CVD Diamond Film Growth Research Articles

Multi-microscopy characterization of threading dislocations in CVD-grown diamond films

We present site-coincident imaging of a high dislocation density boron-doped chemical vapor deposition-grown homoepitaxial (001) diamond film using electron channeling contrast imaging (ECCI), cathodoluminescence, transmission electron microscopy (TEM), and scanning secondary ion mass spectroscopy (SIMS). With growing interest in large area heteroepitaxial substrates, we show that ECCI is a promising technique to accurately evaluate dislocations in diamond films. We find the electron backscatter yield is sufficient to distinguish individual threading dislocations in ECCI despite the low atomic number of carbon, and we have generally good agreement between dislocations observed in ECCI and TEM of the same region. Importantly, relying on luminescence in the 430 nm dislocation-related A-band alone results in an underestimation of the defect density as we find only 20%–40% of the threading dislocations luminesce. We further show that dislocations do not perturb the spatial uniformity of boron doping measured by SIMS, even when the dislocations are clustered with high density, and we can tentatively rule out strong segregation effects at the dislocations. Our results establish the complementary use of microscopy and microanalysis methods to rapidly characterize and understand the impact of dislocations in diamond thin films.

Growth and Characterization of Polycrystalline CVD Diamond Films Obtained by MWPACVD at High Power 2,45GHz Microwave Discharge

Among all the allotropic forms of carbon, diamond has attracted a broad scientific and technological interest for its extreme and unique properties rarely matched by other materials in nature. In a rapid rise from a technological point of view, much has been achieved in the study of obtaining this material through CVD technique. Studies of CVD diamond growth parameters of monocrystalline structure, underway in the team, are very expensive and time-consuming requiring in-depth studies of CVD diamond growth parameters of polycrystalline structure. So, this work presents an analysis focused on obtaining CVD diamond films with polycrystalline structure through the 2.45 GHz microwave plasma activation method (MWPACVD) in high power regime using a modified substrate holder to find a set of parameters appropriated for getting uniform quality and growth rate of thick films. The films were characterized using Raman scattering spectroscopy and scanning electron microscopy. The results point to optimized conditions for depositing films with growth rates of up to 20 µm/h with low levels of intrinsic stress, good structural quality and uniform microcrystalline morphology along the deposition surface.

Characteristics of CVD Grown Diamond Films on Langasite Substrates

Surface acoustic wave (SAW) devices consist of a piezoelectric substrate with interdigitated (IDT) electrodes. These devices can be used to fabricate wireless and passive sensors that can be mounted in remote and/or inaccessible places. If encapsulated with CVD diamond, the SAW devices can be made to operate under extremely hostile conditions. The piezoelectric layer (AlN, ZnO etc.) deposited on the diamond or an inverse system can increase the frequency of the SAW device. Most piezoelectric materials (such as quartz) show phase transition temperatures below diamond deposition temperature (650o-1100ºC), preventing their use as a substrate for diamond growth. Langasite La3Ga5SiO14 (LGS) is recently fabricated piezoelectric material that can withstand high temperatures without being deteriorated. LGS does not have phase transitions up to its melting point of 1470 °C. Here we report the deposition of diamond films by microwave plasma CVD in methane-hydrogen gas mixtures on polished and rough surfaces of the LGS substrates seeded with nanodiamonds. No buffer layer between the substrate and the coating had been used. The effect of substrate pretreatment (PT) was also investigated on the growth behaviour of diamond films on LGS. The resulting films are characterised by Raman spectroscopy, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS). The effect of substrate roughness on the growth behaviour was found to favour bigger grain sizes on the unpolished substrates. Whereas, the effect of substrate pretreatment (PT) was found to produce unique microstructural features with better polycrystalline diamond (PCD) quality than on the substrates without PT. Raman signals confirm the deposition of PCD in all the cases but the X-ray results interestingly show new phase formation of hcp and rhombohedral diamond lattice structures under CVD growth environment.

Express in situ measurement of epitaxial CVD diamond film growth kinetics

We used a low-coherence interferometry for precise continuous in situ measurements of thickness and growth rate of epitaxial single crystal diamond layers in microwave plasma CVD in H2-CH4 gas mixtures in a broad range of substrate temperatures Ts (750–1150°C) and CH4 concentrations (1–13%). Rich growth kinetics is collected in a single experiment by depositing about 60 layers on one (100) Ib HPHT diamond substrate in different regimes (the substrate temperature was controlled by the microwave power) at fixed pressure P=130Torr, without the plasma switch-off. The growth rate is found to follow Arrhenius dependence with activation energy Ea=11.1±1.0kcal/mol. By appropriate choice of the substrate temperature the growth rate can be significantly enhanced. The growth rate as high as 82μm/h is achieved by optimizing the temperature and gas composition. At low CH4 content (1%) growth competes with etching by atomic hydrogen, the etching dominating at high Ts (>1000°C in the present conditions). The etching rate in pure H2 plasma was measured and activation energy Ea=9.8±0.8kcal/mol was deduced. Gas temperature Tg in the plasma core evaluated from optical emission spectra for dimer C2 (Swan band), was found to be either constant or slightly and monotonically increasing with absorbed power, whereas the absorbed microwave power density shows a decreasing, although slight, trend. This suggests the temperature depended surface reactions to play a major role in the diamond growth kinetics under variable microwave power. Raman mapping of cross-section of the produced multilayered sample confirmed high quality of diamond structure over all the deposition regimes explored.

Simulation of CVD Diamond Film Growth by Method of Revised KMC

The growth of CVD diamond film was simulated by using revised KMC method. The simulation was conducted at CH3 radical concentration (0.01%-0.03%) and atomic hydrogen concentration (0.01%-0.5%). The results showed that: The CVD diamond film growth under revised KMC method is superior, which is in good agreement with the experimental results. The concentration of CH3 ([CH3]) and the concentration of atomic H ([H]) can produce important effects on the film deposition rate, surface roughness and the concentration of atom H embedded in the film.

Stability of the surface termination of differently modified ultrananocrystalline diamond/amorphous carbon composite films

We have investigated the stability of the surface termination of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films after their modification with UV/O3 treatments or NH3-containing plasmas. The films were prepared by microwave plasma chemical vapor deposition from CH4/N2 mixtures and possess the H-termination typical for all CVD grown diamond films. The treatment with UV/O3 or NH3/N2 plasma resulted in a change of the surface termination as revealed by contact angle measurements and X-ray photoelectron spectroscopy (XPS). Both processes rendered the as-grown hydrophobic UNCD surface hydrophilic; the influence of the treatment time as well as that of the carrier gas (N2 or Ar) for the plasma process were investigated. The main task of this investigation was to determine the stability of the surface termination with storage time and storage conditions and upon exposure to standard organic solvents, like acetone, ethanol and i-propanol. It was found that for the UV/O3 treated UNCD surfaces the storage in air, and after NH3/N2 plasma modification package under reduced pressure preserved to a great extent the achieved hydrophilic properties in a period up to three months. The changes that occur predominantly during the first days after the modification step were due mostly to interchange of surface groups with the ambient. Similar processes were observed after exposure of the UNCD surfaces to standard organic solvents.

Effect of substrate temperature on hot-filament CVD grown diamond films at constant filament current

This is a systematic study of diamond films grown over silicon substrate by the hot-filament chemical vapour deposition technique at substrate temperatures of 750–50–1,000°C. The resulting films are characterised using the scanning electron microscope, X-ray diffraction and Raman spectroscopy. Our observations are that with the increase in the substrate temperature the morphology of deposited film changed from cauliflower structure to pyramidal featured structure. At substrate temperature of 950°C, planar growth of diamond film was observed, showing good purity crystals. This type of growth has potential for applications where atomically flat surface at localised regions is a prime concern.

Atomic and Electronic Scale Simulation on Low Index Face Growth of Nano CVD Diamond Films

The growth of nano CVD diamond films on low index faces such as (111) face and (100) face under different proposed surface chemical reaction model was simulated by using Kinetic Monte Carlo (KMC) method from atomic scale. The results, for example the influence of deposition timet, substrate temperatureTs, and atomic hydrogen concentration [H] on the film deposition rate, surface roughness, andHembedded in the film under different processing conditions, were systematically analyzed and compared. And the adsorption of various species on {111}-oriented diamond cluster was preliminarily computed from electronic scale by Local Density Approximation (LDA) method to assist understanding the surface adsorption mechanism. It is indicated that the film morphology and quality obtained from atomic scale KMC simulation varies according to the chemical reaction models. And our initial electronic scale computation on {111}-oriented diamond cluster showed that single-carbon species can be adsorbed on the activated site more easily than double-carbon species and the former will result in a more stable state than the latter. In order to reveal the nano CVD diamond film growth mechanism, more work about various species adsorption on many different morphological CVD diamond surfaces is needed.

Simulations of CVD Diamond Film Growth: 2D Models for the identities and concentrations of gas-phase species adsorbing on the surface

ABSTRACTA prerequisite for modelling the growth of diamond by CVD is knowledge of the identities and concentrations of the gas-phase species which impact upon the growing diamond surface. Two methods have been devised for the estimation of this information, and have been used to determine adsorption rates for CxHy hydrocarbons for process conditions that experimentally produce single-crystal diamond, microcrystalline diamond films, nanocrystalline diamond films and ultrananocrystalline diamond films. Both methods rely on adapting a previously developed model for the gas-phase chemistry occurring in a hot filament or microwave plasma reactor. Using these methods, the concentrations of most of the CxHy radical species, with the exception of CH3, at the surface have been found to be several orders of magnitude smaller than previously believed. In most cases these low concentrations suggest that reactions such as direct insertion of C1Hy (y = 0-2) and/or C2 into surface C–H or C–C bonds can be neglected and that such species do not contribute significantly to the diamond growth process in the reactors under study.

Heterodyne detection scheme for light-induced transient grating experiment

A novel heterodyne detection scheme for light-induced transient grating technique is presented. The heterodyne detection is achieved coherently mixing the picosecond pulses of diffracted and scattered light. A phase difference between these pulses is controlled by moving a holographic beam splitter along its grating vector. This approach is employed to study a competition of coexisting electronic and thermal optical nonlinearities in CVD grown diamond films in sub-nanosecond time domain and to determine carrier parameters.

Combination of CVD Diamond and DLC Film Growth with Pulsed Laser Deposition to Enhance the Corrosive Protection of Diamond Layers

CVD diamond layers are often used as protective layers. One of the most important of these applications requires pinhole-free layers to protect against fluid materials, such as found in chemically aggressive environment. These pinholes are present even in very good quality CVD diamond films. In this work we combined the Pulsed Laser Deposition (PLD) technique with Microwave assisted Chemical Vapor Deposition (MW-CVD). We used CVD diamond films prepared under different conditions and layer thicknesses. Both of these proceses produced inperfect protective layers, but we proved that a PLD DLC film over the diamond layer does reduce the number of pinholes in the coating. We used special chemical alcaline etching to detect the remaining pinholes, and to test the corrosion protective properties of the layers. As a result we were able to prepare samples of 1 x 1cm2 with only 0.2 micron thickness without any pinholes, while in CVD diamond layers a thickness of 2,5 micron was needed for the same level of compactness.

Two-dimensional simulations of temperature fields of the reactor wall during hot-filament CVD diamond film growth over a large area

In order to study the growth of diamond films over a large area in a traditional hot-filament chemical vapour deposition (HFCVD) reactor, two-dimensional mathematical models were first developed to investigate the temperature fields of the reactor walls, which made significant contributions to thermal round-flow of the reactant gases under different energy transfer systems. The set of partial differential equations involved in the thermal conduction system was solved with different boundary conditions by the finite control volume method. Numerical simulations showed that the temperature space distributions were heterogeneous when thermal radiation was assumed to be the only mechanism in heat transfer from the filaments to the reactor walls. However, taking into account the effects of thermal conduction under adiabatic and different isothermal temperature boundary conditions, the temperature uniformities improved greatly. In addition, thermal convection did not affect the temperature distributions but only increased the total temperature of the reactor wall. These results not only give insight into the dominant reasons resulting in low nucleation density and low growth rate of diamond films, but also provide a basis for the design of industrial HFCVD reactors to obtain high-quality diamond films over a large area.

Electronic structure study of growth species adsorption and reaction on cluster models for the diamond surface using LDA method

Electronic structure calculation was carried out for the hydrogen-terminated carbon cluster designed to model the {111}-oriented diamond surface, C d (111). Using LDA method with local generalised gradient corrections, the subject of the calculation included the adsorption of single-carbon species and double-carbon species on an activated diamond surface. The results showed that: (1) Single-carbon species will more likely result in {111}-oriented CVD diamond film growth than double-carbon species, however, the role of double-carbon species should not be ignored; (2) The adsorption of single-carbon species on activated site makes the system more stable than that of double-carbon species. (3) Our computation result of CH 3 adsorption on growth surface is in good agreement with that acquired both theoretically and experimentally.

Influences of Process Parameters on 111-Oriented CVD Diamond Film Growth Under Two-Step Method

The growth of 111-oriented CVD diamond film under a two-step model was simulated at atomic scale by using revised KMC method. The simulation was conducted at various substrate temperatures (1100 K-1400 K) and CH3 radical concentration (0.01 that: (1) The 111-oriented CVD diamond film growth under the two-step model is superior to that under corresponding single-step model, which is in good agreement with the experimental results. (2) Substrate temperature (Ts) and the concentration of CH3 ([CH3]) can produce important effects on the film deposition rate, surface roughness and the concentration of atom H embedded in the film. However, both the Ts and [H] should be controlled to a proper range for high quality films.

Parallel Bias-Enhanced Sulfur-Assisted Chemical Vapor Deposition of Nanocrystalline Diamond Films

AbstractThe transformations induced by the application of a continuous bias voltage parallel to the growing surface during the sulfur-assisted hot-filament chemical vapor deposition (HFCVD) of nanocrystalline diamond (n-D) films were investigated by Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The films were deposited on molybdenum substrates using CH4, H2 and H2S. Bias voltages in the range of 0 – 800 VDC were applied parallel to the substrate surface continuously during deposition. The study revealed a significant improvement in the films' density and a lowering in the defect density of the nanocrystalline diamond structure for parallel bias (PB) voltages above 400V. These high PB conditions cause the preferential removal of electrons from the gaseous environment, thus leading to the net accumulation of positive species in the volume above the growing film, which enhances the secondary nucleation. The nanoscale carbon nuclei self-assemble into carbon nano-clusters with diameters in the range of tens of nanometers, which contain diamond (sp3-bonded C) in their cores and graphitic (sp2-bonded C) enclosures. Hence, the observed improvement in film density and in atomic arrangement appears to be connected to the enhanced presence of positively charged ionic species, consistent with models which propose that positively charged carbon species are the crucial precursors for CVD diamond film growth.

Peculiarities of SHB in the 637 nm line of N–V defects in CVD-grown diamond films

Strain field inside nitrogen-doped CVD diamond film has been investigated by using the luminescence and excitation spectra of 637-nm zero-phonon line (ZPL) of N–V centres. At 2 K the ZPL measured in the excitation spectrum had a Lorentzian shape, while the ZPL measured in luminescence spectrum had an asymmetry in shape and was shifted to the red side as compared to the excitation spectrum. The differences vanish with the increase of temperature up to ∼50 K. SHB was performed by using a single-frequency dye laser. It revealed a dependence of the holewidth on the position of the burning frequency inside the ZPL. A model which takes into account a random strain-induced splitting of the excited 3E states in ensemble of N–V defects in a polycrystalline film was used to explain the peculiarities observed in the luminescence and SHB spectra.

Doping of diamond

Diamond is a wide-bandgap semiconductor with unsurpassed physical and chemical properties. When doped, semiconducting diamond can lead to the realization of electronic and optoelectronic devices with exceptional properties. Diamond can now be doped p-type, with boron, both during CVD diamond film growth and by ion-implantation, and n-type with phosphorus during CVD growth. This paper reviews the current status of diamond doping and describes the electronic properties of the doped layers. Some potential applications of doped semiconducting diamond are described.

An investigation of structural defects in diamond films grown at low substrate temperatures

Abstract The incorporation of defects and impurities in CVD diamond films grown at substrate temperatures between 340 and 740 °C has been studied. Raman and infrared spectroscopy (FTIR) investigations reveal that the observed accumulation of structural defects in the low-temperature growth of diamond films is coupled with a strongly increasing incorporation of hydrogen. The defects formed at low substrate temperatures are mainly of the sp 3 bonding type, whereas sp 2 bonding defects seem to be less important. The dominant spectral features of films with decreasing phase purity are the sp 3 CH x stretch region in FTIR spectroscopy, a non-assigned Raman peak centered well below 1500 cm −1 in Raman spectroscopy and intense luminescence signals. The spectra have been decomposed in order to examine the temperature dependence of various defect signals. It was found that the incorporation of defects and impurities depends on nitrogen contamination of the gas phase, and increases exponentially when the substrate temperature for CVD diamond film growth is reduced.

Doping Diamonds and Diamond Films for Electronic Applications

Diamond exhibits extraordinary physical and chemical properties, many of which have already found application in tribology, thermal management and optics. Furthermore, diamond is also a wide-bandgap semiconductor which, when doped, can lead to the realization of electronic and optoelectronic devices with exceptional properties. Diamond can now be doped p-type, with boron, both during CVD diamond film growth and by ion-implantation, and n-type with phosphorus during CVD growth. This paper reviews the current status of diamond doping and describes the electronic properties of the doped layers. Some potential applications of doped semiconducting diamond are described.

Emission and excitation spectra of silicon-related luminescent centers in CVD-grown diamond films

Abstract Luminescence properties of silicon-related centers in CVD-grown diamond films and their spatial distribution along the growth direction have been investigated. It is found that the lineshape and peak position of the emission band depend both on excitation energy and light focalization depth, suggesting the coexistence of two optical centers related to isolated vacancies and to silicon-vacancy complexes. A simple model of the electronic structure of this defect is proposed.