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distripution of impurities in the silicon wafer using diffusion process

Discussion in 'General Electronics' started by Falah Mohammed, Oct 5, 2003.

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  1. Can anyone explain to me why the distribution of impurity ions takes
    either Gaussian or erfc function distribution under thermal diffusion?
  2. Charles Jean

    Charles Jean Guest

    On 5 Oct 2003 00:45:58 -0700, (Falah Mohammed)
    Sorry to "answer" your question with another question, but:
    Is the distribution EVER Gaussian? When I worked with semiconductor
    manufacture, we always assumed that it was erfc, and the empirical
    results(junction depth, device characteristics, etc.) were very close
    to the erfc distribution. This was boron or phosphorus into 1:1:1
    silicon, around 1200 deg. C.
    It's been a long time ago, but doesn't the erfc distribution require
    diffusion from an "infinite" source at the surface? Our diffusions
    were always from a solid solubility of dopant at the surface-as close
    to "infinite" as one can get. If the surface concentration of dopant
    WERE concentration-limited, would that change the distribution type
    from erfc to Gaussian? These are just WAGs, but hope they help.
    Maybe a solid-state physicist out there knows and will jump in
    here-you've piqued my curiosity.
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