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The following text is from "Analog CMOS integrated circuit" book:

For long metal wires, the minimum width is typically larger than that for short wires to avoid "liftoff" problems.

What is the liftoff problem? I have heard about liftoff process, but I think it is different from the liftoff problem. Can you please explain about that?

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    \$\begingroup\$ It’s the lift off process, it is more reliable to use other processes now. \$\endgroup\$
    – UVphoton
    Oct 10, 2022 at 0:43
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    \$\begingroup\$ @Gilbert has the correct answer but there is a lift off process in semiconductor device fabrication where a thin film is deposited on a substrate containing photoresist that has been developed with a pattern. When the photoresist is placed in a solvent, it swells and the metal over the photoresist "lifts off". As UVphoton mentioned there are better methods. \$\endgroup\$
    – Steve Saban
    Oct 10, 2022 at 0:59
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    \$\begingroup\$ Can you add more context from the book? I dont believe this is talking about wire bonds as the accepted answer suggests, but rather the metal lines that are part of the IC. \$\endgroup\$
    – Matt
    Nov 1, 2022 at 0:28

2 Answers 2

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I believe in this context, “liftoff” refers to wires detaching from bond pads on the wafer. Fine wires connect from the wafer to the chip package, and there is some risk that after they are bonded to the wafer, they will detach. Wider wires have a larger bond area and are therefore less likely to detach.

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The book is talking about CMOS design rules. It has nothing to do with wire bonds. For any given CMOS fabrication process there is an extensive list of "design rules" that constrain all kinds of things.

In this case they are talking about the width of a metal line (which they are calling a "wire") and a design rule that reduces the chance of that line coming off the surface that it should be attached to (liftoff). If the metal line is fairly short it can be narrow and will remain in place anchored by whatever is on either end. But if the metal line is long it must be wider to better stick to the surface.

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