Chemical Vapor Deposited Diamond Films Research Articles

Preparation of high quality transparent chemical vapor deposition diamond films by a DC arc plasma jet method

The effects of parameters such as chamber pressure, substrate temperature and methane concentration on the growth rate and the quality of diamond films deposited by DC arc plasma jet were studied. Free standing high quality transparent diamond thick films were produced at a growth rate up to 7–10 μm h −1 under the optimal conditions. Supersaturated atomic hydrogen played an important role in the process, which was produced due to the extremely high temperature of DC arc plasma jet.

Residual stresses in chemical vapour deposited diamond films

Abstract In this paper we report the determination of residual stresses in diamond films grown on Si(100) using a plate bending theory and a bi-metal theory combined with micro-Raman spectroscopy. Raman spectra show that with an increase in the film thickness, the characteristic diamond line shifts from higher wave numbers (>1332 cm −1 ) to lower ( −1 ), indicating a change of compressive to tensile bi-axial stress with increase in the film thickness. A plate bending theory and a bi-metal theory are used to determine the distribution of the stress induced by the thermal mismatch. The modelled results show that the bi-axial stress decreases linearly along the film growth direction and the stress at the film/substrate interface decreases when the film becomes thicker. The difference from the Raman results is attributed to intrinsic stress.

Influences of H+ Implantation on the Boron-Doped Synthesized by Chemical Vapor Deposition Diamond Films

Diamond films (DF) were preliminarily B doped in situ during chemical vapor deposition. Subsequently, the films were implanted with 120 keV H+ to dose of 5 × 1014 ∼ 5 × 1016cm-2. After the implantation, the B doped DF become insulating and Raman measurements indicate that the implantation has amorphous carbon and graphite etched. It is known that the formation of H-B pairs plays an important pole in property changes. However, for larger dose cases, the electrical resistance of DF is influenced by radiation damage and/or non-diamond phases. In addition to them, annealing makes the specimens conducting again. This phenomenon maybe has potential for application in designing DF device.

Relative Abundance of Single and Vacancy-Bonded Substitutional Nitrogen in CVD Diamond

Relations between the concentrations of neutral (N0) and charged (N+) single-substitutional nitrogen and of nitrogen–vacancy (N–V) complexes in chemical vapour deposited diamond films of ≈︂0.2 mm thickness with nitrogen impurity concentration levels of 10 ppm are studied. For this purpose the films were subjected to 8 MeV electron irradiation at room temperature and subsequent annealing at 800 °C. The samples were analysed by micro-photoluminescence, visible and IR absorption, and Electron Spin Resonance techniques. It was found that the concentration of nitrogen in the (N–V) and N+ forms, in as-grown films, is less than 0.1% and 10% of the neutral substitutional nitrogen N0, respectively.

Effect of nitrogen doping on the electron field emission properties of chemical vapor deposited diamond films

Abstract Nitrogen-doped diamond films were successfully synthesized using a urea/methanol saturated solution as a nitrogen source. Scanning electron microscopy (SEM) and Raman spectroscopy revealed that the morphology and quality of the diamond films were not altered due to nitrogen doping. However, increasing the urea/methanol ratio in gas mixture markedly influences the field emission properties of diamond films, which were optimized when the films were grown using H 2 /CH 4 /urea=300:18:6 sccm. The electron field emission of the films can be turned on at a low field as 5.0 V μm −1 and the emission current density as large as J e =1019 μA cm −2 can be attained at 21.6 V μm −1 applied field. The effective work function is φ e =0.034 eV.

Electrical properties of chemical vapor deposition diamond films and electrical response to X-ray

Abstract In this paper, dark current–voltage (I–V) characteristics, current–temperature (I–T) characteristics, and photocurrents under steady-state X-ray excitation of CVD diamond films were investigated. Results indicated that dark currents and photocurrents by X-ray irradiation for the [001] textured CVD diamond film were greater than those for the non-textured one. The differences in dark currents and resistivities were attributed to a large number of grain boundaries contained in the non-textured diamond films. From the I–T curves, at the temperature higher than 500 K, currents clearly followed an exponential behavior because of the activation energy of E a =1.68 eV which was normally attributed to Si trapped to a vacancy in the diamond lattice.

Dielectric characterization of microwave plasma enhanced chemical vapor deposition diamond films with Ar–H2–CH4 gas mixture

Dielectric properties of diamond films grown by microwave plasma enhanced chemical vapor deposition (MPECVD) on tungsten carbide (WC) substrates from Ar–H 2 –CH 4 gas mixture were studied using an impedance analyzer. The dielectric dispersion is observed in the frequency range from 100 Hz to 15 MHz. The real and imaginary parts of impedance of diamond films deposited at the different Ar ratios of the reactive gases consist of a semicircle in the complex plane and can be fitted to the theoretical circuit model. The frequency dependence of the imaginary part of the impedance implies different time constants τ, which are closely related to the diamond film’s AC resistivity ρ and dielectric constant ε. The values of the resistivity of diamond films increase with increasing Ar gas ratio, which is an indication of lower graphite content of the samples with higher Ar gas ratio. Raman spectroscopy also confirmed the results. It is found that Ar ions in a microwave plasma possess the ability to remove the unexpected non-diamond phases and improve the diamond quality.

An elastic/plastic analysis of the intrinsic stresses in chemical vapor deposited diamond films on silicon substrates

Diamond films were grown over Si substrate at 1223 K by the hot filament chemical vapor deposition (CVD) method using CH4/H2 gas mixtures (1%, 2%, 3% CH4,) and the intrinsic stresses in the film were deduced using the ex situ curvature method. After subtracting the curvature change during the cooling process, average stresses in the film during the CVD process, 〈σf〉, were calculated using the elastic/plastic analysis which treated the creep deformation of the substrate. The intrinsic stress kept increasing during the CVD process and was generally several times larger than the 〈σf〉 which tended to saturate around the film thickness (tf) of 10 μm. For thicker films, substrate creep became significant and the substrate stress was substantially relaxed by creep. Fraction of the creep strain with respect to the total strain at the film–substrate interface was around ∼1/3 when tf∼10 μm, and increased as large as 2/3 during the film deposition. The intrinsic stress was believed to arise from the grain growth during the CVD process, because the stress deduced from the actual grain size measurements agreed reasonably with calculated values from the above analysis. Later, the diamond film layer was removed by O2 electron cyclotron resonance etching, and the remaining curvatures of the substrate were compared with those deduced from the elastic/plastic analysis. Residual stresses in the substrate after the film removal were tensile near the interface and the substrate bottom but compressive in the middle.

Micropatterning of Chemical-Vapor-Deposited Diamond Films in Electron Beam Lithography

The micropatterning of chemical-vapor-deposited (CVD) diamond films using electron beam lithography technology has been investigated. The use of metal naphthenates as mask resist materials is proposed, because of their resistance to oxygen plasma in order to form an oxide film on the surface. The exposure characteristics of metal naphthenates, as well as the etching characteristics of CVD diamond and metal naphthenate films processed with electron cyclotron resonance (ECR) oxygen plasma were investigated. Furthermore, the crystal structure of CVD diamond micropatterns fabricated by this process was evaluated using Raman spectroscopy. We found that the metal naphthenates exhibited negative exposure characteristics upon electron beam irradiation. The sensitivity and the gamma value were 2.4×10-3 C/cm2 and 1.6, respectively. A maximum etching selectivity of 10 was obtained under etching conditions of a microwave power of 300 W and oxygen gas flow rate of 3 sccm. Line micropatterns 1 µm and 0.5 µm in width with a height of approximately 1 µm were fabricated with an etching time of 1 h. The crystal structure of the CVD diamond films after etching and the line micropatterns fabricated by this process remained constant; Raman spectra indicated only the presence of a diamond (sp3 bonding) peak at 1333 cm-1.

Low energy carbonaceous and graphite phases on the surfaces of thermochemically polished chemical vapor deposited diamond films

Micro-Raman spectroscopy was used to characterize chemical vapor deposition diamond films that were thermochemically polished at elevated temperatures. A continuous wave He–Ne laser and an argon ion laser both operated at a power of 10 mW on an area of 1 μm2 were used as excitation sources of the Raman setup. New Raman peaks were observed in a spectral range of 100–700 cm−1 in addition to the common graphite related features. These peaks are assumed to be related to carbonaceous phases formed on the surfaces of the films. A peculiarity of these new features is an increase in intensity with increasing laser exposure time. However, it was observed that the intensities of the amorphous and graphite Raman lines at 1326 and the 1577 cm−1, respectively, were independent of the laser exposure time. The temperature dependency of the intensities of the diamond and of the graphite Raman lines was investigated at different polishing temperatures. Low temperature (700 °C) polishing was also done to high temperature pre-polished samples to investigate the dissolution of nondiamond carbon in the polishing plate.

Photo-induced deep level analysis in undoped CVD diamond films

Combined thermally stimulated currents (TSC) and photo-induced current transient spectroscopy (PICTS) have been carried out on undoped high quality chemical vapour deposition (CVD) diamond films. Cross analysis of the experimental data was performed in order to determine the characteristic parameters of the traps affecting the electrical transport processes. Measurements were performed in the temperature range from 120 to 650 K. The traps were excited by means of a pulsed Xenon lamp and a 20 MeV electron beam from a linear accelerator. Both PICTS, performed between room temperature and 650 K, and TSC, from 120 to 320 K, have shown two dominant peaks, simultaneously analysed to carry out a signature of the deep levels consistent with the two different measurements. The TSC analysis at high temperature has detected deep states from 0.95 to 1.3 eV. The concentration of traps of the dominant component at high temperature after 20 MeV electron exposure at a saturation dose of 10 Gy has been calculated from the integrated charge by a direct measurement of the charge collection efficiency of the samples and resulted in a value as high as 4×10 18 cm −3 .

Microelectrical characterisation of diamond films: an attempt to understand the structural influence on electrical transport phenomena

Abstract The properties of microelectrical conduction in microwave plasma assisted chemical vapour deposition (MPCVD) diamond films were investigated using an atomic force microscopy probe, giving a morphological map of the electrical conduction with a spatial resolution better than 500 nm. Also, a cathodoluminescence map with a spatial resolution of about 1 μm was obtained, giving the possibility of correlating the defects involved in the different carrier transport phenomena. Using micro-Raman analysis several bands could be identified. It is found that the defects responsible for the cathodoluminescence (CL) blue band are responsible for the major part of the electrical conduction in diamond films, while the defects localised in 〈111〉 surfaces, responsible for the green CL emission, could be involved in a less conductive process.

Influence of SiC particle addition on the nucleation density and adhesion strength of MPCVD diamond coatings on Si 3 N 4 substrates

Abstract It is generally accepted that SiC layers are often involved in the adhesion efficiency of chemical vapour deposition (CVD) diamond films on Si-containing substrates. Si 3 N 4 –SiC composite substrates with different amounts of SiC particles (0–50 wt%) were then used for diamond deposition. Samples were produced by pressureless sintering (1750°C, N 2 atmosphere, 2–4 h). The diamond films were grown on a commercial MPCVD reactor using H 2 /CH 4 mixtures. Despite there being no special substrate pre-treatment, the films were densely nucleated when SiC was added ( N d ≈1×10 10 cm −2 ) with primary nanosized (∼100 nm) particles, followed by a less dense ( N d ≈1×10 6 cm −2 ) secondary nucleation. Indentation experiments with a Brale tip of up to 588 N applied load corroborated the benefit of SiC inclusion for a strong adhesion. The low thermal expansion coefficient mismatch between Si 3 N 4 and diamond resulted in very low compressive stresses in the film, as proved by micro-Raman spectroscopy.

Field emission mechanism from undoped chemical vapor deposition diamond films

We have investigated the field emission mechanism for nominally undoped diamond films with a thickness ranging from 3.2 to 27.5 μm, epitaxially grown on low p-doped Si(001). The experiments were performed in a field emission scanning microscope, which allows the investigation of μm-sized spots on cm2-sized samples. First, all samples were heated at 300 °C, resulting in electrically insulating properties. Then, current I versus voltage U measurements in electrode contact mode were performed at different temperatures and for both polarities as well as in noncontact mode for different electrode gaps. For local current densities up to 0.5 A/cm2 the field emission was limited by the diamond bulk properties and not by the surface barrier. Conduction through the bulk occurred by a Poole–Frenkel process for traps with overlapping Coulomb potentials. A thermally assisted electron hopping over the Coulomb barriers was proven and an activation energy of 0.43 eV and a trap density of 7.1×1018/cm3 were derived.

Structural and electrical properties of chemical vapor deposited diamond films doped by B[sup +] implantation

Chemical vapor deposited diamond films (DF) were prepared on p-type Si (100) substrates. The films were doped by 140 keV B+ implantation to doses between 1014–6×1016 cm−2. Structural changes were studied by scanning electron microscopy and Raman measurements. The DF become more and more seriously disordered versus dose. Surprisingly, the amorphization process is not as rapid as predicted. Secondary ion mass spectroscopy results show that the implanted B atoms have a strong tendency of outdiffusion during annealing. When experimental parameters are suitable, the B atoms’ profiles indicate perfect Gaussian-like shape and the electrical resistance of DF can be decreased ten orders of magnitude.

Calculation of intrinsic stress by creep deformation of an Si substrate on chemical vapor deposited diamond films

Abstract Diamond films were deposited on a p-type Si substrate by a hot-filament chemical vapor deposition method. We observed intrinsic stress of the film by creep deformation of the Si substrate, and deduced intrinsic residual stresses of films using the power-law creep equation. Thermal strain and creep strain in the Si substrate were subtracted from the total ex situ measured strain. Thermal strain was removed by the numerical method, and creep strains in the substrate were examined by measuring the curvature of Si substrates which had been removed from the diamond films by the electron cyclotron resonance etching process using oxygen plasma. The results showed that creep deformation of the Si substrates must be considered when residual stresses are measured by the curvature method. This is especially true in cases where the film was thick, or when temperature or stress conditions were high. From this study, we propose a new approach to measuring intrinsic stress from the creep deformation of substrates.

Characteristics of chemical vapor deposition diamond films for x-ray mask substrates

In this article we summarize the development and characterization of chemical vapor deposition diamond films used for x-ray mask substrates. Good control of the deposition parameters governing film stress and film thickness has been achieved, and optical transmission greater than 40% has been demonstrated. Novel polishing techniques were employed to reduce the diamond surface roughness to below 3.0 nm Ra. The crystal structure of the diamond material, determined by Raman spectroscopy, transmission electron microscopy and electron diffraction analysis, is polycrystalline, with grain sizes of approximately 10 nm. Accelerated radiation damage testing indicates a correlation between hydrogen content in the films and the degree of distortion. X-ray masks using diamond membranes have been successfully fabricated to provide early learning of image-size and image-placement performance.

WC–Co substrate surface pretreatments with aluminum compounds prior to polycrystalline CVD diamond deposition

Without pretreatment, the adherence of polycrystalline chemical vapour deposition (CVD) diamond films on WC–Co substrates is rather poor due to Co presence in the binder phase. Therefore several attempts to immobilize the Co on the substrate surface have already been investigated. However, results are not fully satisfying. In this paper, solutions or suspensions of various Al compounds have been applied to the WC–Co surface to form stable Co/Al compounds before diamond deposition. By means of SIMS depth profile analysis it is shown that surface pretreatment with Al(OC 2H 5) 3/conc. CH 3COOH or Al(NO 3) 3 leads to the formation of Co/Al compounds which suppress the Co mobility resulting in improved adherence of the diamond layer. Evidence for Co/Al compounds has also been found after pretreatment with Al(OH) 2–OOCCH 3 in neutral solution, although the quality of the diamond crystals was changed to ballas. The use of Al(OH) 2–OOCCH 3 in a basic as well as an acid medium produced no Co/Al reaction.

Morphological and synchrotron X-ray microdiffraction studies of large columnar CVD diamond crystallites

Optical microscopic and goniometric measurements were combined with microradiography, diffraction-pattern analysis and topography to study a 2 mm thick [001]-texture CVD (chemical vapour deposition) diamond film that had developed a coarse-grained structure composed of separate columnar crystallites. Individual columns were capped by large (001) facets, with widths up to 0.5 mm, and which were smooth but not flat, whereas the column sides were morphologically irregular. The refractive deviation of X-rays transmitted through the crystallites was exploited for delineating facet edges, thereby facilitating the controlled positioning of small-cross-section X-ray beams used for recording diffraction patterns from selected volumes in two representative crystallites. Their structure consisted of a [001]-axial core column surrounded by columns in twin orientation with respect to the core. The diamond volume directly below the (001) facets was free from low-angle boundaries, and no dislocation outcrops on the facets were detected. Significant elastic deformation of this volume was only present close to the facet periphery, where misorientations reached a few milliradians. Lattice imperfection was high in the twins, with ∼1° misorientations.

Modeling Chemical Vapor Deposition (CVD) Diamond Film Growth with Diamantane-Derived Radicals in Solution: Permissive Evidence in Support of the Garrison−Brenner Mechanism for Incorporation of Carbon into the Dimer Sites of the {100} Diamond Surface

The synthesis and partial rearrangement of nordiamantanemethyl radical into its more stable diamantyl isomer at 200−300 °C is reported. This solution phase observation attests to the feasibility of similar processes proposed to occur at the surface of {100} diamond film under CVD conditions.