| 摘要 |
PURPOSE:To raise the resolution, by performing parallel setting as to a reference surface, then measuring the flatness of a wafer to set a focal plane, determining such a virtual surface of the wafer that the level of the surface within the depth of focus is maximum, and moving the wafer to make the virtual surface coincide with the focal plane. CONSTITUTION:An accurate screw part 22 is moved up by the rotation of a pulse motor 21 to elevate a wafer 27 through a pressure-sensitive element 23, a parallel setting spherical seat 25, a carrier 24 therefor and a wafer chuck 26. When a part of the wafer 27 is brought into contact with a reference ring 28, parallel setting is performed by the action of the spherical seat 25. When the accurate screw part 22 is slightly moved up further, the pressure-sensitive element minutely deformed to detect set pressure. The deformation of the surface of the wafer 27 is then measured by an air micrometer 29. The mean value of the measured levels of the surface is determined. The wafer is then moved down by the mean value to the focal plane 31 of an optical system, which is located at a certain distance from a reference surface 30. |
