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Device Fabrication

Photoresist Application

Following the creation of a silicon dioxide layer, the wafer is coated with a photosensitive material called a "photoresist."

  • There are two types of photoresists: positive and negative. Positive photoresists undergo weakening when exposed to irradiation, whereas negative photoresists are strengthened. Most semiconductor processes use a positive resist.
  • The photoresist is applied by delivering a small amount of the liquid to the center of the wafer, then spinning the wafer at high speed to spread the material over the entire surface in a thin, uniform coating. Sometimes wafers are primed with an adhesive, hexamethyldisilazane (HMDS). Glycol ethers have been a popular solvent for carrying HMDS, although some manufacturers have switched to alternative solvents like xylene, n-butyl acetate, acetone, and 1,1,1-trichloroethane. Table 1 identifies the component makeup of various photoresist systems.

The following are the potential hazards of photoresist application.

Photoresist Chemicals

Potential Hazard

  • Possible employee exposure to photoresist chemicals (see Table 1).

Possible Solutions

  • Identify chemical hazards and perform appropriate exposure evaluations.
    • Perform exposure measurements for the chemicals used.
    • 29 CFR 1910.1000 Table Z-1 provides permissible exposure limits for various chemicals.
  • Address all dermal exposures.
  • Provide appropriate ventilation to reduce chemical concentration levels in the air.
  • Provide PPE as appropriate to prevent eye and skin contact. [29 CFR 1910 Subpart I]
  • Use respiratory protection when necessary to further reduce exposure and protect employees. [29 CFR 1910.134]
  • Design and use specialized processing, material handling, and storage equipment to properly contain chemicals. Consider both normal use and emergency scenarios.
  • Install emergency facilities to provide immediate treatment in the event of an accidental exposure to corrosive materials. According to 29 CFR 1910.151, provide suitable facilities for quick drenching or flushing of the eyes and body for immediate emergency use whenever the eyes or body may be exposed to corrosive materials.

Additional Information

  • 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:

Solvents

Potential Hazard

  • Possible employee exposure to solvents used for adhesive application.
    • Glycol ethers have been a popular solvent. However, due to reproductive effects associated with exposures, they have been replaced with other chemicals.
    • Replacement solvents for glycol ethers have included chemicals such as xylene, n-butyl acetate, acetone, and 1,1,1-trichloroethane.

Possible Solutions

Additional Information

  • 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.
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