Radiant energy – With charged particle beam deflection or focussing – Magnetic lens
Patent
1996-05-23
1998-03-24
Anderson, Bruce
Radiant energy
With charged particle beam deflection or focussing
Magnetic lens
250396R, H01J 37145
Patent
active
057315868
ABSTRACT:
There is disclosed a high-resolution magnetic-electrostatic compound objective lens for use in a scanning electron microscope, the objective lens having reduced spherical aberration and chromatic aberration. The lens comprises a substantially conically-shaped magnetic pole piece, a coil wound along the inner surface of the magnetic pole piece, a hollow insulator disposed along the inner surface of the coil and a high-resistivity film disposed along the inner surface of the insulator. When the coil is energized, an axially symmetrical magnetic field is produced inside the magnetic lens. The obtained axial magnetic flux density distribution has a peak near the bottom end of the magnetic pole piece. The principal plane of the magnetic lens is brought close to the specimen and results in smaller aberrations. When a high voltage is applied to the high-resistivity film from a voltage source, a feeble electrical current flows from the top end of the film to the bottom end, thus producing a voltage drop in the longitudinal direction of the film. Since the shape and the thickness of the high-resistivity film are symmetrical with respect to the optic axis, the equipotential surface is axially symmetrical.
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"Compound magnetic and electrostatic lenses for low-voltage applications", J. Frosien, E. Plies and K. Anger, J. Vac. Sci. Technol. B, vol. 7, No. 6, Nov./Dec. 1989.
Anderson Bruce
Jeol Ltd.
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