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Substrate Manufacture

Polycrustalline Silicon Production

To manufacture polycrystalline silicon, ultra-pure silicon is produced from raw quartzite (silica sand) that is melted and reduced to silicon in an electric arc furnace at over 1900ºC. This metallurgical-grade silicon is drawn from the furnace and blown with oxygen or an oxygen-chloride mixture to reduce the levels of impurities to achieve approximately 99% pure silicon. Next, the silicon is reacted with hydrogen chloride gas in the presence of a copper-containing catalyst to form trichlorosilane (SiHCl3). The trichlorosilane is reduced to very pure silicon by reacting it with hydrogen at high temperatures (about 1100ºC). This "electronic grade" silicon has less than 1 ppb of impurities.

The following are the potential hazards of polycrustalline silicon production.

Silica (Crystalline)

Potential Hazard

  • Possible employee exposure to crystalline silica used as a raw material. Inhalation of silica can lead to chronic, accelerated or acute silicosis and is associated with bronchitis and tuberculosis. Some studies also indicate an association with lung cancer. Exposures to silicon dust may also occur; controls are similar to those used for crystalline silica.

Possible Solutions

  • Identify silica hazards and perform appropriate exposure evaluations.
  • Provide appropriate ventilation to reduce silica concentration levels in the air.
  • Maintain adequate housekeeping to remove unwanted silica dust and reduce concentration levels.
  • Use respiratory protection when necessary to further reduce exposure and protect employees. [29 CFR 1910.134]

Additional Information

OSHA Safety and Health Topics Pages:

Hydrogen Chloride Gas

Potential Hazard

  • Possible employee exposure to hydrogen chloride gas. Hydrogen chloride is irritating and corrosive to the eyes, skin, and mucous membranes. Exposure to high concentrations can cause laryngitis, bronchitis, and pulmonary edema.

Possible Solutions

  • Identify hydrogen chloride hazards and perform appropriate exposure evaluations.
    • Identify and evaluate all potential exposure scenarios, for example: startup, operations, maintenance, cleaning, emergencies, and so forth.
    • 29 CFR 1910.1000 Table Z-1 provides permissible exposure limits for hydrogen chloride.
    • Occupational Health Guidelines for Chemical Hazards. US Department of Health and Human Services (DHHS), National Institute for Occupational Safety and Health (NIOSH) Publication No. 81-123, (1981, January). Provides a table of contents of guidelines for many hazardous chemicals. The files provide technical chemical information, including chemical and physical properties, health effects, exposure limits, and recommendations for medical monitoring, personal protective equipment (PPE), and control procedures.
  • Provide appropriate ventilation to reduce hydrogen chloride concentration levels in the air.
  • Provide PPE as appropriate to prevent eye and skin contact with hydrogen chloride. [29 CFR 1910 Subpart I]
  • Use respiratory protection when necessary to further reduce exposure and protect employees. [29 CFR 1910.134]

Additional Information

OSHA Safety and Health Topics Pages:

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