| 摘要 |
A wafer is brought into focus with a projection optical system, and a wafer mark on the wafer is also brought into focus with an off-axis alignment sensor highly accurately according to an automatic focusing process. First, a deviation of the surface of the wafer from an image plane of the projection optical system is measured by an oblique-incidence main AF sensor. For measuring the position of the wafer mark with an imaging device of an alignment system, part of a focusing ray of light from the wafer passes through an optical system, which is not telecentric, composed of an AF relay system and a half beam shield plate, and is detected by the imaging device, whereupon an image of a focusing mark projected onto the wafer is formed on the imaging device. The position of the image of the focusing mark on the imaging device is calibrated on the basis of the deviation which has been measured by the oblique-incidence main AF sensor.
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