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Thread: Why don't they make square silicon wafers?

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    Formerly known as Viet Cong Zombi and tuone
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    Why don't they make square silicon wafers?

    I know these the guys that make silicon are really clever, but seeing as all chips are square, why do they decide to make perfectly round silicon wafers, why don't they make square ones so you could fit all your chips on one ?

    Can someone explain? thanks!

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    Formerly known as Viet Cong Zombi and tuone
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    They make the wafers from silicon ingots, which are round due to the process by which they are made. They have a spining starter seed of silicon that is dipped into a vat of molten silicon, as they draw it out it cools and proceeds to grow larger and larger. In the end it looks alot like a super sized Hersheys chocolate kiss.

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    Gaarrrrr! Dav0s's Avatar
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    hmmmm, maybe because the outside of the silicon woud be such poor quality that it wouldnt be worth it? maybe circles offert the best success rate. i dunno im just tihnking out loud

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    Moderator DavidM's Avatar
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    I'd imagine they melt down the remainder bit or something...

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    Administrator Moby-Dick's Avatar
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    I think they grow the Si from a technique called the Czochralski Technique. A seed crystal is pulled up and rotated from a molten pool of Silicon.

    the rotating gives you a circular cross section.

    Wikipedia shows it quite well ( better than my old 2nd year Materials Engineering notes ! )

    http://en.wikipedia.org/wiki/Czochralski_process
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    Senior Amoeba iranu's Avatar
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    ^^ tis correct - that saved me from digging out my 2nd year Materials Engineering notes too. Although it would be funny to see how many transistors were on a 486 dx.
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    Quote Originally Posted by iranu
    ^^ tis correct - that saved me from digging out my 2nd year Materials Engineering notes too. Although it would be funny to see how many transistors were on a 486 dx.
    About 1.2 million...

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    Zad
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    I would imagine that if they managed to grow (or possibly cast) the boule in a square cross-section, it would cool down unevenly, leaving internal stresses that could lead to cracks, or at least creep inside the material. Not what you need when you are working down at that sort of scale.

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