Trichlorosilane hydrogen reduction

The next step is the hydrogen reduction of the trichlorosilane (Reaction 2 above). The end product is a poly crystalline silicon rod up to 200 mm in diameter and several meters in length. The resulting EGS material is extremely pure with less than 2 ppm of carbon and only a few ppb of boron and residual donors. The Czochralski pulling technique is used to prepare large single crystals of silicon, which are subsequently sliced into wafers for use in electronic devices.1 1... 

Hydrogen reduction of trichlorosUane or thermal decomposition or chemical vapor deposition (CVD). In this new and modern method, after distillation, the refined ultrapure trichlorosilane, SiHCl, is mixed with hydrogen gas and the gas mixture fed into a reaction-heated vessel. A heating filament made of pure tantalum is heated by an electric current. The resulting purified polycrystaUine silicon is deposited and grown on the surface of cm electrically heated tantalum-metal hollow wick according to the following reaction ... 

The formation of silicon carbide, SiC (carborundum), is prevented by the addition of a little iron as much of the silicon is added to steel to increase its resistance to attack by acids, the presence of a trace of iron does not matter. (Addition of silicon to bronze is found to increase both the strength and the hardness of the bronze.) Silicon is also manufactured by the reaction between silicon tetrachloride and zinc at 1300 K and by the reduction of trichlorosilane with hydrogen. 

At atmospheric pressure, the conversion to trichlorosilane is limited to about 16%. The conversion of SiCl to HSiCl was found to be at equiUbrium. If contact time was greater than 45 s and the mole ratio of hydrogen to siUcon tetrachloride 1 1, then at 14 kPa (2 psi) and 550°C, the HSiCl mole fraction reached 0.7 but substantial formation of H2SiCl2 occurred (62). Enhancements in yield have been reported through preactivating the siUcon mass by removal of oxides (73) and the rapid thermal quench of the effluent gas stream (74). The reduction of siUcon tetrachloride in a plasma has also been reported (75). 

The production of sihcon tetrachloride by these methods was abandoned worldwide in the early 1980s. Industrial tetrachlorosilane derives from two processes associated with trichlorosilane, the direct reaction of hydrogen chloride on sihcon primarily produced as an intermediate for fumed sihca production, and as a by-product in the disproportionation reaction of trichlorosilane to silane utilized in microelectronics. Substantial quantities of tetrachlorosilane are produced as a by-product in the production of zirconium tetrachloride, but this source has decreased in the 1990s owing to reduction in demand for zirconium in nuclear facihties (see Nuclearreactors). The price of tetrachlorosilane varies between l/kg and 25/kg, depending on grade and container. 

Trichlorosilane is used in the production of semiconductor grade silicon. By repeated distillation the content of boron or phosphorus impurities can be reduced to <0.1 ppb. Elemental silicon is obtained by reduction with hydrogen at high temperatures according to the idealized equation 6. 

Preparative Methods by hydrogenation (5% Rh/C) of optically pure (2-anisyl)phenylmethylphosphine oxide followed by reduction of the phosphine oxide with Trichlorosilane Handling, Storage, and Precautions readily oxidized to the phosphine oxide and should be handled under N2 or Ar. This reagent should be handled in a fume hood. 

Silicon does not react with hydrogen except under extreme conditions in the presence of chlorine, in which case compounds such as trichlorosilane (HSiClj) are obtained. The hydride SiH4 itself may be prepared in the laboratory by hydrolysis of magnesium silicide, in which case a number of other hydrides up to Si4Hi4 are also obtained, or more conveniently by reduction of silicon tetrachloride with lithium tetrahydridoaluminate ... 

Keywords Transfer hydrogenation Organocatalysis Hantzsch ester Trichlorosilane Phosphoric acid Aminocatalysis Thioureas Lewis bases Reduction Hydrosilylation... 

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