Ion implantation

Why is the wafer cooled during high-current ion implantation?

  1. ATo make the implant deeper
  2. BTo prevent the beam energy from heating the wafer, which can degrade the resist mask and change implant conditions
  3. CTo change the mass of the ions
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Answer: B. To prevent the beam energy from heating the wafer, which can degrade the resist mask and change implant conditions

In high-current implants, beam energy flows into the wafer and raises its temperature. If the resist deforms or degrades, mask dimensions change and the resist becomes hard to remove. Temperature also changes how much the crystal damage recovers (how easily it amorphizes), so the wafer is cooled to control temperature.

  • A. Cooling does not make the implant deeper.
  • B. Correct. It prevents resist degradation and similar effects from heating.
  • C. Cooling does not change the ions' mass.
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More Ion implantation questions

  1. What is the typical distribution of crystal damage created by ion implantation?
  2. What method has commonly been used to introduce impurities into a MOSFET's polysilicon gate electrode to lower its resistance?
  3. 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?
  4. 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?
  5. When implanting near the edge of a mask, why do dopants spread laterally under the mask?