Importance

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Abstract

A projection exposure apparatus for projecting a pattern of a reticle upon a wafer by use of a projection lens system, is disclosed. The apparatus is arranged so that a mark illuminating light is projected upon the wafer from between the projection lens system and the wafer and not by way of the projection lens system. The light diffracted by an edge of a wafer alignment mark is photoelectrically detected by way of the projection lens system, whereby an electrical signal corresponding to an image of the alignment mark is obtained. On the basis of the detected signal, the wafer is aligned with the reticle. This arrangement allows detection of the alignment mark without being affected by a photoresist applied to the wafer surface. Thus, the reticle-to-wafer alignment can be made accurately. Also, a novel and unique alignment method is disclosed. The disclosed method assures high-accuracy reticle-to-wafer alignment.

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First Claim