Simplified variably shaped beam for electron beam lithography

It is shown analytically that a shaped beam has 1.8 times higher beam current available than a Gaussian beam for a single pixel exposure system, when spherical aberration is dominant. A stable, small size, and low cost electron optical column is proposed. Critical illumination is adopted and beam size is varied by two shaping apertures, which are close to each other, and four deflectors which are positioned symmetrically with respect to the shaping apertures. The critical illumination condition is maintained by a condenser lens which is positioned between the LaB6 electron gun and shaping aperture. By tilting 45° between the beam side and raster scan direction, pattern edge roughness, including the 45° oblique pattern, may be zero at optimum dose and process conditions.