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Device Fabrication

Mask Alignment and Photoexposure

Stepper deep ultraviolet (DUV) tool

A photomask is aligned and placed on the coated wafer with precision instruments. The wafer and mask are then exposed to ultraviolet (UV) radiation from an intense mercury arc lamp. This causes exposure to the photo resist in places not protected by opaque regions of the mask. With a typical positive photoresist, the areas struck by light undergo a chemical reaction that will make the photoresist more soluble in an alkaline solution. UV exposure is the most common; however, x-ray and electron beam sources also may be used.

Technician examining a reticle

The following are the potential hazards of mask alignment and photo exposure.

Ultraviolet (UV) Radiation

Potential Hazard

  • Possible employee exposure to ultraviolet (UV) radiation during photoexposure.

Possible Solutions

  • Identify UV hazards; perform exposure evaluations when applicable.
  • Enclose operations with UV emissions; provide shielding and interlocks as necessary.
  • Provide PPE as appropriate during operations when exposure is necessary. [1910 Subpart I]
  • Implement UV radiation safety programs to further identify and control UV hazards. Ozone gas may also be generated from the UV radiation.
  • Provide adequate ventilation to control ozone concentrations.

Additional Information

OSHA Safety and Health Topics Pages:

Mercury

Potential Hazard

  • Possible employee exposure to mercury from lamp rupture. Improper maintenance or infrequent bulb replacement can cause deteriorated or older lamps to rupture.

Possible Solutions

  • Implement preventive maintenance to inspect and replace lamps routinely.
  • Implement proper work practices to ensure that lamps are replaced carefully in order to avoid accidental breakage.
  • Store and dispose of lamps properly.
  • Respond to and clean up mercury spills properly.
  • Provide adequate PPE as necessary to minimize exposure.

Additional Information

OSHA Safety and Health Topics Pages:

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