US3812365A - Permanent magnet lens system - Google Patents

Permanent magnet lens system Download PDF

Info

Publication number
US3812365A
US3812365A US00339881A US33988173A US3812365A US 3812365 A US3812365 A US 3812365A US 00339881 A US00339881 A US 00339881A US 33988173 A US33988173 A US 33988173A US 3812365 A US3812365 A US 3812365A
Authority
US
United States
Prior art keywords
lens system
magnets
magnetic
lens
magnetic lens
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
US00339881A
Other languages
English (en)
Inventor
J Lepoole
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.)
Individual
Original Assignee
Individual
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 Individual filed Critical Individual
Application granted granted Critical
Publication of US3812365A publication Critical patent/US3812365A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • 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
    • 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
    • H01J37/143—Permanent magnetic lenses

Definitions

  • FIGJ. 1 A first figure.
  • the invention relates to a magnetic lens system for a flow of charged particles, in particular for an electron beam in an electron microscope, the magnetic field of the lens system having been excited by permanent magnets.
  • a consideration of such a magnetic lens system provided with one or a number of permanent magnets and a flux conductivity circuit teaches that for a certain desirable configuration of this lens system and desirable values of magnetic induction B in the lens fields concerned, a number of ampere windings equivalent to this lens system can be calculated.
  • This number of ampere windings again is determining for the dimensions and, in so far there is freedom as to that, the choice of material for the permanent magnet.
  • An other way of approach with respect to combating the chromatic magnification aberration in magnetic lens systems and to increase magnetic induction, B, as a rule in co-operation with the measures mentioned above, is, analogous to the achromatic lens systems applied in light-optical imaging devices, the assembly of an electron-optical equivalent achromatic, magnetic lens system, e.g., an electron-optic equivalent of the Ramsden ocular well-known among those skilled in the art, the focus of the one lens lying in the centre of the other lens.
  • a magnetic lens system of this type is known from Proceedings of the fourth international conference on electronmicroscopy, Berlin 1958, pp. 53 to 57 and including, H.Kimura and Y.Kikuchi Permanent magnet lens systems and their characteristics.'ln this lens system the magnetic induction values in the lens fields are raised to a high extent by means of permanent magnets magnetized in axial direction with respect to the electron beam, via flux conductivity circuits, provided with a central pole part and two air gaps, formed with the aid of pole shoes, and in the environment of which the lens fields are localized.
  • a magentic lens renders a rotation to a picture of an object represented by the electron beam.
  • a non-isotropic rotation takes place, then a phenomenon occurs indicated by anisotropic image distortion or S distortion, which is reckoned among the previousl stated lens errors.
  • the invention is based on the insight that the ways that so far have been followed for combating or neutralizing the lens errors stated in magnetic lens systems and lenses always have resulted in taking far-reaching measures for improvement of consisting lens systems and lenses, which essentially are of one and the same intention, and that an entire new way results into an exceptionally simple and compact lens system, in which the lens errors stated are simultaneously neutralized.
  • a magnetic lens system of the type stated in the preamble is provided, because two thin small disc magnets, provided with small openings and magnetized axially in opposite directions, are united straight into an electron-optic achromatic as well as rotationfree and distortionfree system that light permanent magnetic lens system without lens errors for an electron microscope that has only some cubic centimeters volume and some grams of weight.
  • the disc magnets the diameter of which amounts to, for instance, approximately mm are united in a very compact way by inserting an iron platelet, while furthermore two iron platelets, that each each time are mounted on the sides of the disc magnets that are turned from the platelets make the system complete, that than can be fixed in a holder or socket.
  • the small disc magnets advantageously each possesses an opening the diameter of which is smaller than the fourth part of the outer diameter, the smallest outer-dimension of the small magnet disc.
  • this diameter of the opening can be maximally equal or practically equal to the thickness of the small disc magnet.
  • the small openings in the small disc magnets of the lens system according to the invention see to it that the field in these small disc magnets becomes practically equal to the coercive force and to a far lesser extent is determined by the energy product.
  • the small disc magnets can be made of a material with a high coercive power, for instance of compounds or of alloys of cobalt with rare earths or platinum. Furthermore, this coercive power advantageously can be greater than 1,400 Oersteds.
  • the lens system according to the invention has a fixed focus. Consequently, for a control of the magnification it is absolutely necessary that this system is mounted in an electron microscope movably in axial direction.
  • the power of the magnetic lens system thus is determined by the construction, the total magnification can be'made continuously variable by displacing one or a number of these systems in axial direction.
  • the lens system according to the invention is very suitable by its very simplicity and slight size.
  • a further advantage of the invention is that it provides lens systems that can easily be interchanged.
  • FIG. 1 a cross-section of a magnetic lens system provided with a permanent magnet and assembled according to a technique known in the art
  • FIG. 2 a lens system known in the art with two disc magents that for the adjustment of the focus are movable with respect to each other and have been provided with large openings
  • FIG. 3 The path of rays in an light-optical lens system of the Ramsden type, ratio x/y being practically equal to l yl
  • FIG. 4 a cross-section of an embodiment of the lens system according to the invention, for the sake of clarity both the proportions and the dimensions not being drawn to scale,
  • FIG. 5 beams in the lens system according to the invention, ratio x/ y, exactly as in the system of the Rams den type, being practically equal to x,/y,
  • FIG. 6 a further embodiment of the lens system ac cording to the invention, provided with platelets with flanges, and
  • FIG. 7 a picture of a lens system according to the invention and displaceable in axial direction in a guiding member.
  • FIG. 1 a magnetic lens system is pictured, which is assembled according to the technique known in the art, a magnetic flux conductivity circuit formed out of parts 1 and 2 guiding the field originating from permanent magnet 3 to air gaps 4 and 5. In the environment of these air gaps 4 and 5 the lens fields are situated that focus an electron beam entering alongside axis 2.
  • the system pictured in FIG. 1 represents only in principle the construction of one of the innumerable permanent magnet lenses known in the art, which in reality have a far more complicated construction. This does not only concern the magnetic flux conductivity circuits but the location and the shape of the permanent magnets as well, with a view to the curbing of magnetic stray fields. In this connection reference is made to what has already been observed before with respect to these stray fields.
  • FIG. 4 the lens system according to the invention, held in a holder or socket 6, is pictured.
  • This system contains two axially in opposite directions magnetized, thin small disc magnets 9, provided with small openings 0. Between these small disc magnets 9 a small spacer 8 has been inserted, for instance, of iron, which also is provided with a fitting opening for the electron beam and determines the distance between the small disc magnets that is required for a desirable lens action.
  • FIG. 2 has not been drawn to scale and the diameter of small openings 0 has been shown relatively too great.
  • end platelets 7 can be provided with flanges U, as FIG. 6 shows. In special cases this also holds good for centre platelet 8.
  • FIG. 7 the lens system according to the invention is shown axially displaceable in a guiding member 11, as the drawn arrows make clear.
  • This guiding member 11 in turn is provided within the space to be evacuated of an electron microscope.
  • a magnetic lens system for a flow of charged particles in particular for an electron beam in an electron microscope, comprising a pair of permanent disc magnets each having a central opening therein of a size substantially less than the size of said magnets, said magnets producing a magnetic field for the lens system and each being magnetized axially in opposite directions, said magnets being coaxially aligned and separated by means of a spacer having a thickness substantially equal to the size of each said opening, an iron plate with a central opening coaxial with said magnet opening being in surface contact with the outer surface of each said magnet, and a holder provided within which said magnets, spacer and plates are fixedly mounted, whereby the lens system compensates for any electronoptic, achromatic and the like distortions as well as being rotation-free and distortion-free.
  • magnets are of a material having'a high coercive power selected from the group consisting of cobalt alloys and cobalt compounds together with materials selected from the group consisting of rare earth metals and platinum.
  • FIGURES 2, 3 and 5 should appear as shown on the attached -sheets.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Beam Exposure (AREA)
  • Magnetic Bearings And Hydrostatic Bearings (AREA)
US00339881A 1972-03-10 1973-03-09 Permanent magnet lens system Expired - Lifetime US3812365A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL7203264A NL7203264A (enrdf_load_stackoverflow) 1972-03-10 1972-03-10

Publications (1)

Publication Number Publication Date
US3812365A true US3812365A (en) 1974-05-21

Family

ID=19815571

Family Applications (1)

Application Number Title Priority Date Filing Date
US00339881A Expired - Lifetime US3812365A (en) 1972-03-10 1973-03-09 Permanent magnet lens system

Country Status (5)

Country Link
US (1) US3812365A (enrdf_load_stackoverflow)
JP (1) JPS48103270A (enrdf_load_stackoverflow)
DE (1) DE2311578A1 (enrdf_load_stackoverflow)
GB (1) GB1426243A (enrdf_load_stackoverflow)
NL (1) NL7203264A (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3984687A (en) * 1975-03-17 1976-10-05 International Business Machines Corporation Shielded magnetic lens and deflection yoke structure for electron beam column
US4315152A (en) * 1977-03-23 1982-02-09 National Research Development Corporation Electron beam apparatus
US4400622A (en) * 1980-01-30 1983-08-23 Nippon Telegraph & Telephone Public Corporation Electron lens equipment
US4806766A (en) * 1986-06-25 1989-02-21 U.S. Philips Corporation Magnetic lens system
US6201251B1 (en) * 1998-08-28 2001-03-13 Nikon Corporation Compensation of space charge in a particle beam system
US20100230590A1 (en) * 2006-06-07 2010-09-16 Fei Company Compact Scanning Electron Microscope

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB201000952D0 (en) * 2010-01-21 2010-03-10 Nfab Ltd A sub miniature low energy scanned beam microscope
JP6323943B2 (ja) * 2013-02-27 2018-05-16 株式会社Ｐａｒａｍ 電子レンズおよび電子ビーム装置

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3984687A (en) * 1975-03-17 1976-10-05 International Business Machines Corporation Shielded magnetic lens and deflection yoke structure for electron beam column
US4315152A (en) * 1977-03-23 1982-02-09 National Research Development Corporation Electron beam apparatus
US4400622A (en) * 1980-01-30 1983-08-23 Nippon Telegraph & Telephone Public Corporation Electron lens equipment
US4806766A (en) * 1986-06-25 1989-02-21 U.S. Philips Corporation Magnetic lens system
US6201251B1 (en) * 1998-08-28 2001-03-13 Nikon Corporation Compensation of space charge in a particle beam system
US20100230590A1 (en) * 2006-06-07 2010-09-16 Fei Company Compact Scanning Electron Microscope
EP2024750A4 (en) * 2006-06-07 2011-04-06 Fei Co ELECTRON MICROSCOPE WITH COMPACT SCAN
US20110133083A1 (en) * 2006-06-07 2011-06-09 Fei Company Compact scanning electron microscope
US8309921B2 (en) 2006-06-07 2012-11-13 Fei Company Compact scanning electron microscope
US9025018B2 (en) 2006-06-07 2015-05-05 Fei Company User interface for an electron microscope
US9865427B2 (en) 2006-06-07 2018-01-09 Fei Company User interface for an electron microscope

Also Published As

Publication number Publication date
JPS48103270A (enrdf_load_stackoverflow) 1973-12-25
DE2311578A1 (de) 1973-09-20
GB1426243A (en) 1976-02-25
NL7203264A (enrdf_load_stackoverflow) 1973-09-12

Similar Documents

Publication Publication Date Title
US4806766A (en) Magnetic lens system
Grivet et al. Electron optics
US2305761A (en) Electron-optical lens
US2503173A (en) Permanent magnetic electron lens system
US7285785B2 (en) Apparatus with permanent magnetic lenses
US3812365A (en) Permanent magnet lens system
US2212206A (en) Electron device
GB810267A (en) Focusing magnet for long electron beams
DE1804199C3 (de) Korpuskularstrahlgerät zur wahlweisen Abbildung eines Präparates oder seines Beugungsdiagrammes
US4578663A (en) Magnetic assembly
EP1042784B1 (en) Wien filter
US3629578A (en) Magnetic deflection system for electron analysis devices
NL7903467A (nl) Kathodestraalbuis voor het weergeven van gekleurde beelden.
TOULOUSE Magnetic electron lenses
Halbach Permanent magnets for production and use of high energy particle beams
US3201631A (en) Short focus lens at focal point of long focus lens
US4078176A (en) Mass spectrometer
US2849636A (en) Magnetic electron lens
Yavor et al. Achromatic quadrupole lenses
US2418432A (en) Magnetic electron lens system
US4468563A (en) Electron lens
GB720776A (en) Improvements relating to magnetic focusing devices for electron beams
US3050653A (en) Magnetic focusing device
US7608838B1 (en) Electron optical component
US5689112A (en) Apparatus for detection of surface contaminations on silicon wafers