JP5953314B2 - Scanning electron microscope - Google Patents

Description

  The present invention relates to a charged particle beam apparatus using a charged particle beam such as an electron beam or an ion beam, and in particular, forms an image of a beam irradiated on a sample, captures secondary electrons and reflected electrons generated from the sample, and captures an image. Belongs to forming technology.

  As a conventional technique, as a method for detecting secondary electrons in a high vacuum, Japanese Patent Application Laid-Open No. 7-192679 discloses that secondary electrons are wound up in an objective lens and an energy separator (E × B) based on the Wien principle is used. The detection method used is described. This is effective for an objective lens of a type that leaks a magnetic field to the sample side like a snorkel objective lens. The feature of the snorkel type objective lens is that observation with a short focal length enables high resolution observation with very small spherical aberration coefficient and chromatic aberration coefficient. Secondary electrons are rolled up by the leaked magnetic field, and the above detection Secondary electrons can be detected with high efficiency by this method.

  The image obtained by combining this snorkel type objective lens and highly efficient secondary electron detection provides an image with very high resolution and excellent information content, but according to the evaluation results, the leakage magnetic field from the objective lens The yield of secondary electrons increases as the intensity of the light increases. On the other hand, it is confirmed that the electron trajectory to be detected changes greatly due to the influence of a strong magnetic field, and then changes the image quality.

  On the other hand, the out-lens objective lens is designed to suppress the leakage magnetic field on the sample as much as possible, and the image is observed with a secondary electron detector or a semiconductor backscattered electron detector installed in the vicinity of the sample. Since the leakage magnetic field of the objective lens does not affect the trajectory of electrons to be detected, the change in image quality due to the above condition change does not occur.

  These two types of characteristics classified according to the objective lens shape are points for selecting a device together with the user's observation purpose, the type of image to be obtained, the resolution, the purchase cost of the device, and the like.

JP-A-7-192679

  First, the advantages and disadvantages of the snorkel type objective lens and the out lens type objective lens are summarized below.

  The advantages of the snorkel type objective lens are that the resolution is improved because each aberration coefficient is reduced due to the extremely short focal point, the detection efficiency is almost 100% due to the secondary electron winding effect by the magnetic field, and the effect of retarding is expected What can be done. On the other hand, the disadvantage is that when the excitation current increases, the coil temperature rises and cooling is essential, and because the magnetic flux in the magnetic pole increases, permendur is often used as the material, but permendur is difficult to process and assemble. The material itself is expensive, and the reflected electrons are affected by the magnetic field, so that the image quality changes, which causes a large error factor in crystal orientation analysis.

  The snorkel type objective lens is extremely powerful for high resolution / high efficiency signal detection. On the other hand, depending on the application, the snorkel type objective lens has drawbacks in the reflected electron image and analysis performance, and the cost merit has been lost due to its configuration.

  On the other hand, the advantage of the out-lens objective lens is that secondary electrons are efficiently detected by the secondary electron detector fixed to the sample chamber, and reflected electrons are not affected by this magnetic field. The point is the smallest, the coil current is small and the temperature rise is small, so pure iron or free-cutting pure iron can be selected as the material, and it can be designed at a low cost. And the tilt performance is good. On the other hand, the disadvantage is that the aberration is larger than that of the snorkel type objective lens, and the secondary electron detector fixed to the sample chamber is used on the outer periphery of the objective lens. One point is that the loss of detection is large.

  As described above, the out-lens objective lens is a general lens as a highly versatile lens. However, due to this aberration and secondary electron detection efficiency, the objective lens is compared with the case where the snorkel objective lens is used. The improvement in image quality and resolution that can be expected by the improvement in performance is limited.

  Therefore, the overall optimum form of the objective lens is a configuration in which the advantages of the snorkel type objective lens and the out-lens type objective lens are compatible and the disadvantages of both are minimized.

  A scanning electron microscope in which secondary electrons generated from a sample are wound up in an objective lens by a magnetic field generated by the objective lens, the electrons are detected by a secondary electron detector, and reflected electrons are emitted from the sample. The objective lens shape is such that a magnetic field having a strength that can reach the backscattered electron detector while the emission direction is maintained is generated in the space between the sample and the objective lens.

  Further, a low vacuum (environmental) type scanning electron that can be divided into a high vacuum in the electron beam passage and a low vacuum in the sample chamber in which the sample is arranged by arranging an orifice for differential exhaust in the vicinity of the main surface of the objective lens. Use a microscope.

  With the image quality and structural advantages of the snorkel objective lens and out-lens objective lens, as a result of achieving both performances, not only high-resolution and high-yield secondary electron image observation, Reflected electron image observation and low-vacuum observation independent of conditions are possible.

1 is an overall configuration example of an apparatus according to an embodiment of the present invention. It is an example of an axial magnetic field intensity by the difference in the kind of objective lens. As an embodiment of the present invention, there is an arrangement example of an objective lens shape and a semiconductor backscattered electron detector. This is an example of simulating on-axis leakage magnetic field and reflected electron trajectory. It is the figure which showed the positional relationship of the backscattered electron track | orbit and semiconductor backscattered electron detector detection element when WD was changed, and the relationship of the image quality obtained. It is a conceptual diagram which shows the difference in the image quality depending on the outgoing angle of reflected electrons.

  Below, the typical Example of this invention is described using figures. Although a general-purpose scanning electron microscope will be described below, the present invention is not limited to this, and is applicable to other charged particle beam apparatuses that generate signals by detecting signals generated by irradiation of charged particle beams. Is possible.

  FIG. 1 shows a schematic diagram of the entire electron optical system, and FIG. 2 shows a magnetic field curve on the objective lens axis.

  FIG. 1 shows an overall configuration based on an electron optical system including the objective lens 7 of the present embodiment. On the observation screen or monitor (display unit: 15), display means for displaying the formed image, and information input means for inputting information necessary for operating the apparatus to the GUI displayed on the display means Etc. It should be noted that each component of the electron optical system, for example, the acceleration voltage of the primary electron beam 18 and the current / voltage applied to each electrode are automatically or the user inputs desired values on the observation screen or monitor, and the observation conditions It is adjusted by the control unit.

  The electron source 1 provided in the scanning electron microscope generally irradiates a primary electron beam 18 of 0.3 kV to 30 kV. The multiple-stage lenses (first condenser lens: 2, second condenser lens 3) are controlled under conditions suitable for observation, and have the effect of converging the primary electron beam 18. Similarly, the objective lens 7 of the present embodiment also has an effect of converging the primary electron beam 18 and forms an image on the sample 8 to be observed and forms a focal point suitable for observation. The deflector 4 scans the irradiation position of the primary electron beam 18 on the sample 8 according to a desired observation visual field range. Further, it is assumed that the scanning speed can be varied by the deflection signal control unit 26 that controls the deflector 4. As the primary electron beam 18 is irradiated, the secondary electrons 10 and the reflected electrons 26 are emitted from the sample.

  In the case of a high vacuum, generally, the focused primary electron beam 18 is scanned over the sample 8, and the secondary electrons 10 generated from the sample 8 are generated from a snorkel type objective lens that oozes out in the sample direction. The lens is wound up by a lens magnetic field 11 and accelerated to several hundred volts by an electrode provided in the lens. Thereafter, the secondary electrons are separated by the energy separator (E × B) 5 into the primary electron beam 18 and the secondary electrons 10 wound up from the sample 8 by the lens magnetic field 11. The secondary electron detector (fixed lens) 6 has an electrode 20 applied at about 10 kV. Secondary electrons are taken into the detector by an electric field generated by the electrode, and the display unit 15 passes through the secondary electron detector amplifier 14. With this, an image is formed. At this time, the secondary electrons 10 generated from the sample 8 are detected by a secondary electron detector for high vacuum in the objective lens. The secondary electron detector (fixed lens) 6 is called an Everhart Thornley type detector and detects a secondary electron 10 with a detector composed of a scintillator and a photomultiplier tube, and +10 kV20 is applied in the vicinity of the scintillator. In addition to this detector, a secondary electron detector (sample chamber fixed) 27 attached to the sample chamber is also provided, which is an Everhart Thornley type detector like the secondary electron detector (lens fixed) 6. At this time, in order to increase the collection efficiency of the secondary electrons 10, typically, a potential gradient is supplied into the sample chamber 23 by the secondary electron collector electrode 28 to which +300 V is applied.

  The electron optical system is not limited to that described above. For example, in order to capture the reflected electrons close to the optical axis 35 in the energy separator (E × B) 5, the reflected electrons near or inside the energy separator. A detector 19 or a reflection electron reflecting plate may be incorporated.

  In the case of a low vacuum, the degree of vacuum inside the sample chamber 23 is controlled by closing and opening the needle valve 16 at the air inlet to the sample chamber 23. This low-vacuum SEM has a high-vacuum observation mode in addition to the low-vacuum observation mode. When observing at a high vacuum, the needle valve 27 is closed and the inside of the sample chamber 23 is 10 −3 Pa or less. Keep in high vacuum.

  The backscattered electrons 26 are detected by a backscattered electron detector 19 installed immediately below the objective lens 7. As the backscattered electron detector 19, a detector such as a semiconductor detector, a microchannel plate, or YAG is used. When a semiconductor detector is used, backscattered electron detection can be performed even in an observation mode at a low vacuum described later. Hereinafter, it is assumed that the backscattered electron detector 19 is a semiconductor detector.

  The detected secondary electron and reflected electron-induced signals are electrically amplified and then A / D converted by the control unit and displayed on the display unit 15 in synchronization with the scanning of the primary electron beam 18. Thereby, the SEM image of the observation visual field range is obtained.

  During observation in a low vacuum, the inside of the sample chamber 23 is kept at a constant gas pressure by closing and opening the needle valve 16. Further, the potential of the secondary electron collector electrode 28 is switched to the ground potential. The gas pressure inside a typical sample chamber is 1 to 300 Pa, but can be controlled up to 3000 Pa in special cases. However, in order to realize low-vacuum observation, it is necessary to keep the electron gun chamber at 10-2 to 10-4 while keeping the sample chamber at a low vacuum (1 Pa to about 3000 Pa). Therefore, the pressure inside the tube must be different from the pressure in the sample chamber. When a snorkel-type objective lens that leaks a magnetic field to the sample side and winds up secondary electrons in the objective lens is used, depending on the position of the diaphragm (a diaphragm for differential exhaust), the secondary electrons may not be wound up, and the secondary electron There is a risk of reducing the detection efficiency of electrons.

  Therefore, the optimum position of the vacuum differential exhaust diaphragm is the main surface position of the objective lens. Scattering of the primary electron beam traveling in the low vacuum region is reduced as the sample is closer to the observation target, and a higher resolution image can be obtained.

  Here, typical characteristics of the shape of the objective lens of the present embodiment will be described. This embodiment mainly focuses on the on-axis magnetic field generated by the objective lens, and considers the influence on the secondary electrons or reflected electrons, thereby making the performance of the snorkel objective lens and the out lens objective lens compatible. I am trying. The on-axis magnetic field curve shown in FIG. 2 is representative, and each of the snorkel objective lens axial magnetic field curve 29, the out-lens objective lens axial magnetic field curve 30, and the objective lens axial magnetic field curve 31 of the present embodiment. Is shown.

  Here, the relationship between the shape of each of the snorkel type, the out lens type, and the lens of this embodiment and the generated on-axis magnetic field will be described with reference to FIG. These are distinguished by the positional relationship between the inner magnetic path and the outer magnetic path shown in the lens shape shown in FIG. In general, when the inner magnetic path protrudes toward the sample side, the objective lens principal surface 25, that is, the position where the on-axis magnetic field strength is strongest is Z as shown in the snorkel type objective lens on-axis magnetic field curve 29 in FIG. Located on the plus side (sample side) of the axis coordinate 0mm. On the other hand, in an out-lens objective lens in which the outer magnetic path is closer to the sample side than the inner magnetic path, the objective lens main surface 25 (the position where the on-axis magnetic field is strongest) is on the negative side of the Z-axis coordinate 0 mm (objective lens). Located on the inner side.

  The fact that the position of the objective lens main surface 25 of the snorkel type objective lens approaches the sample means that the focal length from the objective lens main surface 25 is shortened (short focal length), and each aberration can be reduced. Become a lens. On the other hand, in the case of an out-lens objective lens, since the sample cannot be placed above the position of the outer magnetic path, the distance from the objective lens main surface 25 to the sample is limited, and the short focus is limited. High resolution is also limited.

  As one of the features of the objective lens shape of the present embodiment, the inner magnetic path and the outer magnetic path are positioned between the lens main surface position of the snorkel type objective lens and the lens main surface position of the out lens type objective lens. And the shape is optimized. The important point here is to arrange the inner magnetic path and the outer magnetic path so that the Z axis coordinate near 0 mm is the maximum axial magnetic field.

  The reason is that if the inner magnetic path and the outer magnetic path are arranged so that the Z-axis coordinate 0 mm is on the plus side (sample side) as described above, it becomes a snorkel type objective lens that is a high resolution lens, which is advantageous for resolution observation. However, as shown in the snorkel type on-axis magnetic field curve 29 of FIG. 2, a strong magnetic field approaches the sample, and the reflected electron trajectory generated from the sample is changed under the influence of the strong magnetic field, and the condition ( Depending on the reflected electron emission angle from the sample, the reflected electron trajectory becomes undetectable. In this case, the backscattered electron detector 19 is disposed at the position shown in FIG.

  Therefore, the situation where there are reflected electrons that cannot be detected due to the influence of the magnetic field intensity on the sample is different from the intention of this embodiment.

  On the other hand, when the inner magnetic path and the outer magnetic path are arranged so that the Z-axis coordinate 0 mm is on the minus side (inside the objective lens), the above-described out-lens objective lens is obtained. The out-lens objective lens has a small magnetic field intensity on the sample and does not affect the reflected electron trajectory, so it is in line with the intention of this example, but there is a limit to the focal length from the lens main surface position to the sample. The present invention cannot be achieved in that the resolution is limited.

  For the above reasons, the inner magnetic path and the outer magnetic path are arranged so that the Z axis coordinate near 0 mm is the maximum on-axis magnetic field so that the objective-axis on-axis magnetic field curve 31 of this embodiment shown in FIG. 2 is obtained. Is important.

  Details are described in Examples 2, 3, and 4.

  The ideal on-axis magnetic field is the objective lens magnetic field curve 31 of the present embodiment shown in FIG. 2, but when used in a scanning electron microscope, the magnetic field strength on the observation sample, secondary electrons or reflected electrons The four items of the orbit (the leakage magnetic field strength of the objective lens and the electric field strength due to the lifting electrode), typically the reduction of spherical aberration and chromatic aberration, and the arrangement of the working diaphragm during low-vacuum observation are important points of the invention. In principle, it is advantageous in terms of resolution that the Z-axis coordinate of the peak is large as in the case of the snorkel-type objective lens axial magnetic field curve 29. However, as described above, the snorkel-type objective lens also has drawbacks. The shape of the objective lens is designed so that the objective lens of the example has an intermediate magnetic field characteristic between the snorkel type objective lens and the out lens type objective lens. A magnetic field simulation is used for the design.

  The present embodiment relates to disposing the semiconductor backscattered electron detector 19 on the lower surface of the objective lens 7 in the scanning electron microscope having the configuration of the first embodiment.

  FIG. 3 shows the shape of the objective lens and the shape and arrangement of the semiconductor backscattered electron detector. FIG. 4 shows a simulation result regarding the on-axis magnetic field from the semiconductor backscattered electron detector to the sample to be observed and the backscattered electron trajectory. In the upper graph of FIG. 4, the horizontal axis indicates the Z-axis coordinate (Z-axis coordinate 0 indicates WD = 0 mm, Z-axis coordinate 5.0 mm indicates WD = 5 mm), and the vertical axis indicates the on-axis magnetic field (Gauss ). The lower diagram of FIG. 4 shows a reflected electron trajectory in which only one side of the axisymmetric axis is displayed with the optical axis as the center, and the on-axis magnetic field is varied at the sample position with the Z-axis coordinate of 5.0 mm (WD = 5 mm). It is a simulation result.

  The most important points in this embodiment are “finding the maximum on-axis magnetic field strength of the objective lens that does not affect the trajectory of the reflected electrons generated from the sample” and “the objective capable of generating the on-axis magnetic field strength”. “Minimize spherical aberration coefficient and chromatic aberration coefficient with lens shape”.

  Here, the simulation result shown in FIG. 4 will be described. As a condition, a default objective lens shape is used, and the axial magnetic field strength is plotted while increasing the amount of current flowing through the exciting coil. Thereafter, based on the axial magnetic field strength between the semiconductor backscattered electron detector (BSED) and the sample, the reflected electron trajectory was calculated for each magnetic field strength. As for acceleration voltage, all assumed 30 kV. Therefore, the energy of the primary electron beam and the energy of the reflected electrons generated from the sample are also 30 kV. From this result, the reflected electrons travel straight in the space of about 700 Gauss on the sample and further about 1,500 Gauss at the position of the semiconductor backscattered electron detector, and reach the backscattered electron detecting element without being affected by the magnetic field. I understood it.

Therefore, the specification of the objective lens is as follows.
1. Shape: An objective lens shape (acceleration voltage 30 kV) that generates an on-axis magnetic field that is 700 Gauss or less on the sample and 1,500 Gauss or less at the position of the semiconductor backscattered electron detector.
2. ExB (Wien filter) is mounted in the objective lens and can be used as the main detector during high-resolution observation under high vacuum.
3. A configuration in which the semiconductor backscattered electron detector can be placed on the lower surface of the objective lens.

In this embodiment, the following effects are expected.
1. There is no influence on the trajectory of reflected electrons due to the leakage magnetic field of the objective lens, and there is no change in image quality due to a change in conditions (for example, a change in the WD working distance).
2. Similar to a conventional snorkel type objective lens, a high-resolution and high-resolution image using E × B (Wien filter) can be obtained.
3. Since the lens main surface position moves to the sample side with respect to the out-lens objective lens, the aberration can be reduced and the differential diaphragm (orifice) at the time of low vacuum can be arranged close to the sample. As a result, high-resolution image quality can be improved regardless of whether the vacuum is high or low.

  Based on the simulation of the reflected electron trajectory described above, the objective is used until the objective lens shape is such that the reflected electron reaches the reflected electron detector without being affected by the magnetic field and generates the maximum value of the magnetic field (limit axial magnetic field). The simulation of the magnetic field generated by the objective lens and the reflected electron trajectory is repeated while changing the shape of the lens. As a result, the objective lens finally has a shape that generates a magnetic field such that the reflected electrons generated from the sample reach the reflected electron detector while maintaining the same direction, for example, as shown in FIG. . In other words, by using the objective lens obtained in this way, the backscattered electron detector can be maintained in the space immediately after generation from the sample in the space between the backscattered electron detector and the sample provided under the objective lens. With strength, a leakage magnetic field from the objective lens can be formed.

  Here, FIG. 5 and FIG. 6 show the causes that are considered to be images in which the difference in images when the conditions are changed (for example, the WD working distance is changed).

  The image in FIG. 5 is an image taken with a snorkel type objective lens, and shows a diagram schematically representing the reflected electron trajectory at that time and a corresponding real image. These features are that the composition image approaches the longer the working distance (WD) of the objective lens. When the WD is short, the shape information of the material becomes prominent close to the secondary electron image, but as the WD is gradually lengthened, the stereoscopic effect decreases and the composition information becomes prominent.

  The actual image clearly shows the difference in image quality due to the difference in the trajectory of the reflected electrons between the condition where the WD having the strongest magnetic field effect of the objective lens is short and the condition where the WD having a small magnetic field effect is long. .

  Thus, it is a problem that the image quality is changed by the change of WD. Here, if the objective lens having a shape determined based on the trajectory of the reflected electrons as described above is used, the trajectory of the reflected electrons does not bend, so that an image with a constant image quality can be obtained even if the WD is changed. it can.

  In FIG. 6, the detection element of the detector and the emission angle of the reflected electrons were also considered. When the WD is short, it is considered that many reflected electrons that reach the detection element are shallow angles. Normally, the reflected electrons are elastically scattered, but when reflected electrons with a shallow angle are taken in by the sample shape, a three-dimensional image is obtained. In particular, reflected electrons in the vicinity of the optical axis (reflected electrons generated perpendicularly to the surface of the sample) pass through the hole of the detection element, so that the reflected electrons with three-dimensional information form an image and the composition information is reduced. I think.

  On the other hand, in the case of the long WD, the excitation of the objective lens may be weak, and as the WD becomes longer, the reflected electrons near the optical axis reach the detection element and the composition information increases.

  As described above, according to the present invention, the influence of the leakage magnetic field of the objective lens on the trajectory of the reflected electrons is reduced, and the image quality change due to the change of the working distance of the objective lens is reduced. Further, similarly to the snorkel type objective lens, it is possible to obtain a high-resolution image with high yield using E × B (Wien filter). Further, since the lens main surface position moves to the sample side with respect to the out-lens objective lens, the aberration of the objective lens can be suppressed. In addition, a low-vacuum differential aperture (orifice) can be placed close to the sample, creating an environment that is not affected by the scattering of the primary electron beam, enabling high-resolution observation regardless of high or low vacuum. .

  In the present embodiment, in the scanning electron microscope having the configuration of the first embodiment, the backscattered electron detector 19 or the reflecting plate provided to obtain backscattered electron information above the objective lens main surface 25, that is, inside the objective lens. It is related with the method of arrange | positioning etc. and acquiring an image.

  The reflected electron trajectory simulation diagram shown in FIG. 4 (FIG. 4: WD 5 mm leakage magnetic field comparison diagram) is a reflection of various emission angles generated from the sample when the reflected electron detector 19 is arranged on the lower surface of the objective lens 7. It is a diagram showing that electrons reach the backscattered electron detector 19. Here, paying attention to the reflected electron trajectory near the optical axis 35, it can be seen that the reflected electrons generated near the optical axis go in the internal direction (upward) of the objective lens 7. In order to capture these backscattered electrons, a backscattered electron detector 19 or a reflector provided to obtain backscattered electron information may be arranged near the energy separator (ExB) shown in FIG. In order to capture many electrons in the vicinity of the optical axis 35, it is also effective to widen the opening of the inner magnetic path.

  The present example relates to the scanning electron microscope having the configuration of the first example, which is superior to the snorkel type objective lens in the driving power supply and operating conditions of the objective lens.

  As described in Example 1, the snorkel type objective lens generates an on-axis magnetic field such as the snorkel type objective lens on-axis magnetic field curve 29 in FIG. 2, and the magnetic field strength is also described in Examples 1 to 3. Stronger than that of objective lenses and out-lens objective lenses. In this type of lens, a large driving voltage and exciting current are required, and the heat generation of the coil also increases, so a device such as coil cooling is indispensable. On the other hand, an out-lens objective lens can be operated with a small drive voltage and excitation current, and does not require a device such as coil cooling.

  In the case of the objective lens described in Examples 1 to 3, since the generated on-axis magnetic field is intermediate between the snorkel objective lens and the out-lens objective lens, it is necessary to examine the drive voltage, excitation current, and coil heat generation. However, in a lens shape that can sufficiently achieve the object of the present invention, it can be considered in the same way as an out-lens objective lens, it can be operated with a relatively small driving voltage and excitation current, and coil cooling is not necessary. , Know by simulation.

Therefore, in addition to high resolution (short focus) and efficient backscattered electron detection, it is possible to realize power saving and current operation.

1 Electron Source 2 First Condenser Lens 3 Second Condenser Lens 4 Deflection Coil 5 Energy Separator (E × B)
6, 27 Secondary electron detector 7 Objective lens 8 Sample stage 9 First differential aperture 10 Secondary electron and secondary electron trajectory 11 Objective lens magnetic field range 12 Exhaust system 13 Electron gun exhaust pipe 14 Secondary electron detector amplifier 15 Display unit 16 Needle valve 17 Electron gun 18 Primary electron beam 19 Reflected electron detector 20 Secondary electron detector electrode (+10 kV)
21 First rotary pump (for low vacuum)
22 Second rotary pump (for exhaust system back pressure exhaust)
23 Sample chamber 24 Ground electrode 25 of secondary electron detector Objective lens main surface 26 Reflected electron and reflected electron trajectory 28 Secondary electron collector electrode 29 Snorkel type objective lens on-axis magnetic field curve 30 Out lens type objective lens on-axis magnetic field curve 31 On-axis magnetic field curve 32 of the present invention 32 WD working distance 33 Reflected electron image 34 when WD is short Reflected electron image 35 when WD is long Optical axis

Claims (4)

A charged particle source;
A charged particle optical system that includes an objective lens and focuses a primary charged particle beam emitted from the charged particle source and scans it on the sample;
A secondary electron detector for detecting secondary electrons generated from the sample wound in the objective lens by a magnetic field generated by the objective lens;
A backscattered electron detector that is installed below the objective lens and detects backscattered electrons generated from the sample by irradiation of the primary charged particle beam;
A control unit for controlling the plurality of lenses,
A scanning electron microscope that acquires an image of the sample using signals of the secondary electron detector and the backscattered electron detector,
In the objective lens, an inner magnetic path and an outer magnetic path are arranged so that the vicinity of a position corresponding to a working distance of 0 mm is a maximum on-axis magnetic field, and the reflected electrons remain in the emission direction from the sample. By generating a magnetic field that can reach the detector in the space between the sample and the objective lens, secondary electrons generated from the sample are wound up in the objective lens, and reflected electrons generated from the sample are generated. A scanning electron microscope characterized in that the scanning electron microscope is made to reach the backscattered electron detector installed below the objective lens while maintaining the emission direction from the sample. The scanning electron microscope according to claim 1,
An orifice for differential exhaust is disposed in the vicinity of the main surface of the objective lens,
A scanning electron microscope characterized in that a passage of the electron beam is divided into a high vacuum and a sample chamber in which a sample is arranged is divided into a low vacuum. The scanning electron microscope according to claim 1,
A scanning electron microscope comprising an E × B deflector installed in the objective lens. The scanning electron microscope according to any one of claims 1 to 3 ,
The leakage magnetic field from the objective lens in the space from the sample to the lower surface of the objective lens is variable according to the energy of the reflected electrons, and the reflected electrons generated from the sample with respect to the leakage magnetic field from the objective lens A scanning electron microscope characterized by having an objective lens shape optimized under conditions that do not affect the trajectory.

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