US3890533A - Thermal emission type electron gun - Google Patents

Thermal emission type electron gun Download PDF

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Publication number
US3890533A
US3890533A US377812A US37781273A US3890533A US 3890533 A US3890533 A US 3890533A US 377812 A US377812 A US 377812A US 37781273 A US37781273 A US 37781273A US 3890533 A US3890533 A US 3890533A
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United States
Prior art keywords
filament
wehnelt electrode
opening
anode
wehnelt
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US377812A
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English (en)
Inventor
Akira Tanaka
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Jeol Ltd
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Jeol Ltd
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Filing date
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
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H01J37/063—Geometrical arrangement of electrodes for beam-forming

Definitions

  • ABSTRACT A thermal emisssion type electron gun of improved design embodying an improved Wehnelt electrode and an improved filament arrangement with respect to the Wehnelt electrode thereby ensuring the generation of an electron beam having a high degree of parallelism, high density and uniformity.
  • the thermal emission type electron gun presently in use is inescapable of satisfying all the above requirements. hence the quality of the microscope image leaves a lot to be desired.
  • the reason for this, I have found is primarily related to the improper shape of the Wehnelt electrode and the improper position of the filament with respect to the Wehnelt electrode in prior art devices.
  • An advantage of this invention is to provide a thermal emission type electron gun capable of generating an electron beam having the required high degree of parallelism, high density and uniformity by improving the shape of the Wehnelt electrode and rearranging the filament with respect to the Wehnelt electrode.
  • a further advantage of this invention is to increase the effective working life of the filament.
  • this invention is characterized in part by the fact that the distance H between the tip of the filament and the lower rim of the Wehnelt electrode opening through which the electron beam passes typically satisfies the relations 0.40 S H s 0.8D, where D is the diameter of the Wehnelt electrode opening.
  • the distance between the filament and the Wehnelt electrode is large enough to prevent microdischarge, thereby prolonging the effective working life of the filament.
  • a beam having high density and uniformity enables a low magnification image to be displayed with uniform brightness. It also eliminates the need to adjust the stigmator because beam astigmatism remains almost constant regardless of any change in the accelerating voltage or image magnification.
  • FIG. 1 is a schematic diagram showing a conventional thermal emission type electron gun
  • FIGS. 2 and 3 are schematic diagrams for explaining the characteristics of the electron beam obtained by the electron gun shown in FIG. 1:
  • FIG. 4 is a drawing showing the essential part of the electron gun according to this invention.
  • FIGS. 5, 6, and 7 are schematic diagrams for explaining the characteristics ofthe electron beam obtained by the electron gun according to this invention.
  • an electron gun chamber 1 is mounted upon the microscope column (not shown) and an insulator 2 is filled with insulating pitch 3.
  • a high voltage cable 4 is partially buried in the solidified insulating pitch 3.
  • Lead wires 5, 6, and 7 constitute the electrical conducting path of the high voltage cable 4.
  • One end of said lead wires 5 and 6 and lead wire 7 is connected to a filament heating source 8 and a DC. high voltage source 9, respectively.
  • the opposite ends of the respective lead wires being connected to rods 10, 11 and 12.
  • a filament 13 is connected to rods 10 and 11, said filament being heated by alternating current generated by the filament heating source 8 which is applied via lead wires 5 and 6 and said rods 10 and 11.
  • a Wehnelt electrode 14 is threadably secured to a member 15 fixed to the insulator 2.
  • the electrode is supplied with a negative high voltage generated by the DC. high voltage source 9 which is applied via lead wire 7, rod 12 and the member 15. Resistor 16 connected between lead wires 6 and 7 serves as a bias resistor, in order to control the electrons emitted from the filament by varying the bias voltage.
  • A represents the beam crossover point under the condition that the filament tip aligns with the lower rim of the Wehnelt opening, said crossover point being formed by the electrostatic field generated between the filament and an anode 17.
  • FIG. 2 shows the image of the hairpin filament produced by the prior art thermal emission type electron gun described in FIG. I under comparatively low filament temperature conditions.
  • the filament image consists of a slightly elliptical bright area at the center and two peripheral bright areas which are more or less crescent shaped.
  • FIG. 3 shows the beam intensity distribution curve of the filament image shown in FIG. 2. As indicated by the curve, the beam intensity is strongest at the center of the image and weakens markedly in the peripheral areas. Accordingly, in order to obtain an electron beam having a high degree of parallelism, high density and uniformity, it is necessary to slice off a large portion of the electron beam by inserting a baffle having small diameter lens aperture therein in the beam path.
  • FIG. 4 is a schematic drawing showing the shape of the Wehnelt electrode and the postition of the filament with respect to the Wehnelt according to this invention.
  • the side of the Wehnelt electrode 18 facing the anode is convex and the distance H between the tip of the filament and the lower rim of the Wehnelt electrode opening satisfies the relation 0.4D 5 H 5 0.8D (0.4D less than or equal to H, H less than or equal to 0.8D) where D is the diameter of the Wehnelt electrode opening.
  • the Wehnelt electrode By satisfying the above condition, excellent results are assured.
  • the vertical angle 8 of said cone-shaped position should preferably satisfy the relation 30 S B s 90 (beta greater than or equal to 30, beta less than or equal to 90) and the height b of the cylindrical surface should preferably satisfy the relation 0.2D s b s 0.8D (b less than or equal to (12D, b greater than or equal to 0.8D).
  • FIG. 5 shows the trajectory of the electron beam emitted from the gun filament according to this invention. It will be noted that the angle of beam diversion beyond the crossover point is minimal thereby ensuring the high degree of parallelism.
  • FIGS. 6 and 7 show the filament image produced by the thermal emission type gun according to this invention and the corresponding beam intensity distribution curve under comparatively low filament temperature.
  • the beam intensity distribution curve is the flat topped curve as shown in FIG. 7, because the filament image consists of a very slightly elliptical bright area at the center and a ring-shaped bright area as shown in FIG. 6. Therefore, the electron gun according to this invention generates an electron beam having high density and uniformity.
  • a thermal emission type electron gun comprising a filament for emitting thermal electrons, an anode arranged to face said filament, a voltage source for supplying high potential difference between said filament and anode, a Wehnelt electrode having an opening the rein through which said electrons pass, said Wehnelt electrode arranged between said filament and anode, the side of said Wehnelt electrode facing the anode being convex, and means for supplying a potential to maintain the Wehnelt electrode at a negative potential with respect to the filament, the improvement comprising the distance I-l between the tip of the filament and the lower rim of the Wehnelt opening satisfying the relation 0.4D s H S (18D where D is the diameter of the opening the Wehnelt electrode, and the surface of the Wehnelt electrode near the opening being substantially cylindrical and the surface about the opening facing the filament being substantially cone-shaped and the angle B of said cone-shaped portion with the axis of the cylindrical opening satisfying the relation 30s B S 2.
  • a thermal emission type electron gun comprising a filament for emitting thermal electrons, an anode arranged to face said filament, a voltage source for supplying high potential different between said filament and anode, a Wehnelt electrode having an opening therein through which said electrons pass, said Wehnelt electrode arranged between said filament and anode, the side of said Wehnelt electrode facing the anode being convex, and means for supplying a potential to maintain the Wehnelt electrode at a negative potential with respect to the filament, the improvement comprising the distance H between the tip of the filament and the lower rim of the Wehnelt opening satisfying the relation 0.4D H S 0.8D where D is the diameter of the opening in the Wehnelt electrode and the surface of the Wehnelt electrode near the opening being substantially cylindrical and the surface about the opening facing the filament being substantially cone-shaped and the height b of said cylindrical surface satisfying the relation 02D 5 b s 0.8D.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Sources, Ion Sources (AREA)
US377812A 1972-08-22 1973-07-09 Thermal emission type electron gun Expired - Lifetime US3890533A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP47083891A JPS58148B2 (ja) 1972-08-22 1972-08-22 デンシジユウ

Publications (1)

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US3890533A true US3890533A (en) 1975-06-17

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US377812A Expired - Lifetime US3890533A (en) 1972-08-22 1973-07-09 Thermal emission type electron gun

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US (1) US3890533A (enrdf_load_stackoverflow)
JP (1) JPS58148B2 (enrdf_load_stackoverflow)
FR (1) FR2197230B1 (enrdf_load_stackoverflow)
GB (1) GB1430964A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3150848A1 (de) * 1980-12-27 1982-08-19 Denki Kagaku Kogyo K.K., Tokyo Elektronenkanone fuer grosse helligkeit
US4695773A (en) * 1981-12-18 1987-09-22 The Perkin-Elmer Corporation Field emission gun electrode geometry for improved focus stability
US4910442A (en) * 1985-01-25 1990-03-20 National Institute For Researches In Inorganic Materials Field emission type electron gun

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5075765A (enrdf_load_stackoverflow) * 1973-11-06 1975-06-21
JPS576790B2 (enrdf_load_stackoverflow) * 1974-05-13 1982-02-06
JPH0648619B2 (ja) * 1989-04-20 1994-06-22 北海道電力株式会社 電子銃装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3141993A (en) * 1959-12-24 1964-07-21 Zeiss Jena Veb Carl Very fine beam electron gun
US3185882A (en) * 1961-01-16 1965-05-25 Eitel Mccullough Inc Electron discharge device including cathode-focus electrode assemblies therefor
US3225248A (en) * 1961-05-27 1965-12-21 United Aircraft Corp Device for producing a high-intensity beam of charge carriers of small aperture

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE434952A (enrdf_load_stackoverflow) * 1938-07-16
US3383536A (en) * 1964-09-22 1968-05-14 Westinghouse Electric Corp Cathode ray tube generating circular beam by lineal filament critically spaced from circular aperture

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3141993A (en) * 1959-12-24 1964-07-21 Zeiss Jena Veb Carl Very fine beam electron gun
US3185882A (en) * 1961-01-16 1965-05-25 Eitel Mccullough Inc Electron discharge device including cathode-focus electrode assemblies therefor
US3225248A (en) * 1961-05-27 1965-12-21 United Aircraft Corp Device for producing a high-intensity beam of charge carriers of small aperture

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3150848A1 (de) * 1980-12-27 1982-08-19 Denki Kagaku Kogyo K.K., Tokyo Elektronenkanone fuer grosse helligkeit
US4695773A (en) * 1981-12-18 1987-09-22 The Perkin-Elmer Corporation Field emission gun electrode geometry for improved focus stability
US4910442A (en) * 1985-01-25 1990-03-20 National Institute For Researches In Inorganic Materials Field emission type electron gun

Also Published As

Publication number Publication date
DE2336851B2 (de) 1976-08-12
FR2197230B1 (enrdf_load_stackoverflow) 1976-09-17
FR2197230A1 (enrdf_load_stackoverflow) 1974-03-22
GB1430964A (en) 1976-04-07
JPS4940475A (enrdf_load_stackoverflow) 1974-04-16
DE2336851A1 (de) 1974-03-21
JPS58148B2 (ja) 1983-01-05

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