CPC G03F 9/7019 (2013.01) [G03F 9/7076 (2013.01)] | 17 Claims |
1. A calibration system comprising:
a plate adjacent to a wafer alignment mark disposed on a wafer;
a fixed alignment mark disposed on the plate and configured to act as a reference mark for an initial calibration of the calibration system; and
a variable diffraction grating disposed on the plate and comprising a plurality of unit cells configured to form a plurality of variable alignment marks,
wherein the variable diffraction grating is configured to match the wafer alignment mark in order to calibrate a shift-between-orders of one of the variable alignment marks and the fixed alignment mark.
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