| 摘要 |
PROBLEM TO BE SOLVED: To reduce effect of speckles, or the like down to a desired amount by a small imaging time or an addition count of images, and detect the positional deviation of a substrate with high precision. SOLUTION: There are provided imaging step of picking up images illuminated by pulse beams as an image signal by a CCD camera 9; an image addition step of addition inputting an image signal imaged in the imaging step to a memory by a signal process circuit 11; a light quantity measuring step of measuring the quantity of light in a partial area of the image signal added in the image addition step by a light quantity measuring step; a control step of controlling the repetition of the imaging step, the image addition step and the light quantity measuring step, until the quantity of light measured in the light quantity measuring step satisfies the predetermined conditions. Until the change in the quantity of light in the partial area during the light quantity measuring step becomes a predetermined quantity or smaller, the control step repeats the imaging step, the image addition step and the light quantity measuring step.
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