US3864572A - Electron beam apparatus comprising a point cathode - Google Patents

Electron beam apparatus comprising a point cathode Download PDF

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Publication number
US3864572A
US3864572A US402844A US40284473A US3864572A US 3864572 A US3864572 A US 3864572A US 402844 A US402844 A US 402844A US 40284473 A US40284473 A US 40284473A US 3864572 A US3864572 A US 3864572A
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United States
Prior art keywords
tip
wire
anode
electron beam
cathode
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Expired - Lifetime
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US402844A
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English (en)
Inventor
Der Mast Karel Diederick Van
James Edmond Barth
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US Philips Corp
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US Philips Corp
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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
    • H01J37/075—Electron guns using thermionic emission from cathodes heated by particle bombardment or by irradiation, e.g. by laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H01J3/024—Electron guns using thermionic emission of cathode heated by electron or ion bombardment or by irradiation by other energetic beams, e.g. by laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/06—Sources
    • H01J2237/063—Electron sources
    • H01J2237/06308—Thermionic sources
    • H01J2237/06316—Schottky emission

Definitions

  • the electron source of an electron beam apparatus comprises a cathode wire which is to be heated by a laser beam and which is to be displaced in the wire direction.
  • This cathode wire has a thickness of from 10 to 30 microns.
  • the invention relates to an electron beam apparatus provided with an electron source with a cathode wire, one free end of which is displaceable in a beam path of an auxiliary radiation source.
  • An electron beam apparatus of this kind is known, for example, from German Pat. No. l,028,244.
  • the cathode used therein consists of a tungsten wire having a diameter of from 100 to 200 microns, the end of which is heated by an ion beam.
  • the ion beam is directed onto the wire tip by an electric field which is formed between an ion source having a positive potential with respect to the cathode tip and an electrode which is arranged opposite to the cathode tip and which has a negative potential with respect thereto.
  • the maximum thermal electron emission which can be delivered by a cathode of this kind is determined by the material, the geometry and the temperature of the wire tip.
  • this cathode is set for a high emission current density, the temperature becomes very high, thus causing a comparatively large evaporation of the cathode tip. Therefore, the cathode wire can each time be advanced after a given period of operation. The evaporated material, however, will substantially contaminate the interior of the apparatus and the intermittent advancing of the wire will cause variations in the emission current.
  • an electron beam apparatus of the kind set forth according to the invention is characterized in that opposite to the free end of the cathode wire a punctured electrode is arranged for generating a positive field strength of approximately 10 to KV/m on the surface of the wire end, a coupling between the energy supply from the auxiliary radiation source to the wire end and the movement of the cathode during operation maintaining a point-like end having an at least substantially constant curvature radius of between about 0.2 microns and 2 microns on the cathode wire at a temperature at which deformations occur due to field strength forces.
  • This curvature radius is substantially larger than in field emission sources.
  • a cathode wire having a thickness of approximately 10 microns to 30 microns By using, according to the invention, a cathode wire having a thickness of approximately 10 microns to 30 microns and by heating this wire, preferably by means of a laser beam, on one free end and by displacing the cathode wire in the laser beam during operation, a wire tip having a curvature radius of the desired dimension is maintained if the electric field strength on the surface of the wire end is suitably chosen.
  • the transporting of the cathode wire is controlled by a quantity which is at least co-determined by the temperature of the wire tip. The wire tip remains requirements are satisfied for the so-termed temperature-field emission produced by the Schottky effect.
  • the electrons need neither overcome the entire exit potential (work function), such as is necessary in the case of thermal emission, nor to tunnel the potential barrier as is necessary in the case of field emission.
  • the exit potential to be overcome is substantially reduced by the applied electric field, with the result that at the same temperature the emission can be some factors higher per unit of surface area.
  • a striking and very favourable side-effect of the operation at a temperature just below the melting point of the cathode material is that the electron emission is thus rendered completely independent of the crystal direction. Because at a less high temperature the emission density is substantially lower in the wire direction than in the directions transverse thereto, an additional gain is obtained for the beam current.
  • FIG. 1 is a diagrammatic representation of an electron beam apparatus according to the invention which is constructed as a scanning electron microscope
  • FIG. 2 is a diagrammatic view of a preferred embodiment according to the invention, comprising a laser as controllable auxiliary radiation source, and
  • FIG. 3 shows a preferred embodiment for transporting and holding the cathode wire according to the invention.
  • the scanning electron microscope which is diagrammatically shown in FIG. 1 comprises a cathode wire 2 which is mounted in a holder 1, a first anode 3 and a second anode 4.
  • a free end or tip 5 of the cathode 2 is heated by a beam 6 which is generated in an auxiliary radiation source 8.
  • the auxiliary radiation source is constructed as a laser, a beam in the infrared, visible or ultraviolet wavelength range of which is incident on the wire tip 5 via a window (not shown) which is adapted to the wavelength of the radiation and an opening 9 in the first anode 3.
  • a beam current to be used in the scanning electron microscope is separated from the overall emission current of the wire tip 5.
  • a further opening and window (not shown), preferably arranged on the side of the laser beam, the wire tip can be observed, if desired.
  • the energy current to be applied to the wire tip is controlled by means of a control mechanism l2.
  • a condensor lens 14 a deflection unit 15
  • an objective lens 16 an object or specimen l7
  • detectors l8 and 19 A signal which is received by one of the detectors is displayed, via a signal amplifier 20, on a television monitor 21 which is coupled to the deflection unit 15.
  • the first anode has a potential of
  • the second anode then has a potential of many thousands of volts positive with respect to the wire tip. These potential values obviously are codependent of the geometry of the two anodes, the dimensions of the borings in the anodes, the distance between the anodes, and the distance between the anodes and the wire tip.
  • a field strength of approximately 10 to l KV/m must be generated on the surface of the wire tip so as to achieve the desired emission. Because the emissive tip is also formed by the field strength, a lateral displacement of the wire will not cause an inclined source position, provided it remains within given limits.
  • FIG. 2 is a diagrammatic representation of an arrangement for adjusting the wire cathode to the desired emission properties.
  • a laser beam 30, originating from a continuously radiating laser 31, is converged at 'the area of the wire tip 5, by way of a lens or lens system 32, so as to form a focal spot having a very small transverse dimension which is determined exclusively by deflection phenomena of the coherent laser radiation.
  • the cathode wire 2 is held in a clamping device which is incorporated in the holder 1 and which will be described in detail with reference to FIG. 3.
  • the clamping device serves to hold the wire tip of the wire cathode 2 accurately in a fixed position during operation of the electron beam apparatus, and hence to compensate for the evaporation thereof by supplying cathode material.
  • the first anode 3 is connected to a direct voltage source 33. Due to the emission current, a voltage difference arises across a resistor 34; this difference is compared, by way of a direct voltage amplifier 35, with a voltage originating from a source 36. -A difference signal thus obtained is integrated in an integrator 37 and controls, via a current amplifier 38, a transport mechanism of the clamping device.
  • the cathode wire 2 can be slowly displaced in the wire direction, for example, a few microns per minute.
  • the wire tip 5 then more or less projects into the laser beam, so that the energy supplied thereto is controlled.
  • This adjusting mechanism makes readjustment for any slow variations in the laser intensity or the geometry of the wire tip, for example, caused by evaporation of the material.
  • a control signal is used which is derived from an anode current to be supplied by a high voltage source 39 via a resistor 40. Via a capacitor 41 and an amplifier 42, this signal controls an electrodynamic converter 12 which adjusts the position of a blade 43 which is arranged in the laser beam. Using this blade, part of the laser beam can be intercepted, with the result that the energy applied to the wire tip is reduced. The laser beam can then be constricted on one side, on more than one side, or all around.
  • FIG. 3 shows a preferred embodiment of a clamping device.
  • a straightened tungsten wire 2 is held between jaws 50 and 51.
  • a resilient element 52 which at the same time serves as a hinge for the jaw 51 delivers a clamping force.
  • the jaws 50 and 51, the resilient element 52 and a platform 53 together constitute a grip which can be displaced, by means of a parallel spring system consisting of the springs 54, 55, 56 and 57, in only one direction, i.e., along the axis of the gun.
  • the platform 53 is pulled to a mounting plate 59 by a wire 58.
  • the platform 53, and hence the cathode wire 2 is displaced by thermal length variation of the wire 58.
  • a second set of jaws 59, 60 is open.
  • a coupling between the jaws prevents the two sets from being simultaneously open. This coupling can be rendered inactive for inserting a new cathode wire.
  • This wire 58 is heated during operation by a filament current which is supplied by the current amplifier 38 (see also FIG. 2). Because the clamping faces of the jaws 50, 51 and 59 60 are arranged to be perpendicular with respect to each other, a newly inserted cathode wire 2 will be fixed along the line of intersection of the two clamping faces after a few take-overs. As a result, this mechanism automatically reproduces the location of the wire axis very accurately.
  • the opening and closing of the jaws 50, 51 and 59, 60 for transporting the cathode wire is controlled by current control i.e., thermal length variation or wires 62 and 63.
  • a tungsten wire having a diameter of 10 microns used as the cathode wire thus produces an emission current density in the order of 10 A/cm at a temperature of approximately 3,500 K from a wire tip having a curvature radius of approximately 1 micron which is arranged opposite to an anode which has a voltage of +2,000 V with respect to the wire tip.
  • an electron beam can be readily separated from a source having such a high current density, the said beam being particularly suitable for use as the beam current in a scanning electron microscope employing television techniques for displaying the image information.
  • An electron source according to the invention cannot only be successfully used in the described scanning electron microscope, but also, for example, in a transmission electron microscope, an electron beam machining apparatus, and a microanalyzer.
  • An electron beam source comprising:
  • said tip is maintained substantially point-like with a substantially constant radius of curvature of approximately 0.2 to 2 microns.
  • An electron beam source comprising:
  • an anode positioned adjacent said tip, said anode having an aperture for forming a beam from electrons emitted from said tip; means for supplying to said anode a voltage sufficiently positive with respect to said tip to generate a field strength at said tip of approximately to 10 KV/m;
  • an auxiliary radiation source positioned to focus radiation on said tip to heat said tip to a temperature where deformation of said tip occurs due to said field strength at said tip;
  • An electron beam source as defined in claim 3 wherein said means for supporting and advancing comprises means for controlling the position of said wire in accordance with the anode current of said anode in a direction which tends to maintain said anode current constant.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Sources, Ion Sources (AREA)
  • Particle Accelerators (AREA)
US402844A 1972-10-03 1973-10-02 Electron beam apparatus comprising a point cathode Expired - Lifetime US3864572A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL7213355A NL7213355A (de) 1972-10-03 1972-10-03

Publications (1)

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US3864572A true US3864572A (en) 1975-02-04

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US402844A Expired - Lifetime US3864572A (en) 1972-10-03 1973-10-02 Electron beam apparatus comprising a point cathode

Country Status (10)

Country Link
US (1) US3864572A (de)
JP (1) JPS5241137B2 (de)
BE (1) BE805539A (de)
CA (1) CA992670A (de)
DE (1) DE2349352C3 (de)
FR (1) FR2201540B1 (de)
GB (1) GB1440776A (de)
IT (1) IT994357B (de)
NL (1) NL7213355A (de)
SE (1) SE384759B (de)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0106589A2 (de) 1982-09-29 1984-04-25 Tetra Laval Holdings & Finance SA Nachversorgungsmethode einer kalten Kathode in einem Elektronenstrahlgerät und Kaltkathodenvorrichtung mit Nachversorgung
US4600839A (en) * 1983-03-09 1986-07-15 Hitachi, Ltd. Small-dimension measurement system by scanning electron beam
US4762975A (en) * 1984-02-06 1988-08-09 Phrasor Scientific, Incorporated Method and apparatus for making submicrom powders
US4829177A (en) * 1986-09-11 1989-05-09 Gregory Hirsch Point projection photoelectron microscope with hollow needle
US5015862A (en) * 1990-01-22 1991-05-14 Oregon Graduate Institute Of Science & Technology Laser modulation of LMI sources
EP0434018A2 (de) * 1989-12-19 1991-06-26 Ebara Corporation Elektronenbeschleuniger
US5038034A (en) * 1988-11-15 1991-08-06 Mitsubishi Denki Kabushiki Kaisha Scanning tunneling microscope
US5041724A (en) * 1988-11-24 1991-08-20 Ict Integrated Circuit Testing Gesellschaft Fur, Halbleit Erpruftechnik Mbh Method of operating an electron beam measuring device
US5274234A (en) * 1991-03-22 1993-12-28 Universidad Autonoma De Madrid Realization of an atomic source of metallic ions producing a surface melting by an applied electric field
US5568004A (en) * 1992-09-07 1996-10-22 Kleindiek; Stephan Electromechanical positioning device
US20040108812A1 (en) * 2002-12-10 2004-06-10 Applied Materials, Inc. Current-stabilizing illumination of photocathode electron beam source
US20040124365A1 (en) * 2002-09-26 2004-07-01 Leo Elektronenmikroskopie Gmbh Electron beam source, electron optical apparatus using such beam source and method of operating an electron beam source
US6828996B2 (en) 2001-06-22 2004-12-07 Applied Materials, Inc. Electron beam patterning with a heated electron source
US11417492B2 (en) * 2019-09-26 2022-08-16 Kla Corporation Light modulated electron source

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5533310U (de) * 1978-08-24 1980-03-04
JPS58126376U (ja) * 1982-02-20 1983-08-27 深沢　房次郎 扉のストツパ

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3388280A (en) * 1966-04-19 1968-06-11 Victor E. De Lucia Laser energized hot cathode type of electron discharge device
US3678333A (en) * 1970-06-15 1972-07-18 American Optical Corp Field emission electron gun utilizing means for protecting the field emission tip from high voltage discharges

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3388280A (en) * 1966-04-19 1968-06-11 Victor E. De Lucia Laser energized hot cathode type of electron discharge device
US3678333A (en) * 1970-06-15 1972-07-18 American Optical Corp Field emission electron gun utilizing means for protecting the field emission tip from high voltage discharges

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0106589A3 (de) * 1982-09-29 1986-01-15 Tetra Laval Holdings & Finance SA Nachversorgungsmethode einer kalten Kathode in einem Elektronenstrahlgerät und Kaltkathodenvorrichtung mit Nachversorgung
EP0106589A2 (de) 1982-09-29 1984-04-25 Tetra Laval Holdings & Finance SA Nachversorgungsmethode einer kalten Kathode in einem Elektronenstrahlgerät und Kaltkathodenvorrichtung mit Nachversorgung
US4600839A (en) * 1983-03-09 1986-07-15 Hitachi, Ltd. Small-dimension measurement system by scanning electron beam
US4762975A (en) * 1984-02-06 1988-08-09 Phrasor Scientific, Incorporated Method and apparatus for making submicrom powders
US4829177A (en) * 1986-09-11 1989-05-09 Gregory Hirsch Point projection photoelectron microscope with hollow needle
US5038034A (en) * 1988-11-15 1991-08-06 Mitsubishi Denki Kabushiki Kaisha Scanning tunneling microscope
US5041724A (en) * 1988-11-24 1991-08-20 Ict Integrated Circuit Testing Gesellschaft Fur, Halbleit Erpruftechnik Mbh Method of operating an electron beam measuring device
US5227700A (en) * 1989-12-19 1993-07-13 Ebara Corporation Electron accelerator
EP0434018A2 (de) * 1989-12-19 1991-06-26 Ebara Corporation Elektronenbeschleuniger
EP0434018A3 (en) * 1989-12-19 1992-01-02 Ebara Corporation Electron accelerator
US5015862A (en) * 1990-01-22 1991-05-14 Oregon Graduate Institute Of Science & Technology Laser modulation of LMI sources
US5274234A (en) * 1991-03-22 1993-12-28 Universidad Autonoma De Madrid Realization of an atomic source of metallic ions producing a surface melting by an applied electric field
US5568004A (en) * 1992-09-07 1996-10-22 Kleindiek; Stephan Electromechanical positioning device
US6828996B2 (en) 2001-06-22 2004-12-07 Applied Materials, Inc. Electron beam patterning with a heated electron source
US20040124365A1 (en) * 2002-09-26 2004-07-01 Leo Elektronenmikroskopie Gmbh Electron beam source, electron optical apparatus using such beam source and method of operating an electron beam source
US6828565B2 (en) 2002-09-26 2004-12-07 Leo Elektronenmikroskopie Gmbh Electron beam source, electron optical apparatus using such beam source and method of operating and electron beam source
US20040108812A1 (en) * 2002-12-10 2004-06-10 Applied Materials, Inc. Current-stabilizing illumination of photocathode electron beam source
US6847164B2 (en) 2002-12-10 2005-01-25 Applied Matrials, Inc. Current-stabilizing illumination of photocathode electron beam source
US11417492B2 (en) * 2019-09-26 2022-08-16 Kla Corporation Light modulated electron source
US20220336180A1 (en) * 2019-09-26 2022-10-20 Kla Corporation Light Modulated Electron Source
US11715615B2 (en) * 2019-09-26 2023-08-01 Kla Corporation Light modulated electron source

Also Published As

Publication number Publication date
BE805539A (fr) 1974-04-01
DE2349352A1 (de) 1974-04-11
IT994357B (it) 1975-10-20
FR2201540B1 (de) 1976-11-19
DE2349352B2 (de) 1977-07-21
JPS5241137B2 (de) 1977-10-17
JPS4993798A (de) 1974-09-06
DE2349352C3 (de) 1978-03-30
NL7213355A (de) 1974-04-05
SE384759B (sv) 1976-05-17
GB1440776A (en) 1976-06-23
FR2201540A1 (de) 1974-04-26
CA992670A (en) 1976-07-06

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