US3587013A - Magnetic lens device for corpuscular ray apparatus operating under vacuum - Google Patents

Magnetic lens device for corpuscular ray apparatus operating under vacuum Download PDF

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Publication number
US3587013A
US3587013A US821245A US3587013DA US3587013A US 3587013 A US3587013 A US 3587013A US 821245 A US821245 A US 821245A US 3587013D A US3587013D A US 3587013DA US 3587013 A US3587013 A US 3587013A
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United States
Prior art keywords
cylinders
lens
gap
shielding
lens device
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Expired - Lifetime
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US821245A
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English (en)
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Isolde Dietrich
Reinhard Weyl
Helmut Zerbst
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Siemens AG
Siemens Corp
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Siemens Corp
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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
    • H01J37/09—Diaphragms; Shields associated with electron or ion-optical arrangements; Compensation of disturbing fields
    • 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
    • H01J37/1416—Electromagnetic lenses with superconducting coils
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S505/00—Superconductor technology: apparatus, material, process
    • Y10S505/825—Apparatus per se, device per se, or process of making or operating same
    • Y10S505/871—Magnetic lens

Definitions

  • a magnetic lens device for corpuscular ray apparatus to operate under vacuum is equipped with a pair of tubular shielding cylinders of superconductive material coaxially surrounding the lens axis and spaced from each other along said axis.
  • Cryogenic means are thermally connected with the cylinders, and lens windings surround the cylinders for generating a magnetic field.
  • the respective cylinders terminate in end faces directed toward each other and defining between each other a lens gap in which the cylinders concentrate the field near the axis.
  • the shielding cylinders comprise respective end portions of superconductive material of higher current carrying capacity than the remaining portion of each cylinder, said end faces at said lens gap being formed by said respective end portions.
  • Another object is to simultaneously minimize the possibilities of instabilities of operation as may result from excessively high critical current densities.
  • the two hollow cylindrical shielding structures that form part of the lens device and are spaced from each other alongand in coaxial relation to the lens axis to establish the lens gap between each other, have their respective end portions adjacent to the gap face constituted by superconductor material of higher current-carrying capacity than the remaining portion of each shielding cylinder. Consequently the end portions have a particularly great shielding efi'ect, whereas the other portions of the cylinders are less effective on account of their lower current-carrying capacity. As a result, while a penetration of the magnetic field into the high conductivity portions adjacent to the gap faces of the two cylindrical structures is virtually prevented, the field can penetrate more or less into the other portion of each shielding cylinder without impairing the imaging properties of the lens.
  • FIG. 1 shows schematically and in diametrical section an embodiment of a lens device according to the invention by way of example
  • FIGS. 2 and 3 are graphs explanatory of the operation of such a lens device
  • FIG. 4a and FIG. 412 show respectively a sectional and schematic view of the magnetic field line configuration occurring with planar gap faces and properly rounded gap faces respectively;
  • FIG. 5 is a sectional view of one of the cylindrical shielding structures in alens device according to the invention such as the one shown in FIG. I.
  • the lens device shown in FIG. I is designed for operation as an objective lens in an electron microscope and corresponds generally to the one illustrated and described in the abovementioned copending application Ser. No. 648,623.
  • the device comprises a winding 1 preferably but not necessarily made of superconducting material.
  • the magnetic flux produced by the winding when energized is shielded away from the centrally .located electron-optical axis of the lens device. This is done with the aid of two tubular shielding cylinders 2 and 3 which consist of superconductor material and are in heat-conducting connection with a cyrogenic medium C, such as liquid helium or liquid air, supplied to a jacket space surrounding the coil 1.
  • the jacket structure of heat conducting metal is joined with the respective foot portion of the shielding cylinders 2 and 3 by heat-conducting metal cover It is an object of the presentinvention to improve such lens discs.
  • the two cylinders 2 and 3 are coaxially spaced from each other along and in coaxial relation to the lens axis 1 thus defining a lens gap s between the mutually opposite end faces 6 and 7 of the cylinders.
  • Each end face is bevelled along its periphery so as to be approximately matched to the configuration of the magnetic field lines in the lens gap s.
  • the aperture error constant C is also determined by the field gradient along the axis in the lens gap. Assuming, for explanation, that the field is at least approximately barrel shaped, the magnitude of the field gradient for a given maximum value H, of field intensity in the gap is determined by the so-called half width magnitude 2d of the maximum field intensity. This magnitude, significant to the invention, will be explained presently with reference to FIG. 2.
  • the requirement for minimizing the axial extent of the region in which the lens field acts upon the beam makes it important to minimize the half-intensity width 2d.
  • the magnitude of 2d depends upon the gap width s, the shape of the mutually opposed end faces of the two cylinders that define the gap s, and the wall thickness of the shielding cylinders.
  • the wall thickness is denoted by win FIG. 1, although it should be understood that FIG. I mainly serves as an example of the invention and that the wall thickness need not be uniform in each cylinder and that the wall thickness of one cylinder may also differ from that of the other.
  • the present invention takes advantage of the discovery that the half-intensity width 2d, commencing from a minimum value, is virtually independent of the wall thickness of the shielding cylinders; and this is the fundamental reason this is the fundamental the feature of the present invention according to which, in a magnetic lens device generally of the abovedescribed type and as exemplified in FIG. I, the shielding cylinders 2, 3 in their respective end portions 2a, 30 adjacent to the mutually opposite end faces 6, 7 at the lens gap consist of a superconductor material of higher current-carrying capacity than that of the other portions 2b, 3b of the shielding cylinders.
  • the differentiation between high current-carrying capacity in the superconducting material adjacent to the lens gap and elsewhere in each of the shielding bodies is particularly advantageous, with respect to avoidance of instabilities due to flux jumps, if the shape of the mutually opposite front faces of the cylinders is substantially matched to the configuration of the field lines.
  • the horizontal broken lines apply to constant gap widths of2 mm., 3 mm., 4 mm., 5 mm., and 6 mm. respectively.
  • the broken horizontal straight lines therefore, permit a conclusion as to the efiect of changes in wall thickness w, whereas the full-line curves are indicative of changes in gap width s.
  • the wall thickness w was kept constant; and for each of the curves the gap width s was kept constant.
  • the indicated numerical values resulted from sample tests made in an electrolytic trough. Tests made in a different way or with different devices result in different numeral values but do not affect the conclusion-essential to the present invention, and apparent from the horizontal lines for different constant gap widths s in FIG. 3that a change in wall thickness w does not appreciably change the magnitude 2d here of interest.
  • the field configuration in the lens device is exemplified diagrammatically in FIG. 4a and 4b. These illustrations are also based on test results made in an electrolytic trough.
  • the superconducting cylinders were simulated by insulating cylinders 10, ll, l2, 13 which had central recesses in the respective gap-forming front faces.
  • the opposite end face of each cylinder was provided with an electrode l4, 15, 16 or 17.
  • the phenomena to be studied were simulated by electric voltages between the electrodes, for example at volts, and by the electric fields produced by these voltages.
  • the lens bores are simulated by the recesses in the mutually opposite front faces of the cylinders 10, ll and of the cylinders 12, 13.
  • a lens device In a lens device according to the invention the occurrence of field penetration at the end face regions only, can be prevented by producing these portions of a more fine grandular superconducting starting material than the other portions into which the field is permitted to more or less penetrate without impairing the imaging quality of the lens.
  • the fine granular superconducting material in the end face portion consists for example of Nb,Sn in form of a fine powder, whereas the residual portion (2b, 3b in FIG. 1) of the lens device is made of a more compact material such as Nb -,Sn in the form of a granular material of coarser constitution than the power used for producing the front face portions 2a, 3a.
  • shielding cylinders for or in the lens devices can be produced in different ways. One of them is as follows.
  • a press mold for producing the shielding cylinders is filled with respective layers of superconducting granular material, the grain size of the material in the layer for the end face portion being different from the grain size of the material in the other portion of each cylinder, in accordance with the high current-carrying capacity required for the end face portions as compared with the lower current-carrying capacity in the other portion.
  • the material for the front face portion is entered into the mold as a fine granular powder, preferably of Nb Sn; and the same material but of a courser constitution is used in the other portion of the shielding cylinder.
  • the different materials After thus placing the different materials into the mold, they are conjointly subjected to pressure and temperature treatment in order to bond all of the granules together by fusing or sintering.
  • the corpuscular beam is shielded from the lens field with the exception of the short and narrow region within the lens gap.
  • Another method of producing a device according to the invention is to compose all regions of the shielding cylinders of only one kind of superconductor starting material.
  • this material may be used in granular constitution of a single average grain size, and the material placed into the mold is then compacted by pressure and heat to form a solid body in which all of the granules are bonded together.
  • care must be taken subsequently to produce in the material of the front face portion sufiicient lattice defects that increase the current-carrying capacity.
  • lattice defects can be produced by subjecting the front face portion of the molded workpiece to high energy radiation such as by slow neutrons.
  • this method is preformed by first completing the shaping and solidifying of the shielding cylinders from uniform superconductive starting material, and subsequently subjecting only the front face portions that are to form the lens gap between each other to irradiation with high energy subatomic particles.
  • the shielding cylinders is to form the shielding cylinders from 'asuperconducting material and to alloy fissionable materialinto the material of the front face portion of the workpiece. After thus shaping and, if necessary, compacting and otherwise finishing the cylinders, the alloyed front face portions are subjected to radiation by slow neutrons.
  • Suitable as such an alloying addition is uranium 23S, forexample '(Journal of Applied Physics, Vol. 37, 1966, page 2,2l8.)
  • other fissionable elements or mixtures such as isotope mixtures, may. be also employedin this manner.
  • These materials when subjected to irradiation, likewise produce lattice defects which'increase the current-carrying capacity in a the thin alloyed layer adjacent to the front face. It has been found that the layer thickness of superconducting material alloyed with fissionable material in the just-described manner may amount approximately to 0.1 mm., up to l mm. or to some larger thickness preferably in the order .of magnitude of l mm.
  • FIG 5 illustrates byway of example a shielding cylinder suitable as component of a device according to FIG. 1 and produced by sintering of Nb,Sn powder applied in respectively different grain sizes as described above.
  • the front face portion 20, adjacent to the gap and having a front face shaped in adaptation in the field configuration, is made of a more finely granular material than the remaining portion 21 of the cylinder.
  • the invention is applicable to electromagnetic objective lens devices for electron microscopes, but is also advantageous for other lenses and for use with other corpuscular ray apparatus, such as ion microscopes or difiraction apparatus, wherever it is desirable to have the lens field act upon the corpuscular beam at a highest attainable-field strength within a short distance along the beam direction.
  • a magnetic lends device for corpuscular ray apparatus to operate undervacuum a pairof tubular shielding cylinders of superconductive material coaxially surrounding the lens axis and spaced from each other along said axis, cryogenic means thermally connected with said cylinders, lens winding means surrounding said cylinders for generating a magnetic field,
  • additional field-producing lens windings may be provided in the lens gap, or stigmator coils or coils for adjusting the beam within the lens may also be mounted at or in the lens gap.
  • disc-shaped shielding structures may be provided at the respective other ends of the shielding cylinders remote from ,the lens gap, such a shielding effect being produced, for example, by the disc-shaped structures that connect the shielding cylinders 2 and 3 in FIG.
  • said shielding cylinders comprise respective end portions having a higher superconductance than the remaining portion of said respective cylinders, said end faces at said lens gap being formed by said respective end portions.
  • said end portions consisting of superconductivelmaterial of higher current-carrying capacity than said remaining portions.
  • said end faces of said end portions of the higher current-carrying capacity having a generally convex shape corresponding to the contiguration of the lens field lines at said gap.
  • said shielding cylinders consisting substantially of NbgSn.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Superconductor Devices And Manufacturing Methods Thereof (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
  • Particle Accelerators (AREA)
US821245A 1968-05-31 1969-05-02 Magnetic lens device for corpuscular ray apparatus operating under vacuum Expired - Lifetime US3587013A (en)

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CH815368 1968-05-31

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3708772A (en) * 1970-12-04 1973-01-02 Siemens Ag Magnetic lens arrangement
US3870891A (en) * 1972-09-04 1975-03-11 Nat Res Dev Magnetic lenses
US3916201A (en) * 1973-02-16 1975-10-28 Siemens Ag Electron microscope having a plurality of coaxial cryogenically cooled lenses
EP0555492A4 (enrdf_load_stackoverflow) * 1991-08-30 1994-03-02 Hitachi, Ltd.
US6051839A (en) * 1996-06-07 2000-04-18 Arch Development Corporation Magnetic lens apparatus for use in high-resolution scanning electron microscopes and lithographic processes
USD616528S1 (en) * 2008-04-07 2010-05-25 Festo Ag & Co. Kg Detector for detecting the angular position of a rotatable shaft
USD618309S1 (en) * 2008-04-07 2010-06-22 Festo Ag & Co. Kg Detector for detecting the angular position of a rotatable shaft
USD622349S1 (en) * 2008-04-07 2010-08-24 Festo Ag & Co. Kg Detector for detecting the angular position of a rotatable shaft

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3708772A (en) * 1970-12-04 1973-01-02 Siemens Ag Magnetic lens arrangement
US3870891A (en) * 1972-09-04 1975-03-11 Nat Res Dev Magnetic lenses
US3916201A (en) * 1973-02-16 1975-10-28 Siemens Ag Electron microscope having a plurality of coaxial cryogenically cooled lenses
EP0555492A4 (enrdf_load_stackoverflow) * 1991-08-30 1994-03-02 Hitachi, Ltd.
US5393983A (en) * 1991-08-30 1995-02-28 Hitachi, Ltd. Magnetic electron lens and elctron microscope using the same
US6051839A (en) * 1996-06-07 2000-04-18 Arch Development Corporation Magnetic lens apparatus for use in high-resolution scanning electron microscopes and lithographic processes
US6410923B1 (en) 1996-06-07 2002-06-25 Arch Development Corporation Magnetic lens apparatus for use in high-resolution scanning electron microscopes and lithographic processes
USD616528S1 (en) * 2008-04-07 2010-05-25 Festo Ag & Co. Kg Detector for detecting the angular position of a rotatable shaft
USD618309S1 (en) * 2008-04-07 2010-06-22 Festo Ag & Co. Kg Detector for detecting the angular position of a rotatable shaft
USD622349S1 (en) * 2008-04-07 2010-08-24 Festo Ag & Co. Kg Detector for detecting the angular position of a rotatable shaft

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Publication number Publication date
DE1805585B2 (de) 1976-08-12
DE1805585A1 (de) 1970-04-23
GB1234509A (enrdf_load_stackoverflow) 1971-06-03

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