Scanning electron microscope and sample observation method

Abstract

The present invention comprises a deflector (114) having an electron conversion electrode (141) that is positioned such that secondary electrons emitted from a specimen when irradiated with a primary electron beam collide therewith, a first electrode (142) and a second electrode (143) that are permeable to electrons and are positioned facing one another, and a third electrode (144) that is positioned facing the first electrode (142) with the second electrode (143) interposed therebetween. The electron conversion electrode (141) is segmented into a plurality of segmented electrodes, and the potential of the third electrode (144) has a positive potential difference relative to the potential of the second electrode (143).

Description

[Technical Field]

[0001] The present invention relates to a scanning electron microscope and a sample observation method using the same. [Background technology]

[0002] An electron microscope is a device that uses an electron beam to magnify and observe the surface or interior of a sample. In particular, a scanning electron microscope scans the electron beam and obtains an electron microscope image using secondary electrons or backscattered electrons emitted from the sample as brightness signals.

[0003] Scanning electron microscopes are used as indispensable tools in the development, manufacturing, and analysis of semiconductor devices. In recent years, semiconductor devices have become highly miniaturized and increasingly three-dimensional. This has led to an increasing need to observe trenches with high aspect ratios using scanning electron microscopes.

[0004] It is known that the shape contrast or shadow contrast of an electron microscope image can be improved by providing an electron microscope with an angle discrimination function and detecting signal electrons according to the emission angle. For example, Patent Document 1 discloses a scanning electron microscope that is composed of divided regions to which voltages can be applied independently, and that is equipped with a metal plate for generating tertiary electrons by colliding secondary electrons or reflected electrons. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-3909 Summary of the Invention [Problem to be solved by the invention]

[0006] Many of the secondary electrons generated from the bottom of the trench collide with the sidewalls of the trench and are annihilated, resulting in a small number of secondary electrons escaping the trench and becoming detectable. On the other hand, most of the secondary electrons emitted from the side of the trench (trench top) are detectable. For this reason, when observing a trench with a scanning electron microscope, the bottom of the trench appears dark.

[0007] To observe the trench bottom in a trench with a high aspect ratio, it is necessary to reduce the number of secondary electrons detected from the trench top without reducing the number of secondary electrons detected from the trench bottom. In other words, the BT ratio, which is the ratio of the number of secondary electrons detected from the trench bottom (B) to the number of secondary electrons detected from the trench top (T), should be increased. To achieve this, the emission angle of the secondary electrons should be limited.

[0008] Unless the secondary electron signal from the trench top is sufficiently lower than the secondary electron signal from the trench bottom, it becomes difficult to measure the dimensions of the fine structure at the trench bottom or observe foreign matter. However, Patent Document 1 does not give sufficient consideration to reducing the secondary electron signal from the trench top in order to improve the visibility of the trench bottom.

[0009] An object of the present invention is to provide a scanning electron microscope that is suitable for measuring the dimensions of the fine structure at the bottom of a trench and for observing foreign matter, even in a trench portion with a high aspect ratio. [Means for solving the problem]

[0010] A scanning electron microscope according to one embodiment of the present invention includes an electron source, an objective lens that focuses a primary electron beam emitted from the electron source onto a sample, a deflector that uses at least an electric field between the electron source and the objective lens to deflect electrons, a stage that mounts the sample, a power supply that applies a voltage to the stage that decelerates the primary electron beam, a detector that detects electrons, and a control device, and the deflector includes an electron conversion electrode that is arranged so that secondary electrons emitted from the sample when irradiated with the primary electron beam collide with the electron conversion electrode, The electron conversion electrode is sandwiched between the space where the tertiary electrons emitted by the secondary electrons colliding with the sample move in the initial stage of emission. The detector includes a first electrode and a second electrode that are disposed opposite each other and are electron-transmissible, and a third electrode that is disposed opposite the first electrode with the second electrode interposed therebetween, tertiary electron The electron conversion electrode detects Radial or concentric The electrode is divided into a plurality of divided electrodes, and the control device sets the potential of the third electrode to a positive potential difference with respect to the potential of the second electrode. [Effects of the Invention]

[0011] To provide a scanning electron microscope suitable for measuring the dimensions of the fine structure of a trench bottom and for observing foreign matter.

[0012] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of the overall configuration of an electron microscope. [Figure 2] FIG. 10 is a diagram showing secondary electron emission vectors emitted from a trench. [Figure 3A] 1 is a cross-sectional view of the Wien filter of Example 1 as seen from the side. [Figure 3B] 1 is a cross-sectional view of the Wien filter of Example 1 as seen from the planar direction. [Figure 4] 1A and 1B are diagrams illustrating a state in which secondary electrons are emitted from a trench bottom and a trench top. [Figure 5A] FIG. 2 is a diagram showing the collision position of secondary electrons on the electron conversion electrode. [Figure 5B] FIG. 2 is a diagram showing the collision position of secondary electrons on the electron conversion electrode. [Figure 6A] FIG. 2 is a diagram showing the collision position of secondary electrons on the electron conversion electrode. [Figure 6B] FIG. 2 is a diagram showing the collision position of secondary electrons on the electron conversion electrode. [Figure 7A] 4 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 1. FIG. [Figure 7B] 4 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 1. FIG. [Figure 8A] FIG. 10 is a cross-sectional view of the Wien filter of Example 2 as seen from the side. [Figure 8B] FIG. 10 is a cross-sectional view of the Wien filter of Example 2 as seen from the planar direction. [Figure 9A] 10 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 2. FIG. [Figure 9B] 10 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 2. FIG. [Figure 10A] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 10B] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 11A] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 11B] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 12A] FIG. 11 is a cross-sectional view of the electron deflector of the third embodiment as viewed from the side. [Figure 12B] FIG. 10 is a cross-sectional view of an electron deflector according to a third embodiment, as viewed from a planar direction. [Figure 13A] 10 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 3. FIG. [Figure 13B] 10 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 3. FIG. [Figure 14A]10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 14B] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 15A] FIG. 10 is a cross-sectional view of the Wien filter of Example 4 as seen from the side. [Figure 15B] FIG. 10 is a cross-sectional view of the Wien filter of Example 4 as seen from the planar direction. [Figure 16] 10 is a diagram showing the detailed structure of a beam guide and an electron conversion electrode according to a fourth embodiment. FIG. [Figure 17A] 10 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 4. FIG. [Figure 17B] 10 is a diagram showing the behavior of secondary electrons, reflected electrons, and tertiary electrons in Example 4. FIG. [Figure 18A] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 18B] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 19A] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 19B] 10A and 10B are diagrams showing collision positions of secondary electrons on a beam guide and an electron conversion electrode. [Figure 20] FIG. 10 is a diagram showing an example of a screen displayed on a display of a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electron microscope according to an embodiment of the present invention will now be described with reference to the accompanying drawings. An electron microscope is an apparatus for observing a sample by irradiating the sample with an electron beam. [Example]

[0015] The overall configuration of an electron microscope 100 according to the first embodiment will be described with reference to FIG. 1 . The vertical direction is defined as the Z direction, and the horizontal direction is defined as the X and Y directions. The electron microscope 100 primarily comprises an electron gun 101, an extraction electrode 102, an anode 104, a focusing lens 105, an aperture 106, an adjustment knob 107, an upper deflector 108, a lower deflector 109, a detector 110, a Wien filter 114, an objective lens 118, a sample stage 121, a power supply 124 for applying voltage to the sample stage, a control device 150, a display 151, and a storage device 152. The control device 150 is a device, such as a computer, that controls the operation of each component. The storage device 152 stores a control table 153 that defines control conditions, such as voltage and current, for each component. The control device 150 reads the control table 153 from the storage device 152 and controls each component based on the control conditions defined in the control table 153.

[0016] The electron gun 101 is an electron source that emits electrons, and is, for example, a field emission cathode. A negative voltage of, for example, 4000 V is applied to the electron source. The extraction electrode 102 and the anode 104 are electrodes to which a positive voltage is applied relative to the electron gun 101, and each has an aperture through which the primary electron beam B1, which is electrons emitted from the electron gun 101, passes. Note that the absolute value of the voltage applied to the electron gun 101 is greater for the anode 104 than for the extraction electrode 102. The focusing lens 105 is a lens that focuses the primary electron beam B1. The aperture 106 is a component that determines the aperture angle of the primary electron beam B1 at the objective lens 118, and has an aperture through which the primary electron beam B1 passes. The adjustment knob 107 is used to adjust the center position of the aperture 106. The upper deflector 108 and the lower deflector 109 deflect the primary electron beam B1 to scan it over the sample 120.

[0017] The objective lens 118 is a lens that focuses the deflected primary electron beam B1, and has a rotationally symmetric magnetic pole 116 and an objective lens coil 117. A magnetic field generated by a current flowing through the objective lens coil 117 causes the primary electron beam B1 to become a fine beam.

[0018] The sample stage 121 holds the sample 120 and controls the position and attitude of the sample 120. That is, the sample stage 121 moves the sample 120 horizontally or vertically, and rotates it around the vertical axis. A power supply 124 that applies a voltage to the sample stage is connected to the sample stage 121, and a negative voltage of, for example, 3000 V is applied, forming an electric field that decelerates the primary electron beam B1 between the sample 120 on the sample stage 121 and the objective lens 118 (retarding method).

[0019] When the decelerated primary electron beam B1 is irradiated onto point S on the sample 120, secondary electrons and backscattered electrons are emitted from point S. Secondary electrons and backscattered electrons are generated by different mechanisms: secondary electrons are electrons excited from atoms constituting the sample by inelastic scattering of primary electrons within the sample, while backscattered electrons are electrons that are backscattered during the scattering process of the irradiated primary electrons. For this reason, secondary electrons are electrons with an energy of less than 100 eV, for example, and backscattered electrons are electrons with an energy of 100 eV or more, for example.

[0020] Figure 2 shows a secondary electron emission vector 201 emitted from a trench 200. Figure 2 also shows the definitions of the elevation angle 202 and azimuth angle 203 of the secondary electrons. The elevation angle 202 is the angle measured from the Z axis of the secondary electron emission vector 201, and the azimuth angle 203 is the angle measured from the X axis of a line segment 206 that projects the secondary electron emission vector 201 onto the XY plane. The secondary electrons are emitted with a distribution approximated by a cosine function for the elevation angle and an isotropic distribution for the azimuth angle.

[0021] Returning to the explanation of Figure 1, the electric field that decelerates the primary electron beam B1 accelerates the secondary electrons 122 and pulls them up into the passage of the objective lens 118. The secondary electrons 122 pulled up into the passage are affected by the magnetic field of the objective lens 118 and travel towards the electron gun 101 while tracing a spiral trajectory, and reach the Wien filter 114.

[0022] The detailed structure of the Wien filter 114 and discrimination of secondary electrons will be described later, but here, the principle of secondary electron image generation will be explained. Secondary electrons 122 that reach the Wien filter 114 collide with the upper electron conversion electrode 141. When the secondary electrons 122 collide with the electron conversion electrode 141, tertiary electrons 123 are emitted from the electron conversion electrode 141. Although the tertiary electrons 123 are secondary electrons in terms of their generation mechanism, here, to avoid confusion with secondary electrons emitted from the sample 120, secondary electrons emitted from sources other than the sample 120 and resulting from the secondary electrons 122 are referred to as tertiary electrons.

[0023] When the electron conversion electrode 141 is at ground potential, the tertiary electrons 123 are deflected toward the detector 110 by the electric field 134 and magnetic field 133 in the Wien filter 114. Although the electric field 134 and magnetic field 133 also act on the primary electron beam B1, the effects of these two fields cancel each other out, causing the primary electron beam B1 to travel in a straight line.

[0024] The detector 110 detects the tertiary electrons 123 deflected by the Wien filter 114, and includes a fluorescent screen 111 and a photomultiplier tube 112. The fluorescent screen 111 is a flat plate that emits light when the tertiary electrons 123 are incident on it, and is the detection surface of the detector 110. The photomultiplier tube 112 outputs an electrical signal obtained by amplifying photoelectrons generated by the emission of light from the fluorescent screen 111. That is, the detector 110 transmits a detection signal corresponding to the amount of tertiary electrons 123 incident on the fluorescent screen 111 to the control device 150. The control device 150 generates a secondary electron image of the sample based on the received detection signal. The generated secondary electron image is displayed on a display 151 or stored in a storage device 152.

[0025] The detailed structure of the Wien filter 114 will be explained using Figures 3A and 3B. Figure 3A is a cross-sectional view from the side, and Figure 3B is a cross-sectional view from the top. An electron conversion electrode 141, on which secondary electrons 122 collide, is arranged on top of the Wien filter 114. In this embodiment, this electron conversion electrode 141 is divided into eight radially. Each divided electrode is electrically insulated from the others, and a separation groove is provided between adjacent electrodes so that the application of a positive voltage, a negative voltage, or ground potential can be independently switched to each divided electrode. In addition, there is a gap in the center of the electron conversion electrode 141 through which the primary electron beam B1 passes.

[0026] The Wien filter 114 has a first electrode 142, a second electrode 143, a third electrode 144, and a coil 113. The first electrode 142 is an electrode that can transmit tertiary electrons generated in the electron conversion electrode 141. To make the electrode transmittable for electrons, for example, a grid electrode, a mesh electrode, or the like may be used. The second electrode 143 and the third electrode 144 face the detector 110, and are arranged so that the third electrode 144 is located outside the second electrode 143. The second electrode 143 is an electrode that can transmit electrons that are reflected when the secondary electrons 122 collide with the electron conversion electrode 141.

[0027] A positive voltage of 50 V is applied to the first electrode 142, the second electrode 143 is at ground potential, and a positive voltage of 30 V is applied to the third electrode 144. Furthermore, a current of about 1 A is passed through the coil 113 to generate a magnetic field. As described above, the electric field 134 formed by the first electrode 142 and the second electrode 143 and the magnetic field 133 formed by the coil 113 cancel each other out in electromagnetic force with respect to the primary electron beam B1. Therefore, the primary electron beam B1 traveling from the electron gun 101 toward the sample 120 travels in a straight line. On the other hand, the electric field 134 and the magnetic field 133 act to deflect the tertiary electrons 123 emitted from the electron conversion electrode 141 toward the detector 110.

[0028] The Wien filter 114 has a housing 145 in which electrodes and the like are housed and fixed. Insulators, fixing screws, and the like are also contained within the housing 145 but are not shown.

[0029] FIG. 4 schematically shows how secondary electrons 210 are emitted from the bottom of the trench 200 (trench bottom 204) and from the outer surface of the trench (trench top 205). Among the secondary electrons 210 emitted from the trench bottom 204, secondary electrons 211 that collide with the side surfaces of the trench are annihilated and therefore not detected. As a result, the number of secondary electrons emitted from the trench top 205 is greater than the number of secondary electrons emitted from the trench bottom 204. For this reason, in the secondary electron image, the trench top appears bright and the trench bottom appears dark. When the aspect ratio of the trench 200 is large, that is, when the trench depth is large relative to the trench width, the trench bottom appears much darker than the trench top, making it difficult to discern fine structures or foreign objects at the trench bottom.

[0030] In this embodiment, the electron conversion electrode 141 of the Wien filter is radially divided into eight parts. A power supply is connected to each of the divided electrodes that make up the electron conversion electrode 141, and a control device 150 controls some divided electrodes to be at ground potential or to apply a negative voltage, and some divided electrodes to apply a positive voltage. Tertiary electrons emitted from divided electrodes at ground potential or negative potential are directed toward the detector. On the other hand, tertiary electrons emitted from divided electrodes to which a positive voltage is applied are drawn back to the electron conversion electrode 141 by the electric field and are not detected. This makes it possible to distinguish the secondary electrons to be detected based on the collision position of the secondary electrons on the electron conversion electrode 141.

[0031] Here, the inventors focused on the trajectory of secondary electrons 122 emitted from the sample 120. By assuming the energy distribution, emission elevation angle distribution, emission azimuth angle distribution, etc. of the secondary electrons, it is possible to determine the electron trajectory from the sample 120 to the electron conversion electrode 141 of the Wien filter 114. Therefore, it is possible to determine the collision position of the secondary electrons 122 on the electron conversion electrode 141.

[0032] Figure 5A shows the collision position 301 of the secondary electrons on the electron conversion electrode when 10,000 secondary electrons are emitted from the trench top. It can be seen that the collision positions of the secondary electrons from the trench top spread concentrically from the center of the electron conversion electrode. The radially extending area where no secondary electron collisions are observed corresponds to the separation grooves between the segmented electrodes. The secondary electrons shown in Figure 5A are secondary electrons that can be detected by detector 110, and when the number of secondary electrons colliding with the electron conversion electrode was counted, it was found to be approximately 6,500.

[0033] Figure 5B shows the collision positions 302 of secondary electrons on the electron conversion electrode when 10,000 secondary electrons are emitted from the trench bottom when the trench aspect ratio is 5. It can be seen that the collision positions of secondary electrons from the trench bottom are distributed in an elongated elliptical shape. The long axis of the ellipse is tilted approximately 40° clockwise from the Y axis. This is because the secondary electrons 122 are rotated by the magnetic field of the objective lens 118. The number of secondary electrons that collide with the electron conversion electrode was counted to be approximately 500. Therefore, the ratio of the number of secondary electrons emitted from the trench bottom (500) to the number of secondary electrons emitted from the trench top (6,500) detected, i.e., the BT ratio, is approximately 0.08.

[0034] Comparing Figures 5B and 3B, the electron conversion electrodes that are most frequently hit by secondary electrons from the trench bottom are segmented electrodes 2 and 6 of electron conversion electrode 141. Therefore, segmented electrodes 2 and 6 of electron conversion electrode 141 are set to ground potential, and a positive voltage of 60 V is applied to the other six segmented electrodes, i.e., segmented electrodes 1, 3, 4, 5, 7, and 8. In this case, secondary electrons that collide with segmented electrodes 2 and 6 are detected, while secondary electrons that collide with the other six segmented electrodes are not detected. By dividing the electron conversion electrode radially and setting opposing segmented electrodes to approximately the same potential in this way, azimuthal discrimination suitable for observing the trench bottom can be performed.

[0035] As described above, when only the segmented electrodes 2 and 6 are grounded, secondary electrons from the trench top are shown in FIG. 6A, and those from the trench bottom are shown in FIG. 6B. FIGS. 6A and 6B show the collision positions of secondary electrons on the segmented electrodes 2 and 6 extracted from FIGS. 5A and 5B, respectively. The number of secondary electrons from the trench top was approximately 1,600, about one-fourth the number before discrimination. Meanwhile, the number of secondary electrons from the trench bottom was approximately 500, almost the same as before discrimination. In this case, the BT ratio was approximately 0.3. Thus, by azimuthal discrimination of the secondary electrons emitted from the sample, the number of secondary electrons from the trench top detected by the detector 110 decreases, while the number of secondary electrons from the trench bottom remains approximately the same, thereby improving the BT ratio.

[0036] As shown in FIG. 7A, secondary electrons collide with the electron conversion electrode 141, resulting in the emission of backscattered electrons 160. Because the secondary electrons 122 are accelerated by the retarding voltage, the energy of the secondary electrons 122 is as high as the voltage applied to the sample 120 from the power supply 124. Therefore, the backscattered electrons 160 also have high energy. When the backscattered electrons 160 pass through the second electrode 143 and collide with the third electrode 144, tertiary electrons 161 are emitted from the third electrode 144. In FIG. 7A, the third electrode 144 is at ground potential. If the second electrode 143 is also at ground potential, the tertiary electrons 161 emitted from the third electrode 144 pass through the second electrode 143 and then the first electrode 142 before reaching the detector 110.

[0037] As described above, when a positive voltage is applied to the electron conversion electrode 141, secondary electrons 122 collide with the electron conversion electrode 141, and the emitted tertiary electrons return to the electron conversion electrode 141. On the other hand, as shown in Figure 7A, when the secondary electrons 122 collide with the electron conversion electrode 141, reflected electrons 160 are also emitted, and when the reflected electrons 160 collide with the third electrode 144, tertiary electrons 161 are emitted. Here, while the secondary electrons emitted from the trench bottom hardly collide with the divided electrode to which a positive voltage is applied, many secondary electrons emitted from the trench top also collide with the divided electrode to which a positive voltage is applied.

[0038] As a result, even if an attempt is made to reduce the detection rate of secondary electrons emitted from the trench top by applying a positive voltage to the electron conversion electrode 141, the secondary electrons emitted from the trench top are detected by detecting tertiary electrons 161 generated when reflected electrons 160 collide with the third electrode 144. This makes the trench top relatively bright, reducing the visibility of the trench bottom. Thus, in the case of Figure 7A, the ideal BT ratio of approximately 0.3 is not actually achieved because tertiary electrons 161 originating from reflected electrons 160 are detected.

[0039] FIG. 7B shows a case where the second electrode 143 is at ground potential and a positive voltage of +30 V is applied to the third electrode 144. A power supply 162 that applies a positive voltage is connected to the third electrode 144. In this case, secondary electrons 122 generated in the sample collide with the electron conversion electrode 141, resulting in emitted backscattered electrons 160. These electrons then collide with the third electrode 144, generating tertiary electrons 161. These electrons are pulled back toward the third electrode 144 by the electric field between the second electrode 143, which is at ground potential, and the third electrode 144, to which a positive voltage of +30 V is applied, and are then absorbed and annihilated. Therefore, in the scanning electron microscope image in this case, the BT ratio approaches 0.3. In other words, compared to the case of FIG. 7A, the trench top is relatively dark, improving the visibility of the trench bottom.

[0040] This makes it possible to provide a scanning electron microscope that can measure the dimensions of the fine structure of the trench bottom and observe foreign matter, and also to obtain images of the fine structure of the trench bottom and foreign matter inside the trench.

[0041] It is desirable that the voltage applied to the third electrode 144 be switchable between a positive voltage, a negative voltage, or a ground potential. As mentioned above, applying a positive voltage to the third electrode 144 improves the visibility of the trench bottom. Conversely, applying a negative voltage or grounding the third electrode 144 makes it possible to obtain a bright image when observing the sample surface. Alternatively, a positive voltage may be constantly applied to the third electrode 144. In this case, the sample surface becomes somewhat darker when observed, but a low-cost device can be provided because a power supply or switching system is not required.

[0042] In this embodiment, an example has been described in which the potentials of the divided electrodes of the electron conversion electrode 141 can be switched independently, but it is also possible to apply a positive voltage to a specific divided electrode at all times, while keeping the other divided electrodes at ground potential. This makes it possible to provide a low-cost device suitable for observing trenches, without the need for a power supply or switching system. [Example]

[0043] In Example 2, the electron conversion electrode 141 is divided into two concentric parts. Note that the same reference numerals are used for the same configurations and functions as those described in Example 1, and the description thereof will be omitted.

[0044] The detailed structure of the Wien filter 114 of Example 2 will be described using Figures 8A and 8B. Figure 8A is a cross-sectional view seen from the side, and Figure 8B is a cross-sectional view seen from the top. An electron conversion electrode 141, on which secondary electrons 122 collide, is arranged on top of the Wien filter 114. In this example, as shown in Figure 8B, the electron conversion electrode 141 is divided into two concentric parts. The divided electrodes are electrically insulated from each other, and a concentric separation groove is provided between the two electrodes so that each electrode can be independently switched between application of a positive voltage, application of a negative voltage, or ground potential.

[0045] Furthermore, in this example, a beam guide 146, which is a hollow pipe electrode, is disposed at the center of the electron conversion electrode 141 so as to penetrate the electron conversion electrode 141, through which the primary electron beam B1 passes. The beam guide 146 and the electron conversion electrode 141 are electrically insulated by a concentric separation groove. The beam guide 146 is at ground potential and is provided to shield the primary electron beam B1 from the electric field generated by applying a voltage to the electron conversion electrode 141. This reduces distortion of the primary electron beam B1. Note that, although a pipe-shaped electrode with a circular cross section is illustrated as the beam guide 146 here, it may also be a cylindrical electrode with a polygonal cross section and is not limited to a pipe electrode. Any electrode may be formed of a conductive material and have a passage through which the primary electron beam B1 passes. A pipe-shaped electrode with a circular cross section is suitable for placement at the center of the concentrically divided electron conversion electrode 141. The beam guide does not have to be at ground potential; for example, a low voltage may be applied to the beam guide 146 within a range that does not significantly affect the primary electron beam.

[0046] The Wien filter 114 of this embodiment has a first electrode 142, a second electrode 143, and a third electrode 144 similar to those of the first embodiment. Since the beam guide 146 is at ground potential, tertiary electrons are also emitted from the end face E of the beam guide. In other words, the beam guide also serves as an electron conversion electrode. Due to the electric field formed by the first electrode 142 and the second electrode 143, the tertiary electrons emitted from the electron conversion electrode 141 and the end face E of the beam guide 146 are deflected toward the detector 110.

[0047] In addition to these electrodes, in this embodiment, a fourth electrode 147 that is permeable to secondary electrons and tertiary electrons is provided below the electron conversion electrode 141. The fourth electrode 147 is at ground potential.

[0048] 9A and 9B show the behavior of secondary electrons, reflected electrons, and tertiary electrons when split electrode 141a near the center is set to ground potential and a positive voltage is applied to split electrode 141b far from the center.

[0049] Tertiary electrons 123 emitted from split electrode 141a, which is at ground potential, head toward detector 110. On the other hand, tertiary electrons 148 emitted from split electrode 141b, to which a positive voltage is applied, are pulled back to split electrode 141b by the electric field between split electrode 141b and fourth electrode 147 and are therefore not detected. By providing fourth electrode 147, the pulling back electric field that tertiary electrons 148 emitted from split electrode 141b, to which a positive voltage is applied, is strengthened, and tertiary electrons 148 are reliably prevented from being detected, thereby improving the accuracy of secondary electron discrimination detection.

[0050] In Fig. 9A, the third electrode 144 is set to ground potential, and as in Example 1 (Fig. 7A), tertiary electrons 161 emitted from the third electrode 144 pass through the second electrode 143 and then the first electrode 142 before reaching the detector 110, thereby reducing the accuracy of secondary electron discrimination. In contrast, in Fig. 9B, a positive voltage of +30 V is applied to the third electrode 144 by the power supply 162. In this case, the tertiary electrons 161 are drawn back to the third electrode 144 by the electric field between the second electrode 143 and the third electrode 144 and are not detected. This improves the accuracy of secondary electron discrimination.

[0051] In Example 2, the collision positions of the secondary electrons emitted from the sample onto the beam guide 146 and the electron conversion electrode 141 can also be determined from the results of electron trajectory analysis. FIG. 10A shows collision positions 303 of the secondary electrons onto the beam guide and the electron conversion electrode when 10,000 secondary electrons are emitted from the trench top. The collision positions are divided into three regions and distributed concentrically. From the center, they are the region where the secondary electrons collide with the beam guide 146, the region where the secondary electrons collide with the segmented electrode 141a, and the region where the secondary electrons collide with the segmented electrode 141b. On the other hand, FIG. 10B shows collision positions 304 of the secondary electrons onto the beam guide and the electron conversion electrode when 10,000 secondary electrons are emitted from the trench bottom when the trench aspect ratio is 5. The collision positions are distributed in an elliptical shape, and the major axis of the ellipse is tilted clockwise by approximately 40° from the Y axis. In this case as well, the distribution of collision positions is divided into three regions, namely, from the center, a region where collision occurred on beam guide 146, a region where collision occurred on divided electrode 141a, and a region where collision occurred on divided electrode 141b.

[0052] When the split electrodes 141a and 141b and the beam guide are grounded, almost all secondary electrons are detected except for those that collide with the isolation groove. The number of secondary electrons from the trench top in Figure 10A is approximately 7,800, while the number of secondary electrons from the trench bottom in Figure 10B is approximately 600. Therefore, the BT ratio is approximately 0.08.

[0053] In contrast, when a positive voltage of +50 V is applied to the split electrode 141 b and a positive voltage of +30 V is applied to the third electrode 144, secondary electrons that collide with the beam guide 146 or the split electrode 141 a are detected. Figures 11A and 11B show the collision positions of secondary electrons on the beam guide and the split electrode 141 a extracted from Figures 10A and 10B, respectively. The number of secondary electrons counted from the trench top was approximately 3,000, and the number of secondary electrons counted from the trench bottom was approximately 440. Therefore, the BT ratio was approximately 0.15. In other words, by dividing the electron conversion electrode 141 into two, applying a positive voltage to the outer split electrode 141 b, and applying a positive voltage to the third electrode 144, the BT ratio can be improved by approximately two times. [Example]

[0054] In Example 3, an example is shown in which the electron conversion electrode 141 is not divided, and a beam guide 146 (pipe electrode) is arranged in the center of the electron conversion electrode 141. Furthermore, in Examples 1 and 2, an example is shown in which a Wien filter is used to direct the tertiary electrons toward the detector, but an electron deflector can also be used. Therefore, in Example 3, an example is shown in which an electron deflector is used instead of a Wien filter. When an electron deflector is used, the primary electron beam B1 is also deflected, but the deflection of the primary electron beam B1 by the electron deflector can be eliminated by deflecting it back using a deflector in a subsequent stage. Note that the same reference numerals are used to designate the same configurations and functions as those described in Examples 1 and 2, and descriptions thereof will be omitted.

[0055] The detailed structure of the electron deflector 115 of Example 3 will be described using Figures 12A and 12B. The electron deflector 115 does not use a magnetic field; it deflects electrons using only an electric field. The Wien filter described in Examples 1 and 2 can also be considered a type of electron deflector. Figure 12A is a cross-sectional view from the side, and Figure 12B is a cross-sectional view from the top. An electron conversion electrode 141, onto which secondary electrons 122 impinge, is located above the electron deflector 115. In this example, as shown in Figure 12B, a power supply is connected to the undivided electron conversion electrode 141 so that a positive or negative voltage can be applied. The electrode can be independently switched between positive and negative voltages or ground potential. A hollow pipe-shaped beam guide 146 is located in the center of the electron conversion electrode 141, through which the primary electron beam B1 passes. The beam guide 146 and the electron conversion electrode 141 are electrically insulated by a concentric separation groove. By setting the beam guide 146 to ground potential, tertiary electrons are also emitted from the end face E of the beam guide 146. In other words, the beam guide also serves as an electron conversion electrode. As a result, even if the electron conversion electrode 141 is not divided, the two, the electron conversion electrode 141 and the beam guide 146, can be said to essentially comprise multiple electron conversion electrodes.

[0056] The electron deflector 115 of this embodiment is provided with a fourth electrode 147 similar to that of Example 2, in addition to the first electrode 142, second electrode 143, and third electrode 144 similar to those of Example 1. Furthermore, this embodiment includes a fifth electrode 163 that is disposed on the sample side relative to the first electrode 142 and the second electrode 143. The fifth electrode 163 is an electrode such as a grid electrode or a mesh electrode that can transmit secondary electrons emitted from the sample.

[0057] When observing the trench bottom, a positive voltage of 50 V is applied to the electron conversion electrode 141. Figures 13A and 13B show the behavior of secondary electrons, backscattered electrons, and tertiary electrons when a positive voltage is applied to the electron conversion electrode 141 and the beam guide 146 is at ground potential. In this case, tertiary electrons 148 emitted from the electron conversion electrode 141 are pulled back to the electron conversion electrode 141 due to the potential difference between the electron conversion electrode 141 and the fourth electrode 147, which is at ground potential, and are therefore not detected. The fourth electrode 147 strengthens the pull-back electric field that the tertiary electrons experience, ensuring that the tertiary electrons are not detected, thereby improving the accuracy of secondary electron discrimination and detection. In contrast, tertiary electrons emitted from the end face of the beam guide 146, which is at ground potential, are detected.

[0058] Next, the function of the fifth electrode 163 will be described. In Fig. 13A, the fifth electrode 163 is set to ground potential. In this case, tertiary electrons 161 are generated when electrons 160, which are secondary electrons 122 reflected by the electron conversion electrode 141, collide with the inner wall of the housing 145. This means that secondary electrons that collide with the electron conversion electrode 141 to which a positive voltage is applied are detected, which reduces the accuracy of secondary electron discrimination.

[0059] 13B, a negative voltage of −30 V is applied to the fifth electrode 163 by the power supply 164. In this case, the tertiary electrons 161 generated when the secondary electrons 122 are reflected by the electron conversion electrode 141 and the electrons 160 collide with the housing 145 are pulled back downward by the electric field between the fifth electrode 163 and the housing 145 and are not detected by the detector 110. In other words, the secondary electrons that collide with the electron conversion electrode 141 to which a positive voltage is applied are not detected, and therefore the accuracy of secondary electron discrimination is improved compared to the case of FIG. 13A.

[0060] In Example 3, the collision positions of the secondary electrons emitted from the sample onto the beam guide 146 and the electron conversion electrode 141 can also be determined from the results of electron trajectory analysis. FIG. 14A shows collision positions 305 of the secondary electrons onto the beam guide and the electron conversion electrode when 10,000 secondary electrons are emitted from the trench top. The collision positions are distributed concentrically and are divided into two regions. From the center, there is a region where the secondary electrons collide with the beam guide 146 and a region where the secondary electrons collide with the electron conversion electrode 141. Meanwhile, FIG. 14B shows collision positions 306 of the secondary electrons onto the beam guide and the electron conversion electrode when 10,000 secondary electrons are emitted from the trench bottom when the trench aspect ratio is 5. The collision positions are distributed elliptically, and the major axis of the ellipse is tilted clockwise by approximately 40° from the Y axis. In this case as well, the distribution of the collision positions is divided into two regions, namely, a region where the beams collide with the beam guide 146 and a region where the beams collide with the electron conversion electrode 141 from the center.

[0061] When the electron conversion electrode 141 and the beam guide 146 are grounded, almost all secondary electrons are detected except for those that collide with the isolation groove. The number of secondary electrons from the trench top in Figure 14A is approximately 9,000, while the number of secondary electrons from the trench bottom in Figure 14B is approximately 700. Therefore, the BT ratio is approximately 0.08.

[0062] In contrast, when a positive voltage of +50 V is applied to the electron conversion electrode 141 and a positive voltage is applied to the third electrode 144 so as not to detect secondary electrons that collide with the electron conversion electrode 141, the number of secondary electrons emitted from the trench top and colliding with the beam guide is approximately 1,400, and the number of secondary electrons emitted from the trench bottom and colliding with the beam guide is approximately 250. Therefore, the BT ratio is approximately 0.18. In other words, by applying a positive voltage to the electron conversion electrode 141 without dividing it and applying a positive voltage to the third electrode 144, the BT ratio can be improved by approximately two times.

[0063] It is desirable that the voltage applied to the fifth electrode 163 be switchable between a negative voltage and a ground potential. As mentioned above, applying a negative voltage to the fifth electrode 163 improves the visibility of the trench bottom. Conversely, if the fifth electrode 163 is at ground potential, a bright image can be obtained for an observation target with little unevenness. Alternatively, a negative voltage may be applied to the fifth electrode 163 all the time. In this case, the sample surface will be somewhat darker when observed, but a low-cost device can be provided because a power supply and switching system are not required. [Example]

[0064] In Example 4, an example is shown in which the electron conversion electrode 141 is divided into eight parts radially and into two parts concentrically, that is, the electron conversion electrode 141 is divided into 16 parts. Also, an example is shown in which the housing of the electron microscope is regarded as a third electrode to configure an electron deflector (Wien filter). Note that in Example 4, the same reference numerals are used for configurations and functions that are similar to those described in Examples 1 to 3, and descriptions thereof will be omitted.

[0065] The detailed structure of the Wien filter 114 of Example 4 will be described using Figures 15A and 15B. Figure 15A is a cross-sectional view from the side, and Figure 15B is a cross-sectional view from the top. An electron conversion electrode 141, on which secondary electrons 122 collide, is located above the Wien filter 114. In this example, as shown in Figure 15B, the electron conversion electrode 141 is divided into eight radial sections and two concentric sections, for a total of 16 sections. Each of the 16 divided electrodes is connected to a power supply so that a positive or negative voltage can be applied, and each electrode can be independently switched between applying a positive voltage, applying a negative voltage, or applying a ground potential. A beam guide 146, which is a hollow pipe electrode, is located in the center of the electron conversion electrode 141, through which the primary electron beam B1 passes. The beam guide 146 and the electron conversion electrode 141 are electrically insulated by a concentric separation groove.

[0066] The Wien filter 114 of this embodiment is provided with a first electrode 142 and a second electrode 143, and furthermore, the housing 149 of the electron microscope plays the role of the third electrode 144 in the first to third embodiments.

[0067] 16 shows the detailed structure of the beam guide 146 and the electron conversion electrode 141. The electron conversion electrode 141 is divided into 16 parts. The inside of the electron conversion electrode 141 is divided into divided electrodes 1 to 8, and the outside is divided into divided electrodes 9 to 16. A power supply is connected to each divided electrode, and the control device 150 independently controls switching between application of a positive voltage, application of a negative voltage, or ground potential.

[0068] 17A shows the behavior of secondary electrons, backscattered electrons, and tertiary electrons when segmented electrodes 2 and 6 of the electron conversion electrode 141 are set to ground potential, a positive voltage is applied to the other 14 segmented electrodes, and the second electrode 143 is set to ground potential. In this way, by dividing the electron conversion electrode radially and setting the opposing segmented electrodes to approximately the same potential, azimuthal discrimination suitable for observing the trench bottom can be performed. In particular, this has the effect of simplifying voltage control.

[0069] Furthermore, when the electron conversion electrode 141 is divided radially and different voltages are applied to the divided electrodes as in this embodiment, the effect of the beam guide 146 in suppressing distortion of the primary electron beam B1 is particularly important. This can prevent the voltage application to the electron conversion electrode 141 from distorting the primary electron beam B1 and degrading the observation resolution of the scanning electron microscope. For this reason, it is desirable that the end face E of the beam guide 146 on the sample side be located at approximately the same position as the fourth electrode 147, or located closer to the sample than the fourth electrode 147.

[0070] 17A, the second electrode 143 is at ground potential, so that tertiary electrons 161 generated when secondary electrons 122 are reflected by the electron conversion electrode 141 and collide with the inner wall of the housing 149 of the electron microscope pass through the second electrode 143 and are detected. As a result, secondary electrons that collide with the divided electrodes of the electron conversion electrode 141 to which a positive voltage is applied are detected, which reduces the accuracy of discrimination of secondary electrons.

[0071] In contrast, Figure 17B shows the behavior of secondary electrons, reflected electrons, and tertiary electrons when a negative voltage of -30 V is applied to the second electrode 143 by the power supply 164, as in Figure 17A. In this case, secondary electrons 122 are reflected by the electron conversion electrode 141, and the electrons 160 collide with the inner wall of the electron microscope housing 149 to generate tertiary electrons 161. These electrons are pulled back into the electron microscope housing 149 by the electric field between the second electrode 143 and the electron microscope housing 149, and are not detected by the detector 110. In other words, secondary electrons that collide with the segmented electrodes of the electron conversion electrode 141 to which a positive voltage is applied are no longer detected, thereby improving the accuracy of secondary electron discrimination.

[0072] In the fourth embodiment, it is possible to perform a hybrid of the azimuth angle discrimination of the first embodiment and the elevation angle discrimination of the second embodiment, which has the effect of further improving the BT ratio.

[0073] In Example 4, the collision positions of the secondary electrons emitted from the sample onto the beam guide 146 and the electron conversion electrode 141 can also be determined from the results of electron trajectory analysis. FIG. 18A shows collision positions 307 of the secondary electrons onto the beam guide and the electron conversion electrode when 10,000 secondary electrons are emitted from the trench top. The collision positions are distributed concentrically, and the distribution of the collision positions is divided into 17 regions. From the center, there are the region where the secondary electrons collided with the beam guide 146 and the region where the secondary electrons collided with segmented electrodes 1 to 16. Meanwhile, FIG. 18B shows collision positions 308 of the secondary electrons onto the beam guide and the electron conversion electrode when 10,000 secondary electrons are emitted from the trench bottom when the trench aspect ratio is 5. The collision positions are distributed elliptically, and the major axis of the ellipse is tilted clockwise by approximately 40° from the Y axis. In this case as well, the distribution of collision positions is divided into five regions, namely, from the center, a region where collision occurred on beam guide 146, a region where collision occurred on split electrodes 2 and 6, and a region where collision occurred on split electrodes 10 and 14.

[0074] When all of the segment electrodes and the beam guide were grounded, almost all secondary electrons were detected, except for those that collided with the separation groove. Approximately 6,000 secondary electrons were detected from the trench top in Figure 18A, and approximately 500 secondary electrons were detected from the trench bottom in Figure 18B. Therefore, the BT ratio was approximately 0.08.

[0075] In contrast, when the split electrodes 2 and 6 of the electron conversion electrode 141 are grounded and a positive voltage of +50 V is applied to the split electrodes other than the split electrodes 2 and 6, secondary electrons impinging on the beam guide 146 or the split electrodes 2 and 6 are detected. Figures 19A and 19B show the positions of secondary electrons impinging on the beam guide and the split electrodes 2 and 6, extracted from Figures 18A and 18B, respectively. The number of secondary electrons counted from the trench top was approximately 800, and the number of secondary electrons counted from the trench bottom was approximately 350. Therefore, the BT ratio was approximately 0.44. Here, by applying a negative voltage to the second electrode 143 to prevent the detection of tertiary electrons generated in the electron microscope housing 149, a high BT ratio close to the ideal value can be achieved. Compared to the case of Figure 18A, the BT ratio is improved by approximately five times.

[0076] It is desirable that the voltage applied to the second electrode 143 be switchable between a negative voltage and a ground potential. As mentioned above, when a negative voltage is applied to the second electrode 143, the visibility of the trench bottom can be improved. Conversely, when the second electrode 143 is at ground potential, a bright image can be obtained for an object to be observed that has few irregularities.

[0077] Finally, an example of a screen displayed on the display 151 of the scanning electron microscope will be described with reference to Fig. 20. The screen shown in Fig. 20 displays a secondary electron image 181 when all of the electron conversion electrodes are at ground potential, and a secondary electron image 182, an indicator 183, an electron conversion electrode voltage switch 184, and the like when a positive voltage is applied to some or all of the electron conversion electrodes, as shown in Examples 1 to 4. At this time, as shown in each Example, it is desirable to control the voltages applied to the second electrode 143 (Example 4), the third electrode 144 (Examples 1 to 3), and the fifth electrode 163 (Example 3) in conjunction with the application of a positive voltage to the electron conversion electrode.

[0078] Both the secondary electron image 181 and the secondary electron image 182 are images generated based on the detection signal transmitted from the detector 110. In this case, the electron converting electrode voltage switch 184 is in the ON state, so the secondary electron image 182 when a positive voltage is applied to the electron converting electrode is a real-time image. On the other hand, the secondary electron image 181 displays an image that was previously acquired and stored.

[0079] In the secondary electron image 181, the trench top 185 is observed as bright, but the trench bottom 186 is completely dark and cannot be observed. On the other hand, in the secondary electron image 182, the trench top 185 is relatively dark, and therefore the trench bottom 186 is observed as bright. As a result, the foreign material 187 at the trench bottom can be seen. The secondary electron image 181 is an image suitable for observing the trench top, and the secondary electron image 182 is an image suitable for observing the trench bottom. Depending on the purpose of the observation, it is only necessary to switch between the images. Furthermore, by comparing the two images in this way, the sample structure can be better understood.

[0080] The above describes several embodiments of the electron microscope of the present invention. The present invention is not limited to the above embodiments, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, the components disclosed in the above embodiments can be combined as appropriate as long as no contradictions arise in the combination. Furthermore, some components can be deleted from all the components shown in the above embodiments. [Explanation of symbols]

[0081] 100...electron microscope, 101...electron gun, 102...extraction electrode, 104...anode, 105...focusing lens, 106...diaphragm, 107...adjustment knob, 108...upper deflector, 109...lower deflector, 110...detector, 111...fluorescent screen, 112...photomultiplier tube, 113...coil, 114...Wien filter, 115...electron deflector, 116...magnetic pole, 117...objective lens coil, 118...objective lens, 120...sample, 121...sample stage, 122...secondary electrons, 123...tertiary electrons, 124...power supply, 133...magnetic field, 134...electric field, 141...electron conversion electrode, 142...first electrode, 143...second electrode, 144...third electrode, 145...housing, 146...beam guide, 147...fourth electrode Pole, 148... tertiary electrons, 149... electron microscope housing, 150... control device, 151... display, 152... storage device, 153... control table, 160... backscattered electrons, 161... tertiary electrons, 162... power supply, 163... fifth electrode, 164... power supply, 181, 182... secondary electron image, 183... indicator, 184... electron conversion electrode voltage switch, 185... trench top, 186... trench bottom, 187... foreign matter, 200... trench, 201... secondary electron emission vector, 202... elevation angle, 203... azimuth angle, 204... trench bottom, 205... trench top, 210, 211... secondary electrons, 301, 302, 303, 304, 305, 306, 307, 308... collision position.

Claims

1. an electron source; an objective lens that focuses the primary electron beam emitted from the electron source onto a sample; a deflector disposed between the electron source and the objective lens, the deflector deflecting electrons using at least an electric field; a stage on which the sample is mounted; a power supply that applies a voltage to the stage to decelerate the primary electron beam; a detector for detecting electrons; a control device; the deflector comprises an electron conversion electrode disposed so as to be struck by secondary electrons emitted from the sample when irradiated with the primary electron beam; a first electrode and a second electrode disposed opposite to each other across a space through which tertiary electrons emitted when the secondary electrons emitted from the sample collide with the electron conversion electrode move in the initial stage of emission, the first electrode and the second electrode being electron-transmissible; and a third electrode disposed opposite to the first electrode with the second electrode interposed therebetween; the detector detects the tertiary electrons; the electron conversion electrode is divided into a plurality of divided electrodes radially or concentrically; The scanning electron microscope is characterized in that the control device sets the potential of the third electrode to a positive potential difference with respect to the potential of the second electrode.

2. In claim 1, A scanning electron microscope according to claim 1, wherein the potential of said third electrode is switchable between a positive potential difference with respect to the potential of said second electrode and a negative potential difference or an equipotential.

3. In claim 2, each of the plurality of divided electrodes of the electron conversion electrode is independently switchable between application of a positive voltage and application of a negative voltage or a ground potential; A scanning electron microscope characterized in that the control device switches the potential of the third electrode to a positive potential difference with respect to the potential of the second electrode when a positive voltage is applied to one or more divided electrodes of the electron conversion electrode.

4. In claim 1, the deflector includes a beam guide provided to penetrate the electron conversion electrode and through which the primary electron beam passes; 4. A scanning electron microscope according to claim 1, wherein said electron conversion electrode and said beam guide are electrically insulated from each other.

5. In claim 4, the deflector includes a fourth electrode that is disposed opposite the electron conversion electrode on the sample side and is capable of transmitting electrons; A scanning electron microscope, characterized in that the end face of the beam guide on the sample side is located closer to the sample than the fourth electrode.

6. In claim 1, the deflector includes a fifth electrode that is disposed closer to the sample than the first electrode and the second electrode and that is capable of transmitting electrons; The scanning electron microscope is characterized in that the control device applies a negative voltage to the fifth electrode.

7. In claim 1, the third electrode is a housing of an electron microscope; A scanning electron microscope, characterized in that a negative voltage is applied to the second electrode so that the potential of the third electrode has a positive potential difference with respect to the potential of the second electrode.

8. In claim 1, A scanning electron microscope characterized in that, when the plurality of segmented electrodes are radially segmented, the segmented electrodes facing each other across the radiation center are set to approximately the same potential.

9. In any one of claims 1 to 7, A scanning electron microscope, wherein the deflector is a Wien filter having a coil that generates a magnetic field that deflects electrons.

10. an electron source; an objective lens that focuses the primary electron beam emitted from the electron source onto a sample; a deflector disposed between the electron source and the objective lens, the deflector deflecting electrons using at least an electric field; a stage on which the sample is mounted; a power supply that applies a voltage to the stage to decelerate the primary electron beam; a detector for detecting electrons; a control device; the deflector comprises an electron conversion electrode disposed so as to be struck by secondary electrons emitted from the sample when irradiated with the primary electron beam; a beam guide provided to penetrate the electron conversion electrode and through which the primary electron beam passes; and a first electrode and a second electrode disposed opposite to each other across a space through which tertiary electrons, emitted when the secondary electrons emitted from the sample strike an end face of the beam guide facing the sample, move in the initial stage of their emission, and which are capable of transmitting electrons; the detector detects tertiary electrons that are emitted when secondary electrons emitted from the sample collide with the electron conversion electrode or the end face of the beam guide on the sample side and that have passed through the first electrode; the electron conversion electrode is independently switchable between application of a positive voltage and application of a negative voltage or ground potential; the deflector includes a fourth electrode that is disposed opposite the electron conversion electrode on the sample side and is capable of transmitting electrons; A scanning electron microscope, characterized in that the end face of the beam guide on the sample side is located closer to the sample than the fourth electrode.

11. A method for observing a sample using a scanning electron microscope having an electron source, an objective lens that focuses a primary electron beam emitted from the electron source on a sample, a deflector that deflects electrons using at least an electric field between the electron source and the objective lens, a stage on which the sample is mounted, a power supply that applies a voltage to the stage to decelerate the primary electron beam, a detector that detects electrons, and a control device, the deflector comprises an electron conversion electrode disposed so as to be struck by secondary electrons emitted from the sample when irradiated with the primary electron beam; a first electrode and a second electrode disposed opposite each other across a space through which tertiary electrons emitted when the secondary electrons emitted from the sample collide with the electron conversion electrode move in the initial stage of emission, the first electrode and the second electrode being electron-transmittable; and a third electrode disposed opposite the first electrode across the second electrode, the detector detects the tertiary electrons; the electron conversion electrode is divided into a plurality of divided electrodes radially or concentrically; The sample observation method is characterized in that the control device sets the potential of the third electrode to a positive potential difference with respect to the potential of the second electrode.

12. In claim 11, the potential of the third electrode is switchable between a positive potential difference and a negative potential difference or equipotential with respect to the potential of the second electrode; each of the plurality of divided electrodes of the electron conversion electrode is independently switchable between application of a positive voltage and application of a negative voltage or a ground potential; A sample observation method characterized in that the control device switches the potential of the third electrode to have a positive potential difference with respect to the potential of the second electrode when applying a positive voltage to one or more divided electrodes of the electron conversion electrode.

Images