Process materials (gases and chemicals)

Which units are commonly used to express impurity concentrations in high-purity semiconductor gases and chemicals?

  1. Appb (parts per billion) and ppt (parts per trillion)
  2. BOnly % (parts per hundred)
  3. Ckg
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Answer: A. ppb (parts per billion) and ppt (parts per trillion)

Semiconductor materials must keep metal impurities and the like at extremely low levels, so they are controlled in units such as ppb (10⁻⁹) and ppt (10⁻¹²). Purity managed only in percent would seriously affect device characteristics.

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