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In this study, we thermodynamically reviewed the suitable growth process conditions of α-SiC in the Si-C-H system using tetramethylsilane (TMS) and in the Si-C-H-Cl system using methyltrichlorosilane (MTS). In the Si-C-H-Cl system, pure solid SiC was obtained at high temperatures under a larger range of hydrogen dilution ratios than that tolerated in the Si-C-H system. X-ray diffraction and micro-Raman analysis of the products obtained at 1900, 2000, and 2100 °C showed that the α-SiC becomes more dominant with increasing temperature in the Si-C-H-Cl system. While TMS was unsuitable for high temperature processing due to its high C/Si ratio, MTS was found to be appropriate for growing α-SiC crystals at high temperatures under a range of conditions. These results indicate that a novel method to grow α-SiC single crystals through HTCVD using MTS as a precursor could be established.

The chlorinated precursor methyltrichlorosilane (MTS), CH3SiCl3, has been used to grow epitaxial layers of 4H-SiC in a hot wall chemical vapour deposition (CVD) reactor with growth rates higher than 100mm/h. The addition of chlorinated species to the gas mixture prevents silicon nucleation in the gas phase, thus allowing higher input flows of the precursors resulting in much higher growth rate than that of standard silicon carbide (SiC) epitaxial growth using only silane, SiH4, and hydrocarbons as precursors. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate, morphology, and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor. The growth rate dropped for C/Sio1 but was constant for C/Si41. Further, the growth rate decreased with lower Cl/Si ratio. This study shows that MTS is a promising precursor for homoepitaxial growth of SiC within the concept of chloride-based SiC growth.

Silicon carbide was deposited homoepitaxially at high growth rates (up to 90 μm/h) with methyltrichlorosilane (MTS) as the precursor in chemical vapor deposition. The substrates were 6H- and 4H-SiC (0 0 0 1) wafers with different misorientation ( 1 1 2 ¯ 0 ). At a growth temperature of 1400 °C, the grown film was composed of faceted grains and the surface was very rough. As the growth temperature increased, the crystal grains were enlarged and the films’ surfaces became smoother and smoother. At 1600 °C, on 8° misoriented substrate, a very smooth film with mirror-like surface was generated. Raman spectroscopy showed that the polytypes of the films were affected by the substrate misorientation. When the 6H-SiC substrates were well oriented, i.e. with the offset angle of less than 0.5°, 3C-SiC was deposited with numerous triangular stacking faults (TSFs). When the offset angle of substrates was 3.5°, mixtures of 3C- and 6H-SiC polytypes were deposited. When the offset angle was 8°, the epitaxial growth perfectly replicated the substrates’ polytypes, i.e. high-quality 6H- and 4H-SiC epilayers were generated on the 6H- and 4H-SiC substrates, respectively. The full-width half-maximum (FWHM) of X-ray diffraction rocking curves for the c -plane of pure smooth 6H- and 4H-SiC layers was in the range of 15–20 arcsecs. Photoluminescence (PL) confirmed the polytypes of 6H- and 4H-SiC layers: Both exhibited clear near-band edge emission at room temperature. These results demonstrate that MTS is a suitable precursor for the rapid, high quality SiC epitaxy.

Coatings of β -SiC were prepared from the methyltrichlorosilane by low- pressure chemical vapor deposition (CVD) onto the graphite substrates. The as-deposited coatings were characterized by scanning electron microscopy, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) methods. The surface morphology of CVD SiC shows pyramid structure and (1 1 1) plane is the preferred orientation in the XRD pattern. HRTEM results show that SiC crystal grows according to the preferred orientation of the substrate at the beginning of the deposition, and then the crystal adjusts the growth to (1 1 1) plane.

Silicon carbide (SiC) whiskers as a kind of high strength fibrous material are commonly used as an effective reinforcing element for composite materials. The preparation and characterization of such high aspect ratio materials are of great importance to the understanding of fundamental properties and potential industrial applications of whisker materials. In this study the growth of SiC whiskers by chemical vapor deposition (CVD) from the thermal decomposition of methyltrichlorosilane was performed on Ni-coated graphite substrates in a hot wall reactor with an emphasis on the study of the fundamental nucleation and growth characteristics of the whiskers. Since vapor–liquid–solid mechanism is found to be responsible for the growth of whiskers, the formation of the Ni catalyst and its subsequent evolution on whisker nucleation and growth is a subject of extensive research. Scanning electron microscope is employed to characterize the nucleation and growth of SiC whiskers. It is found that the incubation period for whisker nucleation and growth to noticeable dimension depends on the size of the Ni particles. It takes about 3 min for the first whisker to appear and about 8 min to complete the whole nucleation stage for the case of Ni-coating thickness of about 2.5 μm under the CVD parameters employed in the present study. Besides, due to the balance between the volume and the curvature effect of the liquid droplet of Ni catalyst formed on the graphite substrate during CVD process, the shortest incubation time for SiC whisker nucleation was found for droplets of 2 μm in diameter, instead of those with larger or smaller dimensions.

Synchrotron white beam X-ray topography (SWBXT) has been used to characterize 2H–silicon carbide crystals grown by the chemical reduction of methyltrichlorosilane at 1400°C. The crystals studied had the form of tapered needles around 1 mm long with hexagonal cross-sections 0.4 mm in diameter. SWBXT images recorded from two different crystals showed their excellent quality, as evidenced by the presence of Pendellosung fringes. Topographs recorded with various diffraction vectors revealed no evidence of the axial screw dislocations reported in 2H–SiC by Setaka and Ejiri, based on their observations of spiral growth steps. Neither were there any dislocations with Burgers vectors lying in the crystals’ basal planes. The absence of axial screw dislocations indicates that the growth was not screw dislocation assisted, but occurred by diffusion-controlled growth; and some other influence such as thermodynamics, initial nucleation, and/or impurity assisted growth, was responsible for the isolation of the 2H polytype.

Chemical vapor deposition of silicon carbide whiskers activated by a metal impurity was studied using a gas mixture of methyltrichlorosilane and H 2 on both Ni-coated graphite and Ni foil substrates. The as-grown whiskers were characterized by scanning electron microscopy and their nucleation and growth behaviors were determined. It is found that the melting behavior of Ni coating on a graphite substrate differs from that of a Ni foil, which in turn affects the nucleation of SiC whiskers on the respective substrates. SiC whiskers can be successfully prepared on both substrates by the VLS mechanism, but the growth behavior and the quality of whiskers prepared is determined by the way and characteristics of the metal catalyst provided. With an appropriate choice of the type of catalyst and processing parameters, the bulk form catalyst can also be effective in activating the VLS growth of SiC whiskers; therefore, the necessity for a catalyst-layering step in conventional processes can be avoided.

Silicon carbide (SiC) deposited by chemical vapor deposition (CVD) from methyltrichlorosilane (MTS)H2 was often found to be silicon-rich and micro- or nanocrystalline. We address here the question whether the excess silicon would be localized inside the small SiC crystals contained in the deposit or not. We performed semi-empirical total energy calculations and free energy estimations which show that excess Si atoms should not be localized inside a finite SiC crystal. This is essentially due to the difference between the SiSi and SiC σ overlaps of sp3 hybrids for a given nearest-neighbor distance. Comparison of a crystallographic equation with experimental results from CVD materials suggests that the SiC nanocrystals be of maximum size allowing all excess Si atoms to be localized at the border of the crystals, provided that there are no Si crystals in the deposited material.

Hydrogen reduction of methyltrichlorosilane at 1400–1430°C has been used to deposit single crystals of 2H SiC on graphite substrates. Straight and tapered needles and crystals showing abrupt and continuous changes in direction of crystal growth were obtained. Implantation of 2H SiC crystals with boron and nitrogen ions followed by 1400°C annealing did not produce visible photoluminescence under 365 nm excitation. The Knoop microhardness of 2H SiC, 2460, is practically identical to that of 6H SiC crystals.

Single crystal needles of alpha (2H-wurtzite) silicon carbide have been grown under controlled conditions by the hydrogen reduction of purified methyltrichlorosilane onto silicon carbide coated graphite susceptors. Previous work of Ryan et al. has been extended and more precise specifications of growth conditions of the 2H modifications have been determined. The 2H crystals were grown several millimeters in length by one millimeter diameter. They were optically clear and had sharply defined face. Their growth morphology was compatible with the VLS mechanism. The crystals were characterized by optical microscopy, electron microscopy and electron microprobe techniques. A detailed X-ray investigation of the anomalous behavior of these 2H crystals under thermal annealing is presented in a companion paper (Krishna and Marshall, this meeting).

The growth of beta silicon carbide by the hydrogen reduction of methyltrichlorosilane onto carbon substrates at 1500 °C is discussed. It is shown that alpha inclusions present are the rare 2H (wurtzite) modification of silicon carbide and that their presence resulted from a vapor-liquid-solid growth which was dominated by impurities in the substrate. By carefully cleaning the substrate and purifying the methyltrichlorosilane, the alpha inclusions were eliminated. The 2H alpha crystals were then deliberately grown by introducing selected impurities locally on the substrate. Beta crystals were also intentionally grown by the vapor-liquid-solid technique by introducing other appropriate impurities. Growth of beta silicon carbide from the melt is also briefly discussed.