| 摘要 |
PURPOSE:To detect a relative position of a mask and a wafer insufficiently spaced from each other by using a Fresnel zone plate, instead of a lens, as an image forming element to be inserted between the mask and the wafer. CONSTITUTION:A Fresnel zone plate 3 which is an aggregate of diffraction lattices becoming finer from the center to wafer with a certain regularity, is located between the mask 1 and the wafer having a registration standard 2a on it. Said Fresnel zone is then irradiated with a monochromatic light with an appropriate wavelength, whereby the image of the registration standard 2a is formed on the registration standard 1a of the mask by way of the Fresnel plate. This image is detected through a mirror 4 and a lens 4 to give information concerning relative position of the mask 1 and wafer 2, based on which precise positioning is made possible. when the standard 1a is focused using a Fresnel plate with a focal length f1, with respect to the wavelength lambda1, the standard 2a is in focus by using the wavelength lambda2 satisfying f1lambda1=(f1+d)lambda2 where d is a distance between the mask and the wafer 2, whereby the detection of relative position is possible at the distance L1not equal to L2, facilitating position detection at the distances of several millimeters - several ten millimeters. |
