Space-charge-induced aberrations

The effect of Coulomb interactions in electron-beam lithography systems are usually described in terms of the blur induced by stochastic electron-elec tron interactions. Here, we show both by an efficient Monte Carlo simulatio n and by a global space-charge model, that the aberrations induced by the l ensing action of global space charge can be equally significant. For a 4:1 telecentric reduction projection optics operating at 100 kV beam energy and 25 mu A total current, we obtain about 150 nm blur independent of any stoc hastic effects. The global space-charge model requires less than 5 min comp utation on a 450 MHz workstation. The aberration coefficients of the global space-charge-induced lens can be evaluated, and because they scale directl y with the perveance of the beam, can be used to evaluate the global space- charge effect over a wide variety of conditions. When the Monte Carlo and g lobal space-charge models are used together, the stochastic-only portion of the beam blur can be extracted. (C) 1999 American Vacuum Society. [S0734-2 11X(99)13606-0].