US3201588A - Electrostatic immersion objective comprising an improved intermediate electrode - Google Patents

Electrostatic immersion objective comprising an improved intermediate electrode Download PDF

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Publication number
US3201588A
US3201588A US238239A US23823962A US3201588A US 3201588 A US3201588 A US 3201588A US 238239 A US238239 A US 238239A US 23823962 A US23823962 A US 23823962A US 3201588 A US3201588 A US 3201588A
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US
United States
Prior art keywords
cathode
intermediate electrode
bore
electrode
anode
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Expired - Lifetime
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US238239A
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English (en)
Inventor
Duker Heinrich
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Truh Tauber & Co A G
Truh Tauber & Co AG
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Truh Tauber & Co A G
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Publication date
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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
    • H01J37/285—Emission microscopes, e.g. field-emission microscopes
    • 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
    • H01J37/12—Lenses electrostatic

Definitions

  • FGS. 1, 2 and 3 show known forms of electrostatic immersion objectives
  • FIG. 4 shows an electrostatic immersion objective constructed in accordance with the invention
  • FG. 5 shows the electrostatic immersion objective of EG. 4 connected to a source of operating potentials
  • FIG. 6 shows an enlarged cross-section of an intermediate electrode according to one embodiment of the invention.
  • FIG. 7 shows an enlarged cross-section of an intermediate electrode and cathode according to another embodiment of the invention.
  • the object consists of a cathode K, a control electrode S and an anode A.
  • the cathode K is at a strongly negative potential with respect to the anode;
  • the control electrode S is at a potential which lies in the region ofthe cathode potential.
  • the electrons emitted from the cathode K under some influence are accelerated by the electrostatic iield between the anode A and cathode K and pass through the hole in the anode A into the image space.
  • the arrangement as a whole acts on the electrons like a converging lens, so that in the image space below the anode A an image of tie surface of the cathode K is produced by the emitted electrons.
  • the object of the image is therefore the surface of the cathode K.
  • the resolving power ot such an arrangement is given by the formula denotes the resolving power, e is the mean velocity of the emitted electrons, E is the eld intensity in front of the cathode K and k is a numerical factor depending on the geometry of the objective and the nature of the object.
  • the velocity distribution and hence the value cannot be iniiuenced by the form of objective.
  • the factors E and k have to be intluenced.
  • the field intensity E in front of the cathode K should be as high as possible, while the factor k, which includes the image forming properties of the objective, should be made as small as possible.
  • Good image forming properties mean small lens errors.
  • the immersion objective shown in FlG. 1 represents a compromise which does not create optimal conditions.
  • the electrostatic iield between the anode A and cathode K is heavily screened by the cont-rol electrode S.
  • the iield intensity in front of the cathode K can now be intluenced by altering the distance between the cathode K and the intermediate electrode Z without the properties of the Einzel lens being affected.
  • the properties or" the Einzel len-s can be altered without affecting the field intensity in front of the cathode.
  • an electrostatic immersion objective comprising a cathode, an intermedlate electrode, a control electrode and an anode.
  • the intermediate and control electrodes and the anode each having a bore or opening.
  • the thickness of the intermediate electrode which lies between the cathode and the control electrode is, at least in the vicinity of its bore in it, at most a fifth of the distance between cathode and intermediate electrode.
  • the diameter of the bore in the intermediate electrode is at most a fifth of the distance between cathode and intermediate electrode.
  • FIG. 3 Such a construction is shown in FIG. 3.
  • the dimensions are as follows: the distance a between cathode K and intermediate electrode Z is from 1 to 2 mm. (millimeter-s); the thickness z of the intermediate electrode Z measures 2 mm. (millimeters); the diameter Dz of the bore in the intermediate electrode Z is 1 mm.
  • the immersion objective consists of a cathode K, an intermediate electrode Z, a control electrode S and an anode A.
  • the dimensions in this embodiment are as follows: the distance a is 3 mm. (millimeters); the thickness z of the intermediate electrode is 0.25 mm. (millimeter) in .the middle, but it increases outwardly for greater strength; the diameter of the bore Dz in the intermediate electrode is 0.3 mm. (millimeter).
  • the electrostatic eld between the cathode K and intermediate electrode Z remains homogeneous in this arrangement until near the bore,
  • the characterizing feature of the embodiment described is that the thickness of the intermediate electrode Z is less than a tenth of the distance between cathode K and intermediate electrode Z and the diameter of the bore in theintermediate electrode Z is at most a tenth of the distance between cathode and intermediate electrode.
  • edges Be of the bore may be rounded as shown in FIG. 6.
  • Funnel-shaped bores Bf are particularly suitable, the narrow part of the bore preferably facing the cathode K.
  • the intermediate electrode Z and cathode K By selecting the dimensions of the intermediate electrode Z and cathode K in accordance with the invention, conditions are created in which a homogeneous electrostatic field of great field intensity can be produced -between the cathode K and the intermediate electrode Z without regard to the succeeding electrodes. Because of this the image brightness is increased on the one hand and the prerequisites for obtaining an image with good resolution are fulfilled on the other. This image has to be magnified by the Einzel lens. It is therefore essential for the good resolution to be retained as far as possible For this reason a lens with the least possible aberrations should be chosen. Septiers experiments were with a thick Einzel lens as used for projection lenses low in distortion. These projectionsl lenses are not suitable for use as objective lenses, however, because of their other lens errors. The objective shown in FIG. 4 therefore has a thin Einzel lens of the kindkused as objective lenses in transmission microscopes. In this embodiment the intermediate electrode Z, the control electrode S and the anode A are so constructed that together they have the properties of a good electrostatic objective lens
  • the small bore in the intermediate electrode Z normally, after manufacture and in use, shows certain deviationsfrom rotational symmetry which make themselves Visible in the image as astigmatism. Such errors in the image can be compensated by suitable transerse displacement or by inclination of the various electrodes towards each other. It is therefore an advantage if one or more electrodes can be adjusted while in use. ⁇
  • the field penetration through the bore'in the intermediate electrode Z is very small.
  • the control electrode S therefore really acts as the middle electrode of an Einzel lens and can be operated at a potential identical to or only little different frorn the cathode potential.
  • a special feature of the preferred embodiment is therefore that the potential difference between the control electrode S and the cathode K is less than a tenth of the potential difference between the cathode K and anode A.
  • This potential difference is preferably made variable within the limits given; it then iniluences the focal length of the immersion objective and can be used for sharpfocussing the image.
  • a variable potential which is small compared with the cathode-anode potential difference is applied to the control electrode S to sharp-focus the image. This'can be accomplished by connecting the moving arm W of potentiometer R to the control electrode S as shown in FG. 5.
  • a lower limit is set on the dimensions of the bore in the intermediate electrode Z by the fact that this bore restricts the image size. If the minimum final magnification is set at ldtx and the image diameter at this magnification is set at 60 mm. (millimeters), an approximate lower limit for the bore diameter is rfield, the negative ions which are otherwise masked as to intensity by the electrons stay behind in the beam.
  • the immersion objective is then also suitable for taking ionoptical surface pictures. If all potentials applied to the immersion objective are subjected to polarity reversal, i.e. the cathode and anode interchange, the objective is suitable for image formation with positive ions.
  • the immersion objective of the invention may therefore be adapted to form images both with electrons and with ions.
  • An electrostatic immersion objective comprising a cathode, an intermediate electrode, a control electrode, and an anode, said cathode, intermediate electrode, control electrode and anode beingserially arranged in spaced Y relation in the aforesaid order, the intermediate and conr trol electrodes and anode having aligned bores, said in the bore of the intermediate electrode, said diameter of the bore of the intermediate electrode being less than one-fth of said distance between the flat surfaces of the. cathode and the intermediate electrode while said thick-- 5 ness of the intermediate electrode at said bore is less than one-fifth ofthe aforesaid distance.
  • the thickness of said intermediate electrode is, at least in the region of its bore, a tent'n of the distance between said cathode and said intermediate electrode, and the diameter of the bore in said intermediate electrode is substantially a tenth of the distance between said cathode yand said intermediate electrode.
  • the objective as claimed in claim 1 including means for maintaining a given potential dierence between said anode and said cathode, means for maintaining said intermediate electrode .at substantially the same potential as said anode, and means for maintaining said control electrode at substantially the same potential as said cathode.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Beam Exposure (AREA)
  • Electron Sources, Ion Sources (AREA)
US238239A 1961-11-22 1962-11-16 Electrostatic immersion objective comprising an improved intermediate electrode Expired - Lifetime US3201588A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH1359961A CH391128A (de) 1961-11-22 1961-11-22 Elektrostatisches Immersionsobjektiv

Publications (1)

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US3201588A true US3201588A (en) 1965-08-17

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US238239A Expired - Lifetime US3201588A (en) 1961-11-22 1962-11-16 Electrostatic immersion objective comprising an improved intermediate electrode

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US (1) US3201588A (de)
CH (1) CH391128A (de)
DE (1) DE1188742B (de)
FR (1) FR1339891A (de)
GB (1) GB1025674A (de)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2842527C3 (de) * 1978-09-29 1981-12-17 Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V., 3400 Göttingen Elektrostatische Emissionslinse
GB9016567D0 (en) * 1990-07-27 1990-09-12 Marconi Space Systems Limited Ion thruster vector control

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2410658A (en) * 1943-07-16 1946-11-05 Rca Corp Limiting aperture for electron image devices
US2536878A (en) * 1948-12-03 1951-01-02 Farrand Optical Co Inc Electron lens
US2759117A (en) * 1952-05-16 1956-08-14 Farrand Optical Co Inc Electron lens
US2814729A (en) * 1956-10-01 1957-11-26 Gen Electric X-ray microscope

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2410658A (en) * 1943-07-16 1946-11-05 Rca Corp Limiting aperture for electron image devices
US2536878A (en) * 1948-12-03 1951-01-02 Farrand Optical Co Inc Electron lens
US2759117A (en) * 1952-05-16 1956-08-14 Farrand Optical Co Inc Electron lens
US2814729A (en) * 1956-10-01 1957-11-26 Gen Electric X-ray microscope

Also Published As

Publication number Publication date
CH391128A (de) 1965-04-30
GB1025674A (en) 1966-04-14
DE1188742B (de) 1965-03-11
FR1339891A (fr) 1963-10-11

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