Etching

In a typical etching plasma, how do the numbers of ions and radicals compare?

  1. AThey are always equal
  2. BRadicals far outnumber ions
  3. CIons far outnumber radicals
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Answer: B. Radicals far outnumber ions

In a plasma, molecules dissociate into radicals more readily than they ionize, and radicals, having no charge, also live longer. Radical densities are therefore typically orders of magnitude higher than ion densities. Radicals drive the chemical reactions, while ion bombardment gives them direction.

  • A. They differ in how easily they form and how long they live, so their numbers differ.
  • B. Correct. Radicals typically outnumber ions by orders of magnitude.
  • C. Under typical conditions, ions are fewer.
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More Etching questions

  1. 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?
  2. 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?
  3. 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?
  4. 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?
  5. Which research-stage etching method neutralizes plasma-generated ions before they hit the wafer, suppressing charging and UV damage?