Patent ID: 7072048
Filing Date: 2006-07-04
Classification: G01B,G03F

Abstract:
1. A plural-dimensional displacement measuring system for an apparatus having a bed ( 10 ), a first stage ( 12 ) movable in a first direction (Y) relative to the bed and a second stage ( 18 ) movable in a second direction (X), generally at right angles to the first direction, relative to the first stage, the measuring system employing a first interferometer system ( FIG. 5A ) for measuring linear displacement generally in the first direction between a first reference reflector ( 66 ) and a first target reflector ( 70 ) fixed relative to the first stage and producing a corresponding first output signal, a second interferometer system ( FIG. 5B ) for measuring linear displacement generally in the second direction between a second reference reflector ( 72 ) and a second target reflector ( 82 ) fixed relative to the second stage and producing a corresponding second output signal, and means ( 64 ) for processing the output signals to determine linear displacement of the second stage relative to the bed in the first and second directions, characterised in that: the second interferometer system includes a intermediate reflector (