Oxidation and diffusion

Why does oxide on silicon appear in different colors depending on its thickness?

  1. ABecause of the color of impurities in the oxide
  2. BBecause of interference between light reflected from the top surface of the oxide and from its bottom (the interface with silicon)
  3. CBecause the oxide itself emits light
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Answer: B. Because of interference between light reflected from the top surface of the oxide and from its bottom (the interface with silicon)

SiO2 itself is transparent, but light reflected from the film's surface interferes with light reflected from the silicon interface, reinforcing particular colors depending on thickness. The color therefore indicates approximate thickness. Precise measurement uses ellipsometry or similar methods.

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More Oxidation and diffusion questions

  1. Which equipment is commonly used to thermally oxidize many wafers at once?
  2. In thermal diffusion, what is the step called that drives dopants deeper after a fixed amount has been introduced at the surface?
  3. How does the thermal oxidation rate of silicon depend on crystal orientation?
  4. What is the main purpose of introducing nitrogen into the gate oxide to make an oxynitride (SiON)?
  5. Why can thermal oxide be used as a mask against dopants during diffusion?