Aberration compensation in charged particle projection lithography

Projection systems offer the opportunity to increase the throughput for cha rged particle lithography, because such systems image a large area of a mas k directly on to a wafer as a single shot. Shots have to be imaged over a c ertain range of off-axis distances at the wafer to increase the writing spe ed, because shot sizes are limited to about 0.25 x 0.25 mm(2) due to aberra tions. In a projection system with only lenses, however, the aberrations fo r off-axis shots are still very large, and some aberration compensation ele ments need to be introduced. In this paper, three aberration compensation e lements (deflectors, stigmators and dynamic focus lenses) are first discuss ed, a suite of newly developed software, called PROJECTION, based on this p rinciple and our unified aberration theory [2,3] is then described, and an illustrative example computed with the software is finally given. (C) 1999 Published by Elsevier Science B.V. All rights reserved.