Oxidation and diffusion

Why does the compressive stress in thermally grown oxide become smaller when oxidation is done above about 950 °C?

  1. ABecause at high temperature the oxide can flow viscously and relax the stress
  2. BBecause the silicon melts
  3. CBecause the oxide crystallizes
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Answer: A. Because at high temperature the oxide can flow viscously and relax the stress

When silicon turns into SiO2, its volume roughly doubles, putting the oxide under compressive stress. Above about 950 °C, amorphous SiO2 can flow slowly (viscous flow), relaxing the stress. At lower oxidation temperatures, stress tends to remain, with effects such as slower oxidation at corners.

  • A. Correct. Viscous flow relaxes the stress.
  • B. Silicon does not melt at this temperature.
  • C. Thermal oxide normally remains amorphous.
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More Oxidation and diffusion questions

  1. Why can SiO2 serve as a diffusion mask against boron and phosphorus but works poorly as a mask against gallium and aluminum?
  2. In regions where the impurity concentration far exceeds the intrinsic carrier density, the diffusion coefficient of arsenic and others varies with concentration. Which statement about this is correct?
  3. Which correctly describes the thermal oxidation of heavily doped polycrystalline silicon (polysilicon)?
  4. Which correctly compares dry oxidation (O2) and wet oxidation (H2O) in the thermal oxidation of silicon?
  5. When an SiO2 film of thickness x is formed by thermally oxidizing silicon, approximately how much silicon is consumed?