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epitaxial planar

Discussion in 'Electronic Basics' started by Dany, Aug 6, 2005.

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  1. Dany

    Dany Guest

    can someone explain the meaning of "epitaxial planar type "???
  2. Epitaxy (epitaxial) refers to layers grown on top of a wafer after it
    is polished. The alternative is to create layers by diffusing dopants
    down through the top surface with heat or by driving dopants ions or
    atoms into the wafer via high velocities. Planar just means flat.
    All connections and patterns (except for the bulk wafer connection)
    are on the top surface.
  3. jason

    jason Guest

    Hello All

    By the way

    Anyone knows why in some devices, using epitaxial layer is good? Good
    in what parameters?
    Kindly advise

    Thank you

  4. Dany

    Dany Guest

    Tnx for the explanation
  5. Charles Jean

    Charles Jean Guest


    In the diffused process that John described, say you have a silicon
    N-type wafer and wanted to make a PN junction. A P dopant is
    deposited in a fairly high concentration of the top of an N type
    silicon wafer, then the temperature is raised so that the P dopant
    atoms diffuse into the body of the N silicon. At the end of the
    diffusion step, you would find that the concentration of the P dopant
    atoms decrease from the surface toward to bottom of the wafer, but not
    in a linear way-it follows an error function distribution(erf). The P
    dopant concentration at the surface of the wafer is usually greater
    than the wafer background N atoms, so that the surface of the wafer
    has been converted to P type silicon. As you go deeper and deeper
    into the Si, the concentration of P dopant atoms gradually decreases
    until you reach the point at which P=N. This is the PN junction
    depth. Below this point N>P and you are into N type silicon on the
    other side of the junction. This makes a diffused diode.
    With the epitaxial process, the N wafer is heated while a mixture
    of a silane gas and P dopant gas is passed over the N wafer. Silicon
    doped with P dopant is deposited on the wafer, producing a P type
    silicon layer on top of the N wafer. In contrast to the diffused
    process, the concentration of dopant in the top layer is very nearly
    constant throughout its depth. Ideally, it produces a "step" junction
    with no N type carriers. In some cases, the dopant can be left out
    altogether to produce a carrier free(ideally) top layer, which is
    called "intrinsic" silicon.
    This distribution of carriers around a PN junction will have a
    pronounced effect on the electrical characteristics of a device.
    Leakage current of a diode, for example. Or junction
    capacitance-avoided for high frequency devices, exploited for
    "Sic hoc legere scis nimium eruditionis habes."
    (If you can read this, you're overeducated.)
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