Oxidation and diffusion

What is the common definition of the "junction depth" of a PN junction?

  1. AThe depth from the surface to the point of peak impurity concentration
  2. BThe depth at which the concentration of the diffused impurity equals the original background doping of the substrate
  3. CHalf the wafer thickness
Show answer and explanation

Answer: B. The depth at which the concentration of the diffused impurity equals the original background doping of the substrate

The concentration of an impurity introduced from the surface decreases with depth and, at some depth, equals the concentration of the opposite-type impurity already in the substrate. That depth, where the conductivity type changes, is called the junction depth. Small transistors require shallow junctions.

  • A. The depth of peak concentration is not the junction depth.
  • B. Correct. It is where the introduced and background concentrations are equal.
  • C. It is unrelated to the wafer thickness.
Practice this topic Back to topic

More Oxidation and diffusion questions

  1. What is the phenomenon called in which boron and phosphorus diffuse faster during silicon oxidation than without oxidation?
  2. When thin oxides of a few tens of nanometers or less are grown by dry oxidation, which known deviation from the Deal-Grove model occurs?
  3. In LOCOS, what is the phenomenon called in which a thin nitride forms on the silicon surface under the nitride mask, later causing the gate oxide there to be locally thin or defective?
  4. Why does the compressive stress in thermally grown oxide become smaller when oxidation is done above about 950 °C?
  5. Why can SiO2 serve as a diffusion mask against boron and phosphorus but works poorly as a mask against gallium and aluminum?