Perchlorosilanes and Perchlorocarbosilanes as Precursors to Silicon Carbide
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0911-B05-12
PERCHLOROSILANES AND PERCHLOROCARBOSILANES AS PRECURSORS TO SILICON CARBIDE Vladimir Sevastyanov1, Yurij Ezhov2, Roman Pavelko1, and Nikolaj Kuznetsov1 1 N.S.Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Science, Leninskij av. 31, Moscow, 119991, Russian Federation 2 Institute for High Energy Densities, "IVTAN" Association, Russian Academy of Science, Izhorskaya st. 13/19, Moscow, 125412, Russian Federation
ABSTRACT Homologues with the general stoichiometry a(SiCl4) : bSi : cC : d(SiC) are shown to be potential precursors for the low-temperature gas-phase synthesis of silicon carbide. Thermal decomposition of these precursors yields the chemically stable gaseous species SiCl4 and condensed Si, C, SiC, SiC+Si, or SiC+C. Thermodynamic modeling of the thermal decomposition of octachlorotrisilane, Si3Cl8, is used to analyze the key features of the thermolysis of perchlorosilanes with the general stoichiometry a(SiCl4) : bSi. The equilibrium compositions of reaction products in the Si3Cl8+CO system are determined. This reaction system enables low-temperature (400 – 1200 K) synthesis of silicon carbide.
INTRODUCTION Gas-phase processes play a key role in producing not only coatings but also bulk structures of silicon carbide. In particular, an important step in the fabrication of hightemperature ceramic-matrix composites is chemical vapor infiltration of a carbon skeleton with silicon or silicon monoxide [1, 2]. Organosilicon compounds are of special importance in vaporphase reactions, e.g., in silicon carbide chemical vapor deposition (CVD). Typical precursors for this process are silane--hydrocarbon mixtures [3] or organochlorosilanes, such as methyltrichlorosilane, methylsilane, and hexamethyldisilazane, which are exposed to high temperatures (usually above 1500 K) in hydrogen to give SiC [4]. One obvious drawback to this approach is the formation of highly reactive side products (hydrogen, hydrogen chloride, chlorine, and water vapor), which may be not only corrosive but also explosive, depending on mixture composition. As shown earlier, one of the gaseous products of perchlorocarbosilane thermolysis is silicon tetrachloride, a compound stable in a broad temperature range, up to 1500OC [5]. The solid reaction product is silicon or carbon. The deposition of ultrafine-grained silicon coatings through thermal decomposition of perchlorosilanes is well studied and forms the basis of several processes for the preparation of silicon semiconductor materials [6, 7]. In recent studies, thermal decomposition of perchlorocarbosilanes was used to produce thin films of amorphous carbon [8]. A literature search revealed no reports on the use of perchlorocarbosilane thermolysis for silicon carbide synthesis. This approach might extend the application area of perchlorocarbosilanes and
enable the synthesis of various carbon-silicon materials under mild conditions using simple apparatus. The above led us to systematize the information on perchlorosilanes and perchlorocarbosilanes reported in
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