| 摘要 |
In a lithographic apparatus having a movable object table in vacuum, an interferometer-based alignment system for detecting the position of that object table has a passive part in vacuum and an active part outside the vacuum chamber. The active part contains the beam generator, e.g. a laser, and the electronic detectors whilst the passive part contains the illumination and imaging optics. The two parts are coupled by optical fibers. The interferometer may make use of different diffraction orders from measurement and reference gratings and the order separation may be included in the passive part.
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