Ion implantation

Which is closest to the range of ion implantation doses used in LSI manufacturing?

  1. AAbout 10³⁰ cm⁻² or more
  2. BAbout 10¹¹ to 10¹⁶ cm⁻²
  3. CAbout 10¹ to 10³ cm⁻²
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Answer: B. About 10¹¹ to 10¹⁶ cm⁻²

Threshold-voltage adjustment uses doses of about 10¹¹ to 10¹³ cm⁻², while lowering the resistance of sources, drains and gates uses large doses around 10¹⁵ cm⁻², so overall the range spans roughly 10¹¹ to 10¹⁶ cm⁻². Being able to control this wide range accurately is a strength of ion implantation.

  • A. 10³⁰ cm⁻² vastly exceeds the number of surface atoms on silicon (about 10¹⁵ cm⁻²) and is impossible.
  • B. Correct. About 10¹¹ to 10¹⁶ cm⁻² is used depending on the application.
  • C. 10¹ to 10³ cm⁻² is far too little to change electrical characteristics.
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More Ion implantation questions

  1. What is the main reason the beam path in an ion implanter is kept at high vacuum?
  2. In a typical ion implanter, in what order do ions pass through the system?
  3. When implanted into silicon at the same energy, how do the ranges of arsenic (mass 75) and phosphorus (mass 31) compare?
  4. In an ion implanter, what is the energy of a doubly charged ion (twice the charge) accelerated through 50 kV?
  5. Which type of ion implanter is mainly used for medium-dose implants such as MOSFET threshold-voltage adjustment and wells?