| 摘要 |
A system is configured to measure two separately polarized beams upon diffraction from a substrate in order to determine properties of the substrate (30), in particular to measure parameters of a lithographic pattern on the substrate. Elliptically polarized light from a light source is reflected from the surface of the subtrate and passed via a fixed phase retarder (100) in order to change the phase of one of two orthogonally polarized radiation beams with respect to the other of the two beams. The relative phases of the two radiation beams and other features of the beams as measured in a detector allows to determine properties of the substrate surface.
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