Polysilicon Purification and Processing

The process of producing polysilicon (PS) begins with refining quartz or sand into metallurgical grade silicon, which is then purified in a series of chemical reactions.

Next, during the Müller Rochow process, purified metallurgical grade silicon reacts with hydrogen chloride at elevated temperatures in the presence of a catalyst, to produce trichlorosilane (TCS).

The TCS gas is cooled and liquified. Impurities with higher or lower boiling points than the TCS liquid are then removed using distillation. The refined TCS is now ready for use in reactors that make PS.

The TCS liquid is vaporized, mixed with hydrogen gas and reduced in either a Chemical Vapor Deposition (CVD) furnace resulting in PS rods; or, Fluid Bed Reactor (FBR) to produce PS granules.

Exhaust gases which are released during this process are cooled, liquified and distilled, yielding the co-products silicon tetrachloride (STC) and TCS, which is recycled.

Hydrogen recycle is an important unit operation in PS production. Exhaust gases consisting of hydrogen and chlorosilane from the reduction reaction are recovered.

The hydrogen goes through a clean up process and is then recycled back to the reduction plant in a continuous recovery loop.

Applications for Pall Filtration Products

  • Catalyst fines must be separated from the product stream during the Müller Rochow process. This can be accomplished with Blowback elements made of either ceramic or a special alloy of PSS® filter media.
  • Newly produced or recycled liquid as well as gas phase TCS, are filtered before the reduction reaction. The level of filtration will depend on each site's requirements. Rigimesh® sintered metal mesh filter cartridges are utilized for coarse applications, with all-fluoropolymer Emflon® PF cartridge filters for submicron requirements.
 

Photovoltaics Overview
Photovoltaics - Applications
Photovoltaics - Polysilicon Purification and Processing
Photovoltaics - Crystal Growing
Photovoltaics - Silicon and Process Water Reclamation
Photovoltaics - Crystalline Silicon Cell Processing
Photovoltaics - Thin Film Module Manufacturing
Photovoltaics - Products
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  • Feed gases to the reactor are filtered to submicron levels to protect critical control valves and maintain purity within the reactor. Reactor vent applications capture valuable solid product using cleanable PSS metal filters, with Blowback technology as an option. Recovering product from vent streams increases process yields, reduces loading to pollution control systems and protects downstream equipment from PS build-up. High capacity filtration systems allow for complete production campaigns.
  • Where a recycle hydrogen compressor is used, filtration with Pall metal filters and polishing membrane cartridges protects the compressor from PS deposits and reduces expensive compressor maintenance and associated process downtime.
  • Caustic baths followed by water rinsing are used to clean metal filter elements by dissolving off the PS particulate. These baths are filtered with Profile® II and Profile UP filters to recover the PS and keep it from contaminating waste streams.
  • Depending on the final product, there may be an etching step on the final ingots, rods or granules using either hydrofluoric and/or nitric acid. These etch baths as well as downstream water rinses are filtered to submicron levels using Emflon PF cartridges.
  • Pall provides filtration products and systems for varying grades of water, including ultrapure and wash water, as well as wastewater where there may be a requirement to remove or recover PS fines.
Ceramic Filter Elements for hot gas filtration
Ceramic Filter Elements for hot gas filtration
  Emflon PF Filters for critical chemical filtration
Emflon PF Filters for critical chemical filtration
  Rigimesh Filters for coarse TCS filtration
Rigimesh Filters for coarse TCS filtration