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MIT OpenCourseWare http://ocw.mit.edu 2.672 Project Laboratory Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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1. Proximity Heating Of Silicon Wafer Lithography is a critical processing step in fabrication of advanced microcircuits. It transfers a circuitry layout from a photomask to a silicon wafer. A layer of photosensitive polymers (photoresist) is first spin-coated onto the silicon substrate. A lithography system then projects the image of the photomask onto the resist coating and creates a latent image in the resist. The photoresist in the exposed (or un-exposed) area is then removed by chemical etching The latent image needs to be activated before the etching process. This is accomplished by setting the wafer temperature to around 180 C for a few seconds; etching quality control requires the temperature to be uniform to within 2 C over the entire wafer surface. A hot-plate heating technology is currently used. The wafer is first supported at ~2.5 cm away from the hot-plate surface.
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