INTERFEROMETER MODULE

摘要

The invention relates to a differential interferometer module adapted for measuring a direction of displacement between a reference mirror (81) and a measurement mirror (21). In an embodiment the differential interferometer module is adapted for emitting three reference beams (rb1, rb2, rb3 ) towards a first mirror and three measurement beams (mb1, mb2, mb3 ) towards a second mirror for determining a displacement between said first and second mirror. In a preferred embodiment the same module is adapted for measuring a relative rotation around two perpendicular axes as well. The present invention further relates to a lithography system comprising such a interferometer module and a method for measuring such a displacement and rotations.