Patent ID: 7542141
Filing Date: 2009-06-02
Classification: G03F,H01L

Abstract:
1. An apparatus comprising: a stage configured to be moved; a first laser interferometer configured to be used to measure a position of the stage in a first direction; a second laser interferometer configured to be used to measure a position of the stage in the first direction; and a control unit configured (i) to obtain a position of the stage based on an output of one of the first and second laser interferometers, (ii) to control a position of the stage based on the obtained position of the stage, (iii) to perform switching of one of the first and second laser interferometers to the other of the first and second laser interferometers while the stage is moved at a constant velocity in the first direction, (iv) to calculate a distance by which the stage is to be moved during a time interval, and (v) to set an initial value of the other of the first and second laser interferometers after the switching, based on a position measured by the one of the first and second laser interferometers at a start time of the time interval and the calculated distance.