I think a while ago I heard someone saying (or I read it, can't remember..) that the silicon for our semiconductor industry isn't just simple silicon. More, it is a special type of silicon but I cannot find appropriate information about that. I also can't get my head around of which type the silicon could or should be..

I'm aware of the different dopings which are required but I wouldn't see that as the silicon itself. Am I just wrong respectively do I fail to remember something correctly or is there something more about it, indeed?

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    $\begingroup$ Well the silicon needs to be extremely pure (because even minute amounts of impurities will act like dopants changing the material properties). $\endgroup$ – Sebastian Riese Feb 6 at 17:45
  • $\begingroup$ @SebastianRiese That's true, wasn't aware of that. "Purfying" is not possible, somehow? $\endgroup$ – Ben Feb 6 at 20:43
  • $\begingroup$ I've heard repeatedly in the context of microfabrication that most IC silicon is produced from Australian beach and quarried sand, which is of high purity. Could you be thinking of something like this? $\endgroup$ – Chemomechanics Feb 6 at 21:08
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    $\begingroup$ Purifying is possible (and done – after all the silicon starts out as quartz sand), but some impurities are more expensive to remove or more damaging in even the smallest concentrations than others, so only a small fraction of the sand deposits can be used to produce high grade silicon economically. $\endgroup$ – Sebastian Riese Feb 7 at 13:09

Silicon is an element, so silicon is just silicon. There's no special isotope used for semiconductor technology.

But there are some special features needed:

  • The silicon must be a single crystal. Crystal zone boundaries in the material would disturb the operation of the most common devices such as diodes and transistors. Really large monocrystalline silicon boules are formed by the Czochralski method

    The specific orientation of the crystal structure relative to the surface of the chip where the circuit is formed must also be carefully controlled.

    (Polycrystalline silicon may be used to form certain structures, like the gate of a MOSFET, on the surface of a monocrystalline IC substrate, or to form certain kinds of large devices such as liquid crystal displays or solar cells)

  • The silicon must be extremely pure. Even one part in a billion of impurities in the silicon will change its properties and might make it unsuitable for use in electronics. Purification can be done after the crystal is formed by zone refining

  • Specific impurities, called dopants, are then introduced into the silicon in a controlled way to form devices such as transistors and diodes.

  • Silicon may also be alloyed with a small proportion of germanium to form SiGe. SiGe has somewhat improved properties compared to pure silicon that make it more suitable for very high speed (gigahertz and up) circuits.

  • $\begingroup$ No modern wafers use zone refining. All boules are Czochralski, and are B-doped only. The way to ultra-purify silicon was developed in WW2. $\endgroup$ – Jon Custer Feb 6 at 23:13
  • $\begingroup$ @JonCuster Well you certainly can buy zone refined silicon and n-type wafers right now. So... clearly thats not true. $\endgroup$ – Matt Mar 27 at 23:02
  • $\begingroup$ @Matt - sure, small boules and specialty products. All 150mm and bigger boules are B-doped because of doping uniformity. $\endgroup$ – Jon Custer Mar 27 at 23:13

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