent vaporizes and mixes with gas feeds of hydrogen, methane, and carbon dioxide to form plasma. Rapid diamond growth of diamond seeds at 450 °C by the plasma results in large-grained diamond films on silicon at a high deposition rate of 200 nm/h.

Effect of Mechanically Created Pits Pattern for Direct Diamond Deposition on Stainless-Steel Surface

Direct diamond deposition on a steel surface has been considered very difficult. Recently, we found that high-quality diamond films can be deposited on the surface of stainless-steel X5CrNi 18-10 by drilling multiple regularly arranged pits without interlayers or seeding. The following two hypotheses (A) and (B) can be considered as the reason why a high-quality diamond film can be deposited: (A) unoxidized Cr and Ni exposed to the stainless-steel X5CrNi 18-10 surface prevent carbon diffusion into interior of the stainless-steel, resulting diamond core generation, (B) Surface geometry with regular roughness contributes to stress relaxation and delamination prevention. In the present study, those hypotheses have been examined by quantum chemistry calculation and experimental. For the quantum chemistry calculation, energy barrier and kinetic energy for a carbon atom intrudes into a model cluster has been calculated with an ab-initio computational chemistry software package, Gaussian. The calculation result has supported hypothesis (A). For the experiment, X5CrNi 18-10 stainless-steel substrates with different surface characteristics are prepared by using various mechanical machining methods and used in the direct deposition process for diamond with in-liquid plasma CVD. The experimental result has supported both hypothesis (A) and (B).

The synchronous detection technique for the accurate monitoring of high-energy pulsed X-rays

At high energy, the smaller inelastic nucleon-Carbon cross-section implies that diamond has a radiation hardness an order of magnitude higher than that of silicon. The production of high-quality diamond crystals and films grown using the chemical vapor deposition technique opened the way for the use of synthetic diamonds in the fabrication of detectors for charged particles and high-energy photons. More recently, laser-processing technology for the fabrication of three-dimensional contacts in diamond has been proposed to produce highly efficient detectors, even with ultra-low active volumes. However, buried-contact structures made with laser treatments unavoidably induce structural defects in the volume surrounding the buried columns, thus affecting the detector response due to trap-related charge transport mechanisms. When pulsed radiation is concerned, experimental results reported in this work demonstrate that synchronous signal conditioning can strongly mitigate the trap-mediated contribution, thereby improving the performance of the overall detection system. Significantly, these results pave the way for the application of diamond samples with three-dimensional buried-contacts in the development of detectors for accurate dosimetry.

H-Terminated Diamond MOSFETs on High-Quality Diamond Film Grown by MPCVD

Diamond-based transistors have been considered as one of the best choices due to the numerous advantages of diamond. However, difficulty in the growth and fabrication of diamond needs to be addressed. In this paper, high quality diamond film with an atomically flat surface was grown by microwave plasma chemical vapor deposition. High growth rate, as much as 7 μm/h, has been acquired without nitrogen doping, and the root mean square (RMS) of the surface roughness was reduced from 0.92 nm to 0.18 nm by using a pre-etched process. H-terminated diamond MOSFETs were fabricated on a high-quality epitaxial diamond layer, of which the saturated current density was enhanced. The hysteresis of the transfer curve and the shift of the threshold voltage were significantly reduced as well.

High-speed growth of high-quality polycrystalline diamond films by MPCVD

High-speed growth of high-quality polycrystalline diamond films by MPCVD

Influence of Diamond Seed Attachment Processing on Diamond Films Synthesized on Tungsten Carbide Substrate by Flame Combustion

The flame combustion method enables the synthesis of diamonds via acetylene-oxygen gas flame combustion in ambient air. Tungsten carbide (WC) has recently been utilized as a cutting tool in the machining industry and in dental machining applications. To obtain high-quality diamond films and achieve good adhesion on a WC substrate, diamond films are synthesized on a WC substrate by the flame combustion method. However, the surface roughness of most of the diamond films synthesized by this method increased, and it was necessary to reduce this roughness. Considering the roughness accuracy of the workpiece surface during cutting, and the performance of the cutting tool, a smaller surface roughness of the diamond films synthesized is desirable. In this study, to reduce surface roughness, the amount of diamond paste with diamond seed particles as generation nuclei was carefully varied for diamond seed attachment processing of diamond films. When diamond films were synthesized on the WC substrate surface via the flame combustion, the amount of diamond paste with diamond seed particles affected the surface morphology and surface roughness of the synthesized diamond films. Furthermore, to investigate the reason for this result, generation of nuclei on the substrate in the initial stages of synthesis and diamond seed particles on the substrate surface after the seeding treatment were observed by scanning electron microscopy. The effect of diamond seed attachment processing on the diamond films synthesized by flame combustion was studied. The relationship between the surface roughness, number of diamond generation nuclei on the substrate in the initial stages of synthesis, number of diamond particles on the substrate after the diamond seeding process, and amount of diamond paste were confirmed.

High-rate growth of single-crystal diamond with an atomically flat surface by microwave plasma chemical vapor deposition

High quality single crystal diamond builds the foundation for the applications in high-power, high-frequency electronic devices. In this paper, high-quality (100) single-crystal diamond film grown by microwave plasma chemical vapor deposition (MPCVD) was studied. By optimizing the pre-etching process before growth, where the distance between the substrate and plasma plays an important role, high-quality chemical vapor deposition (CVD) diamond layer with a smooth surface can be acquired. The root-mean-square roughness of CVD diamond surface was reduced to 0.2 nm ∼ 0.5 nm within 5 μm × 5 μm area while maintaining the growth at a high rate of 3 μm/h ∼ 30 μm/h. The sheet resistance of the CVD diamond layer was 6.1 kΩ/sq by transmission line method, indicating a high potential to fabricate high-performance hydrogen-terminal diamond-based electronic devices.

New chemical pathway for large-area deposition of doped diamond films by linear antenna microwave plasma chemical vapor deposition

Today, boron-doped diamond (BDD) is among the key materials for electrochemical sensing and advanced oxidation of micropollutants. Therefore, a cost-effective fabrication of large-area BDD electrodes is of high interest. We present an implementation of a liquid-phase boron precursor trimethyl borate for large-area deposition of boron-doped diamond films by linear antenna microwave plasma CVD. Trimethyl borate vapors were used not only as a source of boron for doping but also as the only source of carbon and oxygen, while completely saturating the requirements for the growth of high-quality boron-doped diamond films. However, to allow for control over the doping level through maintaining the B/C and B/O ratios, carbon dioxide was employed as an additional source of carbon and oxygen. The film morphology was controllable from microcrystalline to ultra-nanocrystalline by changing the concentrations of trimethyl borate. Using this unique precursor system, we were able to grow diamond films with a doping level in range from 8 × 1017 cm−3 to 2 × 1022 cm−3 and resistivity as low as 1.16 × 10−2 Ω·cm. Low activation energies were calculated from the Arrhenius plot and growth rates as high as up to 170 nm/h for the low pressure microwave plasma CVD were reached. The investigation of the plasma emission spectrum revealed a chemical composition similar to that of hydrogen-rich plasmas with methane, and the proposed chemical reactions indicate that the diamond growth takes place via the hydroxyl radical. The results demonstrated that trimethyl borate is a suitable source of carbon and boron for the large-area growth of highly boron-doped diamond via low pressure microwave plasma CVD methods.

Influence of Substrate Surface Roughness on Synthesized Diamond Films by Flame Combustion on Ti Substrate for Dental Implants

The flame combustion method enables the synthesis of diamonds via acetylene-oxygen gas flame combustion in ambient air, and this method has various advantages over other methods. However, most diamond films synthesized by this method delaminate because of thermal stress during cooling. Titanium (Ti) has recently been utilized as a dental implant in the dental industry. In this study, to improve the strength, wear resistance, and biocompatibility of dental implant surfaces, diamond films were synthesized on a Ti substrate, a dental implant material, by the flame combustion method. Moreover, to obtain high-quality diamond films and achieve good adhesion on the Ti substrate, as a pretreatment of the substrate to prevent delamination, scratch processing, in which a substrate is ground with emery paper in one direction, was performed to roughen the surface. The surface roughness of the Ti substrates was varied by scratching with emery paper of #180, #400, and #1500 grain sizes. According to these results, diamond films were synthesized on the Ti substrate surface by flame combustion. The surface morphology of the synthesized films could be altered by varying the scratching process using emery paper. Delamination of the synthesized films during the scratching process with emery paper #180 (Case A) and #400 (Case B) grain size was completely prevented. However, delamination occurred during the scratching process with a grain size of emery paper #1500 (Case C). To investigate the reason for this result, the surface roughness of the pretreated Ti substrate was observed, and it affected the surface roughness of pretreated Ti substrate affected the surface morphology and delamination of the synthesized diamond films.

Cu-Ir thin film alloy as a potential substrate for the heteroepitaxial diamond growth

Due to a relatively low mismatch to the diamond lattice, iridium allows to produce high-quality heteroepitaxial diamond films. However, extremely high price of iridium motivates to find a suitable replacement. In this article, we focus on the new homogeneous Ir(Cu) alloy sputtered on the SrTiO3 as a potential substrate material for the diamond heteroepitaxy. We show that in magnetron-sputtered thin films copper can form a solid solution with iridium at concentrations up to 27 at.% with the same FCC structure. Ir(Cu) alloy can reduce using of iridium with the same quality of heteroepitaxial diamond production.

Fabrication of Q-Carbon Nanostructures, Diamond and Their Composites with Wafer-Scale Integration

We report the formation of Q-carbon nanolayers, Q-carbon nanoballs, nanodiamonds, microdiamonds, and their composites by controlling laser and substrate variables. The choice of these parameters is guided by the SLIM (simulation of laser interactions with materials) computer modeling. For a constant film thickness and initial sp3 content, we obtain different microstructures with increasing pulse energy density as a result of different quenching rate and undercooling. This is related to decreasing undercooling with increasing pulse energy density. The structure of thin film Q-carbon evolves into Q-carbon nanoballs with the increase in laser annealing energy density. These Q-carbon nanoballs interestingly self-organize in the form of rings with embedded nanodiamonds to form Q-carbon nanoballs/diamond composites. We form high quality, epitaxial nano, and micro diamond films at a higher energy density and discuss a model showing undercooling and quenching rate generating a pressure pulse, which may play a critical role in a direct conversion of amorphous carbon into Q-carbon or diamond or their composites. This ability to selectively tune between diamond or Q-carbon or their composites on a single substrate is highly desirable for a variety of applications ranging from protective coatings to nanosensing and field emission to targeted drug delivery. Furthermore, Q-carbon nanoballs and nanodiamonds are utilized as seeds to grow microdiamond films by HFCVD. It is observed that the Q-carbon nanoballs contain diamond nuclei of critical size, which provide available nucleation sites for diamond growth, leading to stress-free, adherent, and denser films, which are needed for a variety of coating applications.

Design and simulation of a novel MPCVD reactor with three-cylinder cavity

A novel microwave plasma chemical vapor deposition (MPCVD) reactor with three-cylinder cavity and outstanding tuning capability was proposed. The electric field and plasma in the reactor were simulated, and four geometric parameters were optimized. After optimization, the electric field intensity above the substrate exceeded 5×103V/m (input power of 1 W), which was 1.6 times that of the similar cylindrical reactors. Only one strong plasma formed above the substrate surface with an input power of 5 kW once the gas pressure exceeds 8 kPa. But the plasma coverage area was decreased with the increase of the gas pressure. The plasma coverage area could be restored by adjusting the height difference between the adjusting mechanism 1 and 2. The frequency detuning caused by the microwave frequency changes also could be returned by adjusting the adjusting mechanisms. The subsequent experimental results showed that uniform and high-quality diamond films could be deposited under the simulation condition (5 kW and 12 kPa). It could verify the accuracy of the simulation and the excellent performance of the new MPCVD reactor.

Structure and Wettability Engineering of Polycrystalline Diamond Films Treated by Thermally Oxidation, Second Growth and Surface Termination

High-quality polycrystalline diamond films with dominated (100)-oriented grains are realized by combining the thermally oxidation and the homogeneous second growth processes. Moreover, we investigate the wettability property of the polycrystalline diamonds in various stages. Different surface structures (with various grain sizes, voids, and orientations, etc.) and terminations (hydrogen or oxygen) have significant effects on the wettability of polycrystalline diamond films. The wettability is further closely related to the polarity of solutions. By measuring the contact angle and calculating the dispersion and polarity components, we estimate the surface energy of polycrystalline diamond films, and explore the factors affecting the surface energy. The modulations in growth quality and wettability property of polycrystalline diamond films provide valuable data for development of diamond-based multiple devices in practical applications.

Improvement on uniformity of diamond coatings on PCB milling cutters with specific cutting edge structures

Recently, specially-designed printed circuit board (PCB) milling cutters with specific cutting edge structures have been extensively applied. Hot filament chemical vapor deposition (HFCVD) diamond coatings uniformly deposited on cemented carbide (WC-Co) cutters can effectively improve their performance. To improve the coating uniformity, the complex cutters were precisely modeled and the temperature field generated by the HFCVD setup was simulated, using the finite volume method (FVM), taking spiral milling cutters as a reference for comparison. Temperature measurements revealed deviations between simulated and measured temperatures smaller than 4%, verifying the accuracy of the constructed model. Effects of some critical HFCVD setup parameters, including the filament height (Hf), the material and height of the sample holder (Ms and Hs), the material and dimensions of the heat insulating block (Mh, Hh and Ah), and the surface convection coefficient (h), were studied by the control variable method. Under the optimized conditions, the axial temperature deviation on cutting edges dropped from 193.3 °C to 64.3 °C for a PCB milling cutter, and from 53.3 °C to 29.6 °C for a spiral cutter, ensuring appropriate temperature ranges for fabricating high-quality diamond films. Besides, the two-dimensional plane temperature field and received radiation field of a cutter were both calculated by MATLAB. The results showed that heat conduction hindrance and heat convection reduction could effectively reduce energy consumption and improve the uniformity of substrate temperature. With the aim to study the specific cutting-edge structures, cross-sectional temperature distributions were further examined by presenting both simulations and numerical calculations. It was seen that the temperature distribution for PCB milling cutters was complicated, which was attributed to the densely-distributed cutting edges and long flute. Lastly, under the optimized HFCVD setup parameters, it was found that the grain size and thickness uniformity of diamond coatings, at different positions along the axial direction, were significantly improved, revealing the effectiveness of simulation as an optimization method.

CVD-synthesis of detector quality diamond for radiation hardness detectors of ionizing radiation

An advanced microwave plasma reactor ARDIS 300 was used to synthesize homoepitaxial structures of monocrystal diamond films at Project Center ITER. High-quality epitaxial diamond films were grown on boron-doped monocrystal diamond substrates using microwave plasma-assisted chemical vapor deposition from methane-hydrogen mixture. Structural and impurity perfection of diamond films were characterized by Raman spectroscopy, photoluminescence, and optical absorption. Prototypes of radiation detectors were created on the basis of grown diamond films with thickness 70-80 μm,. The p-type substrate with boron concentration ~100 ppm served as an electrical contact. Detectors were irradiated by 5.5 MeV particles and 14.7 MeV neutrons, corresponding pulse height spectra were measured and detector sensitivities were determined. Charge collection efficiency for synthesized diamond was shown to achieve 94% and 91% when ~ 4 V/μm electric field applied. Keywords: diamond films, epitaxy, diamond detector

Синтез CVD-алмаза детекторного качества для радиационно-стойких детекторов ионизирующего излучения

An advanced microwave plasma reactor ARDIS 300 was used to synthesize homoepitaxial structures of monocrystal diamond films at Project Center ITER. High-quality epitaxial diamond films were grown on boron-doped monocrystal diamond substrates using microwave plasma-assisted chemical vapor deposition from methane-hydrogen mixture. Structural and impurity perfection of diamond films were characterized by Raman spectroscopy, photoluminescence, and optical absorption. Prototypes of radiation detectors were created on the basis of grown diamond films with thickness 70-80 μm. The p-type substrate with boron concentration ~100 ppm served as an electrical contact. Detectors were irradiated by 5.5 MeV α-particles and 14.7 MeV neutrons, corresponding pulse height spectra were measured and detector sensitivities were determined. Charge collection efficiency for synthesized diamond was shown to achieve 94% and 91% when ~4 V/m electric field applied.

Effects of deposition time on growth of Ir buffer layer on MgO(1 0 0) support layer by magnetron sputtering

The effects of deposition time of Ir buffer layer on MgO(100) support layer were investigated during the fabrication of the Ir/MgO compliant substrates with the use of the magnetron sputtering technique. It was observed that the XRD FWHM of Ir(200) decreases rapidly at first and then slowly with increasing deposition time, and the XRD FWHM data versus the deposition time can be fitted into the Logistic curve. For the surface roughness Ra of the Ir buffer layer, it increases firstly and then declines with increasing deposition time; the experimental data of Ra versus the deposition time can be fitted to the Lorentz curve. And the fitting functions corresponding to the two curves can be used for the determination of the deposition time of desired Ir buffer layer quality easily and conveniently, which provides a solid foundation for subsequent heteroepitaxy of high-quality diamond films on the Ir/MgO compliant substrate.

Seed Dibbling Method for the Growth of High-Quality Diamond on GaN.

The integration of diamond and GaN has been highly pursued for thermal management purposes as well as combining their exceptional complementary properties for power electronics applications and novel semiconductor heterostructures. However, the growth of diamond-on-GaN is challenging due to the high lattice and thermal expansion mismatches. The weak adhesion of diamond to GaN and high residual stresses after the deposition often result in the diamond film delamination or development of cracks, which hinder the subsequent device fabrication. Here, we present a new seed dibbling method for seeding and growing high-quality diamond films on foreign substrates, in particular on cost-effective GaN-on-Si, with significantly improved adhesion. Diamond films grown conformally on patterned GaN-on-Si presented high quality with significantly larger grains and a 95% sp3/sp2 ratio, excellent interface between diamond and GaN, and lower residual stresses (as low as 0.2 GPa) compared to conventional methods. In addition, the method provided excellent adhesion, enabling a reliable polishing of the as-grown diamond films on GaN on Si without any delamination, resulting in smooth diamond-on-GaN substrates with subnanometer root-mean-square roughness. Diamond layers deposited via seed dibbling resulted in a 2-fold improvement in the effective thermal conductivity for GaN-on-Si with only a 20 μm thick diamond layer. This method opens many new possibilities for the development of high-performance power electronic devices and integrated devices with excellent thermal management based on a diamond-on-GaN platform. In addition, this technique could be extended to other substrates to combine the outstanding properties of diamond with other kinds of devices.

Heteroepitaxial growth of diamond films on Y3Al5O12 single crystals

Up to now, it is still challenging to solve the thermal management problem of the solid-state laser. Herein, a new thermal management method is conducted, which is direct deposited diamond films on laser crystals. By microwave plasma chemical vapor deposition (MPCVD) method, we have successfully synthesized high-quality diamond films on Y3Al5O12 (YAG) substrates to improve the thermal performance of YAG crystals. Diamond films were grown with different pre-treatments and deposition parameters, where the pre-treatment method is to expose the substrate to diamond growth conditions before the seeding step. After deposition, the quality, thermal properties, and optical properties of as-grown samples were investigated in detail to study the impact of the pre-treatment and deposition parameters on the properties of the film. The results revealed that a sufficient pre-treatment process is necessary for the deposition of continuous diamond films on YAG substrates, while a relatively high temperature and low methane concentration during the deposition process are conducive to obtaining high-quality diamond films. Furthermore, it was found that depositing diamond films on YAG crystals can effectively improve the thermal conductivity of the materials with slightly affecting their optical properties, which provides a new choice for the thermal management of the solid-state laser.

Evolution of High-Quality Homoepitaxial CVD Diamond Films Induced by Methane Concentration

In this paper, we successfully synthesized homoepitaxial diamond with high quality and atomically flat surface by microwave plasma chemical vapor deposition. The sample presents a growth rate of 3 μm/h, the lowest RMS of 0.573 nm, and the narrowest XRD FWHM of 31.32 arcsec. An effect analysis was also applied to discuss the influence of methane concentration on the diamond substrates.