Wafer chuck for magnification correction in x-ray lithography

Magnification correction has emerged as a critical issue in x-ray lithography for very large scale integrated circuits. We have developed a simple and robust method to correct the magnification, which is suitable for use in a collimated x-ray beam from a storage ring. In our technique the wafer is bent to conform to a chuck whose surface is a portion of a sphere of adjustable radius. Both increases and decreases in the pattern size may be accommodated by using convex and concave spherical surfaces, respectively. The radius of the chuck can be set to achieve desired corrections of up to several parts per million. The maximum attainable correction is determined by the permissible out of plane distortion which accompanies the wafer bending, and is dependent upon the wafer thickness and the field size. The change in the wafer pattern is expected to be very nearly an isotropic magnification; however a limited one-dimensional magnification correction may also be added by differentially scanning the mask and wafer. (C) 1998 American Vacuum Society.