Chemical Vapor Deposition Of SiC Research Articles

Growth Kinetics and Polytype Stability in Halide Chemical Vapor Deposition of SiC

Growth rates and relative stability of 6H- and 4H-SiC have been studied as a function of growth conditions during Halide Chemical Vapor Deposition (HCVD) process using silicon tetrachloride, propane and hydrogen as reactants. The growth temperature ranged from 2000 to 2150 oC. Silicon carbide crystals were deposited at growth rates in the 100-300 μm/hr range in both silicon- and carbon-supply limited regimes by adjusting flows of all three reactants. High resolution x-ray diffraction measurements show that the growth on Si-face of 6H- and C-face of 4H-SiC substrates resulted in single crystal 6H- and 4H-SiC polytype, respectively. The growth rate results have been interpreted using thermodynamic equilibrium calculations.

Halide-CVD Growth of Bulk SiC Crystals

A novel approach to the high growth rate Chemical Vapor Deposition of SiC is described. The Halide Chemical Vapor Deposition (HCVD) method uses SiCl4, C3H8 (or CH4), and hydrogen as reactants. The use of halogenated Si source and of separate injection of Si and C precursors allows for preheating of source gases without causing premature chemical reactions. The stoichiometry of HCVD crystals can be controlled by changing the C/Si flow ratio and can be kept constant throughout growth, in contrast to the Physical Vapor Transport technique. HCVD was demonstrated to deposit high crystalline quality, very high purity 4H- and 6H-SiC crystals with growth rates comparable to other bulk SiC growth techniques. The densities of deep electron and hole traps are determined by growth temperature and C/Si ratio and can be as low as that found in standard silane-based CVD epitaxy. At high C/Si flow ratio, the resistivity of HCVD crystals exceeds 105 _cm. These characteristics make HCVD an attractive method to grow SiC for applications in high-frequency and/or high voltage devices.

Oxidation of Polymer‐Derived SiAlCN Ceramics

The oxidation behavior of polymer‐derived amorphous SiAlCNs was studied in the temperature range of 900°–1200°C. The results revealed that while at 900°C the oxidation of the SiAlCNs follows typical parabolic kinetics, at higher temperatures the oxidation rates of the materials decrease with annealing time. Long‐term oxidation rate of the SiAlCNs is much lower than the lowest values reported for chemical vapor deposition of SiC and Si3N4. Structures of the oxide scales were studied using solid‐state nuclear magnetic resonance. We proposed that oxide scales formed for the SiAlCNs possess a unique network structure of the oxide scale in which aluminum atoms block the path of oxygen diffusion, thus lowering the oxidation rates. Such a unique structure was likely formed gradually with annealing time, leading to a continuous decrease in oxidation rate.

Growth and characterization of 4H–SiC in vertical hot-wall chemical vapor deposition

Vertical hot-wall chemical vapor deposition of SiC at high growth rates has been investigated. 4H–SiC epilayers, with a quality even superior to conventional epilayers, were grown at 25– 60 μm/h , 5–10 times higher than the conventional speed. The correlation of the growth mechanism to Si cluster decomposition is described. Excellent surface morphology of the epilayer grown at 25– 60 μm/h was attained by control of H 2 etching during the heating process, in which C 3H 8 was introduced at 1200°C and SiH 4 at 1300°C. The lowest net donor concentration was 5×10 12 cm −3 . In the low-temperature photoluminescence spectrum, free exciton peaks were remarkably dominant, and no impurity-related peaks were observed. Through DLTS measurements, the EH 6/7 center located at the midgap of E c −1.65 eV was detected. This trap could be suppressed under a C-rich condition as in the case of the Z 1/2 center.

Two- and three-dimensional simulation of chemical vapor deposition SiC epitaxial growth processes

Three-dimensional (3-D) computational fluid dynamics (CFD) tools were applied to enhance capabilities of the two-dimensional (2-D) simulation in predicting such important characteristics of the SiC Chemical Vapor Deposition (CVD) epitaxial growth process as growth rate, growth rate nonhomogeneity in longitudinal and transverse directions, and growth morphology. Depletion of the precursors in the gas phase along the growth direction was shown to be one of the most important sources for the growth rate nonhomogeneity. The rate of precursor depletion along the growth direction in the center of the susceptor is different from that closer to the sides of the susceptor due to the nonhomogeneous temperature profile in the transverse direction. This difference causes a significant increase in the growth rate away from the center of the susceptor toward the reactor walls. Simulated precursor supersaturation above the growth surface was the highest at the leading edge of the susceptor and near the reactor walls, which correlates with the morphology degradation in those regions.

Multiplicity of steady states in the codeposition of silicon carbide and carbon

AbstractPast studies have suggested that the process of chemical vapor deposition of SiC and C from mixtures of methyltrichlorosilane (CH3 SiCl3, MTS), ethylene and hydrogen may exhibit multiple steady states in some regions of its space of operating parameters and conditions. This phenomenon was studied systematically and experimentally in a hot‐wall chemical‐vapor deposition reactor, in which small substrates hung from the sample arm of a sensitive microbalance are used for continuous monitoring of the deposition rate. Multiplicity of steady states occurs in a wide region of the space of process operating parameters, which covers a considerable portion of the range of conditions where deposition of SiC from MTS usually occurs. All cases studied manifest themselves as two stable (observable) deposition states at the same condition, differing by at least one order of magnitude. Various experimental observations and results of the thermochemical equilibrium analysis in the gas phase of the deposition system prove that the appearance of multiplicity in the MTS–C2H4–H2 system manifests the heterogeneous chemistry of the deposition process, not of the homogeneous chemistry or the interactions of the transport and reaction processes. The composition analysis of the deposits reveals that sudden changes of the composition from almost pure carbon at the low deposition rate branch to SiC with excess carbon at the high deposition branch take place at the two limits of the multiplicity region. It indicates that one must operate outside the range of multiple steady states to obtain deposit compositions over the whole range from C to SiC.

Measurement of C2 rotational temperature in Ar-SiH4-CH4 inductively coupled plasma flame with Abel inversion

An inductively coupled plasma (ICP) flame of theAr-SiH4-CH4 system was investigated in situ byspectroscopic methods during chemical vapour deposition of SiC particles.In order to determine the rotational temperature of C2 radicals, wefocused on emission spectra of C2 (0,0) Swan band located at 513.1-516.3 nm. Spectral simulations were performed before measurements of C2 spectra, and temperatures were determined from fits ofexperimentally observed peak intensities before and after Abelinversions with calculated spectra. Simulations were performed in 50 Ksteps from 2000 to 6000 K. Since spectral intensities after Abelinversions dropped to near zero, the measurable ranges of temperature wererestricted. The rotational temperatures of C2 radicals determined variedfrom 2850 to 4750 K, depending on experimental conditions andradial positions from the plasma centre. The present results werecomparable to various numerical analyses of ICP flames reported by manyauthors.

Numerical study of SiC CVD in a vertical cold-wall reactor

The conventional heat and mass transport model is extended to describe silicon cluster formation in the gas phase and is employed for a numerical analysis of SiC chemical vapor deposition in a commercial vertical rotating disc reactor. The model is verified by comparing the computed growth rate with available experimental data. The growth rate is studied as a function of precursor flow rates varied in a wide range of values. It is found that the growth rate is limited by the gas mixture depletion in silicon atoms due to homogeneous nucleation. The secondary phase formation on the growing surface is analyzed. The SiC growth window depending on the precursor flow rates is calculated, and a significant influence of the homogeneous nucleation on the window width is shown. The model results predict that the Si/C ratio on the wafer can considerably differ from that at the reactor inlet.

Investigation of the temperature profile in a hot-wall SiC chemical vapor deposition reactor

The chemical vapor deposition (CVD) technique is widely used to grow epitaxial layers of silicon carbide. To meet the demands for high quality epitaxial layers, which have good morphology and a minimum variation of the doping and thickness, a good knowledge of the CVD process is essential. The present work uses a simulation tool to investigate several parameters influencing the heating of a hot-wall CVD reactor. The simulations are set up as 2D axisymmetric problems and validation is made in a 2D horizontal hot-wall CVD reactor. By applying the knowledge achieved from the simulations, the temperature profile is optimized to give as large area as possible with homogeneous temperature. New susceptor and coil designs are tested. A very good agreement between the simulated and the measured results is obtained. The new design has a temperature variation of less than 0.5% over more than 70% of the total susceptor length at an operating temperature of 1650°C. In addition, the power input needed to reach the operating temperature is decreased by 15% compared to the original design. 3D simulations are performed to show that the changes made in the 2D case give similar results for the real 3D case.

Chemical vapor deposition of silicon carbide at various temperatures and surface area/volume ratios

Chemical vapor deposition of SiC from methyltrichlorosilane and hydrogen was studied as a function of temperature using substrates with different surface area / volume ratios. Deposition rates and composition of the deposits at various temperatures and surface area / volume ratios were determined as a function of reactor or substrate length, respectively. The gas phase composition was analyzed as a function of residence time. Si is deposited in high excess at low temperatures and especially low surface area / volume ratios. The unusual temperature dependence of the overall deposition rate with rate maxima at about 900 and 1025 °C is caused by temperature selective depositions of both, SiC and Si. Deposition of stoichiometric SiC and a continuous increase of the deposition rate are obtained at a high surface area / volume ratio. The results are discussed on the basis of a novel chemical model.

Infrared study of carbon incorporation during chemical vapor deposition of SiC using methylsilanes

We use infrared absorption spectroscopy (IRAS) in the multiple internal reflection geometry to investigate the carbon incorporation during chemical vapor deposition of SiC on Si(100) using methylsilanes, SiHx(CH3)4−x (x=1–3). We have measured IRAS spectra in the SiH stretching vibration region of the Si(100) surface that was dosed with methylsilanes at temperatures ranging from 300 to 500°C. IRAS data demonstrate that at temperatures below 400°C, methylsilane is thermally decomposed to form a doubly occupied dimer (DOD, HSi–SiH) and a mixed adatom dimer (HSi–SiH). At higher temperatures, carbon atoms that are released from the methyl group, attack the backbonds of surface Si atoms to generate amorphous carbon-incorporated layers that include Si atoms having two or three C atoms bound to them. It is found that the carbon incorporation is enhanced with the increase of the number of methyl groups of methylsilane.

Chemical Vapor Deposition of SiC by the Temperature Oscillation Method

Chemical Vapor Deposition of SiC by the Temperature Oscillation Method

Kinetics of SiC chemical vapor deposition from methylsilane

The kinetics of heterogeneous decomposition of methylsilane in a pumped hot-wall reactor were studied just below the critical partial pressure for homogeneous decomposition. The activation energies of the process derived from gas-phase conversion measurements and from deposition rates of SiC were found to be equal (about 230 kJ/mol). The nature of the diluent (H2, He, or Ar) has only a weak effect on the reaction order in methylsilane (m ≃= 1 ), as well as on the composition and structure of amorphous Si0.53C0.47 films.

Experimental study of atmospheric pressure chemical vapor deposition of silicon carbide from methyltrichlorosilane

A comprehensive study of the chemical vapor deposition of SiC from methyltrichlorosilane at atmospheric pressure was conducted in this study; its main objectives were to identify the range of operating parameters in which stoichiometric SiC could be deposited and the generation of reliable kinetic data that could be used for the design of atmospheric pressure processes of chemical vapor deposition or chemical vapor infiltration of SiC. Deposition experiments were conducted in a hot-wall, cylindrical reactor at temperature ranging from 1273 to 573 K on flat graphite substrates or thin molybdenum wires aligned with the axis of the reactor. The obtained results showed that the deposition rate and the deposit stoichiometry varied markedly with the distance from the entrance of the reactor. The deposition rate exhibited, depending on the reaction temperature, one or two pronounced maxima before the beginning of the isothermal zone of the reaction, whereas the deposit stoichiometry showed an abrupt transition from almost silicon to stoichiometric silicon carbide after the first maximum. Experiments with HCl added in the feed showed that the presence of HCl could cause complete suppression of the deposition of silicon and lead to smoother variation of the SiC deposition rate with the residence time in the reactor. It is believed that this effect could be exploited to improve the uniformity of SiC deposition in chemical vapor deposition reactors or in the interior of porous preforms.

Growth Kinetics of Silicon Carbide Chemical Vapor Deposition from Methyltrichlorosilane

The epitaxial chemical vapor deposition of SiC on (100) and (111) Si substrates has been conducted in a cold wall furnace from methyltrichlorosilane (MTS) as the single source material. In the temperature range from 1100°C to 1350°C, both surface-reaction-limited growth and diffusion-limited growth have been observed. The activation energy for growth was decreased using a two-step process route in which an intermediate layer was deposited by controlling only the partial pressure of the MTS.

Mass transfer and kinetics of the chemical vapor deposition of SiC onto fibers

An internally consistent set of data was generated for the chemical vapor deposition (CVD) of SiC from methyltrichlorosilane (MTS) and H2 at atmospheric pressure. A moving fiber tow was used as the substrate. Coating rates between 0.3 and 3.7 µm/min and deposition efficiencies between 24 and 48% were obtained for MTS and H2 flow rates in the range 30 to 200 cm3/min and 300 to 2000 cm3/min, respectively. The data were analyzed and found to be best fit under a mass transfer regime. Based on this fit, a value of the constant in the Chilton–Colburn j factor expression for a moving fiber tow was estimated to be 2.74 × 10−6 with a standard deviation of 3.2 × 10−7. The efficiency of the reaction was found to decrease with increases in the total flow rate, indicating that the effect of the decreased residence time of reagents in the reactor was larger than the increase in the mass transfer coefficient. Finally, a comparison between the efficiencies for a stationary and a moving tow revealed that the moving tow had a higher efficiency, possibly due to a disruption of the boundary layer by the tow motion or due to the decrease in the canning of the moving tow.

The coating of continuous carbon fiber bundles with sic by chemical vapor deposition: A mathematical model for the CVD-process

A mathematical model is presented for the description of the chemical vapor deposition of SiC on continuous fibers bundles consisting of several hundreds or even several thousands of individual filaments. Based on chemical engineering kinetics, the model predicts the mean layer thickness and the layer thickness distribution on the monofilaments of the bundle. The model presupposes that the kinetics of the deposition on the outer surface, the effective diffusion coefficient and the geometry of the fiber bundle are known. The results of the calculations are presented in terms of the change of the diameter of the fibers as a function of the distance from the axis of the bundle for different positions in the reactor and as the relative concentration of the precursor as a function of the distance from the axis of the bundle for different positions in the reactor and for different deposition conditions. Using the model presented the mean layer thickness was calculated for different reaction conditions and a comparison between calculated and measured values is given.

The adsorption of hydrogen chloride on polycrystalline β-silicon carbide

The reactivity of HCl, a by-product of SiC chemical vapor deposition (CVD) from chlorine-containing precursors, is of particular interest because it has been reported that addition of HCl inhibits the SiC CVD process. In this study, HCl adsorption on polycrystalline β-SiC was examined with Auger electron spectroscopy and temperature-programmed desorption (TPD). HCl adsorbs readily on SiC at 300 K with an initial sticking probability of 0.11 and forms a strong bond with an activation energy for desorption of 64 kcal/mol. The only product detected by TPD is HCl, which desorbs in a peak centered at 1010 K. No silicon- or carbon-containing desorption products are found, demonstrating that HCl does not etch the SiC surface under these conditions. HCl inhibition of SiC CVD can be accounted for qualitatively with a surface site-blocking mechanism.

Incorporation mechanism of N, Al, and B impurities in chemical vapor deposition of SiC

In situ doping characteristics of N, Al, and B in step-controlled epitaxy of SiC have been investigated. Clear C/Si ratio dependence was observed in the growth on (0001)Si faces. Doping efficiency of N decreased and those of Al and B increased under the C-rich condition, which agrees with a model proposed as ‘‘site-competition epitaxy.’’ However, doping efficiencies were almost independent of the C/Si ratio on (0001̄)C faces. Based on the results, the incorporation mechanism is discussed.

Experimental kinetic study of the chemical vapour deposition of SiC-based ceramics from [formula omitted] gas precursor

A detailed kinetic study is presented in order to determine the limiting steps in the chemical vapour deposition of SiC from CH 3SiCl 3 (MTS) H 2 gaseous mixture. On the basis of growth rate measurements, transitions from chemical kinetic control to mass transfer control are found to be induced either by decreasing total flow rate or by increasing temperature and/or total pressure. A pressure-temperature diagram, giving the boundaries between the different domains observed is presented. The chemical kinetics controlled domain includes either 2 or 3 sub-domains, depending on the α = P H 2 P MTS ratio. By taking into account the apparent activation energy, determined in each sub-domain, and the results of the outlet gas phase analysis by mass-spectrometry, three limiting kinetic processes are proposed: CH 3SiCl 3 homogeneous decomposition, heterogeneous formation of SiC and growth inhibition by HCl.