Analysis method

Abstract

To provide an analysis method which can reduce damage on a sample due to the electron beam irradiation and acquire an electron diffraction image highly accurately.SOLUTION: There is provided an analysis method by a scanning transmission electron microscope including: a dark field detector 21 which irradiates a sample 31 with an electron beam 10 and detects the transmitted or scattered electron beam to detect a dark field image; and an electron beam detector 22 which detects the electron beam passing through a hollow part of the dark field detector 21 out of the electron beams passing through or scattered from the sample to detect an electron diffraction image at an irradiation point 311 of the electron beam. The method simultaneously performs detection of the dark field image of a region of interest AA by scanning the plurality of irradiation points 311 set in the region of interest AA by sequentially irradiating them with the electron beam 10 at a preset incidence angle, and detection of an NBD image for each of the plurality of irradiation points 311.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] This embodiment relates to an analysis method.

Background Art

[0002] In metals and semiconductor materials, as a method for specifying the crystal orientation in a local region, an analysis method using nano-beam electron diffraction (NBD) by a scanning transmission electron microscope (STEM) is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of this embodiment is to provide an analysis method capable of reducing damage to a sample caused by electron beam irradiation and acquiring an electron diffraction image with high precision.

Means for Solving the Problems

[0005] The analysis method of this embodiment accelerates the electron beam emitted from the beam irradiation unit, irradiates the sample so that the focus of the electron beam is located thereon, and detects the electron beam transmitted through the sample or scattered by the sample, thereby detecting a dark-field image of the sample with an annular first detector, and detecting an electron diffraction image at the irradiation position of the electron beam of the sample by detecting the electron beam that has passed through the hollow portion of the first detector among the electron beams transmitted through the sample or scattered by the sample. It is an analysis method using a scanning transmission electron microscope having a second detector. By scanning a plurality of irradiation points set in the analysis region on the surface of the sample by sequentially irradiating the electron beam at a preset incident angle, detection of the dark-field image of the analysis region and detection of the electron diffraction image for each of the plurality of irradiation points are performed simultaneously. In the process, setting a plurality of the incident angles, detecting, for each of the set incident angles, the dark-field image and the electron diffraction images for each of the plurality of irradiation points, detecting a relative displacement amount of the plurality of detected dark-field images, correcting the position of the irradiation point based on the displacement amount, and generating an integrated electron diffraction image by integrating the plurality of electron diffraction images obtained from the irradiation points with the same position after correction. The incident angle is set as a combination of a first angle formed between a direction perpendicular to the surface of the sample and the incident central axis direction of the electron beam, and a second angle formed between a direction for scanning the plurality of irradiation points and the incident central axis direction of the electron beam, and the first angle and the second angle can be set independently of each other Characterized by this.

Brief Description of the Drawings

[0006]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0007] Hereinafter, embodiments will be described with reference to the drawings. (1. Apparatus) FIG. 1 is a schematic diagram for explaining a configuration example of a scanning transmission electron microscope in an embodiment. The scanning transmission electron microscope of this embodiment includes a beam irradiation unit 11, a condenser lens 12, a scan coil 13, an objective lens 14, an intermediate lens 15, a de-scan coil 16, and a projection lens 17. The scanning transmission electron microscope also includes a dark-field detector 21, an electron beam detector 22, and a control unit 40. Note that the scanning transmission electron microscope may further include a display unit 50 for displaying analysis results. The sample 31 is held by a specimen holding unit (not shown) and is disposed between the objective lens 14 and the intermediate lens 15.

[0008] When two orthogonal directions parallel to the surface of the sample 31 (the surface on which the electron beam 10 is incident) are defined as the x direction and the y direction, and the direction perpendicular to the surface of the sample 13 (the direction perpendicular to the xy plane) is defined as the z direction, along the z direction, the beam irradiation unit 11, the condenser lens 12, the scan coil 13, the objective lens 14, the specimen 31, the intermediate lens 15, the de-scan coil 16, the projection lens 17, the dark-field detector 21, and the electron beam detector 22 are arranged in this order.

[0009] The beam irradiation unit 11 includes a field emission electron gun 111 that serves as an electron source for emitting an electron beam 10, and an acceleration unit 112 that accelerates the emitted electron beam 10. The condenser lens 12 converges the electron beam 10 accelerated in the acceleration unit 112. The scan coil 13 scans the irradiation position of the electron beam 10 on the surface of the sample 31 in the x direction and / or the y direction. The objective lens 14 further converges the electron beam 10 to form an extremely fine electron beam (nanobeam).

[0010] The intermediate lens 15 magnifies the electron diffraction image formed by the objective lens 14 and forms an image on the object plane of the subsequent projection lens 17. The de-scan coil 16 returns the positional deviation of the electron beam 10 from the optical axis caused by the scan coil 13 to the optical axis. That is, the irradiation position of the electron beam 10 is corrected by shifting the irradiation position of the electron beam 10 in the opposite direction by the amount by which the irradiation position of the electron beam 10 is shifted from the optical axis of the condenser lens 12 by the scan coil 13. The projection lens 17 further magnifies the electron diffraction image magnified by the intermediate lens 15 and forms an image on the dark field detector 21 and the electron beam detector 22.

[0011] The dark field detector 21 as the first detector is a ring-shaped electron beam detector having an opening formed in the central portion. It detects electrons that are scattered and diffracted at high angles among the electrons transmitted through the sample 31. In the following description, the electron diffraction image detected by the dark field detector 21 is referred to as a dark field image (annular dark field image). The electron beam detector 22 as the second detector detects electrons that have passed through the opening of the dark field detector 21 among the electrons transmitted through the sample 31. As the electron beam detector 22, for example, a fluorescent plate or a camera capable of directly detecting an electron beam is used. In the case of a fluorescent plate, the detected electrons are converted into light to obtain an electron diffraction image. In the following description, the electron diffraction image detected by the electron beam detector 22 is referred to as an NBD image.

[0012] The control unit 40 includes a central processing unit (CPU) 401 as a processor and a RAM 402. The CPU 401 operates according to a program stored in a memory (not shown), and has a control function for controlling the operations and settings of each part (such as the beam irradiation unit 11, condenser lens 12, scan coil 13, objective lens 14, intermediate lens 15, descan coil 16, projection lens 17, etc.) that constitutes the scanning transmission electron microscope. It also has a data analysis function for analyzing the electron diffraction images output from the dark field detector 21 and the electron beam detector 22. That is, it analyzes the electron diffraction images input from the dark field detector 21 and the electron beam detector 22 to identify the crystal orientation of the target region of the sample 31. The RAM 22 stores the analyzed data and various setting values. In addition, the RAM 22 may also store a database used for matching with the measured electron diffraction images for identifying the crystal orientation. (2. Analysis method) (2-1. Incident angle of electron beam) Next, an analysis method using the transmission electron microscope as described above will be explained. FIGS. 2A to 2C are diagrams for explaining the incident angle of the electron beam. The transmission electron microscope obtains an electron diffraction image while scanning the surface of the sample 31 with the electron beam 10. At this time, the electron beam 10 is irradiated while being tilted by a predetermined angle with respect to the surface of the sample 31 (see FIG. 2A). Prior to the explanation of the analysis method, the incident angle of the electron beam 10 will be defined using FIGS. 2B and 2C.

[0013] In each of FIGS. 2A to 2C, the central axis of the electron beam 10 is shown as axis CE. Also, the scanning direction of the electron beam 10 (the moving direction of the irradiation point 311 of the electron beam 10 on the sample 31) is indicated by a thick white arrow. Further, the two-dot chain line with an arrow indicates the direction (z direction) perpendicular to the surface of the sample 31. FIG. 2B is a view of the sample 31 seen from the y direction (xz plane view). As shown in FIG. 2B, the angle formed by the direction perpendicular to the surface of the sample 31 and the central axis CE of the electron beam 10 is defined as angle θ (first angle). Also, FIG. 2C is a view of the sample 31 seen from the direction (xy plane view). As shown in FIG. 2C, the angle formed by the scanning direction of the electron beam 10 and the axis CE of the electron beam 10 is defined as angle φ (second angle). That is, the incident angle of the electron beam 10 with respect to the surface of the sample 31 can be uniquely determined by angle θ and angle φ. (2-2. Analysis procedure) FIG. 3 is a flowchart for explaining an example of the analysis procedure of the sample. As shown in FIG. 3, the analysis of the sample 31 is performed in three steps. First, an observation region OA is set on the surface of the sample 31, and an image (electron diffraction image) in the observation region OA is acquired (S1). Subsequently, based on the electron diffraction image acquired in S1, a region of interest AA as an analysis region for crystal orientation analysis is set, and an image (electron diffraction image) in the region of interest AA is acquired (S2). Finally, the electron diffraction image acquired in S2 is analyzed to generate the crystal orientation distribution of the region of interest AA (S3). That is, S1 is a preliminary procedure for extracting the region (region of interest AA) for performing crystal orientation analysis, and S2 is a procedure for acquiring a high-precision electron diffraction image used for crystal orientation analysis.

[0014] FIG. 4 is a diagram for explaining the acquisition region of the electron diffraction image in each step of the analysis procedure. The observation region OA is a part of the surface of the sample 31. Inside the observation region OA, a region of interest AA is set. For example, the observation region OA is set to be several μm square in size, and the region of interest AA is set to be several nm to several tens of nm square in size.

[0015] For each step of the analysis procedure shown in FIG. 3, the specific procedure will be described below. Prior to the description of the specific procedure of the embodiment, the specific procedure of the comparative example will be described with reference to FIGS. 5 to 8. FIG. 5 is a flowchart for explaining an example of the analysis procedure in the comparative example. The procedure shown in FIG. 5 shows the specific procedure of S1 in FIG. 3.

[0016] First, an observation region OA is set on the surface of the sample 31, and an irradiation point interval PI1 is set (S101). Also, as the incident angle θ of the electron beam 10, a first precession angle θp1 is set. FIG. 6 is a diagram for explaining an example of the arrangement of irradiation points in the observation region. As shown in FIG. 6, the irradiation points 311_1, 311_2, …, 311_n of the electron beam 10 in the observation region OA are arranged at a constant interval PI1 along the scanning direction. Compared with the size of the observation region OA, the diameter of the irradiation point 311 (for example, about 1 nm in diameter) is small. When arranging the irradiation points 311 so that the entire observation region OA is evenly irradiated with the electron beam 10, the number of irradiation points 311 becomes extremely large and the processing time becomes long. Since S1 is a step for specifying the region of interest AA and obtaining an electron diffraction image necessary for analysis in the subsequent S2, in S101, the irradiation points 311_1, 311_2, …, 311_n are discretely arranged at a constant interval PI1 to reduce the number of irradiation points 311 and shorten the processing time.

[0017] Next, the irradiation position of the electron beam 10 is set to the first irradiation point 311_1 in the observation region OA (S102). That is, the control unit 40 controls the scan coil 13 so that the irradiation position (the convergence point on the surface of the sample 31) of the electron beam 10 coincides with the irradiation point 311_1.

[0018] Subsequently, the electron beam 10 is irradiated onto the surface of the sample 31 to obtain an electron diffraction image (S103). At this time, as shown by the dashed-dotted line with an arrow in FIG. 6, the electron beam 10 is subjected to precession motion (0° ≤ φ ≤ 360°) at the incident angle θp1. While the electron beam 10 irradiates the irradiation point 311_1, the electron detector 22 continuously detects electrons (integrates the detected electrons). That is, an electron diffraction image by integration is output from the electron detector 22. The time during which the electron detector 22 continuously detects electrons at one irradiation point 311 is referred to as the exposure time. The longer the exposure time is set, the more the detection amount of electrons increases, and thus the electron diffraction image becomes clearer. Note that the electron diffraction image obtained while the electron beam 10 is subjected to precession motion as in S103 is called a precession NBD image.

[0019] If the current irradiation point 311_i set as the irradiation position of the electron beam 10 is not the last irradiation point 311_n, that is, if there is an irradiation point 311 in the observation region OA for which a precession NBD image has not been obtained (S104, NO), the irradiation position of the electron beam 10 is moved from the current irradiation point 311_i to the next irradiation point 311_(i + 1) according to the irradiation point interval PI1 set in S101 (S105). Then, for the set irradiation point 311_(i + 1), S103 is executed to obtain a precession NBD image.

[0020] On the other hand, when the current irradiation point 311_i is the last irradiation point 311_n, that is, when the acquisition of the precession NBD images for all the irradiation points 311 in the observation region OA is completed (S104, YES), a transmission spot intensity map of the precession NBD images acquired at each irradiation point 311 is generated (S106). The transmission spot intensity map is obtained by pseudo-generating a bright-field image from the precession NBD images. From the precession NBD images acquired at each irradiation point 311, the electron intensity of the region due to the electrons transmitted through the sample 31 is extracted. Specifically, the electron intensity detected in the central region of the precession NBD image is extracted. By mapping the respective electron intensities to the positions of the respective irradiation points 311 in the observation region OA, a pseudo bright-field image is generated. Through the above series of procedures from S101 to S106, the acquisition (S1) of the image (electron diffraction image) in the observation region OA is completed.

[0021] FIG. 7 is a flowchart for explaining an example of the analysis procedure in the comparative example. The procedure shown in FIG. 7 shows the specific procedure of S2 in FIG. 3. First, a target region AA is set within the observation region OA. Also, the irradiation point interval PI2 and the second precession angle θp2, which is the incident angle θ of the electron beam 10, are set (S201). The target region AA is a region to be analyzed for specifying the crystal orientation. The target region AA is extracted from the pseudo bright-field image generated in S1.

[0022] For example, in a semiconductor device having a wiring region formed such that a plurality of metal wirings are regularly arranged on a silicon substrate, when analyzing the crystal orientation of the interface layer between the silicon substrate and the metal wiring, a cross-section of the wiring region (a cross-section including the silicon substrate and the metal wiring and cut along a plane perpendicular to the silicon substrate surface) is set as the observation region OA. Referring to the pseudo bright-field image of the observation region OA generated in S1, the position of the interface layer between the metal wiring and the silicon substrate in the observation region OA is specified. Then, the specified interface layer is extracted as the target region AA.

[0023] FIG. 8 is a diagram for explaining an example of the arrangement of irradiation points in the region of interest. As shown in FIG. 8, the irradiation points 311_1, 311_2, …, 311_m of the electron beam 10 in the region of interest AA are arranged at a constant interval PI2 along the scanning direction. The irradiation point interval PI2 is set according to the fineness of the analysis target. For example, when the analysis target is a fine substance such as fine particles or a narrow band such as an interface, the irradiation point interval PI2 is set small. Note that the irradiation point interval PI2 may be set to a value equal to or less than the diameter of the electron beam 10 so that adjacent irradiation points 311 have an overlap.

[0024] The second precession angle θp2 is set according to the diffraction pattern of the analysis target and the order of the diffraction line to be obtained. Generally, when the incident angle θ of the electron beam 10 is increased, the influence of the dynamical effect becomes smaller, so that higher-order diffraction becomes more clearly visible. However, when the incident angle θ is increased, the positional resolution decreases. The second precession angle θp2 is set in consideration of these. Note that the second precession angle θp2 may be the same angle as the first precession angle θp1.

[0025] Next, the irradiation position of the electron beam 10 is set to the first irradiation point 311_1 in the region of interest AA (S202). That is, the control unit 40 controls the scan coil 13 so that the irradiation position (the convergence point on the surface of the sample 31) of the electron beam 10 coincides with the irradiation point 311_1. Subsequently, the electron beam 10 is irradiated onto the surface of the sample 31 while performing precession motion (0° ≦ φ ≦ 360°) at a predetermined angle (the second precession angle θp2) set in advance, and a precession NBD image is acquired (S203).

[0026] When the current irradiation point 311_j set as the irradiation position of the electron beam 10 is not the last irradiation point 311_m, that is, when there is an irradiation point 311 for which the precession NBD image has not been acquired within the target region AA (S204, NO), the irradiation position of the electron beam 10 is moved from the current irradiation point 311_j to the next irradiation point 311_(j + 1) in accordance with the irradiation point interval PI2 set in S201 (S205). Then, for the set irradiation point 311_(j + 1), S203 is executed to acquire the precession NBD image.

[0027] On the other hand, when the current irradiation point 311_j is the last irradiation point 311_m, that is, when the acquisition of the precession NBD image has been completed for all the irradiation points 311 within the target region AA (S204, YES), the acquisition (S2) of the image (electron diffraction image) in the target region AA is terminated.

[0028] Finally, the precession NBD images acquired in S2 are analyzed to specify the crystal orientation of the target region AA (S3). Specifically, each of the plurality of precession NBD images acquired in S2 is compared with a plurality of NBD images (templates) that have been calculated in advance for various crystal orientations and stored in a database. The crystal orientation of the template with the highest degree of matching is specified as the crystal orientation at the irradiation point where the precession NBD image was acquired. In this way, the distribution of the crystal orientation in the target region AA of the sample 31 can be obtained. Note that crystal orientation mapping of the target region AA can be generated by assigning the same mark to the irradiation points having the same crystal orientation or connecting the irradiation points having the same crystal orientation with a line.

[0029] Next, the specific procedure of the embodiment will be described. While using FIGS. 9 to 14, the specific procedure of each step of the analysis procedure shown in FIG. 3 will be described below. FIG. 9A is a flowchart for explaining an example of the analysis procedure in the embodiment. The procedure shown in FIG. 9A shows the specific procedure of S1 in FIG. 3. Further, FIG. 9B is a diagram for explaining an example of the arrangement of the irradiation points in the observation region in the embodiment.

[0030] First, an observation region OA is set on the surface of the sample 31, and an irradiation point interval PI1 is set (S11). The setting of the observation region OA and the setting of the irradiation point interval PI1 in S11 are performed in the same manner as S101 in FIG. 5. That is, as shown in FIG. 9B, the arrangement of the irradiation points 311_1, 311_2, …, 311_n of the electron beam 10 in the observation region OA is the same as the arrangement in the comparative example (FIG. 6). That is, in S11, the irradiation points 311_1, 311_2, …, 311_n are discretely arranged at a constant interval PI1 to reduce the number of irradiation points 311 and shorten the processing time. Next, the incident angle θ of the electron beam 10 is set to 0° (S12). That is, the scan coil 13 is controlled so that the electron beam 10 is incident perpendicularly to the surface of the sample 31.

[0031] Subsequently, the irradiation position of the electron beam 10 is set to the first irradiation point 311_1 in the observation region OA (S13). That is, the control unit 40 controls the scan coil 13 so that the irradiation position (the convergence point on the surface of the sample 31) of the electron beam 10 coincides with the irradiation point 311_1. Then, the electron beam 10 is irradiated onto the surface of the sample 31, and the dark field intensity is detected by the dark field detector 21 (S14).

[0032] If the current irradiation point 311_i set as the irradiation position of the electron beam 10 is not the last irradiation point 311_n, that is, if there is an irradiation point 311 in the observation region OA for which the dark field intensity has not been detected (S15, NO), the irradiation position of the electron beam 10 is moved from the current irradiation point 311_i to the next irradiation point 311_(i + 1) according to the irradiation point interval PI1 set in S11 (S16). Then, for the set irradiation point 311_(i + 1), S14 is executed to obtain the dark field intensity.

[0033] On the other hand, if the current irradiation point 311_i is the last irradiation point 311_n, that is, if the detection of the dark field intensity for all the irradiation points 311 in the observation region OA has been completed (S15, YES), the dark field intensities obtained at each irradiation point 311 are mapped to generate a dark field image (S17). Through the above series of procedures from S11 to S17, the acquisition (S1) of the image (electron diffraction image) in the observation region OA is completed.

[0034] Figure 10A is a flowchart for explaining an example of the analysis procedure in the embodiment. The procedure shown in Figure 10A shows the specific procedure of S2 in Figure 3. Also, Figure 10B is a diagram for explaining an example of the arrangement of irradiation points on the region of interest in the embodiment. First, a region of interest AA is set within the observation region OA. Also, an irradiation point interval PI2 is set (S21). The region of interest AA is a region to be analyzed for specifying the crystal orientation. The region of interest AA is extracted from the dark field image generated in S1. As shown in Figure 10B, the irradiation point interval PI2 is set in the same manner as in the comparative example described with reference to Figure 8.

[0035] Next, the incident angle (θk, φl) of the electron beam 10 and the scan speed are set (S22). In the embodiment, for one irradiation point 311_j, the electron beam 10 is incident a plurality of times while changing the angles θ and φ. Specifically, in S22, k incident angles are set in the θ direction and l incident angles are set in the φ direction. That is, for one irradiation point 311_j, the electron beam 10 is irradiated at k×l = M incident angles obtained by combining k incident angles θk and l incident angles φ.

[0036] The angle θ is set according to the diffraction pattern of the analysis target or the order of the diffraction line to be obtained. Also, the angle φ is set according to the symmetry of the diffraction pattern and the measurement time. Also, the angle φ is preferably set to have symmetry with respect to the scanning direction. For example, when the angle φ = 5° is set in the first irradiation, the angle φ = -5° is set in any subsequent irradiation. Note that the incident angles θ and φ do not necessarily need to be set according to the predetermined rule as described above, and may be set irregularly. The scan speed defines the irradiation time of the electron beam 10 for one irradiation point 311_j in one irradiation. The exposure time at the irradiation point 311 is calculated as the product of the irradiation time of the electron beam 10 in one irradiation and the number of irradiations. That is, the slower the scan speed and the larger the number of irradiations, the longer the exposure time and the clearer the electron diffraction image.

[0037] Next, set the incident angles (θ, φ) of the electron beam 10 to the incident angles (θ1, φ1) set at S22 for the first irradiation (S23). Also, set the irradiation position of the electron beam 10 to the first irradiation point 311_1 in the target region AA (S24). That is, the control unit 40 controls the scan coil 13 so that the irradiation position (the convergence point on the surface of the sample 31) of the electron beam 10 coincides with the irradiation point 311_1 and the incident angles of the electron beam 10 are the angles θ1 and φ1. Subsequently, irradiate the surface of the sample 31 with the electron beam 10 at the set incident angles (θ1, φ1), and acquire the NBD image and the dark field intensity (S25).

[0038] If the current irradiation point 311_о set as the irradiation position of the electron beam 10 is not the last irradiation point 311_m, that is, if there is an irradiation point 311 in the target region AA for which the NBD image and the dark field intensity have not been acquired (S26, NO), move the irradiation position of the electron beam 10 from the current irradiation point 311_о to the next irradiation point 311_(о + 1) according to the irradiation point interval PI2 set at S21 (S261). Then, execute S25 for the set irradiation point 311_(о + 1) to acquire the NBD image and the dark field intensity.

[0039] On the other hand, if the current irradiation point 311_о is the last irradiation point 311_m, that is, if the acquisition of the NBD image and the dark field intensity has been completed for all the irradiation points 311 in the target region AA (S26, YES), determine whether the scanning of the target region AA has been performed for all the incident angles set at S22 with respect to the incident angle φ (S27).

[0040] If there is an angle for which the scanning has not been performed with respect to the incident angle φ (S27, NO), change the incident angle φ of the electron beam 10 from the currently set incident angle φj to the next incident angle φ(j + 1) (S271). Then, execute the series of steps from S24 to S27, and use the set incident angles (θi, φ(j + 1)) to acquire the NBD image and the dark field intensity for all the irradiation points 311_1 to 311_m in the target region AA.

[0041] On the other hand, when scanning is performed for all the incident angles set in S22 with respect to the incident angle φ (S27, YES), it is determined whether or not scanning of the target region AA has been performed for all the incident angles set in S22 with respect to the incident angle θ (S28). When there is an angle for which scanning has not been performed with respect to the incident angle θ (S28, NO), the incident angle θ of the electron beam 10 is changed from the currently set incident angle θi to the next incident angle θ(i + 1). Also, the incident angle φ of the electron beam 10 is changed from the currently set incident angle φl to the first incident angle φ1 (S281). Then, a series of procedures from S24 to S27 are executed to obtain the NBD image and the dark-field intensity for all the irradiation points 311_1 to 311_m in the target region AA using the set incident angles (θ(i + 1), φ1).

[0042] On the other hand, when scanning is performed for all the incident angles set in S22 with respect to the incident angle θ (S28, YES), it is determined that acquisition of the NBD image and the dark-field intensity has been completed for the set k × l = M incident angles, and acquisition of the image (electron diffraction image) in the target region AA (S2) is terminated.

[0043] FIG. 11 is a flowchart for explaining an example of the analysis procedure in the embodiment. The procedure shown in FIG. 11 shows the specific procedure of S3 in FIG. 3. First, for each incident angle (θk, φl), the dark-field intensity acquired at each irradiation point 311_1 to 311_m is mapped to generate a dark-field image (S31). FIG. 12 is an image diagram for explaining an example of the dark-field image in the target region. By executing S31, M dark-field images DFI as shown in FIG. 12 are generated.

[0044] Next, based on the M dark-field images DFI generated in S31, position correction is performed (drift correction, S32). In the process of acquiring the NBD image while scanning the inside of the target region AA in S2, there is a possibility that the incident position of the electron beam 10 may shift during the M scans. Therefore, the position is corrected so that the reference patterns of the M dark-field images DFI_1 to DFI_M match.

[0045] Drift correction is performed as follows, for example. First, using the dark-field image DFI_1 acquired first as a reference image, a reference pattern RF for position shift correction is set. For example, a site where the change between light and dark is clearly shown and the shape is easy to identify, such as the rectangle surrounded by the dotted line in FIG. 12, may be set as the reference pattern RF, or a marker serving as a reference pattern may be formed in advance within the region of interest AA. Next, in each of the second to M-th dark-field images DFI_2 to DFI_M (reference images), the reference pattern RF is detected. Then, the difference in position between the position of the reference pattern RF in the reference image and the reference pattern in each reference image is detected. Finally, the coordinates of the irradiation points 311_1 to 311_m in each reference image are corrected according to the difference.

[0046] FIG. 13 is a diagram for explaining drift correction using a dark-field image. As shown on the left side of FIG. 13, by performing drift correction using M dark-field images DFI_1 to DFI_M and using a reference pattern RF or the like, as shown on the right side of FIG. 13, the positions of the respective dark-field images DFI are corrected. In the M dark-field images DFI_1 to DFI_M after drift correction shown on the right side of FIG. 13, the region where all the images overlap is shown as the correction region CA.

[0047] Next, using the corrected coordinates after drift correction, from the NBD images acquired for each incident angle (θk, φl), NBD images having the same coordinates (corrected coordinates) of the irradiation point 311 are extracted (S33). In S33, among the plurality of irradiation points whose corrected coordinates exist within the correction region CA, the NBD image of the selected irradiation point 311 is extracted. Subsequently, the M extracted NBD images are integrated to generate an integrated NBD image (S34). Specifically, for the M NBD images extracted in S33, the electron detection intensities at the same coordinates (the same coordinates in the reciprocal space) are integrated. FIG. 14 is an image diagram showing an example of the integrated NBD image. By acquiring and integrating a plurality of NBD images at different incident angles, the electron detection intensity can be increased, so the detection accuracy is improved.

[0048] Finally, the crystal orientation of the irradiation point 311 selected in S33 is analyzed using the integrated NBD image (S35). Specifically, the integrated NBD image generated in S34 is compared with a plurality of NBD images (templates) that have been calculated in advance for various crystal orientations and stored in a database. The crystal orientation of the template with the highest degree of match is identified as the crystal orientation at the selected irradiation point.

[0049] Note that for a plurality of irradiation points where correction coordinates exist within the correction region CA, the crystal orientation is analyzed using the integrated NBD, and the same mark is assigned to the irradiation points having the same crystal orientation, or the irradiation points having the same crystal orientation are connected by a line. Thus, similar to the comparative example, the crystal orientation mapping of the correction region CA can be generated.

[0050] As described above, according to the analysis method of the embodiment, for each of the plurality of irradiation points 311 set within the target region AA, the target region AA is scanned multiple times while changing the incident angle of the electron beam 10. Specifically, the target region AA is scanned at a certain incident angle, and the NBD images of all the irradiation points 311 within the target region AA are acquired. Then, the target region AA is scanned at the next incident angle, and the NBD images of all the irradiation points 311 within the target region AA are acquired. On the other hand, in the comparative example, for one irradiation point 311, an NBD image (precession NBD image) is acquired while precessing the electron beam 10. That is, the integrated NBD image generated by superimposing a plurality of NBD images acquired in a time-division manner in the embodiment corresponds to the precession NBD image of the comparative example.

[0051] In the analysis method of the embodiment, the time for which the electron beam 10 irradiates one irradiation point 311 in one scan is, for example, about several μs, whereas in the comparative example, the time for which the electron beam 10 irradiates one irradiation point 311 in order to precess the electron beam 10 is, for example, about several tens of μs to several ms. Therefore, since the time (electron beam residence time) for which the electron beam 10 continuously irradiates one irradiation point 311 can be shortened compared to the comparative example, damage to the sample 13 by the electron beam 10 can be reduced.

[0052] Also, according to the analysis method of the embodiment, the dark-field intensity is also acquired simultaneously with the NDB image. By comparing the dark-field images generated for each incident angle, which are generated based on the dark-field intensity, it is possible to detect the deviation of the irradiation position of the electron beam 10. Further, the position of the irradiation point 311 where each NBD image is acquired can be corrected using the detected deviation. In the comparative example, although there is a possibility that the irradiation position of the electron beam 10 may deviate during the precession movement, since the diffracted electrons are continuously integrated and detected during the precession movement, the precession NBD image may become an image including the deviation of the irradiation position, and the detection accuracy may decrease. On the other hand, according to the analysis method of the embodiment, since the integrated NBD image is generated using the NBD images with the same position of the corrected irradiation point, the detection accuracy can be improved.

[0053] As described above, according to the analysis method of the embodiment, it is possible to obtain an electron diffraction image with high accuracy while reducing the damage to the sample due to electron beam irradiation.

[0054] Note that according to the analysis method of the embodiment, since the incident angle (θ, φ) of the electron beam 10 can be arbitrarily set, in addition to the NBD image used for generating the crystal orientation mapping by the above-described template matching, it is possible to acquire NBD images for various methods. For example, it is possible to acquire an NBD image used for crystal structure analysis by the RED method (Rotation Electron Diffraction). Specifically, for a specific irradiation point of the sample, the sample is tilted in one direction, and while tilting the electron beam 10, a plurality of NBD images are acquired. (A plurality of NBD images are acquired while changing the angle.) By three-dimensionally reconstructing these plurality of NBD images, the crystal structure of the sample can be analyzed.

[0055] Also, in the above description, the method of extracting the target region AA using the dark-field image has been described. However, similar to the comparative example, the electron intensity of the region caused by the electrons transmitted through the sample 31 may be detected by the electron beam detector 22 to generate a pseudo bright-field image, and the target region AA may be extracted using the pseudo bright-field image.

[0056] Furthermore, in the above description, after extracting NBD images with the same coordinates (corrected coordinates) of the irradiation point 311 from the NBD images obtained for each incident angle (θk, φl), the electron beam intensities were integrated to generate an integrated NBD image (planar image in reciprocal space). However, it is also possible to perform three-dimensional reconstruction of the extracted NBD images to generate a three-dimensional NBD image (stereoscopic image in reciprocal space). For example, three-dimensional reconstruction can be achieved by converting the two-dimensional coordinates (kx, ky) of other NBD images into three-dimensional coordinates (kx´, ky´, kz´) based on the incident angle θk, with the NBD image at the incident angle θ = 0° as a reference.

[0057] Although some embodiments of the present invention have been described, these embodiments are shown by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0058] 10… electron beam, 11… beam irradiation unit, 12… condenser lens, 13… scan coil, 14… objective lens, 15… intermediate lens, 16… de-scan coil, 21… dark field detector, 22… electron beam detector, 31… sample, 40… control unit, 50… display unit, 111… field emission electron gun, 112… acceleration unit, 311… irradiation point, 401… CPU, 402… RAM, OA… observation region, AA… region of interest, CA… correction region

Claims

1. An analytical method using a scanning transmission electron microscope, comprising: accelerating an electron beam emitted from a beam irradiation unit and irradiating a sample so that the focus of the electron beam is located on the sample, and detecting a dark-field image of the sample by detecting electrons transmitted through the sample or scattered by the sample; and detecting an electron diffraction image at the irradiation position of the electron beam on the sample by detecting electrons that have passed through the hollow portion of the first detector among the electrons transmitted through the sample or scattered by the sample. In a process of scanning a plurality of irradiation points set in an analysis region on the surface of the sample by sequentially irradiating the electron beam at a preset incident angle, and simultaneously detecting the dark-field image of the analysis region and the electron diffraction images for each of the plurality of irradiation points, setting a plurality of the incident angles; for each set incident angle, detecting the dark-field image and the electron diffraction images for each of the plurality of irradiation points; detecting a relative displacement amount of the plurality of detected dark-field images; correcting the position of the irradiation point based on the displacement amount; generating an integrated electron diffraction image by integrating the plurality of electron diffraction images obtained from the irradiation points having the same position after correction; including: The incident angle is set as a combination of a first angle formed between a direction perpendicular to the surface of the sample and the incident central axis direction of the electron beam, and a second angle formed between a direction in which the plurality of irradiation points are scanned and the incident central axis direction of the electron beam, and the first angle and the second angle can be set independently of each other. Analytical method, characterized in that.

2. The analytical method according to claim 1, wherein the electron beam is converged and irradiated onto the sample as an extremely fine electron beam.

3. The analytical method according to claim 1, wherein each of the plurality of electron diffraction images obtained from the same irradiation point at the corrected position is converted into three-dimensional coordinates based on the first angle, and the electron diffraction images are integrated based on the converted coordinates to generate an integrated electron diffraction image.

Images