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Safety and Health Topics > Semiconductors > Silicon > Substrate Manufacture: Wafer Preparation

Substrate Manufacture: Wafer Preparation
Wafer saw To prepare the wafers, ingots are sliced into individual wafers with multiple-blade inner-diameter saws. This operation is done with wet lubricants, and in some processes the wafers are stored in plastic reservoirs containing water or methanol. The sliced wafers are mechanically lapped under pressure using a counter-rotating machine to achieve flatness and parallelism on both sides of the wafer. Most lapping operations use slurries of either aluminum oxide or silicon carbide. The edges of the individual wafers are also rounded by the use of wet automatic grinders.

After lapping, wafers are etched with a solution containing nitric, acetic, and hydrofluoric acids. Etching may be done in manual etch tanks or by automated etching machines. This etching process removes external surface damage and reduces the thickness of the wafer.

Technician adjusting wafer polisher Next, the wafers are polished using an aqueous mixture of colloidal silica and sodium hydroxide. The wafers are mounted onto a metal carrier plate that is attached by vacuum to the polishing machine. The polishing process usually involves two or three polishing steps with progressively finer slurry, which decreases wafer thickness and results in a mirror-like finish. Sometimes carrier pads must be stripped from the metal carrier plates. The pads are usually stripped with solvents such as methylene chloride, methyl ethyl ketone, or a glycol ether mixture.

Wafers Finally, the wafers are cleaned to remove any particles or residue remaining on the exterior surface of the polished wafer. Various cleaning steps and solutions containing ammonia, hydrogen peroxide, hydrofluoric acid, hydrochloric acid, and deionized water may be used.

The finished wafers are inspected and packaged for shipping. It should be noted that most semiconductor manufacturers purchase wafers from firms that specialize in wafer production.

Potential Hazards
Methanol
Potential Hazard
  • Possible employee exposure to methanol during wafer washing and storage.
Possible Solutions
  • Identify methanol hazards and perform appropriate exposure evaluations.

    • Perform exposure measurements.

    • Keep exposures below acceptable exposure levels.

    • Address all dermal exposures.
  • Provide appropriate ventilation to reduce solvent concentration levels in the air.

  • Provide PPE [1910 Subpart I] as appropriate to prevent eye and skin contact.

  • Use respiratory protection [1910.134] when necessary to further reduce exposure and protect employees.
Additional Information

OSHA Safety and Health Topic pages:


Acids
Potential Hazard
  • Possible employee exposure to acids used during etching. Typical acids may include HF, CH3COOH, and HNO3.
Possible Solutions Additional Information


Solvents
Potential Hazard
  • Possible employee exposure to solvents used for stripping carrier pads. Typical solvents may include methylene chloride, MEK, and glycol ethers.
Possible Solutions Additional Information


Chemicals
Potential Hazard
  • Possible employee exposure to additional chemicals used for final cleaning. Typical chemicals may include NH3, H2O2, HF, and HCl.
Possible Solutions Additional Information

OSHA Health Guidelines pages:


 
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