Etching

What is the general effect of adding a little oxygen to fluorine-based etching gas?

  1. AEtching stops completely
  2. BSelectivity to the mask always increases
  3. CPolymer deposition on sidewalls and elsewhere decreases, and the resist erodes faster
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Answer: C. Polymer deposition on sidewalls and elsewhere decreases, and the resist erodes faster

Oxygen burns away carbon-containing polymer, reducing deposition on sidewalls and surfaces, and it also increases fluorine radicals so etching proceeds more readily. However, the resist is also eroded more easily by oxygen, so selectivity to the mask tends to drop. The amount added balances profile against selectivity.

  • A. A small amount of oxygen does not stop etching.
  • B. Because resist erodes more easily, selectivity actually tends to drop.
  • C. Correct. Polymer decreases and the resist erodes faster.
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More Etching questions

  1. In a typical etching plasma, how do the numbers of ions and radicals compare?
  2. 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?
  3. 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?
  4. Exposing silicon to XeF2 gas and an argon ion beam simultaneously etches it far faster than the sum of either alone. What property of dry etching does this show?
  5. In plasma etching of high-aspect-ratio patterns, which phenomenon has electrons blocked by sidewalls so negative charge builds at the top of the pattern while positive ions are deflected at the bottom, causing profile defects and damage?