| 摘要 |
PROBLEM TO BE SOLVED: To exactly measure surface shape of thin plate by correcting the effects of bend caused when negative pressure is worked on a thin plate such as a semiconductor wafer. SOLUTION: A first negative pressure and a second negative pressure are set with a pressure controller 20 capable of controlling negative pressure at least in two steps. At a single or a plurality of predetermined positions on the surface of the thin plate 12, vertical displacement between the surface of the thin plate when the first negative pressure works and that when the second negative pressure works is measured with an elevation detector means 18. Based on the pressure variation between the first negative pressure and the second negative pressure set with the pressure controller 20 and the displacement measured with the elevation detector means, the surface shape of the thin plate 12 is obtained when no deformation due to the negative pressure working on the thin plate 12 and due to that and self weight of the thin plate 12 do not exist.
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