Large Area Diamond Films Research Articles

Structural evolution and self-destructive behavior of Mo/Ti transition layers during free-standing diamond-film preparation

Graphite-based metal transition-layer substrates hold great potential for preparing large-area diamond films and achieving crack-free release. In this study, a five-inch crack-free free-standing diamond film was prepared on a graphite substrate with a sacrificial Mo/Ti double-layer transition layer using direct-current arc plasma jet chemical vapor deposition (DC jet CVD). The interfacial bonding and diffusion behavior between the diamond and the transition layers were investigated. The effect of abundant metal particles and elemental diffusion between layers on film adhesion and stress release are discussed and analyzed. The surface of Ti layer prepared by the multi-arc ion-plating contains numerous metal particles that provide a template for the fine-crystalline Mo layer. Metal particles are encapsulated and embedded in the diamond and act as anchors that ensure the stability of the substrate–diamond bond during high-temperature deposition. After deposition, those metal particles act as weak points and play crucial stress-release roles. Mutual elemental diffusion occurs between the Ti, Mo, and diamond layers. Ti penetrates the Mo layer to form a continuous 140-nm-thick thin layer during the initial deposition period, facilitating diamond nucleation. Carbon from the plasma and diamond diffuses into the metal transition layer. Thermal stress generated between the diamond and the graphite substrate is released by destroying the metal transition layer with high thermal expansion coefficient and low elastic modulus during cooling from the deposition temperature. Cracks rapidly propagate along the interface between destroyable transition layers and graphite substrate, which results in the liftoff of a fully crack-free diamond film.

Explore the growth mechanism of high-quality diamond under high average power density in the MPCVD reactor

Investigating the mechanism behind the high-efficiency deposition of high-quality diamond has always been a prominent topic in related research. This paper investigates the CH4-H2 plasma characteristics and related chemical reaction kinetics in the average power density range of 18–100 W·cm−3, which is a typical range for large-area diamond film deposition. The number densities of H, CH3 and C2H2 increase linearly with the average power density. C2H2 is the main hydrocarbon in the discharge, and CH3 is the main single-carbon hydrocarbon. The number density and radial uniformity of CH3 and C2H2 increase with the average power density, which is necessary for the high rate and uniform deposition of diamond films. The plasma's optical emission spectra indicate an acceleration in the C2 production rate at high power density. The diamond film deposition experiment demonstrates the efficacy of high average power density in achieving high-quality diamond deposition at a high growth rate.

Investigation on the preparation of large area diamond films with 150–200 mm in diameter using 915 MHz MPCVD system

In this work, the diamond films with 150 mm in diameter were prepared in our home-made 915 MHz microwave plasma chemical vapor deposition (MPCVD) system. The appropriate height of the pocketed substrate holder was researched in order to reduce the edge effect as much as possible. And the diamond thin films which were deposited in the designed substrate holder present relative high uniformity which demonstrated the feasibility of the structure of the substrate holder. Furthermore, the φ 150 mm diamond thick film was deposited using relative higher gas mixture flow rate and microwave power. The thickness variation of the diamond thick film is about 13.4% and the full width at half maximum (FWHM) of the diamond peak increases from 5.78 cm−1 to 7.23 cm−1 with the distance to the center of the diamond film increasing from 0 mm to 70 mm. The I(C2)/I(Hα) across the plasma shows a relative uniform distribution which was kept in the range of 2.9–3.4 in our experiments. Besides that, the φ 200 mm diamond film was attempt to synthesis which illustrates the feasibility of depositing the diamond films with the diameter more than 150 mm, although some improvements on the plasma environment should be considered.

Reduction of dislocation density in single crystal diamond by Ni-assisted selective etching and CVD regrowth

The development of large-area diamond films with low dislocation density plays a key role in diamond-based devices. In this study, we present a straightforward and reasonably priced Ni-assisted etching and re-growth method to decrease the dislocation density of diamond. By adjusting the annealing temperature, a high-density inverted pyramid and/or trapezoidal pit can be effectively exposed because the interaction between carbon and Ni metal. The Ni tends to dissolve the diamond surrounding the dislocation at high temperature while maintaining the surface's flatness. The precipitated graphite layer is removed using wet etching, and the step flow mode is then restored via the re-growth procedure. It shows that the dislocations located beneath the etching pits are partially annihilated during the lateral coalescence, resulting in a decrease in dislocation density.

CVD Diamond Growth Enhanced by a Dynamic Magnetic Field

A dynamic magnetic field (DMF) with different angular frequencies (50, 100, and 150 π rad/s) was introduced during diamond growth via hot filament chemical vapor deposition (HFCVD). The effects of the dynamic magnetic field on the growth rate, diamond quality, growth orientation, and deposition uniformity of large-area diamond films were investigated with scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The correlation between diamond growth and angular frequency was discussed. The results showed that a faster growth rate (about 2.5 times) and higher diamond quality were obtained by increasing the angular frequency of the DMF. A (100) textured polycrystalline diamond film was achieved, and the preferential orientation was found to evolve from (110) to (100), while the expected uniform deposition of a large-area diamond film under DMF was not achieved. The enhancement effect of the DMF was ascribed to the activation of more gas molecules, which participated in CVD diamond growth.

Dislocation density reduction using overgrowth on hole arrays made in heteroepitaxial diamond substrates

The growth of large-area diamond films with low dislocation density is a landmark in the fabrication of diamond-based power electronic devices or high-energy particle detectors. Here, we report the development of a growth strategy based on the use of micrometric laser-pierced hole arrays to reduce dislocation densities in heteroepitaxial chemical vapor deposition diamond. We show that, under optimal growth conditions, this strategy leads to a reduction in dislocation density by two orders of magnitude to reach an average value of 6 × 105 cm−2 in the region where lateral growth occurred, which is equivalent to that typically measured for commercial type Ib single crystal diamonds.

Large-area diamond thin film on Q-carbon coated crystalline sapphire by HFCVD

The growth of diamond on transparent substrates like sapphire presents a great challenge because of the large thermal misfit between the film and the substrate, absence of any carbide layer during diamond growth, and low nucleation density during chemical vapor deposition (CVD) growth process. In this study, we report on the use and the role of Q-carbon as an intermediate layer to successfully deposit large-area diamond film on c-sapphire by hot filament chemical vapor deposition (HFCVD). The Q-carbon consists of very high-density diamond tetrahedra which act as the embryo for diamond nucleation. Different techniques such as X-ray diffraction, scanning electron microscopy, and Raman spectroscopy show that continuous diamond films with good crystallinity and without any impurity phase can be deposited on the Q-carbon coated single crystal sapphire substrate. The Q-carbon layer is very adherent and it negates the thermal mismatch between the diamond film and the sapphire substrate. A small blue shift in the Raman peak of the diamond from its equilibrium position suggests the deposition of the CVD diamond film with minimal stress (1.14 GPa). This technique of growing large-area continuous diamond thin film with excellent crystalline quality on a single crystal sapphire substrate can serve as a platform for the development of next-generation corrosion and erosion resistant infrared windows, state-of-the-art optoelectronic devices, and advanced scanning probe microscopy systems.

Multimode cavity type MPACVD reactor for large area diamond film deposition

A novel microwave plasma-assisted CVD reactor for large area diamond film deposition is described. Reactor is based on cylindrical cavity with diameter that allows exciting of three axially symmetric modes ТМ01n, ТМ02n and ТМ03n at frequency 2.45 GHz. Upper and lower walls of the cavity act as mode converters. On the lower wall of the cavity, outside the quartz dome and near the side wall of the cavity, is a ledge of variable profile with an external diameter equal to inner diameter of cavity and inner diameter selected so that the TM03n mode decays along the axis over a section of cavity with the ledge. As a result of superposition of three modes: TM01n, TM02n and decaying TM03n, the distribution of the near electric field is formed in the cavity over the substrate with diameter 80 mm so that the diamond films deposited in H2 + CH4 mixture have 5% thickness difference over a diameter of 75 mm. Based on numerical simulations the CVD reactor equipped pulsed magnetron operating with a 5 kW mean power have been realized. Deposition of high quality diamond films with diameter 80 mm and thickness 0.5–2 mm, having not more than ±5% thickness uniformity over a diameter of 75 mm, have been demonstrated in pulsed mode operation of CVD reactor.

Study on the Large Area Diamond Film Deposition in a Self- built Overmoded Microwave Power Chemical Vapor Deposition Device

With a self-built overmoded microwave plasma chemical vapor deposition device, the effect of the gas flow rate variation on the uniform deposition of diamond films on molybdenum of 100 millimeter diameter was studied. The plasma density was 1.0×1019/m3 when the microwave power was 5.0 kW and the gas pressure was 10.0 kPa. The ovemoded MPCVD device presented good stability of the gas flow rate field distribution. The substrate surface can be well covered when the hydrogen flow rate varied from 50 to 800 sccm. The uniform diamond film with good quality was obtained at an intermediate gas flow rate, 300 sccm. The diamond film with good quality, 5.74 cm-1 as FWHM value and high growth rate, 5.8 μm/h was deposited when the gas flow rate was 300 sccm.

A 915 MHz/75 kW cylindrical cavity type microwave plasma chemical vapor deposition reactor with a ladder-shaped circumferential antenna developed for growing large area diamond films

A 915MHz/75kW cylindrical cavity type microwave plasma chemical vapor deposition reactor was set up by scaling a 2.45GHz TM021 mode microwave resonant cavity. The new reactor retains a cylindrical geometry, which makes it possible to set up an adjustment mechanism for plasma distribution in the reactor during its operation. In addition, a ladder-shaped circumferential antenna was used as the microwave coupling mechanism, so that sealing reliability of the deposition chamber and high power capability of the reactor are ensured. Experimentally, 3–5inch diameter crack-free diamond films were prepared. The pressure was set at between 15 and 20kPa and input power used was between 40 and 60kW, respectively. Growth rate of diamond films ranged between 1.6 and 5.6μm/h for different size and quality materials, with deviations in thickness within a range of about ±4% and ±8% over 3 and 5inch areas. Morphology, crystalline quality as well as purity of the diamond films were characterized by using optical microscopy, Raman and photoluminescence spectra, and the results proved that the quality and the purity of the diamond films were excellent.

Seed-free deposition of large-area adhesive diamond films on copper surfaces processed and patterned by femtosecond lasers

We demonstrate that femtosecond (fs) laser patterning of Cu can be exploited to realize seed-free deposition of large-area adhesive diamond films on Cu. Fs-laser-induced nanostructures promote diamond nucleation density and result in diamond film formation within a laser fluence window from 2.6 to 3.6Jcm−2. Diamond films deposited on Cu surfaces prepared outside this window experience either complete film detachment or formation of low-quality ball-like diamond grains. Diamond/substrate interface roughness plays a critical role in controlling diamond quality and adhesion between substrates and diamond films. Large-area adhesive diamond films have been achieved on Cu substrate surfaces that were first modified with fs-laser irradiation and then scribed into grid patterns. The scribed channels function as expansion joints for stress relief. Strain-free diamond films have been achieved by optimizing the grid size. Using fs-laser processing for seed-free deposition of large-area diamond films on Cu is of great significance for diverse applications, such as thermal management and power electronic devices.

High-rate ultrasonic polishing of polycrystalline diamond films

We report on fast polishing of polycrystalline CVD diamond films by ultrasonic machining in a slurry with diamond particles. The material removal mechanism is based on diamond micro-chipping by the bombarding diamond particles subjected to action of an ultrasonic radiator. The treated samples were characterized with optical profilometry, SEM, AFM and micro-Raman spectroscopy. The developed method demonstrates the polishing rate higher than those known for mechanical or thermo-mechanical polishing, particularly, the surface roughness of 0.5mm thick film can be reduced in a static regime from initial value Ra≈5μm to Ra≈0.5μm for the processing time as short as 5min. No appearance of amorphous carbon on the lapped surface was revealed, however, formation of defects in a sub-surface layer of a few microns thickness was deduced using Raman spectroscopy. The polishing of a moving workpiece confirmed the possibility to treat large-area diamond films.

Structural evolution of Ti destroyable interlayer in large-size diamond film deposition by DC arc plasma jet

The addition of titanium (Ti) interlayer was verified to reduce the residual stress of diamond films by self-fracturing and facilitate the harvest of a crack-free free-standing diamond film prepared by direct current (DC) arc plasma jet. In this study, the evolution of the Ti interlayer between large-area diamond film and substrate was studied and modeled in detail. The evolution of the interlayer was found to be relevant to the distribution of the DC arc plasma, which can be divided into three areas (arc center, arc main, and arc edge). The formation rate of titanium carbide (TiC) in the arc main was faster than in the other two areas and resulted in the preferred generation of crack in the diamond film in the arc main during cooling. Sandwich structures were formed along with the growth of TiC until the complete transformation of the Ti interlayer. The interlayer released stress via self-fracture. Avoiding uneven fragile regions that formed locally in the interlayer and achieving cooperatively released stress are crucial for the preparation of large crack-free diamond films.

Synthesis and characterization of microcrystalline diamond to ultrananocrystalline diamond films via Hot Filament Chemical Vapor Deposition for scaling to large area applications

This paper focuses on reporting systematic studies on the effect of the precursor gas chemistry ratio between hydrogen/methane (H2/CH4) and argon (Ar) to tailor control of the grain size, morphology and roughness of large area diamond films. Films ranging from a microcrystalline diamond structure (MCD 1–3μm grain size) all the way to an ultrananocrystalline diamond (UNCD 3–7nm grain size) structure were grown over 100mm diameter areas, as a pathway for scaling diamond film growth processes by Hot Filament Chemical Vapor Deposition (HFCVD) to large areas (≥150mm in diameter). H2-rich/CH4 chemistry was used to synthesize the MCD films, while Ar-rich/CH4/H2 chemistry was used to grow the UNCD films. The synthesis of the diamond films using the HFCVD process indicates that the Ar content is critical to achieve the characteristic UNCD film structure with roughness, chemical bonding and thickness uniformity in the range of 5% across large areas. The ratio of Ar/H2 in the range 70/30sccm to 90/10sccm, all with 2sccm of CH4 gas, yields films with grain size from 10–50nm for nanocrystalline diamond (NCD) films to 3–7nm for the UNCD films, respectively. The extremely smooth UNCD films (~3–5nm rms) are achieved using Ar (90sccm)/H2 (10sccm)/CH4 (2sccm) gas flows.

Preparation and characterization of diamond film on Cu substrate using Cu-diamond composite interlayer

Large area diamond films were fabricated on copper substrates by a multi-step process comprised of electroplating Cu–diamond composite layer on Cu substrate, plating a Cu layer to fix the protruding diamond particles, and depositing continuous diamond film on composite interlayer by hot-filament chemical vapor deposition (HFCVD). The interface characteristics, internal stress and adhesion strength were investigated by scanning electron microscopy, Raman analysis and indentation test. The results show that the continuous film without cracks is successfully obtained. The microstructure of the film is a mixture of large cubo-octahedron grains grown from homo-epitaxial growth and small grains with (111) apparent facets grown from lateral second nuclei. The improved adhesion between diamond film and substrate results from the deep anchoring of the diamond particles in the Cu matrix and the low residual stress in the film.

Investigation of depositing large area uniform diamond films in multi-mode MPCVD chamber

In this work, diamond films were deposited in a 10kW, 2450MHz MPCVD apparatus, of which the chamber allows a multi-mode microwave electric field to be overlapped and high microwave power to be employed. The two primary modes of TM01 and TM02 overlap around the substrate and generate a large scale plasma ball which ensures the deposition of large area diamond films. The deposition temperature across the substrate was primarily investigated in order to deposit uniform diamond films in the multi-mode chamber. And the optical emission spectra, scanning electron microscope and Raman were used to characterize the diamond films. The results showed that higher microwave power should be selected to generate large plasma ball and obtain needed temperature uniformity for a given deposition pressure. And the temperature variation was decreased obviously when the substrate holder was improved. With the optimized parameter and the improved stage configuration, the diamond thin films deposited on Φ=80mm silicon wafers obtained excellent uniformity in morphology, thickness and quality. And the results of investigating growth rate further confirm that the improved substrate holder and the employment of high microwave power are useful to achieve uniform diamond films with large area and high deposition rate.

Improved interfacial adhesion between diamond film and copper substrate using a Cu(Cr)–diamond composite interlayer

Large area diamond films were successfully fabricated on copper (Cu) substrates by first electroplating a Cu–diamond composite layer with a tiny amount (0.05–0.1wt.%) of chromium (Cr) in Cu and then growing the continuous diamond film on the composite interlayer by hot-filament chemical vapor deposition (HFCVD). The interfacial characteristics were investigated in detail by scanning electron microscopy and indentation test. The results show that using this new approach, the diamond coating could be firmly adhered to the substrate during rapid cooling after HFCVD. Doping Cr into the Cu–diamond composite interlayer and anchoring the diamond particles deep in the Cu(Cr) matrix are responsible for the much improved interface adhesion between coating and substrate.

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.