Image generation apparatus and image generation method

Abstract

To provide a technique capable of generating an energy selection image with high energy resolution, a wide field of view, and high sensitivity.SOLUTION: The image generator includes a Wien filter 108 having a multipole structure, an operation controller 150 configured to cause the Wien filter to form an axially symmetric lens field by applying the same voltage to all of a plurality of poles while causing the Wien filter to form an electric field and a magnetic field satisfying Wien conditions, a lower shunt 120 disposed below the Wien filter 108 and having a through-hole 123, and an electron detector 107 configured to detect secondary electrons having at least a predetermined energy among secondary electrons dispersed according to energy by the Wien filter 108.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for generating an image from secondary electrons (including backscattered electrons) generated from a sample, and more particularly to a technique for generating an image from secondary electrons having a selected energy. [Background technology]

[0002] In scanning electron microscopes used to observe semiconductor devices, it is common to capture as many secondary electrons as possible emitted from the sample and create an image. However, because secondary electrons carry different information about the sample's properties depending on their energy, it would be useful to develop a method for detecting and imaging only secondary electrons with specific energies. For example, by utilizing the fact that the energy distribution of secondary electrons differs depending on the elements that make up the sample, it would be possible to map the elemental composition of the sample surface. Alternatively, by acquiring images that reflect the surface potential, it is possible to observe the state of semiconductor pn junctions and the distribution of defects.

[0003] Patent Document 1 discloses a technique for using a Wien filter as a beam separator to separate the primary electron beam heading toward a sample from the secondary electron beam returning from the sample, and as an energy analyzer to disperse the secondary electrons according to their energy. This technique enables high-resolution energy analysis over a wide energy range by superimposing a quadrupole field component on the uniform electric field and uniform magnetic field, which are the original components of a Wien filter, and also enables the acquisition of images after selecting the high-resolution energy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-153537 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the technology of Patent Document 1, by superimposing a quadrupole field component on the electric and magnetic fields that constitute a Wien filter, it is possible to focus secondary electrons in the energy dispersion direction for each energy. However, under the action of the quadrupole field, secondary electrons diverge in the direction perpendicular to the energy dispersion direction, so the secondary electron beam at the detection surface is not a normal point focus but a line focus, forming a linearly elongated pattern. For this reason, the detection surface of the detector needs to have an extension corresponding to the range of this extension. However, in many actual device configurations, there is a limit to the space that can be secured for the detector, and sensitivity is lost due to the area that cannot be detected.

[0006] Furthermore, this divergence occurs while the secondary electron beam is passing through the Wien filter, causing some of the secondary electron beam to collide with the electromagnetic poles inside the Wien filter and not reach the detector. Alternatively, even if there is no collision with the electromagnetic poles, this divergence may prevent the beam from passing through the slit-shaped opening in the upper shunt of the Wien filter. These factors limit the field of view ultimately observed as a secondary electron image, resulting in a phenomenon known as field vignetting. This field vignetting also occurs when secondary electrons emitted from the specimen are expanded upward by the magnetic field of the objective lens and the field created by the deflector, resulting in a mechanical restriction by the lower shunt of the Wien filter. These phenomena must be addressed to enable wide-field observations.

[0007] Therefore, the present invention provides a technique that can generate an energy-selective image with high energy resolution, a wide field of view, and high sensitivity. [Means for solving the problem]

[0008] In one aspect, an image generating device is provided, comprising: an electron beam source for generating a primary electron beam; an electron optical system for guiding the primary electron beam to a sample and focusing and deflecting it; a Wien filter having a multipole structure; an operation control unit for forming an axially symmetric lens field in the Wien filter by applying the same voltage to all of the multiple poles while forming electric and magnetic fields that satisfy the Wien conditions in the Wien filter; a lower shunt having a through hole arranged below the Wien filter; an electron detector for detecting secondary electrons having at least a predetermined energy among the secondary electrons dispersed according to energy by the Wien filter; and an imaging device for generating an image from the secondary electrons having the predetermined energy. [Effects of the Invention]

[0009] Applying the same voltage to all poles of the Wien filter creates an axially symmetric lens effect, which focuses secondary electrons at the slit plane for each energy level, achieving high energy resolution while minimizing vignetting due to collisions of secondary electrons inside the Wien filter and at the upper shunt aperture. Furthermore, the axially symmetric lens effect focuses the secondary electron beam at the detection plane, which is advantageous in terms of detection sensitivity. These features enable high-resolution, energy-selected secondary electron images to be observed with a wide field of view and high sensitivity. Furthermore, focusing the secondary electron beam from the sample surface at the lower shunt position of the Wien filter using a secondary electron focusing lens placed above the objective lens prevents vignetting at this position. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a scanning electron microscope. [Figure 2] FIG. 1 is a schematic diagram showing an embodiment of an 8-pole structure of a Wien filter. [Figure 3] FIG. 2 is a cross-sectional perspective view of a Wien filter. [Figure 4]FIG. 10 is a perspective view illustrating an embodiment of an upper shunt positioned above a Wien filter. [Figure 5] FIG. 10 is a perspective view illustrating one embodiment of a lower shunt positioned below the Wien filter. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of a scanning electron microscope. The scanning electron microscope shown in FIG. 1 is applicable to an image generating device that disperses a secondary electron beam emitted from a sample 106 according to energy and generates an image from only secondary electrons having a specific energy. In FIG. 1, a primary electron beam 103 generated by an electron gun 101, which is an electron beam source, is guided to the sample 106 by electron optical systems 102 and 105. More specifically, the primary electron beam 103 is focused by a condenser lens system 102 composed of multiple lenses. The primary electron beam 103 passes through a Wien filter 108, is further focused by an objective lens 105, and is irradiated onto the sample 106. The primary electron beam 103 is deflected by a deflector 112 and scans the surface of the sample 106.

[0012] An upper shunt 115 is disposed above the Wien filter 108, and a lower shunt 120 is disposed below the Wien filter 108. Secondary electrons emitted from the sample 106 form a secondary electron beam 104. This secondary electron beam 104 is focused by a secondary electron focusing lens 135 onto a surface (more specifically, the lower surface) 120a of the lower shunt 120 of the Wien filter 108, and then deflected according to energy by the Wien filter 108. At the same time, the secondary electron beam 104 is focused onto a surface 130a of a slit 130 by an axially symmetric lens field superimposed on the Wien filter 108. The surface 130a of the slit 130 is an energy dispersion plane on which the secondary electron beam 104 deflected and dispersed according to energy is focused. Only secondary electrons with a specific energy pass through the slit 130 and are detected by the electron detector 107. An imaging device 121 connected to the electron detector 107 forms an image using only the detection signals of secondary electrons in an energy range selected based on the characteristics of the sample 106. This image is the secondary electron image we were looking for.

[0013] The Wien filter 108 and the electron detector 107 are connected to an operation control unit 150, and the operations of the Wien filter 108 and the electron detector 107 are controlled by the operation control unit 150. The operation control unit 150 includes a storage device 150a that stores a program, a calculation device 150b that executes calculations according to instructions included in the program, and a power supply 150c that applies a voltage to the Wien filter 108.

[0014] The operation of the Wien filter 108 is explained below. The Wien filter 108 is used as a beam separator that separates the primary electron beam 103 and the secondary electron beam 104. If the optical axis direction is taken as the z-coordinate, the Wien filter 108 is basically composed of a uniform electric field (intensity E1) in the x-direction and a uniform magnetic field (intensity B1) in the y-direction. In this case, the directions of the forces exerted by the electric field and the magnetic field on the primary electron beam 103 are opposite, and by appropriately selecting the relationship between E1 and B1, the electric field and the magnetic field can be made to cancel each other out. This balance condition is called the Wien condition, and is expressed as E1 = vB1, where v is the velocity of the primary electron beam 103.

[0015] If the primary electron beam 103 is made up of electrons of various energies, energy dispersion occurs for each energy at the bottom surface of the Wien filter 108. This is the original function of the Wien filter 108 as an energy analyzer, and the fact that the optical axis of the analyzer is a straight line is an advantage of the Wien filter compared to other types of analyzers.

[0016] However, this energy dispersion of the primary electron beam 103 is undesirable when the Wien filter 108 is used as a beam separator. To address this issue, the condenser lens system 102 can be set so that the primary electron beam 103 forms a crossover at the center of the Wien filter 108, thereby canceling out the effect of this energy dispersion on the specimen surface. In this situation, even if the primary electron beam 103 has an energy distribution, the spatial resolution of the secondary electron image is not affected. This embodiment assumes that the condenser lens system 102 is set in this manner.

[0017] When the Wien filter 108 satisfies the Wien condition, if the secondary electron beam 104 enters the Wien filter 108 from the opposite direction along the optical axis, the direction of the force from the magnetic field is reversed. Therefore, the electric and magnetic fields exert forces on the secondary electron beam 104 in the same direction, and the Wien filter 108 functions as a deflector. If the secondary electron beam 104 is composed of electrons of various energies, the deflection angle differs for each energy, resulting in energy dispersion at the exit of the Wien filter 108. However, this is the opposite direction of electron incidence from when the Wien filter 108 operates as an energy analyzer, and its performance as an analyzer, i.e., its energy resolution, is not guaranteed. Unless some countermeasure is taken, the beam separated by energy will be significantly blurred, resulting in low energy resolution. In this embodiment, an axially symmetric lens field is superimposed on the Wien filter 108 as a means of improving the energy resolution for an electron beam entering in the opposite direction.

[0018] Next, the structure of the Wien filter 108 will be described. In order to satisfy the Wien condition, which is a balance condition for the primary electron beam 103, over a wide range in the xy plane, and to minimize deflection aberration for the secondary electron beam 104, the electric field and magnetic field must be distributed as uniformly as possible. For this reason, a multipole lens type Wien filter 108 is used. The minimum configuration for a multipole lens type is a four-pole structure, but a structure with eight or more poles is desirable in terms of the uniformity of the electric field and magnetic field to be achieved.

[0019] FIG. 2 is a schematic diagram showing one embodiment of the octupole structure of the Wien filter 108, illustrating a top view of the Wien filter 108 viewed from a direction perpendicular to the beam axis. The eight poles 109 are arranged at equal intervals around the center line of the Wien filter 108. Each of these poles 109 is equipped with a coil 109a, and voltages Vn (n = 1, 2, ..., 8) and excitations ATn (n = 1, 2, ..., 8) can be applied to all of the poles 109. Because all of the poles 109 function as both electrodes and magnetic poles, each pole 109 is made of a magnetic material such as permalloy. By setting Vn and ATn using the operation control unit 150, uniform electric and magnetic fields are formed.

[0020] By superimposing the same voltage on all poles 109 for Vn (n=1, 2, ..., 8) to form a uniform electric field, it is possible to simultaneously give the Wien filter 108 an axially symmetric lens effect. In one embodiment, the operation control unit 150 applies the same voltage to all eight poles 109 of the Wien filter 108 to cause the Wien filter 108 to form an axially symmetric lens field.

[0021] The voltage applied to form an axially symmetric lens field acts as an acceleration-type electrostatic lens if it is a positive voltage, or as a deceleration-type electrostatic lens if it is a negative voltage. Both have the effect of focusing the beam. In this embodiment, this effect is used to focus the secondary electron beam 104, but for the purposes of this embodiment, using a negative voltage is advantageous. This is because the magnitude of dispersion of secondary electrons by the Wien filter 108 is proportional to ΔE / E, where E is the energy when passing through the Wien filter 108 and ΔE is the energy difference. Therefore, a smaller E allows for greater dispersion. Therefore, using a deceleration-type lens, which reduces energy within the Wien filter 108, is advantageous in terms of energy resolution. Another reason why a negative voltage is suitable is that when obtaining a focusing effect using an electrostatic lens, the absolute value of the voltage applied can be smaller for a deceleration-type lens than for an acceleration-type lens.

[0022] In general, it is common practice to decelerate the incident beam to improve the energy resolution of a Wien filter. However, in this embodiment, the incident direction of the beam that causes energy dispersion is opposite to that of a conventional Wien filter, and therefore the deceleration in this embodiment is different from the deceleration method used for a Wien filter as an energy analyzer. However, the principle is the same in that it utilizes the effect that deceleration increases energy dispersion.

[0023] To obtain a lens effect on the secondary electron beam, it is also possible to superimpose a quadrupole field instead of an axially symmetric lens field. However, in this case, there is no deceleration effect, which is disadvantageous in terms of energy resolution. Furthermore, using a quadrupole field causes a divergence effect in the direction perpendicular to the energy dispersion, resulting in a line focus on the detection surface 107a of the electron detector 107. This necessitates the widening of the detection surface in the direction perpendicular to the energy dispersion, but this is limited in practical device configurations. Furthermore, the divergence effect of the quadrupole field increases the frequency of secondary electron collisions inside the Wien filter and the upper shunt. Therefore, the method of superimposing an axially symmetric lens field is advantageous from the standpoints of detection sensitivity and field vignetting.

[0024] When an axially symmetric lens field is superimposed on the Wien filter 108, the Wien filter 108 also exerts a lens effect on the primary electron beam 103. Normally, the energy of the primary electron beam 103 is greater than that of the secondary electron beam 104, and therefore the lens effect of the Wien filter 108 on the primary electron beam 103 is small, but not negligible. However, as mentioned above, in order to cancel out the energy dispersion of the Wien filter 108 on the primary electron beam 103, a crossover is created in the center of the Wien filter 108 by the condenser lens system 102.

[0025] In this situation, if the Wien filter 108 had no thickness in the optical axis direction and could be considered a so-called thin lens in terms of lens action, its lens action on the primary electron beam 103 would completely disappear. In reality, the Wien filter 108 has a finite thickness in the optical axis direction, so its lens action does not completely disappear. However, this is simply a phenomenon in which the primary electron beam 103 is out of focus. In actual instrument adjustment procedures, the objective lens 105 is always used to adjust the focus of the primary electron beam 103 on the sample surface. In this case, the effect of the lens action of the Wien filter 108 is automatically corrected, and it is not necessary to be aware of the weak lens action of the Wien filter 108 when adjusting the instrument. If a quadrupole field is superimposed on the Wien filter 108 rather than an axially symmetric lens, astigmatism will be imparted to the primary electron beam 103, which must be canceled out by an astigmatism corrector located elsewhere. Ultimately, control is required to correct the astigmatism of the primary electron beam, taking into account the effects of the Wien filter 108 and an astigmatism corrector located elsewhere.

[0026] 3 is a cross-sectional perspective view of the Wien filter 108. The upper surface of the center end of each pole 109 is composed of a tapered surface 109b that slopes downward toward the center line of the Wien filter 108. The tapered surfaces 109b of the eight poles 109 are arranged at equal intervals around the center line of the Wien filter 108, forming an upward-facing truncated cone-shaped surface. Secondary electrons emitted from the sample 106 form a secondary electron beam 104, which enters the Wien filter 108 from below and exits from the exit of the Wien filter 108 composed of the tapered surfaces 109b.

[0027] The tapered surface 109b on the exit side (upper side) of the Wien filter 108 from which the secondary electrons are emitted enables deflection at a large angle, which enables the electron detector 107 to detect the secondary electron beam 104 dispersed over a wide energy range.

[0028] Next, we will explain the shunts 115 and 120 of the Wien filter 108. With the Wien filter 108 alone, the electric field and magnetic field leak in the optical axis direction at its inlet and outlet, resulting in different distributions of the electric and magnetic fringe fields. This is because the environment around the Wien filter 108 in a real device generally has different effects on the electric and magnetic fields. For this reason, even if the Wien condition is satisfied in the central part of the Wien filter 108, it breaks down in the fringe region, causing the primary electron beam to be unable to travel in a straight line.

[0029] Therefore, in this embodiment, magnetic shunts 115, 120 are placed above and below the Wien filter 108 to attenuate the electric and magnetic fields in the same manner. Figure 4 is a perspective view showing an embodiment of the upper shunt 115 placed above the Wien filter 108. The upper shunt 115 has at least one slit 116, which extends radially from the optical axis toward the off-axis. The reason for extending the slit radially is that, as will be described later, the opening position of the slit 130 that selects the energy-dispersed secondary electron beam is not necessarily fixed, so it is desirable to allow beams with a wide range of energies to pass at the position of the upper shunt 115. The same applies when an image sensor is used as a detector. Ideally, the slit 116 only needs to be placed in the direction in which the secondary electrons are dispersed. However, to maintain symmetry of the electromagnetic field and prevent astigmatism from being introduced into the primary electron beam, it is ideal to arrange slits 116 of the same shape in all directions of the octapoles.

[0030] FIG. 5 is a perspective view showing an embodiment of the lower shunt 120 disposed below the Wien filter 108. The lower shunt 120 has a through-hole 123 at its center. The secondary electron beam 104 emitted from the sample 106 passes through the through-hole 123 and travels toward the Wien filter 108. Unlike the upper shunt 115, the lower shunt 120 does not have radially extending slits. To attenuate the electric field and the magnetic field in the same manner, it is desirable to make the hole diameters of the through-holes 117 and 123 of the shunts 115 and 120 as small as possible. The shunts 115 and 120 are made of a magnetic material at earth potential, such as permalloy.

[0031] When focusing secondary electron beams using a quadrupole field rather than an axially symmetric lens field, the secondary electron beams are subject to divergence within the Wien filter 108 in a direction perpendicular to the extension direction of the slit 116. This means that the secondary electron beams are blocked without passing through the slit 116, potentially resulting in vignetting of the field of view. If the opening of the slit 116 were widened to address this issue, the Wien filter 108's function as a shunt to attenuate the fringe field could be impaired. Note that the upper shunt 115 and the lower shunt 120 function as part of the electrodes of an electrostatic lens when an axially symmetric lens field is superimposed on the Wien filter 108. As a result, the Wien filter 108 in this embodiment constitutes a so-called Einzel lens, in which electrodes at earth potential are arranged on both sides of an electrode to which a voltage is applied.

[0032] Next, we will explain how to control secondary electrons from the sample 106. In scanning electron microscopes, when high spatial resolution is required for secondary electron images, an objective lens 105 that generates a strong magnetic field at the position of the sample 106 is used. When the sample 106 is placed completely between the magnetic poles, it is called an in-lens type, and when the sample is placed slightly away from the magnetic poles, it is called a semi-in-lens type. With this type of objective lens 105, the secondary electron beam 104 emitted from the sample 106 quickly wraps around the magnetic field lines because of its small initial energy and travels upward along the magnetic field lines in a spiral motion. As the magnetic field lines diverge radially from the optical axis with increasing distance from the sample 106, the secondary electron beam 104 is also guided away from the optical axis.

[0033] Furthermore, since the secondary electron beam 104 rises while being affected by the field of the deflector 112 that scans the primary electron beam 103, the secondary electron beam 104 is also deflected in the same direction as the primary electron beam 103, and this effect also causes the secondary electron beam 104 to move away from the optical axis. Therefore, the wider the scanning range on the surface of the sample 106, i.e., the wider the field of view, the more the secondary electron beam 104 spreads above the area of ​​the objective lens 105. For this reason, if the Wien filter 108 is placed above the objective lens 105, the secondary electron beam 104 cannot be captured outside of the field of view, and the secondary electron beam 104 is more likely to collide with the lower shunt 120 or the inner wall of the Wien filter 108 as it approaches the outside of the field of view, resulting in a phenomenon called field vignetting.

[0034] As described above, the diameters of the through holes 117 and 123 of the shunts 115 and 120 of the Wien filter 108 are designed to be as small as possible, so the location where the secondary electron beam 104 is most restricted is the lower shunt 120. In this embodiment, this restriction is avoided by providing a secondary electron focusing lens 135 for focusing the secondary electron beam 104 on the surface (more specifically, the lower surface) 120a of the lower shunt 120. The secondary electron focusing lens 135 is located below the lower shunt 120 and above the objective lens 105 and the deflector 112. The lens strength of the secondary electron focusing lens 135 for focusing the secondary electron beam on the surface 120a of the lower shunt 120 can be determined in advance by simulation. Alternatively, during actual device adjustment, the lens strength may be adjusted while observing a secondary electron image to minimize vignetting of the field of view.

[0035] When the secondary electron beam 104 is focused on the surface 120a of the lower shunt 120, the secondary electron beam 104 quickly spreads inside the Wien filter 108. However, in this embodiment, an axially symmetric lens field is superimposed on the Wien filter 108, so the secondary electron beam 104 quickly converges inside the Wien filter 108 and is finally focused on the surface 130a of the slit 130. The applied voltage for the axially symmetric lens field superimposed on the Wien filter 108 is set so that the surface 120a of the lower shunt 120 and the surface (energy dispersion surface) 130a of the slit 130 are conjugate.

[0036] In another embodiment, a wide field of view may not be required, and only high energy resolution may be required. In this case, the secondary electron focusing lens 135 is not necessary, and only secondary electrons passing through the through hole 123 of the lower shunt 120 need to be detected under the condition that the secondary electron beam from the sample 106 diverges as it ascends. In this case, the applied voltage for the axially symmetric lens field superimposed on the Wien filter 108 is set so that the secondary electron beam passing through the lower shunt 120 is focused on the surface (energy dispersion surface) 130a of the slit 130.

[0037] The primary electron beam 103 is also subjected to the lens action of the secondary electron focusing lens 135. However, similar to the above explanation regarding the lens action superimposed on the Wien filter 108, the energy of the primary electron beam 103 is greater than that of the secondary electron beam 104, so the effect of the secondary electron focusing lens 135 is small, and this effect is corrected when the objective lens 105 is adjusted so that the primary electron beam 103 is focused on the surface of the sample 106.

[0038] The secondary electron beam 104 is deflected by the Wien filter 108 at different angles depending on the energy of the secondary electrons. Of the energy-dispersed secondary electron beam 104, only those that pass through the slit 130 are incident on the detection surface 107a of the electron detector 107. Placing a scintillator on the detection surface 107a converts the electron signal into light, and the detector 107 can be, for example, a photomultiplier tube. To set the energy of the secondary electron beam passing through the slit 130, the opening position of the slit 130 can be mechanically moved. Alternatively, the deflection angle can be varied by simultaneously changing the uniform electric field intensity E1 and the uniform magnetic field intensity B1 of the Wien filter 108 while maintaining the ratio between E1 and B1 so that they satisfy the Wien condition. This method allows the energy of the secondary electrons passing through the slit 130 to be changed while keeping the position of the slit 130 fixed.

[0039] In another embodiment, it is also possible to place an image sensor such as a CCD in its place without placing the slit 130, and to generate a pattern image of the secondary electrons deflected by the Wien filter 108 using the image sensor. In this case, energy selection can be performed by detecting only electrons that are incident on a part of the image sensor.

[0040] A scanning electron microscope configured in this way is capable of generating images only from secondary electrons with a specific energy.

[0041] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0042] 101 Electron Gun 102 Condenser lens system 103 Primary electron beam 104 Secondary electron beam 105 Objective Lens 106 samples 107 Electron Detector 108 Vienna Filter 109 poles 109a Coil 109b Tapered surface 112 Deflector 115 Upper Shunt 120 Lower Shunt 121 Imaging Devices 123 Through hole 130 slit 130a Energy dispersive surface 135 Secondary electron focusing lens 150 Motion control section

Claims

1. an electron beam source for generating a primary electron beam; an electron optical system that guides the primary electron beam to a sample and focuses and deflects the beam; A Wien filter with a multipole structure, an operation control unit that applies the same voltage to all of the plurality of poles while forming an electric field and a magnetic field that satisfy the Wien condition in the Wien filter, thereby forming an axially symmetric lens field in the Wien filter; a lower shunt having a through hole disposed below the Wien filter; an electron detector that detects secondary electrons having at least a predetermined energy among the secondary electrons dispersed according to energy by the Wien filter; an imaging device that generates an image from the secondary electrons having the predetermined energy;

2. 2. The image generating device of claim 1, further comprising a secondary electron focusing lens that focuses a secondary electron beam emitted from the sample onto the surface of the lower shunt, and the intensity of the axially symmetric lens field of the Wien filter is set so that the surface of the lower shunt and the energy dispersion plane are conjugate.

3. The image generating device according to claim 1 , wherein the operation control unit is configured to cause the Wien filter to form the axially symmetric lens field by applying the same negative voltage to all of the plurality of poles.

4. A primary electron beam generated by an electron beam source is guided to a sample. The secondary electron beam emitted from the sample is passed through a through hole of a lower shunt disposed below a Wien filter; While forming an electric field and a magnetic field that satisfy the Wien condition in the Wien filter and forming an axially symmetric lens field in the Wien filter by applying the same voltage to all of the multiple poles of the Wien filter, secondary electrons generated from the sample are dispersed by the Wien filter according to their energy; detecting, by an electron detector, secondary electrons having at least a predetermined energy among the secondary electrons dispersed by the Wien filter; An image generation method, comprising generating an image from the secondary electrons having the predetermined energy using an imaging device.

5. 5. The image generating method of claim 4, wherein the secondary electron beam emitted from the sample is focused onto the surface of the lower shunt by a secondary electron focusing lens, and the intensity of the axially symmetric lens field of the Wien filter is set so that the surface of the lower shunt and the energy dispersion plane are conjugate.

6. The image generating method of claim 4 , wherein the axisymmetric lens field is formed in the Wien filter by applying the same negative voltage to all of the plurality of poles.

Images