Method of and apparatus for aligning photomask

Abstract

A method of making a mask and a wafer intimately contact each other by means of such a mask aligning apparatus comprising a base having a chamber, a piston apparatus movable up and down in the chamber, a wafer chuck provided at one end of the piston apparatus and adapted to fix the wafer, means for fixing the mask to the upper surface of the wafer in a superposed relationship, drive means adapted to impart a driving force to the piston, so as to move the wafer toward the mask, and means for biasing the piston apparatus in the direction to move the wafer away from the mask. The method comprises the steps of bringing the wafer by the drive means into positive contact with the mask fixed by the fixing means, sealing the wafer in an airtight manner in cooperation with the mask, lowering the pressure of the atmosphere around the wafer below atmospheric pressure, so as to cause a bending of the mask from the fixed position, to thereby cause the wafer to contact pressingly the central area of the mask, and expelling gas from the wafer chuck so as to make the entire region of the wafer intimately contact the mask. By adopting the method and apparatus of the invention, it is possible to smoothly bring the mask and wafer into intimate contact with each other, without adversely affecting the previously obtained mutual alignment of these two members. At the same time, the separation of the mask and the wafer from each other, after the contact and exposure, can be made in a shorter time. As a result, damaging of the mask pattern in the course of the mask alignment is avoided, and the yield of the wafer product is much improved.