In ion implantation dopant ions are directly bombarded into the semiconductor (silicon for example)? But if say P ions (P+) were implanted then it does not have an extra electron to donate into the silicon. How does the process work then?

  • $\begingroup$ Yes, the ions carry charge. However, the substrate is grounded so that current flow to keep the substrate neutral. Otherwise a potential would rapidly build up, changing the implant profile and/or arcing. $\endgroup$ – Jon Custer Aug 19 '15 at 14:42
  • $\begingroup$ @JonCuster: that should be an answer. $\endgroup$ – John Rennie Aug 19 '15 at 16:02

Yes, the ions carry charge. However, the substrate is grounded so that current flows to keep the substrate neutral (and to measure the implanted dose). Otherwise a potential would rapidly build up (possibly up to the accelerating potential), changing the implant profile and/or causing arcing. (As an aside, this causes some difficulties when implanting or performing ion beam analysis on insulating substrates - usually a thin conductive carbon or metal coating is needed to prevent arcing.)

Once the impurities are implanted, the substrates have to be annealed to eliminate all the damage to the lattice from the implant, allow the dopants to move on to lattice sites, and thus become active.

Ultimately, whether the ions are singly charged (positive or negative), or multiply positively charged, makes no difference in the end result.

  • $\begingroup$ The binding energy of an electron to a donor (cation) and of a hole to an acceptor (anion) is "just" ~45meV. Is that what drives the neutralization via the grounded substrate? $\endgroup$ – Sparkler Jul 16 '16 at 16:51
  • $\begingroup$ @Sparkler - no, not really. You just need the path to ground and enough conductivity to handle the beam current. It really isn't much current at all, typically microAmps to 100's of milliAmps. Intrinsic silicon is not a problem. Sapphire is (without a coating). $\endgroup$ – Jon Custer Jul 16 '16 at 16:55
  • $\begingroup$ I thought the beam is P+ ions (video) $\endgroup$ – Sparkler Jul 16 '16 at 17:11
  • $\begingroup$ And? You need a path to ground to conduct the current. In this case that means electrons flowing from ground into the samples to preserve charge neutrality. $\endgroup$ – Jon Custer Jul 16 '16 at 19:03

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