Ion implantation

What is the main purpose of halo (pocket) implants, which implant dopants of the same type as the channel at an angle near the source/drain edges?

  1. ATo lower the gate electrode resistance
  2. BTo suppress short-channel effects
  3. CTo make the transistor emit light
Show answer and explanation

Answer: B. To suppress short-channel effects

Halo implants locally place a high concentration of dopants of the channel's type near the source/drain edges. This limits the depletion region spreading from the drain, so short-channel effects such as threshold voltage roll-off and punch-through are suppressed even as gate length shrinks.

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More Ion implantation questions

  1. Why is BF2⁺ sometimes implanted instead of boron alone to form shallow p-type layers?
  2. What is the phenomenon called in which diffusion of boron and other dopants is temporarily accelerated early in annealing because of interstitial silicon created by implantation?
  3. Which type of ion implanter is used to implant large doses in a short time, as for source/drain formation?
  4. Under the same annealing conditions, how does the sheet resistance of the implanted layer generally change when the implant dose is increased?
  5. What must be considered when using photoresist as a mask for ion implantation?