Electron optical image correction subsystem in electron beam projection lithography

Abstract

To obtain ultimate image fidelity in the PREVAIL electron beam projection lithography system (EB stepper) [Pfeiffer et al., J. Vac. Sci. Technol. B 17, 2840 (1999)], precise dynamic corrections [Zhu et al., Proc. SPIE 2522, 66 (1995)] of an exposed reticle subfield image on the wafer are required. The electron beam column for the EB stepper covers a large deflection area by a curvilinear variable axis lens (CVAL) [Stickel and Langner, J. Vac. Sci. Technol. B 17, 2847 (1999)] type deflection with high current, and very large 0.25 mm square beam. Because of these features together with tighter specifications for electron optics in below 70 nm node, aberrations which can be negligible in prior art electron beam lithography systems, can no longer be ignored. Therefore the electron optical image correction subsystem in the EB stepper is required to precisely correct the increased numbers of possible measurable aberrations caused by deflection as well as by space charge effects. In this article, a systematic overview of beam corrections is described.