Radiant energy – With charged particle beam deflection or focussing – Magnetic lens
Patent
1997-01-14
2000-05-23
Anderson, Bruce
Radiant energy
With charged particle beam deflection or focussing
Magnetic lens
250396R, 250305, H01J 3714
Patent
active
060668520
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electronic energy filter which is arranged to separate only electrons having specific energy from an electron beam and form an image of those electrons.
BACKGROUND ART
In a transmission electron microscope, electrons transmitted through a specimen suffer from energy loss that is peculiar to one or more elements composing the specimen. To overcome this shortcoming, the electrons transmitted through the specimen are passed through an energy filter for analyzing energy of those electrons, separating only the electrons suffering from the specific energy loss, and forming an image of the separated electrons. The formed image corresponds to a mapping image of one or more specific elements contained in the specimen. Further, the use of only the electrons having specific energy for forming an image allows the energy loss of the electrons caused by the thickness of the specimen to be restricted to only specific electrons. The resulting image has excellent contrast.
For the electron energy filter used for this kind of purpose, there have been known an omega type energy filter (U.S. Pat. No. 4,740,704) and an alpha type energy filter (U.S. Pat. No. 4,760,261).
The omega type energy filter is composed of three electromagnets as shown in FIG. 2. The first electromagnet 1 has an opposite deflecting direction to the second and the third electromagnets 2 and 3. Incident electrons 4 are traced like an omega (.OMEGA.) and are fired in the same direction as the incident one, for selecting only the electrons having specific energy loss. As shown, a numeral 5 denotes a crossover point. A numeral 6 denotes an inlet image surface. A numeral 7 denotes an outlet image surface. A numeral 8 denotes an energy dispersion surface.
The alpha type energy filter is composed of three electromagnets 11, 12 and 13 having the same deflecting directions as each other as shown in FIG. 3. Incident electrons 4 are traced like an alpha (.alpha.) and finally outgoes in the same direction as the incident one, for selecting only the electrons that suffer from specific energy loss. Another kind of alpha type energy filter is shown in FIG. 4 (Perez, J. P., Sirven, J., Sequela, A., and Lacaze, J. C., Journal de Physique, (Paris), 45, Coll. Cs, 171 to 174 (1984)). This energy filter is constructed so that an electromagnet 14 having a deflecting angle of 70.degree. is located as opposed to the other electromagnet 15 having a deflecting angle of 220.degree. with narrow middle space 16, in which those electromagnets yield the corresponding magnetic field intensities. In the construction, an incident electron beam 4 goes around the inside of the filter for analyzing the energy of the electron beam.
DISCLOSURE OF INVENTION
The electron energy filter is required to form an energy dispersion surface and an image surface with a small aberration. That is, the electrons 4 transmitted through the specimen enter at the crossover point 5 formed on a lens into the electron energy filter, pass through the filter and reach the energy dispersion surface 8 where the electrons having the specific energy are converged in the same direction though the electrons having the other energy are dispersed. On the energy dispersion surface 8, hence, the aberration has to be eliminated in order to restrict a lower resolution of the electrons passing through a slit. Moreover, the image formed on an inlet image surface 6 before the electron energy filter is required to be similarly formed on an outlet image surface point 7. Hence, the aberration has to be reduced to a minimum for suppressing the distortion of the image as much as possible.
A convergence condition of the electron optical system provided in the electron energy filter arranged to use a fanlike electromagnet may be calculated by using a calculation program of an ion optical system used for designing a mass spectrometer. The convergence characteristic up to a three degrees, which considers the effect of an end magnetic field, can be precisely calculated by the calcu
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Taniguchi Yoshifumi
Taya Shunroku
Anderson Bruce
Hitachi , Ltd.
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