Silicon wafers

Check the basics of silicon wafers — making single crystals by the CZ and FZ methods, and wafer diameters — with multiple-choice questions.

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Silicon wafers: key points

Most semiconductor devices are made on wafers sliced from high-purity single-crystal silicon. Single crystals are grown either by the CZ method, which pulls a crystal from silicon melted in a crucible, or by the FZ method, which uses no crucible.

The grown crystal becomes wafers through slicing, polishing and cleaning. Wafer diameters have kept increasing, and 300 mm wafers are now standard in leading-edge production lines.

All Silicon wafers questions (50)

  1. Which method is most widely used to produce single-crystal silicon for LSIs?
  2. Which wafer diameter is currently mainstream in leading-edge logic and memory production lines?
  3. Which is a characteristic of single-crystal silicon made by the FZ (floating zone) method?
  4. What is the main role of the notch (small cutout) on the edge of a silicon wafer?
  5. Which correctly describes gettering?
  6. Which impurity is incorporated in relatively large amounts from the crucible into silicon crystals grown by the CZ method?
  7. What is the most appropriate order of steps for making wafers from a single-crystal ingot?
  8. Which correctly describes a typical method of manufacturing SOI wafers?
  9. Which crystal orientation is commonly used for silicon wafers for CMOS LSIs?
  10. Which correctly describes the relationship between the resistivity of a silicon wafer and its doping concentration?
  11. Which is closest to the standard thickness of a 300 mm silicon wafer?
  12. In the CZ method, what is the main purpose of controlling the ratio of pull rate to temperature gradient in the crystal (V/G)?
  13. Which is the typical method for producing high-purity polycrystalline silicon?
  14. What is a wafer called that is run through a process separately from products to check equipment condition or measure film thickness?
  15. What is the main reason silicon wafers must be very flat?
  16. Which equipment is commonly used to slice a silicon ingot into many wafers at once?
  17. What is the main purpose of chamfering (beveling) the edge of a wafer?
  18. Which impurity is typically added to the melt to make p-type silicon crystals by the CZ method?
  19. When a doped crystal is pulled by the CZ method, the dopant concentration tends to be higher toward the bottom of the crystal (later in the pull). Why?
  20. Which correctly describes 450 mm wafers, developed as the next diameter after 300 mm?
  21. What is the purpose of using bulk microdefects (BMDs), formed by oxygen precipitation inside CZ wafers?
  22. Heat treatment of a wafer diffuses oxygen out from near the surface, creating a low-defect layer at the surface where devices are made. What is this layer called?
  23. What is the purpose of the laser mark (ID mark) inscribed on the front or back of a wafer?
  24. Which polishing method is common for 300 mm wafers?
  25. What is a used monitor wafer called after its surface films are removed and it is repolished for reuse?
  26. Which method is used to measure wafer resistivity without contact?
  27. Which method irradiates FZ silicon with neutrons to convert some silicon into phosphorus, making it uniformly n-type?
  28. Which method applies a magnetic field to the crucible in the CZ method to suppress melt convection and control oxygen concentration and other properties?
  29. Which conditions are mainly adjusted during pulling to keep the diameter of a silicon single-crystal ingot constant?
  30. Which is one reason SiC wafers are difficult and expensive to manufacture?
  31. Roughly what size in inches is a silicon wafer 300 mm in diameter commonly called?
  32. What is the cylindrical block of single-crystal silicon grown by the CZ method or similar, before it is cut into wafers, called?
  33. What is the main reason silicon wafers are round?
  34. Which pair of Japanese companies holds a large share of the global silicon wafer market?
  35. In the CZ method, what is the purpose of growing a thin neck just after the seed crystal at the start of pulling (necking)?
  36. What causes "slip", a problem when large-diameter wafers are heat-treated at high temperature?
  37. Which is closest to the mass of one silicon wafer 300 mm in diameter and 775 µm thick? (Silicon density is about 2.33 g/cm³.)
  38. Which method has been used to make multicrystalline silicon ingots for solar cells cheaply and in large volumes?
  39. When finishing a CZ pull, why is the ingot diameter gradually reduced (a tail cone is formed) before separating it from the melt?
  40. Which is closest to the typical concentration of interstitial oxygen in silicon crystals grown by the CZ method?
  41. In the mirror polishing (final CMP polishing) of silicon wafers, what is commonly used as the abrasive in the slurry?
  42. What is the main use of low-resistivity n⁺ silicon wafers heavily doped with arsenic or antimony?
  43. When CZ silicon is heat-treated around 450 °C, oxygen atoms can cluster and act as donors, changing the wafer's resistivity. What is this called?
  44. To analyze metal contamination on a wafer surface with high sensitivity, which preparation method dissolves the surface oxide with hydrofluoric acid vapor and collects it in a droplet for analysis?
  45. What are the very gentle undulations on a wafer surface, with lateral wavelengths of a few millimeters and heights of tens of nanometers, called?
  46. Compared with FZ silicon, how does the interstitial oxygen in CZ silicon affect the wafer's mechanical strength?
  47. Which is a known effect of adding a trace of nitrogen during CZ crystal growth (nitrogen doping)?
  48. Which method selectively and shallowly etches defect regions so that dislocations and stacking faults in silicon can be observed with an optical microscope?
  49. In CZ crystals, what are the periodic, striped variations in dopant or oxygen concentration caused by fluctuations such as temperature at the growth interface called?
  50. Along which crystal planes does single-crystal silicon cleave most easily?

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