Described herein are methods for making a chlorinated silane or chlorosilane such as, for example, monochlorosilane or dichlorosilane. Silanes with low chlorine content are desirable precursors for the production of functionalized silanes containing the —SiH3 or —SiH2— moieties. The properties of the functionalized silanes have proven to be highly tunable by variation of their substituents and have found growing application in the deposition of, for example, thin silicon dioxide or silicon nitride films which can be used in the manufacture of microelectronic devices.
Although the chlorinated silane monochlorosilane is produced on a large scale as an intermediate in the industrial synthesis of silane by disproportionation of trichlorosilane (Equations 1, 2), it is seldom isolated due to the highly-integrated nature of silane production, and the high commercial demand for silane relative to monochlorosilane.2SiCl3H←→SiH2Cl2+SiCl4  (Equation 1)2SiH2Cl2←→SiH3Cl+SiCl3H  (Equation 2)
Though monochlorosilane can be prepared by disproportionation of dichlorosilane, or conproportionation of silane and a higher chlorosilane (e.g., SiCl4, SiHCl3, SiH2Cl2), it is well established that the equilibrium constants for these reactions do not favor monochlorosilane, and that extensive byproduct recycling akin to that used for silane production would be necessary to efficiently produce monochlorosilane by this method. More direct routes for the synthesis of monochlorosilane have been reported in the literature, but are not amenable to large scale synthesis due to a variety of factors including hazardous reaction conditions, co-formation of more highly chlorinated silanes, and/or undesirable catalyst properties. For example, the direct chlorination of silane with chlorine proceeds violently even in the absence of a catalyst and generates a mixture of chlorosilanes. Likewise, the aluminum trichloride catalyzed reaction of HCl with silane to form monochlorosilane is complicated in continuous processes by the volatility of AlCl3, and by also by the ability of AlCl3 to act as a disproportionation catalyst (in batch or continuous processes). The problems associated with AlCl3 volatility have been partially addressed by use of molten salt catalysts such as LiAl2Cl7 at or above their eutectic melting points. However, these salts are highly corrosive and retain some AlCl3 volatility, which unless accounted for, results in a continuously increasing melting point. Synthesis at higher temperatures exacerbates molten salt corrosivity, increases the rate of AlCl3 loss, and reduces end product selectivity.