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Epitaxy

Reactor Load and Unload

To begin, the degreased and polished wafers initially receive a pre-epitaxy etch and cleaning step. This involves a sequential wet chemical dipping operation using sulfuric acid, hydrogen peroxide, and water (5:1:1); a de-ionized water rinse; and finally, an isopropyl alcohol clean/dry.

The primary technique in use for VPE in LED processing is the III-halogen and V-hydrogen system. It involves a two-cycle process; first, growing the epitaxial layer of GaAsP on the GaAs substrate, next, an etch cycle to clean the quartz reactor chamber of impurities. During the epitaxial growth cycle, the pre-cleansed GaAs wafers are loaded into a vertical quartz reactor chamber containing an upper reservoir of elemental liquid gallium over which anhydrous HCl gas is metered, forming GaCl3. A V-hydrogen-hydride gas mixture of 10%-AsH3 and 5%-PH3/H3 carrier is also metered into the reaction chamber with the addition of 50 ppm dimethyl telluride and 25 ppm diethyl telluride gaseous dopants. The chemical species in the "hot zone" of the quartz reactor react, and in the "cold zone" form the desired layer of GaAsP on the wafer substrate as well as on the interior of the reactor chamber. Effluents from the reactor are routed to a hydrogen torch system for pyrolysis and vented to a wet scrubber system or other exhaust conditioning system.

The etch cycle is performed at the end of the grow cycle and on new quartz reactors to clean the interior surface of impurities. Undiluted hydrogen chloride gas is metered into the chamber for periods of 5-15 minutes. The effluents are vented to the wet scrubber system for neutralization. At the end of both the growth and etch cycles, an extended nitrogen purge is used to flush the reactor chamber of toxic and corrosive gases.

The following are potential hazards of reactor load and unload.
Chemicals

Potential Hazard

  • Possible employee exposure to chemicals used for pre-cleaning. Common chemicals include acids (H2SO4), caustics (H2O2), and isopropyl alcohol.

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.
Flammable Gases, Fire

Potential Hazard

  • Possible ignition of flammable gases, resulting in fire and/or explosion. Possible exposure to gases above permissible limits.

Possible Solutions

  • See Possible Solutions: Flammable Gases, Fire.
  • Provide PPE as appropriate to prevent contact with gases. [29 CFR 1910 Subpart I]
  • 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.

Additional Information

OSHA Safety and Health Topics Pages:

Toxic, Irritative, and Corrosive Gases

Potential Hazard

  • Possible employee exposure to toxic, irritative, and corrosive gases, including HCl, AsH3, and PH3.

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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