Ion implantation

In a typical ion implanter, in what order do ions pass through the system?

  1. AIon source → mass analysis → accelerator → scanning → wafer
  2. BAccelerator → ion source → mass analysis → wafer
  3. CMass analysis → ion source → wafer → accelerator
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Answer: A. Ion source → mass analysis → accelerator → scanning → wafer

The ion source turns gas into plasma and extracts ions, the analyzer magnet selects only the desired ions, and the accelerator brings them to the required energy. The beam is then scanned to implant uniformly over the whole wafer (some tools differ in the order of acceleration and analysis).

  • A. Correct. It starts at the source, then selection, acceleration and scanning before reaching the wafer.
  • B. Ions cannot be accelerated before they are created.
  • C. Mass analysis cannot come before the ion source.
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More Ion implantation questions

  1. When implanted into silicon at the same energy, how do the ranges of arsenic (mass 75) and phosphorus (mass 31) compare?
  2. In an ion implanter, what is the energy of a doubly charged ion (twice the charge) accelerated through 50 kV?
  3. Which type of ion implanter is mainly used for medium-dose implants such as MOSFET threshold-voltage adjustment and wells?
  4. 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?
  5. Why is the wafer cooled during high-current ion implantation?