Electron optics using multipole lenses for a low energy electron beam direct writing system

The Coulomb interaction is the dominant factor respecting the electron optical properties, and its dominance is particularly marked in the case of the low energy electron beam direct writing system. To reduce the Coulomb interaction contributions, we propose a concept: the use of a multipole electron optical system providing a nonrotationally symmetric cross section of the electron beam. The system consists of an illumination optics, character projection apertures, an imaging optics providing the electrostatic quadrupole quadruplets and deflectors with the optics length of 100 mm. The optical properties are optimized under the following conditions: main deflection field size of 0.5 mm×1.5 mm, beam convergence angle on the wafer of 1 mrad, shot size of 5 μm square, beam voltage of 5 kV, and reduction ratio of 10. The blur due to the Coulomb interaction is estimated using Monte Carlo simulation with a thin lens approximation. The calculated Coulomb blur can be reduced to less than 60 nm in the x–z plane and...