Etching

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)?

  1. AAbout 1 µm
  2. BAbout 10 µm
  3. CAlmost 0
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Answer: A. About 1 µm

In isotropic etching, material is removed at the same rate vertically and laterally, so by the time 1 µm has been removed and the underlayer reached, about 1 µm has also been removed sideways from the mask edge. This produces dimensional changes comparable to the film thickness, making it unsuitable for fine patterns.

  • A. Correct. About 1 µm is etched laterally, the same as vertically.
  • B. In isotropic etching, the lateral amount is about the same as the vertical, not ten times.
  • C. No lateral etching is the case for ideal anisotropic etching.
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More Etching questions

  1. Which metric expresses how far the sidewall of an etched hole or trench tilts from vertical?
  2. What is the general effect of adding a little oxygen to fluorine-based etching gas?
  3. In a typical etching plasma, how do the numbers of ions and radicals compare?
  4. Which method inserts a small electrode into a plasma and measures the current as the voltage is varied to determine the plasma's electron temperature and density?
  5. In dry etching, what is the profile defect called in which the bottom of a trench is etched deeper near the sidewalls than in the center, creating narrow grooves?