WO2007030819A2 - Electron beam source for use in electron gun - Google Patents
Electron beam source for use in electron gun Download PDFInfo
- Publication number
- WO2007030819A2 WO2007030819A2 PCT/US2006/035319 US2006035319W WO2007030819A2 WO 2007030819 A2 WO2007030819 A2 WO 2007030819A2 US 2006035319 W US2006035319 W US 2006035319W WO 2007030819 A2 WO2007030819 A2 WO 2007030819A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- electron beam
- magnetic disk
- beam source
- emitter
- electrode
- Prior art date
Links
- 238000010894 electron beam technology Methods 0.000 title claims abstract description 62
- 238000000605 extraction Methods 0.000 claims description 18
- KPLQYGBQNPPQGA-UHFFFAOYSA-N cobalt samarium Chemical compound [Co].[Sm] KPLQYGBQNPPQGA-UHFFFAOYSA-N 0.000 claims description 5
- 230000035699 permeability Effects 0.000 claims description 5
- 229910000938 samarium–cobalt magnet Inorganic materials 0.000 claims description 5
- 229910001220 stainless steel Inorganic materials 0.000 claims description 4
- 239000010935 stainless steel Substances 0.000 claims description 4
- 230000005415 magnetization Effects 0.000 claims description 2
- 230000004075 alteration Effects 0.000 description 17
- 230000004907 flux Effects 0.000 description 13
- 238000013459 approach Methods 0.000 description 3
- 238000013461 design Methods 0.000 description 3
- 238000001493 electron microscopy Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000000523 sample Substances 0.000 description 3
- QJVKUMXDEUEQLH-UHFFFAOYSA-N [B].[Fe].[Nd] Chemical compound [B].[Fe].[Nd] QJVKUMXDEUEQLH-UHFFFAOYSA-N 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000000609 electron-beam lithography Methods 0.000 description 2
- 238000003384 imaging method Methods 0.000 description 2
- 239000000696 magnetic material Substances 0.000 description 2
- 229910001172 neodymium magnet Inorganic materials 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 206010010071 Coma Diseases 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 201000009310 astigmatism Diseases 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 239000012809 cooling fluid Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000001459 lithography Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 238000010943 off-gassing Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical group [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
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
- H01J37/06—Electron sources; Electron guns
- H01J37/065—Construction of guns or parts thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
- H01J23/02—Electrodes; Magnetic control means; Screens
- H01J23/06—Electron or ion guns
-
- 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
- H01J29/48—Electron guns
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
- H01J3/02—Electron 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
- H01J37/143—Permanent magnetic lenses
-
- 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
- H01J2237/06—Sources
- H01J2237/063—Electron sources
- H01J2237/06308—Thermionic sources
- H01J2237/06316—Schottky emission
-
- 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
- H01J2237/06—Sources
- H01J2237/063—Electron sources
- H01J2237/06325—Cold-cathode sources
- H01J2237/06341—Field emission
Definitions
- Embodiments of the present invention generally relate to electron guns (sources), and more particularly, electron guns that may be used, for instance, in electron beam lithography or electron microscopy.
- Electron beam columns are well known for use, for instance, in electron beam lithography for imaging a pattern onto a substrate typically coated with a resist sensitive to electron beams. Subsequent development of the exposed resist defines a pattern in the resist which later can be used as a pattern for etching or other processes. Electron beam columns are also used in electron microscopy for imaging surfaces and thin samples. Conventional electron beam columns for electron microscopy and lithography are well known and typically include an electron gun having an electron emitter for producing an electron beam. The beam from the gun may be used to produce a scanning probe or illuminate a sample or an aperture using a series of electron beam lenses, which may be magnetic or electrostatic.
- Electron beam columns generally include a source of electrons, such as a Schottky emission gun or a field emission gun, which typically includes an emitter (cathode), an electrostatic pre-accelerator lens that focuses the electron beam and a series of lenses that refocuses and images the source aperture or sample onto the target.
- a source of electrons such as a Schottky emission gun or a field emission gun, which typically includes an emitter (cathode), an electrostatic pre-accelerator lens that focuses the electron beam and a series of lenses that refocuses and images the source aperture or sample onto the target.
- the emitter tip and the extraction region are immersed in a magnetic field, which results in a significant increase in the operating solid angle of emission compared to all-electrostatic systems.
- one disadvantage of this design is that the lens coil and its cooling fluid may float at near the tip potential, which requires a more complicated high voltage power supply and cable.
- the mechanical design is a large departure from conventional Schottky or field emission designs, which adds further complication to the approach.
- Various embodiments of the invention are generally directed to an electron beam source for use in an electron gun.
- the electron beam source includes an emitter terminating in a tip.
- the emitter is configured to generate an electron beam.
- the electron beam source further includes a suppressor electrode laterally surrounding the emitter such that the tip of the emitter protrudes through the suppressor electrode and an extractor electrode disposed adjacent the tip of the emitter.
- the extractor electrode comprises a magnetic disk whose magnetic field is aligned with an axis of the electron beam.
- Various embodiments of the invention are also generally directed to an electron beam source for use in an electron gun.
- the electron beam source includes an emitter terminating in a tip.
- the emitter is configured to generate an electron beam.
- the electron beam source further includes a suppressor electrode laterally surrounding the emitter such that the tip of the emitter protrudes through the suppressor electrode and an extractor electrode disposed adjacent the tip of the emitter.
- the extractor electrode comprises an extraction support and a magnetic disk disposed on the extraction support.
- the magnetic disk is a permanent magnet.
- Figure 1 illustrates a side cross sectional view of a portion of an electron gun in accordance with one or more embodiments of the invention.
- Figure 2 illustrates a side cross sectional view of a portion of an electron gun in accordance with another embodiment of the invention.
- Figure 3 illustrates a top view and a cross sectional view of a magnetic disk in accordance with one or more embodiments of the invention.
- Figure 4 illustrates a plot of the magnetic field for the magnetic disk along the beam axis (axial flux density) in accordance with one or more embodiments of the invention.
- Figure 5 illustrates the effect of a shunt on the axial flux density between the magnetic disk and the focus electrode in accordance with one or more embodiments of the invention.
- Figure 1 illustrates a side cross sectional view of a portion of an electron gun 10 in accordance with one or more embodiments of the invention.
- the electron gun 10 may be a field emission or Schottky emission gun. Details of such a device are described in L. Swanson and G. Schwind, "A Review of The ZrO/W Schottky Cathode", Handbook of Charged Particle Optics editor Jon Orloff, CRC Press LLC, New York, (1997), which is incorporated herein by reference.
- the electron gun 10 includes an emitter (cathode) 14, which is configured to generate an electron beam.
- the emitter 14 may be an oriented single crystal tungsten structure with a sharp point (approximately r micrometer radius) and mounted on a hair pin filament (not shown).
- the emitter 14 may be surrounded by a negatively biased suppressor electrode 16, which may be a conductive structure that prevents thermionically emitted electrons from leaving the emitter 14 anywhere but near its tip.
- the pointed tip of the emitter 14 protrudes slightly from the suppressor electrode 16 and faces an extractor electrode 24, which defines an upper aperture 29.
- the extractor electrode 24 may be biased positively with respect to the emitter 14 and defines a lower aperture 28 below the upper aperture 29 to shape the electron beam entering the downstream gun lens (not shown).
- the extractor electrode 24 includes a magnetic disk 100 disposed on an extraction support 150, which may be made from a non magnetic material.
- the magnetic disk 100 may be a permanent magnet made from materials such as samarium cobalt, neodymium iron boron and the like.
- the magnetic disk 100 is ring shaped (toroidal) having an opening 110 for allowing the electron beam to pass therethrough.
- the top surface of the magnetic disk 100 is about 1 mm apart from the tip of the emitter 14.
- the magnet disk 100 is disposed such that the axis of the opening 110 is aligned with the beam axis. In this manner, the magnetic disk 100 acts as a fixed focal length lens.
- the magnetic disk 100 may be encased in a stainless steel sheath for increasing structural rigidity or reducing contamination, e.g., outgassing or particulates.
- the electron gun 10 may further include a focus electrode 25, such as an electrostatic lens, to further focus the electron beam coming out of the extractor electrode 24. In this manner, the magnetic disk 100 has a fixed focal length, while the focus electrode 25 has a variable focal length (by varying the voltage).
- FIG. 2 illustrates a side cross sectional view of a portion of an electron gun 210 in accordance with another embodiment of the invention.
- the electron gun 210 has an extractor electrode 224, which includes an extraction aperture disk 220 disposed on a magnetic disk 200, both of which supported by an extraction support 250.
- the extraction aperture disk 220 is configured to protect the magnetic disk 200 from being bombarded by the electron beam.
- the extraction aperture disk 220 may be made from non magnetic material, such as molybdenum, stainless steel, titanium and the like.
- the magnetic disk 200 may be a permanent magnet made from ' ⁇ materraiS" ! ⁇ u ' chr ! 'as" 'samarium cobalt, neodymium iron boron and the like.
- the magnetic disk 200 is ring shaped (toroidal) having an opening 230 for allowing the electron beam to pass therethrough.
- the rest of the components of the electron gun 210 e.g., an emitter 214 and a suppressor electrode 216, are substantially the same as the components of the electron gun 10. Accordingly, other details of various components of the electron gun 210 are provided with reference to the electron gun 10 described above.
- Figure 3 illustrates a top view and a cross sectional view of a magnetic disk 300 in accordance with one or more embodiments of the invention.
- the magnetic disk 300 has an inner diameter (ID) of about 1 mm, an outer diameter (OD) of about 5 mm, a thickness (L) of about 1.025 mm, a taper bore angle ( ⁇ ) of about 0 degrees, and a saturation magnetization (M s ) of about 875 emu/cm 3 , which has been selected to match samarium cobalt type 32 HS.
- ID inner diameter
- OD outer diameter
- L thickness
- ⁇ taper bore angle
- M s saturation magnetization
- the magnetic disk 300 may be used to reduce the spherical aberration coefficient from about 19.8 mm (without magnetic disk) to about 2.9 mm (with magnetic disk).
- embodiments of the invention may be used to reduce the spherical aberration coefficient of a conventional 5OkV electron gun by a factor of about 6.
- the spherical aberration coefficient may be further reduced to less than about 2.5 mm by increasing the OD to about 10 mm and decreasing the ID to about 0.5 mm.
- the spherical aberration coefficient may also be reduced by moving the magnetic disk closer to the emitter 14.
- the magnetic field of the magnetic disk may collimate the electron beam, thereby increasing the effective angular intensity of the beam current.
- the magnetic field of the magnetic disk 100, 200, 300 is aligned with the beam axis.
- the magnetic field may be calculated everywhere in space, using a charge density method, such as one described in "Field Computation By Moment Methods” by Roger F. Harrington, Wiley-IEEE Press (1993).
- the magnetic field along the beam axis (axial flux density) may then be extracted to a file, which may be used as an input to an electron optical simulation program ABER by Munro's Electron Beam Software Ltd., headquartered in London, England.
- the optical properties and aberrations of the lenses are then computed.
- Such aberrations include spherical aberration, chromatic aberration, distortion, astigmatism, coma, and field curvature.
- the geometric parameters, i.e., ID, OD, L and ⁇ , of the " magnefic disR ⁇ Ts weir as the location of the magnet disk may be varied to affect the optical properties and aberrations.
- Figure 4 illustrates a plot of the magnetic field 400 for the magnetic disk along the beam axis (axial flux density) in accordance with one or more embodiments of the invention.
- the axial flux density 400 is greatest at or substantially near the location of the magnetic disk.
- FIG. 5 illustrates the effect of a shunt 500 on the axial flux density between the magnetic disk 100 and the focus electrode 25.
- the solid line represents the axial flux density 510 for the electron gun with the shunt 500
- the dotted line represents the axial flux density 520 for the electron gun without the shunt 500.
- axial flux density 510 between the magnetic disk 100 and the focus electrode 25 is significantly reduced to substantially zero.
- the spherical aberration coefficient may be higher for the electron gun with a shunt than for the electron gun without a shunt.
- placing a shunt as part of the suppressor electrode 16 may cause the axial flux density to extend farther into the extraction region, which may reduce aberrations.
- the thickness (L) of the magnetic disk may be reduced to reduce the magnitude of the axial flux density between the magnetic disk 100 and the focus electrode 25. Further, the magnetic disk 100 may be disposed closer to the emitter 14 to reduce the spherical aberration coefficient.
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- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Electron Sources, Ion Sources (AREA)
- Electron Beam Exposure (AREA)
Abstract
An electron beam source (Fig 1) for use in an electron gun The electron beam source (10) includes an emitter (14) terminating in a ti The emitter is configured to generate an electron beam The electron beam source (10) further includes a suppressor electrode (16) laterally surrounding the emitter (14) such that the tip of the emitter protrudes through the suppressor electrode (16) and an extractor electrode (24) disposed adjacent the tip of the emitter (14) The extractor electrode (24) compπses a magnetic disk (100) whose magnetic field is aligned with an axis of the electron beam
Description
ELECTRON BEAM SOURCE FOR USE IN ELECTRON GUN
BACKGROUND OF THE INVENTION Field of the Invention
[0001] Embodiments of the present invention generally relate to electron guns (sources), and more particularly, electron guns that may be used, for instance, in electron beam lithography or electron microscopy.
Description of the Related Art
[0002] Electron beam columns are well known for use, for instance, in electron beam lithography for imaging a pattern onto a substrate typically coated with a resist sensitive to electron beams. Subsequent development of the exposed resist defines a pattern in the resist which later can be used as a pattern for etching or other processes. Electron beam columns are also used in electron microscopy for imaging surfaces and thin samples. Conventional electron beam columns for electron microscopy and lithography are well known and typically include an electron gun having an electron emitter for producing an electron beam. The beam from the gun may be used to produce a scanning probe or illuminate a sample or an aperture using a series of electron beam lenses, which may be magnetic or electrostatic.
[0003] Electron beam columns generally include a source of electrons, such as a Schottky emission gun or a field emission gun, which typically includes an emitter (cathode), an electrostatic pre-accelerator lens that focuses the electron beam and a series of lenses that refocuses and images the source aperture or sample onto the target.
[0004] It has generally been difficult to obtain very high beam currents focused into a small spot using Schottky electron sources. Although the brightness of the emitter is high in such sources, the angular intensity of the electron beam emerging from the emitter region is limited by the properties of the emitter itself. Consequently, a rather large aperture angle must be used in the electron gun, which makes spherical and chromatic aberration in the gun lens a major factor in limiting the small spot size that can be achieved, which is generally referred to as the smallest cross-section diameter of the beam.
[0005J- One" approach to reduce aberrations in the gun lens is to use a magnetic lens as the focus element. Using this approach, the emitter tip and the extraction region are immersed in a magnetic field, which results in a significant increase in the operating solid angle of emission compared to all-electrostatic systems. However, one disadvantage of this design is that the lens coil and its cooling fluid may float at near the tip potential, which requires a more complicated high voltage power supply and cable. Further, the mechanical design is a large departure from conventional Schottky or field emission designs, which adds further complication to the approach.
[0006] Other attempts to reduce aberrations in the gun lens have been made. However, those attempts have proven to be difficult since the size and focal length of standard electrostatic lenses are limited by the large stand-off distance required in high voltage systems.
[0007] Therefore, a need exists in the art for a new electron beam source for an electron gun with minimal aberrations.
SUMMARY OF THE INVENTION
[0008] Various embodiments of the invention are generally directed to an electron beam source for use in an electron gun. The electron beam source includes an emitter terminating in a tip. The emitter is configured to generate an electron beam. The electron beam source further includes a suppressor electrode laterally surrounding the emitter such that the tip of the emitter protrudes through the suppressor electrode and an extractor electrode disposed adjacent the tip of the emitter. The extractor electrode comprises a magnetic disk whose magnetic field is aligned with an axis of the electron beam.
[0009] Various embodiments of the invention are also generally directed to an electron beam source for use in an electron gun. The electron beam source includes an emitter terminating in a tip. The emitter is configured to generate an electron beam. The electron beam source further includes a suppressor electrode laterally surrounding the emitter such that the tip of the emitter protrudes through the suppressor electrode and an extractor electrode disposed adjacent the tip of the emitter. The extractor electrode comprises an extraction support and a magnetic disk disposed on the extraction support. The magnetic disk is a permanent magnet.
BRIEF DESCRIPTION DF THE DRAWINGS
[0010] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
[0011] Figure 1 illustrates a side cross sectional view of a portion of an electron gun in accordance with one or more embodiments of the invention.
[0012] Figure 2 illustrates a side cross sectional view of a portion of an electron gun in accordance with another embodiment of the invention.
[0013] Figure 3 illustrates a top view and a cross sectional view of a magnetic disk in accordance with one or more embodiments of the invention.
[0014] Figure 4 illustrates a plot of the magnetic field for the magnetic disk along the beam axis (axial flux density) in accordance with one or more embodiments of the invention.
[0015] Figure 5 illustrates the effect of a shunt on the axial flux density between the magnetic disk and the focus electrode in accordance with one or more embodiments of the invention.
DETAILED DESCRIPTION
[0016] Figure 1 illustrates a side cross sectional view of a portion of an electron gun 10 in accordance with one or more embodiments of the invention. The remainder of the electron gun 10 is not shown. The electron gun 10 may be a field emission or Schottky emission gun. Details of such a device are described in L. Swanson and G. Schwind, "A Review of The ZrO/W Schottky Cathode", Handbook of Charged Particle Optics editor Jon Orloff, CRC Press LLC, New York, (1997), which is incorporated herein by reference. The electron gun 10 includes an emitter (cathode) 14, which is configured to generate an electron beam. The emitter 14 may be an oriented single crystal tungsten structure with a sharp point
(approximately r micrometer radius) and mounted on a hair pin filament (not shown). The emitter 14 may be surrounded by a negatively biased suppressor electrode 16, which may be a conductive structure that prevents thermionically emitted electrons from leaving the emitter 14 anywhere but near its tip. The pointed tip of the emitter 14 protrudes slightly from the suppressor electrode 16 and faces an extractor electrode 24, which defines an upper aperture 29. The extractor electrode 24 may be biased positively with respect to the emitter 14 and defines a lower aperture 28 below the upper aperture 29 to shape the electron beam entering the downstream gun lens (not shown).
[0017] In accordance with one embodiment of the invention, the extractor electrode 24 includes a magnetic disk 100 disposed on an extraction support 150, which may be made from a non magnetic material. The magnetic disk 100 may be a permanent magnet made from materials such as samarium cobalt, neodymium iron boron and the like. The magnetic disk 100 is ring shaped (toroidal) having an opening 110 for allowing the electron beam to pass therethrough. In one embodiment, the top surface of the magnetic disk 100 is about 1 mm apart from the tip of the emitter 14. The magnet disk 100 is disposed such that the axis of the opening 110 is aligned with the beam axis. In this manner, the magnetic disk 100 acts as a fixed focal length lens. The magnetic disk 100 may be encased in a stainless steel sheath for increasing structural rigidity or reducing contamination, e.g., outgassing or particulates. The electron gun 10 may further include a focus electrode 25, such as an electrostatic lens, to further focus the electron beam coming out of the extractor electrode 24. In this manner, the magnetic disk 100 has a fixed focal length, while the focus electrode 25 has a variable focal length (by varying the voltage).
[0018] Figure 2 illustrates a side cross sectional view of a portion of an electron gun 210 in accordance with another embodiment of the invention. The electron gun 210 has an extractor electrode 224, which includes an extraction aperture disk 220 disposed on a magnetic disk 200, both of which supported by an extraction support 250. The extraction aperture disk 220 is configured to protect the magnetic disk 200 from being bombarded by the electron beam. The extraction aperture disk 220 may be made from non magnetic material, such as molybdenum, stainless steel, titanium and the like. The magnetic disk 200 may be a permanent magnet made from
'ιmaterraiS"!^u'chr!'as" 'samarium cobalt, neodymium iron boron and the like. The magnetic disk 200 is ring shaped (toroidal) having an opening 230 for allowing the electron beam to pass therethrough. The rest of the components of the electron gun 210, e.g., an emitter 214 and a suppressor electrode 216, are substantially the same as the components of the electron gun 10. Accordingly, other details of various components of the electron gun 210 are provided with reference to the electron gun 10 described above.
[0019] Figure 3 illustrates a top view and a cross sectional view of a magnetic disk 300 in accordance with one or more embodiments of the invention. In one embodiment, the magnetic disk 300 has an inner diameter (ID) of about 1 mm, an outer diameter (OD) of about 5 mm, a thickness (L) of about 1.025 mm, a taper bore angle (α) of about 0 degrees, and a saturation magnetization (Ms) of about 875 emu/cm3, which has been selected to match samarium cobalt type 32 HS. With such geometry, the magnetic disk 300 may be used to reduce the spherical aberration coefficient from about 19.8 mm (without magnetic disk) to about 2.9 mm (with magnetic disk). In this manner, embodiments of the invention may be used to reduce the spherical aberration coefficient of a conventional 5OkV electron gun by a factor of about 6. The spherical aberration coefficient may be further reduced to less than about 2.5 mm by increasing the OD to about 10 mm and decreasing the ID to about 0.5 mm. The spherical aberration coefficient may also be reduced by moving the magnetic disk closer to the emitter 14. In addition, the magnetic field of the magnetic disk may collimate the electron beam, thereby increasing the effective angular intensity of the beam current.
[0020] In one embodiment, the magnetic field of the magnetic disk 100, 200, 300 is aligned with the beam axis. The magnetic field may be calculated everywhere in space, using a charge density method, such as one described in "Field Computation By Moment Methods" by Roger F. Harrington, Wiley-IEEE Press (1993). The magnetic field along the beam axis (axial flux density) may then be extracted to a file, which may be used as an input to an electron optical simulation program ABER by Munro's Electron Beam Software Ltd., headquartered in London, England. The optical properties and aberrations of the lenses are then computed. Such aberrations include spherical aberration, chromatic aberration, distortion, astigmatism, coma, and field curvature. The geometric parameters, i.e., ID, OD, L and α, of the
"magnefic disR εTs weir as the location of the magnet disk may be varied to affect the optical properties and aberrations.
[0021] Figure 4 illustrates a plot of the magnetic field 400 for the magnetic disk along the beam axis (axial flux density) in accordance with one or more embodiments of the invention. Notably, the axial flux density 400 is greatest at or substantially near the location of the magnetic disk.
[0022] It has been assumed that the axial flux density between the magnetic disk 100 and the focus electrode 25 would increase aberrations. Accordingly, a high permeability shunt may be added to the electron gun to reduce the axial flux density between the magnetic disk 100 and the focus electrode 25. The shunt may be disposed as part of the extraction support 150 or the suppressor electrode 16. Figure 5 illustrates the effect of a shunt 500 on the axial flux density between the magnetic disk 100 and the focus electrode 25. The solid line represents the axial flux density 510 for the electron gun with the shunt 500, while the dotted line represents the axial flux density 520 for the electron gun without the shunt 500. Notably, axial flux density 510 between the magnetic disk 100 and the focus electrode 25 is significantly reduced to substantially zero. However, the spherical aberration coefficient may be higher for the electron gun with a shunt than for the electron gun without a shunt. On the other hand, placing a shunt as part of the suppressor electrode 16 may cause the axial flux density to extend farther into the extraction region, which may reduce aberrations.
[0023] In addition to adding a shunt to the electron gun, the thickness (L) of the magnetic disk may be reduced to reduce the magnitude of the axial flux density between the magnetic disk 100 and the focus electrode 25. Further, the magnetic disk 100 may be disposed closer to the emitter 14 to reduce the spherical aberration coefficient.
[0024] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims
1. An electron beam source for use in an electron gun, comprising: an emitter terminating in a tip, wherein the emitter is configured to generate an electron beam; a suppressor electrode laterally surrounding the emitter such that the tip of the emitter protrudes through the suppressor electrode; and an extractor electrode disposed adjacent the tip of the emitter, wherein the extractor electrode comprises a magnetic disk whose magnetic field is aligned with an axis of the electron beam.
2. The electron beam source of claim 1 , wherein the magnetic disk is a permanent magnet.
3. The electron beam source of claim 1 , wherein the magnetic disk is made from samarium cobalt.
4. The electron beam source of claim 1 , wherein the magnetic disk is toroidal in shape.
5. The electron beam source of claim 1 , wherein the electron gun is one of a field emission gun and a Schottky emission gun.
6. The electron beam source of claim 1 , wherein the magnetic disk is encased in a stainless steel sheath.
7. The electron beam source of claim 6, wherein the stainless steel sheath is configured to protect the magnetic disk from being bombarded by the electron beam.
8. The electron beam source of claim 1 , wherein the magnetic disk defines an opening that faces the tip of the emitter.
9. The electron beam source of claim 1 , wherein the magnetic disk is disposed about 1 mm or less from the tip of the emitter.
10. The electron beam source of claim 1 , wherein the magnetic disk defines an opening having an axis aligned with the electron beam axis.
11. The electron beam source of claim 1 , further comprising a focus electrode disposed adjacent the extractor electrode, wherein the focus electrode is configured to further focus the electron beam coming out of the extractor electrode.
12. The electron beam source of claim 1 , wherein the extractor electrode further comprises an extraction aperture disk disposed in front of the magnetic disk.
13. The electron beam source of claim 12, wherein the extraction aperture disk is configured to protect the magnetic disk from being bombarded by the electron beam.
14. The electron beam source of claim 1 , wherein the magnetic disk has an inner diameter of about 1 mm.
15. The electron beam source of claim 1 , wherein the magnetic disk has an outer diameter of about 5 mm.
16. The electron beam source of claim 1 , wherein the magnetic disk has thickness of about 1.025 mm.
17. The electron beam source of claim 1 , wherein the magnetic disk has a taper bore angle of about 0 degrees.
18. The electron beam source of claim 1 , wherein the magnetic disk has a saturation magnetization of about 875 emu/cm3.
19. The electron beam source of claim 1 , wherein the extractor electrode comprises an extraction support for supporting the magnetic disk and a high permeability shunt disposed as part of the extraction support.
20':' The "electron1 Deam source of claim 19, further comprising a focus electrode disposed adjacent the extractor electrode, wherein the high permeability shunt is configured to reduce the magnetic field between the magnetic disk and the focus electrode.
21. The electron beam source of claim 1 , wherein the extractor electrode comprises an extraction support for supporting the magnetic disk; and a high permeability shunt disposed as part of the suppressor electrode.
22. An electron beam source for use in an electron gun, comprising: an emitter terminating in a tip, wherein the emitter is configured to generate an electron beam; a suppressor electrode laterally surrounding the emitter such that the tip of the emitter protrudes through the suppressor electrode; and an extractor electrode disposed adjacent the tip of the emitter, wherein the extractor electrode comprises an extraction support and a magnetic disk disposed on the extraction support, wherein the magnetic disk is a permanent magnet.
23. The electron beam source of claim 22, wherein the magnetic disk is made from samarium cobalt.
24. The electron beam source of claim 22, further comprising a focus electrode disposed adjacent the extractor electrode, wherein the extraction support comprises a high permeability shunt configured to reduce the magnetic field between the magnetic disk and the focus electrode.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP06803335A EP1941527A4 (en) | 2005-09-10 | 2006-09-11 | Electron beam source for use in electron gun |
JP2008530020A JP2009508303A (en) | 2005-09-10 | 2006-09-11 | Electron beam source for electron gun |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US71597305P | 2005-09-10 | 2005-09-10 | |
US60/715,973 | 2005-09-10 | ||
US11/286,802 US7372195B2 (en) | 2005-09-10 | 2005-11-22 | Electron beam source having an extraction electrode provided with a magnetic disk element |
US11/286,802 | 2005-11-22 |
Publications (2)
Publication Number | Publication Date |
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WO2007030819A2 true WO2007030819A2 (en) | 2007-03-15 |
WO2007030819A3 WO2007030819A3 (en) | 2008-09-18 |
Family
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/US2006/035319 WO2007030819A2 (en) | 2005-09-10 | 2006-09-11 | Electron beam source for use in electron gun |
Country Status (5)
Country | Link |
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US (1) | US7372195B2 (en) |
EP (1) | EP1941527A4 (en) |
JP (1) | JP2009508303A (en) |
KR (1) | KR20080048528A (en) |
WO (1) | WO2007030819A2 (en) |
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JP2009187684A (en) * | 2008-02-02 | 2009-08-20 | Stanley Electric Co Ltd | Method for controlling electron flow of field emission type electron source |
WO2011089439A3 (en) * | 2010-01-21 | 2011-11-17 | Nfab Limited | A miniature low- energy electron beam generator |
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KR101118692B1 (en) * | 2006-10-11 | 2012-03-12 | 전자빔기술센터 주식회사 | An electron column using a magnetic lens layer |
WO2011055520A1 (en) * | 2009-11-06 | 2011-05-12 | 株式会社日立ハイテクノロジーズ | Electron microscope |
JP5687157B2 (en) | 2011-08-22 | 2015-03-18 | 株式会社日立ハイテクノロジーズ | Electron gun, field emission electron gun, charged particle beam apparatus, and transmission electron microscope |
US8513619B1 (en) * | 2012-05-10 | 2013-08-20 | Kla-Tencor Corporation | Non-planar extractor structure for electron source |
US9799484B2 (en) * | 2014-12-09 | 2017-10-24 | Hermes Microvision, Inc. | Charged particle source |
US10211021B2 (en) * | 2016-04-11 | 2019-02-19 | Kla-Tencor Corporation | Permanent-magnet particle beam apparatus and method incorporating a non-magnetic metal portion for tunability |
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US20220108862A1 (en) * | 2020-10-05 | 2022-04-07 | Kla Corporation | Electron source with magnetic suppressor electrode |
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Also Published As
Publication number | Publication date |
---|---|
US20070057617A1 (en) | 2007-03-15 |
EP1941527A2 (en) | 2008-07-09 |
KR20080048528A (en) | 2008-06-02 |
JP2009508303A (en) | 2009-02-26 |
WO2007030819A3 (en) | 2008-09-18 |
EP1941527A4 (en) | 2010-03-24 |
US7372195B2 (en) | 2008-05-13 |
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