Etching

In plasma tools such as capacitively coupled ones, what is the phenomenon called in which the wafer-side electrode naturally acquires a negative DC potential that accelerates ions toward the wafer?

  1. AThe Hall effect
  2. BThe Seebeck effect
  3. CSelf-bias
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Answer: C. Self-bias

On an electrode driven with RF power, the light, mobile electrons flow onto it more readily than ions, so the electrode acquires a negative average DC potential (self-bias). This potential difference accelerates positive ions from the plasma toward the wafer on the electrode, enabling anisotropic etching.

  • A. The Hall effect is a voltage perpendicular to current in a magnetic field.
  • B. The Seebeck effect is a voltage produced by a temperature difference.
  • C. Correct. A negative potential arises from the difference in electron flow.
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More Etching questions

  1. What is the masking scheme called that stacks three layers, an organic (carbon) film at the bottom, a silicon-containing middle layer and resist on top, to etch fine patterns deeply?
  2. Which gas can etch silicon isotropically without a plasma, for example to remove sacrificial layers in MEMS?
  3. Which technique gradually thins an exposed resist pattern with plasma to create lines narrower than the exposure limit?
  4. In gate electrode etching, what is commonly done to preserve the thin gate insulator underneath?
  5. 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)?