Various mixtures of wet chemical acid solutions are used in plastic baths in locally exhausted etch stations, some provided with laminar HEPA filtered supply systems which are vertically mounted. The primary acids in use are H2SO4, HF, HCl and H3PO4. As in silicon processing, H2O2 is used with H2SO4 and NH4OH to provide a caustic etch. A cyanide solution (sodium or potassium) is also used for etching aluminum. (See Silicon Device Manufacturing - Device Fabrication - Etching)
The following are potential hazards of wet etching.
Acids and Caustics
- Possible employee exposure to acids and caustics used for wet chemical etching. Typical acids may include mixtures of HF, HCl, H2SO4, H3PO4, etc., while common caustics include H2O2 and NH4OH. Cyanide solutions of NaCN and PCN are also used.
- 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.