摘要 |
An embodiment of the invention may be applied to measure the positions of features in a alignment region on a mask with a sensor. The positions of the features in the alignment region are known from the design. A feature of which the position is measured, is identified by comparing the relative positions between measured features with relative positions known from the design. The known position of the identified feature is subtracted from a measured position of the identified feature to give the position of the mask.
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