Method and Apparatus for Refining Metallurgical Grade Silicon to Produce Solar Grade Silicon
AssigneeCrystal System, Inc.
InventorsFrederick Schmid, David B. Joyce
Life of this patent
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Abstract
A method and apparatus for refining metallurgical silicon to produce solar grade silicon for use in photovoltaic cells. A crucible in a vacuum furnace receives a mixture of metallurgical silicon and a reducing agent such as calcium disilicide. The mix is melted in non-oxidizing conditions within the furnace under an argon partial pressure. After melting, the argon partial pressure is decreased to produce boiling and the process ends with directional solidification. The process reduces impurities, such as phosphorus, to a level compatible with solar-grade silicon and reduces other impurities significantly.
Claims18
A process for refining metallurgical grade silicon in a reactor including a heat zone to remove a plurality of impurities therefrom comprising the steps of:
- A) selecting an agent for reducing a level of at least one of the impurities,
- B) mixing the silicon with the selected agent,
- C) refining the silicon and the selected agent mix in the reactor in a non-oxidizing environment at an elevated temperature and at a reduced pressure that minimizes volatilization of the selected agent thereby to produce a refined material, and
- D) thereafter directionally solidifying the refined material in the same reactor thereby to segregate impurities during said directional solidification.
12-21. (canceled)
A process for refining in a reactor metallurgical grade silicon that includes a plurality of impurities with an agent for reacting with at least one of said impurities by:
- A) mixing in a non-oxidizing crucible the metallurgical grade silicon and the agent,
- B) melting the mix in the reactor while maintaining a reduced pressure that controls volatilization of the agent,
- C) reducing the pressure in the reactor to remove at least one of the impurities in the non-oxidizing crucible in a vacuum environment, and
- D) segregating other impurities by directional solidification in the crucible and reactor.
Dependencies are inferred from the claim text.