Method of purifying silicon

Claim 1

A batch method of producing crystalline silicon having an iron concentration less than about one-twentieth of the iron concentration of the mother liquor, said method comprising introducing a molten mother liquor of silicon contaminated with iron at a temperature higher than the melting point of pure silicon into a ladle-shaped mold having a bottom and side walls, maintaining the mold at a temperature sufficient to cause silicon crystals to grow thereon, providing relative movement between the mold wall with the growing silicon crystals and the molten mother liquor to continuously wash the exposed growing surfaces of the silicon crystals with the mother liquor during the further growth of the silicon crystals and maintaining the top surface thereof substantially liquid by providing relative movement between the mold with the silicon crystals thereon and the molten mother liquor, decanting the mother liquor from the mold before the liquor temperature reaches 2206° F. to leave a hollow ladle-shaped silicon ingot of less than about 60% by weight of the original mother liquor having an outer zone adjacent to the mold and an inner zone centrally of said silicon ladle-shaped ingot, both the outer and inner zones having more than one-twentieth of the iron concentration of the mother liquor, and discarding the outer and inner zones to leave an annular crystalline portion of the silicon ingot with an iron concentration less than about one-twentieth of the iron concentration in the original mother liquor.