Primary distillation boron reduction
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.
1. A method for manufacturing polycrystalline silicon having a reduced amount of boron compounds, comprising:
reacting metallurgical grade silicon with hydrogen chloride to produce a reacted gas, including trichlorosilane, boron compounds as impurities and other compounds, in a fluidized-bed reactor;
condensing the reacted gas to form a liquid containing trichlorosilane, boron compounds as impurities and other compounds;
feeding the liquid into a distillation unit below a liquid level inside the distillation unit;
distilling the liquid to separate the trichlorosilane from other compounds and to remove boron compounds impurities; and
using the trichlorosilane obtained from the distilling step to deposit polycrystalline silicon on silicon seed rods.
2. The method for manufacturing polycrystalline silicon having a reduced amount of boron compounds according to claim 1 , wherein the distillation unit has a low reflux ratio of <5 gpm.
3. The method for manufacturing polycrystalline silicon having a reduced amount of boron compounds according to claim 1 , wherein boron discharged from the distillation unit is less than about 40 ppm.