Etching

Which gas can etch silicon isotropically without a plasma, for example to remove sacrificial layers in MEMS?

  1. AO2 (oxygen)
  2. BN2 (nitrogen)
  3. CXeF2 (xenon difluoride)
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Answer: C. XeF2 (xenon difluoride)

XeF2 reacts spontaneously with silicon near room temperature to form SiF4 and similar products, etching silicon isotropically without plasma. It is highly selective against oxide, nitride and many metals, and because no liquid is involved, stiction is unlikely, so it is used to release MEMS structures and the like.

  • A. Oxygen is used to remove organic materials such as resist.
  • B. Nitrogen does not etch silicon.
  • C. Correct. It is a gas that etches silicon without plasma.
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More Etching questions

  1. Which technique gradually thins an exposed resist pattern with plasma to create lines narrower than the exposure limit?
  2. In gate electrode etching, what is commonly done to preserve the thin gate insulator underneath?
  3. When a 1 µm film is etched just down to the underlayer by perfectly isotropic wet etching, roughly how much is etched laterally from the mask edge (undercut)?
  4. Which metric expresses how far the sidewall of an etched hole or trench tilts from vertical?
  5. What is the general effect of adding a little oxygen to fluorine-based etching gas?