Scanning transmission electron microscope and aperture alignment method

Abstract

To provide a scanning transmission electron microscope in which the position of an aperture can be easily adjusted.SOLUTION: A scanning transmission electron microscope according to the present invention includes an electron source that generates an electron beam, an optical system having a focusing lens, an aperture, and an objective lens that focuses the electron beam generated by the electron source to form an electron probe, and a control unit that controls the electron source and the optical system, and the optical system is in a state in which an image does not move at the center of a Ronchigram even when an acceleration voltage for accelerating the electron beam is varied, and the control unit performs the following processes: inserting the aperture into the path of the electron beam; acquiring a first STEM image with the acceleration voltage set to a first voltage value while the aperture is inserted; acquiring a second STEM image with the acceleration voltage set to a second voltage value different from the first voltage value while the aperture is inserted; and moving the aperture based on the positional deviation between the first STEM image and the second STEM image.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a scanning transmission electron microscope and a method for aligning an aperture. [Background technology]

[0002] A scanning transmission electron microscope (STEM) is a device that focuses an electron beam generated by an electron source to form an electron probe, scans a sample with the electron probe, and detects the electrons that have passed through the sample to obtain a scanning transmission electron microscope image (STEM image).

[0003] In scanning transmission electron microscopes, a Ronchigram is used to adjust the optical system, such as for axial adjustment and aberration correction. A Ronchigram is a projection image (figure) of a sample that is created on the diffraction plane when an electron beam is focused near the sample in a scanning transmission electron microscope.

[0004] In a scanning transmission electron microscope, the center of the aperture of the illumination system is aligned with the center of the Ronchigram in order to reduce the aberration of the illumination system. Such an aperture alignment method is disclosed in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-176143 Summary of the Invention [Problem to be solved by the invention]

[0006] In the aperture alignment method disclosed in Patent Document 1, a Ronchigram is formed using an amorphous region of the sample, and the aperture is moved while checking the Ronchigram to align the center of the aperture with the center of the Ronchigram. In the aperture alignment method disclosed in Patent Document 1, a Ronchigram must be formed in an amorphous region of the sample each time an aperture is inserted and aligned. [Means for solving the problem]

[0007] One aspect of the scanning transmission electron microscope according to the present invention is an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; a control unit that controls the electron source and the optical system; Including, The optical system is in a state where the image does not move at the center of the Ronchigram even when the acceleration voltage for accelerating the electron beam is changed, The control unit inserting the aperture into the path of the electron beam; acquiring a first STEM image with the aperture inserted and the acceleration voltage set to a first voltage value; acquiring a second STEM image by setting the acceleration voltage to a second voltage value different from the first voltage value while the aperture is inserted; moving the aperture based on a positional deviation between the first STEM image and the second STEM image; Do the following.

[0008] In this type of scanning transmission electron microscope, the center of the aperture can be aligned with the center of the Ronchigram using the first and second STEM images, eliminating the need to check the Ronchigram each time the aperture is aligned. Therefore, aperture alignment can be easily performed in this type of scanning transmission electron microscope.

[0009] One aspect of the scanning transmission electron microscope according to the present invention is an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; a control unit that controls the optical system; Including, The optical system is in a state where an image does not move at the center of the Ronchigram even when the excitation current of the objective lens is changed, The control unit inserting the aperture into the path of the electron beam; acquiring a first STEM image with the aperture inserted and the excitation current set to a first current value; acquiring a second STEM image by setting the excitation current to a second current value different from the first current value while the aperture is inserted; moving the aperture based on a positional deviation between the first STEM image and the second STEM image; Do the following.

[0010] In this type of scanning transmission electron microscope, the center of the aperture can be aligned with the center of the Ronchigram using the first and second STEM images, eliminating the need to check the Ronchigram each time the aperture is aligned. Therefore, aperture alignment can be easily performed in this type of scanning transmission electron microscope.

[0011] The aperture alignment method according to the present invention includes the steps of: an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; A method for aligning the aperture in a scanning transmission electron microscope, comprising: inserting the aperture into the path of the electron beam in a state in which the image at the center of the Ronchigram does not move even when the acceleration voltage for accelerating the electron beam by the optical system is changed; acquiring a first STEM image with the aperture inserted and the acceleration voltage set to a first voltage value; acquiring a second STEM image while the aperture is inserted and the acceleration voltage is set to a second voltage value different from the first voltage value; moving the aperture based on a positional shift between the first STEM image and the second STEM image; Includes.

[0012] With this aperture alignment method, the center of the aperture can be aligned with the center of the Ronchigram using the first and second STEM images, eliminating the need to check the Ronchigram each time the aperture is aligned. Therefore, with this aperture alignment method, the center of the aperture can be easily aligned with the center of the Ronchigram.

[0013] The aperture alignment method according to the present invention includes the steps of: an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; A method for aligning the aperture in a scanning transmission electron microscope, comprising: inserting the aperture into the path of the electron beam in a state in which the image at the center of the Ronchigram does not move even when the optical system varies the excitation current of the objective lens; acquiring a first STEM image with the aperture inserted and the excitation current set to a first current value; acquiring a second STEM image while the aperture is inserted and the excitation current is set to a second current value different from the first current value; moving the aperture based on a positional shift between the first STEM image and the second STEM image; Includes.

[0014] With this aperture alignment method, the center of the aperture can be aligned with the center of the Ronchigram using the first and second STEM images, eliminating the need to check the Ronchigram each time the aperture is aligned. Therefore, with this aperture alignment method, the center of the aperture can be easily aligned with the center of the Ronchigram. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a scanning transmission electron microscope according to a first embodiment. [Figure 2] This is a diagram showing the state in which an aperture is inserted so that the center of the aperture coincides with the optical axis of the illumination system, when the optical axis of the illumination system is aligned with the center of the Ronchigram. [Figure 3] FIG. 10 is a diagram showing the state in which an aperture is inserted so that the center of the aperture coincides with the optical axis of the illumination system when the optical axis of the illumination system is shifted from the center of the Ronchigram. [Figure 4] 10 is a flowchart showing an example of a method for aligning an aperture. [Figure 5] Ronchigrams taken before and after changing the accelerating voltage, with the optical axis of the illumination system aligned with the center of the Ronchigram. [Figure 6] Ronchigrams taken before and after changing the accelerating voltage, with the optical axis of the illumination system offset from the center of the Ronchigram. [Figure 7] STEM images taken before and after changing the accelerating voltage, with the center of the aperture aligned with the center of the Ronchigram. [Figure 8] STEM images taken before and after changing the accelerating voltage when the aperture center was shifted from the center of the Ronchigram. [Figure 9]A diagram showing the state when the center of the aperture is aligned with the center of the Ronchigram. [Figure 10] A diagram showing the state where the center of the aperture is offset from the center of the Ronchigram. [Figure 11] 10 is a flowchart showing an example of an aperture alignment process performed by a control unit. [Figure 12] 10 is a flowchart showing an example of a method for aligning an aperture. [Figure 13] 10 is a flowchart showing an example of an aperture alignment process performed by a control unit. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

[0017] 1. First embodiment 1.1. Scanning Transmission Electron Microscope First, a scanning transmission electron microscope according to a first embodiment will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of a scanning transmission electron microscope 100 according to the first embodiment.

[0018] The scanning transmission electron microscope 100 is an apparatus for acquiring a scanning transmission electron microscope image (hereinafter also referred to as a "STEM image") by scanning a sample S with an electron probe and detecting electrons transmitted through the sample S. The scanning transmission electron microscope 100 is equipped with a STEM mode for acquiring a STEM image and a TEM mode for acquiring a transmission electron microscope image (hereinafter also referred to as a "TEM image").

[0019] As shown in FIG. 1, the scanning transmission electron microscope 100 includes an electron source 10, an optical system 20, a sample stage 30, a sample holder 32, a detector 40, and a control unit 50.

[0020] The electron source 10 generates an electron beam. The electron source 10 is, for example, an electron gun that accelerates electrons emitted from a cathode by an anode to emit an electron beam. The electron beam generated by the electron source 10 is accelerated by a predetermined acceleration voltage. The acceleration voltage is a voltage for accelerating the electron beam generated by the electron source 10 and irradiated onto the sample S. The acceleration voltage is controlled by the control unit 50.

[0021] The optical system 20 includes an irradiation system 20a and an imaging system 20b. The irradiation system 20a is an optical system for irradiating the sample S with the electron beam emitted from the electron source 10. The irradiation system 20a focuses the electron beam emitted from the electron source 10 to form an electron probe, and the sample S can be scanned with the electron probe.

[0022] The illumination system 20a includes a focusing lens 21, an aperture 22, a scanning deflector 24, and an objective lens 26. The focusing lens 21 focuses the electron beam emitted from the electron source 10. The focusing lens 21, together with the objective lens 26, focuses the electron beam to form an electron probe.

[0023] The aperture 22 is incorporated into the irradiation system 20a. In order to reduce the aberration of the irradiation system 20a, the aperture 22 cuts off unnecessary electrons that are far from the optical axis of the irradiation system 20a and passes only electron beams that are near the optical axis. The aperture 22 is, for example, a metal plate with a circular opening formed therein to allow the electron beams to pass. The aperture 22 is, for example, disposed within the focusing lens 21, i.e., in the magnetic field that functions as the focusing lens 21.

[0024] The scanning transmission electron microscope 100 has a movement mechanism 23 that moves the aperture 22. The movement mechanism 23 moves the aperture 22 in a plane perpendicular to the optical axis of the illumination system 20a. By moving the aperture 22 with the movement mechanism 23, the aperture 22 can be inserted into or removed from the path of the electron beam.

[0025] The scanning deflector 24 two-dimensionally deflects the electron beam emitted from the electron source 10. By deflecting the electron beam with the scanning deflector 24, the sample S can be scanned with the electron probe.

[0026] The objective lens 26 forms a TEM image in TEM mode, and focuses the electron beam to form an electron probe in STEM mode. The objective lens 26 creates a forward magnetic field in front of the sample S (the focusing lens 21 side) and a backward magnetic field behind the sample S (the intermediate lens 27 side). An electron diffraction pattern, a Ronchigram, etc. are formed on the back focal plane of the objective lens 26.

[0027] The scanning transmission electron microscope 100 does not include an aberration corrector for correcting the spherical aberration of the illumination system 20a, and therefore the scanning transmission electron microscope 100 cannot correct the spherical aberration of the illumination system 20a.

[0028] It should be noted that the illumination system 20a may include optical elements other than the focusing lens 21, the aperture 22, the scanning deflector 24, and the objective lens 26, such as lenses, apertures, deflectors, and the like.

[0029] The sample stage 30 holds a sample holder 32 that supports the sample S. The sample stage 30 is equipped with, for example, a movement mechanism that moves the sample S.

[0030] The imaging system 20b guides the electron beam that has passed through the sample S to the detector 40. The imaging system 20b includes an objective lens 26, an intermediate lens 27, and a projection lens 28. The intermediate lens 27 adjusts the excitation current to change the focal length, thereby focusing the diffraction pattern or TEM image produced by the objective lens 26, magnifying it, and forming an image of it on the object plane of the projection lens 28. The projection lens 28 further magnifies the image magnified by the intermediate lens 27 and forms an image of it on the detector 40.

[0031] The imaging system 20b may include optical elements other than the objective lens 26, the intermediate lens 27, and the projection lens 28, such as lenses, apertures, and deflectors.

[0032] The detector 40 detects electrons that have passed through the sample S. The detector 40 is, for example, a bright-field STEM detector. The bright-field STEM detector detects electrons that have passed through the sample S without being scattered and electrons that have been scattered at small angles. Although not shown, the scanning transmission electron microscope 100 may also be equipped with a circular dark-field STEM detector that detects electrons that have been scattered at large angles.

[0033] Although not shown, the scanning transmission electron microscope 100 includes an imaging device for capturing a Ronchigram. The imaging device is a digital camera capable of recording the Ronchigram as a two-dimensional digital image.

[0034] The control unit 50 controls each part of the scanning transmission electron microscope 100. The control unit 50 includes, for example, a processor such as a CPU (Central Processing Unit) and storage devices (memories) such as RAM (Random Access Memory) and ROM (Read Only Memory). The storage devices store programs and data for various controls. The functions of the control unit 50 can be realized by executing the programs with the processor. The control unit 50 may be realized, for example, by a general-purpose circuit such as a microcontroller or microprocessor that operates according to a program, or by a dedicated circuit such as an ASIC (Application Specific Integrated Circuit).

[0035] The control unit 50 performs processes such as focusing, correcting astigmatism, adjusting the gain and offset of the detector 40, and aligning the position of the aperture 22. For this reason, the scanning transmission electron microscope 100 is equipped with an autofocus function for automatically adjusting the focus, an autostigma function for automatically correcting astigmatism, an autogain / offset adjustment function for automatically adjusting the gain and offset, and a function for automatically aligning the position of the aperture 22.

[0036] The control unit 50 performs the focusing process, the astigmatism correction process, and the gain and offset adjustment process using known techniques. The process of aligning the aperture 22 will be described later in "1.3. Aperture Alignment Process."

[0037] The scanning transmission electron microscope 100 has a STEM mode in which it functions as a scanning transmission electron microscope, and a TEM mode in which it functions as a transmission electron microscope.

[0038] In STEM mode, the electron beam emitted from the electron source 10 is focused by the focusing lens 21 and the objective lens 26 to form an electron probe on the sample S, and is deflected by the scanning deflector 24. This causes the sample S to be scanned with the electron probe. The imaging system 20b guides the electron beam that has passed through the sample S to the detector 40, and the electron beam that has passed through the sample S is detected by the detector 40. A STEM image can be obtained by synchronizing the intensity of the electron beam detected by the detector 40 with the scanning of the electron probe.

[0039] In the TEM mode, an electron beam emitted from the electron source 10 is focused by a focusing lens 21 and irradiated onto a sample S. An objective lens 26 forms a TEM image using the electron beam that has passed through the sample S. The TEM image formed by the objective lens 26 is then focused onto an imaging device by an intermediate lens 27 and a projection lens 28. This allows a TEM image to be acquired.

[0040] When switching from TEM mode to STEM mode in the scanning transmission electron microscope 100, the focus is adjusted, astigmatism is corrected, the gain and offset of the detector 40 are adjusted, and the position of the aperture 22 is aligned. The scanning transmission electron microscope 100 is equipped with an autofocus function, an autostigma function, an auto gain / offset adjustment function, and a function for automatically aligning the position of the aperture 22, so that adjustment of the optical system 20 when switching from TEM mode to STEM mode can be performed automatically.

[0041] 1.2. Aperture alignment 1.2.1. Principle In aligning the aperture 22, the center of the aperture 22 is aligned with the center of the Ronchigram. The center of the aperture 22 is the center of the opening of the aperture 22.

[0042] A Ronchigram is a projection image (pattern) of a sample S that is created on a diffraction plane by focusing an electron beam near the sample S. A Ronchigram is a diffraction pattern of an electron beam that has passed through the sample S and is formed along the optical axis.

[0043] The Ronchigram is compatible with the electron probe, so by aligning the center of the aperture 22 with the center of the Ronchigram, aberrations can be reduced and the size of the electron probe can be reduced, thereby improving resolution.

[0044] In the method for aligning the aperture 22 in the scanning transmission electron microscope 100, the center of the aperture 22 is aligned with the optical axis of the illumination system 20a in a state where the optical axis of the illumination system 20a is aligned with the center of the Ronchigram, thereby aligning the center of the aperture 22 with the center of the Ronchigram.

[0045] Fig. 2 shows the state in which aperture 22 is inserted so that the center of aperture 22 coincides with the optical axis of illumination system 20a when the optical axis of illumination system 20a is aligned with the center of the Ronchigram. Fig. 3 shows the state in which aperture 22 is inserted so that the center of aperture 22 coincides with the optical axis of illumination system 20a when the optical axis of illumination system 20a is deviated from the center of the Ronchigram.

[0046] Note that Fig. 2 shows an image showing a state in which the optical axis of irradiation system 20a is aligned with the center of the Ronchigram, and an image showing a state in which aperture 22 is inserted so that the center of aperture 22 is aligned with the optical axis of irradiation system 20a. Fig. 3 shows an image showing a state in which the optical axis of irradiation system 20a is deviated from the center of the Ronchigram, and an image showing a state in which aperture 22 is inserted so that the center of aperture 22 is aligned with the optical axis of irradiation system 20a. Note that in Figs. 2 and 3, the intersection of two straight lines represents the optical axis of irradiation system 20a.

[0047] 2, with the optical axis of the illumination system 20a aligned with the center of the Ronchigram, the aperture 22 is moved so that the center of the aperture 22 coincides with the optical axis of the illumination system 20a. This allows the center of the aperture 22 to be aligned with the center of the Ronchigram.

[0048] As shown in Figure 3, when the optical axis of the illumination system 20a is shifted from the center of the Ronchigram, even if the aperture 22 is moved so that the center of the aperture 22 coincides with the optical axis of the illumination system 20a, the center of the aperture 22 will still be shifted from the center of the Ronchigram.

[0049] Here, the optical axis of the illumination system 20a is the voltage axis. In the scanning transmission electron microscope 100, when the acceleration voltage is varied, the image expands and contracts concentrically. The center of this expansion and contraction is the voltage axis. When the optical axis of the illumination system 20a is aligned with the center of the Ronchigram, when the acceleration voltage is varied, the image expands and contracts concentrically around the center of the Ronchigram. Therefore, when the optical axis of the illumination system 20a is aligned with the center of the Ronchigram, the image does not move at the center of the Ronchigram even if the acceleration voltage is varied. This fact can be utilized to align the center of the aperture 22 with the center of the Ronchigram. A method for aligning the aperture 22 will be described in detail below.

[0050] 1.2.2. Aperture alignment method FIG. 4 is a flowchart showing an example of a method for aligning the aperture 22.

[0051] First, the optical system 20 is adjusted so that the image does not move at the center of the Ronchigram even when the acceleration voltage is changed, and the optical axis (voltage axis) of the irradiation system 20a is aligned with the center of the Ronchigram (step S10).

[0052] Specifically, first, the optical system 20 is set to a state in which the Ronchigram can be observed, and the center of the Ronchigram is confirmed. Next, the Ronchigrams are observed before and after changing the acceleration voltage, and the irradiation system 20a is adjusted so that the image at the center of the Ronchigram does not shift even when the acceleration voltage is changed. For example, the optical axis of the irradiation system 20a is aligned with the center of the Ronchigram by deflecting the electron beam with a deflector built into the irradiation system 20a. By adjusting the irradiation system 20a so that the image at the center of the Ronchigram does not shift even when the acceleration voltage is changed, the optical axis of the irradiation system 20a can be aligned with the center of the Ronchigram.

[0053] Figure 5 shows Ronchigrams taken with the optical axis of the irradiation system 20a aligned with the center of the Ronchigram, before and after changing the accelerating voltage. Figure 6 shows Ronchigrams taken with the optical axis of the irradiation system 20a shifted from the center of the Ronchigram, before and after changing the accelerating voltage.

[0054] As shown in Fig. 5, when the optical axis of the irradiation system 20a is aligned with the center of the Ronchigram, the image does not move before and after changing the accelerating voltage. In contrast, as shown in Fig. 6, when the optical axis of the irradiation system 20a is deviated from the center of the Ronchigram, the image moves before and after changing the accelerating voltage. Therefore, as shown in Fig. 5, the irradiation system 20a is adjusted so that the image does not move before and after changing the accelerating voltage.

[0055] The positional relationship between the center of the Ronchigram and the optical axis of the irradiation system 20a hardly changes, so once the optical axis of the irradiation system 20a is aligned with the center of the Ronchigram, this operation does not need to be repeated thereafter.

[0056] Next, with the optical axis of the illumination system 20a aligned with the center of the Ronchigram, that is, with the image at the center of the Ronchigram not moving even when the accelerating voltage is changed, aperture 2 2 is inserted into the path of the electron beam (step S12).

[0057] Next, the optical system 20 is set to a state where it can capture a STEM image, and STEM images are captured before and after the acceleration voltage is changed (step S14).

[0058] Specifically, first, a STEM image of the sample S is taken. The location where the STEM image is taken is not particularly limited as long as it is an area on the sample S that includes a landmark image within the field of view. Next, the acceleration voltage is changed, and a STEM image of the sample S after the acceleration voltage change is taken. The conditions for taking the STEM image before and after changing the acceleration voltage are the same except for the voltage value of the acceleration voltage.

[0059] Next, the STEM images before and after changing the accelerating voltage are compared to calculate the positional deviation between the STEM images before and after changing the accelerating voltage (step S16). The positional deviation between the STEM images before and after changing the accelerating voltage includes the amount and direction of the positional deviation between the STEM images before and after changing the accelerating voltage. For example, the amount of positional deviation between the STEM images before and after changing the accelerating voltage is calculated by calculating the cross-correlation between the two STEM images.

[0060] Next, the aperture 22 is moved based on the positional deviation between the STEM images before and after the acceleration voltage is changed (step S18).

[0061] Specifically, first, the positional shift between the center of the aperture 22 and the center of the Ronchigram (i.e., the optical axis of the illumination system 20a) is calculated from the positional shift between the STEM images before and after changing the acceleration voltage. Here, the illumination system 20a is in a state where the image at the center of the Ronchigram does not move even when the acceleration voltage is changed. Therefore, the positional shift between the STEM images before and after changing the acceleration voltage corresponds to the positional shift between the center of the aperture 22 and the center of the Ronchigram. Therefore, the positional shift between the center of the aperture 22 and the center of the Ronchigram can be calculated from the positional shift between the STEM images before and after changing the acceleration voltage.

[0062] Next, the amount and direction of movement of the aperture 22 so that its center coincides with the center of the Ronchigram are calculated from the positional deviation between the center of the aperture 22 and the center of the Ronchigram. Here, the relationship between the distance on the STEM image and the amount of movement of the aperture 22 is calibrated in advance. Similarly, the relationship between the direction on the STEM image and the direction of movement of the aperture 22 is calibrated in advance. Therefore, the amount and direction of movement of the aperture 22 are determined from the positional deviation between the center of the aperture 22 and the center of the Ronchigram using the calibration results. Next, the aperture 22 is moved according to the determined amount and direction of movement of the aperture 22. This allows the aperture 22 to be moved so that its center coincides with the center of the Ronchigram.

[0063] Figure 7 shows STEM images taken with the center of the aperture 22 aligned with the center of the Ronchigram, before and after changing the accelerating voltage. Figure 8 shows STEM images taken with the center of the aperture 22 shifted from the center of the Ronchigram, before and after changing the accelerating voltage.

[0064] As shown in Figure 7, when the center of aperture 22 is aligned with the center of the Ronchigram, the image does not move before and after changing the accelerating voltage. In contrast, as shown in Figure 8, when the center of aperture 22 is shifted from the center of the Ronchigram, the image moves before and after changing the accelerating voltage.

[0065] The above-described process of taking STEM images before and after changing the accelerating voltage, calculating the positional deviation, and moving the aperture 22 may be repeated until there is no positional deviation between the STEM images before and after changing the accelerating voltage, i.e., until the center of the aperture 22 is aligned with the center of the Ronchigram.

[0066] By the above steps, the center of the aperture 22 can be aligned with the center of the Ronchigram.

[0067] Figure 9 shows a state in which the center of the aperture 22 is aligned with the center of the Ronchigram. Figure 10 shows a state in which the center of the aperture 22 is deviated from the center of the Ronchigram. By using the above-described method for aligning the aperture 22, the center of the aperture 22 can be aligned with the center of the Ronchigram, as shown in Figure 9.

[0068] 1.3. Aperture alignment process In the scanning transmission electron microscope 100, the optical system 20 is adjusted so that the optical axis (voltage axis) of the illumination system 20a is at the center of the Ronchigram. That is, in the scanning transmission electron microscope 100, the optical system 20 is in a state where the image does not move at the center of the Ronchigram even when the acceleration voltage is changed.

[0069] FIG. 11 is a flowchart showing an example of the positioning process of the aperture 22 by the control unit 50.

[0070] The control unit 50 determines whether or not the user has issued an instruction to start the alignment process of the aperture 22 (step S100). Although not shown, the control unit 50 determines that the user has issued the start instruction when an alignment start button on a GUI (Graphical User Interface) of the scanning transmission electron microscope 100 is pressed or when an instruction to start alignment is input via an input device.

[0071] When the control unit 50 determines that the user has issued a start instruction (Yes in step S100), it causes the movement mechanism 23 to insert the aperture 22 into the path of the electron beam (step S102). At this time, the control unit 50 places the aperture 22 at a preset initial position. The initial position may be, for example, the position of the aperture 22 determined by performing a previous positioning process for the aperture 22, or may be an arbitrary set position.

[0072] Next, with the aperture 22 inserted, the control unit 50 sets the acceleration voltage to a first voltage value and captures a first STEM image (step S104). The control unit 50 sets the acceleration voltage to the first voltage value and controls the optical system 20 to scan the sample S with the electron probe. This allows the first STEM image to be acquired. The first voltage value can be set to any value. For example, in the case of a scanning transmission electron microscope with an acceleration voltage of 200 kV, the first voltage value may be 200 kV.

[0073] Next, the control unit 50 changes the acceleration voltage from the first voltage value to a second voltage value (step S106). The second voltage value is different from the first voltage value. The second voltage value can be set to any value as long as it is different from the first voltage value. The rate of change of the second voltage value relative to the first voltage value is, for example, about 0.5%.

[0074] Next, the control unit 50 captures a second STEM image with the aperture 22 inserted (step S108). The control unit 50 controls the optical system 20 to scan the sample S with the electron probe. This makes it possible to acquire the second STEM image. The imaging conditions for capturing the second STEM image are the same as those for capturing the first STEM image, except that the acceleration voltage is a second voltage value. The shooting conditions are the same as those of

[0075] Next, the control unit 50 calculates the positional deviation between the first STEM image and the second STEM image (step S110). The control unit 50 calculates the amount of positional deviation by calculating the cross-correlation between the first STEM image and the second STEM image.

[0076] The control unit 50 determines whether the calculated amount of misalignment is equal to or less than a tolerance (step S112). The tolerance is set according to the amount of misalignment that can be tolerated between the center of the aperture 22 and the center of the Ronchigram. The tolerance can be set to any value. For example, if the amount of misalignment between the first STEM image and the second STEM image is expressed in terms of the number of pixels, the tolerance is also expressed in terms of the number of pixels.

[0077] If the control unit 50 determines that the amount of positional deviation is not less than the allowable value (No in step S112), that is, if it determines that the amount of positional deviation is greater than the allowable value, it causes the moving mechanism 23 to move the aperture 22 based on the amount of positional deviation (step S114).

[0078] The storage device of the control unit 50 stores the calibration results of the distance on the STEM image and the amount of movement of the aperture 22, and the calibration results of the direction on the STEM image and the direction of movement of the aperture 22. Using these calibration results, the control unit 50 calculates the amount and direction of movement of the aperture 22 from the positional deviation between the first STEM image and the second STEM image.

[0079] The control unit 50 causes the movement mechanism 23 to move the aperture 22 by the calculated movement amount and in the movement direction of the aperture 22. After causing the movement mechanism 23 to move the aperture 22 (after step S114), the control unit 50 returns to step S104 and captures a first STEM image with the acceleration voltage set to the first voltage value (step S104).

[0080] The control unit 50 changes the acceleration voltage from the first voltage value to the second voltage value (step S106), captures a second STEM image (step S108), and calculates the positional deviation between the first STEM image and the second STEM image (step S110).

[0081] The control unit 50 repeats the processes of steps S114, S104, S106, S108, S110, and S112 until it is determined that the amount of positional deviation is equal to or less than the allowable value.

[0082] If the control unit 50 determines that the amount of positional deviation is equal to or less than the allowable value (Yes in step S112), the control unit 50 ends the positioning process of the aperture 22.

[0083] The control unit 50 executes the above-described positioning process for the aperture 22, so that the center of the aperture 22 can be aligned with the center of the Ronchigram.

[0084] Effects The scanning transmission electron microscope 100 includes an electron source 10 that generates an electron beam, an optical system 20 that has a focusing lens 21, an aperture 22, and an objective lens 26 and focuses the electron beam generated by the electron source 10 to form an electron probe, and a control unit 50 that controls the electron source 10 and the optical system 20. The optical system 20 is in a state in which an image does not move at the center of the Ronchigram even when the acceleration voltage is changed. The control unit 50 also controls the following processes: a process of inserting the aperture 22 into the path of the electron beam; a process of acquiring a first STEM image with the acceleration voltage set to a first voltage value while the aperture 22 is inserted; a process of acquiring a second STEM image with the acceleration voltage set to a second voltage value different from the first voltage value while the aperture 22 is inserted; and moving the aperture 22 based on the positional deviation between the first image and the second STEM image.

[0085] Therefore, in the scanning transmission electron microscope 100, the center of the aperture 22 can be aligned with the center of the Ronchigram using the first STEM image and the second STEM image before and after changing the accelerating voltage. Therefore, in the scanning transmission electron microscope 100, it is not necessary to check the Ronchigram every time the aperture 22 is inserted and aligned. Therefore, in the scanning transmission electron microscope 100, the aperture 22 can be aligned easily.

[0086] For example, when inserting the aperture 22 and aligning the center of the aperture 22 with the center of the Ronchigram while checking the center of the Ronchigram with an imaging device or visually, a Ronchigram of the amorphous region of the sample S is required to confirm the center of the Ronchigram. Also, the optical system 20 needs to be switched to a condition that allows observation of the Ronchigram.

[0087] In contrast, the scanning transmission electron microscope 100 can align the aperture 22 using a STEM image of any region of the sample S. In other words, it is not necessary to check the Ronchigram each time the aperture 22 is aligned. Therefore, the scanning transmission electron microscope 100 can easily align the aperture 22. Furthermore, since it is not necessary to move to an amorphous region of the sample S to align the aperture 22, drift that accompanies movement of the field of view can be reduced.

[0088] In the scanning transmission electron microscope 100, the user can easily align the aperture 22 by inputting an instruction to start the alignment process of the aperture 22, and the control unit 50 will align the center of the aperture 22 with the center of the Ronchigram.

[0089] The scanning transmission electron microscope 100 is equipped with an autofocus function, an autostigma function, an autogain / offset adjustment function, and a function for automatically adjusting the position of the aperture 22, so that when the user switches from the TEM mode to the STEM mode, the user does not need to adjust the focus, correct astigmatism, adjust the gain and offset of the detector 40, or adjust the position of the aperture 22. Therefore, with the scanning transmission electron microscope 100, the user can easily acquire a STEM image after switching from the TEM mode to the STEM mode.

[0090] In the scanning transmission electron microscope 100, the control unit 50 calculates the positional deviation between the center of the aperture 22 and the center of the Ronchigram from the positional deviation between the first STEM image and the second STEM image in the process of moving the aperture 22. Therefore, in the scanning transmission electron microscope 100, it is possible to know the amount of positional deviation between the center of the aperture 22 and the center of the Ronchigram without checking the Ronchigram.

[0091] In the scanning transmission electron microscope 100, the control unit 50 moves the aperture 22 so that the center of the aperture 22 is aligned with the center of the Ronchigram in the process of moving the aperture 22. Therefore, in the scanning transmission electron microscope 100, the aperture 22 can be easily aligned.

[0092] The scanning transmission electron microscope 100 is not equipped with an aberration corrector for correcting the spherical aberration of the optical system 20. Here, in a scanning transmission electron microscope without an aberration corrector, spherical aberration is dominant, and coma aberration cannot be confirmed. Therefore, the shape of the Ronchigram cannot be confirmed with such a scanning transmission electron microscope. Therefore, it is difficult to align the center of the aperture 22 with the center of the Ronchigram while checking the center of the Ronchigram.

[0093] In contrast, with the scanning transmission electron microscope 100, the center of the aperture 22 can be aligned with the center of the Ronchigram from STEM images before and after changing the accelerating voltage, without having to check the Ronchigram. Therefore, with the scanning transmission electron microscope 100, the center of the aperture 22 can be easily aligned with the center of the Ronchigram, even if it is not equipped with an aberration corrector.

[0094] The method for aligning the aperture 22 in the scanning transmission electron microscope 100 includes the steps of: inserting the aperture 22 into the path of the electron beam in a state in which the image does not move at the center of the Ronchigram even when the acceleration voltage for accelerating the electron beam by the optical system 20 is changed; acquiring a first STEM image with the aperture 22 inserted and the acceleration voltage set to a first voltage value; acquiring a second STEM image with the aperture 22 inserted and the acceleration voltage set to a second voltage value different from the first voltage value; and moving the aperture 22 based on the positional deviation between the first STEM image and the second STEM image.

[0095] In this way, in this method of aligning the aperture 22, the center of the aperture 22 is aligned with the center of the Ronchigram using the first STEM image and the second STEM image before and after changing the accelerating voltage. Therefore, in this method of aligning the aperture 22, it is not necessary to check the Ronchigram every time the aperture 22 is inserted and aligned. Therefore, the aperture 22 can be aligned easily.

[0096] The method for aligning the aperture 22 in the scanning transmission electron microscope 100 includes, before the step of inserting the aperture 22, a step of adjusting the optical system 20 so that the image at the center of the Ronchigram does not move even when the acceleration voltage is changed. This step enables the optical system 20 to be in a state in which the optical axis of the illumination system 20a is aligned with the center of the Ronchigram.

[0097] In the method for aligning the aperture 22 in the scanning transmission electron microscope 100, the positional deviation between the center of the aperture 22 and the center of the Ronchigram is calculated from the positional deviation between the first STEM image and the second STEM image in the step of moving the aperture 22. Therefore, in this method for aligning the aperture 22, the positional deviation between the center of the aperture 22 and the center of the Ronchigram can be calculated without checking the Ronchigram.

[0098] In the method for aligning the aperture 22 in the scanning transmission electron microscope 100, in the step of moving the aperture 22, the aperture 22 is moved so that the center of the aperture 22 is aligned with the center of the Ronchigram. Therefore, the aperture 22 can be easily aligned.

[0099] 2. Second embodiment 2.1. Scanning Transmission Electron Microscope Next, a scanning transmission electron microscope according to a second embodiment will be described. The configuration of the scanning transmission electron microscope according to the second embodiment is the same as the configuration of the scanning transmission electron microscope 100 according to the first embodiment shown in FIG. 1, and therefore a description thereof will be omitted.

[0100] 2.2. Aperture alignment 2.2.1. Principle In the first embodiment described above, the aperture 22 is positioned such that the optical axis of the illumination system 20a is aligned with the center of the Ronchigram, and the center of the aperture 22 is aligned with the optical axis of the illumination system 20a, thereby aligning the center of the aperture 22 with the center of the Ronchigram. Here, in the first embodiment, the optical axis of the optical system 20 is the voltage axis. In contrast, in the second embodiment, the optical axis of the optical system 20 is the current axis.

[0101] When the excitation current of the objective lens 26 is varied, the image expands and contracts concentrically. The center of this expansion and contraction is the current axis. That is, in the second embodiment, the current axis of the illumination system 20a is aligned with the center of the Ronchigram. When the optical axis of the illumination system 20a is aligned with the center of the Ronchigram, varying the excitation current of the objective lens 26 causes the image to expand and contract concentrically around the center of the Ronchigram. Therefore, when the optical axis of the illumination system 20a is aligned with the center of the Ronchigram, varying the excitation current of the objective lens 26 does not move the image at the center of the Ronchigram. Utilizing this, the center of the aperture 22 can be aligned with the center of the Ronchigram.

[0102] A detailed description will now be given of a method for aligning the aperture 22. Note that a description of the same points as in the method for aligning the aperture 22 in the first embodiment will be omitted.

[0103] 2.2.2. Aperture alignment method FIG. 12 is a flowchart showing an example of a method for aligning the aperture 22.

[0104] First, the optical system 20 is adjusted so that the image does not move at the center of the Ronchigram even when the excitation current of the objective lens 26 is changed, and the optical axis (current axis) of the irradiation system 20a is aligned with the center of the Ronchigram (step S20).

[0105] Specifically, first, the optical system 20 is set to a state in which a Ronchigram can be observed, and the center of the Ronchigram is confirmed. Next, the Ronchigrams are observed before and after changing the excitation current of the objective lens 26, and the illumination system 20a is adjusted so that the image at the center of the Ronchigram does not shift even when the excitation current of the objective lens 26 is changed. For example, the optical axis of the illumination system 20a can be aligned with the center of the Ronchigram by deflecting the electron beam with a deflector incorporated in the illumination system 20a. By adjusting the illumination system 20a so that the image at the center of the Ronchigram does not shift even when the excitation current of the objective lens 26 is changed, the optical axis of the illumination system 20a can be aligned with the center of the Ronchigram.

[0106] The positional relationship between the center of the Ronchigram and the optical axis of the irradiation system 20a hardly changes, so once the optical axis of the irradiation system 20a is aligned with the center of the Ronchigram, this operation does not need to be repeated thereafter.

[0107] Next, with the optical axis of the illumination system 20a aligned with the center of the Ronchigram, i.e., with the image at the center of the Ronchigram not moving even when the excitation current of the objective lens 26 is varied, the aperture 22 is inserted into the path of the electron beam (step S22).

[0108] Next, the optical system 20 is set to a state where it can capture a STEM image, and STEM images are captured before and after the excitation current of the objective lens 26 is changed (step S24).

[0109] Specifically, first, a STEM image of the sample S is taken. Next, the excitation current of the objective lens 26 is changed, and a STEM image of the sample S is taken after changing the excitation current of the objective lens 26. The conditions for taking the STEM image before changing the excitation current of the objective lens 26 and the conditions for taking the STEM image after changing the excitation current of the objective lens 26 are the same except for the current value of the excitation current of the objective lens 26.

[0110] Next, the STEM images before and after changing the excitation current of the objective lens 26 are compared to calculate the positional deviation between the STEM images before and after changing the excitation current of the objective lens 26 (step S26). The positional deviation between the STEM images before and after changing the excitation current of the objective lens 26 is calculated by calculating the amount and direction of the positional deviation between the STEM images before and after changing the excitation current of the objective lens 26. Includes direction.

[0111] Next, the aperture 22 is moved based on the positional deviation between the STEM images before and after changing the excitation current of the objective lens 26 (step S28).

[0112] Specifically, first, the positional shift between the center of the aperture 22 and the center of the Ronchigram is calculated from the positional shift between the STEM images before and after changing the excitation current of the objective lens 26. Here, the illumination system 20a is in a state where the image at the center of the Ronchigram does not move even when the excitation current of the objective lens 26 is changed. Therefore, the positional shift between the STEM images before and after changing the excitation current of the objective lens 26 corresponds to the positional shift between the center of the aperture 22 and the center of the Ronchigram. Therefore, the positional shift between the center of the aperture 22 and the center of the Ronchigram can be calculated from the positional shift between the STEM images before and after changing the excitation current of the objective lens 26.

[0113] Next, the amount and direction of movement of the aperture 22 so that the center of the aperture 22 coincides with the center of the Ronchigram are calculated from the positional deviation between the center of the aperture 22 and the center of the Ronchigram. The calculation of the amount and direction of movement of the aperture 22 is performed in the same manner as in step S18 described above.

[0114] The above-described process of taking STEM images before and after changing the excitation current of the objective lens 26, calculating the positional deviation, and moving the aperture 22 may be repeated until there is no positional deviation between the STEM images before and after changing the excitation current of the objective lens 26, i.e., until the center of the aperture 22 is aligned with the center of the Ronchigram.

[0115] By the above steps, the center of the aperture 22 can be aligned with the center of the Ronchigram.

[0116] 2.3. Aperture alignment process In the scanning transmission electron microscope 100, the optical system 20 is adjusted so that the optical axis (current axis) of the illumination system 20a is at the center of the Ronchigram. That is, in the scanning transmission electron microscope 100, the optical system 20 is in a state where the image does not move at the center of the Ronchigram even if the excitation current of the objective lens 26 is changed.

[0117] 13 is a flowchart showing an example of the process of aligning the aperture 22 by the control unit 50. Note that a description of the same points as in the process of aligning the aperture 22 shown in FIG.

[0118] The control unit 50 determines whether or not the user has issued an instruction to start the alignment process of the aperture 22 (step S200). If the control unit 50 determines that the user has issued an instruction to start (Yes in step S200), it causes the moving mechanism 23 to insert the aperture 22 into the path of the electron beam (step S202).

[0119] Next, with the aperture 22 inserted, the control unit 50 sets the excitation current of the objective lens 26 to a first current value and captures a first STEM image (step S204). The control unit 50 sets the excitation current of the objective lens 26 to the first current value and controls the optical system 20 to scan the sample S with the electron probe. This allows the first STEM image to be acquired. The first current value can be set to any value.

[0120] Next, the control unit 50 changes the excitation current of the objective lens 26 from the first current value to a second current value (step S206). The second current value is different from the first current value. It can be set to any value as long as it is different from the flow value.

[0121] Next, the control unit 50 captures a second STEM image with the aperture 22 inserted (step S208). The control unit 50 controls the optical system 20 to scan the sample S with the electron probe. This allows the second STEM image to be acquired. The imaging conditions for capturing the second STEM image are the same as the imaging conditions for capturing the first STEM image, except that the excitation current of the objective lens 26 is set to a second current value.

[0122] Next, the control unit 50 calculates the positional deviation between the first STEM image and the second STEM image (step S210), and determines whether the calculated positional deviation is equal to or less than an allowable value (step S212).

[0123] When the control unit 50 determines that the amount of positional deviation is not equal to or less than the allowable value (No in step S212), the control unit 50 causes the movement mechanism 23 to move the aperture 22 based on the amount of positional deviation (step S214).

[0124] After causing the moving mechanism 23 to move the aperture 22 (after step S214), the control unit 50 returns to step S204 and captures a first STEM image (step S204) with the excitation current of the objective lens 26 set to a first current value. The control unit 50 then changes the excitation current of the objective lens 26 from the first current value to a second current value (step S206), captures a second STEM image (step S208), and calculates the positional deviation between the first and second STEM images (step S210).

[0125] The control unit 50 repeats the processes of steps S214, S204, S206, S208, S210, and S212 until it is determined that the amount of positional deviation is equal to or less than the allowable value.

[0126] If the control unit 50 determines that the amount of positional deviation is equal to or less than the allowable value (Yes in step S212), the control unit 50 ends the positioning process of the aperture 22.

[0127] The control unit 50 executes the above-described positioning process for the aperture 22, so that the center of the aperture 22 can be aligned with the center of the Ronchigram.

[0128] Effects In the scanning transmission electron microscope 100, the optical system 20 is in a state in which the image does not move at the center of the Ronchigram even when the excitation current of the objective lens 26 is varied. The control unit 50 also performs the following processes: inserting the aperture 22 into the path of the electron beam; acquiring a first STEM image by setting the excitation current of the objective lens 26 to a first current value while the aperture 22 is inserted; acquiring a second STEM image by setting the excitation current of the objective lens 26 to a second current value different from the first current value while the aperture 22 is inserted; and moving the aperture 22 based on the positional deviation between the first STEM image and the second STEM image.

[0129] Therefore, in the scanning transmission electron microscope 100, the center of the aperture 22 can be aligned with the center of the Ronchigram using the first STEM image and the second STEM image before and after changing the excitation current of the objective lens 26. Therefore, in the scanning transmission electron microscope 100, the positioning of the aperture 22 can be easily performed.

[0130] The method for aligning the aperture 22 in the scanning transmission electron microscope 100 includes the steps of inserting the aperture 22 into the path of the electron beam in a state in which the image at the center of the Ronchigram does not move even when the optical system 20 varies the excitation current of the objective lens 26, and The method includes a step of acquiring a first STEM image while the objective lens 26 is inserted, with the excitation current of the objective lens 26 set to a first current value; a step of acquiring a second STEM image while the aperture 22 is inserted, with the excitation current of the objective lens 26 set to a second current value different from the first current value; and a step of moving the aperture 22 based on the positional deviation between the first STEM image and the second STEM image.

[0131] In this way, in this method of aligning the aperture 22, the center of the aperture 22 is aligned with the center of the Ronchigram using the first STEM image and the second STEM image before and after changing the excitation current of the objective lens 26. Therefore, in this method of aligning the aperture 22, it is not necessary to check the Ronchigram every time the aperture 22 is inserted and aligned. Therefore, the aperture 22 can be aligned easily.

[0132] The method for aligning the aperture 22 in the scanning transmission electron microscope 100 includes, before the step of inserting the aperture 22, a step of adjusting the optical system 20 so that the image does not move at the center of the Ronchigram even when the excitation current of the objective lens 26 is changed. This step allows the optical system 20 to be in a state where the optical axis of the illumination system 20a is aligned with the center of the Ronchigram.

[0133] 3. Variations The scanning transmission electron microscope 100 according to the first and second embodiments described above has a STEM mode for acquiring STEM images and a TEM mode for acquiring TEM images, but it may also have only the STEM mode.

[0134] Furthermore, in the first and second embodiments described above, the scanning transmission electron microscope 100 is described as not being equipped with an aberration corrector for correcting spherical aberration, but the scanning transmission electron microscope 100 may be equipped with an aberration corrector for correcting spherical aberration.

[0135] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially identical to the configurations described in the embodiments. A substantially identical configuration means, for example, a configuration with the same function, method, and result, or a configuration with the same purpose and effect. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that achieve the same effects or purposes as the configurations described in the embodiments. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments. [Explanation of symbols]

[0136] 10...electron source, 20...optical system, 20a...illumination system, 20b...imaging system, 21...focusing lens, 22...aperture, 23...moving mechanism, 24...scanning deflector, 26...objective lens, 27...intermediate lens, 28...projection lens, 30...sample stage, 32...sample holder, 40...detector, 50...controller, 100...scanning transmission electron microscope

Claims

1. an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; a control unit that controls the electron source and the optical system; Including, The optical system is in a state where the image does not move at the center of the Ronchigram even when the acceleration voltage for accelerating the electron beam is changed, The control unit inserting the aperture into the path of the electron beam; acquiring a first STEM image with the aperture inserted and the acceleration voltage set to a first voltage value; acquiring a second STEM image while the aperture is inserted and setting the acceleration voltage to a second voltage value different from the first voltage value; moving the aperture based on a positional deviation between the first STEM image and the second STEM image; Scanning transmission electron microscope.

2. an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; a control unit that controls the optical system; Including, The optical system is in a state where an image does not move at the center of the Ronchigram even when the excitation current of the objective lens is changed, The control unit inserting the aperture into the path of the electron beam; acquiring a first STEM image with the aperture inserted and the excitation current set to a first current value; acquiring a second STEM image while the aperture is inserted and the excitation current is set to a second current value different from the first current value; moving the aperture based on a positional deviation between the first STEM image and the second STEM image; Scanning transmission electron microscope.

3. In claim 1 or 2, The control unit calculates the positional shift between the center of the aperture and the center of the Ronchigram from the positional shift between the first STEM image and the second STEM image in the process of moving the aperture.

4. In claim 1 or 2, In the process of moving the aperture, the control unit moves the aperture so that the center of the aperture is aligned with the center of the Ronchigram.

5. In claim 1 or 2, the control unit performs processing to determine whether or not a positional deviation amount between the first STEM image and the second STEM image is equal to or less than a tolerance value; When the control unit determines that the difference is not equal to or less than the allowable value, the control unit moves the aperture. A scanning transmission electron microscope is used to process the specimen.

6. In claim 1 or 2, A scanning transmission electron microscope not equipped with an aberration corrector for correcting spherical aberration of the optical system.

7. an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; A method for aligning the aperture in a scanning transmission electron microscope, comprising: inserting the aperture into the path of the electron beam in a state in which the image at the center of the Ronchigram does not move even when the acceleration voltage for accelerating the electron beam by the optical system is changed; acquiring a first STEM image with the aperture inserted and the acceleration voltage set to a first voltage value; acquiring a second STEM image while the aperture is inserted and the acceleration voltage is set to a second voltage value different from the first voltage value; moving the aperture based on a positional deviation between the first STEM image and the second STEM image; An alignment method comprising:

8. In claim 7, The alignment method includes, before the step of inserting the aperture, a step of adjusting the optical system so that an image does not move at the center of the Ronchigram even when the acceleration voltage is changed.

9. an electron source that generates an electron beam; an optical system having a focusing lens, an aperture, and an objective lens, which focuses the electron beam generated by the electron source to form an electron probe; A method for aligning the aperture in a scanning transmission electron microscope, comprising: inserting the aperture into the path of the electron beam in a state in which the image at the center of the Ronchigram does not move even when the optical system varies the excitation current of the objective lens; acquiring a first STEM image with the aperture inserted and the excitation current set to a first current value; acquiring a second STEM image while the aperture is inserted and the excitation current is set to a second current value different from the first current value; moving the aperture based on a positional deviation between the first STEM image and the second STEM image; An alignment method comprising:

10. In claim 9, The alignment method includes, before the step of inserting the aperture, a step of adjusting the optical system so that an image does not move at the center of the Ronchigram even when the excitation current is varied.

11. In any one of claims 7 to 10, In the step of moving the aperture, a positional shift between the center of the aperture and the center of the Ronchigram is calculated from a positional shift between the first STEM image and the second STEM image.

12. In any one of claims 7 to 10, In the step of moving the aperture, the aperture is moved so that the center of the aperture is aligned with the center of the Ronchigram.

13. In any one of claims 7 to 10, The alignment method, wherein the scanning transmission electron microscope does not include an aberration corrector for correcting spherical aberration of the optical system.

Images