Aberrations as a Function of Reduction Factor in Symmetric Magnetic Doublet for Electron Beam Image Projection System

Abstract

When the object-image distance is 546 mm and the main- and sub-field sizes are 20 and 0.25 mm, the distortions for the reduction factors of 1/4, 1/2.5, 1/2, 1/1.6 and 1/1 are 2.1, 1.8, 1.3, 0.6, and 0.2 nm, respectively. The maximum obtainable beam currents for the reduction factors of 1/2.5, 1/2, 1/1.6, and 1/1 respectively are 1.6 1.7, 2.0, and 2.0 times as large as that for the reduction factor of 1/4. A new lithography system is studied, in which a ×4 master reticle is delineated by the electron beam reticle writer, many ×2 working reticles are formed by the first electron reduction projector, and patterns are formed on wafers by the final electron reduction projector. An electron optical column for formation of the working reticle is designed and the aberrations are calculated. For an object-image distance of 600 mm and main- and subfield sizes of 40 and 0.5 mm, respectively, the residual radial and azimuthal distortions are 6.4 and 5.7 nm, respectively, and the beam blur is less than 45 nm for beam semi-angles from 0.06 to 0.25 mrad.