Observation method and observation device

Abstract

To provide an observation method by which a predetermined defect included in a specimen having a crystal structure can be easily selected and observed with high accuracy.SOLUTION: An observation method of the present invention is a method for observing a defect of a specimen 101 having a crystal structure using a transmission electron microscope 100, and includes the steps of: adjusting a direction of the specimen 101 in such a manner that a predetermined crystal zone axis included in the specimen 101 installed in the transmission electron microscope 100 becomes parallel with a symmetry axis 102A of distribution of electron beams 102 with which the specimen 101 is irradiated; adjusting a position of an opening 104A of a rear objective lens diaphragm 104 in such a manner that the symmetric axis of the distribution of the electron beams 102 contributing to image formation becomes non-parallel with an optical axis 107 of the transmission electron microscope 100; and performing irradiation with and detection of the electron beams 102 in a STEM mode, scanning a predetermined region and obtaining a STEM image using an electronic detector 103 which is installed so as to face the opening 104A.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an observation method and an observation apparatus for observing defects of a sample having a crystal structure using a transmission electron microscope.

Background Art

[0002] When observing defects of a sample having a crystal structure, a transmission electron microscope (TEM) is used. Observation modes by a transmission electron microscope include a CTEM mode and a STEM mode. The CTEM mode is a mode in which a parallel electron beam is irradiated onto the entire observation region at once to obtain a projection image with a camera, whereas the STEM mode is a mode in which a convergent electron beam is moved without limitation over the observation region to obtain a scanned image. In addition, with respect to the incident condition of the electron beam by a transmission electron microscope, there are an on-zone condition in which the symmetry axis of the distribution of the incident electron beam is parallel to a predetermined zone axis included in the sample, and an off-zone condition in which it is inclined. In addition, with respect to the imaging condition of the electron beam by a transmission electron microscope, there are an on-axis condition in which the symmetry axis of the distribution of the imaging electron beam overlaps with the optical axis, and an off-axis condition in which it does not overlap with the optical axis.

[0003] Selective observation of defects using an electron microscope has long been carried out in the CTEM mode, and in the electron beam incidence conditions and imaging conditions, a combination of off-zone conditions and on-axis conditions suitable for the CTEM mode is often selected (Non-Patent Document 1). However, in this combination, for the selection of an appropriate diffraction spot according to the nature of the defect to be observed, a delicate adjustment of the sample tilt angle is essential, and advanced techniques are required. Regarding the off-axis condition of selecting a diffraction spot away from the optical axis, since the selected electron beam reaches a position off the optical axis of the projection lens, sufficient spatial resolution cannot be obtained, so it is considered unfavorable. It is known that sufficient spatial resolution can be obtained even under off-axis conditions by using the STEM mode that only detects the electron beam intensity near the back focal plane without using a projection lens (Non-Patent Document 2). However, conventionally, the off-zone condition has been exclusively adopted, and delicate adjustment of the sample tilt angle is essential, and the requirement for advanced techniques is the same as in the CTEM mode.

[0004] In the observation of defects such as point defects, dislocation lines, and dislocation loops, an operation of selecting defects of the same nature is performed. Since this operation is carried out under a large number of conditions for one sample, it is required to have high resolution, high imaging selectivity, and be easy.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide an observation method and an observation apparatus that enable easy selection and observation of predetermined defects contained in a sample having a crystal structure with high precision.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention employs the following means.

[0008] (1) An observation method according to an aspect of the present invention is a method for observing defects in a sample having a crystal structure using a transmission electron microscope, the method including: a sample adjustment step of adjusting the orientation of the sample so that a predetermined zone axis included in the sample installed in the transmission electron microscope is parallel to the symmetry axis of the distribution of the electron beam irradiating the sample; a rear objective lens aperture adjustment step of adjusting the position of the aperture of the rear objective lens so that the symmetry axis of the distribution of the electron beam contributing to imaging is non-parallel to the optical axis of the transmission electron microscope; and a STEM image acquisition step of performing irradiation and detection of the electron beam in STEM mode, scanning a predetermined region, and obtaining a STEM image using an electron detector installed so as to face the aperture.

[0009] (2) In the observation method described in (1) above, in the rear objective lens aperture adjustment step, it is preferable to adjust the position of the aperture so as to select a diffraction disk existing in a direction orthogonal to the major axis direction of the defect to be observed from the optical axis.

[0010] (3) In the observation method described in (1) above, in the rear objective lens aperture adjustment step, it is preferable to adjust the position of the aperture so as to select a diffraction disk including Kikuchi lines orthogonal to the major axis direction of the defect to be observed.

[0011] (4) In the observation method according to any one of (1) to (3) above, in the rear objective lens aperture adjustment step, it is preferable to adjust the position of the aperture so that a diffraction disk existing outside the diffraction disk closest to the transmission disk is selected.

[0012] (5) In the observation method according to any one of (1) to (4) above, it is preferable to further include a condenser lens aperture adjustment step of adjusting the condenser lens aperture so that the convergence angle of the electron beam with respect to the sample is 1 mrad or more and 10 mrad or less.

[0013] (6) In the observation method according to (5) above, it is preferable to select, with the rear objective lens aperture, a range that is the same as the size of the diffraction disk determined by the size and position of the condenser lens aperture and the excitation current of the front objective lens.

[0014] (7) In the observation method according to (6) above, a diffraction disk selection step of selecting a diffraction disk may be further included by adjusting at least one of the size and position of the aperture of the rear objective lens aperture, the excitation current of the front objective lens, and the distance between the rear objective lens aperture and the rear objective lens.

[0015] (8) An observation apparatus according to one aspect of the present invention is an observation apparatus used in the observation method according to any one of (1) to (3) above, and includes the transmission electron microscope, and an arithmetic unit that calculates a range of the tilt angle of the sample corresponding to the diameter of the selected diffraction disk at the back focal plane, and the distance between the selected diffraction disk and the closest diffraction disk.

[0016] (9) The observation apparatus according to (7) above further includes an adjustment unit that adjusts at least one of the position and size of the aperture of the rear objective lens aperture and the distance between the rear objective lens aperture and the rear objective lens based on the calculation result of the arithmetic unit.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide an observation method and an observation apparatus that can easily select and observe a predetermined defect contained in a sample having a crystal structure with high accuracy.

Brief Description of the Drawings

[0018]

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Mode for Carrying Out the Invention

[0019] Hereinafter, an observation method and an observation apparatus according to an embodiment to which the present invention is applied will be described in detail with reference to the drawings. Note that the drawings used in the following description may show the characteristic portions enlarged for the sake of clarity, and the dimensional ratios of the respective components are not necessarily the same as the actual ones. Also, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and it can be appropriately modified and implemented without changing the gist thereof.

[0020] FIG. 1 is a diagram for explaining an observation apparatus 100A according to an embodiment of the present invention. The observation apparatus 100A is an apparatus for observing defects of a sample 101 having a crystal structure, and includes a transmission electron microscope 100 and an arithmetic unit 113.

[0021] The transmission electron microscope 100 is a generally known transmission type electron microscope, and mainly includes an electron gun (not shown) that irradiates an electron beam 102 onto the sample 101, optical systems 104, 106, 116 to 119, etc. that adjust the width of the electron beam 102, and a camera 105 that detects the diffraction disk of the electron beam 102 that has passed through the sample 101. FIGS. 2(a) to (c) are diagrams showing the positional relationships that adjacent diffraction disks 103 among the detected diffraction disks 103 can take.

[0022] The arithmetic unit 113 calculates the magnitude θ of the capture angle corresponding to the radius of the diffraction disk 103 at the rear focal plane of the transmission electron microscope 100 C , and the capture angle θ corresponding to the distance between the selected diffraction disk and the nearest diffraction disk I It is a device having a function of calculating θ. θ I ≧2θ C In the case of (Figs. 2(a) and (b)), θ I less than θ / 2 (preferably 0.8×θ C or more), the radius r of the aperture 104A of the back objective lens aperture 104 A , and the combination of the distance H between the back objective lens aperture 104 and the sample 101 are calculated. θ I <2θ C In the case of (Fig. 2(c)), θ C -θ I less than -θ / 2 (preferably 0.8×(θ C -θ I / 2) or more), the radius r of the aperture 104A that satisfies the angular range A , and the combination of the distance H are calculated.

[0023] The observation device 100A may further include an adjustment device 114. The adjustment device 114 is a device having a function of adjusting at least one of the position and size of the aperture 104A of the back objective lens aperture 104 and the distance H between the back objective lens aperture 104 and the sample 101 based on the calculation result of the arithmetic unit 113.

[0024] Figs. 3(a) to (d) are diagrams for explaining an observation method (observation conditions) according to an embodiment of the present invention. The observation method of this embodiment is a method of observing defects of a sample 101 having a crystal structure using a transmission electron microscope 100 or an observation device 100A, and includes a sample adjustment step and a back objective lens aperture adjustment step. In the observation method of this embodiment, the irradiation of the electron beam 102 is performed in the STEM mode of scanning a predetermined region (observation region). As a result, the electron beam 102 is evenly irradiated over the entire sample 101, so that a high-resolution image can be obtained regardless of the position of the sample 101.

[0025] Regarding the electron beam incidence conditions in a transmission electron microscope, an on-zone condition is adopted where the symmetry axis of the incident electron beam distribution is parallel to a predetermined zone axis contained in the sample. Therefore, the orientation of the sample can be easily fixed, and advanced techniques and labor for adjusting the tilt angle of the sample are unnecessary.

[0026] Regarding the electron beam imaging conditions in a transmission electron microscope, an off-axis condition is adopted where the symmetry axis of the imaging electron beam distribution does not overlap with the optical axis. Therefore, an arbitrary diffraction disk considering conditions such as the shape and distribution of defects can be selected.

[0027] (Sample adjustment process) As shown in Fig. 3(a), a sample 101 is placed on a support stage (not shown) of a transmission electron microscope 100, and the sample 101 is irradiated with an electron beam. From among a plurality of zone axes contained in the sample 101, as shown in Fig. 3(b), a predetermined zone axis 101A to be observed is searched for. The support stage is tilted biaxially (rotation angles α, β) so that the found zone axis 101A is parallel to the symmetry axis 102A of the distribution of the electron beam (incident electron beam) irradiating the sample 101, and the orientation of the sample 101 is adjusted. The diffraction disk 103 of the electron beam 102 that has passed through the sample 101 is detected by a camera 105.

[0028] (Rear objective lens aperture adjustment process) As shown in Fig. 3(c), the position of the aperture 104A of the rear objective lens aperture 104 is adjusted so that the symmetry axis 102B of the distribution of the electron beam (imaging electron beam) contributing to imaging is non-parallel (intersects) with the optical axis 107 of the transmission electron microscope 100 and so that the electron beam forming the diffraction disk passes through. The selection conditions for the diffraction disk will be described later.

[0029] Select, with the rear objective lens aperture 104, a range that is the same as the size of the diffraction disk determined by the size and position of the condenser lens aperture and the excitation current of the front objective lens. A diffraction disk selection step of selecting the diffraction disk 103 may further be included by adjusting at least one of the size and position of the aperture 104A of the rear objective lens aperture, the excitation current of the front objective lens, and the distance between the rear objective lens aperture 104 and the rear objective lens 106.

[0030] (STEM image acquisition step) As shown in FIG. 3(d), perform irradiation and detection of the electron beam in the STEM mode, detect only the electron beam that has passed through the aperture 104A with the electron detector 115 installed so as to face the aperture 104A, and obtain a STEM image.

[0031] FIGS. 4 and 5 are diagrams for explaining the selection conditions of the diffraction disk. Here, the major axis directions L 1 , L 2 having two types of defects (dislocation loops) C 1 , C 2 are formed inside the sample 101 and are assumed to be mixed. Let the direction of the major axis of the defect C 1 be L 2 , and let the direction of the major axis of the defect C 2 be L 1 .

[0032] FIG. 4(a) is an image diagram of the camera image of the diffraction disk on the rear focal plane under the on-zone condition. As an example, the first diffraction disk 103A located at the position of the direction L 1 from the optical axis 107 is selected and is indicated by a dashed line. FIG. 4(b) is an image diagram of the camera image of the rear objective lens aperture with the position of the aperture 104A aligned with the position of the first diffraction disk 103A selected in FIG. 4(a). FIG. 4(c) is an image diagram of the scanning image obtained by detecting the electron beam 102 passing through the aperture 104A in FIG. 4(b). By selecting the first diffraction disk 103A, the defect C 1 having a major axis in the direction L 2 disappears, and the direction L 1 and the direction L orthogonal to it2 Defect C having a major axis in 1 only is displayed.

[0033] Fig. 5(a) is an image diagram of a camera image with a diffraction disk on the rear focal plane under on-zone conditions. As another example, from the optical axis 107 in the direction L 2 the second diffraction disk 103B located at the position of is selected and shown by a dashed line. Fig. 5(b) is an image diagram of a camera image of a rear objective lens aperture with the position of the aperture 104A aligned with the position of the second diffraction disk 103B selected in Fig. 5(a). Fig. 5(c) is an image diagram of a scanning image obtained by detecting the electron beam 102 passing through the aperture 104A in Fig. 5(b). By selecting the second diffraction disk 103B, the defect C 2 having a major axis in 1 disappears, and only the defect C 2 having a major axis in the direction L 1 orthogonal to becomes in a state where only it is displayed. 2

[0034] By utilizing these phenomena, only specific defects can be selected and observed. For example, when observing only the defect C 2 having a major axis in the 1 direction L, the position of the aperture 104A of the rear objective lens aperture is adjusted so that only the electrons constituting the diffraction disk 103A existing away in the direction L 1 orthogonal to the major axis direction L 2 of the defect C to be observed from the optical axis 107 pass through. Then, as shown in Fig. 4(c), since the defect C 1 having a major axis in the direction L 1 disappears, only the defect C 2 having a major axis in the remaining direction L 2 can be observed. 1

[0035] Conversely, for example, when observing only the defect C 1 having a major axis in the 2 direction L, from the optical axis 107, the major axis direction L 2 of the defect C to be observed 1Direction L orthogonal thereto 2 Adjust the position of the aperture 104A of the rear objective lens stop so that only the electrons constituting the diffraction disk 109 existing away in the direction L orthogonal to the long axis direction L shown in Fig. 5(c) pass through. Then, as shown in Fig. 5(c), the defect C having the long axis direction L 2 disappears, so that only the defect C having the remaining long axis direction L 1 can be observed. 1 Defect C having 2

[0036] Fig. 6 is a diagram showing a preferable position of the selected area 109 on the rear focal plane 116 when enhancing the contrast between the defect and the portion (matrix phase) excluding the defect. Adjust the position of the aperture 104A of the rear objective lens stop to the area (diffraction disk) 109 including the Kikuchi line 110 orthogonal to the long axis direction L 3 of the defect C to be observed. Then, in the imaging area 106C, the contrast of the defect C 3 with respect to the matrix phase can be enhanced. 3

[0037] Fig. 7 is a diagram showing a preferable position of the selected area 109 on the rear focal plane 116. When selecting the imaging area 109A of the diffraction disk closest to the transmission disk including the optical axis 107 with the rear objective lens, the sharpness of the imaging is lost compared to the case where the diffraction disks after the second closest and subsequent ones outside this area 109A are selected with the rear objective lens stop. On the other hand, as the distance from the optical axis 107 increases, the amount of electrons passing through the rear objective lens stop decreases, and the S / N ratio of the imaging tends to deteriorate. Therefore, adjust the position of the aperture 105A of the rear objective lens stop so that only the electron beams constituting the diffraction disk 109A closest to the transmission disk intersecting the optical axis 107, preferably the diffraction disk closest to the second, and the diffraction disk closest to the third pass through. Then, an imaging with enhanced sharpness can be obtained.

[0038] (Condenser lens stop adjustment step) ​​Figs. 8(a) and 8(b) are diagrams for explaining the cases where the diffraction disks (diffraction spots) appearing on the back focal plane overlap and do not overlap when the condenser lens aperture 111 is adjusted. It is preferable to adjust the convergence angle 112 of the electron beam with respect to the sample using the condenser lens aperture 111 so that only a region of about several milliradians (mrad) passes from the center of the Ronchigram.

[0039] If the convergence angle 112 is made too large, as shown in Fig. 8(a), the diffraction disks appearing on the back focal plane overlap with each other, making it difficult to discriminate defects. When the convergence angle 112 is set to an appropriate size, as shown in Fig. 8(b), the diffraction disks are separated from each other, making it easy to discriminate defects. Note that if the convergence angle 112 is made too small, a stripe pattern occurs in the matrix phase, making it difficult to discriminate defects. The appropriate size of the convergence angle 112 depends on the crystal structure of the observed sample and the selected zone axis, but is preferably generally 3.4 mrad or more and 9.4 mrad or less, and more preferably about 6.4 mrad.

[0040] As described above, in the observation method of the present embodiment, the irradiation and detection of the electron beam are performed in the STEM mode, and the imaging electron beam is directly detected by the electron detector. Therefore, an image of the imaging region can be obtained with high resolution regardless of the distance between the imaging electron beam and the optical axis.

[0041] Also, in the observation method of the present embodiment, as the incident condition of the electron beam by the transmission electron microscope, an on-zone condition is adopted in which the symmetry axis of the distribution of the incident electron beam is parallel to a predetermined zone axis included in the sample. Therefore, the orientation of the sample can be easily fixed, and advanced techniques and labor for adjusting the tilt angle of the sample are not required.

[0042] Also, in the observation method of the present embodiment, as the imaging condition of the electron beam by the transmission electron microscope, an off-axis condition is adopted in which the symmetry axis of the distribution of the imaging electron beam does not overlap with the optical axis. Therefore, an arbitrary diffraction disk considering conditions such as the shape and distribution of defects can be selected to obtain a STEM image.

Example

[0043] Hereinafter, the effects of the present invention will be made clearer by examples. Note that the present invention is not limited to the following examples, and can be implemented with appropriate modifications without changing the gist thereof.

[0044] (Example 1) In accordance with the above embodiment, defect observation of a sample was performed. As the sample, a plate material of <001> single crystal pure aluminum (purity 99.99% or more) containing an intrusion-type dislocation loop was used. The intrusion-type dislocation loop was generated by irradiating a plate material of <001> single crystal pure aluminum with an argon ion beam of 100 V and then irradiating it with an electron beam. The generated intrusion-type dislocation loops included those with the major axis parallel to

[0440] and those parallel to

[0440] . In the back objective lens aperture adjustment step, the position of the aperture of the back objective lens was adjusted so that only the electron beam constituting 440, which is one of the disks second closest to the transmission disk, passed through.

[0045] FIG. 9(a) is an image showing the positions of an electron detector (circular) and the back objective lens aperture on the back focal plane. FIG. 9(b) is a STEM image obtained only with the electron beam constituting the diffraction disk of 440. In this image, the defects with the major axis parallel to

[0440] disappear, and only the defects with the major axis orthogonal to

[0440] can be confirmed. From this result, it can be seen that by adjusting the position of the aperture of the back objective lens at the

[0001] zone axis incidence and imaging only with the electron beam constituting the diffraction pattern away from the optical axis in the direction

[0440] orthogonal to the major axis direction

[0440] of the defect to be observed, only the defect to be observed can be selected and displayed.

[0046] (Example 2) In the back objective lens aperture adjustment step, defect observation of the sample was performed in the same manner as in Example 1, except that the position of the aperture of the back objective lens was adjusted so that only the electron beam constituting 440, which is one of the disks second closest to the transmission disk, passed through.

[0047] Figure 9(c) is a STEM image obtained only with the electron beam constituting the diffraction disk of 440. In this image, the defect with the major axis parallel to

[0440] disappears, and only the defect with the major axis orthogonal to

[0440] can be confirmed. From this result, by adjusting the position of the aperture of the back objective lens at the time of

[0001] zone axis incidence, and imaging the electron beam in the region away from the optical axis in the direction

[0440] orthogonal to the major axis direction

[0440] of the defect to be observed, it can be understood that only the defect to be observed can be selected and displayed.

[0048] (Comparative Example 1) Defect observation of the sample was performed in the same manner as in Example 1, except that the back objective lens aperture was not used and the electron detector (circular) was in a state of detecting the entire transmission disk and a part of the diffraction disk closest to the transmission disk. Figure 9(d) is a bright-field STEM image obtained only with the entire transmission disk and a part of the diffraction disk closest to the transmission disk. In this image, it can be seen that two defects are mixed and displayed, and for example, it is difficult to visually recognize the major axis of the fine dislocation loop existing in the elliptical region surrounded by the solid line as parallel to

[0440] .

[0049] When eliminating the display of a specific defect, in the prior art, it was necessary to perform a precise sample tilt to search for the same field of view and readjust the focus, etc. In contrast, in the present invention, as in Examples 1 and 2, by using the back objective lens aperture, it is only necessary to move the aperture of the back objective lens to the region away from the optical axis in the direction parallel to the major axis direction of the defect that is not desired to be displayed, and simplification can be achieved.

[0050] (Examples 3, 4, 5) Defect observation of the sample was performed in the same manner as in Example 1, except that the diffraction disks appearing in the directions

[0240] ,

[0420] ,

[0420] including the Kikuchi lines orthogonal to the major axis direction of the defect were selected.

[0051] Figure 10(a) is an image showing the positions of the electron detector (circular) and the rear objective lens aperture on the rear focal plane. In this image, the Kikuchi lines of the (220) plane and the (220) plane are shown as solid white lines and dotted white lines. All of the Kikuchi lines are orthogonal to the

[0440] direction. Figure 10(b) is a STEM image obtained only with the electron beams that constitute the diffraction disk of 240. Figure 10(c) is a STEM image obtained only with the electron beams that constitute 420. Figure 10(d) is a STEM image obtained only with the electron beams that constitute 420. Figure 10(e) is a STEM image obtained only with the electron beams that constitute the diffraction disk of 440 that does not include the Kikuchi line orthogonal to the major axis of the defect (corresponding to Example 2). Figure 10(f) is a bright-field STEM image obtained only with the entire transmission disk and a part of the diffraction disk closest to the transmission disk (corresponding to Comparative Example 1).

[0052] In the images of Figures 10(b) to (d), the contrast of the dislocation loop with respect to the matrix phase is high. Furthermore, in the same images, the luminance inside the dislocation loop is particularly high. By measuring the distance between the outside of the dislocation loop where the luminance is particularly high and the boundary with the matrix phase, the size of the dislocation loop can be known. On the other hand, in Figure 10(e), the dislocation loop with the major axis parallel to the

[0440] direction has completely disappeared, and although the imaging selectivity is high, the contrast of the defect with respect to the matrix phase is low. In Figure 10(f), selective imaging of the dislocation loop itself has not occurred.

[0053] Figure 11 is a graph showing the distribution of the luminance of the defect calculated from the images of Figures 10(b), (c), and (e). The horizontal axis of the graph indicates the distance (nm) from the center of the dislocation loop in region A. The vertical axis of the graph indicates the luminance normalized by the minimum value. From this graph, it can be seen that the luminance of the defect when 240 and 420 are selected is increased to about 1.5 times the luminance of the defect when 440 is selected. From this result, it can be seen that by selecting the diffraction disk including the Kikuchi line orthogonal to the major axis, it becomes possible to observe the dislocation loop in an image with high contrast.

[0054] FIG. 12 is a graph showing the luminance distribution of defects calculated from the images of FIGS. 10(b), (d), and (f). The horizontal axis of the graph indicates the distance (nm) from the center of the dislocation loop in region B. The vertical axis of the graph indicates the luminance. From this graph, it can be seen that for the defects observed in bright field, the luminances of the two peaks on opposite sides are different, whereas for the defects observed when 420, 420 is selected, the luminances of the two peaks are comparable. Also, when 420 is selected, the peak luminance is particularly high, and it can be seen that there is a peak luminance inside the actual position of the dislocation loop (the peak position in the bright field image). From this result, it can be understood that by selecting a diffraction disk including Kikuchi lines, precise measurement of the defect size becomes possible.

[0055] (Examples 6, 7) In the back objective lens aperture adjustment step, defect observation of the sample was performed in the same manner as in Example 1, except that the position of the aperture of the back objective lens was adjusted so that only the electron beams constituting the diffraction disks of 220, 220 that are closest to the transmission disk passed through.

[0056] FIG. 13(a) is an image showing the positions of the electron detector (circular) and the back objective lens aperture on the back focal plane. FIG. 13(b) is a STEM image obtained only with the electron beams constituting the diffraction disk of 220. FIG. 13(d) is a STEM image obtained only with the electron beams constituting the diffraction disk of 220. FIG. 13(c) is a bright field STEM image obtained using only the entire transmission disk and a part of the diffraction disk closest to the transmission disk without using the back objective lens aperture (corresponding to Comparative Example 1).

[0057] When the diffraction disk closest to the first one is selected as in Examples 6 and 7 (FIGS. 13(b) and (d)), it can be seen that the sharpness is lost compared to when the diffraction disk closest to the second one is selected as in Examples 1 and 2 (FIGS. 9(b) and (c)). From this result, it can be understood that when seeking the sharpness of imaging, it is more preferable to select the diffraction disk closest to the second one than to select the diffraction disk closest to the first one.

[0058] (Example 8) The defect observation of the sample was performed in the same manner as in Example 1, except that a diffraction disk in the direction 420 including Kikuchi lines orthogonal to the major axis direction of the defect was selected.

[0059] (Comparative Example 2) The defect observation of the sample was performed in the same manner as in Example 1, except that the electron beam irradiation was performed in the CTEM mode in which a parallel electron beam was irradiated onto the entire observation region at once and detected by a camera.

[0060] FIG. 14(a) is an image showing each position of the rear objective lens aperture at the back focal plane in Comparative Example 2 where the electron beam irradiation and detection are performed in the CTEM mode. FIG. 14(b) is a CTEM image obtained by selecting a transmission spot with the rear objective lens aperture in Comparative Example 2. FIG. 14(c) is a CTEM image obtained by selecting a diffraction spot of 420 with the rear objective lens aperture in Comparative Example 2. FIG. 14(d) is an image showing the positions of the electron detector (annular) and the rear objective lens aperture at the back focal plane in Example 8 where the electron beam irradiation and detection are performed in the STEM mode. FIG. 14(e) is a STEM image obtained by selecting a transmission disk with the electron detector (annular) in Example 8. FIG. 14(f) is a STEM image obtained by selecting a diffraction disk of 420 in Example 8.

[0061] In Example 8, a clear image of the defect was obtained, while in Comparative Example 2, an image that allows accurate confirmation of the defect was not obtained. This difference is due to the difference in resolution at positions away from the optical axis. That is, in Example 8 using the STEM mode, since the electron beam transmitted through the back objective lens aperture is directly detected by the electron detector, even if the selected area by the back objective lens aperture is away from the optical axis, an image can be obtained with the same resolution as near the optical axis. On the other hand, in Comparative Example 2 using the CTEM mode, when the selected area by the back objective lens aperture, where the electron beam transmitted through the back objective lens aperture is imaged on the camera via a projection lens or the like installed behind the back focal plane, is away from the optical axis, the resolution becomes lower than that near the optical axis. From this result, it can be understood that even when enhancing the selection control of the bonding region at a position away from the optical axis, in order to be able to acquire an image with high resolution, it is necessary to perform electron beam irradiation and detection in the STEM mode.

Explanation of Signs

[0062] 100 ··· Transmission electron microscope 101 ··· Specimen 101A ··· Zone axis 102 ··· Electron beam 102A ··· Symmetry axis of incident electron beam 102B ··· Symmetry axis of imaging electron beam 103, 103A, 103B ··· Diffraction disk 104 ··· Back objective lens aperture 104A ··· Aperture 105 ··· Camera 106 ··· Objective lens 107 ··· Optical axis 108 ··· Transmission disk 109 ··· Diffraction disk 109A ··· Diffraction disk closest to the transmission disk 109B ··· Diffraction disk second closest to the transmission disk 110 ··· Kikuchi line 111 ··· Condenser lens aperture 112 ··· Convergence angle 113 ··· Arithmetic unit 114 ··· Adjusting device 115 ··· Electronic detector 116 ··· Rear focal plane

Claims

1. A method for observing defects in a sample having a crystal structure using a transmission electron microscope, comprising: a sample adjustment step of adjusting the orientation of the sample so that a predetermined zone axis included in the sample installed in the transmission electron microscope is parallel to the symmetry axis of the distribution of the electron beam irradiating the sample; a rear objective lens aperture adjustment step of adjusting the position of the aperture of the rear objective lens so that the symmetry axis of the distribution of the electron beam contributing to imaging is non-parallel to the optical axis of the transmission electron microscope; a STEM image acquisition step of performing irradiation and detection of the electron beam in STEM mode, scanning a predetermined region, and obtaining a STEM image using an electron detector installed so as to face the aperture.

2. In the rear objective lens aperture adjustment step, The observation method according to claim 1, wherein the position of the aperture is adjusted so as to select a diffraction disk existing in a direction orthogonal to the major axis direction of the defect to be observed from the optical axis.

3. In the rear objective lens aperture adjustment step, The observation method according to claim 1, wherein the position of the aperture is adjusted so as to select a diffraction disk including Kikuchi lines orthogonal to the major axis direction of the defect to be observed.

4. In the rear objective lens aperture adjustment step, The observation method according to any one of claims 1 or 2, wherein the position of the aperture is adjusted so that a diffraction disk existing outside the diffraction disk closest to the transmission disk is selected.

5. The observation method according to any one of claims 1 or 2, further comprising a condenser lens aperture adjustment step of adjusting, using a condenser lens aperture, the convergence angle of the electron beam with respect to the sample to be 1 mrad or more and 10 mrad or less.

6. The observation method according to claim 5, wherein the same range as the size of the diffraction disk determined by the size and position of the condenser lens aperture and the excitation current of the front objective lens is selected by the rear objective lens aperture.

7. The observation method according to claim 6, further comprising a diffraction disk selection step of selecting a diffraction disk by adjusting at least one of the size and position of the aperture of the rear objective lens, the excitation current of the front objective lens, and the distance between the rear objective lens aperture and the rear objective lens.

8. An observation apparatus used in the observation method according to any one of claims 1 to 3, the transmission electron microscope, and a computing device that computes a range of the tilt angle of the sample corresponding to the diameter of the selected diffraction disk and a distance between the selected diffraction disk and the nearest diffraction disk at a rear focal plane. The observation apparatus is characterized by comprising these components.

9. Based on the computation result of the computing device, the observation apparatus according to claim 8, further comprising an adjustment device that adjusts at least one of a position and a size of an aperture of the rear objective lens diaphragm and a distance between the rear objective lens diaphragm and the rear objective lens.

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