| 摘要 |
An apparatus for detecting a focussing position in a projection exposure system. The apparatus constitutes a detection system for causing the so-called automatic focussing apparatus to operate more precisely with greater reliability and the focussing height at the respective portions of a mask pattern are separately determined, thereby making the accurate discrimination of the focussing position even in cases where any special mark is not used or the intentity of the exposure light is varied moment by moment. This apparatus includes a reference surface formed with a transparent pattern of a given configuration and provided on a stage, an illuminating system for directing an illuminating light to the transparent pattern, and a detection system whereby the reflected light from the mask pattern surface of the projected image of the transparent pattern formed by the projection optical system under the application of the illuminating light is detected through the projection optical system and the transparent pattern thereby detecting a variation in the light quantity of the reflected light. The position (height) where the light quantity variation of the reflected light attains the maximum or minimum represents the focussing position.
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