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Why photomasks are laser etched but ICs arent

  1. May 5, 2016 #1
    When an IC photomask is being fabricated, a laser carefully dissolves specific portions of the photo resist to develop the precise pattern. But when we make ICs, we use a photomask to place over the silicon and shine coherent light over it at once.

    Since most of the engineering problems arise from this photolithographic process using a photomask, why do we not just laser etch the silicon wafers themselves? Would it take too long?
     
  2. jcsd
  3. May 6, 2016 #2

    f95toli

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    We DO use laser lithographers for making ICs; but only for prototyping and one-offs (they are becoming quite common in university labs).
    However. using a mask is just much faster if you want to make many copies of something.

    Also, lasers are only useful for fairly crude lithography (hundreds of nm); you can't use it to make masks for chips with small feature sizes; these are made using e-beam lithography. Hence, laser lithographers are often used to defined conctacts etc whereas you still need e-beam lithography for the actual device.
     
  4. May 6, 2016 #3

    analogdesign

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    I wouldn't say "most" of the engineering problems are due to photolithography, although it is a very challenging area of wafer production. f95toli is correct that any kind of direct writing of features on a wafer would be much, much, much more expensive than mass producing with a mask and photolithography. Like many things in the IC business, it is an economic decision as much as a feasibility decision.
     
  5. May 6, 2016 #4

    davenn

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    thanks mate :smile:

    learn something new every day

    Dave
     
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