US3786268A - Electron gun device of field emission type - Google Patents

Electron gun device of field emission type Download PDF

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Publication number
US3786268A
US3786268A US00243215A US3786268DA US3786268A US 3786268 A US3786268 A US 3786268A US 00243215 A US00243215 A US 00243215A US 3786268D A US3786268D A US 3786268DA US 3786268 A US3786268 A US 3786268A
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United States
Prior art keywords
cathode tip
gun device
electron gun
field emission
emission type
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Expired - Lifetime
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US00243215A
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English (en)
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S Nomura
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Hitachi Ltd
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Hitachi 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
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
    • 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
    • H01J3/021—Electron guns using a field emission, photo emission, or secondary emission electron source
    • 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
    • H01J37/073—Electron guns using field emission, photo emission, or secondary emission electron sources

Definitions

  • This invention relates to an electron gun device of the field emission type which is suitable for use as an electron source in an electron microscope and the like, and more particularly to stabilizing means for stabilizing the electron beam emitted from said electron gun.
  • an electron gun device of the field emission type is so'constructed as to emit electrons from a cathode tip of needle shape disposed in a vacuum by applying a strong electric field for electron emission to said cathode tip.
  • the electron beam density obtained from such an electron gun device is remarkably higher than that of the thermal electron emission type, it has become important for use as an electron gun device for electron optical apparatus, such as an electron microscope and the like.
  • the emitted electron beam density depends to a great extent upon the surface condition of said cathode tip. Since the surface of said cathode tip has a tendency to become contaminated due to absorption of residual gas in vacuum during use and also is destroyed by means of ion bombardment, the emitted electron beam density from said cathode tip varies with time; and thus, the duration during which a stable electron beam density can be maintained is very short.
  • the prime object of the invention is to provide a new and original electron gun device of field emission type wherein the emitted electron beam can be stably maintained for a long time.
  • Another object of the invention is to provide an electron gun device of the type described capable of being adjusted and controlled for stabilizing the electron beam without interrupting the operation of said electron gun device.
  • a further object of the invention is to provide an electron gun device of the type described which is economical to manufacture and simple and easy to stabilize during use.
  • the invention is characterized in that the cathode tip is intermittently heated under the condition wherein the electric field for electron emission is applied to its surface, thereby maintaining an extremely stable electron beam emitted during the intermittent heating of said cathode tip.
  • FIGS. 1, 8 and 9 are schematic diagrams showing various embodiments of electron gun devices of the field emission type according to the invention.
  • FIG. 2 is a curve showing the successive variation of the emitted electron beam in a conventional electron gun device operated without heating the cathode tip;
  • FIG. 3 is a curve showing the successive variation of the emitted electron beam in a conventional electron gun device when the field emission is interrupted and reconstruction due to heating of the cathode tip is done;
  • FIG. 4 is a curve showing the successive variation of the emitted electron beam for the case where intermittent heating of the cathode tip is performed in accordance with the present invention
  • FIG. 5 is a diagram to explain the intermittent heating of the cathode tip in accordance with the invention.
  • FIGS. 6a and 6b are diagrams to explain the variation of the electron beam at the time when the intermittent heating of the cathode tip is interrupted.
  • FIGS. 7a and 7b are diagrams to explain the variation of the electron beam in the case where the heating temperature of the cathode tip is excessively high.
  • FIG. 1 shows an electron gun device of the field emission type according to the invention which is suitable for use in an electron microscope and the like.
  • the electron gun structure includes a cathode tip 1 of needle shape for electron emission and usually made of tungsten, an anode 2 for forming an electric field for producing electron emission (a first anode), an accelerating anode 3 (a second anode), a filament 4 for heating the cathode tip 1, a vacuum container 5, a high voltage source 6 connected between the cathode and the anode for forming an electric field for electron emission, a voltage source 7 connected between the respective anodes for accelerating the emitted electrons, and a cathode heating power source 8 connected between the terminals of the filament 4 for supplying a pulsating current to heat the filament 4 intermittently.
  • the vacuum container is evacuated to obtain a high degree of vacuum of about Torr therein and a voltage of about 1 to 5 KV is applied between the cathode l and the first anode 2. Also, a voltage of about to 100 KV is applied between the first anode 2 and the second anode 3. At this time, it is not intended to heat the cathode tip 1.
  • FIG. 2 shows an example of the successive variation of the emitted electron beam in a conventional electron gun device.
  • the cathode tip is made sufficiently clean and smooth by flashing the surface thereof and then field emission there-from is effected in a high vacuum of about 10" Torr without heating the cathode tip.
  • the intensity of the emitted electron beam gradually decreases during the time period A.
  • This time duration B is about 5 to 10 minutes with a degree of vacuum of 2 X 10" Torr and under the condition where the intensity ofthe electron beam is minimum.
  • FIG. 3 shows the variation of the emitted electron beam in the case where application of the electric field for electron emission is stopped so as to interrupt elec tron emission for one minute during every heating period of about 10 minutes while reconstruction of the cathode surface is effected by heating the cathode tip 1 to about 2,000C.
  • the emitted electron beam varies similarly to the above case after reconstruction of the cathode surface is com pleted and thus also the time duration for obtaining a comparatively stable electron beam is a short time of about 5 to 7 minutes. Further, in this case, since the cathode tip is heated to a high temperature, the cathode tip itself is in danger of modification.
  • the cathode tip is steadily heated under the condition wherein the electric field for electron emission is steadily applied to its surface; but in this case, when the heating temperature of the cathode tip is higher than 1,000C., there is the danger of modification of the structure thereof. On the other hand, if said heating temperature is less than C, the desired effect of reconstruction of the cathode surface is hardly obtained.
  • the cathode tip When the cathode tip is steadily heated within the temperature range of 150 to l,000C., the cathode tip is not modified and this is effective to some extent in producing emanation of the absorbed gas from the cathode tip and the desired smoothing thereof; however, steady heating within such temperature range produces a movement in the absorbed gas remaining on the cathode surface so that the locally emitted electron beam is not sufficiently stable.
  • an extremely stable emitted electron beam can be obtained by intermittently heating the cathode tip under the condition wherein the electric field for electron emission is continuously applied to the cathode surface during this intermittent heating.
  • This is believed to result from the fact that the absorbed gas on the cathode surface is removed by the instantaneous heating of the surface and at the same time disarray of the atomic arrangement of the cathode surface produced by means of the ion bombardment, etc., is eliminated. Then, the cathode temperature decreases at once with elimination of the heating, thereby preventing movement of the absorbed gases and ions thereon.
  • FIG. 4 shows the example of this stabilized phenomena. Firstly, when field emission is effected in a vacuum of about 2 X l0 Torr by using the cathode tip immediately after flashing and without heating it, as aforementioned, the intensity of the emitted electron beam first decreases and then increases again. Next, at point e of FIg. 4, when intermittent heating of the cathode tip (a heating period of seconds, a heating timewidth of 0.1 second, a heating temperature of about 500C.) is again started under the condition wherein the electric field for electron emission is continuously applied to the cathode surface, during the time period B", the electron beam becomes extremely stable.
  • FIG. 5 shows the waveform of a filament heating current pulse supplied from the power source 8 to the filament 4 so as to intermittently heat the cathode tip.
  • r is the heating period (the repetition period of said pulse) and T is the heating time width (the time widthof said pulse).
  • the heating period 1, is determined in accordance with thedegree of vacuum in the device and the condition of use thereof, but usually may be about 10 seconds. Further, the heating time width 1', depends upon the heating temperature of the cathode and heating condition therein, but usually maybe less than 1 second. It is desirable to set the heating time width T at 0.1 to 0.2 seconds and the heating period 1, at l to seconds.
  • the amplitudes of the respective heating currents depend upon the heating temperature of the cathode and heating condition therein, but it is desirable to select it in such a manner that the heating temperature of the cathode is within the temperature range of 150 to 1,000C. If said heating temperature-is less than 150C, the desired reconstruction of thecathode surface is hardly obtained. On the contrary, if the heating temperature is higher than l,00OC., since the cathode surface reaches proper condition immediately after flashing during every heating period, the initial reduction of the emitted electron beam due to absorption of the residual; gas in vacuurnafter heating becomes larger and variation of the emitted electron beam is larger.
  • FIG. 7 shows the variation of the electron beam in a case where the heating temperature of the cathode tip is set to about 1,500C. As shown in FIG. 7b, the emitted electron beam greatly varies as a result of the intermittent heating of the cathode.
  • FIG. 6 shows the variation of the electron beam in a case where the intermittent heating of the cathode is periodically interrupted.
  • the heating is effected during a period t and is interrupted during a period of t, the emitted electron beam is stably maintained during the period 1,, as shown in FIG. 6b, but gradually increases during the period However, the electron beam returns to an original value again upon reapplication of the heating and becomes stable.
  • Such intermittent heating of the cathode is effected by applying a pulsating current, as shown in FIG. 7a, from the heating power source 8 to the filament 4 in the arrangement of FIG. 1.
  • This power source 8 is constructed in a well known manner; for example, a pulse oscillator utilizing controlled charge and discharge of a condenser may be used as the power source 8.
  • the intermittent heating of the cathode tip may be started simultaneously with the starting operation of the electron gun device, or it may be selectively begun upon detection that the emitted electron beam has begun to be unstable.
  • FIG. 8 shows an exemplary heating power source constructed according to the latter operation.
  • the power source 8 includes a pulse oscillator 9, a direct current source 10, and a switch 11.
  • the emitted electron beam can be stably maintained for a long time by means of a very simple manipulation for merely intermittently heating the cathode tip as electron emission is continued.
  • an electron gun device of the field emission type according to the invention as an electron gun device suitable for an electron beam device requiring an electron beam which has a high electron beam density and is stable for a long time.
  • the electron gun device of the invention is used as the electron gun device of a scanning type electron microscope, as shown in FIG. 9, it is possible to observe a bright and stable specimen image without completely disturbing the image by effecting the intermittent heating synchronously with electron beam scanning on a specimen 15, for example, within the time t required for blanking the fly-back line of the imageon an oscilloscope 17.
  • the arrangement includes an electron gun device 12 of the invention, a focusing lens 13, a deflector 14, a secondary electron detector 16, and a scanning signal source 18.
  • An'electron gun device of the field emission type comprising: a filament of hair pin shape; a cathode tip of needle shape secured to said filament; at least one anode; means for continuously applying an electric voltage between said cathode tip and said anode so as to produce an electric field therebetween which causes electrons to be emitted from said. cathode tip toward said anode; and heating power source means for supplying a pulsating current to said filament so as to intermittently heat said cathode tip while the electric field between said cathode tip and said anode is continuously applied, whereby an electron beam emitted from said cathode tip can be stably maintained for a long time.
  • heating power source means includes a pulse oscillator for generating said pulsating current.
  • heating power source means further includes a direct current source, and switching means for switching from the connection between said filament and said direct current source to the connection between said filament and said pulse oscillator and vice versa.
  • a scanning type electron microscope including an electron gun device of field emission type; focusing lens means for focusing the electron beam; deflector means for scanning the electron beam on a specimen; secondary electron detector means for detecting secondary electrons; an oscilloscope connected to said detector means so that the intensity of an electron beam therein is modulated by the output of said detector means and having a deflector for scanning said electron beam therein; scanning signal source means for supplying scanning signals to the deflector means and the deflector in said oscilloscope; said electron gun device comprising: a filament of hair pin shape; a cathode tip of needle shape secured to said filament; at least one anode; means for applying an electric voltage between said cathode tip and said anode so as to produce an electric field therebetween which causes electrons to be emitted from said cathode tip toward said anode; and heating power source means for supplying a pulsating current to said filament so as to intermittently heat said cathode tip, whereby an electron beam emitted from said cath
  • pulsive current supplying means includes means for causing the time width of said pulsating current to be within a time required for eliminating a fly-back line of an image on the oscilloscope.
  • heating power source means includes a pulse oscillator for generating said pulsating current.
  • heating power source means further includes a direct current source, and switching means for switching from the connection between said filament and said direct current source to the connection between said filament and said pulse oscillator and vice versa.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Sources, Ion Sources (AREA)
US00243215A 1971-04-12 1972-04-12 Electron gun device of field emission type Expired - Lifetime US3786268A (en)

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JP2233871A JPS5323663B1 (enrdf_load_stackoverflow) 1971-04-12 1971-04-12

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JP (1) JPS5323663B1 (enrdf_load_stackoverflow)
DE (1) DE2217660A1 (enrdf_load_stackoverflow)
NL (1) NL155979B (enrdf_load_stackoverflow)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3887835A (en) * 1972-06-09 1975-06-03 Hitachi Ltd Field emission electron gun
US4309607A (en) * 1978-11-30 1982-01-05 Kernforschungsanlage Julich Gesellschaft Mit Beschrankter Haftung Electron-impact spectrometer
EP0066409A1 (en) * 1981-05-22 1982-12-08 Hitachi, Ltd. Charged particle source
WO1987004846A1 (en) * 1986-02-03 1987-08-13 Crewe Albert V Electron beam memory system with ultra-compact, high current density electron gun
US4740705A (en) * 1986-08-11 1988-04-26 Electron Beam Memories Axially compact field emission cathode assembly
US4760567A (en) * 1986-08-11 1988-07-26 Electron Beam Memories Electron beam memory system with ultra-compact, high current density electron gun
FR2714208A1 (fr) * 1993-12-22 1995-06-23 Mitsubishi Electric Corp Cathode, canon à électrons comportant une telle cathode et tube à rayons cathodiques comportant un tel canon.
US5848118A (en) * 1997-06-19 1998-12-08 Lear Corporation Method and apparatus for detecting inhomogeneities in seat assemblies
FR2792770A1 (fr) * 1999-04-22 2000-10-27 Cit Alcatel Fonctionnement a haute pression d'une cathode froide a emission de champ
EP1760761A1 (en) * 2005-09-05 2007-03-07 ICT, Integrated Circuit Testing Gesellschaft für Halbleiterprüftechnik Mbh Charged particle beam emitting device and method for operating a charged particle beam emitting device
US20110089336A1 (en) * 2008-06-20 2011-04-21 Keigo Kasuya Charged particle beam apparatus, and method of controlling the same
US20110221360A1 (en) * 2010-03-10 2011-09-15 ICT Integrated Circuit Testing Gesellschaft für Halbleiterprüftechnik mbH Feedback loop for emitter flashing
US8188451B1 (en) * 2008-09-24 2012-05-29 Kla-Tencor Corporation Electron generation and delivery system for contamination sensitive emitters
CN115380355A (zh) * 2020-04-16 2022-11-22 日商光电魂股份有限公司 电子枪、电子射线应用装置以及电子束的射出方法

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6345273B2 (ja) 2014-12-26 2018-06-20 株式会社日立ハイテクノロジーズ 複合荷電粒子線装置およびその制御方法

Citations (1)

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Publication number Priority date Publication date Assignee Title
US3646344A (en) * 1969-01-02 1972-02-29 Graham Plows Scanning electron beam apparatus for viewing potential distribution on specimen surfaces

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3646344A (en) * 1969-01-02 1972-02-29 Graham Plows Scanning electron beam apparatus for viewing potential distribution on specimen surfaces

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Electron Gun Using a Field Emission Source, A. V. Crewe, Review of Scientific Instruments, Vol. 39 No. 4, April 68 p. 576 583. *

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3887835A (en) * 1972-06-09 1975-06-03 Hitachi Ltd Field emission electron gun
US4309607A (en) * 1978-11-30 1982-01-05 Kernforschungsanlage Julich Gesellschaft Mit Beschrankter Haftung Electron-impact spectrometer
EP0066409A1 (en) * 1981-05-22 1982-12-08 Hitachi, Ltd. Charged particle source
WO1987004846A1 (en) * 1986-02-03 1987-08-13 Crewe Albert V Electron beam memory system with ultra-compact, high current density electron gun
US4740705A (en) * 1986-08-11 1988-04-26 Electron Beam Memories Axially compact field emission cathode assembly
US4760567A (en) * 1986-08-11 1988-07-26 Electron Beam Memories Electron beam memory system with ultra-compact, high current density electron gun
FR2714208A1 (fr) * 1993-12-22 1995-06-23 Mitsubishi Electric Corp Cathode, canon à électrons comportant une telle cathode et tube à rayons cathodiques comportant un tel canon.
US5848118A (en) * 1997-06-19 1998-12-08 Lear Corporation Method and apparatus for detecting inhomogeneities in seat assemblies
FR2792770A1 (fr) * 1999-04-22 2000-10-27 Cit Alcatel Fonctionnement a haute pression d'une cathode froide a emission de champ
EP1052668A1 (fr) * 1999-04-22 2000-11-15 Alcatel Fonctionnement à haute pression d'une cathode froide à émission de champ
US6559442B1 (en) 1999-04-22 2003-05-06 Alcatel High-pressure operation of a field-emission cold cathode
US20070158588A1 (en) * 2005-09-05 2007-07-12 Fang Zhou Charged particle beam emitting device and method for operating a charged particle beam emitting device
EP1993119A1 (en) 2005-09-05 2008-11-19 ICT, Integrated Circuit Testing Gesellschaft für Halbleiterprüftechnik Mbh Charged particle beam emitting device and method for operating a charged particle beam emitting device
US7595490B2 (en) * 2005-09-05 2009-09-29 Ict, Integrated Circuit Testing Gesellschaft Fur Halbleiterpruftechnik Mbh Charged particle beam emitting device and method for operating a charged particle beam emitting device
EP1760761A1 (en) * 2005-09-05 2007-03-07 ICT, Integrated Circuit Testing Gesellschaft für Halbleiterprüftechnik Mbh Charged particle beam emitting device and method for operating a charged particle beam emitting device
US8772735B2 (en) 2008-06-20 2014-07-08 Hitachi High-Technologies Corporation Charged particle beam apparatus, and method of controlling the same
US20110089336A1 (en) * 2008-06-20 2011-04-21 Keigo Kasuya Charged particle beam apparatus, and method of controlling the same
DE112009001537T5 (de) 2008-06-20 2011-04-28 Hitachi High-Technologies Corp. Vorrichtung mit geladenem Teilchenstrahl und Verfahren zum Steuern der Vorrichtung
DE112009001537B4 (de) 2008-06-20 2018-10-18 Hitachi High-Technologies Corporation Vorrichtung mit geladenem Teilchenstrahl und Verfahren zum Steuern der Vorrichtung
US8319193B2 (en) 2008-06-20 2012-11-27 Hitachi High-Technologies Corporation Charged particle beam apparatus, and method of controlling the same
US8188451B1 (en) * 2008-09-24 2012-05-29 Kla-Tencor Corporation Electron generation and delivery system for contamination sensitive emitters
US8530867B1 (en) 2008-09-24 2013-09-10 Kla-Tencor Corporation Electron generation and delivery system for contamination sensitive emitters
US8674300B2 (en) * 2010-03-10 2014-03-18 ICT Integrated Circuit Testing Gesellschaft fur Halbleiterprüftechnik mbH Feedback loop for emitter flashing
US20110221360A1 (en) * 2010-03-10 2011-09-15 ICT Integrated Circuit Testing Gesellschaft für Halbleiterprüftechnik mbH Feedback loop for emitter flashing
CN115380355A (zh) * 2020-04-16 2022-11-22 日商光电魂股份有限公司 电子枪、电子射线应用装置以及电子束的射出方法

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NL155979B (nl) 1978-02-15
DE2217660A1 (de) 1972-11-16
NL7204863A (enrdf_load_stackoverflow) 1972-10-16
JPS5323663B1 (enrdf_load_stackoverflow) 1978-07-15

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