Etching

In gate electrode etching, what is commonly done to preserve the thin gate insulator underneath?

  1. AEtching with the same aggressive conditions from start to finish
  2. BEtching most of the way with fast conditions, then switching to conditions with high selectivity to the underlayer as it is approached
  3. CContinuing with aggressive conditions for a while after the underlayer appears
Show answer and explanation

Answer: B. Etching most of the way with fast conditions, then switching to conditions with high selectivity to the underlayer as it is approached

Gate etching first removes most material with fast conditions that define the profile (main etch); once the endpoint is detected, it switches to high-selectivity conditions that hardly attack the thin insulator below (over-etch) to clear the rest. This allows processing without punching through an insulator only a few nanometers thick.

  • A. Aggressive conditions throughout would also etch the thin underlayer.
  • B. Correct. Conditions are switched in stages to preserve the underlayer.
  • C. Continuing aggressive etching would punch through the underlayer.
Practice this topic Back to topic

More Etching questions

  1. 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)?
  2. Which metric expresses how far the sidewall of an etched hole or trench tilts from vertical?
  3. What is the general effect of adding a little oxygen to fluorine-based etching gas?
  4. In a typical etching plasma, how do the numbers of ions and radicals compare?
  5. 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?