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9.5.11: Yield

  • Page ID
    89991
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    Perhaps a word about feature size, chip size and yield would be in order. We saw earlier that circuits are repeated many times across a wafer's surface during the photolithographic stage. Although great care is exercised in trying to prevent defects from becoming part of a wafer surface (through the use of clean rooms, "bunny" suits, ultra-pure chemicals, etc.), each wafer that goes through a fab will end up with some "killer" defects distributed across the wafer surface as in Figure \(\PageIndex{1}\).

    Top-down view of a silicon wafer, shaped like a circle with a slightly flattened bottom edge, which has six small dots representing defects scattered across its surface.Figure \(\PageIndex{1}\): A wafer with defects

    Imagine that we try to manufacture some chips of a certain size. A glance at Figure \(\PageIndex{2}\) shows that we would have 15 good chips out of a total of 21, for a yield of about 71%. Suppose we could, through improved technology, perform a 30% "shrink" on the circuit — i.e., make its dimensions 30% smaller. Now, as Figure \(\PageIndex{3}\) shows, we get 40 good chips/wafer instead of 15 (and they cost no more to produce) and our yield has gone to 40 out of 46 or 87%. We will be rich! Or at least we won't go out of business!

    The wafer from Figure 1 above is patterned with 21 small squares, each of the 6 defects falling into a separate square.Figure \(\PageIndex{2}\): Six killed circuits
    The wafer from Figure 1 above is patterned with 40 very small squares, each of the 6 wafer defects falling into a different square.Figure \(\PageIndex{3}\): Lots more good ones

    Yield, reliability and manufacturability are all critical issues in the semiconductor industry. The business is highly competitive, and the technology keeps moving rapidly. It is an exciting and challenging field, one which demands the very best, but which rewards someone who is willing to never stop thinking and to bring forth the very best creative solutions to hard problems.


    This page titled 9.5.11: Yield is shared under a CC BY-NC-SA 1.0 license and was authored, remixed, and/or curated by Bill Wilson via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.