Ion implantation

What is the purpose of pre-amorphization implantation (PAI)?

  1. ATo form a thick oxide on the wafer surface
  2. BTo make the surface amorphous by implanting Ge or similar species, suppressing channeling in subsequent implants and giving shallow junctions
  3. CTo remove metal contamination
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Answer: B. To make the surface amorphous by implanting Ge or similar species, suppressing channeling in subsequent implants and giving shallow junctions

Implanting germanium or silicon first makes the surface amorphous, eliminating the crystal arrangement, so channeling of subsequently implanted boron or other dopants is suppressed and shallow junctions can be formed. The amorphous layer recrystallizes during annealing.

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More Ion implantation questions

  1. What is used to suppress wafer charging (charge-up) during ion implantation?
  2. Singly charged ions are implanted into a wafer area of 100 cm² at a dose of 1×10¹⁵ ions/cm². With a beam current of 1 mA, approximately how long does the implant take? (Elementary charge 1.6×10⁻¹⁹ C)
  3. In CMOS well formation, what is a well called in which high-energy implantation makes the dopant concentration higher deep below the surface?
  4. 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?
  5. Why is BF2⁺ sometimes implanted instead of boron alone to form shallow p-type layers?