Atmospheric Pressure Chemical Vapor Deposition of 3C-SiC
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SSachs/Freeman
Associates, Landover, MD 20785
Abstract Optically transparent SiC deposits were grown via atmospheric pressure chemical vapor deposition (APCVD) on graphite substrates from methyltrichlorosilane (MTS) in hydrogen in a cold-walled, RF-induction furnace. Structural morphology was examined by scanning electron microscopy and correlated to substrate temperature, MTS/H2 ratio, and hydrogen flow. Photoluminescence revealed that high quality cubic material was grown. The PL spectra exhibited a zero phonon line (2.3787 eV) attributable to an exiton bound to a neutral nitrogen donor, in addition to TA, LA, TO, and LO phonon replicas. Observed broadening and splitting of the PL spectral lines was associated with the morphological habit and internal strain of individual crystallites. In addition, the PL spectra for samples grown at higher MTS/H2 ratios and low H2 flows exhibited weak shoulders on the low energy side of the five-line spectra which might be associated with nonstoichiometric defects such as Si interstitials or C vacancies. Introduction In addition to its superior mechanical properties, the wide band gap (2.3 eV), high breakdown field, and high saturated electron velocity of cubic silicon carbide (3C-SiC) make it an attractive candidate for elevated-temperature, high-frequency, and high-power electronic devices. Chemical vapor deposition has been demonstrated to yield dense, high purity 3C-SiC which has found applications as wear and corrosion-resistant coatings and as a semiconductor device material particularly in aggressive environments [1]. Previous work at the A.A. Baikov Institute in Moscow demonstrated that high quality, high purity 3C-SiC single crystals (-3 mm) could be grown on graphite rods by APCVD using MTS in H2. [2] In the Baikov work, however, the effects of system geometry and gas phase chemistry on the growth of high quality material were not fully elucidated. An important objective of this study was to examine the effect of deposition parameters on the microstructure and optical properties of the deposited layers. This work focused on reconstructing the success of the Baikov effort with the goal of realizing a reproducible process for large-area high quality 3C-SiC. Deposition conditions which favored single crystal growth were of particular interest. Experimental Procedure The growth of 3C-SiC was carried out at atmospheric pressure by the thermal decomposition of methyltrichlorosilane (MTS) in excess hydrogen in a vertical quartz reaction chamber (2.54 cm ID x 30.5 cm). A 5 kW RF induction power supply was used to heat a graphite substrate (1.27 cm 0 x 2.54 cm) which was suspended in the quartz tube by a tungsten filament. Prior to each deposition run the reaction chamber was evacuated to 0.1 torr and then purged with hydrogen. The substrate was preheated for 15 minutes in flowing hydrogen at the deposition temperature prior to initiating the MTS flow.
351 Mat. Res. Soc. Symp. Proc. Vol. 410 01996 Materials Research Society
The hydrogen flow rate was controlled with a mass f
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