Single Crystal Ingot Growth
Almost all crystal growth is done by the Czochralski (Cz) method. This method begins by heating electronic-grade polycrystalline silicon in a quartz crucible to 1200ºC in an argon atmosphere. Either radiofrequency (RF) or resistance heating is used. A starter or "seed" crystal of silicon is placed onto the end of a rod and dipped into the melt to form the crystal. The seed and crucible are rotated in opposite directions while the seed is withdrawn. Silicon atoms attach to the rod and the crystal grows in size. Careful control of temperature, rotation speed, and vertical withdrawal determines the size of the ingot. Different atmospheres (inert, oxidizing, reducing) and pressures (vacuum, high pressure) also are maintained in the growth chamber depending on the type of crystal desired.
Controlled amounts of impurities are added during crystal growth to establish the desired electrical properties for the silicon. The melt is usually "doped" with elements like boron, phosphorous, arsenic, or antimony.
The following are the potential hazards of single crystal ingot growth.
Metals and Salts
- Possible employee exposure to various metals and salts used for elemental dopants, including phosphorous, boron, arsenic, antimony, magnesium, etc.
- Identify metal hazards and perform appropriate exposure evaluations.
- Perform exposure measurements for the compounds used.
- Keep exposures below acceptable exposure levels.
- Address all dermal exposures.
- Provide appropriate ventilation to reduce concentration levels in air.
- Provide PPE as appropriate to prevent contact. [29 CFR 1910 Subpart I]
- Use respiratory protection when necessary to further reduce exposure and protect employees. [29 CFR 1910.134]
- Maintain adequate housekeeping to remove unwanted metals and reduce concentration levels.
- Preventing Occupational Illnesses through Safer Chemical Management. OSHA.
- 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.
OSHA Safety and Health Topics Pages:
- Dermal Exposure
- Personal Protective Equipment (PPE)
- Respiratory Protection
- Sampling and Analysis
- Toxic Metals