US3355615A - Ion source having critically dimensioned extraction means - Google Patents

Ion source having critically dimensioned extraction means Download PDF

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US3355615A
US3355615A US447792A US44779265A US3355615A US 3355615 A US3355615 A US 3355615A US 447792 A US447792 A US 447792A US 44779265 A US44779265 A US 44779265A US 3355615 A US3355615 A US 3355615A
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enclosure
ion source
ion
plasma
ions
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Bihan Raymond Le
Maugis Daniel
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J27/00—Ion beam tubes
    • H01J27/02—Ion sources; Ion guns
    • H01J27/26—Ion sources; Ion guns using surface ionisation, e.g. field effect ion sources, thermionic ion sources

Definitions

  • the present invention relates to ion source, and especially to an improved mode of extracting the ions from the source.
  • Another object of this invention is to provide an ion source capable of producing a high degree of ionization.
  • Still another object of this invention is to provide an ion source of high efiiciency.
  • a further object of the present invention is to provide an ion source in which the power required for heating the source is relatively reduced.
  • a still further object of the invention is to provide an ion source of relatively simple construction.
  • an ion source including an enclosure, means for producing a plasma in said enclosure by ionization of a gaseous substance, and means for extracting the ions from said enclosure, characterized by the fact that the extracting means comprise one or several grids having extraction holes of circular or other shape, the value of the diameter or the width of the holes being, in meters, equal to or less than 2R where T being the temperature in degrees Kelvin of the enclosure, and 11 the number of ions or electrons per m. of the plasma, the thickness of the grids being of the same order of magnitude as the diameter or the width of the holes.
  • FIG. 1 represents diagrammatically an example of an embodiment of the invention
  • FIGURES 2 and 3 explain the principle of the invention
  • FIG. 4 is an example of an abacus usable in achieving the invention.
  • an ion source comprising an ionization chamber or enclosure 1 having tantalum walls 2 that may be brought to a desired temperature for example, by means of a heater filament 3.
  • the enclosure 1 communicates 'by way of a channel 4 with a reservoir of caesium 5 which may likewise be brought to a desired temperature by appropriate means, not shown in this figure.
  • the upper Wall of enclosure 1 is partially apertured and the apertures are covered by grids 6.
  • An extractor electrode 7, disposed above enclosure 1 and set at a negative potential with respect to the enclosure by means of a source of potential (not shown) comprises apertures facing the grids 6.
  • caesium vapor produced by heating the reservoir 5, penetrates into enclosure 1 which is maintained at a high temperature, say between 1400 K. and 2200 K., and the caesium atoms are dissociated into electrons and positive ions.
  • This phenomenon known as surface ionization or contact ionization, results in the formation of a plasma in the interior of enclosure 1.
  • the plasma that comprises electrons, positive ions also a certain proportion of neutral atoms
  • a sheath composed to a great extent of ions, is comprised between the walls and the plasma if the work function of the walls is higher than the plasma potential.
  • the ion density (number of ions per unit volume) is therefore considerably higher in the sheath adjacent the walls than in the plasma which occupies the remainder of the enclosure.
  • FIGURES 2 and 3 permit to see what happens when the radius of the extraction orifice does or does not exceed the thickness of the ion sheath.
  • the plasma is designated by reference numeral 8
  • the enclosure wall by 2
  • the ion sheath, indicated by the signs is designated by the reference 9.
  • the radius of the orifice provided in wall 2 is greater than the thickness of sheath 9. Within this orifice the ions of sheath 9 surround a portion of plasma 8. On the contrary, in the case of FIGURE 3 where the orifice radius is equal to the thickness of sheath 9, only the ions of the sheath traverse the orifice without any portion of the plasma being drawn along. As a result, the mean density of the ion current and the ionization degree are much higher in the case of FIG. 3 than in the case of FIG. 2. I
  • the orifices of the grids 6 are given a radius equal to or less than the thickness R of the ion sheath.
  • the units employed are those of the international system (M.K.S.A.).
  • FIGURE 4 is an abacus indicating the thickness R, in microns, of the ion layer in a tantalum enclosure versus the temperature T (in degrees Kelvin) of a caesium reservoir for different temperatures T of the tantalum. It may be seen on this abacus that, for example, for tantalum walls heated at 1600 K. and a reservoir of caesium at 425 K. the thickness of the ion sheath is 2071.. Under these conditions use is made, in accordance with the invention, of extraction orifices of a diameter that does not exceed 40 i, and thus ion currents of the order of 40 ma./cm. are obtained.
  • the thickness of grids 6 is given a value of preferably the same order as the diameter or the width of the orifices. It has been found, in effect, that the ion current is not affected by the thickness of the grids. On the other hand, it is obvious that thick grids (deep holes) bring about pressure losses which are practically inexistent in thin grids (non-deep holes), so that with thin grids it sufiices to heat the reservoir that supplies the metal vapor, to a lower temperature than in the case of thick grids.
  • caesium and tantalum have been mentioned, but instead of caesium other metals may be used that are easy to ionize (potassium, lithium, rubidium, sodium, etc.) and the tantalum may be replaced by other metals having a high work function (tungsten, molybdenum, rhenium, etc.).
  • tungsten molybdenum, rhenium, etc.
  • the extraction orifices may have a cross-section of any desired shape: circular, square, rectangular, triangular, etc., and the grids may be replaced by nets of parallel wires, separated by narrow intervals.
  • the ion extraction is effected, in accordance with the invention, through passages whose width does not exceed the double of the thickness of the ion sheath, adjacent the walls of the isothermal cavity.
  • An ion source including an enclosure, means for producing a plasma in said enclosure by ionization of a gaseous substance, andmeans for extracting the ions from said enclosure, said extracting means including at least one grid provided with substantially circular extraction holes having a diameter at most equal, in meters,
  • T being the temperature in degrees Kelvin of the enclosure
  • n the number of ions or electrons per m. of the plasma.
  • T being the temperature in degrees Kelvin of the enclosure
  • n the number of ions or electrons per m9 of the plasma.

Description

Nov. 28, 1967 R. LE BIHAN ET AL 3,355,615
ION SOURCE HAVING CRITICALLY DIMENSIONED EXTRACTION MEANS Filed April 15, 196s 5 'SheetsfSheet 1 INVENTORS R. LE Ell-MN 6 DMJUG/S Nov. 28, 1967 BlHAN ET AL 3,355,615
ION SOURCE HAVING CRITICALLY DIMENSIONED EXTRACTION MEANS Filed April 15, 1965 3 Sheets-Sheet 2 FIG 3.
INVENTORSI R. LE BIHA/V & amuals v ATTORNEY NOV. 28, 1967 LE BlHAN ET AL 3,355,615
ION SOURCE HAVING cRITIcALLY DIMENSIONED EXTRACTION MEANS Filed April m 1965 3 Sheets-Sheet s INVENTORS R. LE B/HA/V 6 D-MAUG/S United States Patent Ofi ice 3,355,615 Patented Nov. 28, 1967 4 Claims. 61. 31363) The present invention relates to ion source, and especially to an improved mode of extracting the ions from the source.
It is an object of this invention to provide an ion source capable of producing an intense beam of ions.
Another object of this invention is to provide an ion source capable of producing a high degree of ionization.
Still another object of this invention is to provide an ion source of high efiiciency.
A further object of the present invention is to provide an ion source in which the power required for heating the source is relatively reduced.
A still further object of the invention is to provide an ion source of relatively simple construction.
In accordance with the invention the above objects are achieved by providing an ion source including an enclosure, means for producing a plasma in said enclosure by ionization of a gaseous substance, and means for extracting the ions from said enclosure, characterized by the fact that the extracting means comprise one or several grids having extraction holes of circular or other shape, the value of the diameter or the width of the holes being, in meters, equal to or less than 2R where T being the temperature in degrees Kelvin of the enclosure, and 11 the number of ions or electrons per m. of the plasma, the thickness of the grids being of the same order of magnitude as the diameter or the width of the holes.
The invention will be more fully understood from the following description and the accompanying drawings.
FIG. 1 represents diagrammatically an example of an embodiment of the invention,
FIGURES 2 and 3 explain the principle of the invention, and
FIG. 4 is an example of an abacus usable in achieving the invention.
Referring to FIG. 1, there is represented an ion source comprising an ionization chamber or enclosure 1 having tantalum walls 2 that may be brought to a desired temperature for example, by means of a heater filament 3.
The enclosure 1 communicates 'by way of a channel 4 with a reservoir of caesium 5 which may likewise be brought to a desired temperature by appropriate means, not shown in this figure.
The upper Wall of enclosure 1 is partially apertured and the apertures are covered by grids 6.
An extractor electrode 7, disposed above enclosure 1 and set at a negative potential with respect to the enclosure by means of a source of potential (not shown) comprises apertures facing the grids 6.
In operation, caesium vapor, produced by heating the reservoir 5, penetrates into enclosure 1 which is maintained at a high temperature, say between 1400 K. and 2200 K., and the caesium atoms are dissociated into electrons and positive ions. This phenomenon, known as surface ionization or contact ionization, results in the formation of a plasma in the interior of enclosure 1.
Now the plasma, that comprises electrons, positive ions also a certain proportion of neutral atoms, is not in contact with the walls of enclosure 1 because a sheath, composed to a great extent of ions, is comprised between the walls and the plasma if the work function of the walls is higher than the plasma potential. The ion density (number of ions per unit volume) is therefore considerably higher in the sheath adjacent the walls than in the plasma which occupies the remainder of the enclosure.
FIGURES 2 and 3 permit to see what happens when the radius of the extraction orifice does or does not exceed the thickness of the ion sheath. In these two FIG- URES 2 and 3, the plasma is designated by reference numeral 8, the enclosure wall by 2, and the ion sheath, indicated by the signs is designated by the reference 9.
In FIGURE 2, the radius of the orifice provided in wall 2 is greater than the thickness of sheath 9. Within this orifice the ions of sheath 9 surround a portion of plasma 8. On the contrary, in the case of FIGURE 3 where the orifice radius is equal to the thickness of sheath 9, only the ions of the sheath traverse the orifice without any portion of the plasma being drawn along. As a result, the mean density of the ion current and the ionization degree are much higher in the case of FIG. 3 than in the case of FIG. 2. I
In accordance with the invention, the orifices of the grids 6 (FIG. 1) are given a radius equal to or less than the thickness R of the ion sheath.
The thickness R may be predetermined by the formula Ra g mentioned above, the value of n being given 'by the relation where n,; is the density of the metal vapor in the enclosure prior to the ionization, t=the temperature of the enclosure and V =the ionization potential of the metal vapor. The units employed are those of the international system (M.K.S.A.).
FIGURE 4 is an abacus indicating the thickness R, in microns, of the ion layer in a tantalum enclosure versus the temperature T (in degrees Kelvin) of a caesium reservoir for different temperatures T of the tantalum. It may be seen on this abacus that, for example, for tantalum walls heated at 1600 K. and a reservoir of caesium at 425 K. the thickness of the ion sheath is 2071.. Under these conditions use is made, in accordance with the invention, of extraction orifices of a diameter that does not exceed 40 i, and thus ion currents of the order of 40 ma./cm. are obtained.
In accordance with the invention, the thickness of grids 6 is given a value of preferably the same order as the diameter or the width of the orifices. It has been found, in effect, that the ion current is not affected by the thickness of the grids. On the other hand, it is obvious that thick grids (deep holes) bring about pressure losses which are practically inexistent in thin grids (non-deep holes), so that with thin grids it sufiices to heat the reservoir that supplies the metal vapor, to a lower temperature than in the case of thick grids.
In the example described, caesium and tantalum have been mentioned, but instead of caesium other metals may be used that are easy to ionize (potassium, lithium, rubidium, sodium, etc.) and the tantalum may be replaced by other metals having a high work function (tungsten, molybdenum, rhenium, etc.). Thus with a tungsten enclosure, heated at 1800 K., it is possible by applying the principle of the invention, to extract an ion density of the order of 500 ma./cm. and more than 1 a./cm. at 1900 K.
The extraction orifices may have a cross-section of any desired shape: circular, square, rectangular, triangular, etc., and the grids may be replaced by nets of parallel wires, separated by narrow intervals. In all cases, the ion extraction is effected, in accordance with the invention, through passages whose width does not exceed the double of the thickness of the ion sheath, adjacent the walls of the isothermal cavity.
While this invention has been described in a specific embodiment using surface ionization, it will be obvious to those skilled in the art that the invention applies generally to all types of ion sources comprising an enclosure or ionization chamber in the interior of which a plasma is formed. Thus the invention is not to be limited to the details shown, except as defined in the following claims.
We claim:
-1. An ion source including an enclosure, means for producing a plasma in said enclosure by ionization of a gaseous substance, andmeans for extracting the ions from said enclosure, said extracting means including at least one grid provided with substantially circular extraction holes having a diameter at most equal, in meters,
to 2R where T being the temperature in degrees Kelvin of the enclosure, and n the number of ions or electrons per m. of the plasma.
T being the temperature in degrees Kelvin of the enclosure, and n the number of ions or electrons per m9 of the plasma.
4. An ion source as claimed in claim 3, wherein the thickness of said grids is substantially equal to the width of said holes.
References Cited UNITED STATES PATENTS 5/1965 Hoyer et al. 313-61 8/1966 Sunderland et al. 31363 DAVID J. GALVIN, Primary Examiner.
JAMES W. LAWRENCE, Examiner.
S. A. SCHNEEBERGER, Assistant Examiner.

Claims (1)

  1. 3. AN ION SOURCE INCLUDING AN ENCLOSURE, MEANS FOR PRODUCING A PLASMA IN SAID ENCLOSURE BY IONIZATION OF A GASEOUS SUBSTANCE, AND MEANS FOR EXTRACTING THE IONS FROM SAID ENCLOSURE, SAID EXTRACTING MEANS INCLUDING AT LEAST ONE GRID PROVIDED WITH EXTRACTION HOLES HAVING A WIDTH AT MOST EQUAL, IN METERS, TO 2R WHERE
US447792A 1964-04-27 1965-04-13 Ion source having critically dimensioned extraction means Expired - Lifetime US3355615A (en)

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Cited By (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3660715A (en) * 1970-08-18 1972-05-02 Atomic Energy Commission Ion source with mosaic ion extraction means
US3864575A (en) * 1970-07-25 1975-02-04 Nujeeb Hashmi Contact ionization ion source
US3930163A (en) * 1974-03-22 1975-12-30 Varian Associates Ion beam apparatus with separately replaceable elements
US3955091A (en) * 1974-11-11 1976-05-04 Accelerators, Inc. Method and apparatus for extracting well-formed, high current ion beams from a plasma source
US4001582A (en) * 1974-06-28 1977-01-04 Agence Nationale De Valorisation De La Recherche (Anvar) Local surface analysis
EP0021140A1 (en) * 1979-06-29 1981-01-07 International Business Machines Corporation Ion source in a vacuum chamber and method for its operation
US4246481A (en) * 1978-02-08 1981-01-20 Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften E.V. Contact ionization apparatus
US4833319A (en) * 1987-02-27 1989-05-23 Hughes Aircraft Company Carrier gas cluster source for thermally conditioned clusters
US20020108933A1 (en) * 2000-03-17 2002-08-15 Applied Materials, Inc. Plasma reactor with overhead RF electrode tuned to the plasma with arcing suppression
US6586886B1 (en) 2001-12-19 2003-07-01 Applied Materials, Inc. Gas distribution plate electrode for a plasma reactor
US20040226657A1 (en) * 2003-05-16 2004-11-18 Applied Materials, Inc. Plasma density, energy and etch rate measurements at bias power input and real time feedback control of plasma source and bias power
US20050178748A1 (en) * 2000-03-17 2005-08-18 Applied Materials, Inc. Plasma reactor overhead source power electrode with low arcing tendency, cylindrical gas outlets and shaped surface
US7141757B2 (en) 2000-03-17 2006-11-28 Applied Materials, Inc. Plasma reactor with overhead RF source power electrode having a resonance that is virtually pressure independent
US7186943B2 (en) 2000-03-17 2007-03-06 Applied Materials, Inc. MERIE plasma reactor with overhead RF electrode tuned to the plasma with arcing suppression
US7220937B2 (en) 2000-03-17 2007-05-22 Applied Materials, Inc. Plasma reactor with overhead RF source power electrode with low loss, low arcing tendency and low contamination
US7359177B2 (en) 2005-05-10 2008-04-15 Applied Materials, Inc. Dual bias frequency plasma reactor with feedback control of E.S.C. voltage using wafer voltage measurement at the bias supply output
US7452824B2 (en) 2003-05-16 2008-11-18 Applied Materials, Inc. Method of characterizing a chamber based upon concurrent behavior of selected plasma parameters as a function of plural chamber parameters
US7470626B2 (en) 2003-05-16 2008-12-30 Applied Materials, Inc. Method of characterizing a chamber based upon concurrent behavior of selected plasma parameters as a function of source power, bias power and chamber pressure
US7795153B2 (en) 2003-05-16 2010-09-14 Applied Materials, Inc. Method of controlling a chamber based upon predetermined concurrent behavior of selected plasma parameters as a function of selected chamber parameters
US7901952B2 (en) 2003-05-16 2011-03-08 Applied Materials, Inc. Plasma reactor control by translating desired values of M plasma parameters to values of N chamber parameters
US7910013B2 (en) 2003-05-16 2011-03-22 Applied Materials, Inc. Method of controlling a chamber based upon predetermined concurrent behavior of selected plasma parameters as a function of source power, bias power and chamber pressure
US7955986B2 (en) 2002-05-22 2011-06-07 Applied Materials, Inc. Capacitively coupled plasma reactor with magnetic plasma control
US8048806B2 (en) 2000-03-17 2011-11-01 Applied Materials, Inc. Methods to avoid unstable plasma states during a process transition
US8617351B2 (en) 2002-07-09 2013-12-31 Applied Materials, Inc. Plasma reactor with minimal D.C. coils for cusp, solenoid and mirror fields for plasma uniformity and device damage reduction

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JP3268180B2 (en) * 1994-11-18 2002-03-25 株式会社東芝 Ion generator, ion irradiation device, and method of manufacturing semiconductor device
USD978226S1 (en) * 2020-11-10 2023-02-14 Emart International Inc Collapsible screen

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US3185849A (en) * 1962-11-30 1965-05-25 Exxon Production Research Co Pulsed neutron source utilizing an accelerator tube
US3263415A (en) * 1961-03-06 1966-08-02 Aerojet General Co Ion propulsion device

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FR1327142A (en) * 1961-04-10 1963-05-17 Du Pont Process for the polymerization of ethylenically unsaturated compounds and catalyst for this process

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US3263415A (en) * 1961-03-06 1966-08-02 Aerojet General Co Ion propulsion device
US3185849A (en) * 1962-11-30 1965-05-25 Exxon Production Research Co Pulsed neutron source utilizing an accelerator tube

Cited By (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3864575A (en) * 1970-07-25 1975-02-04 Nujeeb Hashmi Contact ionization ion source
US3660715A (en) * 1970-08-18 1972-05-02 Atomic Energy Commission Ion source with mosaic ion extraction means
US3930163A (en) * 1974-03-22 1975-12-30 Varian Associates Ion beam apparatus with separately replaceable elements
US4001582A (en) * 1974-06-28 1977-01-04 Agence Nationale De Valorisation De La Recherche (Anvar) Local surface analysis
US3955091A (en) * 1974-11-11 1976-05-04 Accelerators, Inc. Method and apparatus for extracting well-formed, high current ion beams from a plasma source
US4246481A (en) * 1978-02-08 1981-01-20 Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften E.V. Contact ionization apparatus
EP0021140A1 (en) * 1979-06-29 1981-01-07 International Business Machines Corporation Ion source in a vacuum chamber and method for its operation
US4833319A (en) * 1987-02-27 1989-05-23 Hughes Aircraft Company Carrier gas cluster source for thermally conditioned clusters
US7186943B2 (en) 2000-03-17 2007-03-06 Applied Materials, Inc. MERIE plasma reactor with overhead RF electrode tuned to the plasma with arcing suppression
US20050178748A1 (en) * 2000-03-17 2005-08-18 Applied Materials, Inc. Plasma reactor overhead source power electrode with low arcing tendency, cylindrical gas outlets and shaped surface
US7030335B2 (en) 2000-03-17 2006-04-18 Applied Materials, Inc. Plasma reactor with overhead RF electrode tuned to the plasma with arcing suppression
US7141757B2 (en) 2000-03-17 2006-11-28 Applied Materials, Inc. Plasma reactor with overhead RF source power electrode having a resonance that is virtually pressure independent
US20020108933A1 (en) * 2000-03-17 2002-08-15 Applied Materials, Inc. Plasma reactor with overhead RF electrode tuned to the plasma with arcing suppression
US7196283B2 (en) 2000-03-17 2007-03-27 Applied Materials, Inc. Plasma reactor overhead source power electrode with low arcing tendency, cylindrical gas outlets and shaped surface
US7220937B2 (en) 2000-03-17 2007-05-22 Applied Materials, Inc. Plasma reactor with overhead RF source power electrode with low loss, low arcing tendency and low contamination
US8048806B2 (en) 2000-03-17 2011-11-01 Applied Materials, Inc. Methods to avoid unstable plasma states during a process transition
US6586886B1 (en) 2001-12-19 2003-07-01 Applied Materials, Inc. Gas distribution plate electrode for a plasma reactor
US7955986B2 (en) 2002-05-22 2011-06-07 Applied Materials, Inc. Capacitively coupled plasma reactor with magnetic plasma control
US8617351B2 (en) 2002-07-09 2013-12-31 Applied Materials, Inc. Plasma reactor with minimal D.C. coils for cusp, solenoid and mirror fields for plasma uniformity and device damage reduction
US7585685B2 (en) 2003-05-16 2009-09-08 Applied Materials, Inc. Method of determining wafer voltage in a plasma reactor from applied bias voltage and current and a pair of constants
US7452824B2 (en) 2003-05-16 2008-11-18 Applied Materials, Inc. Method of characterizing a chamber based upon concurrent behavior of selected plasma parameters as a function of plural chamber parameters
US7470626B2 (en) 2003-05-16 2008-12-30 Applied Materials, Inc. Method of characterizing a chamber based upon concurrent behavior of selected plasma parameters as a function of source power, bias power and chamber pressure
US7521370B2 (en) 2003-05-16 2009-04-21 Applied Materials, Inc. Method of operating a plasma reactor chamber with respect to two plasma parameters selected from a group comprising ion density, wafer voltage, etch rate and wafer current, by controlling chamber parameters of source power and bias power
US7553679B2 (en) 2003-05-16 2009-06-30 Applied Materials, Inc. Method of determining plasma ion density, wafer voltage, etch rate and wafer current from applied bias voltage and current
US7795153B2 (en) 2003-05-16 2010-09-14 Applied Materials, Inc. Method of controlling a chamber based upon predetermined concurrent behavior of selected plasma parameters as a function of selected chamber parameters
US7901952B2 (en) 2003-05-16 2011-03-08 Applied Materials, Inc. Plasma reactor control by translating desired values of M plasma parameters to values of N chamber parameters
US7910013B2 (en) 2003-05-16 2011-03-22 Applied Materials, Inc. Method of controlling a chamber based upon predetermined concurrent behavior of selected plasma parameters as a function of source power, bias power and chamber pressure
US7247218B2 (en) * 2003-05-16 2007-07-24 Applied Materials, Inc. Plasma density, energy and etch rate measurements at bias power input and real time feedback control of plasma source and bias power
US20040226657A1 (en) * 2003-05-16 2004-11-18 Applied Materials, Inc. Plasma density, energy and etch rate measurements at bias power input and real time feedback control of plasma source and bias power
US7375947B2 (en) 2005-05-10 2008-05-20 Applied Materials, Inc. Method of feedback control of ESC voltage using wafer voltage measurement at the bias supply output
US7359177B2 (en) 2005-05-10 2008-04-15 Applied Materials, Inc. Dual bias frequency plasma reactor with feedback control of E.S.C. voltage using wafer voltage measurement at the bias supply output

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DE1261605B (en) 1968-02-22
FR1402020A (en) 1965-06-11
GB1033447A (en) 1966-06-22

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