Abstract: As the integration density of VLSI device increases, the overlay accuracy in the photolithography becomes more and more important. In the sub-quarter micron technology, the registration budget is less than 70 nm. Registration error can be induced by the repeatability error of alignment sensor, mask fabrication error, tool induced shift, process induced shift, and so on. One of these misregistration error sources, overlay parameter difference between DI and FI, can cause significant damage to the device because, in most cases, overlay accuracy is checked only in the mask step. In this paper, we studied the relationship of the Edge Detection Algorithm (EDA) and the overlay mark structure to the wafer scale difference. !3
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