Electron beam optical system with large field coverage for submicron lithography

Abstract

A low aberration and low landing error deflective focusing system has been developed for submicron electron beam lithography. The deflection system consists of a one-stage electrostatic deflector and a one-stage magnetic lens, which is simple and desirable for a practical electron beam lithography system. The design method is based upon the low aberration and telecentric properties of the ideal uniform magnetic focusing and uniform electrostatic deflection fields. Fringe fields, which are generated in practice, degrade the optical properties, but their distributions are optimized to minimize additional aberration and landing error. Overall aberration is 0.2 μ and landing error is 20 mrad at a 10 mm field corner with a 5 mrad beam half angle after dynamic focus correction. Eight pole and twelve pole electrostatic deflectors are constructed and their performances are obtained and studied. Studies of higher order aberrations show the importance of fifth order rotational invariance for a large area deflection. Using this system, 0.5 μ rule LSI patterns are successfully exposed over a 10×10-mm field.