In electron-beam lithography, two well-known problems are proximity effects due to electron scattering and slow throughput because of limited exposure rate and resist sensitivity. We have investigated the generation of finely focused electron beams of low landing energy (?5 keV) and their application to materials processing. Lenses employing magnetic and retarding electric fields are found to have very low spherical and chromatic aberrations, thus facilitating the production of beams of low-energy electrons without seriously sacrificing current density. With such beams the power dissipated per unit volume at the surface of a bulk target is higher than with high-energy electrons, thus increasing the speed to exposure of very thin resists and dramatically reducing proximity effects. This compact volume of high-power dissipation is also attractive for selected area annealing.
Although low current beams of low energy electrons can be finely focused through the use of retarding field focusing optics, it had been suggested that the reduced axial spacing of the low energy electrons could lead to serious defocusing because of electron‐electron interactions. However, the Monte Carlo simulation of such electron‐electron interactions in the region between final lens and target plane shows that there are no appreciable differences in energy spread and spot diameter with beam currents up to 5 μA transported through aperture sizes greater than 0.01 mm in radius at energies of 10 keV, 1 keV, and 100 eV. Preliminary experimental results indicate that current density of 250 A/cm2 of 1 keV electrons can be obtained by using hairpin tungsten filaments.
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