Method and apparatus for setting the gap distance between a mask and a

Abstract

An apparatus for setting the gap distance between a mask and a wafer, facing with each other to a predetermined distance, is arranged as follows. A wafer stage is movable along a reference plane defined as a plane parallel to the transferring direction of the wafer and supports the wafer. The wafer stage has a .theta..sub.Y table for tilting the wafer and a first displacement sensor. A mask stage supports the mask and has a .theta..sub.Y table for tilting the mask and two second displacement sensors. The first sensor scans the mask in response to the movement of the wafer stage, whereby an error in the parallelism of the wafer with respect to the reference plane is measured. The mask is kept parallel to the reference plane by tilting the mask so as to eliminate the error in the parallelism. Distances from the second sensors to two points on the wafer are measured by the second sensors. The gap distances between the mask and two points on the wafer are obtained by substracting the distance between the mask and second sensors from the measured distances, individually. The mask and the wafer are kept parallel to each other by tilting the wafer so as to eliminate the error in the parallelism thus obtained, and the gap distance between the mask and wafer is adjusted to be set at the predetermined distance.