Ion implantation

What is the main reason the beam path in an ion implanter is kept at high vacuum?

  1. ATo make the equipment lighter
  2. BTo cool the wafer
  3. CTo prevent ions from colliding with gas molecules and being scattered or neutralized
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Answer: C. To prevent ions from colliding with gas molecules and being scattered or neutralized

If gas remains in the beam path, ions collide with gas molecules and change direction or lose their charge and become neutral. They would then not be implanted at the intended location, energy or dose, so the beamline is kept at high vacuum.

  • A. It has nothing to do with equipment weight.
  • B. The vacuum is not for cooling the wafer.
  • C. Correct. It prevents scattering and neutralization of ions.
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More Ion implantation questions

  1. In a typical ion implanter, in what order do ions pass through the system?
  2. When implanted into silicon at the same energy, how do the ranges of arsenic (mass 75) and phosphorus (mass 31) compare?
  3. In an ion implanter, what is the energy of a doubly charged ion (twice the charge) accelerated through 50 kV?
  4. Which type of ion implanter is mainly used for medium-dose implants such as MOSFET threshold-voltage adjustment and wells?
  5. What is the pair of a vacancy and an interstitial atom called, created in the crystal when an implanted ion knocks a silicon atom out of place?