Wafer chuck for magnification correction in x-ray lithography

Magnification correction has emerged as a critical issue in x-ray lithograp hy 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 b ent to conform to a chuck whose surface is a portion of a sphere of adjusta ble radius. Both increases and decreases in the pattern size may be accommo dated by using convex and concave spherical surfaces, respectively. The rad ius 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, an d is dependent upon the wafer thickness and the field size. The change in t he wafer pattern is expected to be very nearly an isotropic magnification; however a limited one-dimensional magnification correction may also be adde d by differentially scanning the mask and wafer. (C) 1998 American Vacuum S ociety.