US20190259565A1 - Compact deflecting magnet - Google Patents
Compact deflecting magnet Download PDFInfo
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- US20190259565A1 US20190259565A1 US16/401,948 US201916401948A US2019259565A1 US 20190259565 A1 US20190259565 A1 US 20190259565A1 US 201916401948 A US201916401948 A US 201916401948A US 2019259565 A1 US2019259565 A1 US 2019259565A1
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- 239000002245 particle Substances 0.000 claims abstract description 10
- 230000005291 magnetic effect Effects 0.000 claims description 33
- 229910000595 mu-metal Inorganic materials 0.000 claims description 6
- 238000010894 electron beam technology Methods 0.000 abstract description 10
- 238000010884 ion-beam technique Methods 0.000 abstract description 7
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- 229910052734 helium Inorganic materials 0.000 description 2
- 239000001307 helium Substances 0.000 description 2
- 238000001459 lithography Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910001369 Brass Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000003302 ferromagnetic material Substances 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
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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
- H01J37/147—Arrangements for directing or deflecting the discharge along a desired path
- H01J37/1472—Deflecting along given lines
- H01J37/1474—Scanning means
- H01J37/1475—Scanning means magnetic
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
- G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
- G21K1/08—Deviation, concentration or focusing of the beam by electric or magnetic means
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F7/00—Magnets
- H01F7/02—Permanent magnets [PM]
- H01F7/0273—Magnetic circuits with PM for magnetic field generation
- H01F7/0278—Magnetic circuits with PM for magnetic field generation for generating uniform fields, focusing, deflecting electrically charged particles
- H01F7/0284—Magnetic circuits with PM for magnetic field generation for generating uniform fields, focusing, deflecting electrically charged particles using a trimmable or adjustable magnetic circuit, e.g. for a symmetric dipole or quadrupole magnetic field
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
- H01J29/58—Arrangements for focusing or reflecting ray or beam
- H01J29/64—Magnetic lenses
- H01J29/66—Magnetic lenses using electromagnetic means only
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
- H01J29/70—Arrangements for deflecting ray or beam
- H01J29/72—Arrangements for deflecting ray or beam along one straight line or along two perpendicular straight lines
- H01J29/76—Deflecting by magnetic fields only
-
- 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
- H01J37/08—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 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
- H01J37/147—Arrangements for directing or deflecting the discharge along a desired path
-
- 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
- H01J37/153—Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
- H05H7/04—Magnet systems, e.g. undulators, wigglers; Energisation thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/15—Means for deflecting or directing discharge
- H01J2237/152—Magnetic means
- H01J2237/1526—For X-Y scanning
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/26—Electron or ion microscopes
- H01J2237/28—Scanning microscopes
- H01J2237/2803—Scanning microscopes characterised by the imaging method
- H01J2237/2806—Secondary charged particle
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/30—Electron or ion beam tubes for processing objects
- H01J2237/317—Processing objects on a microscale
- H01J2237/31749—Focused ion beam
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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
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/266—Measurement of magnetic or electric fields in the object; Lorentzmicroscopy
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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
- H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
- H01J37/317—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation
- H01J37/3174—Particle-beam lithography, e.g. electron beam lithography
Definitions
- the present disclosure relates to magnets, and more specifically, to compact magnets for deflection and focusing of electron and ion beams.
- the devices include, among others, Cathode Ray Tubes, X-ray Tubes, Electron Beam Computed Tomography Scanners, Klystrons, Scanning Electron Microscopes, Helium Ion Microscopes, Electron and Ion Lithography Devices.
- the beam-deflecting magnets prefferably have a uniform (dipole) magnetic field and also produce a quadrupole focusing field.
- the magnets should be scan-able through a range of deflection angles and the field components should be magnetically rotatable about the initial beam axis.
- Past solutions to the above-mentioned design requirements of the magnets have generally involved complex magnetic coil arrangements.
- the present disclosure is directed to magnets for deflection and focusing of electron and ion beams.
- the magnet produces dipole and quadrupole fields from the same coil set.
- a particle beam device including a magnet.
- the device includes: a particle beam source configured to emit electron and ion beams; a plurality of yokes arranged in a substantially rectangular shape; a coil set including a plurality of coils, wherein windings of the plurality of coils are uniformly distributed across and wound around the plurality of yokes, wherein the coil set is configured to produce both dipole and quadrupole fields, wherein the magnet is configured to deflect and focus electron and ion beams.
- a magnet in another implementation, includes: a plurality of yokes arranged in a substantially rectangular shape; a coil set including a plurality of coils, wherein windings of the plurality of coils are uniformly distributed across and wound around the plurality of yokes, wherein the coil set is configured to produce both dipole and quadrupole fields.
- FIG. 1 is a 3-D view of a compact magnet in accordance with one implementation of the present disclosure
- FIG. 2A is a cross-sectional view (x-z plane) of the compact magnet in accordance with one implementation of the present disclosure
- FIG. 2B is another cross-sectional view (y-z plane) of the compact magnet in accordance with one implementation of the present disclosure
- FIG. 3 is another cross-sectional view (x-y plane) of the compact magnet in accordance with one implementation of the present disclosure
- FIG. 4 is an example graph of the dipole magnetic fields (B Y ) due to equal currents in the two Y coils;
- FIG. 5 is an example graph of the dipole magnetic fields (B Y ) due to equal currents in the two X coils;
- FIG. 6 is an example graph of the quadrupole magnetic fields due to opposing currents in the two Y coils
- FIG. 7 is an example graph of the combined dipole and quadrupole magnetic fields, due to combined currents in the two Y coils;
- FIG. 8 shows an example of the 45° quadrupole magnetic fields due to the currents in the four QB coils at the corners of the yoke
- FIG. 9 shows a yoke configured into two halves in accordance with one implementation of the present disclosure.
- FIG. 10 shows one implementation of the present disclosure in which the magnetic yoke of a parallel sided magnet is divided into identical strips.
- alternative solution includes the magnet which produces dipole and quadrupole fields from the same coil set in contrast to the prior design in which the dipole and quadrupole fields are produced by separate sets of coils.
- the design of the alternative solution described here is not only simple, but unlike some conventional designs, the magnet can also be assembled around the beam tube after the tube is completed. Further, the newly-designed magnet is capable of producing greater deflection angles than conventional designs.
- FIG. 1 is a 3-D view of a compact magnet 100 in accordance with one implementation of the present disclosure.
- the compact magnet 100 is used in a particle beam device such as a cathode ray tube, X-ray tube, electron beam computed tomography scanner, klystron, scanning electron microscope, helium ion microscope, or electron and ion lithography device.
- the particle beam device may also include a particle beam source, in addition to the magnet.
- the compact magnet 100 is used for deflection and focusing of electron and ion beams emitted by the particle beam source.
- the compact magnet 100 is a horn-shaped with an inlet opening 110 that is substantially rectangular in shape (in the x-y plane).
- the substantially rectangular shape also includes octagonal corners 120 , 122 , 124 , 126 (e.g., the corners are in 45° angles).
- the coils in the octagonal corners 120 , 122 , 124 , 126 are configured as quadrupole type B (QB).
- QB quadrupole type B
- the exit contour of the yoke on the downstream side is arcuate to provide a quadrupole focusing field which may be used to oppose that of the natural focusing effect, due to deflection, by the uniform field.
- FIG. 2A is a cross-sectional view (x-z plane) 200 of the compact magnet 100 in accordance with one implementation of the present disclosure.
- the cross-sectional view 200 of FIG. 2A shows coil Y 1 ( 210 ) and coil Y 2 ( 212 ) and yokes 220 , 222 .
- the design assumes that the beam deflection is mostly in one plane (i.e., the x-z plane).
- the form is based on a classic “window frame” design which has a very uniform internal dipole magnetic field provided the coil currents are uniformly distributed across the respective faces of the yoke.
- FIG. 2A also illustrates some alternative shapes 230 , 232 , 234 for the magnetic yoke and coils for which the magnetic field distribution at the beam would be the same.
- FIG. 2B is another cross-sectional view (y-z plane) 250 of the compact magnet 100 in accordance with one implementation of the present disclosure.
- the cross-sectional view 250 of FIG. 2B also shows the yoke 220 .
- FIG. 3 is another cross-sectional view (x-y plane) 300 of the compact magnet 100 in accordance with one implementation of the present disclosure.
- various coils are shown (designated as coil Y 1 ( 310 ), coil Y 2 ( 312 ), coil X 1 L ( 320 ), coil X 1 R ( 322 ), X 2 L ( 330 ), X 2 R ( 332 )) with reference to the coordinate system defined in FIGS. 1, 2A, 2B, and 3 .
- each coil is uniformly distributed across their respective faces of the yoke.
- Each pair (L, R) of X coils 320 / 322 or 330 / 332 is connected electrically as a single coil although they are mechanically on separate halves of the yoke.
- the two halves of the yoke are connected at butt joints 340 , 342 where there is zero magnetic flux across the joint 340 or 342 due to the dominant magnetic field inside the yoke, B Y .
- the currents in the X coils 320 , 322 , 330 , 332 and the Y coils 310 , 312 produce both dipole and quadrupole magnetic fields as described below.
- the cross section shown in FIG. 3 is generally rectangular, its form parallel to the beam direction (in the z direction) may be horn-shaped or parallel-sided.
- FIG. 3 also shows the optional QB coils (e.g., 350 ).
- the exit contour of the yoke on the downstream side is arcuate to provide a quadrupole focusing field which may be used to oppose that of the natural focusing effect, due to deflection, by the uniform field. The calculation of the radius for this arc is described below.
- I DY the dipole current in coil Y
- I QY the quadrupole current in coil Y
- I DX the dipole current in coil X
- I QX the quadrupole current in coil X
- B y ⁇ o g ⁇ [ N Y ⁇ I DY + 2 ⁇ x w ⁇ ( N Y ⁇ I QY + N X ⁇ I QX ) ] + term ⁇ 1 ⁇ [ 5 ]
- B x ⁇ o w ⁇ [ N X ⁇ I DX + 2 ⁇ y g ⁇ ( N Y ⁇ I QY + N X ⁇ I QX ) ] + term ⁇ 1 ⁇ [ 6 ]
- N Y the number of turns in each separate Y coil
- N X the number of turns in each separate X coil
- g the vertical height of the yoke.
- the magnitude of the effective magnetic field gradient is as follows:
- the quadrupole lens strength can be calculated as follows:
- p is the beam momentum
- the two Y coils are supplied with separate currents I Y1 and I Y2 .
- each coil includes two windings, one carrying the dipole current, I DY , and the other the quadrupole current, I QY . The decision for selecting one implementation over another depends on practical considerations such as the cost of coil drivers.
- the dipole component of the magnetic field may be approximated by a thin lens element having both cylindrical and quadrupole focusing strengths in the electron beam-optics system.
- I DY is the dominant coil current so that the deflection is entirely in the x-z plane (as shown in FIG. 2A )
- the radial focusing strength (which is a function of beam radius only and independent of azimuthal angle, ⁇ ) of the magnet is then calculated to the first order in
- the design value of S at the maximum deflection will determine the required minimum divergence of the incident electron beam.
- a solenoid focusing lens can be included in the beam-optical system to compensate for the smaller focusing strength of the dipole field.
- the quadrupole focusing strength (Q) may be zero or close to zero. Thus, this may require ⁇ 1 ⁇ 2* ⁇ and R ⁇ L(0). If Q is to be small but non-zero as in the current application, appropriate values of ⁇ and R are chosen to produce the required value of Q at the maximum deflection. At lesser deflections, the quadrupole strength is supplemented by coil current I QY to generate the necessary field gradient
- the yoke is a high quality mu-metal (e.g., soft ferromagnetic material with the permeability ( ⁇ ) greater than 50,000) whose thickness is 1.5 mm or more.
- the coils are single layers, where each layer uses the 14 American wire gauge (AWG) copper wire wound directly onto the yoke.
- AMG American wire gauge
- the dipole component of the magnetic field required to deflect a 200 kV beam 45° is 94 Gauss. This is provided by 375 Ampere-turns in each of the Y coils. These coils are preferably wound with the turns touching as shown in FIG.
- N Y 28 turns with a maximum wire current of 13.3 A.
- the maximum vertical deflection of 3.10 is provided by up to 50 Ampere-turns, for example, for each pair of X coils. Each half of each X coil has 10 turns with a current of 2.5 A. The turns of the X coils are widely and uniformly spaced as indicated.
- the exit side of the magnet yoke forms an arc which is centered on the beam axis upstream of the magnet.
- This configuration ensures that, the dipole field of the magnet acts as a converging lens with approximately equal focusing strengths in both planes.
- a quadrupole field is produced at the beam exit by this contour of the yoke, which approximately cancels the effective focusing due to the deflection.
- the resultant strength of the overall quadrupole lens for example, is about 0.2 Diopter at a deflection of 45°.
- the total quadrupole lens strength is also required to be about the same value.
- FIG. 4 is an example graph of the dipole magnetic fields (B y ) due to equal currents in the two Y coils.
- FIG. 5 is an example graph of the dipole magnetic fields (B x ) due to equal currents in the two X coils.
- FIG. 6 is an example graph of the quadrupole magnetic fields due to opposing currents in the two Y coils.
- FIG. 7 is an example graph of the combined dipole and quadrupole magnetic fields, due to combined currents in the two Y coils.
- an orthogonal quadrupole field may be required (oriented at 45° with respect to the coordinate axes) to combine with the quadrupole fields of the main coils.
- the positions of the QB coils 350 required to produce such fields are indicated in FIG. 3 and illustrated in FIG. 1 .
- FIG. 8 shows an example of the 45° quadrupole magnetic fields due to the currents in the four QB coils at the corners of the yoke.
- FIG. 9 shows a yoke 900 configured into two halves 910 , 912 in accordance with one implementation of the present disclosure.
- the two halves 910 , 912 are clamped together at points 920 , 922 where the magnetic induction in the mu-metal is near zero for the main deflection field.
- the clamp facilitates attachment to a beam tube system.
- the two halves 910 , 912 may be fastened by non-magnetic strips which are attached by brass screws.
- the magnet 1000 if the magnet 1000 is to be used in a scanning beam tube where the coil currents and magnetic fields must change rapidly, it may be necessary to prevent induced eddy currents in the magnetic yoke. This can be achieved by slotting the mu-metal and/or using multiple layers 1010 of material.
- FIG. 10 shows one implementation of the present disclosure in which all the mu-metal strips would be advantageously identical.
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Abstract
A particle beam device including a magnet, the device including: a particle beam source configured to emit electron and ion beams; a plurality of yokes arranged in a substantially rectangular shape; a coil set including a plurality of coils, wherein windings of the plurality of coils are uniformly distributed across and wound around the plurality of yokes, wherein the coil set is configured to produce both dipole and quadrupole fields, wherein the magnet is configured to deflect and focus electron and ion beams.
Description
- This application claims the benefit of priority under 35 U.S.C. § 119(e) of co-pending U.S. Provisional Patent Application No. 62/491,122, filed Apr. 27, 2017, entitled “COMPACT MAGNET FOR DEFLECTION AND FOCUSING OF ELECTRON AND ION BEAMS.” The disclosure of the above-referenced application is incorporated herein by reference.
- The present disclosure relates to magnets, and more specifically, to compact magnets for deflection and focusing of electron and ion beams.
- Many charged particle beam devices require beam deflecting, scanning and focusing magnets. The devices include, among others, Cathode Ray Tubes, X-ray Tubes, Electron Beam Computed Tomography Scanners, Klystrons, Scanning Electron Microscopes, Helium Ion Microscopes, Electron and Ion Lithography Devices.
- It would be desirable for the beam-deflecting magnets to have a uniform (dipole) magnetic field and also produce a quadrupole focusing field. The magnets should be scan-able through a range of deflection angles and the field components should be magnetically rotatable about the initial beam axis. Past solutions to the above-mentioned design requirements of the magnets have generally involved complex magnetic coil arrangements.
- The present disclosure is directed to magnets for deflection and focusing of electron and ion beams. In one implementation, the magnet produces dipole and quadrupole fields from the same coil set.
- In one implementation, a particle beam device including a magnet is disclosed. The device includes: a particle beam source configured to emit electron and ion beams; a plurality of yokes arranged in a substantially rectangular shape; a coil set including a plurality of coils, wherein windings of the plurality of coils are uniformly distributed across and wound around the plurality of yokes, wherein the coil set is configured to produce both dipole and quadrupole fields, wherein the magnet is configured to deflect and focus electron and ion beams.
- In another implementation, a magnet is disclosed. The magnet includes: a plurality of yokes arranged in a substantially rectangular shape; a coil set including a plurality of coils, wherein windings of the plurality of coils are uniformly distributed across and wound around the plurality of yokes, wherein the coil set is configured to produce both dipole and quadrupole fields.
- Other features and advantages should be apparent from the present description which illustrates, by way of example, aspects of the disclosure.
- The details of the present disclosure, both as to its structure and operation, may be gleaned in part by study of the appended drawings, in which like reference numerals refer to like parts, and in which:
-
FIG. 1 is a 3-D view of a compact magnet in accordance with one implementation of the present disclosure; -
FIG. 2A is a cross-sectional view (x-z plane) of the compact magnet in accordance with one implementation of the present disclosure; -
FIG. 2B is another cross-sectional view (y-z plane) of the compact magnet in accordance with one implementation of the present disclosure; -
FIG. 3 is another cross-sectional view (x-y plane) of the compact magnet in accordance with one implementation of the present disclosure; -
FIG. 4 is an example graph of the dipole magnetic fields (BY) due to equal currents in the two Y coils; -
FIG. 5 is an example graph of the dipole magnetic fields (BY) due to equal currents in the two X coils; -
FIG. 6 is an example graph of the quadrupole magnetic fields due to opposing currents in the two Y coils; -
FIG. 7 is an example graph of the combined dipole and quadrupole magnetic fields, due to combined currents in the two Y coils; -
FIG. 8 shows an example of the 45° quadrupole magnetic fields due to the currents in the four QB coils at the corners of the yoke; -
FIG. 9 shows a yoke configured into two halves in accordance with one implementation of the present disclosure; and -
FIG. 10 shows one implementation of the present disclosure in which the magnetic yoke of a parallel sided magnet is divided into identical strips. - As described above, past solutions to the above-mentioned design requirements for beam deflecting magnets have generally involved complex magnetic coil arrangements. Certain implementations of the present disclosure provide an alternative solution which significantly reduces the complexity of the magnet design. That is, alternative solution includes the magnet which produces dipole and quadrupole fields from the same coil set in contrast to the prior design in which the dipole and quadrupole fields are produced by separate sets of coils.
- Further, the design of the alternative solution described here is not only simple, but unlike some conventional designs, the magnet can also be assembled around the beam tube after the tube is completed. Further, the newly-designed magnet is capable of producing greater deflection angles than conventional designs. After reading these descriptions, it will become apparent how to implement the disclosure in various implementations and applications. However, although various implementations of the present disclosure will be described herein, it is understood that these implementations are presented by way of example only, and not limitation. As such, this detailed description of various implementations should not be construed to limit the scope or breadth of the present disclosure.
-
FIG. 1 is a 3-D view of acompact magnet 100 in accordance with one implementation of the present disclosure. In one implementation, thecompact magnet 100 is used in a particle beam device such as a cathode ray tube, X-ray tube, electron beam computed tomography scanner, klystron, scanning electron microscope, helium ion microscope, or electron and ion lithography device. The particle beam device may also include a particle beam source, in addition to the magnet. Thus, in one implementation, thecompact magnet 100 is used for deflection and focusing of electron and ion beams emitted by the particle beam source. - In the illustrated implementation of
FIG. 1 , thecompact magnet 100 is a horn-shaped with aninlet opening 110 that is substantially rectangular in shape (in the x-y plane). In an alternative implementation, the substantially rectangular shape also includesoctagonal corners octagonal corners -
FIG. 2A is a cross-sectional view (x-z plane) 200 of thecompact magnet 100 in accordance with one implementation of the present disclosure. Thecross-sectional view 200 ofFIG. 2A shows coil Y1 (210) and coil Y2 (212) andyokes FIG. 2A , the form is based on a classic “window frame” design which has a very uniform internal dipole magnetic field provided the coil currents are uniformly distributed across the respective faces of the yoke.FIG. 2A also illustrates somealternative shapes -
FIG. 2B is another cross-sectional view (y-z plane) 250 of thecompact magnet 100 in accordance with one implementation of the present disclosure. Thecross-sectional view 250 ofFIG. 2B also shows theyoke 220. -
FIG. 3 is another cross-sectional view (x-y plane) 300 of thecompact magnet 100 in accordance with one implementation of the present disclosure. In the illustrated implementation ofFIG. 3 , various coils are shown (designated as coil Y1 (310), coil Y2 (312), coil X1 L (320), coil X1 R (322), X2 L (330), X2 R (332)) with reference to the coordinate system defined inFIGS. 1, 2A, 2B, and 3 . - The windings of each coil are uniformly distributed across their respective faces of the yoke. Each pair (L, R) of X coils 320/322 or 330/332 is connected electrically as a single coil although they are mechanically on separate halves of the yoke. The two halves of the yoke are connected at
butt joints - In the illustrated implementation of
FIG. 3 , the currents in the X coils 320, 322, 330, 332 and the Y coils 310, 312 produce both dipole and quadrupole magnetic fields as described below. Although the cross section shown inFIG. 3 is generally rectangular, its form parallel to the beam direction (in the z direction) may be horn-shaped or parallel-sided.FIG. 3 also shows the optional QB coils (e.g., 350). As described above with respect toFIG. 1 , the exit contour of the yoke on the downstream side is arcuate to provide a quadrupole focusing field which may be used to oppose that of the natural focusing effect, due to deflection, by the uniform field. The calculation of the radius for this arc is described below. - The algorithm behind the design of the
compact magnet 100 shown as different views inFIGS. 1, 2A, 2B, and 3 is described below. Thus, in one case, the coil currents of thecompact magnet 100 may be written as follows: -
I Y1 =I DY +I QY; [1] -
I Y2 =I DY −I QY; [2] -
I X1 =I DX +I QX; [3] -
I X2 =I DX −I QX. [4] - where IDY=the dipole current in coil Y,
- IQY=the quadrupole current in coil Y,
- IDX=the dipole current in coil X,
- IQX=the quadrupole current in coil X, and
- all four component currents are independent.
- Using Ampere's Circuital law, the coil currents described in Equations [1]-[4] produce the magnetic field in the region of the beam as follows:
-
- where NY=the number of turns in each separate Y coil,
- NX=the number of turns in each separate X coil,
- μo=the magnetic permeability constant,
- μ=the permeability of the magnetic yoke material,
- w=the internal width of the yoke, and
- g=the vertical height of the yoke.
- Thus, based on the above-described magnetic fields and coil currents, the magnitude of the effective magnetic field gradient is as follows:
-
- Accordingly, the quadrupole lens strength can be calculated as follows:
-
- where L(δ)=the effective length of the magnet,
- e=the electronic charge,
- c=the speed of light, and
- p is the beam momentum.
- In one implementation, the two Y coils are supplied with separate currents IY1 and IY2. In another implementation, each coil includes two windings, one carrying the dipole current, IDY, and the other the quadrupole current, IQY. The decision for selecting one implementation over another depends on practical considerations such as the cost of coil drivers.
- For non-zero deflections, the dipole component of the magnetic field may be approximated by a thin lens element having both cylindrical and quadrupole focusing strengths in the electron beam-optics system. Thus, in the approximation that IDY is the dominant coil current so that the deflection is entirely in the x-z plane (as shown in
FIG. 2A ), for a given length of the magnet along the incident beam axis L(0), at a maximum deflection (δ) and a beam exit angle (β): -
- The radial focusing strength (which is a function of beam radius only and independent of azimuthal angle, φ) of the magnet is then calculated to the first order in
-
- as follows:
-
- and the quadrupole focusing strength is calculated as follows:
-
- The total focusing strength is T=S+Q*cos(2φ). These definitions apply regardless of the shape of the coils and yoke. Thus, it should be sufficient to state that the total focusing strength (T) in the x-z plane is S+Q and in the y-z plane is S−Q.
- The corresponding radius of the exit boundary of the yoke is then calculated as follows:
-
- where the necessary values of β and R can be calculated for the required maximum values of δ and Q.
- The design value of S at the maximum deflection will determine the required minimum divergence of the incident electron beam. At lesser values of deflection, a solenoid focusing lens can be included in the beam-optical system to compensate for the smaller focusing strength of the dipole field.
- Many applications may require the quadrupole focusing strength (Q) to be zero or close to zero. Thus, this may require β≈½*δ and R≈L(0). If Q is to be small but non-zero as in the current application, appropriate values of β and R are chosen to produce the required value of Q at the maximum deflection. At lesser deflections, the quadrupole strength is supplemented by coil current IQY to generate the necessary field gradient
-
- as described above.
- In one example implementation, the yoke is a high quality mu-metal (e.g., soft ferromagnetic material with the permeability (μ) greater than 50,000) whose thickness is 1.5 mm or more. The coils are single layers, where each layer uses the 14 American wire gauge (AWG) copper wire wound directly onto the yoke. Thus, using the design dimensions of length (L(0))=125 mm, width (w)=125 mm, and gap (g)=50 mm, for example, the dipole component of the magnetic field required to deflect a 200 kV beam 45° is 94 Gauss. This is provided by 375 Ampere-turns in each of the Y coils. These coils are preferably wound with the turns touching as shown in
FIG. 3 . This results in NY=28 turns with a maximum wire current of 13.3 A. The maximum vertical deflection of 3.10 is provided by up to 50 Ampere-turns, for example, for each pair of X coils. Each half of each X coil has 10 turns with a current of 2.5 A. The turns of the X coils are widely and uniformly spaced as indicated. - As shown in
FIG. 2A , the exit side of the magnet yoke forms an arc which is centered on the beam axis upstream of the magnet. This configuration ensures that, the dipole field of the magnet acts as a converging lens with approximately equal focusing strengths in both planes. At large deflection angles, a quadrupole field is produced at the beam exit by this contour of the yoke, which approximately cancels the effective focusing due to the deflection. The resultant strength of the overall quadrupole lens, for example, is about 0.2 Diopter at a deflection of 45°. For smaller deflection angles, the total quadrupole lens strength is also required to be about the same value. The necessary quadrupole field strength is supplied by opposing currents in the Y coils, for example, of IQY=0.33 A. Since IQX is redundant, it is not used. -
FIG. 4 is an example graph of the dipole magnetic fields (By) due to equal currents in the two Y coils. -
FIG. 5 is an example graph of the dipole magnetic fields (Bx) due to equal currents in the two X coils. -
FIG. 6 is an example graph of the quadrupole magnetic fields due to opposing currents in the two Y coils. -
FIG. 7 is an example graph of the combined dipole and quadrupole magnetic fields, due to combined currents in the two Y coils. - In an alternative implementation of using an octagonal option for rotatable quadrupole fields, if the required beam profile following deflection is elliptical and is not oriented with its major axes vertical or horizontal, an orthogonal quadrupole field may be required (oriented at 45° with respect to the coordinate axes) to combine with the quadrupole fields of the main coils. The positions of the QB coils 350 required to produce such fields are indicated in
FIG. 3 and illustrated inFIG. 1 . -
FIG. 8 shows an example of the 45° quadrupole magnetic fields due to the currents in the four QB coils at the corners of the yoke. -
FIG. 9 shows ayoke 900 configured into twohalves FIG. 9 , the twohalves points halves - In one implementation, if the
magnet 1000 is to be used in a scanning beam tube where the coil currents and magnetic fields must change rapidly, it may be necessary to prevent induced eddy currents in the magnetic yoke. This can be achieved by slotting the mu-metal and/or usingmultiple layers 1010 of material.FIG. 10 shows one implementation of the present disclosure in which all the mu-metal strips would be advantageously identical. - Various modifications to these implementations will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other implementations without departing from the spirit or scope of the disclosure. Accordingly, the techniques are not limited to the specific examples described above. Thus, it is to be understood that the description and drawings presented herein represent a presently possible implementation of the disclosure and are therefore representative of the subject matter that is broadly contemplated by the present disclosure. It is further understood that the scope of the present disclosure fully encompasses other implementations that may become obvious to those skilled in the art and that the scope of the present disclosure is accordingly limited by nothing other than the appended claims.
Claims (16)
1-21. (canceled)
22. A magnet comprising:
a yoke having a set of four faces and a set of four corners;
a first set of four coils, each wound, respectively, on the set of four faces; and
a second set of four coils, each wound, respectively, on the set of four corners.
23. The magnet of claim 22 , the second set of four coils electrically connected to each other to provide a quadrupole magnetic field in response to a current in the second set of four coils.
24. The magnet of claim 23 , the yoke having an exit side with an arcuate contour.
25. The magnet of claim 24 , wherein a pair of faces in the set of four faces have the arcuate contour at the exit side.
26. The magnet of claim 25 , the pair of faces parallel to each other.
27. The magnet of claim 26 , wherein the yoke is horn-shaped.
28. The magnet of claim 22 , the yoke having an exit side with an arcuate contour.
29. The magnet of claim 22 , the yoke comprising two parts attached together.
30. The magnet of claim 29 , a first part of the two attached parts including a first part of a face, a second part of the two attached parts including a second part of the face, wherein a coil in the first set of coils wound on the face comprises:
a first part coil wound on the first part of the face; and
a second part coil wound on the second part of the face, the second part coil electrically connected to the first part coil to form the coil.
31. The magnet of claim 22 , the yoke comprising mu-metal.
32. A system comprising:
a beam tube system;
a magnet attached to the beam tube system, the magnet comprising:
a yoke having a set of four faces and a set of four corners;
a first set of four coils, each wound, respectively, on the set of four faces; and
a second set of four coils, each wound, respectively, on the set of four corners; and
a particle beam source to emit electrons, the magnet attached to the beam tube system to deflect the emitted electrons in response to a current in the first set of four coils.
33. The system of claim 32 , the yoke having an exit side with an arcuate contour, the magnet to provide a converging lens for the emitted electrons in response to a current in the first set of four coils.
34. The system of claim 32 , the magnet having a window frame design to deflect the emitted electrons in a first plane and a second plane in response to a current in the first set of four coils.
35. The system of claim 34 ,
the yoke having an exit side with an arcuate contour;
the magnet to provide a converging lens for the emitted electrons in the first and second planes in response to a current in the first set of four coils; and
the second set of four coils electrically connected to each other to provide a quadrupole magnetic field in response to a current in the second set of four coils.
36. The system of claim 32 , the yoke comprising mu-metal.
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US16/401,948 US20190259565A1 (en) | 2017-04-27 | 2019-05-02 | Compact deflecting magnet |
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US201762491122P | 2017-04-27 | 2017-04-27 | |
US15/625,921 US10290463B2 (en) | 2017-04-27 | 2017-06-16 | Compact deflecting magnet |
US16/254,203 US10332718B1 (en) | 2017-04-27 | 2019-01-22 | Compact deflecting magnet |
US16/401,948 US20190259565A1 (en) | 2017-04-27 | 2019-05-02 | Compact deflecting magnet |
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US15/625,921 Active 2037-06-28 US10290463B2 (en) | 2017-04-27 | 2017-06-16 | Compact deflecting magnet |
US16/254,203 Expired - Fee Related US10332718B1 (en) | 2017-04-27 | 2019-01-22 | Compact deflecting magnet |
US16/401,948 Abandoned US20190259565A1 (en) | 2017-04-27 | 2019-05-02 | Compact deflecting magnet |
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US16/254,203 Expired - Fee Related US10332718B1 (en) | 2017-04-27 | 2019-01-22 | Compact deflecting magnet |
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EP (2) | EP3396696A1 (en) |
JP (2) | JP2018190709A (en) |
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US10290463B2 (en) | 2017-04-27 | 2019-05-14 | Imatrex, Inc. | Compact deflecting magnet |
US10504687B2 (en) * | 2018-02-20 | 2019-12-10 | Technische Universiteit Delft | Signal separator for a multi-beam charged particle inspection apparatus |
US10395887B1 (en) * | 2018-02-20 | 2019-08-27 | Technische Universiteit Delft | Apparatus and method for inspecting a surface of a sample, using a multi-beam charged particle column |
US11114270B2 (en) * | 2018-08-21 | 2021-09-07 | Axcelis Technologies, Inc. | Scanning magnet design with enhanced efficiency |
DE102019004124B4 (en) * | 2019-06-13 | 2024-03-21 | Carl Zeiss Multisem Gmbh | Particle beam system for the azimuthal deflection of individual particle beams and its use and method for azimuth correction in a particle beam system |
CN118120040A (en) | 2021-12-07 | 2024-05-31 | 株式会社日立高新技术 | Multipole lens and charged particle beam device |
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- 2018-04-23 JP JP2018082367A patent/JP2018190709A/en active Pending
- 2018-04-24 EP EP18168953.0A patent/EP3396696A1/en not_active Withdrawn
- 2018-04-24 EP EP19171647.1A patent/EP3537469A1/en not_active Withdrawn
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- 2018-04-25 KR KR1020180047916A patent/KR20180120603A/en active Search and Examination
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JP7022718B2 (en) | 2022-02-18 |
RU2693565C1 (en) | 2019-07-03 |
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JP2018190709A (en) | 2018-11-29 |
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US10290463B2 (en) | 2019-05-14 |
US10332718B1 (en) | 2019-06-25 |
TW201842523A (en) | 2018-12-01 |
KR20180120603A (en) | 2018-11-06 |
US20180315578A1 (en) | 2018-11-01 |
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JP2019149387A (en) | 2019-09-05 |
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