Oxidation and diffusion

Learn the difference between dry and wet oxidation, how much silicon thermal oxidation consumes, and how diffusion coefficients depend on temperature through multiple-choice questions.

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Oxidation and diffusion: key points

Heating silicon in oxygen or water vapor forms a high-quality SiO2 film on its surface. This is called thermal oxidation, and it has been used for gate insulators, device isolation, masks and more.

Thermal diffusion introduces impurities into silicon at high temperature by atomic diffusion. Because diffusion depends strongly on temperature, careful control of temperature and time is important.

All Oxidation and diffusion questions (50)

  1. Which correctly compares dry oxidation (O2) and wet oxidation (H2O) in the thermal oxidation of silicon?
  2. When an SiO2 film of thickness x is formed by thermally oxidizing silicon, approximately how much silicon is consumed?
  3. How does the diffusion coefficient of dopants in silicon depend on temperature?
  4. Which method is mainly used for device isolation in scaled LSIs?
  5. Once the oxide has become sufficiently thick in thermal oxidation, how does its thickness relate to oxidation time?
  6. Why does oxide on silicon appear in different colors depending on its thickness?
  7. Which equipment is commonly used to thermally oxidize many wafers at once?
  8. In thermal diffusion, what is the step called that drives dopants deeper after a fixed amount has been introduced at the surface?
  9. How does the thermal oxidation rate of silicon depend on crystal orientation?
  10. What is the main purpose of introducing nitrogen into the gate oxide to make an oxynitride (SiON)?
  11. Why can thermal oxide be used as a mask against dopants during diffusion?
  12. What is the heat treatment called, performed in a hydrogen-containing atmosphere to reduce interface states at the Si/SiO2 interface?
  13. What is the main purpose of adding a small amount of chlorine-containing gas such as hydrogen chloride (HCl) during thermal oxidation?
  14. When boron-doped silicon is thermally oxidized, how does the boron concentration on the silicon side near the interface tend to change?
  15. What is the heat treatment called that heats wafers one at a time to high temperature for a few seconds using lamps or similar sources?
  16. Which value is closest to the relative permittivity of SiO2 formed by thermal oxidation?
  17. Which is one of the major reasons silicon has been so widely used as a material for MOS devices?
  18. What problem occurs when mobile ions such as sodium are present in the gate oxide?
  19. Which n-type dopant diffuses relatively slowly in silicon during heat treatment, making shallow junctions easier to form?
  20. Which correctly describes pyrogenic oxidation (hydrogen combustion oxidation)?
  21. What is the approximate breakdown field of high-quality thermal oxide (SiO2)?
  22. Which method reacts hydrogen and oxygen near the wafer surface to form a high-quality thin oxide in a short time?
  23. What is the treatment called that introduces plasma-generated nitrogen into the surface of a thin gate oxide?
  24. When etched in the same dilute hydrofluoric acid, how do the etch rates of thermal oxide and CVD oxide generally compare?
  25. Which defect grows when excess interstitial silicon generated by oxidation is injected into the silicon during thermal oxidation?
  26. If the thermal oxidation temperature is raised, how does the oxide thickness obtained in the same time change?
  27. In LOCOS (local oxidation), what is the phenomenon called in which oxide encroaches like a bird's beak under the edge of the nitride mask?
  28. What is an advantage of performing thermal oxidation in a high-pressure oxidizing atmosphere?
  29. Which is a characteristic of radical oxidation, which uses oxygen radicals?
  30. According to the Deal-Grove model, where does thermal oxidation take place?
  31. Which chemical reaction occurs in the dry thermal oxidation of silicon?
  32. Which is closest to the temperature range at which silicon thermal oxidation is generally carried out?
  33. Which correctly describes "diffusion" of impurities in semiconductor manufacturing?
  34. Which is a typical use of thermally grown silicon oxide?
  35. What is the correct unit of the diffusion coefficient D?
  36. Which correctly expresses Fick's first law? (J: diffusion flux, D: diffusion coefficient, C: concentration, x: position)
  37. When diffusing impurities at the same temperature, if the diffusion time is quadrupled, by roughly what factor does the spreading distance change?
  38. 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?
  39. Which compound has been used as a liquid diffusion source for introducing phosphorus into silicon by thermal diffusion?
  40. Which set represents the commonly used classification of charges in and at the interface of the oxide in a MOS structure?
  41. In the Deal-Grove model, what is the relationship between oxide thickness and time early in thermal oxidation, while the oxide is still thin?
  42. Which generally describes the thickness relationship between the field oxide used for isolation such as LOCOS and the gate oxide of a MOSFET?
  43. What is the common definition of the "junction depth" of a PN junction?
  44. What is the phenomenon called in which boron and phosphorus diffuse faster during silicon oxidation than without oxidation?
  45. 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?
  46. 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?
  47. Why does the compressive stress in thermally grown oxide become smaller when oxidation is done above about 950 °C?
  48. Why can SiO2 serve as a diffusion mask against boron and phosphorus but works poorly as a mask against gallium and aluminum?
  49. 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?
  50. Which correctly describes the thermal oxidation of heavily doped polycrystalline silicon (polysilicon)?

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