Primary distillation boron reduction

Abstract

The present invention relates to an apparatus and a method for producing polycrystalline silicon having a reduced amount of boron compound impurities. Especially, the boron compounds are removed from the process for producing polycrystalline silicon, while the trichlorosilane is purified by distillation. The invention feeds condensed liquid trichlorosilane into a primary distillation tower below the liquid level inside the primary distillation tower thereby scrubbing the boron impurities upon contact inside the primary distillation tower. There result is trichlorosilane leaving the primary distillation tower with total amount of boron at least 10 times less.

What is claimed is: 
     
         1 . An apparatus for manufacturing polycrystalline silicon having a reduced amount of boron compounds, comprising:
 a fluidized-bed reactor for reacting metallurgical grade silicon with hydrogen chloride gas for producing trichlorosilane and other compounds;   a condenser for condensing trichlorosilane and other compounds produced in the fluidized-bed reactor into a liquid;   a distillation unit for purifying the trichlorosilane wherein the liquid trichlorosilane and other compounds enters the distillation unit below a liquid level in the distillation unit; and   a reactor for depositing polycrystalline silicon on a surface of silicon seed rods.   
     
     
         2 . The apparatus for manufacturing polycrystalline silicon according to  claim 1 , further comprising:
 a trichlorosilane tank, for keeping a liquid trichlorosilane and for constantly feeding the trichlorosilane to the distillation unit, located between the fluidized-bed reactor and the distillation unit; and   an evaporator for vaporizing the trichlorosilane fed to the reactor.   
     
     
         3 . The apparatus for manufacturing polycrystalline silicon according to  claim 1 , wherein the distillation tower has a low reflux ratio of ≦5 gpm. 
     
     
         4 . The apparatus for manufacturing polycrystalline silicon according to  claim 1 , whereby boron discharged from the distillation tower is less than about 40 ppm. 
     
     
         5 . A method for manufacturing polycrystalline silicon reduced boron compounds, comprising:
 reacting metallurgical grade silicon with hydrogen chloride to produce a reacted gas, including trichlorosilane and other compounds, a fluidized-bed reactor;   condensing the reacted gas, including trichlorosilane and other compounds, into a liquid;   feeding the liquid trichlororsilane and other compounds into a distillation unit below a liquid level inside the distillation unit;   distilling the liquid trichlorosilane for purifying; and   depositing polycrystalline silicon on silicon seed rods.   
     
     
         6 . The method for manufacturing polycrystalline silicon reduced boron compounds according to  claim 5 , wherein the distillation unit has a low reflux ratio of ≦5 gpm. 
     
     
         7 . The method for manufacturing polycrystalline silicon reduced boron compounds according to  claim 5 , whereby boron discharged from the distillation unit is less than about 40 ppm.