US3863069A - Electron microscope with energy analyzer - Google Patents

Electron microscope with energy analyzer Download PDF

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Publication number
US3863069A
US3863069A US435725A US43572574A US3863069A US 3863069 A US3863069 A US 3863069A US 435725 A US435725 A US 435725A US 43572574 A US43572574 A US 43572574A US 3863069 A US3863069 A US 3863069A
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Prior art keywords
lens
slit
electron beam
energy
electron
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Expired - Lifetime
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US435725A
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English (en)
Inventor
Kohei Shirota
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Jeol Ltd
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Jeol Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
    • H01J37/05—Electron or ion-optical arrangements for separating electrons or ions according to their energy or mass
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
    • H01J37/10—Lenses
    • H01J37/14—Lenses magnetic
    • H01J37/141—Electromagnetic lenses

Definitions

  • This invention relates to an apparatus for measuring the energy of an electron beam by utilizing the imageforming lens system in a conventional electron microscope.
  • a microscopic image is formed by passing an electron beam through a thin specimen.
  • it is of prime importance to analyze the specimen by measuring the energy of the electron beam passing through a specific spot on the specimen.
  • an electron beam energy analyzer which not only functionally restricts the microscope but also adversely affects the operability of the instrument.
  • the electron beam path is split by the intermediate lens field chromatic aberration in accordance with the energy of the electron beam.
  • said aperture image is also split, an energy spectrum is formed and magnified images are projected onto a fluorescent screen or photoplate by the projector lens.
  • a typical transmission electron microscope is provided with additional features which enable the use of the field (offaxial) chromatic aberration of the intermediate lens to disperse and thereby enable analysis of the energies of the electrons in the electron beam.
  • an electron gun creates an electron beam which is condensed and directed by a condensing lens system.
  • the condensing lens system comprises two condenser lenses enabling the direction of the electron beam along an optical axis for striking the thin specimen substantially perpendicular thereto.
  • the microscope includes an image forming lens system comprising at least an objective lens and an intermediate lens and usually a projector lens. The specimen is placed near or within the objective lens in a typical fashion.
  • shiftable baffle is provided with a slit therein to be positioned (during beam energy analysis) aligned with the optical axis in the image forming lens system to substantially prevent an electron beam passing through said specimen off the axis from also passing through said slit.
  • This is achieved, for example, by placing the slit at the image plane of the objective lens.
  • Deflecting devices such as deflecting coils (during the beam energy analysis) deflect the electron beam passing through said baffle to enter the intermediate lens offaxially so that the intermediate lens disperses the beam according to the energies of the electrons therein.
  • the dispersed electron beam is then directed at an imaging device such as a fluorescent screen.
  • a projector lens may project the dispersed beam upon the screen.
  • a deflection coil deflects the dispersed beam to pass through the vicinity of the front focal point of the projector lens so that the image of the dispersed beam will be about at the center of the screen placed at the imaging plane of the projector lens.
  • the deflection devices are disabled when the microscope is being used for creating transmission electron images and not for analyzing the energies of the transmitted electron beam. It may also be necessary to withdraw the baffle from the electron optical axis.
  • FIG. 1 is a schematic diagram showing the electron microscope according to this invention.
  • FIG. 2 is a schematic diagram showing the electron beam path of the microscope optical system shown in FIG. 1;
  • FIGS. 3 and 4 are schematic diagrams showing the electron beam paths of the embodiments according to this invention respectively;
  • FIG. 5 is a schematic diagram of an optical system in which the intermediate lens of a conventional apparatus is used as an energy analyzer
  • FIG. 6 is a schematic diagram for explaining the field chromatic aberration of an objective lens
  • FIG. 7 is a schematic diagram for explaining the field chromatic aberration of an intermediate lens
  • FIG. 8 is a schematic diagram for explaining the various aberrations of an intermediate lens.
  • FIG. 9 is a schematic drawing of magnetic pole pieces of the intermediate lens.
  • FIG. 1 is a sectional view of a microscope column 1 at the upper end of which an electron gun 2 comprising a filament, a Wehnelt electrode 3, and an anode 4 is provided.
  • Condenser lenses 5 and 6 operate to make the electron beam generated by electron gun I run almost in parallel with the optical axis thereby striking a specimen 7 more or less perpendicularly.
  • the specimen 7 is positioned in the gap between the objective lens magnetic pole pieces by means of a specimen holding and manipulating device (not shown) installed in the specimen chamber 8.
  • the electron beam thus irradiating the specimen 7, passes through an image forming system consisting of an objective lens 9, an intermediate lens 10 and a projector lens 11 which operates to form and project a magnified image of the specimen on a fluorescent screen 12 installed in a viewing chamber 13 equipped with a viewing window 14.
  • the embodiments according to this invention are provided with a shifting device 15, located between the objective lens 9 and the intermediate lens 10, for inserting and withdrawing a baffle having a slit 16 therein to and away from the optical axis.
  • the stages of deflection coils 17a and 17b, complete with a power source 18 are located between the objective lens 9 and the intermediate lens 10.
  • a single deflection coil 19, complete with a power source 20 is located between the intermediate lens and the projector lens 11.
  • FIG. 2 is a ray diagram showing the center axis of the electron beam paths obtained by using the apparatus illustrated in FIG. 1.
  • those having the same energy, after passing through the slit 16 are deflected by deflection coils 17a and 17b and enter the intermediate lens 10 off-axially.
  • the slit By manipulating the slit shifting device (not shown) the slit can be located close to the axis 21 on the image plane of the objective lens 9 and by controlling the current passing through the deflection coils 17a and 17b, the electron beam can be deflected away from the slit.
  • the electron beam having entered and passed through the intermediate lens off-axially forms a slit image at the imaging position of the intermediate lens which is projected onto the fluorescent screen 12 by the projector lens 11.
  • the electron beam would enter the projector lens off-axially and the slit image would appear well off-center of the fluorescent screen as shown by the broken line.
  • the electron beam is deflected to pass through the projector lens in the vicinity of the lens axis thereby projecting a magnified slit image onto the approximate center of the fluorescent screen as shown by the solid line.
  • FIG. 3 is a ray diagram showing the electron beam path obtained by a simplified version of the apparatus illustrated in FIG. 1.
  • the deflection coil I9 has been dispensed with and one stage deflecting coil 17c located just behind the slit I6 is used instead of the two deflecting coils 17a and 17b.
  • a simple optical system is provided which is almost as effective as the one shown in FIG. 2.
  • FIG. 4 is a ray diagram showing the center axis and electron beam paths in one embodiment according to this invention, which explains the principle of this invention.
  • an electron beam having two different energies is split into two beam components by the field chromatic aberration of the intermediate lens with the result that each respective beam component produces a slit image on the fluorescent screen 12.
  • information on the specimen can be obtained by analyzing the energy of the transmitted electrons since part of the energy, depending on the specimen material, is lost when the beam passes through the specimen. Accordingly, in the optical system illustrated in FIG. 4, many slit images, i.e. energy spectra, are produced on the fluorescent screen 12.
  • FIG. 5 is a ray diagram showing an optical system not according to this invention, in which the intermediate lens of a conventional apparatus is used as an energy analyzer.
  • the slit 16 is located at some distance from the optical axis so that the electron beam enters the intermediate lens off-axially.
  • the electron beam which passes through a slit 16 is affected by the field chromatic aberration of the objective lens because said beam has passed through the objective lens offaxially.
  • FIG. 6 illustrates the field chromatic aberration of an objective lens.
  • the two electron beams passing through the lens off-axially have focal lengths which differ according to the energy of the respective electron beams.
  • the energy spectrum is measured without knowing for sure through which part of the specimen the electron beam is passed.
  • the optical system according to this invention the adverse effect of the objective lens field chromatic aberration is eliminated by utilizing the electron beam passing through the center of the objective lens.
  • FIG. 7 is a ray diagram for explaining the field chromatic aberration of an intermediate lens.
  • the diagram shows the electron beam path for dispersing the energy of a spot image formed by an objective lens at a distance Z, from an intermediate lens, the image of said spot image being formed on the image forming plane of said intermediate lens located at a distance Z, from said intermediate lens on the projector lens (not shown) side.
  • the energy dispersion 8H on the image plane is expressible as where a is the incident angle of the electron beam.
  • M is the magnification of the lens
  • V is the accelerating voltage of theelectron beam
  • AV variation width of the electron beam energy
  • Cr is the (onaxis) chromatic aberration coefficient of the intermediate lens.
  • the various lens aberrations for example in F IG. 8. the amount of de-focus A fi, image blurring SSL and image shift 1-1 in terms of the image forming plane of the intermediate lens can be expressed as follows:
  • the half-width value of the magnetic field distrito a microscope using a three-stage or more image bution of the magnetic field produced by the intermediforming lens system comprising, for example, an objecate lens magnetic pole pieces shown in FIG. 9' is extive lens, two intermediate lens, and two projector lens.
  • s is the distance between an upper pole piece 23 and a lower P Piece 24 and 1, 2 e the inside
  • an image forming lens system comprising at least diameters of the pp P Pieces and the lower an objective lens and intermediate lenses defining pole pieces as shown in FIG. 9. an i l axis,
  • shiftable baffle means having a slit therein posiduced by such pole pieces is Bell-shaped as manifested tionable during beam energy analysis to align the by the theory based on Glasers Aberration Theory; slit with the optical axis of th image forming lens to moreover, by taking into account the fact that the absosubstantially prevent an electron beam passing lute value
  • An intermediate lens satisfying such requirements is capable of reducing lens aberrations other than field chromatic aberration. to a minimum; in addition to which, the image-forminglens system, when used as an electron energy analyzer would guarantee sufficient en- ..is Obs r cted. t6 the abo e through the following stage lenses in the vicinity of the lens axis. described embodiments; for example, it can be applied therein,
  • imaging means upon whichthe dispersed beam is projected such that the beam energy may be analyzed

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
US435725A 1973-01-31 1974-01-23 Electron microscope with energy analyzer Expired - Lifetime US3863069A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP48012654A JPS5145221B2 (de) 1973-01-31 1973-01-31

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JP (1) JPS5145221B2 (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4160905A (en) * 1976-11-27 1979-07-10 Kratos Limited Electron microscopes
US5336885A (en) * 1991-10-24 1994-08-09 U.S. Philips Corporation Electron beam apparatus
US20080179536A1 (en) * 2004-06-28 2008-07-31 Hitachi High-Technologies Corportion Changed particle beam emitting device and method for adjusting the optical axis

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3256432A (en) * 1962-03-27 1966-06-14 Hitachi Ltd Equal energy selection in an electron microscope using electron optics
US3619607A (en) * 1967-03-30 1971-11-09 Takeo Ichinokawa Electron microscope including an electromagnetic electron energy analyzing lens

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3256432A (en) * 1962-03-27 1966-06-14 Hitachi Ltd Equal energy selection in an electron microscope using electron optics
US3619607A (en) * 1967-03-30 1971-11-09 Takeo Ichinokawa Electron microscope including an electromagnetic electron energy analyzing lens

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4160905A (en) * 1976-11-27 1979-07-10 Kratos Limited Electron microscopes
US5336885A (en) * 1991-10-24 1994-08-09 U.S. Philips Corporation Electron beam apparatus
US20080179536A1 (en) * 2004-06-28 2008-07-31 Hitachi High-Technologies Corportion Changed particle beam emitting device and method for adjusting the optical axis

Also Published As

Publication number Publication date
JPS49100951A (de) 1974-09-24
JPS5145221B2 (de) 1976-12-02

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