| 摘要 |
PROBLEM TO BE SOLVED: To enable to measure the change in the direction of focus by detecting the position relative to the optical axis of the same point on the surface of an object, by driving a stage and forming a table for correcting the change in the direction of the optical axis of the stage on the basis of the measured value. SOLUTION: A pre-reading sensor 805 measures the focus position of a point P on a wafer 12 and the value is measured as Zp (y0). A stage is driven by Ly and, when the stage position becomes Y=y1, a central sensor 803 measures the focus of the point P on the wafer 12 measured by the pre-reading sensor 805 on Y=y0. For correction, if the stage is driven upward, correction is made by using a table formed by the pre-reading sensor 805 and the central sensor 803. When the stage is driven downward, a table formed by the pre-reading sensor 805 and the central sensor 803 is used.
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