US3852597A - Method and apparatus for observing a low magnification electron microscope image - Google Patents

Method and apparatus for observing a low magnification electron microscope image Download PDF

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Publication number
US3852597A
US3852597A US00359669A US35966973A US3852597A US 3852597 A US3852597 A US 3852597A US 00359669 A US00359669 A US 00359669A US 35966973 A US35966973 A US 35966973A US 3852597 A US3852597 A US 3852597A
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Prior art keywords
lens
aperture
excitation current
condenser lens
low magnification
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Expired - Lifetime
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US00359669A
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English (en)
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T Yanaka
K 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
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/261—Details
    • H01J37/265—Controlling the tube; circuit arrangements adapted to a particular application not otherwise provided, e.g. bright-field-dark-field illumination
    • 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

Definitions

  • ABSTRACT A method and apparatus for observing a low magnification wide field, low aberration electron microscope image characterized in that the objective lens is not used, the focal length of the final stage condenser lens is adjusted so as to focus a crossover image on an aperture located near an intermediate lens and the position of the specimen is kept fixed regardless of magnification range.
  • the specimen When observing a low magnification image with an electron microscope, the specimen is usually placed some little distance from the objective lens in order to increase the focal length and thereby widen the field of view, and also to enhance image contrast.
  • the use of a small diameter objective lens aperture for enhancing image contrast has the disadvantage of restricting the field of view. For instance, if a micron diameter aperture is used when observing an image magnified 1000 times, the diameter of the image on the photographic film or fluorescent screen is only about 20mm. Even if a larger aperture is used at the sacrifice of contrast, the diameter of the image will only be 100mm at most, which corresponds to a field of view of about 100 microns. This is not sufficient for practical purposes.
  • the image formed by the electron beam becomes distorted and blurred due to intermediate lens field (off-axial) aberration.
  • spond by preventing the specimen from moving during 3,629,575 describes a method for observing a low magnification image whereby the objective lens energizing current is adjusted to a fixed value lyingoutside the normal control range in order to shift the focal plane of the objective lens facing the image from the contrast intensifying diaphragm to the objective-limiting diaphragm.
  • lens aberration is appreciable making it impossible to obtain a low magnification image having the required amount of resolving power.
  • an object of this invention to provide a method and apparatus capable of displaying a high contrast, wide field, low aberration image.
  • Another object of this invention is to make the field of view of the low and high magnification images correimage observation.
  • FIGS. 1 and 2 are schematic diagrams showing the electron microscope according to this invention.
  • FIG. 3 is a schematic diagram showing the electron beam path of the microscope optical system shown in FIG. 1 incorporating the method according to this invention
  • FIG. 4 is a schematic diagram showing the electron optical system, complete with power circuits, of a practical embodiment of this invention.
  • FIG. 5 is a diagram showing the aberration features of electron optical system according to this invention.
  • a microscope column 1 comprises a chamber 2 containing an electron gun 3, an anode 4, first and second condenser lenses 5 and 6, a specimen chamber 7 containing a specimen 8, an objective lens 9, first and second intermediate lenses l0 and 11, a projector lens 12 and a viewing chamber 13 complete with a viewing window 14 and a fluorescent screen 15.
  • Excitation current supply sources 16 l7, l8, 19 are provided for the various lenses.
  • A' switch 20 is arranged between the objective lens 9 and its excitation current supply source 18.
  • a deflecting coil 21 is arranged above the sample and has an associated'deflecting current supply source 22.
  • a stigmator coil 23 for the objective lens is associated with current supply source 24.
  • a condenser lensaperture plate 25 is held by a supporting means 26.
  • the aperture plate is provided with three apertures, 25a, 25b, and 250, as shown in FIG. 2.
  • a contrast aperture plate 27 is held by a supporting means 28.
  • FIG. 3 shows the electron beam path of the microscope optical system shown in FIG. '1 incorporating the method according to this invention.
  • a four stage'image forming lens system is used in the embodiment as showmfive or more stages or three stages are, of course, applicable.
  • Thespecimen 8' is placed in the magnetic flux gap between the pole pieces of the objective lens as in the-case of high magnification image observation.
  • the aperture plate 27 is used for enhancing image contrastand can be used as a field limiting aperture in the conventional electron microscope.
  • the objective lens current is first of all switched off.
  • the second condenser lens aperture plate ispositioned so that the largest aperture 25a having a diameter of 0.5mm or more aligns with the beam path and the contrast aperture plate 27 is similarly inserted in the electron beam path by means of the supporting means 28.
  • the axis of the electron irradiating lens system including the final stage condenser lens 6 and the axis of the first intermediate lens 10 are then mutually aligned by means of the deflecting coil.
  • the condenser lens excitation current is adjusted so as to form a crossover image on the aperture plate 27.
  • the first intermediate lens current is adjusted so as to produce a specimen imageon the image source point of the second interme diate lens 11. By so doing, a low magnification wide field image is displayed on the fluorescent screen 15.
  • FIG. 4 shows the electron optical system, complete with power circuits, of a practical embodiment utilizing the method according to this invention.
  • the supply source 22 of the deflecting coil 21 is controlled by the switch. 20.
  • the switch When the switch is disengaged, the axis of the electron beam irradiating lens system is automatically aligned with the axis of the first flecting coil 21.
  • the switch 20 is disengaged automatically when .the image magnification decreases to below, let's say 1,000 times (or 2,000 times or3,000 times if desired) by controlling the current supply source 19. 7
  • a is the diameter of the observed specimen area
  • b is the diameter of the aperture
  • K is the distance between the aperture and the specimen 8
  • the intensity of the contrast depends on the aperture angle oz, at which the electrons transmitted through the specimen pass through the contrast aperture 27 and the quantity of electrons scattered by the specimen which are blocked by the aperture plate 27, as shown by the broken lines in FIG. 3.
  • the aperture angle or is given by a, C/L, where C is the diameter of the aperture 27.
  • C is the diameter of the aperture 27.
  • the aperture angle ct will be 10 rad. or smaller depending on the value of L which is roughly 100 mm' to 300 mm in conventional electron microscopes. This compares ver y favorably with the aperture angle utilizing the method as practiced by the present state of the art which is about 10 rad.; at best l0 rad. assuming a very small diameter contrast aperture 1 is used.
  • the aperture angle is 10 rad. or smaller, due to its negligible proportions.
  • Image blurring caused by image field curvature and field astigmatism is also proportional to ct and, since the electron beam passes near the optical axis of the first intermediate lens, the various aberration coefficients are minimized.
  • the blurring factor AF due to field chromatic aberration and the over fringe width Dsf due to the defocus factor caused by image field curvature and field astigmatism are given as follows based on Glasers Blenden Freien System" of calculation.
  • FIG. 5 shows the values of AF and Dsfwith respect to I.
  • A indicates the position I L at which the contrast aperture plate is placed.
  • Dsf and AF are very small.
  • a method for observing a low magnification image using a typical electron microscope having an electron beam condenser lens system including one or more lenses, and a projector lens'system including an objective lens and one or more intermediate lenses arranged in sequential order along the optical axis of the microscope, an imaging means and means for adjusting the excitation current to the lens comprising the steps for:
  • a projector lens system including an objective lens and at least intermediate lenses and associated excitation current sources;
  • D a switching means arranged between the objective lens and its associated excitation current supply source for disconnecting the excitation current
  • E. means for replacing the final stage condenser lens aperture with an aperture having a diameter at least 0.5mm;
  • F. means for placing a contrast aperture in the electron beam path adjacent the intermediate lens on the object side thereof;
  • G first means for adjusting the condenser lens excitation current soas to form a focal point on the contrast aperture when observing a low magnification image
  • H second means for adjusting the current in the projector lens system to focus a low magnification image on the imaging means.
  • a projector lens system including an objective lens and at least one intermediate lens and associated excitation current sources;
  • D a switching means arranged between the objective lens and its associated excitation current supply source for disconnecting the excitation current
  • E. means for replacing the final stage condenser lens aperture with an aperture having a diameter of at least 0.5mm;
  • F. means for placing a contrast aperture in the electron path adjacent the intermediate lens on the object side thereof;
  • G first means for adjusting the condenser lens excitation current so as to form a focal point on the contrast aperture when observing a low magnification image
  • I second means for adjusting the current in the projector lens system to focus a low magnification image on the imaging means.
  • a projector lens system including an objective lens and at least one intermediate lens
  • D a switching means arranged between the objective lens and its associated excitation current supply source for disconnecting the excitation current
  • E. means for replacing the final stage condenser lens aperture with an aperture having a diameter of at least 0.5mm;
  • F. means for placing a contrast aperture in the electron beam path adjacent the intermediate lens on the object side thereof;
  • G first means for adjusting the condenser lens excitation current so as to form a focal point on the contrast aperture when observing a low magnification image

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Sources, Ion Sources (AREA)
US00359669A 1972-05-22 1973-05-14 Method and apparatus for observing a low magnification electron microscope image Expired - Lifetime US3852597A (en)

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JP47050594A JPS5136196B2 (fr) 1972-05-22 1972-05-22

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4209702A (en) * 1977-07-25 1980-06-24 Kabushiki Kaisha Akashi Seisakusho Multiple electron lens
US4245159A (en) * 1977-11-25 1981-01-13 Dr. Ing. Rudolf Hell Gmbh Quick-acting electron-optical lenses
US5336891A (en) * 1992-06-16 1994-08-09 Arch Development Corporation Aberration free lens system for electron microscope
US5627373A (en) * 1996-06-17 1997-05-06 Hewlett-Packard Company Automatic electron beam alignment and astigmatism correction in scanning electron microscope
US20080048117A1 (en) * 2006-08-22 2008-02-28 Hitachi High-Technologies Corporation Scanning Electron Microscope
US20090039258A1 (en) * 2005-01-13 2009-02-12 Toshifumi Honda Scanning Electron Microscope And Method For Detecting An Image Using The Same
US20140001355A1 (en) * 2009-08-10 2014-01-02 Hitachi High-Technologies Corporation Charged particle beam device and image display method

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2494442A (en) * 1946-01-05 1950-01-10 Hartford Nat Bank & Trust Co Electron microscope comprising magnetic focusing
US2802110A (en) * 1953-09-04 1957-08-06 Kazato Kenji Electron microscope
US3090864A (en) * 1960-06-18 1963-05-21 Kabushikikaisha Nihondenshi Ko Electron microscope
US3359418A (en) * 1964-12-11 1967-12-19 Gunter F Bahr Electromagnetic actuating means for a shutter mechanism in an electron microscope
US3374346A (en) * 1964-07-15 1968-03-19 Hitachi Ltd Spectroscopic electron microscope wherein a specimen is irradiated with x-rays and the electrons emitted are energy analyzed
US3560781A (en) * 1967-02-24 1971-02-02 Max Planck Gesellschaft Corpuscular beam microscope apparatus
US3629575A (en) * 1966-08-13 1971-12-21 Philips Corp Electron microscope having object limiting and contrast intensifying diaphragms
US3715582A (en) * 1970-02-13 1973-02-06 Hitachi Ltd Method of and apparatus for attaining focusing following variation in magnification in electron microscope

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2494442A (en) * 1946-01-05 1950-01-10 Hartford Nat Bank & Trust Co Electron microscope comprising magnetic focusing
US2802110A (en) * 1953-09-04 1957-08-06 Kazato Kenji Electron microscope
US3090864A (en) * 1960-06-18 1963-05-21 Kabushikikaisha Nihondenshi Ko Electron microscope
US3374346A (en) * 1964-07-15 1968-03-19 Hitachi Ltd Spectroscopic electron microscope wherein a specimen is irradiated with x-rays and the electrons emitted are energy analyzed
US3359418A (en) * 1964-12-11 1967-12-19 Gunter F Bahr Electromagnetic actuating means for a shutter mechanism in an electron microscope
US3629575A (en) * 1966-08-13 1971-12-21 Philips Corp Electron microscope having object limiting and contrast intensifying diaphragms
US3560781A (en) * 1967-02-24 1971-02-02 Max Planck Gesellschaft Corpuscular beam microscope apparatus
US3715582A (en) * 1970-02-13 1973-02-06 Hitachi Ltd Method of and apparatus for attaining focusing following variation in magnification in electron microscope

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4209702A (en) * 1977-07-25 1980-06-24 Kabushiki Kaisha Akashi Seisakusho Multiple electron lens
US4245159A (en) * 1977-11-25 1981-01-13 Dr. Ing. Rudolf Hell Gmbh Quick-acting electron-optical lenses
US5336891A (en) * 1992-06-16 1994-08-09 Arch Development Corporation Aberration free lens system for electron microscope
US5627373A (en) * 1996-06-17 1997-05-06 Hewlett-Packard Company Automatic electron beam alignment and astigmatism correction in scanning electron microscope
US20090039258A1 (en) * 2005-01-13 2009-02-12 Toshifumi Honda Scanning Electron Microscope And Method For Detecting An Image Using The Same
US8405025B2 (en) * 2005-01-13 2013-03-26 Hitachi High-Technologies Corporation Scanning electron microscope and method for detecting an image using the same
US20080048117A1 (en) * 2006-08-22 2008-02-28 Hitachi High-Technologies Corporation Scanning Electron Microscope
US7772553B2 (en) * 2006-08-22 2010-08-10 Hitachi High-Technologies Corporation Scanning electron microscope
US20140001355A1 (en) * 2009-08-10 2014-01-02 Hitachi High-Technologies Corporation Charged particle beam device and image display method
US9202669B2 (en) * 2009-08-10 2015-12-01 Hitachi High-Technologies Corporation Charged particle beam device and image display method for stereoscopic observation and stereoscopic display

Also Published As

Publication number Publication date
DE2326042A1 (de) 1973-12-06
DE2326042B2 (de) 1975-07-03
JPS4917168A (fr) 1974-02-15
JPS5136196B2 (fr) 1976-10-07

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