Oxidation and diffusion

Which generally describes the thickness relationship between the field oxide used for isolation such as LOCOS and the gate oxide of a MOSFET?

  1. AThe gate oxide is much thicker
  2. BBoth have the same thickness
  3. CThe field oxide is much thicker
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Answer: C. The field oxide is much thicker

Field oxide is made thick, around hundreds of nanometers, so that parasitic transistors under wiring and similar do not turn on. Gate oxide, by contrast, is made very thin, a few nanometers, so the gate field couples strongly to the channel.

  • A. Gate oxide is made thin to transmit the field strongly.
  • B. Their roles differ, so their thicknesses differ greatly.
  • C. Correct. Isolation oxide is made much thicker.
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More Oxidation and diffusion questions

  1. What is the common definition of the "junction depth" of a PN junction?
  2. What is the phenomenon called in which boron and phosphorus diffuse faster during silicon oxidation than without oxidation?
  3. 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?
  4. 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?
  5. Why does the compressive stress in thermally grown oxide become smaller when oxidation is done above about 950 °C?