Apparatus and method for producing polycrystalline silicon having a reduced amount of boron compounds by forming phosphorus-boron compounds
The invention concerns an apparatus and a method for manufacturing polycrystalline silicon having a reduced amount of boron compounds. The invention provides an apparatus and a method which mix an unpurified trichlorosilane with purified hydrogen gas from an activated carbon tower. The mixture is sent to a distillation apparatus for purifying trichlorosilane.
1. A method for manufacturing polycrystalline silicon having a reduced amount of boron compounds, comprising:
reacting metallurgical silicon with hydrogen chloride to produce an unpurified trichlorosilane;
distilling the unpurified trichlorosilane, wherein the distilling has a condenser for separating trichlorosilane from vapor fractions to form purified trichlorosilane;
depositing polycrystalline silicon on silicon seed rods in a reactor by reducing and thermally decomposing the purified trichlorosilane by hydrogen reduction of trichlorosilane and thermal decomposition of trichlorosilane;
purifying hydrogen discharged from the reactor in an activated carbon tower;
mixing the vapor fractions from the condenser with a regeneration gas containing phosphorus compounds produced by the activated carbon tower, to form a mixture and combining the mixture with the unpurified trichlorosilane;
feeding a mixture of the unpurified trichlorosilane, the regeneration gas, and the vapor fractions to the step of distilling the unpurified trichlorosilane, and
removing high boiling point boron-phosphorus complex compounds as a residue fraction from the distilling step and separating trichlorosilane from vapor fractions.
2. The method for manufacturing polycrystalline silicon having a reduced amount of boron compounds according to claim 1 , wherein an amount of boron in an initial feed line to the step of distilling the unpurified trichlorosilane is within the range of about 0 to 500 ppbwt.