Etching

In plasma etch tools, what is the main role of the focus ring surrounding the wafer edge?

  1. ATo etch the back of the wafer
  2. BTo shape the plasma and sheath near the wafer edge so that edge areas are etched with profiles and rates similar to the center
  3. CTo cool the wafer
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Answer: B. To shape the plasma and sheath near the wafer edge so that edge areas are etched with profiles and rates similar to the center

Near the wafer edge, the sheath (the layer that accelerates ions) bends because of the electrode edge, so ions arrive at an angle and profiles tilt or rates change. A focus ring around the wafer shapes these conditions so even edge chips are processed uniformly. The ring is gradually eroded by the plasma and replaced periodically.

  • A. It is not a part for etching the wafer back.
  • B. Correct. It makes edge processing match the center.
  • C. Wafer cooling is done with the electrostatic chuck and backside gas.
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More Etching questions

  1. Which correctly describes anisotropic etching?
  2. Which correctly describes 'selectivity' in etching?
  3. Which is a general characteristic of wet etching?
  4. Which correctly describes reactive ion etching (RIE)?
  5. Which method is commonly used to detect the endpoint of dry etching?