Silicon nitride is often used as a final passivating or protective layer for silicon devices. Passivation is accomplished with a chemical vapor deposition process using silane and ammonia gases. Sometimes a layer known as "p-glass" is deposited with a layer of SiO2 doped with phosphorous. Phosphine gas is used as a source for phosphorous for this type of deposition.
The following are the potential hazards of passivation.
- Possible employee exposure to toxic gases. Typical gases include silane, ammonia, and phosphine.
- Identify gas hazards and perform appropriate exposure evaluations.
- Perform exposure measurements for the chemicals used.
- 29 CFR 1910.1000 Table Z-1 contains permissible exposure limits for various chemicals.
- Provide appropriate ventilation to reduce 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]
- Use gas monitoring systems with automatic shut-offs and alarm systems, as appropriate.
- Design and use specialized processing, material handling, and storage equipment for gases. Consider both normal use and emergency scenarios.
- Reduce gas cylinder inventories and quantity of gas per cylinder, when possible.
- 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:
- Compressed Gas and Equipment
- Personal Protective Equipment (PPE)
- Process Safety Management (PSM)
- Respiratory Protection
- Sampling and Analysis