charged particle gun

Abstract

While high-brightness charged particle sources have high brightness, their angular current density is low. When a large current is obtained, the aberration of the downstream electron lens system increases, degrading spatial resolution. In the charged particle gun of the present invention, a first electrode is placed directly below the emitter tip, and a second electrode is placed directly above it. A permanent magnet is sandwiched between the first and second electrode ends, forming a magnetic circuit, with the ends of the first and second electrodes serving as magnetic poles. An extraction electrode is placed downstream of the first electrode. The electrodes and potentials are arranged so that a convex potential distribution toward the emitter tip and a peak value of the axial magnetic flux density occur at the emitter tip. This causes charged particles emitted from the emitter tip to immediately approach the optical axis, and a convex potential distribution is formed on the extraction electrode facing away from the emitter, resulting in gentle divergence without crossover. The asymptotic trajectory of the charged particles after the extraction electrode forms a virtual light source on the emitter side, narrowing the emission angle and reducing the aberration of the electrostatic lens, resulting in a large angular current density and high brightness.

Description

[Technical Field]

[0001] The present invention relates to a device and method for controlling the brightness and angular current density of a charged particle beam emitted from a charged particle source in a charged particle gun equipped with the charged particle source. [Background technology]

[0002] As an example of a device for emitting charged particles, a cold cathode field emission electron gun will be described with reference to the drawings.

[0003] Non-Patent Document 1 describes the principle of electron field emission by applying a strong electric field to the tip of a cold cathode emitter, and the technology for implementing it as an electron gun. Figure 5 shows a conventional cold cathode field emission electron gun. The cold cathode field emission electron gun is housed in a container (not shown) maintained at a high vacuum. The emitter 1 is fixed to a wire 2, which is fixed to a wire support electrode 3, which is held in place by an insulator 4. A strong electric field is formed at the tip of the emitter 1 between the emitter 1 and an extraction electrode 8 due to an extraction voltage applied to the extraction electrode 8, causing charged particles 23 to be emitted from the tip of the emitter 1. The container is typically at ground potential, and an acceleration electrode (not shown) downstream of the extraction electrode 8, which has the same ground potential as the container, accelerates the charged particles (electrons) 23 emitted from the tip of the emitter 1. An acceleration voltage is applied to the emitter 1 from an acceleration power supply (not shown). An extraction voltage is applied to the extraction electrode 8 from an extraction power source (not shown).

[0004] The strength of the electric field is shown as the density of equipotential lines 22 as the potential distribution between the emitter 1 and the extraction electrode 8. As shown in the figure, the density of the equipotential lines 22 at the tip of the emitter 1 is extremely high, indicating a strong electric field. This can be seen from the fact that the axial potential 20 on the optical axis rapidly approaches the emitter potential near the emitter.

[0005] The paraxial trajectory of the charged particle 23 after being emitted from the emitter 1 is expressed by equation 1. In equation 1, the optical axis 11 is defined as the z-coordinate, and the direction perpendicular to the optical axis 11 is defined as the x-coordinate in a rotating coordinate system (x, z) centered on the optical axis 11.

[0006]

number

[0007] φ indicates the axial potential, and φ' and φ'' indicate the first and second derivatives of φ with respect to z, respectively. Bz indicates the magnetic flux density 20 on the optical axis. Also, e indicates the electric charge, m indicates the electron mass, and c indicates the speed of light.

[0008] From Equation 1, if the coefficient of the third term of Equation 1 is ξ shown in Equation 2, it can be seen that when the coefficient ξ is positive with respect to the optical axis 11, there is convergence, and when the coefficient ξ is negative there is divergence.

[0009]

number

[0010] Now, assuming that there is no magnetic flux density Bz, in the case of the potential distribution shown in FIG. 5, the second derivative φ'' 27 of φ becomes negative, which indicates that the charged particles (electrons) 23 always diverge with respect to the optical axis (11)z after being emitted from the tip of the emitter 1. Since the charged particles (electrons) 23 are emitted perpendicular to the tip surface of the emitter 1, the degree of divergence increases as the tip radius of the emitter 1 decreases. Therefore, generally, emitters with a small tip radius have the characteristic of higher brightness but lower angular current density.

[0011] Non-Patent Document 2 describes a method for increasing the angular current density by arranging a magnetic lens directly below the extraction electrode 8 below the emitter 1, so that the magnetic field generated by the magnetic lens reaches the tip of the emitter 1, and so that the charged particles (electrons) 23 are subjected to a converging action in the direction of the optical axis 11 after being emitted from the tip of the emitter 1, thereby increasing the angular current density. Figure 6 shows an example of the configuration of this electron gun. The magnetic lens is arranged directly below the extraction electrode 8 and is located in an ultra-high vacuum. Furthermore, in order to ensure that the magnetic field reaches the tip of the emitter 1, magnetic poles 5A and 5B of the magnetic lens face the emitter 1.

[0012] In order to increase the angular current density, it is necessary to strengthen the magnetic field of the magnetic lens so that the value of the coefficient ξ shown in Equation 2 becomes positive. However, in order to deal with the heat and gas generated by the magnetic lens, it is necessary to keep a distance from the emitter 1, and the peak position of the magnetic flux density 16 is inevitably far from the emitter 1.

[0013] 5, the charged particles (electrons) 23 emitted from the tip of the emitter 1 travel straight at a large divergence angle, and the main surface of the magnetic lens is located near the magnetic pole. As a result, the trajectory height of the electron beam 10 from the optical axis 11 increases, resulting in large aberrations in the electron lens (not shown) located downstream of the magnetic lens. Furthermore, a high voltage of several kV is applied to the extraction voltage 8 to extract the charged particles (electrons) 23 from the tip of the emitter 1. As shown in FIG. 5, the axial potential is a strong electric field only near the tip of the emitter 1, and most of the area between the tip of the emitter 1 and the extraction electrode 8 is a high potential with a small potential difference. Therefore, a large axial magnetic flux density (16)Bz is required to produce a significant focusing force.

[0014] Patent Document 1 describes a method for reducing the aberration of the electron lens downstream of the electron gun by bringing the magnetic poles 5A and 5B of the magnetic lens closer to the emitter 1, thereby bringing the main surface 30 of the magnetic lens closer to the emitter 1. FIG. 7 shows an example of the configuration of an electron gun using a Schottky emitter as the emitter 1. The magnetic lens is placed in the atmosphere, isolated from the vacuum vessel (not shown) in which the emitter 1 is located. At both ends of the yoke 28, the emitter-side outer magnetic pole (downstream) 5A is located, and the other end is the outer magnetic pole (upstream) 5B. However, the magnetic pole 5A is insulated by a partition (not shown) and is located in the vacuum vessel, below the emitter 1, and an extraction voltage is applied to it. The tip of the emitter 1 is held protruding downward from the suppressor 31 of the Schottky emitter. In order to position the Schottky emitter including the suppressor 31 directly above the outer magnetic pole (downstream) 5A, which also serves as the extraction electrode 8, the magnetic lens including the coil 29 in the atmosphere and the outer magnetic pole (upstream) 5B have a diameter several tens of times larger than the diameter of the outer magnetic pole (downstream) 5A. Because the coil 29 is in the atmosphere, a large current can flow through the coil 29. If the magnetic lens brings the lens main surface 30 closer to the tip of the emitter 1, aberrations generated by an electron lens (not shown) located downstream of the magnetic lens can be reduced. However, because the diameter of the outer magnetic pole (upstream) 5B is several tens of times larger than the diameter of the outer magnetic pole (downstream) 5A, the peak value of the axial magnetic flux density 16 generated by the magnetic lens moves above the emitter 1. Therefore, the value of the axial magnetic flux density 16 that effectively acts on the tip of the emitter 1 is only a few percent of the peak value. Therefore, a strong magnetic field must be generated to generate a significant axial magnetic flux density 16. However, the magnetic lens is large, and measures must be taken to prevent expansion of the structure due to heat generated by the coil, vacuum deterioration due to gas emission, and discharge, which poses problems of technical difficulty and high manufacturing costs.

[0015] Furthermore, since the axial potential between the tip of the emitter 1 and the outer magnetic pole (downstream) 5A is the same as the potential distribution indicated by the equipotential lines 22 as shown in Figure 5, the charged particles (electrons) 23 emitted from the tip of the emitter 1 travel straight at a large divergence angle, and the main surface 30 of the magnetic lens is formed in the vicinity of the outer magnetic pole (downstream) 5A. As a result, the trajectory height of the electron beam 10 from the optical axis 11 becomes large, which causes a problem of large aberration occurring in an electron lens (not shown) located downstream of the magnetic lens. Furthermore, a high voltage of several kV is applied to the outer magnetic pole (downstream) 5A in order to draw out the charged particles (electrons) 23 from the tip of the emitter 1, and as shown in Figure 5, the axial potential 20 is a strong electric field only near the tip of the emitter 1, and most of the area between the tip of the emitter 1 and the outer magnetic pole (downstream) 5A is a high potential with a small potential difference, and a large axial magnetic flux density (16)Bz is required in order to generate a significant focusing force as φ^ in equation (2) is large.

[0016] Patent Document 2 describes a method of using a permanent magnet instead of the coil 29 to reduce the size of the magnetic lens. Figure 8 shows an example of the configuration of an electron gun using a Schottky emitter. The magnetic lens is located in a vacuum chamber (not shown) containing the emitter 1. At both ends of a yoke 28, the emitter side is designated as an outer magnetic pole (downstream) 5A, and the other end is designated as an outer magnetic pole (upstream) 5B. The outer magnetic pole (downstream) 5A and the inner magnetic pole 6A sandwich the permanent magnet 7. The outer magnetic pole (downstream) 5A is positioned below the emitter 1 and an extraction voltage is applied to it. The tip of the emitter 1 protrudes downward from the suppressor 31 of the Schottky emitter. To position the Schottky emitter, including the suppressor 31, directly above the outer magnetic pole (downstream) 5A, which also serves as the extraction electrode 8, the inner magnetic pole 6A has a diameter several tens of times larger than that of the outer magnetic pole (downstream) 5A. A neodymium magnet is used for the permanent magnet 7. The magnetic lens brings the lens main surface 30 closer to the tip of the emitter 1, thereby reducing aberrations that occur in an electron lens (not shown) located downstream of the magnetic lens. However, because the diameter of the inner magnetic pole 6A is several tens of times larger than the diameter of the outer magnetic pole (downstream) 5A, the peak value of the axial magnetic flux density 16 generated by the magnetic lens moves above the emitter 1, and the value of the axial magnetic flux density 16 that effectively acts on the tip of the emitter is only a few percent of the peak value. In order to achieve a significant axial magnetic flux density 16, a strong magnetic field must be generated. However, with the arrangement of the permanent magnet 7 and the magnetic poles 5A and 6A, it is impossible to obtain an axial magnetic flux density 16 of significant strength at the tip of the emitter 1. Therefore, the magnetic lens mainly serves as a means for slightly reducing the divergence of the electron beam 10 emitted from the tip of the emitter 1.

[0017] Furthermore, since the axial potential between the tip of the emitter 1 and the outer magnetic pole (downstream) 5A is the same as the potential distribution indicated by the equipotential lines 22 as shown in FIG. 5, the charged particles (electrons) 23 emitted from the tip of the emitter 1 travel in a straight line at a large divergence angle, and the main surface 30 of the magnetic lens is also located near the outer magnetic pole (downstream) 5A. As a result, the trajectory height of the electron beam 10 from the optical axis 11 increases, which causes a problem of increased aberration occurring in an electron lens (not shown) located downstream of the magnetic lens. Furthermore, a high voltage of several kV is applied to the outer magnetic pole (downstream) 5A in order to draw out the charged particles (electrons) 23 from the tip of the emitter, and as shown in Figure 5, the axial potential 20 is a strong electric field only near the tip of the emitter 1, and most of the area between the tip of the emitter 1 and the outer magnetic pole (downstream) 5A is a high potential with a small potential difference, and a large axial magnetic flux density (16)Bz is required to produce a significant focusing force as φ^ in equation (2) is large. [Prior art documents] [Non-patent literature]

[0018] [Non-Patent Document 1] AV Crewe, DN Eggenberger, J. Wall, LM Welter, “Electron Gun Using a Field Emission Source”, The review of scientific instruments, Vol.39, Num.4, 1967 [Non-patent document 2] M. Troyon, “New field emission gun with energy filtering effect”, J. Appl. Phys. 66 (1), 1 July 1989, p.1-4 [Patent documents]

[0019] [Patent Document 1] Patent Publication No. 2-297852 [Patent Document 2] Patent Publication No. 2006-210254 Summary of the Invention [Problem to be solved by the invention]

[0020] 5, in order to emit charged particles 23 from the emitter 1, a sufficiently strong electric field must be formed at the tip of the emitter 1. Arc-shaped equipotential lines 22 are densely formed near the tip of the emitter 1 according to the surface shape, and the emitted charged particles (electrons) 23 fly away under the force in the normal direction of the equipotential lines 22. Therefore, the emission angle of the charged particle beam formed by the charged particles (electrons) 23 emitted from the emission surface of the emitter 1 is large, and it is common to use a charged particle beam whose angle is limited by an aperture provided between the emitter 1 and a sample (not shown).

[0021] However, if the emission angle is limited to a small angle, the brightness increases, but the number of the charged particles 23 passing through the aperture decreases, and the angular current density decreases, resulting in a problem that when the electron beam passing through the aperture is used in, for example, a charged particle microscope, the S / N (Signal to Noise) of the observed value becomes extremely poor. Also, if the aperture diameter is increased to increase the emission angle in order to improve the S / N, the brightness decreases, and further, the aberration of the electron lens (not shown) downstream of the emitter 1 also increases. Therefore, when used in, for example, a charged particle microscope, the diameter of the charged particle beam at the sample position (not shown) becomes large, resulting in a problem of poor resolution.

[0022] Furthermore, if the emission angle of the charged particle beam is large, most of the charged particles (electrons) 23 forming the charged particle beam collide with the extraction electrode 8 or the acceleration electrode, generating secondary electrons and gas molecules from the surface of the extraction electrode 8 or the acceleration electrode. The emitted secondary electrons are accelerated and collide with the emitter 1, damaging the emitter 1, and the emitted gas molecules deteriorate the degree of vacuum, reducing the amount of emission and inducing damage to the emitter 1 due to discharge.

[0023] One approach considered was to place a magnetic lens near the emitter 1 in order to increase the angular current density without restricting the emission angle to a small angle. However, the coil required to generate a strong magnetic field is large, and it is not possible to place the coil inside the ultra-high vacuum vessel. Furthermore, if the coil is placed outside the ultra-high vacuum vessel that houses the emitter 1, the axial magnetic flux density on the optical axis will be further reduced, which is a problem.

[0024] Furthermore, there is a problem that the heat generated by the magnetic lens causes vacuum failure, and the generated heat induces expansion of the structure, resulting in axis failure.

[0025] One approach considered was to place a magnetic field lens using a permanent magnet near the emitter 1 in order to increase the angular current density without restricting the emission angle to a small angle. However, the permanent magnet alone cannot create a magnetic field of sufficient strength at the tip of the emitter 1, so the permanent magnet must be held in place by a soft magnetic material, a magnetic circuit must be formed, and magnetic poles must be formed near the tip of the emitter 1. However, with a Schottky emitter having a suppressor, it is necessary to leave a sufficient distance between the magnetic poles to avoid interference with the suppressor, which poses the problem that a magnetic field of sufficient strength cannot be created at the tip of the emitter.

[0026] Furthermore, even in a field emission emitter that does not have the suppressor, there is only a steep potential gradient at the tip of the emitter 1, and most of the area from the tip of the emitter 1 to the extraction electrode is at high potential, so an even stronger magnetic field is required to converge the charged particles (electrons) 23 after field emission, and there is a problem in that a magnetic field of sufficient strength cannot be created at the tip of the emitter even if the distance between the magnetic poles is reduced.

[0027] Furthermore, since the magnetic field strength generated by each permanent magnet is constant, there is a problem in that variations in the magnetic field strength cannot be corrected.

[0028] The object of the present invention is to solve the above-mentioned problems of the prior art and to provide a high-brightness charged particle gun that does not deteriorate the degree of vacuum even when a large current is emitted from the emitter, has a large angular current density that does not reduce the S / N ratio even when the angle of the charged particle beam emitted from the emitter is limited, and can maintain high resolution. [Means for solving the problem]

[0029] In order to solve the above problems, the present invention provides a charged particle gun comprising: an emitter that emits charged particles; a first electrode that is a magnetic body and is arranged rotationally symmetrically on an optical axis including the emitter directly below the emitter; a second electrode that is a magnetic body and is arranged between the first electrode and the second electrode to surround the tip of the emitter; a permanent magnet sandwiched between the first electrode and the second electrode; and an extraction electrode that is arranged below the first electrode, and the axial magnetic flux density distribution formed on the optical axis by the first electrode, the second electrode, and the permanent magnet is such that the axial magnetic flux density distribution is oriented toward the tip of the emitter. The electric potential distribution formed between the extraction electrode and the first electrode spreads convexly from the hole in the first electrode toward the emitter side and from the hole in the extraction electrode in the opposite direction to the emitter, and the electromagnetic field in which the axial magnetic flux density distribution and the electric potential distribution are superimposed focuses the charged particles radially emitted from the tip of the emitter in the direction of the optical axis, and then makes them parallel to the optical axis between the first electrode and the extraction electrode without crossing over with the optical axis.

[0030] The charged particle gun is also characterized in that a portion of the first electrode on the side away from the optical axis is in contact with the permanent magnet, and a portion of the first electrode extends upstream parallel to the optical axis from outside the permanent magnet without touching the permanent magnet.

[0031] The charged particle gun is characterized in that the first electrode and the second electrode are at the same potential.

[0032] The charged particle gun is also characterized in that the voltage applied to the first electrode is positive with respect to the voltage applied to the emitter, and the voltage applied to the extraction electrode is higher than the voltage applied to the first electrode.

[0033] The charged particle gun is also characterized in that the second-order differential value of the axial potential is positive at the tip of the emitter, there is a region where it is zero between the tip of the emitter and the extraction electrode, and it is negative at the extraction electrode.

[0034] The charged particle gun is also characterized in that the angular current density and brightness of the charged particle beam are adjusted by combining the voltage VS applied to the first electrode and the voltage VE applied to the extraction electrode.

[0035] Furthermore, the charged particle gun is characterized in that even if the magnetic field strength generated by the permanent magnet fluctuates, the electric field strength at the tip of the emitter is kept constant by combining the voltage VS applied to the first electrode and the voltage VE applied to the extraction electrode.

[0036] The charged particle gun is also characterized in that the ratio R2 / R1 of the radius R1 of the hole in the first electrode to the radius R2 of the hole in the second electrode is 2 or less.

[0037] The charged particle gun is also characterized in that the ratio L / R1 of the distance L between the tip of the emitter and the first electrode to the radius R1 of the hole in the first electrode is 1 or less.

[0038] The charged particle gun is also characterized in that the ratio L / D of the distance L between the tip of the emitter and the first electrode to the distance D between the first electrode and the extraction electrode is 4 or less.

[0039] The charged particle gun is also characterized in that, based on the voltage applied to the emitter, the voltage applied to the first electrode is 1 kV or less, and the voltage applied to the extraction electrode is 20 kV or less.

[0040] In the charged particle gun, the permanent magnet is a samarium-cobalt magnet or a neodymium magnet.

[0041] In addition, in the charged particle gun, the emitter is any one of a thermionic electron emission source, a thermal field emission electron source, a cold cathode electron source, a nanotip, a carbon nanotube, a superconducting electron source, a stacked electron source, an emitter array, a liquid metal ion source, and a helium ion source.

[0042] A charged particle device according to the present invention is characterized by comprising the above-described charged particle gun. [Effects of the Invention]

[0043] High brightness charged particle sources have high brightness but low angular current density, and brightness drops significantly when a large current flows. However, the present invention can increase both angular current density and brightness.

[0044] Since the emission angle is small, the electrode structure is not unnecessarily irradiated, the amount of gas emitted from the electrode surface is small, the degree of vacuum is not deteriorated, and the electrode surface is not contaminated.

[0045] Because of its high angular current density, even when the angle of the charged particle beam is restricted, a large number of charged particles pass through, and the signal S / N ratio obtained by irradiating the sample is high. In addition, because brightness does not decrease, high resolution can be maintained.

[0046] Since the permanent magnet is used as a magnetic lens, the charged particle gun can be made compact.

[0047] By adjusting the voltage applied to the two electrodes, the characteristics (brightness, angular current density) of the charged particle beam emitted from the charged particle source can be changed depending on the application.

[0048] Variations in the magnetic field strength of the permanent magnet can be corrected by adjusting the voltages applied to the two electrodes.

[0049] After being emitted from the emitter, the charged particles are parallel to the optical axis without crossover, resulting in a highly coherent charged particle beam with small energy dispersion and high current density.

[0050] When the present invention is applied to a charged particle microscope, the angular current density can be changed, so there is no need for an electron lens for adjusting the amount of current on the sample side as viewed from the emitter, and the charged particle microscope can be made compact.

[0051] When the present invention is applied to a charged particle microscope, the emission angle is small and the diameter of the charged particle beam does not deviate significantly from the optical axis, so that the aberration generated by the lens on the sample side as seen from the emitter can be kept small. Even when a charged particle beam is focused on the sample surface at a large current, the blurring of the charged particle beam diameter due to aberration is small, allowing for high-resolution observation, shortening the observation and analysis time, and reducing sample damage.

[0052] When the present invention is applied to an electron beam exposure apparatus, the exposure time is shortened because exposure is performed with an electron beam having a high current density.

[0053] When the present invention is applied to an electron beam inspection apparatus, even when a charged particle beam is focused on the surface of a sample at a large current, the electron beam diameter is not blurred due to aberration, and the sample can be inspected with high precision and speed with high spatial resolution.

[0054] When the present invention is applied to an electron beam measurement device, even when a charged particle beam is focused on the surface of a sample at a large current, the electron beam diameter is not blurred due to aberration, and the sample can be measured with high precision and speed with high spatial resolution. [Brief explanation of the drawings]

[0055] [Figure 1] 1 is a schematic diagram showing an embodiment of the present invention; [Figure 2] 1 is a schematic diagram illustrating an example of the operation of a charged particle gun according to the present invention. [Figure 3] 1 is a schematic diagram illustrating an example of the operation of a charged particle gun according to the present invention. [Figure 4] 10A and 10B are diagrams showing the results of calculation of charged particle trajectories, explaining an example of the operation of the charged particle gun according to the present invention. [Figure 5] FIG. 1 is a schematic diagram showing the configuration of a conventional charged particle gun. [Figure 6] FIG. 1 is a schematic diagram illustrating the configuration of a conventional charged particle gun. [Figure 7] FIG. 1 is a schematic diagram illustrating the configuration of a conventional charged particle gun. [Figure 8] FIG. 1 is a schematic diagram illustrating the configuration of a conventional charged particle gun. [Figure 9] FIG. 10 is a schematic diagram showing another embodiment of the charged particle gun according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0056] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same functions will be assigned the same reference numerals, and repeated description thereof may be omitted.

[0057] The charged particle device includes a charged particle gun equipped with a charged particle source.

[0058] A charged particle gun comprises an emitter that emits charged particles, a first electrode made of a magnetic material that is arranged directly below the emitter in rotational symmetry on an optical axis that includes the emitter, a second electrode made of a magnetic material that surrounds the tip of the emitter and is arranged between the first electrode, a permanent magnet sandwiched between the first electrode and the second electrode, and an extraction electrode that is arranged below the first electrode.

[0059] The axial magnetic flux density distribution formed on the optical axis by the first electrode, the second electrode, and the permanent magnet reaches a maximum at the tip of the emitter, and then disappears between the first electrode and the extraction electrode, and the potential distribution formed between the extraction electrode and the first electrode seeps out in a convex shape toward the emitter from the hole in the first electrode and then seeps out in a convex shape in the opposite direction from the emitter from the hole in the extraction electrode, and the electromagnetic field formed by the superposition of the axial magnetic flux density distribution and the potential distribution focuses the charged particles emitted radially from the tip of the emitter in the direction of the optical axis, and then becomes parallel to the optical axis between the first electrode and the extraction electrode without crossing over with the optical axis.

[0060] A part of the first electrode on the side away from the optical axis is in contact with the permanent magnet, and a part of the first electrode extends upstream in parallel with the optical axis from outside the permanent magnet so as not to contact the permanent magnet.

[0061] The first electrode and the second electrode are at the same potential.

[0062] With respect to the voltage applied to the emitter as a reference, the voltage applied to the first electrode is positive, and the voltage applied to the extraction electrode is higher than the voltage applied to the first electrode.

[0063] The second derivative of the axial potential is positive near the tip of the emitter, has a region where it is zero between the tip of the emitter and the extraction electrode, and is negative at the extraction electrode.

[0064] The angular density and brightness of the charged particle beam are adjusted by the combination of the voltage VS applied to the first electrode and the voltage VE applied to the extraction electrode.

[0065] The electric field intensity at the tip of the emitter is made constant by a combination of the voltage VS applied to the first electrode and the voltage VE applied to the extraction electrode.

[0066] The ratio R2 / R1 of the radius R1 of the hole in the first electrode to the radius R2 of the hole in the second electrode is 2 or less.

[0067] The ratio L / R1 of the distance L between the tip of the emitter and the first electrode to the radius R1 of the hole in the first electrode is 1 or less.

[0068] The ratio L / D of the distance L between the tip of the emitter and the first electrode to the distance D between the first electrode and the extraction electrode is 4 or less.

[0069] With respect to the voltage applied to the emitter as a reference, the voltage applied to the first electrode is 1 kV or less, and the voltage applied to the extraction electrode is 20 kV or less.

[0070] The permanent magnet is a samarium-cobalt magnet or a neodymium magnet.

[0071] The emitter may be, for example, a thermionic electron source, a thermal field emission electron source, a cold cathode electron source, a nanotip, a carbon nanotube, a superconducting electron source, a stacked electron source, an emitter array, a liquid metal ion source, or a helium ion source. [Example]

[0072] FIG. 1 shows one embodiment of the present invention. A detailed description will be given below with reference to the drawings. The figure shows a cross section of an emitter 1 and electrodes, which are rotationally symmetrical about an optical axis 11. A first electrode 5, which is a magnetic material, is disposed directly below the emitter 1, which emits charged particles 23. A second electrode 6, which is a magnetic material and surrounds the tip of the emitter 1, is disposed between the first electrode 5 and the second electrode 6. A permanent magnet 7, such as a samarium-cobalt magnet or a neodymium magnet, is sandwiched between the first electrode 5 and the second electrode 6. The tip of the emitter 1 is located on the optical axis 11 between the first electrode 5 and the second electrode 6. An extraction electrode 8 is disposed below the first electrode 5.

[0073] In addition, a portion of the first electrode 5 on the side away from the optical axis 11 contacts the permanent magnet 7, and a portion extends upstream parallel to the optical axis 11 from outside the permanent magnet 7 without touching the permanent magnet 7.

[0074] The emitter 1 is fixed to a wire 2 , the wire 2 is fixed to an emitter electrode 3 , and the emitter electrode 3 is fixed to an insulator 4 .

[0075] The second electrode 6 is basically at the same potential as the first electrode 5, but may be applied with a potential independent of the first electrode 5 via an insulator (not shown). In this embodiment, the first electrode 5 and the second electrode 6 are at the same potential.

[0076] An acceleration voltage is applied to the emitter 1 from an acceleration voltage power supply 12 via the emitter electrode 3, an electric field suppression voltage VS is applied to the second electrode 6 from an electric field suppression voltage power supply 13, and an extraction voltage VE is applied to the first electrode 5 from an extraction voltage power supply 14, and the electric field suppression voltage power supply 13 and the extraction voltage power supply 14 are floated on the output of the acceleration voltage power supply 12.

[0077] A strong electric field is formed at the tip of the emitter 1 by the voltage VE applied to the extraction electrode 8 and the voltage VS applied to the first electrode 5, and charged particles 23 field-emitted from the tip of the emitter 1 by this strong electric field are emitted as an electron beam 10 along the optical axis 11.

[0078] Figure 2(A) shows the left side of the configuration diagram shown in Figure 1, magnetic field lines 15 generated from the permanent magnet 7 sandwiched between the first electrode 5 and the second electrode 6, and an axial magnetic flux density 16 formed on the optical axis 11.

[0079] The permanent magnet 7, the first electrode 5, and the second electrode 6 form a magnetic circuit, and most of the magnetic field lines 15 generated from the permanent magnet 7 are guided to and leak out of the magnetic poles 5A and 6A near the optical axis 11, forming the axial magnetic flux density 16 on the optical axis 11 where the emitter 1 is located. In addition, some of the magnetic field lines 15 generated from the permanent magnet 7 form a magnetic pole 5B at an end along the first electrode 5 that extends upstream in parallel to the optical axis 11 from outside the permanent magnet 7 so as not to touch the permanent magnet 7, and the axial magnetic flux density 16 that is negative relative to the axial magnetic flux density 16 formed near the emitter 1 is formed upstream of the emitter 1.

[0080] The position on the optical axis 11 where the magnetic field near the tip of the emitter 1 forms a maximum value of the axial magnetic flux density 16 on the optical axis 11 is between the first electrode 5 and the second electrode 6, and the axial magnetic flux density 16 decreases sharply below the first electrode 5 and disappears between the first electrode 5 and the extraction electrode 8.

[0081] FIG. 2(B) shows the left side of the configuration diagram shown in FIG. 1, equipotential lines 22 representing the potential distribution formed by the voltage VE applied to the extraction electrode 8 from near the tip of the emitter 1 to near the extraction electrode 8 and the voltage VS applied to the first electrode 5, the axial potential (20)φ on the optical axis 11, and the second-order differential (27)φ'' of the axial potential (20)φ.

[0082] With the voltage applied to the emitter 1 as the reference, the voltages applied to the first electrode 5 and the second electrode 6 are positive, and the voltage applied to the extraction electrode 8 is higher than the voltages applied to the first electrode 5 and the second electrode 6, so that the potential distribution spreads out in a convex shape from the hole in the first electrode 5 to the emitter 1 side, and the potential distribution spreads out in a convex shape from the hole in the extraction electrode 8 downward.

[0083] The axial potential 20 is a low potential of 1 kV or less near the tip of the emitter 1, but if the radius of the emitter 1 is set to 1 μm or less, the electric field strength at the tip of the emitter 1 is high, 1×10 6V / m or more, and the potential gradient between the first electrode and the extraction electrode 8 is constant for the most part.

[0084] As shown in Figures 2(A) and 2(B), the magnetic field leaking out from the first electrode 5 and the second electrode 6 toward the emitter 1 and the potential distribution leaking out in a convex shape toward the emitter 1 from the hole in the first electrode 5 are superimposed in the vicinity of the emitter 1.

[0085] FIG. 3(A) shows the electrode arrangement and equipotential lines 22 near the emitter 1 and the trajectory of the charged particle 23 emitted from the tip of the emitter 1 in the configuration diagram shown in FIGS. 2(A) and 2(B) when there is no magnetic field.

[0086] Near the tip of the emitter 1, the potential distribution protrudes in a convex shape from the hole in the first electrode 5 toward the emitter 1, so the second derivative φ'' of the axial potential φ becomes positive, and as shown in Figure 3(A), the coefficient ξ becomes positive near the tip of the emitter 1.

[0087] In the vicinity of the extraction electrode 8, the potential distribution protrudes downstream from the hole in the extraction electrode 8 in a convex shape, so the second-order differential (27)φ″ of the axial potential (20)φ becomes negative, and the coefficient (21)ξ becomes negative in the vicinity of the extraction electrode 8.

[0088] If the value of the coefficient (21)ξ, which is expressed by the formula 2 in the third term of the paraxial trajectory equation of the charged particle 23 expressed by the formula 1, on the optical axis 11 is positive, it indicates a converging action, and if it is negative, it indicates a diverging action. Therefore, the charged particle 23 emitted from the tip of the emitter 1 at a large divergence angle with respect to the optical axis 11 in the normal direction of the equipotential line 22 formed near the tip of the emitter 1 is bent toward the optical axis 11 due to the converging action, but is diverged near the extraction electrode 8 and moves in a direction away from the optical axis 11.

[0089] If the downstream of the extraction electrode 8 is at an equipotential, the charged particle 23 will not receive any force and will travel in a straight line. If an asymptote 24 of the trajectory is created for all the charged particles emitted from the tip of the emitter 1, it will become a virtual light source 25 with a size located upstream of the emitter 1.

[0090] Figure 3(B) shows the electrode arrangement near the emitter 1 when a magnetic field is present in the configuration diagrams shown in Figures 2(A) and 2(B), the equipotential lines 22 and equimagnetic field lines 26, and the trajectory of the charged particles 23 emitted from the tip of the emitter 1.

[0091] The potential distribution is the same as that shown in Figure 3(A), and so is the second-order differential (27)φ'' of the axial potential (20)φ. On the other hand, the coefficient (21)ξ expressed by equation 2 has a larger value because the axial magnetic flux density (16)Bz in the equation has a value, and the convergence force is stronger.

[0092] 3A, the trajectory of the charged particles 23 emitted from the tip of the emitter 1 is bent more toward the optical axis 11, but since the charged particles 23 do not have a crossover downstream of the extraction electrode, the axial magnetic flux density 16 rapidly attenuates at the lower end of the extraction electrode 8. Therefore, the ratio R2 / R1 of the radius R1 of the hole in the first electrode 5 to the radius R2 of the hole in the second electrode 6 is set to 2 or less, and the ratio L / R1 of the distance L between the tip of the emitter 1 and the first electrode 5 to the radius R1 of the hole in the first electrode 5 is set to 1 or less. For example, R1=0.2 mm, R2=0.15 mm, and L=0.15 mm.

[0093] The distance D between the first electrode 5 and the extraction electrode 8 is set to satisfy Equation 3 so that the axial magnetic flux density (16)Bz becomes 0 between the first electrode 5 and the extraction electrode 8 and the coefficient (21)ξ becomes negative downstream thereof. For example, L=0.15 mm, D=0.6 mm.

[0094]

number

[0095] The charged particles 23 emitted from the tip of the emitter 1 are bent toward the optical axis 11 by a converging action, and then are diverged in the vicinity of the extraction electrode 8 without crossing over with the optical axis 11, so that the voltage VS applied to the first electrode 5 and the voltage VE applied to the extraction electrode 8 are set with respect to the axial magnetic flux density (16) Bz on the optical axis 11 created by the permanent magnet 7 so that the trajectory has an absolute value of the divergence angle with respect to the optical axis 11 of 50 mrad or less.

[0096] If the downstream of the extraction electrode 8 is at an equipotential, the charged particles 23 will travel in a straight line since they are not subjected to any force, and if the asymptote 24 of the trajectory is created for all the charged particles 23 emitted from the tip of the emitter 1, it will become a virtual light source 25 with a size located upstream of the emitter 1.

[0097] The optical characteristics of the charged particle beam 10 are adjusted by the combination of the voltage VS applied to the first electrode 5 and the voltage VE applied to the extraction electrode 8. For example, even if the magnetic field strength of the permanent magnet 7 fluctuates, the electric field strength at the tip of the emitter 1 can be kept constant by adjusting the combination of the voltage VS applied to the first electrode 5 and the voltage VE applied to the extraction electrode 8, and the amount of charged particles emitted from the emitter 1 can be kept constant.

[0098] Although the electric field strength between the vicinity of the tip of the emitter 1 and the first electrode 5 is high, the potential is a low voltage of 1 kV or less, so that the charged particles 23 emitted from the tip of the emitter 1 can be controlled with a small electromagnetic force. For example, the voltage Vs applied to the first electrode 5 is 1 kV or less, and the maximum value of the axial magnetic flux density (16) Bz at the tip of the emitter 1 is 1 tesla or less. Although the potential is low, the divergence angle of the charged particles 23 after being emitted from the tip of the emitter 1 is large, so the Coulomb effect between the charged particles 23 is small. Furthermore, since the potential distribution is convex from the hole in the first electrode 5 toward the emitter 1, the charged particles 23 are converged in the direction of the optical axis 11 near the first electrode 5, but are accelerated at a high potential of 1 kV or more and 20 kV or less between the first electrode 5 and the extraction electrode 8, and the charged particles 23 diverge without crossing over with the optical axis 11, so the Coulomb effect is small.

[0099] 3(A), the angular current density of the charged particle beam 10 emitted from the emitter 1 can be increased, but the brightness decreases due to increased aberration of the electrostatic lens formed by the emitter 1, the first electrode 5, and the extraction electrode 8. However, if the emitter originally has high brightness even when the angular current density is small, the angular current density can be increased by reducing the brightness to a usable level, and this is useful for, for example, analytical electron microscopes, electron beam exposure devices, X-ray sources, and processing devices that require large currents.

[0100] Furthermore, in the electrode arrangement, electric potential distribution, and magnetic field distribution shown in Figure 3(B), a magnetic field distribution is superimposed on the electrode arrangement and electric potential distribution shown in Figure 3(A), which makes it possible to reduce the aberration of the electrostatic lens and simultaneously increase the angular current density and the converted brightness, thereby improving the performance of, for example, all electron microscopes, ion microscopes, measurement devices, inspection devices, electron beam exposure devices, and micro X-ray CT devices that are equipped with emitters.

[0101] Figure 4(A) shows the calculation results of electron trajectory 15 emitted from the tip of the emitter, assuming that the charged particle 23 is an electron, with the electrode arrangement and potential distribution shown in Figure 3(A). The radius of the emitter tip was set to 25 nm, and the voltage VS applied to the first electrode 5, the voltage VE applied to the extraction electrode 8, the radius R1 of the hole in the first electrode 5, the radius R2 of the hole in the second electrode 6, the distance L between the tip of the emitter 1 and the first electrode 5, and the distance D between the first electrode 5 and the extraction electrode 8 were set as follows: The voltage applied to the second electrode was set to the same as the voltage applied to the first electrode. The hole diameter of the extraction electrode 8 was set to the same as the hole diameter of the first electrode 5.

[0102] VS=40V VE=4kV R1=0.2mm R2=0.15mm L=0.15mm D=0.6mm

[0103] As can be seen in the figure, the potential distribution spreads out in a convex shape from the hole in the first electrode toward the emitter 1, and the potential distribution spreads out in a convex shape downward from the hole in the extraction electrode 8, and the second derivative (27)φ'' of the axial potential (20)φ on the optical axis 11 is positive near the tip of the emitter 1, there is a region where it is zero between the tip of the emitter 1 and the extraction electrode 8, and it is negative near the extraction electrode 8. Therefore, from Equation 2, the coefficient (21)ξ is positive near the tip of the emitter 1 and negative near the extraction electrode 8.

[0104] The electron trajectory 15 calculated when the probe current is limited to 16.5 nA is obtained by multiplying the optical axis 11 by 5 in the X direction, with the optical axis 11 being the Z coordinate and the direction perpendicular to the optical axis 11 being the X coordinate. Electrons emitted at an angle from the tip of the emitter 1 diverge with respect to the optical axis 11, but are bent toward the optical axis 11 near the first electrode 5, and diverge near the extraction electrode 8 without crossing over with the optical axis 11.

[0105] In this case, the angular current density is about 500 μA / sr, and the converted luminance is about 5x10 8 A / m 2 When the emitter is operated with the conventional electrode arrangement and potential distribution shown in FIG. 5, the angular current density of the emitter 1 is 10 μA / sr, and the converted luminance is 1×10 10 A / m 2 / sr / V, and the luminance can be reduced to a level that does not pose a practical problem, while the angular current density can be increased by one order of magnitude or more.

[0106] 4(B) shows the calculation results of electron trajectories 15 emitted from the tip of the emitter 1 when the electrode arrangement, potential distribution, and operating conditions shown in FIG. 4(A) are the same, and further, a magnetic field is generated from the magnetic pole 5A formed at the tip of the first electrode 5 and the magnetic pole 6A formed at the tip of the second electrode 6, forming an axial magnetic flux density 16 of a maximum value of 0.9 tesla on the optical axis 11. The value of the coefficient (21)ξ near the tip of the emitter 1 is larger than in the case shown in FIG. 4(A), and electrons emitted at an angle from the tip of the emitter 1 immediately bend toward the optical axis 11, but gradually become parallel to the optical axis 11 without crossing over with the optical axis 11 due to the divergence effect that occurs near the extraction electrode 8.

[0107] In this case, the distance of the electron orbit 15 from the optical axis 11 is small, so the aberration generated by the electrostatic lens is small, and the angular current density and the converted luminance are 5.0 A / sr and 4.3×10, respectively, from the calculation results shown in FIG. 4(A). 15 A / m 2 / sr / V and higher.

[0108] Figure 4(C) shows the calculation results of electron trajectories 15 emitted from the tip of the emitter 1 when the electrode arrangement and potential distribution are the same as those in Figures 4(A) and 4(B), but a magnetic field is generated from the magnetic pole 5A formed at the tip of the first electrode 5 and the magnetic pole 6A formed at the tip of the second electrode 6 to form an axial magnetic flux density 16 with a maximum value of 0.8 Tesla on the optical axis 11, and the voltage VS applied to the first electrode 5 and the voltage VE applied to the extraction electrode 8 are set as follows so that the electric field intensity at the tip of the emitter 1 is the same as in Figures 4(A) and 4(B).

[0109] VS=100V VE=1kV

[0110] In this case, the angular current density is 3.6A / sr, and the converted luminance is 9.7x10 15 A / m 2 / sr / V. By slightly increasing the voltage VS applied to the first electrode, the angular current density becomes slightly smaller, and conversely, the converted luminance becomes slightly higher.

[0111] Since the variation in the magnetic field of the permanent magnet 7 is less than 0.1 Tesla, it may be assumed that the variation is not as great as the difference in the angular current density and the difference in the converted brightness between Figures 4(B) and 4(C). Furthermore, the optical characteristics of the emitted electron beam can be changed by the combination {Bz, VS, VE} of the axial magnetic flux density (16) Bz, the voltage VS applied to the first electrode 5, and the voltage VE applied to the extraction electrode 8. [Example]

[0112] The charged particle gun includes an emitter array that emits charged particles, a first electrode made of a magnetic material and arranged directly below the emitter array in rotational symmetry on an optical axis including the emitter array, a second electrode made of a magnetic material that surrounds the tip of the emitter array and is arranged between the first electrode, a permanent magnet sandwiched between the first electrode and the second electrode, and an extraction electrode arranged below the first electrode; The axial magnetic flux density distribution formed on the optical axis by the first electrode, the second electrode, and the permanent magnet reaches a maximum at the tip of the emitter array, and then disappears between the first electrode and the extraction electrode, and the potential distribution formed between the extraction electrode and the first electrode seeps out in a convex shape toward the emitter array from the hole in the first electrode and then seeps out in a convex shape in the opposite direction to the emitter array from the hole in the extraction electrode, and the electromagnetic field formed by the superposition of the axial magnetic flux density distribution and the potential distribution focuses the charged particles emitted radially from the tip of the emitter array in the direction of the optical axis, and then becomes parallel to the optical axis between the first electrode and the extraction electrode without crossing over with the optical axis.

[0113] FIG. 9 shows an embodiment of the present invention. The following describes this embodiment in detail with reference to the drawings. The operation of this embodiment is the same as that of the first embodiment, but it is applied to an emitter array 32 in which multiple emitters are arranged on the same plane. The second electrode is insulated from the permanent magnet 7 by an insulator 33, and an acceleration voltage is applied to the emitter array 32 and the second electrode from an acceleration voltage power supply 12. Similar to the first embodiment, charged particles 23 emitted from each emitter (not shown) of the emitter array 32 are parallel to the optical axis 11, providing a charged particle gun that supplies a charged particle beam 10 parallel to the optical axis 11 and having a high angular current density and high brightness. [Explanation of symbols]

[0114] 1: Emitter 2: Wire 3: Wire supported electrode 4: Insulator 5: First electrode 5A: Magnetic pole (downstream of the first electrode) 5B: Magnetic pole (upstream of the first electrode) 6: Second electrode 6A: Magnetic pole (second electrode) 7: Permanent magnet 8: Extraction electrode 9: Accelerating electrode 10: Charged particle beam 11: Optical axis 12: Accelerating voltage power supply 13: First electrode voltage power supply 14: Extraction voltage power supply 15:Electron orbit 16: Axial magnetic flux density 17: Magnetic field maximum position 18: Emitter tip position 19: Extraction electrode emitter side position 20: Axial potential 21: Coefficient ξ 22: Equipotential lines 23: Charged particle 24: Asymptotes 25: Virtual light source 26: Magnetic field lines 27: Second derivative of the axial potential 28: York 29: Coil 30: Lens principal surface position 31: Suppressor 32: Emitter array 33: Insulator

Claims

1. The device comprises an emitter that emits charged particles, a first electrode made of a magnetic material and arranged directly below the emitter in rotational symmetry on an optical axis including the emitter, a second electrode made of a magnetic material and arranged between the first electrode and surrounding the tip of the emitter, a permanent magnet sandwiched between the first electrode and the second electrode, and an extraction electrode arranged below the first electrode, a potential distribution formed between the extraction electrode and the first electrode in a convex shape toward the emitter from the hole in the first electrode and a potential distribution formed between the extraction electrode and the first electrode; an electromagnetic field formed by the superposition of the axial magnetic flux density distribution and the potential distribution, which focuses the charged particles radially emitted from the tip of the emitter in the direction of the optical axis, and then makes the charged particles parallel to the optical axis between the first electrode and the extraction electrode without crossing over with the optical axis.

2. 2. The charged particle gun according to claim 1, wherein a portion of the first electrode on a side away from the optical axis is in contact with the permanent magnet, and a portion of the first electrode extends upstream parallel to the optical axis from outside the permanent magnet so as not to contact the permanent magnet.

3. 2. A charged particle gun according to claim 1, wherein the first electrode and the second electrode are at the same potential.

4. 2. The charged particle gun according to claim 1, wherein the voltage applied to the first electrode is positive with respect to the voltage applied to the emitter, and the voltage applied to the extraction electrode is higher than the voltage applied to the first electrode.

5. 2. The charged particle gun according to claim 1, wherein a second-order differential value of the axial potential on the optical axis is positive at the tip of the emitter, has a region where it is zero between the tip of the emitter and the extraction electrode, and is negative at the extraction electrode.

6. 2. The charged particle gun according to claim 1, wherein the angular current density and brightness of the charged particle beam are adjusted by a combination of a voltage VS applied to the first electrode and a voltage VE applied to the extraction electrode.

7. 2. The charged particle gun according to claim 1, wherein the electric field intensity at the tip of the emitter is made constant by a combination of a voltage VS applied to the first electrode and a voltage VE applied to the extraction electrode.

8. 2. A charged particle gun according to claim 1, wherein a ratio R2 / R1 of a radius R1 of the hole in the first electrode to a radius R2 of the hole in the second electrode is 2 or less.

9. 2. The charged particle gun according to claim 1, wherein a ratio L / R1 of a distance L between the tip of the emitter and the first electrode to a radius R1 of the hole in the first electrode is 1 or less.

10. 2. The charged particle gun according to claim 1, wherein a ratio L / D of a distance L between the tip of the emitter and the first electrode to a distance D between the first electrode and the extraction electrode is 4 or less.

11. 2. The charged particle gun according to claim 1, wherein the voltage applied to the first electrode is 1 kV or less and the voltage applied to the extraction electrode is 20 kV or less, based on the voltage applied to the emitter.

12. 2. The charged particle gun according to claim 1, wherein the permanent magnet is a samarium-cobalt magnet or a neodymium magnet.

13. 2. The charged particle gun according to claim 1, wherein the emitter is any one of a thermionic electron emission source, a thermal field emission electron source, a cold cathode electron source, a nanotip, a carbon nanotube, a superconducting electron source, a stacked electron source, an emitter array, a liquid metal ion source, and a helium ion source.

14. A charged particle device comprising the charged particle gun according to any one of claims 1 to 13.

Images