| 摘要 |
PURPOSE:To improve accuracy in measuring or determining the position of a stage by accurately measuring the bending degrees of plane mirrors without using a reference plane mirror. CONSTITUTION:As measuring means for detecting the local bending amounts of the reflecting surfaces of two plane mirrors MX and MY, theta interferometers Xtheta1 and Ytheta1 are provided. The plane mirrors MX and MY are provided on a stage ST so as to form a right angle to each other. The bending amounts of the reflecting surfaces of the two plane mirrors MX and MY are measured approximately at the same time with the two theta interferometers Xtheta1 and Ytheta1. The difference between both measured values is obtained. The error in straight advancing property of the stage ST is offset, and the true bending amounts of the reflecting surfaces are obtained. Then, the bending amounts of the plane mirrors are stored. The coordinate position of the stage ST which is detected at the time when the position is measured or determined is corrected according to the bending amounts of the mirrors. In this way, the same accuracy as the accuracy obtained when plane mirrors having the ideal reflecting surfaces are used can be obtained. |
