JP3696827B2 - Energy filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an energy filter that selectively allows only charged particles having a specific energy to pass therethrough, and more particularly, to an energy filter used in a monochromator such as a transmission electron microscope or an energy analyzer.
[0002]
[Prior art]
In recent years, a transmission electron microscope has been developed in which an energy filter is disposed in an electron optical system that enlarges and projects an electron beam transmitted through a sample onto a fluorescent screen. According to the transmission electron microscope having such an energy filter, it is possible to form a microscope image based only on transmission electrons having a specific energy among transmission electrons (transmission charged particles) affected by the sample.
In the analysis using such an energy filter, in order to obtain high energy resolution, the spread of the energy of electrons before irradiation of the sample, which is produced by an electron gun, may be an obstacle. In such a case, an energy filter is also placed between the electron gun and the sample to reduce the energy width of the irradiation beam. An energy filter used for such a purpose is called a monochromator.
[0003]
(Conventional example 1)
FIG. 8 shows an electron beam trajectory by a Wien filter using a uniform electric field and a uniform magnetic field. The electron beam emitted from the electron gun converges (images) once in the X direction (in the ZX plane) perpendicular to the traveling direction (Z direction) during the traveling process in the filter, and is perpendicular to the X direction. Convergence (image formation) does not occur in the Y direction.
[0004]
However, in this Wien filter, when a crossover is made just before the filter and the incident beam is put into the filter, the shape of the electron beam emitted from the filter is focused in the X direction and dispersed, but in the Y direction. Became a long beam, and subsequent handling was difficult.
[0005]
(Conventional example 2)
FIG. 9 shows the electron beam trajectory with a non-uniform field Wien filter that overcomes the above-mentioned drawbacks. This inhomogeneous field Wien filter achieves focusing in the Y direction by adding a quadrupole field (inhomogeneous field), and a round lens type focus that produces a round cross-section beam anywhere in the filter. Do.
[0006]
However, in this non-uniform field Wien filter, an energy selection slit is arranged at the outlet of the filter. Accordingly, when this is used as a monochromator, the energy of the subsequent beam differs depending on the position of the beam (Chromatic), while the beam shape becomes an elongated shape cut by the slit, which is inconvenient in practice.
[0007]
(Conventional example 3)
FIG. 10 shows an electron beam trajectory by a two-stage energy filter that overcomes the disadvantages of the non-uniform field Wien filter.
This two-stage type energy filter has two Wien filters arranged at intervals in the traveling direction of the electron beam, an energy selection slit is arranged after the first stage energy filter, and the energy is selected by the energy selection slit. After the selection, the energy dispersion is returned to zero by the second stage energy filter (Achromatic).
[0008]
(Conventional example 4)
By the way, when an energy filter is used in the immediate vicinity of an electron gun under a small acceleration voltage, when electrons starting from the electron gun form a crossover and fly close to each other, the energy of the electrons is caused by the electron-clonal interaction. There was a problem that the spread and the beam diameter might increase.
FIG. 11 shows an electron beam trajectory by a two-stage energy filter that solves the above problem (Japanese Patent Laid-Open No. 2001-23558).
As shown in the figure, this energy filter focuses twice in the X direction orthogonal to the traveling direction of the electron beam and focuses only once in the Y direction. Therefore, astigmatic focusing is performed instead of round lens focusing. A slit is disposed at the second focus position in the X direction, and energy selection is performed.
[0009]
[Problems to be solved by the invention]
In the energy filter of Conventional Example 4, the axial length of the second-stage filter is shorter than that of the first-stage filter, and the slit position in the beam traveling direction is not located at the center of the entire length of the energy filter. Therefore, there is a concern that aberration due to the energy filter occurs.
[0010]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an energy filter with less aberration.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, an energy filter according to the present invention is an energy filter that combines an electric field and a magnetic field so as to allow only charged particles having a specific energy to pass through, and the charged particles traveling in the energy filter. Is converged at least once in the ZX plane defined by the Z axis parallel to the traveling direction and the X axis orthogonal thereto, and is determined by the Z axis and the Y axis orthogonal to the Z axis / X axis. The energy selection slit is disposed at the convergence position in the ZX plane having a width equal to or greater than a predetermined value at the convergence position. Preferably, the longitudinal cross-sectional shapes in the ZX plane and the ZY plane are symmetric with respect to the center position of the energy filter in the Z-axis direction.
[0012]
In the energy filter, the charged particles have at least one first filter portion having an X coordinate value having a predetermined sign in the ZX plane, and at least one first coordinate portion having an X coordinate value having an opposite sign to the predetermined sign. Two filter parts,
The length of each filter portion is set so that the aberration that occurs when the charged particles travel through the first filter portion and the aberration that occurs when the charged particles travel through the second filter portion cancel each other out. .
[0013]
Preferably, the energy filter has one first filter portion and one second filter portion having substantially the same length disposed along the optical axis, and the charged particles are in the ZX plane. And converge once between the first filter portion and the second filter portion.
[0014]
Preferably, the distribution of the magnetic field and the electric field has a plane symmetry with the XY plane including the center position of the energy filter along the optical axis as a symmetry plane, and the trajectory of the charged particle is a light beam in the ZX plane. It has 180 ° rotational symmetry about the center position of the energy filter on the axis.
[0015]
Preferably, the charged particle beam converges once in the ZX plane, has a width of a predetermined value or more over the entire length of the energy filter in the ZY plane, and the slit extends along the Z axis. Is arranged in the center of the energy filter.
[0016]
Preferably, the charged particle beam forms a parallel beam over the entire length of the energy filter in the ZY plane.
[0017]
Preferably, the energy filter includes two Wien filters having substantially the same length in the Z-axis direction.
[0018]
Preferably, in the charged particle beam, the longitudinal cross-sectional shape in the ZX plane and the ZY plane forms a parallel beam at the filter entrance.
[0019]
Preferably, the energy filter includes a plurality of spaced apart Wien filters, each Wien filter generating a uniform electric and magnetic field therein.
[0020]
Another aspect of the present invention resides in an electron microscope having any one of the energy filters.
[0021]
Preferably, in the electron microscope, the lens or the lens group disposed immediately before the energy filter is adjusted so that the electron beam incident on the energy filter forms a parallel beam at the entrance of the energy filter.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a conceptual diagram showing an embodiment of an energy filter according to the present invention. 2 is a schematic diagram showing the physical configuration of this embodiment, FIG. 3 is a perspective view illustrating the structure of a Wien filter used in this embodiment, and FIG. 4 is used in this embodiment. It is a front view of an energy selection slit board.
[0023]
As shown in these drawings, the energy filter 10 of this embodiment is generally an energy filter that combines an electric field and a magnetic field to pass only charged particles having a specific energy, and the energy filter 10 The charged particles traveling in the beam converge at least once in the ZX plane defined by the Z axis parallel to the traveling direction and the X axis orthogonal thereto, and are orthogonal to the Z axis and the Z axis / X axis. In the ZY plane determined by the Y axis, the convergence position has a width equal to or larger than a predetermined value, and the energy selection slit 13a is arranged at the convergence position in the ZX plane.
[0024]
In the energy filter 10, the charged particles have at least one first filter portion 11 having an X coordinate value having a predetermined sign in the ZX plane, and at least one having an X coordinate value having an opposite sign to the predetermined sign. Each of the filter portions 11 and 12 has a length that occurs when the charged particles travel through the first filter portion 11 and when the charged particles travel through the second filter portion 12. The aberration is set so as to cancel out each other.
[0025]
Preferably, the energy filter has one first filter portion 11 and one second filter portion 12 having substantially the same length arranged along the optical axis O, and the charged particles are in the ZX plane. It converges once between the first filter part 11 and the second filter part 12.
[0026]
Further, the distribution of the magnetic field and the electric field has surface symmetry with the XY plane including the center position M of the energy filter 10 along the optical axis O as a symmetry plane, and the trajectory of the charged particles is in the ZX plane. , And 180 ° rotational symmetry about the energy filter center position M on the optical axis O.
[0027]
More details are as follows.
As shown in FIGS. 1 and 2, the energy filter 10 used in, for example, an electron microscope is a single stage disposed along an electron beam center orbit O (hereinafter referred to as an optical axis) parallel to the Z axis. An eye filter 11, a second-stage filter 12, and an energy selection slit plate 13 disposed at a center position M in the Z-axis direction of the energy filter 10 are included. The energy selection slit plate 13 has an energy selection slit 13a.
[0028]
A pre-stage electrostatic lens 14 for adjusting the electron trajectory of the electron beam emitted from the cathode 16 of the electron gun is provided in the front stage of the energy filter 10. Further, a post-stage electrostatic lens 15 for adjusting the trajectory of the electron beam to the sample (not shown) is provided at the rear stage of the energy filter 10.
[0029]
As shown in FIG. 2, the first-stage filter 11 and the second-stage filter 12 each have an electric field E1 and a magnetic field H1 orthogonal to an electron beam e traveling along the Z axis, or an electric field E2 and a magnetic field. It consists of a Wien filter that applies H2.
[0030]
As shown in FIG. 3, each Wien filter 11, 12 is a magnetic pole plate (magnetic pole N) that is opposed to the vertical direction (Y direction) across the optical axis O in order to generate the magnetic fields H 1, H 2. 21 and a magnetic pole plate (magnetic pole S) 22. The magnetic pole plates 21 and 22 generate uniform magnetic fields H1 and H2 inside the Wien filter.
[0031]
Each Wien filter 11, 12 has a pair of a positive electrode plate 23 and a negative electrode plate 24 that are arranged opposite to each other in the left-right direction (X direction) across the optical axis O in order to generate the electric fields E1, E2. Have The electrode plates 23 and 24 generate uniform electric fields E1 and E2 inside the Wien filter.
[0032]
As shown in FIG. 2, the first-stage filter 11 and the second-stage filter 12 have a plane-symmetric structure with the XY plane including the position M of the slit 13a (or slit plate 13) as a symmetry plane. Accordingly, the filter lengths L1 and L2 of the filters 11 and 12 have substantially the same length.
[0033]
Therefore, the distributions of the electric fields E1 and E2 and the magnetic fields H1 and H2 are plane symmetric (symmetric in FIG. 2) with the XY plane including the center position M in the Z-axis direction of the energy filter 10 as a symmetry plane.
[0034]
Shunt members 101 and 103 for preventing interference between the electromagnetic field generated from the filters 11 and 12 and the electromagnetic field generated by the surrounding electro-optic elements are provided at the entrance and exit of the energy filter 10.
[0035]
With the above configuration, the electric field E1, E2 parallel to the X direction perpendicular to the optical axis O and the magnetic field H1, parallel to the Y direction perpendicular to the X direction, around the optical axis O parallel to the Z axis. A uniform field in which H2 is superimposed is formed. For this reason, the electrons incident along the optical axis O travel along a predetermined trajectory determined by the forces received from the orthogonal electric fields E1 and E2 and the magnetic fields H1 and H2 and the energy of each electron.
[0036]
More specifically, the directions and strengths of the electric fields E1 and E2 and the magnetic fields H1 and H2 are adjusted so as to satisfy the following conditions 1 and 2.
[0037]
1. The charged particle beam traveling in the energy filter 10 converges once in the ZX plane determined by the Z axis and the X axis, and covers the entire length of the filter 10 in the ZY plane determined by the Z axis and the Y axis. A parallel beam is formed.
[0038]
2. The electron trajectory has 180 ° rotational symmetry with the Y axis passing through the center position M of the energy filter 10 on the optical axis O as the symmetry axis.
[0039]
FIG. 4 shows a front view of the slit plate 13 including the slit 13a.
As shown in the figure, the slit 13a has a narrow width d in the X-axis direction and a wide width D in the Y-axis direction. The slit plate 13 is provided so as to be movable in the X-axis direction.
[0040]
Next, the operation of the energy filter 10 will be described with reference to FIGS. In FIG. 5, each number 16, 14, 11, 13a, 12, 15 indicates the position in the Z direction of each element corresponding to each number.
[0041]
FIG. 5A shows the trajectory shape on the ZX plane of the electron beam passing through the front stage electrostatic lens 14, the first stage filter 11, the energy selection slit 13, the second stage filter 12, and the rear stage electrostatic lens 15. Show.
[0042]
As shown in the figure, the electron beam ER from the cathode 16 is not converged but is made into a parallel beam by the electron lens action of the front electrostatic lens 14 and is incident on the first-stage filter 11 (the lens 14 is , Acting as a collimator lens in terms of optics). The beam width BW of the parallel beam at the entrance of the filter 11 can be set by, for example, an aperture (not shown) disposed in front of the lens 14 or between the lens 14 and the filter 11.
[0043]
The electron beam ER incident in parallel to the first-stage filter 11 is behind the filter 11 by the electric field E1 and the magnetic field H1 generated by the filter 11 (in the X direction or XZ plane orbit), and the energy filter 10 Convergence (image formation) is performed at the center position M in the Z direction.
[0044]
The converged electron beam ER passes through the slit 13a at the position M (assuming that an energy condition described later is satisfied).
[0045]
The electron beam ER that has passed through the slit 13a has an electric field E2 and a magnetic field H2 generated by a second-stage filter 12 having a plane-symmetrical structure and electromagnetic field distribution with respect to the first-stage filter 11 at the outlet of the filter 12. The beam width is returned to the same beam width BW as that at the entrance of the stage filter 11.
[0046]
Accordingly, in the ZX plane, the electron beam trajectory ER has a 180 ° rotational symmetry about the filter center position M.
[0047]
At that time, the aberration of the electron beam is canceled before and after the slit position (symmetry point) M. More details are as follows.
[0048]
As shown in FIG. 5 (a), the trajectory (electron trajectory) of each electron beam passes through the optical axis O at the intermediate position M, and the X-rays inside the first-stage filter 11 and the second-stage filter 12 are X. The coordinate value is reversed.
[0049]
On the other hand, the aberration of the electron trajectory is expressed by the product of the magnitude of the magnetic field or electric field and the height of the trajectory (X coordinate value).
[0050]
The magnetic field and electric field are directed in the same direction in the first stage filter 11 and the second stage filter 12.
[0051]
Therefore, the X-coordinate value of the electron trajectory is inverted between the first-stage filter 11 and the second-stage filter 12, so that the aberration in the first filter 11 and the aberration in the second filter 12 cancel each other.
[0052]
For example, when an electron trajectory having a certain trajectory height has a positive aberration by the first-stage filter 11, the second-stage filter has a negative aberration of almost the same magnitude. Therefore, these aberrations cancel out, and the energy filter as a whole has small aberrations.
[0053]
FIG. 5B shows the trajectory shape (or beam shape) of the electron beam on the YZ plane.
Similar to the beam shape on the XZ plane, the electron beam ER from the cathode 16 is converted into a parallel beam having a beam width BW by the electron lens action of the front-stage electrostatic lens 14 without having convergence. 11 is incident.
[0054]
Therefore, the electron beam ER generally has a circular cross section having a diameter BW at the entrance of the first stage filter 11.
[0055]
On the other hand, as already shown (FIGS. 2 and 3), the Wien filters 11 and 12 do not exert a force on the electron beam in the Y-axis direction.
[0056]
Accordingly, in the YZ plane, the electron beam ER incident as a parallel beam on the first-stage filter 11 is never converged in the energy filter 10 and remains a parallel beam (that is, maintains the beam width BW). I) Injected from the outlet of the second stage filter 12.
[0057]
Accordingly, the orbit ER of each electron beam has a 180 ° rotational symmetry with the Y axis passing through the position M on the optical axis O as the symmetry axis.
[0058]
The width D in the Y-axis direction of the slit 13a is set larger than the width BW of the electron beam ER in the Y-axis direction.
[0059]
FIG. 5C shows the electron dispersion trajectory of the electron beam ER (the fluctuation of the dispersion amount of the electron beam ER in the X-axis direction along the Z-axis).
[0060]
As shown in the figure, the electron beam ER has a dispersion amount greater than or equal to a predetermined value at the position M. That is, electron beams having different energies pass through different X-axis positions at the position M.
[0061]
FIG. 6 shows the shape of the electron beam or electron beam on the slit plate 13.
As shown in the figure, an electron beam emitted from the cathode 16 and having a predetermined energy (center energy value) has a long width (BW) in the Y-axis direction at the position M by the electron lens 14 and the first-stage filter 11. And an image IM having a short width in the X-axis direction. Here, the width BW in the Y-axis direction of the image IM is set to about 10 times or more when the width in the X-axis direction is 1 μm.
[0062]
Further, an electron beam having an energy different from the energy forms an image IM ′ at a position shifted from the image IM in the X-axis direction.
[0063]
Accordingly, by moving the slit plate 13 in the X-axis direction and selectively moving or arranging the energy selection slit 13a to the position of the image IM, IM ′, etc., only an electron beam having a desired energy can be selectively selected. Can be passed through.
[0064]
In this case, the images IM and IM ′ are converged only in the X-axis direction and are not converged in the Y-axis direction. Therefore, even when the electron beam has a relatively low energy, the energy spread and the beam diameter do not increase due to the influence of the inter-electron Coulomb interaction when the energy is selected.
[0065]
Further, according to the energy filter 10, the magnetic field / electric field distribution has a plane symmetry (left-right symmetry in FIGS. 2 and 4) with the plane of the slit plate 13 (XY plane including the filter center position M) as a symmetry plane. The trajectory of each electron beam has 180 ° rotational symmetry with the Y axis passing through the beam center axis O and the position M as the symmetry axis. Thereby, as described above, the aberration of the electron beam is canceled before and after the slit position (symmetry point), and the generation of aberration in the energy filter can be reduced.
[0066]
In the above, the distribution of the electric fields E1 and E2 and the magnetic fields H1 and H2 is uniform in the filters 11 and 12. However, any distribution may be used as long as the electric field / magnetic field distribution in the energy filter 10 is plane symmetric (symmetric in FIG. 2) with the XY plane including the center position M in the Z-axis direction as a symmetry plane.
[0067]
The energy filter 10 has one first filter portion 11 and one second filter portion 12. However, the energy filter 10 can have a plurality of first filter portions or a plurality of second filter portions. In this case, the total length of the first filter portion group and the second filter portion group are set such that the sum of aberrations by the first filter portion group and the sum of aberrations by the second filter portion group cancel each other. It is preferable to set the total length of
In FIG. 6, the width BW of the image IM in the Y-axis direction can be about several times the width in the X-axis direction (for example, 1 μm).
[0068]
7A and 7B show the configuration of an electron microscope incorporating the energy filter of the present invention.
[0069]
FIG. 7A shows an example in which the energy filter of the present invention is arranged between a field emission electron gun (FEG) and an accelerator.
[0070]
An electron beam having a relatively low energy of about 1 keV to several keV emitted from the FEG 51 is incident on a deceleration type energy filter 57 including an incident aperture 52, a deceleration unit 53, an energy filter unit 54, an acceleration unit 55, and an emission aperture 56. The
[0071]
In this decelerating type energy filter 57, incident electrons are decelerated to an energy of about several hundreds eV by the decelerating unit 53, and then only those having a predetermined energy are selected in the filter unit 54. The light is accelerated so as to have the light and is emitted from the emission aperture 56. Here, the energy filter unit 54 has the structure shown in FIGS. 1 to 3.
[0072]
The electron beam emitted from the emission aperture 56 is accelerated to a desired high energy (for example, about 200 keV) by the accelerator 58 and then irradiated to the sample 61 through the condenser lens group 59 and the objective lens 60.
[0073]
FIG.7 (b) shows the example which has arrange | positioned the energy filter of this invention in the back | latter stage of an accelerator.
In this example, an electron beam having a relatively low energy of about 1 keV to several keV emitted from the FEG 51 is accelerated to a desired high energy (for example, about 200 ekV) by the accelerator 58 and then decelerated via the condenser lens 62. The light enters the energy filter 57. The decelerating type energy filter 57 includes an incident aperture 52, a decelerating unit 53, an energy filter unit 54, an accelerating unit 55, and an exit aperture 56.
[0074]
In this decelerating type energy filter 57, incident electrons are decelerated to energy of about several hundreds eV by the decelerating unit 53, and then only those having predetermined energy are selected in the energy filter unit 54, and the original energy is again obtained by the accelerating unit 55 And is emitted from the emission aperture 57. The energy filter unit 54 has the structure shown in FIGS.
[0075]
The electron beam emitted from the emission aperture 56 is applied to the sample 61 through the condenser lens group 59 and the objective lens 60.
[0076]
The deceleration unit 53 and the acceleration unit 55 of the deceleration type energy filter 57 need to decelerate high energy electrons to energy of about several hundred eV and further accelerate to the original high energy. It is preferable to use multi-stage acceleration as in
[0077]
According to the above electron microscope, the electron beam emitted from the FEG 51 passes through the monochromator while passing through the accelerating tube and being accelerated to a high voltage. Since focusing is performed only once and the number of focusing is small, it is possible to suppress the spread of energy and the increase of the beam diameter due to Coulomb interaction, as compared with the same type of energy filter.
[0078]
Further, by using the energy filter 10 with less aberration as a monochromator, the sample can be irradiated with a small beam diameter without increasing the size of the beam that has passed through the filter.
[0079]
As described above, according to the energy filter of this embodiment, the trajectory of the charged particles and the magnetic field distribution are symmetrical with respect to the slit position, and the aberration is canceled before and after the slit position, thereby reducing the occurrence of aberration. I can do it.
[0080]
【The invention's effect】
As can be understood from the above description, the energy filter according to the present invention can reduce the occurrence of aberrations.
[Brief description of the drawings]
FIG. 1 is an overall conceptual diagram showing an embodiment of an energy filter according to the present invention.
FIG. 2 is a schematic diagram showing a physical configuration of the embodiment.
FIG. 3 is a perspective view illustrating the structure of a Wien filter used in the embodiment.
FIG. 4 is a front view of an energy selection slit plate used in the embodiment.
FIG. 5 (a) is an explanatory view showing the trajectory of the electron beam passing through the energy filter on the ZX plane. FIG. 5B similarly shows the trajectory of the electron beam on the ZY plane. FIG. 5C also shows the electron dispersion trajectory of the electron beam.
FIG. 6 is a schematic diagram showing the shape of an electron beam on the slit plate.
FIGS. 7A and 7B are schematic views each showing a configuration of an electron microscope incorporating the energy filter according to the embodiment of the present invention.
8 is an explanatory diagram showing an electron beam trajectory in the energy filter of Conventional Example 1. FIG.
FIG. 9 is an explanatory diagram showing the trajectory of an electron beam in the energy filter of Conventional Example 2.
FIG. 10 is an explanatory diagram showing the trajectory of an electron beam in the energy filter of Conventional Example 3.
FIG. 11 is an explanatory diagram showing the trajectory of an electron beam in the energy filter of Conventional Example 4.

Claims (9)

An energy filter that combines an electric field and a magnetic field to pass only charged particles with a specific energy,
The charged particles traveling in the energy filter converge at least once in a ZX plane defined by a Z axis parallel to the traveling direction and an X axis orthogonal thereto, and the Z axis, the Z axis, and the X axis In the ZY plane determined by the Y axis orthogonal to the width of the predetermined value or more at the convergence position,
An energy selection slit is disposed at a convergence position in the ZX plane, and the energy filter includes at least one first filter portion in which the trajectory of the charged particles is reversed with the slit plane as a boundary in the ZX plane. And at least one second filter portion, the lengths of the first filter portion and the second filter portion are substantially equal, and the first filter portion has a charged particle beam on the slit, An energy filter adjusted to have a cross-sectional shape extending in the Y direction substantially orthogonal to the X direction, which is a charged particle dispersion direction by the filter portion.   The energy filter according to claim 1, wherein the distribution of the magnetic field and the electric field has a plane symmetry with an XY plane including a center position of the energy filter along the optical axis as a symmetry plane, and the trajectory of the charged particles is In the ZX plane, it has 180 ° rotational symmetry about the center position of the energy filter on the optical axis. An energy filter that combines an electric field and a magnetic field to pass only charged particles with a specific energy,
The charged particles traveling in the energy filter converge at least once in a ZX plane defined by a Z axis parallel to the traveling direction and an X axis orthogonal thereto, and the Z axis, the Z axis, and the X axis In the ZY plane determined by the Y axis orthogonal to the width of the predetermined value or more at the convergence position,
An energy selection slit is disposed at a convergence position in the ZX plane, and the energy filter includes at least one first filter portion in which the trajectory of the charged particles is reversed with the slit plane as a boundary in the ZX plane. And at least one second filter portion, the lengths of the first filter portion and the second filter portion are the aberration that occurs when the charged particles travel through the first filter portion and the second filter portion. The first filter portion is set in the X direction, which is a charged particle dispersion direction by the first filter portion, on the slit. An energy filter adjusted to have a cross-sectional shape extending in a substantially orthogonal Y direction. The energy filter according to claim 1 or 3,
One first filter portion and one second filter portion having substantially the same length disposed along the optical axis, and the charged particles are separated from the first filter portion and the first filter portion in the ZX plane. Converge once between the two filter parts. The energy filter according to claim 4,
The charged particle beam forms a substantially parallel beam over the entire length of the energy filter in the ZY plane. The energy filter according to claim 1, 2, or 4,
In the charged particle beam, the longitudinal cross-sectional shape in the ZX plane and the ZY plane forms a parallel beam at the filter entrance. The energy filter according to any one of claims 1 to 4,
A plurality of Wien filters arranged at intervals, each Wien filter generating a uniform electric and magnetic field within each.   An electron microscope in which the energy filter according to any one of claims 1 to 5 is disposed closer to an electron gun than a sample.   9. The electron microscope according to claim 8, wherein the lens or the lens group disposed immediately before the energy filter is adjusted so that an electron beam incident on the energy filter forms a parallel beam at an energy filter entrance. What

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