Ion implantation

What method has commonly been used to introduce impurities into a MOSFET's polysilicon gate electrode to lower its resistance?

  1. AShining light on the gate
  2. BIon implantation (often done together with the source/drain implant)
  3. CSoaking the gate in water for a long time
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Answer: B. Ion implantation (often done together with the source/drain implant)

Polysilicon gates are made conductive by heavy doping. n-type dopants are implanted into nMOS gates and p-type into pMOS gates, often together with the source/drain implant. The dopants are then activated by annealing.

  • A. Shining light does not introduce impurities.
  • B. Correct. Impurities are introduced by ion implantation.
  • C. Soaking in water does not introduce impurities.
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More Ion implantation questions

  1. What is the technique of implanting n-type impurities into an already p-type region to lower the net doping or invert the conductivity type called?
  2. In low-energy implants using decel mode (transporting at high energy and decelerating just before the wafer), what causes the "energy contamination" that requires care?
  3. When implanting near the edge of a mask, why do dopants spread laterally under the mask?
  4. Which pair correctly names the two mechanisms by which implanted ions lose energy in a material?
  5. When implanting aluminum or similar into SiC, why is the wafer often heated to several hundred degrees Celsius during implantation (hot implantation)?