Step and Repeat
What good is it to make just one copy of a little chip onto a big wafer? Don't we need to fill the whole wafer with hundreds of copies of the chip? Indeed we do, and that's why these machines are called steppers. After projecting one image onto the wafer long enough for the photoresist to harden, the stepper moves the wafer slightly to the left and projects the image through the reticle again. After that chip is done, the wafer moves over one more position, and again the process is repeated. Like plowing a field from one corner to the other, a stepper passes from left to right, and top to bottom until the entire wafer has been exposed (see Figure 4.7). The entire process takes just a few minutes.
Figure 4.7. This wafer has been ...
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