| 摘要 |
PURPOSE:To detect the shifted location with high precision by a method wherein the alignment reference points on the mask and the wafer are illuminated by the single color light with the specified wave length to form the image of each location data on the same plane by means of diffracting the Fresnel zone plate. CONSTITUTION:The single color light with the wave length of lambda is illuminated through the intermediary of the prism 6 to provide the Fresnel zone plate with the focus f1 at the first degree of diffraction on the image forming location focussing on the alignment reference point 4 on the wafer 3. In case the gap between the mask 1 and the wafer 3 is d, if the expression fXlambda=n(f1-d)Xlambda with the n degrees selected is satisfied, the Fresnel zone plate 7 can also focus the alignment point 2 of the mask 1. Thus the alignment reference points 4, 2 of the wafer 3 and the mask 1 may become parallel with each other at the first and the n-th diffraction of the Fresnel zone plate and the image are formed on the light receiving surface of the photoelectric detector 9 by means of the relay lens 8 detecting the relative locations easily with high precision. |
