| 摘要 |
PURPOSE:To eliminate the retraction of a microscope objective for improving the throughput and to enable the positions of a mask and a wafer to be detected also during light exposure, by inclining the microscope objective with respect to the perpendicular of a surface to be detected. CONSTITUTION:The optical axis of an objective 1 is inlined by 10-60 deg. with respect to a perpendicular of an object matter 2. For example, the optical axis 9 of a microscope objective 1 of about ten magnifications is inclined by theta1 from the perpendicular 8 of the surface to be detected 2. A difference (a) between the distances from the microscope objective 1 to the A point 3 and the B point 4 which are spaced from each other by a distance l can be represented by lXsintheta1. When light is obliquely applied by 7 to the A point 3 and the B point 4 and they are detected by the microscope objective 1, the image of the A point 3 is formed at a A' point 6. The image formation plane defined by connecting the A' point 5 and the B' point 6 makes an angle of with respect to the optical axis 9. If a diffraction grating 10 whose grating pitch (d) can be represented by a predetermined formula is arranged approximately according with the image formation plane, the linear reflection light of wavelength lambdabecomes approximately at right angle to the diffraction grating. |
