Fluorspar/Iodide process for reduction,purificatioin, and crystallization of silicon
First Claim
1. A method of producing silicon tetrafluoride gas from the aqueous reaction of crude fluorspar and concentrated sulfuric acid, said method comprising the steps of:
- (a) bubbling SO.sub.3 gas into dilute H.sub.2SO.sub.4 to produce concentrated (greater than 70% by weight) sulfuric acid and(b) combining milled fluorspar ore or fluorspar tailings with sulfuric acid to produce a liquor of dilute sulfuric acid and fluosilicic acid, and insoluble product CaSO.sub.4 and(c) combining the concentrated sulfuric acid from step (a) with the sulfuric/fluosilicic acid liquor from step (b) to generate silicon tetrafluoride gas and produce aforementioned dilute sulfuric acid in step (a).
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Accused Products
Abstract
Method and apparatus for producing molten purified crystalline silicon from low-grade siliceous fluorspar ore, sulfur trioxide gas, and a metallic iodide salt. Method involves: (1) initially reacting silicon dioxide-bearing fluorspar ore and sulfur trioxide gas in sulfuric acid to create silicon tetrafluoride gas and fluorogypsum; (2) reacting the product gas with a heated iodide salt to form a fluoride salt and silicon tetraiodide; (3) isolating silicon tetraiodide from impurities and purifying it by washing steps and distillation in a series of distillation columns; (4) heating the silicon tetraiodide to its decomposition temperature in a silicon crystal casting machine, producing pure molten silicon metal ready for crystallization; and pure iodine gas, extracted as liquid in a cold-wall chamber. The system is batch process-based, with continuous elements. The system operates largely at atmospheric pressure, requiring limited inert gas purges during batch changes.
3 Citations
20 Claims
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1. A method of producing silicon tetrafluoride gas from the aqueous reaction of crude fluorspar and concentrated sulfuric acid, said method comprising the steps of:
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(a) bubbling SO.sub.3 gas into dilute H.sub.2SO.sub.4 to produce concentrated (greater than 70% by weight) sulfuric acid and (b) combining milled fluorspar ore or fluorspar tailings with sulfuric acid to produce a liquor of dilute sulfuric acid and fluosilicic acid, and insoluble product CaSO.sub.4 and (c) combining the concentrated sulfuric acid from step (a) with the sulfuric/fluosilicic acid liquor from step (b) to generate silicon tetrafluoride gas and produce aforementioned dilute sulfuric acid in step (a). - View Dependent Claims (2, 3, 4)
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5. A method of producing silicon tetraiodide gas from the gas-phase reaction of silicon tetrafluoride with a halogen salt, said method comprising:
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(a) Introducing SiF.sub.4 gas into a container with heated Iodine-bearing salt and (b) Using a cold trap to capture product SiI.sub.4 from the mixed gas phase and (c) Collecting the product salt for separation into fluoride-bearing byproduct and iodine-bearing salt for reuse - View Dependent Claims (6, 7, 8, 9, 10)
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11. A method of producing molten high purity silicon and high purity iodine gas from the purification and thermal decomposition of crude silicon tetraiodide gas, said method comprising:
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(a) Repeated washing steps with nonreactive chemicals to separate impurities by boiling and freezing the crude SiI.sub.4 material and (b) Fractional distillation of the crude SiI.sub.4 material to produce pure SiI.sub.4 material and (c) Introduction of the SiI.sub.4 material to a heated crystallization furnace to produce molten Si metal and I2 gas and (d) Collection of I.sub.2 gas and (e) Crystallization of a melt of sufficient size to produce semiconductor-grade ingots, sheets, or boules suitable for wafering and further processing - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification