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Metallization

Metal Etch

Technician loading wafer carrier into metal etch system

Reactive ion etching (RIE) is commonly used to etch metal layers. This process uses a combination of physical sputtering and chemically reactive species for etching at low pressures. RIE uses ion bombardment to achieve directional etching and a chemically reactive gas (carbon tetrafluoride, carbon tetrachloride, boron trichloride, and others) to maintain good etched layer selectivity. A wafer is placed into a chamber and given a negative electrical charge. The chamber is heated and brought to a low pressure, and then filled with a positively charged plasma of the reactive gas. The opposing electrical charges cause the rapidly moving plasma molecules to align themselves and strike the wafer surface vertically, thereby reacting with and volatizing the exposed metal layer. After etching, the remaining photoresist is stripped in a similar manner as during Device Fabrication.

The following are the potential hazards of metal etching.

Reactive Gases

Potential Hazard

  • Possible employee exposure to chlorinated and other reactive gases used for reactive ion etching.

Possible Solutions

  • Identify gas hazards and perform appropriate exposure evaluations.
    • Identify and evaluate all potential exposure scenarios, for example: startup, operations, maintenance, cleaning, emergencies, and so forth.

    • 29 CFR 1910.1000 Table Z-1 contains permissible exposure limits for various substances.
  • Provide appropriate ventilation to reduce gas concentration levels in the air.
  • Provide PPE as appropriate to prevent contact with gases. [29 CFR 1910 Subpart I]
  • Use respiratory protection when necessary to further reduce exposure and protect employees. [29 CFR 1910.134]
  • 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. Process Safety Management (PSM) requirements may also apply. [29 CFR 1910.119]

Additional Information

OSHA Safety and Health Topics Pages:

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