Patent ID: 6936385

Claim:
A method of calibrating an alignment system capable of aligning to alignment markers on opposite sides of a substrate, the alignment system directing an alignment beam of radiation directly onto one side and directing the alignment beam onto the other side via an optical system, the method comprising: providing a calibration substrate having first and second opposite surfaces and being transparent to the radiation of the alignment beam, the calibration substrate having a reference marker on a first surface thereof, the reference marker being detectable from both the first and second surfaces; performing a first alignment to the reference marker with the alignment beam directed onto the first surface; and performing a second alignment to the reference marker with the alignment beam directed onto the second surface and propagating through the calibration substrate to the first surface, while a plane plate is interposed into the alignment beam so that a focal position of the alignment system is displaced to the position of the first marker; wherein the first and second alignments may be performed in any order.