| 摘要 |
PURPOSE:To measure the depth of a fine recessed part with high accuracy by projecting a fine light spot on the top surface and bottom surface of the fine recessed part through the reverse surface of a body to be measured, and moving an objectively lens which has a large numerical aperture and adjusting its focus. CONSTITUTION:Illumination light from a light source 21 illuminates the wafer 7 and an image of a hole 8 and its periphery is observed through an image pickup tube 27 and an ITV 28. Laser luminous flux 2 from a laser light source 1 is reflected by a dichroic mirror 5 and then converged through a lens 6 to form a laser spot image through the reverse surface 7b. Then the spot is positioned on the bottom surface 8a of the hole 8 and then the lens 6 moves in an optical-axis direction so that the output signal of the photodetecting element 14 of an automatic focus detection part 10 is maximum, thereby adjusting the focus. Then the laser spot is projected on the top surface 7a from the reverse side, and consequently the lens 6 is displaced in the optical-axis direction according to the output signal of the element 6. At this time, the step from the bottom surface 8a to the top surface 7a is found from the displacement quantity of the lens 6.
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