| 摘要 |
PURPOSE:To accurately detect the inclination angle at a position to be detected of an element to be detected by projecting a rectangular parallel light beams through a mask plate to at least two positions of the element, photodetecting the parallel lights shielded partly by the position to be detected by photoelectric conversion means, and calculating the inclination angle of the position by calculating means on the basis of an output detection signal. CONSTITUTION:Lights 4a, 4b from light sources 3a, 3b are converted by lenses 6a, 6b to parallel light beams 5a, 5b to become rectangular parallel light beams 9a, 9b through the slits 7a, 7b of a mask plate 8, and partly shielded by a wafer 2 to be photodetected by photoelectric converters 10a, 10b, respectively. The voltage value Va1 corresponding to the photodetecting area Sa of the converter 10a is contained in a calculator 13 through an A/D converter 12a, and an output voltage Vb1 is similarly contained in the calculator 13. The calculator 13 stores output voltages Va0, Vb0 corresponding to the photodetected area S when the wafer 2 is not presented in advance. Then, the calculator 13 takes the ratio of the output voltages Va0, Va1, and the ratio of the output voltages Vb0, Vb1, thereby obtaining the inclination angle theta from the reference line 16 of an orientation flat part 1 on the basis of them.
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