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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.

• Electricity
• Flammable, Explosive, and Pyrophoric Gases
• Toxic, Irritative, and Corrosive Gases
• Radiofrequency (RF) and Infrared (IR) Radiation
• Thermal Burns
• Reaction-Product Residues

Toxic, Irritative, and Corrosive Gases

Potential Hazard

• Possible employee exposure to toxic, irritative, and corrosive gases, including SiH₄ and NH₃.

Possible Solutions

• See Possible Solutions: Toxic, Irritative, and Corrosive Gases.

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

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

• See Possible Solutions: Acid and Caustic.

Additional Information

OSHA/NIOSH/DOE Health Guidelines

• Hydrogen Chloride
• Hydrogen Fluoride
• Hydrogen Peroxide

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 720ºC, utilizing a nitrogen carrier gas. (See Silicon Device Manufacturing - Device Fabrication - Doping (Junction Formation))

The following is a potential hazard of diffusion.

• Arsenic

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.

• X-ray Radiation
• Metals and Solvents

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

• See Possible Solutions: Solvents.
  
  
• Substitution of water for methanol as a cleaning solvent, when feasible.

Additional Information

• Toxic Metals. OSHA Safety and Health Topics Page.

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.

• Arsenic
• Nuisance Dust
• Machinery
• Chemicals
• Solvents

Chemicals

Potential Hazard

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

Possible Solutions

• See Possible Solutions: Chemicals.

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