Silicon wafers

In the CZ method, what is the purpose of growing a thin neck just after the seed crystal at the start of pulling (necking)?

  1. ATo save seed crystal
  2. BTo raise the oxygen concentration
  3. CTo let dislocations introduced by thermal shock when the seed touches the melt escape, giving a dislocation-free crystal
Show answer and explanation

Answer: C. To let dislocations introduced by thermal shock when the seed touches the melt escape, giving a dislocation-free crystal

Dipping the seed into the hot melt introduces dislocations through thermal shock. Growing a narrow neck a few millimeters in diameter lets the dislocations escape to the crystal surface, after which a dislocation-free single crystal can be grown to full diameter. This is called the Dash method (Dash necking).

  • A. Saving seed crystal is not the purpose.
  • B. It is not a method for adjusting oxygen concentration.
  • C. Correct. Dislocations are removed to give a dislocation-free crystal.
Practice this topic Back to topic

More Silicon wafers questions

  1. What causes "slip", a problem when large-diameter wafers are heat-treated at high temperature?
  2. 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.)
  3. Which method has been used to make multicrystalline silicon ingots for solar cells cheaply and in large volumes?
  4. When finishing a CZ pull, why is the ingot diameter gradually reduced (a tail cone is formed) before separating it from the melt?
  5. Which is closest to the typical concentration of interstitial oxygen in silicon crystals grown by the CZ method?