Measurement method and electron microscope

Abstract

To provide a measuring method that can change an electron beam irradiation angle without tilting a sample or deflecting an electron beam.SOLUTION: A measuring method is for an electron microscope including an electron source that emits an electron beam and an irradiation system that includes an irradiation system aperture that restricts the passage of the electron beam and converges the electron beam to irradiate a sample. The measuring method includes the steps for setting an irradiation angle of the electron beam incident on the sample to a first irradiation angle by arranging a position of the irradiation system aperture at a first position and setting the irradiation angle of the electron beam incident on the sample to a second irradiation angle that is different from the first irradiation angle by arranging the position of the irradiation system aperture to a second position different from the first position.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a measurement method and an electron microscope. [Background technology]

[0002] In transmission electron microscopes, atom location by channeling enhanced microanalysis (ALCHEMI) is known, which identifies the locations of impurity atoms in crystals by utilizing the phenomenon of incident electrons passing through specific atomic positions (electron channeling).

[0003] For example, in Patent Document 1, alchemy is performed to measure which parts of the main phase, which is the crystalline structure that determines the properties of the material, are substituted by the added trace elements. In Patent Document 1, the angle of incidence of the electron beam on the sample is changed to detect characteristic X-rays, and the parts of the main phase that are substituted by the trace elements are identified from the difference in the intensity of the characteristic X-rays due to the change in the angle of incidence.

[0004] Patent Document 1 describes two methods for changing the angle of incidence of the electron beam on the sample: tilting the sample using a sample stage with a tilting mechanism, and tilting the electron beam using a deflector. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-124492 Summary of the Invention [Problem to be solved by the invention]

[0006] When tilting the sample using a sample stage to change the incident angle of the electron beam on the sample, the sample position may shift because the sample stage moves mechanically, which results in a shift in the analysis position each time the incident angle of the electron beam is changed.

[0007] Furthermore, when tilting the electron beam with a deflector to change the angle of incidence of the electron beam on the sample, the electron beam may deviate from the optical axis, which requires adjustment of the optical system, such as an aberration corrector, each time the angle of incidence of the electron beam is changed. [Means for solving the problem]

[0008] One aspect of the measurement method according to the present invention is an electron source that emits an electron beam; an irradiation system including an irradiation system aperture that limits passage of the electron beam, for converging the electron beam and irradiating the sample with the electron beam; A measurement method in an electron microscope, comprising: a step of setting the irradiation angle of the electron beam incident on the sample to a first irradiation angle by placing the position of the irradiation system aperture at a first position; a step of setting the position of the irradiation system aperture at a second position different from the first position, thereby setting the irradiation angle of the electron beam incident on the sample to a second irradiation angle different from the first irradiation angle; Includes.

[0009] In this measurement method, the irradiation angle of the electron beam is changed by changing the position of the irradiation system aperture, so there is no need to tilt the sample or deflect the electron beam to change the irradiation angle. It's okay.

[0010] One aspect of the electron microscope according to the present invention is an electron source that emits an electron beam; an irradiation system including an irradiation system aperture that limits passage of the electron beam, for converging the electron beam and irradiating the sample with the electron beam; a control unit for controlling the illumination system aperture; Including, The control unit a process of setting the irradiation angle of the electron beam incident on the sample to a first irradiation angle by placing the position of the irradiation system aperture at a first position; a process of setting the irradiation angle of the electron beam incident on the sample to a second irradiation angle different from the first irradiation angle by disposing the position of the irradiation system aperture at a second position different from the first position; Do the following.

[0011] In such an electron microscope, the irradiation angle of the electron beam can be changed by changing the position of the irradiation system aperture, so there is no need to tilt the sample or deflect the electron beam to change the irradiation angle. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of an electron microscope according to an embodiment of the present invention. [Figure 2] Ray diagram of a focused electron beam irradiating a sample. [Figure 3] Ronchigram corresponding to the ray diagram shown in Figure 2. [Figure 4] This is a ray diagram when the position of the illumination system aperture is changed while a converged electron beam is irradiated onto a sample. [Figure 5] Ronchigram corresponding to the ray diagram shown in Figure 4. [Figure 6] This is a ray diagram when the position of the illumination system aperture is changed while a converged electron beam is irradiated onto a sample. [Figure 7] Ronchigram corresponding to the ray diagram shown in Figure 6. [Figure 8] This is a ray diagram when the position of the illumination system aperture is changed while a converged electron beam is irradiated onto a sample. [Figure 9] Ronchigram corresponding to the ray diagram shown in Figure 8. [Figure 10] 10 is a flowchart showing an example of processing by a control unit. [Figure 11] EDS spectrum of InP. [Figure 12] EDS spectrum of InP. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] 1. Electron Microscopy First, an electron microscope according to one embodiment of the present invention will be described with reference to the drawings. Figure 1 is a diagram showing the configuration of an electron microscope 100 according to one embodiment of the present invention.

[0015] The electron microscope 100 includes an electron source 10, an illumination system lens 20, an illumination system aperture 22, an aberration correction device 30, a sample stage 40, an objective lens 50, an intermediate lens 60, a projection lens 70, an imaging device 80, an X-ray detector 90, and a control unit 110.

[0016] The electron source 10 emits 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.

[0017] The illumination system lens (condenser lens) 20 converges the electron beam emitted from the electron source 10 and illuminates the sample S. For example, a plurality of illumination system lenses 20 are arranged.

[0018] The illumination system aperture 22 limits the passage of the electron beam emitted from the electron source 10. The illumination system aperture 22 is, for example, a condenser aperture disposed in the illumination system lens (condenser lens) 20. The illumination system aperture 22 has a plurality of aperture holes with different diameters. The illumination system aperture 22 can move the positions of the aperture holes. In other words, the illumination system aperture 22 is a movable aperture that allows the diameter of the aperture hole to be selected and the position of the aperture hole to be adjusted.

[0019] The electron microscope 100 includes a drive unit for moving the illumination system aperture 22, and the control unit 110 can operate the drive unit to move the illumination system aperture 22 (aperture hole). The drive unit includes, for example, a drive device such as a motor for moving the illumination system aperture 22.

[0020] Although not shown, the electron microscope 100 is equipped with a deflector that two-dimensionally deflects the electron beam. By two-dimensionally deflecting the electron beam focused by the deflector, the electron beam can be scanned over the sample S. By scanning the sample S with the electron beam and detecting the electrons that have transmitted through the sample S, a scanning transmission electron microscope image (STEM image) can be obtained.

[0021] The aberration corrector 30 corrects the aberration of the illumination system 2. The aberration corrector 30 is, for example, a spherical aberration corrector that corrects the spherical aberration of the illumination system 2. The aberration corrector 30 corrects the spherical aberration of the illumination system 2 by generating negative spherical aberration to cancel out the positive spherical aberration of the illumination system 2.

[0022] In the electron microscope 100, the illumination system 2 for irradiating the sample S with an electron beam includes an illumination system lens 20, an illumination system aperture 22, an aberration corrector 30, and a forward magnetic field of the objective lens .

[0023] The sample stage 40 holds the sample S. The sample stage 40 holds the sample S fixed to, for example, a sample holder 42. In the example shown, the sample stage 40 is a side entry stage into which the sample S is inserted from the side of the pole piece of the objective lens 50.

[0024] The objective lens 50 is a first-stage lens for forming an image of the electron beam transmitted through the sample S. The objective lens 50 has a pole piece (not shown), and generates a magnetic field between the upper and lower poles of the pole piece to converge the electron beam. The sample S is placed between the upper and lower poles of the pole piece. When acquiring a STEM image, the electron beam is converged by the forward magnetic field of the objective lens 50, forming a tiny probe on the sample S.

[0025] The intermediate lens 60 magnifies and transfers the electron diffraction pattern formed on the back focal plane of the objective lens 50. The projection lens 70 projects the electron diffraction pattern magnified and transferred by the intermediate lens 60 onto the imaging device 80.

[0026] The imaging device 80 is disposed on the back focal plane of the objective lens 50 or on a plane conjugate to the back focal plane of the objective lens 50. The imaging device 80 can capture a Ronchigram. The imaging device 80 is, for example, a digital camera capable of recording a Ronchigram as a two-dimensional digital image. A Ronchigram is a projection image (figure) of a sample that is formed on the diffraction plane (back focal plane) when an electron beam is focused near the sample.

[0027] Although not shown, the electron microscope 100 is equipped with detectors for detecting electrons that have passed through the sample S, such as an annular detector for acquiring a high-angle scattered dark-field image (HAADF-STEM image) and a bright-field detector for acquiring a bright-field STEM image.

[0028] The X-ray detector 90 detects characteristic X-rays emitted from the sample S when the sample S is irradiated with an electron beam. When detecting X-rays, the X-ray detector 90 is disposed near the sample S. The X-ray detector 90 is, for example, an energy dispersive X-ray detector, and is capable of performing EDS analysis (energy dispersive X-ray spectroscopy). As the X-ray detector 90, for example, a silicon drift detector (SDD), a Si(Li) detector, or the like can be used.

[0029] The control unit 110 includes, for example, a processor such as a CPU (Central Processing Unit) and a storage device such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage device stores programs and data for performing various controls. The functions of the control unit 110 can be realized by the processor executing the programs.

[0030] The control unit 110 controls each unit of the electron microscope 100. The control unit 110, for example, controls the position of the irradiation system aperture 22 to adjust the irradiation angle of the electron beam irradiated onto the sample S. The control unit 110 can perform alchemy by repeatedly changing the irradiation angle of the electron beam and acquiring an EDS spectrum. The process of performing alchemy will be described in detail later.

[0031] 2. Operation In the electron microscope 100, the irradiation angle of the electron beam incident on the sample S can be adjusted by using the irradiation system 2 to converge the electron beam and controlling the position of the irradiation system aperture 22.

[0032] 2 is a ray diagram showing a state in which an electron beam EB is converged and irradiated onto a sample S. FIG. 3 is a Ronchigram corresponding to the ray diagram shown in FIG.

[0033] As shown in Fig. 2, the electron beam EB is converged into a cone shape using the irradiation system 2 and irradiated onto one location on the sample S. As a result, a circle corresponding to the angular range of the electron beam EB converged on the sample S can be confirmed in the Ronchigram as shown in Fig. 3. In this case, the circle becomes larger by increasing the convergence angle 2θ of the electron beam EB irradiated onto the sample S, and the range of irradiation angles of the electron beam EB that can be selected by the irradiation system aperture 22 can be increased.

[0034] 4, 6, and 8 are ray diagrams obtained when the position of the illumination system aperture 22 is changed while the electron beam EB is converged and irradiated onto the sample S. FIG. 5 is a Ronchigram corresponding to the ray diagram shown in FIG. 4. FIG. 7 is a Ronchigram corresponding to the ray diagram shown in FIG. 6. FIG. 9 is a Ronchigram corresponding to the ray diagram shown in FIG. 8.

[0035] As shown in Figures 4 to 9, the irradiation angle of the electron beam EB with respect to the sample S can be changed by changing the position of the irradiation system aperture 22. The irradiation angle of the electron beam EB is expressed by the incident angle of the electron beam EB and the incident orientation of the electron beam EB. The incident angle of the electron beam EB is the angle formed by the perpendicular to the surface of the sample S and the electron beam EB incident on the sample S. The incident orientation of the electron beam EB is the direction of the incident electron beam EB within the surface of the sample S at the incident position of the electron beam EB on the surface of the sample S.

[0036] The position of the irradiation system aperture 22 corresponds to the irradiation angle of the electron beam EB. Therefore, by changing the position of the irradiation system aperture 22, the irradiation angle of the electron beam EB can be changed.

[0037] The diameter of the irradiation system aperture 22 corresponds to the range of the irradiation angle of the electron beam EB. By reducing the diameter of the aperture of the irradiation system aperture 22, it is possible to narrow the range of the irradiation angle of the electron beam EB irradiated onto the sample S. In other words, by reducing the diameter of the aperture of the irradiation system aperture 22, it is possible to reduce the convergence angle (vertex angle) of the electron beam EB converging in a conical shape.

[0038] 3. Alchemy In the electron microscope 100, Alchemy can be performed using the above-described method for adjusting the irradiation angle of the electron beam EB. In the electron microscope 100, the control unit 110 performs processing for performing Alchemy. Figure 10 is a flowchart showing an example of the processing performed by the control unit 110.

[0039] First, the user places the sample S on the sample holder 42 and mounts it on the sample stage 40. The sample S fixed to the sample holder 42 is placed in the sample chamber inside the microscope column. An electron beam EB is irradiated onto the sample S placed in the sample chamber, and observation of the sample S begins. Then, the sample S is tilted to the tilt amount desired for performing alchemy, and the electron beam EB is irradiated onto the analysis position on the sample S.

[0040] As shown in FIG. 2, the control unit 110 controls the irradiation system 2 to converge the electron beam EB into a cone shape at a large convergence angle and irradiate the analysis position of the sample S (S10).

[0041] Next, the control unit 110 adjusts the aberration corrector 30 to correct the aberration of the illumination system 2 (S20).

[0042] Next, the control unit 110 moves the irradiation system aperture 22 to the initial position (first position) (S30), whereby the electron beam EB is irradiated onto the sample S at an irradiation angle (first irradiation angle) according to the position of the irradiation system aperture 22 (aperture hole).

[0043] Next, the control unit 110 acquires an EDS spectrum (S40). In the electron microscope 100, when the electron beam EB is irradiated onto the sample S, characteristic X-rays are emitted from the sample S. The characteristic X-rays emitted from the sample S are detected by the X-ray detector 90. The X-ray detector 90 discriminates the detected X-rays by energy to obtain an EDS spectrum. The control unit 110 acquires the obtained EDS spectrum and stores it in a storage device in association with the irradiation angle of the electron beam EB (the position of the irradiation system aperture 22).

[0044] Next, the control unit 110 determines whether EDS spectra have been acquired at all of the preset irradiation angles (S50). If the control unit 110 determines that EDS spectra have not been acquired at all of the irradiation angles (No in S60), the control unit 110 returns to step S30, moves the irradiation system aperture 22 from the first position to the second position, and changes the irradiation angle from the first irradiation angle to the second irradiation angle (S30). In this way, the irradiation angle is changed by moving the position of the irradiation system aperture 22, so that no positional shift of the sample S or axial shift of the electron beam EB occurs. Therefore, even if the irradiation angle is changed, there is no need to correct the position of the sample S or adjust the aberration corrector 30.

[0045] The control unit 110 acquires the EDS spectrum, associates the EDS spectrum with the irradiation angle, and stores the EDS spectrum in the storage device (S40), and determines whether or not EDS spectra have been acquired at all irradiation angles (S50).

[0046] The control unit 110 repeats the steps of moving the illumination system aperture 22 (S30), acquiring the EDS spectrum (S40), and determining whether or not the EDS spectrum has been acquired at all the illumination angles (S50) until it is determined that the EDS spectrum has been acquired at all the preset illumination angles.

[0047] When the control unit 110 determines that EDS spectra have been acquired at all irradiation angles (Yes in S52), it ends the process of performing Alchemy.

[0048] In the above, we have described the case where the control unit 110 performs processes S10, S20, S30, S40, S50, and S60 to implement Alchemy, but at least some of these processes may also be performed manually by the user.

[0049] Figures 11 and 12 show EDS spectra of InP. The measurement conditions for the EDS spectrum shown in Figure 11 and the EDS spectrum shown in Figure 12 are the same except for the position of the aperture 22 in the illumination system.

[0050] 11 and 12, the intensity ratio of the In L line and the P K line changes significantly by moving the position of the irradiation system aperture 22. This is due to the effect of electron channeling. In other words, this change in the intensity ratio indicates that the irradiation angle of the electron beam EB with respect to the sample S changes by moving the position of the irradiation system aperture 22.

[0051] 4. Effects The measurement method in the electron microscope 100 includes a step of setting the irradiation angle of the electron beam EB incident on the sample S to a first irradiation angle by placing the irradiation system aperture 22 at a first position, and a step of setting the irradiation angle of the electron beam EB incident on the sample S to a second irradiation angle different from the first irradiation angle by placing the irradiation system aperture 22 at a second position different from the first position.

[0052] In this way, in the measurement method using the electron microscope 100, the irradiation angle of the electron beam EB is changed by changing the position of the irradiation system aperture 22, so there is no need to tilt the sample S or deflect the electron beam EB to change the irradiation angle. Therefore, in the measurement method using the electron microscope 100, there is no shift in the analysis position due to tilting the sample S, and no shift in the electron beam EB relative to the optical axis due to deflection of the electron beam EB. Therefore, in the electron microscope 100, there is no need to correct the shift in the analysis position or adjust the aberration corrector 30 every time the irradiation angle of the electron beam EB is changed.

[0053] Furthermore, in the electron microscope 100, the irradiation angle can be changed by changing the position of the irradiation system aperture 22, so that the irradiation angle can be adjusted more finely than when the irradiation angle is adjusted by tilting the sample S.

[0054] In the measurement method in the electron microscope 100, the electron beam EB is converged using the illumination system 2 including the aberration corrector 30. Therefore, in the electron microscope 100, the electron beam EB can be accurately converged onto one point on the sample S at a large convergence angle.

[0055] The measurement method using the electron microscope 100 uses the irradiation system 2 to converge the electron beam EB into a cone shape and irradiate it onto an analysis position on the sample S. The method also includes the steps of detecting X-rays with the X-ray detector 90 while the irradiation angle of the electron beam EB is set to a first irradiation angle to obtain a first spectrum, and detecting X-rays with the X-ray detector 90 while the irradiation angle of the electron beam EB is set to a second irradiation angle to obtain a second spectrum. As described above, the measurement method using the electron microscope 100 does not require correction of the deviation of the analysis position or adjustment of the aberration corrector 30 each time the irradiation angle is changed, and therefore multiple spectra obtained under different irradiation angle conditions can be easily obtained.

[0056] In the electron microscope 100, the control unit 110 performs a process of setting the irradiation angle of the electron beam EB incident on the sample S to a first irradiation angle by placing the position of the irradiation system aperture 22 at a first position, and a process of setting the irradiation angle of the electron beam EB incident on the sample S to a second irradiation angle different from the first irradiation angle by placing the position of the irradiation system aperture 22 at a second position different from the first position. Therefore, it is not necessary to tilt the sample S or deflect the electron beam EB in order to change the irradiation angle.

[0057] In the electron microscope 100, the control unit 110 uses the irradiation system 2 to focus the electron beam EB into a cone shape and irradiate the analysis position of the sample S. The control unit 110 also performs a process of acquiring a first spectrum obtained by the X-ray detector 90 with the irradiation angle of the electron beam EB set to a first irradiation angle, and a process of acquiring a second spectrum obtained by the X-ray detector 90 with the irradiation angle of the electron beam EB set to a second irradiation angle. Therefore, in the electron microscope 100, the control unit 110 acquires multiple spectra obtained under conditions with different irradiation angles, making it easy to perform alchemy.

[0058] 5. Variations 5.1. First Variant In the above-described embodiment, the case where the illumination system diaphragm 22 is a condenser diaphragm has been described, but the illumination system diaphragm 22 is not limited to a condenser diaphragm as long as it is a diaphragm incorporated in the illumination system 2.

[0059] 5.2. Second Variant In the above-described embodiment, the method of changing the irradiation angle of the electron beam EB using the irradiation system aperture 22 is described as being applied to Alchemy, but the method of changing the irradiation angle of the electron beam EB using the irradiation system aperture 22 may also be applied to analyses other than Alchemy.

[0060] For example, the technique of changing the irradiation angle of the electron beam EB using the irradiation system aperture 22 may be used for beam locking, in which the electron beam EB irradiated onto the sample S is fixed at one point on the sample S and the incident angle of the electron beam EB is changed over a certain angle range.

[0061] 5.3. Third Variant In the above-described embodiment, the electron microscope 100 is a transmission electron microscope (scanning transmission electron microscope), but the electron microscope 100 may also be a scanning electron microscope.

[0062] The above-described embodiment and modifications are merely examples, and the present invention is not limited to these. For example, the embodiments and modifications can be combined as appropriate.

[0063] 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]

[0064] 2...Illumination system, 10...Electron source, 20...Illumination system lens, 22...Illumination system aperture, 30...Aberration corrector, 40...Sample stage, 42...Sample holder, 50...Objective lens, 60...Intermediate lens, 70...Projection lens, 80...Imaging device, 90...X-ray detector, 100...Electron microscope, 110...Control unit

Claims

1. an electron source that emits an electron beam; an irradiation system including an irradiation system aperture that limits passage of the electron beam, for converging the electron beam and irradiating the sample with the electron beam; A measurement method in an electron microscope, comprising: a step of setting the irradiation angle of the electron beam incident on the sample to a first irradiation angle by placing the position of the irradiation system aperture at a first position; a step of setting the irradiation angle of the electron beam incident on the sample to a second irradiation angle different from the first irradiation angle by disposing the position of the irradiation system aperture at a second position different from the first position; , including, a measurement method.

2. In claim 1, The illumination system includes an aberration corrector.

3. In claim 1 or 2, a step of converging the electron beam into a cone shape using the irradiation system and irradiating the electron beam onto an analysis position of the sample.

4. In any one of claims 1 to 3, the electron microscope includes an X-ray detector that detects X-rays emitted from the sample when the sample is irradiated with the electron beam, and obtains a spectrum; detecting X-rays with the X-ray detector while the irradiation angle of the electron beam is set to the first irradiation angle, and acquiring a first spectrum; detecting X-rays with the X-ray detector while the irradiation angle of the electron beam is set to the second irradiation angle, and acquiring a second spectrum; , including, a measurement method.

5. an electron source that emits an electron beam; an irradiation system including an irradiation system aperture that limits passage of the electron beam, for converging the electron beam and irradiating the sample with the electron beam; a control unit for controlling the illumination system aperture; Including, The control unit a process of setting the irradiation angle of the electron beam incident on the sample to a first irradiation angle by placing the position of the irradiation system aperture at a first position; a process of setting the irradiation angle of the electron beam incident on the sample to a second irradiation angle different from the first irradiation angle by disposing the position of the irradiation system aperture at a second position different from the first position; Electron microscope.

6. In claim 5, The illumination system includes an aberration corrector.

7. In claim 5 or 6, The control unit uses the irradiation system to focus the electron beam into a cone shape and irradiate the analysis position of the sample.

8. In any one of claims 5 to 7, an X-ray detector that detects X-rays emitted from the sample when the sample is irradiated with the electron beam, and obtains a spectrum; The control unit acquiring a first spectrum obtained by the X-ray detector with the electron beam irradiation angle set to the first irradiation angle; acquiring a second spectrum obtained by the X-ray detector with the electron beam irradiation angle set to the second irradiation angle; Electron microscope.

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