US3707628A - Magnetic lenses - Google Patents

Magnetic lenses Download PDF

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Publication number
US3707628A
US3707628A US126930A US3707628DA US3707628A US 3707628 A US3707628 A US 3707628A US 126930 A US126930 A US 126930A US 3707628D A US3707628D A US 3707628DA US 3707628 A US3707628 A US 3707628A
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United States
Prior art keywords
coil
lens
lengths
conical
electromagnetic lens
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Expired - Lifetime
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US126930A
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English (en)
Inventor
Richard Bassett
Thomas Mulvey
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National Research Development Corp UK
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National Research Development Corp UK
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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
    • H01J37/10—Lenses
    • H01J37/14—Lenses magnetic
    • H01J37/141—Electromagnetic lenses

Definitions

  • a magnetic lens, for focusingabeam of charged partiabandonedcles includes a coil at least part of which, at an end thereof, tapers conically with a half-angle between 20 [30] Foreign Application Priority Data and 85.
  • the coil may comprise a plurality of conductors laid concurrently, and cooling means may be pro- Aug. 18, 1967 Great Britain ..38,250/67 I vided in Contact with the inner surface.
  • the coil is shrouded, at least in part, with material of high [52] 0 gg gggg/ t magnetic permeability.
  • Radiation such as X-rays, from a target in focus beyond the tapering end of the coil, [51] lnt.Cl ..H0lj 37/26, G01n 23/22 b d t t d l l 58 Field oiSearch Vietnamese250/49.5 D, 49.5 PE; 313/84; may 7 e arge ange 11 Claims, 10 Drawing Figures MAGNETIC LENSES This application is a continuation of our earlier copending application Ser. No.” 753,127 filed Aug. 16, 1968, now abandoned.
  • This invention relates to magnetic lenses for the focusing of beams of charged particles, in particular of beams of-electrons.
  • the area in which the beam is concentrated should be as small and compact as possible and it is therefore essential that the aberrations of the lens and in particular the spherical aberration, should be as small as possible.
  • This form of microanalysis depends on the detection of X-rays emitted from the region of a specimen bombarded by electrons, the Xrays being characteristic of elements present at the region of bombardment. With commonly known forms of lens only a relatively small proportion of the X-rays emitted can be received by a detector, and these at an angle to the normal to the surface of the specimen approaching 90, on account of the bulk of the lens and its proximity to the specimen. This is a disadvantage in that thesensitivity of the apparatus is reduced, since so much of the X-radiation goes undetected.
  • a magnetic lens particularly for focusing beams of charged particles such as electrons in apparatus, such as for example an X-ray micro-analysis apparatus, comprises a coil of which at least an end part thereof is substantially frusto-conical and tapers towards the end of the coil with a half angle which lies between 20 and 85, preferably between 20 and 75.
  • the coil is positioned around the beam of charged particles with its frusto-conical end nearest the object being irradiated and as a result the obstruction of emitted radiation on its way to a detector may be considerably reduced.
  • the coil is cooled by means located on its inner surface, which further reduces obstruction to emitted radiation.
  • the coil is preferably wound with a plurality of separate, concurrently laidlengths of conducting wire, the field distribution being further improved by enclosing the coil, at least in part, by a shroud of material of high magnetic permeability.
  • the cooling of the coil is assisted by making its radial depth small compared with its dimension in the direction of a generator of the coil surface, and the ratio of said dimension to the radial depth is preferably not less than :1.
  • the half width, as defined herein, of the axial distribution of the magnetic field of the lens' is preferably large compared with the working distance, as defined herein, from the lens to its focus.
  • FIGS. 1(a) and 1(b). are plan and elevational views of a magnetic lens coil according to the invention.
  • FIGS. 2 and 3 are cross-sectional views respectively of a conventional magnetic lens and a magnetic lens in use according to the invention.
  • FIG. 4 illustrates means for cooling a magnetic lens coil according to the invention.
  • FIG. 5 illustrates an alternative form of lens construction according to the invention.
  • FIGS. 6(a) (b) (c) and (d) illustrate axial distribution of magnetic field within a magnetic lens coil according to the invention.
  • the coil consists of a number of separate, concurrently laid lengths of conducting wire wound side by side, the construction illustrated being for six such conductors. Other numbers could be employed equally well, but preferably not fewer than six.
  • the coil is an annulus of conducting sections, insulated from each other and indicated by 12(a) to (f) and 13(a) to(f).
  • One conductor of the coil may, for example, commence .at section 12(b) and terminate at section 13(c). Another would commence at 12(c) and terminate at 13(d) and so on.
  • the conductors are wound on the surface of a cone and to this end a conical former is used to which the part-annular sections 12, 13 are attached temporarily.
  • the conductors are wound preferably three or more at a time and if multilayer construction is required, the conductors are all wound in the same axial sense by returning the conductor from the end of one layer, along a generator of the cone, to the commencement of the next. In order to obtain satisfactory bedding of the conductors it is found necessary to wind from the smaller to the larger end of the cone.
  • each layer of conductors is bonded to the next layer below by the application of a coating of a thermosetting resin of good electrical properties, e.g. an epoxy resin. When a sufficient total number of turns of conductor have been applied, the whole may be removed from the conical former.
  • a coil with six conductors could be arranged for example so that all six were fed with current in parallel; or three symmetrically disposed conductors in parallel could be connected in series with the remaining three, also symmetrically disposed, again in parallel. Arrangements of a similar sort may be made with larger numbers of conductors. The number of conductors is desirably a multiple of three.
  • the coil in FIGS. 1(a) and 1(b) has a half conical angle of 45 and the coils of greatest utility have a half angle lying in the range 30 to 60. However, useful results may be obtained with half angles within the range 20 to 85. Purely by way of example, a coil might have a larger diameter of 3 inches and be'wound with enamelled copper wire of 32 s.w.g.; the half-angle being 45.
  • FIGS. 2 and 3 illustrates an advantage of the magnetic lens according to the invention over magnetic lenses of conventional form.
  • FIG. 2 illustrates a conventional lens, the arrow 11 indicating the direction of electron flow.
  • the lens comprises a coil 15 enclosed within a shroud 16 of material of high magnetic permeability.
  • the shroud is formed with close-set annular pole pieces 17, 18, concentric with't he average path followed by the electron beam as indicated by arrow 11,
  • the magnetic field between the pole pieces focuses the electrons in the beam on to the specimen under investigation at 19.
  • the working distance of .the lens is here defined as the distance d, that is the shortest distance between the lens structure and the specimen.
  • FIG. 3 illustrates diagrammatically a magnetic lens in use according to the invention.
  • a beam of electrons from a source S is focused by the lens coil 20 on to a specimen 19, the arrow 11 indicating the sense and average path of the electron beam.
  • Radiation emitted from the specimen 19 is detected by a detector D, which is designed and positioned to receive the emitted radiation desired.
  • the working distance d is the same as in FIG. 2.
  • FIG. 4 illustrates cooling means according to the invention.
  • This block 21 contains cooling passages 22, as close as practicable to the inner surface of the coil.
  • the cooling passages are provided with an inlet, 23, and an outlet, 24, through which cooling fluid may be passed in order to remove heat conducted from the coil.
  • the cooling passages may be in the form of a tube around which the block 21 is cast.
  • the block 21 is desirably of material having a high thermal conductivity, e.g. copper.
  • FIG. 4 illustrates another desirable feature of the invention, viz. that the coil is of small radial depth or thickness in comparison with its slant height, and desirably the ratio of slant height to radial thickness would not be less than :1, but could be very considerably greater. Small thickness of the coil is desirable in order to facilitate removal of heat therefrom and also to maximize the angle 0 shown in FIG. 3. It is possible to avoid all heating effects in the coil by operating it at superconducting temperatures, but it is difficult to arrange this and at the same time preserve a large angle 0 as mentioned above, because the cryogenic equipment tends to be bulky.
  • the working distance d is indicated, that is the distance between the extremity of the coil and the location of the focus of the electron beam and also of the specimen. It is a characteristic of the invention that the half-width as defined above is substantially larger than the working distance, and in general the half-width will not be less than twice the working distance.
  • FIG. 6(0) is a half section of a shrouded coil. The effect of this on the field strength is shown in FIG. 6(d) viz. to increase the field strength generally and to broaden the peak of the curve.
  • the definition of half-width remains as before and the tendency is to increase the ratio between half-width and working distance.
  • An electromagnetic lens for focusing a beam of charged particles comprising:
  • said coil having two open substantiallymagnetically unshrouded ends and an inner and an outer surface, at least an end part of which is substantially frusto-conical in shape tapering towards one unshrouded end of the coil with a half conical angle lying between 20? and said frusto-conical shape causing an increased magnetic field intensity towards said one unshrouded end of the coil to result in focussing an axially directed beam of charged particles.
  • An electromagnetic lens as in claim 1 further including:
  • An electromagnetic lens as in claim 1 further including:
  • return conductor means disposed substantially parallel to a geometrical generator of said frusto-conical coil end for providing an external electrical connection to the small end of said coil.
  • An electromagnetic lens as in claim 1 wherein said plurality of lengths comprises an even number whereby alternate lengths can be electrically connected in parallel to form two such parallel circuits which, in turn, may be connected in series with each other to help insure circumferentially uniform current distributions.
  • An electromagnetic lens as in claim 1 in which the coil is enclosed on the outer surface only thereof, at least in part, by a shroud consisting of material of high magnetic permeability.
  • An apparatus for analyzing an object of which comprises:
  • a magnetic lens for focusing said beam of charged particles onto said object, the magnetic lens comprising;

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Beam Exposure (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
US126930A 1967-08-18 1971-03-22 Magnetic lenses Expired - Lifetime US3707628A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB3825067 1967-08-18

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US3707628A true US3707628A (en) 1972-12-26

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US (1) US3707628A (ja)
DE (1) DE1764835A1 (ja)
FR (1) FR1594573A (ja)
GB (1) GB1234183A (ja)
NL (1) NL6811733A (ja)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4315152A (en) * 1977-03-23 1982-02-09 National Research Development Corporation Electron beam apparatus
US4541890A (en) * 1982-06-01 1985-09-17 International Business Machines Corporation Hall ion generator for working surfaces with a low energy high intensity ion beam
US4639597A (en) * 1983-10-24 1987-01-27 Anelva Corporation Auger electron spectrometer capable of attaining a high resolution
US5023457A (en) * 1989-05-30 1991-06-11 Seiko Instruments, Inc. Electron beam device
US5065027A (en) * 1989-11-16 1991-11-12 Jeol Ltd. Electromagnetic lens
US5079428A (en) * 1989-08-31 1992-01-07 Bell Communications Research, Inc. Electron microscope with an asymmetrical immersion lens
US5311028A (en) * 1990-08-29 1994-05-10 Nissin Electric Co., Ltd. System and method for producing oscillating magnetic fields in working gaps useful for irradiating a surface with atomic and molecular ions
US5382800A (en) * 1992-01-13 1995-01-17 Fujitsu Limited Charged particle beam exposure method and apparatus
US5446432A (en) * 1992-02-24 1995-08-29 Murata Mfg. Co., Ltd. Saddle type deflection coil
EP1943658A2 (en) * 2005-09-30 2008-07-16 Applied Materials, Inc. Cooling module for charged particle beam column elements
US11213891B2 (en) * 2015-04-21 2022-01-04 Varian Semiconductor Equipment Associates, Inc. Semiconductor manufacturing device with embedded fluid conduits

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2477827A1 (fr) * 1980-03-04 1981-09-11 Cgr Mev Dispositif accelerateur de particules chargees fonctionnant en ondes metriques

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3346736A (en) * 1964-09-22 1967-10-10 Applied Res Lab Inc Electron probe apparatus having an objective lens with an aperture for restricting fluid flow
US3374349A (en) * 1966-11-14 1968-03-19 Victor G. Macres Electron probe having a specific shortfocal length magnetic lens and light microscope
US3394254A (en) * 1964-06-06 1968-07-23 Philips Corp Electron-optical system with a magnetic focussing lens having a cooling means

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3394254A (en) * 1964-06-06 1968-07-23 Philips Corp Electron-optical system with a magnetic focussing lens having a cooling means
US3346736A (en) * 1964-09-22 1967-10-10 Applied Res Lab Inc Electron probe apparatus having an objective lens with an aperture for restricting fluid flow
US3374349A (en) * 1966-11-14 1968-03-19 Victor G. Macres Electron probe having a specific shortfocal length magnetic lens and light microscope

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4315152A (en) * 1977-03-23 1982-02-09 National Research Development Corporation Electron beam apparatus
US4541890A (en) * 1982-06-01 1985-09-17 International Business Machines Corporation Hall ion generator for working surfaces with a low energy high intensity ion beam
US4639597A (en) * 1983-10-24 1987-01-27 Anelva Corporation Auger electron spectrometer capable of attaining a high resolution
US5023457A (en) * 1989-05-30 1991-06-11 Seiko Instruments, Inc. Electron beam device
US5079428A (en) * 1989-08-31 1992-01-07 Bell Communications Research, Inc. Electron microscope with an asymmetrical immersion lens
US5065027A (en) * 1989-11-16 1991-11-12 Jeol Ltd. Electromagnetic lens
US5311028A (en) * 1990-08-29 1994-05-10 Nissin Electric Co., Ltd. System and method for producing oscillating magnetic fields in working gaps useful for irradiating a surface with atomic and molecular ions
US5393984A (en) * 1990-08-29 1995-02-28 Nissin Electric Co., Inc. Magnetic deflection system for ion beam implanters
US5483077A (en) * 1990-08-29 1996-01-09 Nissin Electric Co., Ltd. System and method for magnetic scanning, accelerating, and implanting of an ion beam
US5382800A (en) * 1992-01-13 1995-01-17 Fujitsu Limited Charged particle beam exposure method and apparatus
US5446432A (en) * 1992-02-24 1995-08-29 Murata Mfg. Co., Ltd. Saddle type deflection coil
EP1943658A2 (en) * 2005-09-30 2008-07-16 Applied Materials, Inc. Cooling module for charged particle beam column elements
WO2007041059A3 (en) * 2005-09-30 2009-04-09 Applied Materials Inc Cooling module for charged particle beam column elements
EP1943658A4 (en) * 2005-09-30 2010-06-16 Applied Materials Inc COOLING MODULE FOR COLUMN ELEMENTS OF LOADED PARTICLE RAYS
US11213891B2 (en) * 2015-04-21 2022-01-04 Varian Semiconductor Equipment Associates, Inc. Semiconductor manufacturing device with embedded fluid conduits

Also Published As

Publication number Publication date
FR1594573A (ja) 1970-06-08
GB1234183A (ja) 1971-06-03
DE1764835A1 (de) 1971-11-04
NL6811733A (ja) 1969-02-20

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