JPS57172726A - Position alignment of mask substrate and wafer - Google Patents

Abstract

PURPOSE:To detect and align the mutual positions with high precision even if the mask and the substrate are not sufficiently separated from each other by a method wherein the standard pattern on the wafer is formed into the Fresnel zone pattern as the reflecting image formation element. CONSTITUTION:The light source 5 emitting a single color light illuminates the Fresnel zone pattern 4 on the wafer 3 through the intermediary of the lens 6, the filter 7, the prism 8 and the mask 1. The image of the alignment reference 2 on the lower surface of the mask 1 is formed on the light receiving surface of the photoelectric detecting element 10. If the focus f of said pattern 4 is set up to be equivalent to the distance d between the mask and the substrate, the reflecting light from the pattern 4 is focussed on the lower surface of the mask 1 forming the location data of the wafer 3 on the plane similar to the plane where the alignment reference point 2 is located. With each image being detected 10, the relative location data of the mask and the wafer are available. In this case, the mutual positions are easily detected with high precision, because the optical systems such as the lens 9, the detecting element 10 and the like being fixed, there are no positioning errors due to the movement of the focus.