Diamond Growth Rate Research Articles

Nitrogen addition during flame deposition of diamond: a study of nitrogen-enhanced growth, texturing and luminescence

Abstract The effect of nitrogen addition during flame deposition of diamond on the growth rate, morphology and spatial distribution of luminescent point defects in the layers has been studied. For this, well-defined amounts of nitrogen were added to the acetylene and oxygen source gases. The samples were grown under conditions that are known to give diamond deposits with a central area which is unaffected by in-diffusion of nitrogen from the ambient. Consequently, the observed features in this region must be totally ascribed to the deliberately added nitrogen. Upon nitrogen addition, the diamond growth rate in the central area of the deposits initially increases from 54 to 125 μm/h, while at the same time a {001} texture develops. With further increasing nitrogen concentrations, the growth rate drops again while the diamond crystallites in the layer start to deteriorate and become increasingly separated from each other. This results in a morphology which is usually observed in an annulus around the central area of flame deposited diamond. Photoluminescence spectroscopy and cathodoluminescence topography reveal an increasing incorporation of nitrogen as nitrogen–vacancy pairs and a loss of homogeneity in the central area of the diamond layers with increasing nitrogen addition. Based on the results of the present study, a recipe is given for reproducible flame deposition by the use of a commercially available welding torch and 99.6% pure acetylene.

Growth-rate dependence of the thermal conductivity of chemical-vapor-deposited diamond

The in-plane thermal diffusivity of chemical-vapor-deposited diamond films was measured as a function of diamond-growth rate. The films, 0.1–0.4 mm thick, were prepared in microwave-plasma reactor at growth rates ranging from 1 to 10 μm/h. A modification of Ångstöm's method was used to perform the diffusivity measurements. The thermal conductivity calculated from the thermal diffusivity shows an inverse relationship with growth rate. Analyses of Raman spectra indicate that both the line shifts and the line widths of the diamond Raman peak are practically independent of the deposition rate, except for the specimen grown at the highest growth rate.

Homoepitaxial growth and hydrogen incorporation on the chemical vapor deposited (111) diamond

A systematic study of the effect of growth conditions (temperature, microwave power, and pressure) on the hydrogen incorporation and growth rate of (111) homoepitaxial diamond synthesized by microwave plasma assisted chemical vapor deposition is carried out by secondary ion mass spectrometry. Significant quantities of hydrogen incorporation in the (111) homoepitaxial diamond are detected for the growth conditions employed. Hydrogen concentration and growth rate are found to increase with an increase in the substrate temperatures. The increase of microwave power decreases the hydrogen incorporation and increases the growth rate. The effect of pressure rise is similar to that of microwave power. However, the effect of pressure rise over 50 Torr on hydrogen incorporation and growth rate is small. The decrease of hydrogen incorporation can be explained by the suppression of defects in the growing film by atomic hydrogen in the gas phase.

Prospects of novel hybrid methods for the activated chemical vapor deposition of diamond

Abstract High-intensity activation of the vapor phase is a necessary condition for diamond synthesis in the customary chemical vapor deposition (CVD) of diamond. In this paper a novel approach to activated CVD (ACVD) of diamond based on the combined or hybrid ACVD techniques will be discussed. By hybrid diamond ACVD we mean a technique that employs more than one way of activating the crystallization medium. Together with the basic activation mode, the hybrid method includes different supplementary activation modes that influence the physical and physico-chemical processes in the vapor phase and also on the diamond crystal surface. The role of added activation in changing the growth kinetics of diamond film (DF) and microcrystals has been considered. The published research works and our own data are indicative of the remarkable influence of added activation in such hybrid ACVD techniques as chemical transport reaction, HF (Hot Filament) or DC arcjet in combination with electrical activation, and also in MW ACVD with the addition of ultraviolet-irradiation. Along with the increase in the DF growth rate there also may be changes in the constitution and crystalline perfection of DF and microcrystals grown by hybrid methods. Depending on the combination of the methods used as well as the ratio of the activation levels and crystallization temperature the linear growth rate of diamond can be raised by 1.2–6 times as compared to the rate gained via the single-activation technique. It is a striking fact that the added power of the secondary activation may amount from several to several tens of percent of the main activation power. In conclusion the possible reasons for the growth gain obtained in the novel hybrid ACVD of diamond will be considered.

Synthesis of diamond in high power-density microwave methane/hydrogen/oxygen plasmas at elevated substrate temperatures

Resumen Effects of elevated substrate temperatures and oxygen additive on the chemical vapor deposition of diamond are presented. High power-density microwave plasmas in a high concentration of methane diluted by hydrogen led to high diamond growth rates at elevated substrate temperatures up to around 1450°C. When methane and hydrogen were the only reactant gases and the substrate temperature was higher than 1450°C, graphitic deposits started to show up. With the addition of a small amount of oxygen (less than 2%), diamond films deposited at substrate temperatures higher than 1450°C at 30 μm h −1 were achieved. Diamond deposition at substrate temperatures exceeding 1600°C was achieved on molybdenum substrates. At such high temperatures, diamond grows well but the nucleation density was low. Raman spectra and surface morphologies of diamond films are correlated with the growth conditions.

Diamond Deposition and Behavior of Atomic Carbon Species in a Low-Pressure Inductively Coupled Plasma

Diamond was successfully synthesized by using H2-rich CH4/CO/H2 and H2-rich CH4/H2 inductively coupled plasmas at a pressure of 11 Pa. The ratio of particle size to deposition time, as a criterion of the diamond growth rate, in H2-rich CH4/CO/H2 mixture gas plasmas was higher than that in H2-rich CH4/H2 mixture gas plasmas. The deposits in H2-rich CH4/H2 and H2-rich CH4/CO/H2 mixture gas plasmas were found to contain nondiamond phases, as confirmed by Raman spectroscopy. In order to investigate the mechanism involved in diamond formation, C-atom densities in the plasmas were measured by vacuum ultraviolet absorption spectroscopy with a carbon hollow cathode lamp. In addition, CH, OH and H-atom emission intensities were measured by optical emission spectroscopy. As a result, it was found that the C-atom densities increased considerably with increasing mixture ratio of CO to CH4. On the basis of the correlation between the quality of deposits and the C-atom densities, C-atoms were determined to probably contribute to the formation of nondiamond phases in the deposits.

Laser diagnostics of CH in a diamond depositing flame

Abstract Cavity ring down spectroscopy was applied as a laser diagnostic tool to measure CH radical concentrations in a diamond depositing oxyacetylene flame. CH column densities were determined during diamond growth at about 0.4 mm above the deposition substrate. By applying Abel inversion processing absolute concentration profiles are obtained which are compared to diamond growth rate profiles. A correlation is found between the CH density distribution and the local growth rate. From this it can be concluded that the CH radical possibly plays a role in the formation of an annulus of enhanced diamond growth.

Nitrogen-doped diamond films

We found that very high concentrations (up to 20% vol) of nitrogen in the ethanol/hydrogen gas mixture do not prejudice the diamond quality as determined by Raman spectroscopy. Nitrogen addition also increases the diamond growth rate, as was previously reported at low nitrogen concentrations. We observed that after a second heating cycle in air at temperatures between 300 and 673 K the electrical resistance versus temperature curves of the as-grown films presented a bulk semiconductor behavior. This stabilization was due to the oxidation of the as-grown hydrogenated surface. The electrical ionization energy Ed was found to be in the range of 1.62–1.90 eV corresponding to films produced with 0 to 20% vol nitrogen in the feed. The room temperature photoluminescence spectra of films produced at low nitrogen concentration suggest that Ed results from pure electronic transitions in the nitrogen-vacancy neutral defects; for samples produced with nitrogen concentrations in the range 15–20% vol the Ed values may be due to, among others, GR1 “vibronic” transitions and charged nitrogen-vacancy defects.

Diamond deposition on copper: studies on nucleation, growth, and adhesion behaviours

This paper presents a systematic study on diamond growth on copper by microwave plasma chemical vapour deposition (MPCVD). It includes the following four main parts. 1. Effect of substrate pre-treatment on diamond nucleation. 2. Effect of deposition conditions on diamond nucleation and growth. 3.Preparation of free-standing diamond films using copper substrate. 4. Adherent diamond coating on copper using an interlayer. In the first part we show that diamond nucleation on copper is strongly affected by the substrate pre-treatment. The residues of abrasives left in the surface of the copper substrate play an important role in the diamond nucleation. In the second part we show that the diamond growth rate increases with microwave power and gas pressure. The effect of the microwave power is mainly an effect of substrate temperature. Increasing methane concentration results in a higher nucleation density and higher growth rate, but at the cost of a lower film quality. Gas flow rate has little influence on the diamond nucleation density and growth rate. In the third part we demonstrate the possibility of preparing large area free-standing diamond films using copper substrate, which has nearly no carbon affinity and usually leads to weak adhesion of the diamond films. The normally observed film cracking phenomenon is discussed and a two-step growth method is proposed for stress release. In the fourth part we show that adherent diamond coating on copper can be obtained using a titanium interlayer. Residual stress in the films is evaluated by Raman spectroscopy. It is found that with increase in the film thickness, the diamond Raman line shifts from higher wave numbers to lower, approaching 1332 cm−1. The stress variation along the depth of the film is also analysed using Airy stress theory.

Adherent diamond coating on copper using an interlayer

With a titanium interlayer, adherent diamond coating on copper is obtained. The diamond nucleation density is enhanced significantly by scratching the substrate with diamond powder and is influenced by the deposition conditions. It is found that the diamond growth rate increases with microwave power, gas pressure and methane concentration. However, a higher methane concentration results in increased growth defects and non-diamond phases. Under typical deposition conditions, the diamond crystals exhibit a (111) face dominating. The coating adhesion is accessed by pull-off tests and scratch tests. The former indicates that the coating adhesion is better than the strength of the adhesive, at ca 13 MPa. The latter shows a critical load about 8 N.

Diagnostics of the diamond depositing inductively coupled plasma by electrostatic probes and optical emission spectroscopy

Electrostatic probe methods and optical emission spectroscopy have been used for diagnostics of the low-pressure inductively coupled radio frequency plasma at pressures between 5 and 80 mTorr under real environments of diamond deposition. The single, triple, and emissive probe methods were used alone or combined to obtain electron temperature (Te) and electron density (ne). The single or triple probe method combined with the emissive probe method allowed the determination of ne with high reliability as confirmed by cross-checking. Comparison with the grown deposits suggested the existence of a critical ne value of around 2×1010 cm−3, which was responsible for the drastic decrease in diamond growth rate observed below 10 mTorr and the resulting no growth at around 5 mTorr. The energy distribution of excitation levels of the H atom Balmer series was almost constant and the distribution equilibrium was not established except the case of 5 mTorr, which was ascribed to the difference in the excitation process of H atoms.

Effect of oxygen addition on boron incorporation on semiconductive diamond CVD

The suppression effect of oxygen on elemental incorporation in homoepitaxial diamond films grown by microwave assisted CVD is investigated by secondary ion mass spectrometry. In the H2–CH4–B2H6–O2 gas system, boron incorporation into CVD diamond decreases with increasing oxygen addition, and boron concentration can be controlled by oxygen addition. In the H2–CH4–B2H6 gas system, a linear relationship between diborane in the gas and boron incorporation is observed. The growth rate of diamond is reduced by small amount of diborane.

HFCVD diamond grown with added nitrogen: film characterization and gas-phase composition studies

Recently there has been considerable interest in the addition of nitrogen to precursor gas mixtures and its influence on the properties of the resulting diamond films. Careful control of the nitrogen concentration in the CVD process results in changes to both the film growth rate and morphology. In addition to the well-defined and precisely controlled deposition conditions, thorough characterization of the vapour-grown material is indispensable in order to tailor diamond film properties according to specific applications. High quality diamond films have been produced via hot filament CVD (HFCVD) using a precursor gas mixture of 1% methane in hydrogen with N 2 additions varying from 50 to 5000 ppm (N/C 0.01–1.0). We report the results from both the structural and compositional characterization of the as-deposited HFCVD diamond films by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. Both the diamond phase purity and growth rate are maximized with 200 ppm N 2 in the gas mixture with further additions resulting in reduced growth rates and poorer film quality. We explain these findings in terms of the concentrations of gas phase species obtained from chemical equilibrium calculations and in particular the importance of the CN radical to the diamond growth process.

Mechanisms of low temperature growth of diamond using halogenated precursor-gases

Abstract The addition of halogenated gases allows a significant lowering of the substrate temperature T sub for diamond growth compared to the conventional system containing hydrogen and methane. We succeed in diamond film deposition at T sub = 350°C in HFCVD and MWCVD using CHF 3 , C 2 H 5 Cl and Cl 2 . A further decrease of T sub is possible on the expenses of the growth rate and the deposition time. The composition of the gas phase is analyzed using quadrupole mass spectroscopy (QMS) and optical emission spectroscopy (OES). Almost all chlorine from the precursor-gas reacts to HCl, resulting in a composition of pure hydrocarbons almost the same as that for the H 2 /CH 4 system. The quality of the deposited films is analyzed using Raman spectroscopy and the atomic composition of the films is detected by secondary ion mass spectroscopy (SIMS). A decrease of T sub leads to a decrease of diamond film quality and growth rate. The SIMS measurements show at high deposition temperatures an almost complete lack of chlorine atoms in the films but a high concentration on the diamond surface. At deposition temperatures below 500°C the chlorine concentration increases also in the bulk. The atomic concentration is in the range of 100 ppm. These data suggest that the halogens are involved in surface reactions. At high T sub they desorb in the CVD growth process and cannot be detected in the film. If T sub is lowered the desorption of the halogens is incomplete and chlorine is incorporated in the diamond film. We assume that the halogens make possible low temperature growth of diamond by surface reactions leading to the formation of active surface sites at which diamond growth species can be adsorbed.

The effects of the simultaneous addition of diborane and ammonia on the hot-filament assisted chemical vapor deposition of diamond

Abstract The effects of the simultaneous addition of diborane and ammonia on the nucleation density and growth rate of diamond prepared by hot-filament assisted chemical vapor depositions were examined. The diamond nucleation density and growth rate decreased as the B/C and N/B input ratios were increased owing to poisoning of the diamond surface and depletion of methyl radicals. This reduction in the amount of diamond could be compensated for by increasing the substrate and filament temperatures, and increasing the concentration of diamond growth species. Up to a B/C input reactant gas ratio of approximately 0.1, faceted diamond particles and an amorphous BCN continuous film were codeposited. For B C >0.1 , only the BCN film was formed.

Chemical Kinetic Calculations Of The Gas Phase In Atmospheric Pressure Microwave Plasma-Assisted Chemical Vapour Deposition Of Diamond

The authors develop a numerical model for the atmospheric pressure microwave plasma chemical vapour deposition (CVD) of diamond in a two-dimensional field. The continuity, momentum, energy, and chemical kinetic calculations are carried out using a finite-difference control volume method. The microwave dissipated power was calculated using Maxwell’s equations. The temperature field, stream lines, and species concentration profiles were obtained for two different MW powers. We found that the species concentrations inside the MW reactor are not in chemical equilibrium, and the viscosity and thermal conductivity of pure hydrogen may be used as the mixture properties without any major loss of accuracy. However, these properties must be calculated based on the local concentrations of atomic and molecular hydrogen. By increasing the power, we increase the molar ratio of [H]/[CH3], which is advantageous in the CVD of diamond, and the product of [H]Ð[CH3] does not change. The latter parameter affects the rate of diamond growth. We also found that at low microwave power the effect of the thermal diffusion can be negligible.

Modeling of H 2 and H 2 /CH 4 Moderate-Pressure Microwave Plasma Used for Diamond Deposition

One-dimensional transport models of moderate-pressure H 2 and H 2 /CH 4 plasmas obtained in a diamond deposition microwave reactor are presented. These models describe the plasma as a thermochemically nonequilibrium flow with three different energy modes. The solution of the one-dimensional plasma transport equations enabled the estimation of plasma species concentrations and temperatures on the axis of the reactor. As far as pure H 2 plasmas are concerned, results showed that the model predictions of gas and vibration temperatures are in good agreement with experimental measurements. The model also yields a relatively good qualitative prediction of the variations of H-atom mole fraction with the power density absorbed by the plasma. The results obtained for H 2 /CH 4 discharges showed that the model prediction on the variations of H-atom mole fraction with methane percentage in the discharge is in good qualitative agreement with experimental results. They also showed that methane is rapidly converted to acetylene before reaching the discharge zone. The concentrations of neutral hydrocarbon species in the reactor are mainly governed by thermal chemistry. The addition of methane strongly affects the ionization kinetics of the plasma. Three major ions are generally obtained in H 2 /CH 4 plasmas: C 2 H 2 + , C 2 H 3 + , and C 2 H 5 + . The relative predominance of these ions depends on the considered plasma region and on the discharge conditions. The ionic species concentrations are also mainly governed by chemistry, except very near the substrate surface. Finally the use of this transport model along with the surface chemistry model of Goodwin (1) enabled us to estimate the diamond growth rate for several discharge conditions.

A study of the initial stages of diamond deposition on ferrous substrates coated by a nitrided chromium interlayer and on nitrided polycrystalline chromium substrates

The use of a nitrided chromium interlayer has been found to improve the interfacial properties of diamond films deposited on ferrous substrates. This is achieved by hindering diffusion process of carbon and iron, good adhesion of the interlayer to the steel substrate, and very stable mechanical and chemical bonding between the interlayer and the diamond film. In the present study the initial stages of diamond deposition on steel substrates coated by a nitrided chromium interlayer and on nitrided polycrystalline chromium substrates are reported. Nitridation of chromium films deposited by electrochemical methods and polycrystalline chromium substrates resulted in the formation of two chromium nitrides phases, CrN and Cr2N, and a rough surface morphology. The initial stages of diamond deposition were found to be accompanied by carburization of the substrates surface resulting in chromium carbide formation. The incubation time, diamond particle density and growth rate at the very initial stages of the deposition process were found to differ for these two substrates. It is suggested that these differences originate from different carburization rates of the two substrates. Phase transformation, recrystallization and diffusion processes in the near surface regions of both substrates resulted in very stable chemical bonding and good adhesion of the diamond film to the substrates. Raman spectra of the deposited films, on both substrates, show shift of the diamond peak position to higher wave numbers and split of the peak. These effects are associated with compressive stresses in the diamond film. Residual stresses in the deposited films were calculated from the shift of the diamond Raman peak. The residual stresses, as calculated from the Raman spectra, were found to increase with deposition time reaching values of 8.4 and 6.9 GPa for continuous diamond films on steel substrate coated with the nitrided chromium film and on nitrided chromium substrates, respectively. Based on a simple model it was estimated that thermal stress, arising from mismatch between the thermal expansion coefficient of diamond and the underlying substrates, is the major component of the compressive stress in the diamond films.

Enhancement of the HFCVD diamond growth process by directed gas flow

The effect of gas flow rate on the growth rate of hot-filament CVD diamond is reported. With increasing gas flow rate, the growth rate of the HFCVD diamond film increases. The crux of increasing the growth rate of the HFCVD diamond film is to increase the mass flow passing through the filamentary heater region and to increase the quantity of reactive gas mixture reaching the substrate surface per unit time. Eventually the growth rate of 8.67 μm/h was obtained at the gas flow rate of 800 sccm.

Growth Rate of Diamond on Polycrystalline 〈110〉 Diamond Substrates from Carbon Disulfide in Hydrogen by Hot‐Filament‐Assisted Chemical Vapor Deposition

The growth rates for the deposition of diamond by hot‐filament‐assisted chemical vapor deposition using carbon disulfide (CS2) in hydrogen and methane (CH4) in hydrogen were investigated on polished, 〈110〉 textured, polycrystalline diamond substrates. The carbon concentration in each system was varied from 1% to 2.5%. The deposition rate increased proportionately with carbon concentration for both systems. The CH4‐H2 system gave higher growth rates with an essentially constant difference in rate between CS2 and CH4. Possible explanations for this are discussed with the most likely either a catalytic effect of sulfur or sulfur‐containing species on gas‐phase homogeneous atomic hydrogen recombination, or the surface chemisorption of relatively less labile sulfur‐containing species at the diamond surface.