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Nitride Deposition | Photolithography | Wet Etching | Plasma Etching and Ashing | Diffusion | Metallization | Alloying | Backlapping | Final Test

Nitride Deposition

A high-temperature chemical vapor deposition (CVD) of silicon nitride (Si3N4) is performed, using a standard diffusion furnace. The gaseous sources are silane (SiH4) and ammonia (NH3) with a nitrogen carrier gas. (See Silicon Device Manufacturing - Device Fabrication - Deposition)

The following are potential hazards of nitride deposition. Toxic, Irritative, and Corrosive Gases

Potential Hazard
  • Possible employee exposure to toxic, irritative, and corrosive gases, including SiH4 and NH3.
Possible Solutions
Photolithography

The standard photoresist, aligning, exposure, developing and stripping process is used as in silicon device processing.
(See Silicon Device Manufacturing - Device Fabrication)


Wet Etching

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

Potential Hazard
  • 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.
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.

Plasma Etching and Ashing

As an alternative to wet etching, plasma etching and ashing are used. The reactor configurations and reactant gases are similar to those used in silicon device processing.
(See Silicon Device Manufacturing - Device Fabrication - Etching and Photoresist Stripping)


Diffusion

A closed ampoule zinc diarsenide solid source diffusion is performed in a vacuum diffusion furnace at 720C, utilizing a nitrogen carrier gas. (See Silicon Device Manufacturing - Device Fabrication - Doping (Junction Formation))

The following is a potential hazard of diffusion.
Metallization

An initial aluminum evaporation is performed utilizing an e-beam evaporator. After backlapping (see below), gold evaporation is performed using a filament evaporator. (See Silicon Device Manufacturing - Metallization)


The following are potential hazards of metallization. Metals and Solvents

Potential Hazard
  • Possible employee exposure to metals and solvents during evaporator cleaning, bell jar cleaning, and maintenance operations. Typical metal exposures include gold and silver. Methanol is a popular cleaning solvent.
Possible Solutions Additional Information
Alloying

A final alloying step is performed in a low-temperature diffusion furnace, utilizing a nitrogen inert atmosphere.
(See Silicon Device Manufacturing - Metallization - Alloying and Annealing)


Backlapping

Backlapping is done to remove deposited materials (GaAsP, Si3N4, etc.) from the backside of the wafer. The wafers are wax-mounted to a lapper plate and wet-lapped with a colloidal silica slurry. Then the wax is removed by wet-stripping the wafers in an organic stripper containing phenol, sulfonic acid, and chlorobenzenes in a locally exhausted wet chemical etch station. The wafers then receive a final cleaning. (See Silicon Device Manufacturing - Metallization - Backlapping and Backside Metallization)

The following are potential hazards of backlapping. Chemicals

Potential Hazard
  • Possible employee exposure to chemicals used for wet chemical etching. Common chemicals include phenol, sulfonic acid, and chlorobenzenes.
Possible Solutions
Final Test

As in silicon device processing, the completed LED circuits are computer-tested and marked.
(See Silicon Device Manufacturing - Non-Fabrication Processing)


Nitride Deposition | Photolithography | Wet Etching | Plasma Etching and Ashing | Diffusion | Metallization | Alloying | Backlapping | Final Test