| 摘要 |
PURPOSE:To improve a detecting rate, by providing a position detecting means for a bright field state and a position detecting means for a dark field state, providing a switching means for both detecting means, switching the field states, and performing the signal detection again. CONSTITUTION:As a lighting source 11, e.g., a halogen lamp is used. A condenser lens 12 and a bright field spot 13A and a dark field stop 13B, which are attached and removed in a replacing mode, are provided. The bright field stop 13A is placed in a light path. The image of the lighting source 11 is formed on the stop 13 through the condenser lens 12. As the stop 13, at first the bright stop 13A is used, and whether a pre-alignment mark on the surface of a wafer 4 is located within the image pick-up field of an image pick-up tube 7 or not is acknowledged. Then, the stop 13 is replaced by the dark field stop 13B, and the field is switched to the dark field state so that the image of the pre- alignment mark is clearly visible. The image is picked up and the position of the image of the pre-alignment mark is detected. Since both the dark field state and the bright field state can be used, the detecting rate of the peak signal of the mark is improved.
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