| 摘要 |
The present invention is directed to an improvement in an alignment system for a scanning mask aligner employing a pattern on the mask or the wafer or both in the scribe lines that run in the direction of scanning, the improvement comprising a viewing system having optical grids, a system for moving the patterns across the optical grids in the viewing system, the grids corresponding to the directions and spacings of the patterns so that light transmitted through the grid is strongly modulated, and circuitry for comparing the phase modulation from the mask and wafer alignment targets to obtain alignment error signals; further according to the invention, the same system used to measure alignment can also be used to measure how well the mask is focused on the wafer. In this case two images of the mask pattern are arranged so that one is slightly inside of focus and the other is slightly outside of focus, and by comparing the amount of modulation on the two channels it is possible to deduce which of the two is closer to focus and therefore how to shift the focus so that they are equal.
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