US3377506A - Electromagnetic current control for a hollow cathode - Google Patents

Electromagnetic current control for a hollow cathode Download PDF

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Publication number
US3377506A
US3377506A US538862A US53886266A US3377506A US 3377506 A US3377506 A US 3377506A US 538862 A US538862 A US 538862A US 53886266 A US53886266 A US 53886266A US 3377506 A US3377506 A US 3377506A
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US
United States
Prior art keywords
current
cathode
chamber
hollow cathode
control
Prior art date
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
US538862A
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English (en)
Inventor
Conrad M Banas
Clyde O Brown
Donald E Powers
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.)
Raytheon Technologies Corp
Original Assignee
United Aircraft Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by United Aircraft Corp filed Critical United Aircraft Corp
Priority to US538862A priority Critical patent/US3377506A/en
Priority to GB01461/67A priority patent/GB1183751A/en
Priority to FR98841A priority patent/FR1543191A/fr
Priority to DE19671614917 priority patent/DE1614917A1/de
Application granted granted Critical
Publication of US3377506A publication Critical patent/US3377506A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/135—Circuit arrangements therefor, e.g. for temperature control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J27/00—Ion beam tubes
    • H01J27/02—Ion sources; Ion guns
    • 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, ion-optical arrangement
    • 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, ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H01J37/077—Electron guns using discharge in gases or vapours as electron sources
    • 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
    • H01J37/24—Circuit arrangements not adapted to a particular application of the tube and not otherwise provided for
    • 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
    • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
    • H01J37/304—Controlling tubes by information coming from the objects or from the beam, e.g. correction signals

Definitions

  • a magnetic current control device for a hollow cathode structure which operates in a glow dis charge and produces a collimated beam of electrons from the volume enclosed by the cathode structure.
  • the number of electrons produced in the beam is controlled by subjecting the plasma within the hollow cathode structure to a magnetic field and varying the intensity of the field to produce the desired beam current.
  • This invention relates to a device for controlling the current in a beam of charged particles emanating from an aperture in a hollow electrode. More specifically, it relates to a device for controlling the magnitude of the current in a beam of charged particles produced from a plasma in a hollow electrode with a magnetic lield acting on the plasma.
  • the aperture size has a strong influence on the operatd ing mode and the characteristics of the beam. Its dimensions must be approximately equal or larger than the cathode fall. This dimensional requirement will vary with different gases and gas densities.
  • a large fraction of the electrons for the beam are obtained from a plasma generated by an intense discharge within the chamber enclosed bythe cathode.
  • Various controls have been proposed to vary the current obtainable from the hollow cathode chamber and to maintain the electron beam current within precisely controlled limits.
  • One such control would involve varying the anode-to-cathode potential to maintain the desired current.
  • One disadvantage of varying this potential is that the focal length of an electron lens depends upon it and compensation would have to lbe made in order to maintain a fixed beam spot size on a workpiece. This is especially so 3,377,506 Patented Apr. 9, 1968 ICC at the low pressure end of the cathode operating regime in which a small variation in the potential may even result in extinguishment of the discharge.
  • Still another approach involves the use of a control grid which operates adjacent to the emitting surfaces of the hollow cathode and suppresses electron ow from the cathode to the plasma when a suitable negative potential is applied.
  • the disadvantage of this type of current control is that contact with the high density plasma leads to disintegration of the control grid.
  • FIGURE l shows a cross-sectional view of the current control.
  • FIGURE 2 shows the linearity of the current control device at different anode-to-cathode potentials.
  • FIGURE 3 shows a block diagram of an automatic control system which is used to maintain the electron beam current from the hollow cathode at a preselected reference value.
  • FIGURE 4 shows the eifectiveness of this current control with varying pressure conditions.
  • a cathode 10 shown in sectional form, comprises a cylindrical hollow member which is Amade of a non-magnetic material such as tantalum.
  • the back wall 11 and the peripheral wall 13 define the cylindrical chamber 15.
  • the peripheral wall is shaped to form an aperture 12. substantially concentric therewith and opposite the back wall.
  • the cathode 10 is electrically connected to a highvolt age supply 18 via a supporting conductor 14 and a lead 16.
  • the aperture dimensions are approximately 1A ythat of the face in which it appears.
  • a discharge suppressor shield 20 Surrounding the cathode 10 is a discharge suppressor shield 20 which extends back to the wall of the chamber 22 and surrounds the conductor 14 as well as the nonemitting surfaces of the cathode 10.
  • a typical hollow cathode cylindrical structure having an insulator shield is described in the copending application tiled by Conrad M. Banas and Clyde O. Brown 3 entitled Insulator Shielded Cathode, Ser. No. 506,237, filed Now 3, 1965, and assigned to the same assignee.
  • a solenoid-type coil 24 located generally at the center of the cathode and provides a magnetic field that is substantially parallel to the cylindrical axis of the cathode 10.
  • the coil 24 is so located withr respect to the cathode that its magnetic field acts predominantly on the plasma generated within the chamber 15. The field may also diverge from the cylindrical axis in the manner of solenoids.
  • the current for the control coil 24 is provided by a control power supply 26 that is located outside of the chamber 22.
  • an additional magnetic coil 30 Spaced from the cathode aperture 12 is an additional magnetic coil 30 designed to further focus the beam emanating from the hollow cathode 10 at the workpiece 32.
  • the workpiece in this instance operates as the anode but as described in the previously-mentioned patent application to Ferreira, the anode may be located anywhere within the chamber 22 provided it is sufficiently distant from the cathode 10
  • the current for the focusing coil 30 is supplied from an external supply 34.
  • a shield 28 Interposed between the control coil 24 and the workpiece 32 is a shield 28 to protect the control coil from the heat generated by the working of the electron beam on the workpiece $2. ⁇
  • This shield 28 may be of the same material as shield 20.
  • the control coil 24 produces an electromagnetic field that acts through the shield 20 and the wall of the cathode 10 on the plasma enclosed -by the hollow cathode 10. Contrary to what prior experience in plasma physics might lead one to expect, application of a magnetic field within the hollow cathode increases the current from the hollow cathode through the aperture 12., As is shown in FIGURE 2, in the absence of any current flowing through the control coil 24, the hollow cathode operates in its normal fashion producing various currents for different anode-to-cathode potential differences. As the magnetic field of the control coil 24 is increased, the electron beam current increases as well. The effect of the magnetic field on the discharge is similar to that obtained by variation in chamber pressure.. Hence, a substantial simplification of current control is possible with change in operating pressures.
  • a hollow cathode operates at 20 kilovolts and the field strength from control coil 24 as fixed by the field references 58 is 20 gauss
  • the current in the electron beam is about 190 milliamperes with a pressure of 8 microns (.008 mm.) of mercury.
  • the cathode operates at point C in FIGURE 4.
  • the pressure in the chamber rises to 9 microns, the operating point of the device will shift to point A along the 20 gauss line and to compensate for this increase in current without changing the pressure the control current.
  • the curve of FIGURE 4 is for a constant voltage source.
  • a three-dimensional model could be envisioned if voltage is also a variable.
  • the design operating conditions are in general a function of various requirements such as imposed by the material, stability of the beam, type of work to be accomplished, etc.,
  • the hollow electrode may be used to generate a plasma therein from which a beam of ions is extracted.
  • This invention although described in relation with an electron beam is also applicable to beams of ion particles and control the current magnitude of the ion beam. Higher field strengths are needed to control the heavier ion particles and this is simply provided by increasing the coupling between the coil 24 and the cavity or cham-ber 15G
  • An automatic control as shown in FIGURE 3 operates as follows.
  • the resistor 50 is shown in series with the high voltage supplier 18 so that the voltage developed across it will have a direct relationship with the current emanating from the hollow cathode 10. This resistor may actually ybe the current sensing element of the electron beam power supply.
  • the voltage developed across resistor 50 is fed to a difference amplifier 52 to generate an output signal that refiects the difference 4between the current sensed by the resistor 50 and a preselected reference value set by the circuitry 54.
  • the reference value indicates the desired beam current from the hollow cathode.
  • the amplifier 52 output signal is then applied through a magnetic amplifier 56 to the control coil 24 to provide the desired magnetic field strength.
  • the initial operating point of the magnetic amplifier 56 corresponding to point C is determined by the field reference circuit 58.
  • the error signal from differential amplifier 52 is superimposed on the field reference signal, By selecting the polarity of the current sensed by the resistor 50 on the difference amplifier 52 current may be appropriately increased or decreased and a fast and reliable current control for a hollow cathode discharge may be provided by driving the error signal to a minimum.
  • a device for controlling the flow of charged particles from a hollow cathode operating at a high potential difference with respect to an anode in a gaseous environment comprising:
  • a hollow cathode structure having a chamber evacuated to a predetermined gaseous pressure
  • said chamber being provided with an aperture
  • a device for controlling the flow of electrons from a hollow cathode operating at a high negative potential difference with respect to an anode in a gaseous environment comprising:
  • a hollow cathode structure having a chamber evacuated to a predetermined gaseous pressure
  • said chamber being provided with an aperture having dimensional characteristics for establishing a beam of electrons therefrom, and
  • a device as recited in claim 2 wherein the hollow cathode structure comprises:
  • a solenoid externally adjacent to the chamber and substantially coaxial therewith for producing a magnetic field in the chamber that is substanm tially parallel with said cylindrical axis.
  • the shield is selectively spaced from and substantially encloses the cylindrical wall of said chamu ber to suppress the glow discharge therebetween.
  • a device for controlling the magnitude of the current in a beam of electrons produced by a hollow cathode operating in a glow discharge to perform work on workn pieces comprising:
  • said cathode structure having a back wall
  • peripheral wall further forming an aperture from which the beam of electrons emerges
  • means supplying current through said electromagnetic coil to vary the strength of the magnetic field and control the magnitude of the current in the beam.
  • said shield being selectively spaced from and substan-x tially enclosing the peripheral wall to suppress the glow discharge there-between, and
  • a heat shield extending outwardly from said peripheral wall in between the beam of electrons and said electromagnetic coil toshield the coil from the heating effects of said beam of electrons upon the workpieces.
  • peripheral wall comprises:
  • said magnetic coil is a solenoid to produce a magnetic field substantially coaxial with said single cylindrical wall.
  • said magnetic field generating means comprises an electromagnetic coil adjacent the cathode chamber and varying the numn1 ber of electrons in the beam from said cathode chamber aperture as a function of the strength of the magnetic field.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Electron Sources, Ion Sources (AREA)
  • Plasma Technology (AREA)
US538862A 1966-03-30 1966-03-30 Electromagnetic current control for a hollow cathode Expired - Lifetime US3377506A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US538862A US3377506A (en) 1966-03-30 1966-03-30 Electromagnetic current control for a hollow cathode
GB01461/67A GB1183751A (en) 1966-03-30 1967-03-10 Charged Particle Generator with Electromagnetic Current Control.
FR98841A FR1543191A (fr) 1966-03-30 1967-03-15 Contrôle électromagnétique du courant pour une cathode creuse
DE19671614917 DE1614917A1 (de) 1966-03-30 1967-03-30 Vorrichtung zur Steuerung des Flusses der aus einer Hohlelektrode,insbesondere Hohlkathode austretenden geladenen Teilchen

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US538862A US3377506A (en) 1966-03-30 1966-03-30 Electromagnetic current control for a hollow cathode

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US3377506A true US3377506A (en) 1968-04-09

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US (1) US3377506A (de)
DE (1) DE1614917A1 (de)
GB (1) GB1183751A (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3678334A (en) * 1968-09-05 1972-07-18 Atomic Energy Authority Uk Non-thermionic glow discharge devices
US3798488A (en) * 1971-07-28 1974-03-19 N Pleshivtsev Plasma source of charged particles
US3825839A (en) * 1971-04-30 1974-07-23 Jeol Ltd Constant current field emission electron gun
US3936756A (en) * 1971-04-30 1976-02-03 Nihon Denshi Kabushiki Kaisha Field emission electron gun having automatic current control
US4101772A (en) * 1976-01-19 1978-07-18 Matsushita Electric Industrial Co., Ltd. Ion-beam etching method and an apparatus therefor
DE3038644A1 (de) * 1980-10-13 1982-05-19 Vsesojuznyj elektrotechničeskij institut imeni V.I. Lenina, Moskva Steuerungsverfahren fuer eine gasentladungs-elektronenkanone

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH696179A5 (de) * 2000-06-08 2007-01-31 Satis Vacuum Ind Vertriebs Ag Plasma-Verdampfungsquelle für eine Vakuum Beschichtungsanordnung zum Aufbringen von Vergütungsschichten auf optische Substrate.

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1954025A (en) * 1929-01-22 1934-04-10 American Telephone & Telegraph Electrooptical system
US2940010A (en) * 1959-05-18 1960-06-07 Gen Precision Inc Automatic control circuit
US2945160A (en) * 1957-07-29 1960-07-12 Phillips Petroleum Co Emission regulator
US3152238A (en) * 1962-05-11 1964-10-06 United Aircraft Corp Electron beam centering apparatus
US3243570A (en) * 1963-04-30 1966-03-29 Gen Electric Automatic gas pressure control for electron beam apparatus
US3320475A (en) * 1963-04-30 1967-05-16 Gen Electric Nonthermionic hollow cathode electron beam apparatus

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1954025A (en) * 1929-01-22 1934-04-10 American Telephone & Telegraph Electrooptical system
US2945160A (en) * 1957-07-29 1960-07-12 Phillips Petroleum Co Emission regulator
US2940010A (en) * 1959-05-18 1960-06-07 Gen Precision Inc Automatic control circuit
US3152238A (en) * 1962-05-11 1964-10-06 United Aircraft Corp Electron beam centering apparatus
US3243570A (en) * 1963-04-30 1966-03-29 Gen Electric Automatic gas pressure control for electron beam apparatus
US3320475A (en) * 1963-04-30 1967-05-16 Gen Electric Nonthermionic hollow cathode electron beam apparatus

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3678334A (en) * 1968-09-05 1972-07-18 Atomic Energy Authority Uk Non-thermionic glow discharge devices
US3825839A (en) * 1971-04-30 1974-07-23 Jeol Ltd Constant current field emission electron gun
US3936756A (en) * 1971-04-30 1976-02-03 Nihon Denshi Kabushiki Kaisha Field emission electron gun having automatic current control
US3798488A (en) * 1971-07-28 1974-03-19 N Pleshivtsev Plasma source of charged particles
US4101772A (en) * 1976-01-19 1978-07-18 Matsushita Electric Industrial Co., Ltd. Ion-beam etching method and an apparatus therefor
DE3038644A1 (de) * 1980-10-13 1982-05-19 Vsesojuznyj elektrotechničeskij institut imeni V.I. Lenina, Moskva Steuerungsverfahren fuer eine gasentladungs-elektronenkanone

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Publication number Publication date
GB1183751A (en) 1970-03-11
DE1614917A1 (de) 1970-12-23

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