Oxidation and diffusion

Which correctly describes "diffusion" of impurities in semiconductor manufacturing?

  1. AA method that accelerates impurities in one direction with an electric field and implants them
  2. BDissolving impurities in a liquid and washing them away
  3. CThe thermally driven spreading of impurity atoms from regions of high concentration to regions of low concentration
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Answer: C. The thermally driven spreading of impurity atoms from regions of high concentration to regions of low concentration

Diffusion is the spreading of impurities from high-concentration regions to low-concentration regions by the thermal motion of atoms; it proceeds faster at higher temperatures. It was once used to introduce impurities from the surface, but today diffusion mostly occurs during the heat treatment after impurities are introduced by ion implantation.

  • A. Accelerating and implanting with an electric field is ion implantation.
  • B. Washing away is cleaning, not diffusion.
  • C. Correct. Impurities spread thermally from high to low concentration.
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More Oxidation and diffusion questions

  1. Which is a typical use of thermally grown silicon oxide?
  2. What is the correct unit of the diffusion coefficient D?
  3. Which correctly expresses Fick's first law? (J: diffusion flux, D: diffusion coefficient, C: concentration, x: position)
  4. When diffusing impurities at the same temperature, if the diffusion time is quadrupled, by roughly what factor does the spreading distance change?
  5. In thermal diffusion, which pair correctly gives the profile shapes for diffusion with a constant surface concentration and for diffusion of a fixed amount of impurity?