Image processing method and electron microscope system

Abstract

To provide an image processing method with high accuracy of boundary information detection while having a small influence due to a noise of a microscopic image.SOLUTION: An image processing method for determining a structural boundary position of a first phase and a second phase in a microscope image of a sample, in which the first and second phase are contacted in a structural boundary, includes the steps of: calculating a luminance profile to a direction crossed to a long direction of the structural boundary region in the microscope image; calculating a movement standard deviation profile by using a plurality of calculation widths from the luminance profile; specifying each calculation width of the movement reference deviation profile in which the convex-shape wave of the movement reference deviation profile is in a peak, and of which a half width in a convex-shape wave is narrowest; and determining a peak position of the movement reference deviation profile calculated by using the specified calculation width as a structural boundary position.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to an image processing device and an electron microscope system. [Background technology]

[0002] In processing microscope images, there are several methods for extracting edges from noisy images, but general noise removal processing requires the selection of a processing method and parameter adjustment, and reduces position accuracy. For example, Patent Document 1 is a document on edge extraction of image data, and discloses that a luminance variance difference between a luminance variance of a first pixel in image data and a luminance variance of a second pixel surrounding the first pixel is calculated, and edge pixels of the image data are determined based on the luminance variance difference.

[0003] Semantic segmentation using machine learning has also become widely recognized in recent years, but pre-training requires a lot of effort and time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-163407 A Summary of the Invention [Problem to be solved by the invention]

[0005] A transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM) is used to observe electrons that pass through or are diffracted from a thin film sample. To perform proper observations with a TEM / STEM, it is necessary to align the sample orientation so that the optical axis of the electron beam coincides with the three-dimensional structure of the sample. Sample orientation is generally performed using the diffraction pattern of the single crystal part. However, when the sample to be observed is a semiconductor device without a single crystal part, the orientation is adjusted to the structure of the thin film sample. For example, if the sample to be observed is a thin film sample containing phases A and B, currently, the sample angle at which the structural boundary between phases A and B is parallel to the electron beam is adjusted by the operator by visually judging the TEM / STEM image. For this reason, sample orientation is a highly difficult task that depends on the individual, and there is a problem that operators who are not familiar with TEM / STEM operations have difficulty in aligning the sample orientation with high accuracy. [Means for solving the problem]

[0006] An image processing method according to one embodiment of the present invention is an image processing method for determining a structural boundary position between a first phase and a second phase in a microscope image of a sample, in which the first phase and the second phase are in contact at a structural boundary region, the image processing method including a first step of specifying a second direction in the microscope image, the second step of specifying a luminance profile along the second direction, the second step of specifying a moving standard deviation of the luminance profile using a plurality of calculation widths to obtain a moving standard deviation profile, a fourth step of calculating a half-width of a convex waveform included in each moving standard deviation profile calculated using the plurality of calculation widths, a fifth step of specifying a calculation width of a moving standard deviation profile in which the convex waveform has a peak and the half-width of the convex waveform is narrowest, among the plurality of moving standard deviation profiles, and a sixth step of determining a peak position of the moving standard deviation profile calculated using the specified calculation width as the structural boundary position. Effect of the Invention

[0007] The present invention provides an image processing method that is less affected by noise in a microscope image and has high accuracy in detecting boundary information, and an electron microscope system using the same. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 13 is a diagram showing a flow of determining a structure boundary position. [Figure 1B] FIG. 13 is a diagram showing a flow of determining a structure boundary width. [Figure 2A] 11A to 11C are diagrams specifically illustrating a process for determining a structure boundary position / width for a model image. [Figure 2B] 11A to 11C are diagrams specifically illustrating a process for determining a structure boundary position / width for a model image. [Figure 2C] 11A to 11C are diagrams specifically illustrating a process for determining a structure boundary position / width for a model image. [Figure 2D] 11A to 11C are diagrams specifically illustrating a process for determining a structure boundary position / width for a model image. [Figure 2E] 11A to 11C are diagrams specifically illustrating a process for determining a structure boundary position / width for a model image. [Figure 2F] 11A to 11C are diagrams specifically illustrating a process for determining a structure boundary position / width for a model image. [Figure 3A] FIG. 13 is a diagram specifically illustrating a process for determining a structure boundary position / width in a TEM image. [Figure 3B] FIG. 13 is a diagram specifically illustrating a process for determining a structure boundary position / width in a TEM image. [Figure 3C] FIG. 13 is a diagram specifically illustrating a process for determining a structure boundary position / width in a TEM image. [Figure 3D] FIG. 13 is a diagram specifically illustrating a process for determining a structure boundary position / width in a TEM image. [Figure 3E] FIG. 13 is a diagram specifically illustrating a process for determining a structure boundary position / width in a TEM image. [Figure 3F] FIG. 13 is a diagram specifically illustrating a process for determining a structure boundary position / width in a TEM image. [Figure 4A] FIG. 1 is a diagram illustrating a basic configuration of a scanning transmission electron microscope system. [Figure 4B] 2 is an example of a hardware configuration of a computer. [Diagram 5] FIG. 13 is a diagram for explaining the relationship between a structural boundary surface and a structural boundary region. [Figure 6] FIG. 13 is a diagram showing a flow of adjusting the sample tilt for aligning the sample orientation. [Figure 7] FIG. 13 is a diagram showing the relationship between the sample azimuth angle and the structure boundary width. [Figure 8] FIG. 13 is a diagram showing the relationship between the sample azimuth angle and the structure boundary width. [Figure 9] 13A and 13B are diagrams for explaining a method of determining a structure boundary position and a structure boundary width according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 4A shows a schematic diagram of the basic configuration of a scanning transmission electron microscope (STEM) system. The STEM system includes a STEM 51 and a control system 42. The STEM 51 includes an electron optical system and a detector 31, the main components of which include an electron beam source 1, an extraction electrode 2, a condenser lens 11, a condenser aperture 12, an axis adjustment deflector 13, an astigmatism corrector 14, a scan deflector 15, an objective lens 20, an objective aperture 23, an axis adjustment deflector 24, a selected area aperture 25, and an imaging lens 30. A sample 21 is placed on a sample stage 22 and inserted between the upper and lower magnetic poles of the objective lens 20. The imaging lens 30 is not necessarily required to function as a STEM.

[0010] A primary electron beam (probe) generated by an electron beam source 1 is extracted by an extraction electrode 2 and irradiated toward a sample 21. A condenser lens 11 adjusts the focusing conditions of the primary electron beam. A condenser aperture 12 controls the aperture angle of the primary electron beam. An axis adjustment deflector 13 adjusts the position of the primary electron beam relative to an objective lens 20. An astigmatism corrector 14 adjusts the beam shape of the primary electron beam incident on the sample 21. A scan deflector 15 raster-scans the primary electron beam incident on the sample 21. An objective lens 20 adjusts the focus position of the primary electron beam relative to the sample 21. An objective aperture 23 transmits transmitted electrons and / or specific diffracted electrons. An axis adjustment deflector 24 adjusts the position of the transmitted electron beam transmitted through the sample 21 relative to a detector 31. A selected area aperture 25 limits the area of ​​the sample when an electron diffraction pattern is displayed. An imaging lens 30 forms an image of the transmitted electron beam. A detector 31 detects the imaged transmitted electron beam.

[0011] The control system 42 includes a control device 40 and a computer 41. The computer 41 stores a control program and an image processing program for the STEM 51, and by executing these programs, the computer 41 functions as a control unit that controls the STEM 51, or an image processing unit that processes the STEM image generated by the STEM 51. The control device 40 receives a control signal from the computer 41 and controls each component of the STEM 51. The control device 40 includes an AD converter, a DA converter, a memory, and an arithmetic device such as an FPGA or a microprocessor.

[0012] The process of generating a STEM image by the STEM 51 will be described. This process is controlled by the control system 42. The electron beam source 1 irradiates the sample 21 on the sample stage 22 with a primary electron beam. The focus of the primary electron beam is roughly adjusted by adjusting the Z position of the sample stage 22 or adjusting the control parameters of the objective lens 20. Then, the XY movement mechanism of the sample stage 22 is used to select a field of view for adjusting the electron optical system. The deviation, focus, and astigmatism of the optical system are corrected in the field of view for adjusting the electron optical system. Specifically, the adjustment parameters of the axis adjustment deflector 13, the astigmatism corrector 14, and the objective lens 20 are adjusted.

[0013] Next, the observation field is moved to the photographing field using the specimen stage 22, and the focus of the objective lens 20 is fine-tuned by the operator or adjusted to an appropriate focus position using the focus tracking function so that a sharp image can be observed. When the primary electron beam is incident on the specimen 21, most of the electrons are transmitted through the specimen 21. The imaging lens 30 directs the transmitted electron beam onto the detector 31 at an appropriate angle, and a STEM image is obtained. The magnification of the STEM image is set by the scan deflector 15.

[0014] 4B shows an example of the hardware configuration of the computer 41. The computer 41 includes a processor 411, a memory (main storage device) 412, an auxiliary storage device 413, an output device 414, an input device 415, and a communication interface (I / F) 416. These components are connected to each other via a bus 417 so as to be able to communicate with each other.

[0015] The memory 412 is composed of, for example, a semiconductor memory, and is mainly used to hold programs and data being executed. The processor 411 executes various processes according to the programs stored in the memory 412. The processor 411 operates according to the programs to realize various functional units. The auxiliary storage device 413 is composed of, for example, a large-capacity storage device such as a hard disk drive or a solid-state drive, and is used to hold programs and data for a long period of time. The programs and data stored in the auxiliary storage device 413 are loaded into the memory 412, and the processor 411 executes the programs, thereby performing various processes of the computer 41.

[0016] The input device 415 is a hardware device that allows an operator to input instructions, information, etc. to the computer 41. The output device 414 is a hardware device that presents various images for input and output, such as a display device or a printing device. The communication I / F 416 is an interface for connection to a network.

[0017] Fig. 1A shows a structure boundary position determination flow for determining a structure boundary position of a microscope image, and Fig. 1B shows a structure boundary width determination flow for determining a structure boundary width of a microscope image. These flows are processes realized by computer 41 executing a program stored in auxiliary storage device 413. Figs. 2A to 2F show how the structure boundary position and structure boundary width of model image 101 are determined according to the flows of Figs. 1A and 1B. The flows of Figs. 1A and 1B will be described below with reference to Figs. 2A to 2F. First, the flow of Fig. 1A will be described.

[0018] First, a microscope image is acquired by the STEM 51 (S01). A model image 101 shown in Fig. 2A is a model image created assuming a TEM image of a thin film sample having a structure in which three phases are arranged (hereinafter, images acquired by a TEM or STEM are collectively referred to as a TEM image (transmission electron microscope image)). An example of determining the structure boundary position and structure boundary width at the boundary between a first phase 103 and a second phase 104 will be described below.

[0019] Next, an evaluation region is specified on the acquired microscopic image (S02). For example, for the microscopic image displayed on the output device 414, an operator can specify an evaluation region using the input device 415. The evaluation region 102 shown in FIG. 2A is set as a strip-shaped region extending in the y direction and the x direction perpendicular thereto when the direction in which the boundary between the phase 103 and the phase 104 extends is the y direction. The size of the evaluation region 102 is such that in the y direction it is 1 pixel or more, and in the x direction it is large enough to include at least the phase boundary and the phases 103 and 104 adjacent to the boundary at that boundary. In the example of FIG. 2A, the size of the evaluation region 102 in the x direction is the entire range in the x direction of the model image 101.

[0020] Next, a luminance profile of the evaluation region 102 is calculated (S03). FIG. 2B is the luminance profile calculated for the evaluation region 102. The horizontal axis indicates the position in the x direction (pixel position), and the vertical axis indicates the luminance. The actual microscopic image contains noise. By setting the evaluation region 102 to a size of k pixels in the y direction and, for example, taking the luminance average of k pixels as the luminance at the pixel position in the x direction, the influence of noise can be reduced.

[0021] Next, a calculation width is set (S04), and based on the set calculation width, the moving standard deviation of the luminance at each pixel position in the x direction of the evaluation region is calculated to obtain a moving standard deviation profile (S05). For example, when the calculation width is set to 7 pixels, the standard deviation at the i pixel position is obtained for each pixel position as the standard deviation of the luminance at 7 pixel positions from (i - 3) pixel to (i + 3) pixels. A plurality of calculation widths are set, and the moving standard deviation profiles of the luminance calculated for each calculation width are displayed (S06). FIG. 2C shows the profiles of the moving standard deviation of the luminance calculated for the evaluation region 102 by setting 5 calculation widths A to E (where A < B < C < D < E). In this way, a convex waveform appears at the position where the phase boundary exists in the moving standard deviation profile. Based on this convex waveform, the structural boundary position and the structural boundary width are specified.

[0022] First, the peak of the convex waveform is extracted (S07). In the graph of FIG. 2C, the convex waveform for calculation widths A and B has a flat top and no peak is observed, whereas the convex waveform for calculation widths C, D, and E has a peak. The reason for this difference in the shape of the convex waveform is that, in the cases of calculation widths A and B, the calculation width is short relative to the structure boundary width W, and the calculation width at multiple pixel positions is included within the structure boundary region 105. In contrast, when the calculation width is sufficiently long relative to the structure boundary width W (in the cases of calculation widths C, D, and E), a peak p appears in the convex waveform.

[0023] Next, the half-width is calculated for each convex waveform, and the half-width of the convex waveform for each calculation width is displayed in a graph (S08). FIG. 2D is a graph showing the half-width of the convex waveform for each calculation width calculated from the moving standard deviation profile of FIG. 2C. It can be seen from the graph of FIG. 2D that, among the calculation widths C, D, and E in which the peak p appears in the convex waveform, the half-width of the convex waveform for calculation width C is the smallest, and the steepest convex waveform is obtained. When the calculation width is about the same as the structure boundary width W, the convex waveform becomes a steep waveform with a peak, and as the calculation width becomes larger beyond the structure boundary width W, the ratio of the phase part with little fluctuation in brightness in the calculation width increases, and the base of the convex waveform changes to become wider. From the above, in this example, it can be determined that the convex waveform of the moving standard deviation profile of brightness calculated for calculation width C most accurately represents the structure boundary region. Therefore, the calculation width for determining the structure boundary position and the structure boundary width is specified as the calculation width where a peak appears and a convex waveform with the smallest half-width is obtained (calculation width C in this case) (S09). The position where the peak of the convex waveform of the moving standard deviation profile of brightness calculated with the specified calculation width appears is displayed as the structure boundary position on the microscope image (S10). That is, FIG. 2F shows the position where the peak of the convex waveform exists in the case of calculation width C as the structure boundary position 112 on the model image 101. In this way, by using the moving standard deviation of brightness as an index, the structure boundary position can be determined even from a noisy microscope image without image processing for noise removal.

[0024] Next, the flow of Fig. 1B will be described. In this flow, processing is performed on the moving standard deviation profile of luminance calculated in the calculation width (calculation width C in this example) determined in the flow of Fig. 1A. First, the element difference of the moving standard deviation profile of luminance between adjacent pixel positions is calculated to obtain a moving standard deviation difference profile (S11) and display it (S12). Fig. 2E shows the moving standard deviation difference profile of the moving standard deviation profile of luminance calculated in calculation width C. Note that, although an example in which the waveform of the standard deviation of luminance is treated as a discrete value for each pixel position to calculate the difference value is described here, the same processing can also be performed by treating the waveform of the standard deviation of luminance as a continuous value to calculate the differential value at the pixel position and creating a moving standard deviation differential profile of luminance.

[0025] Next, a pair of maximum and minimum points in the standard moving deviation difference profile is extracted (S13). A maximum point 110 and a minimum point 111 are shown in the moving standard deviation difference graph in FIG. 2E. The region sandwiched between the positions where the difference in the moving standard deviation becomes an extreme value is specified as the structure boundary region 105. Therefore, the structure boundary width W is calculated from the difference between the positions where the standard moving deviation difference profile gives an extreme value (S14), and the structure boundary width W is displayed on the microscope image (S15). FIG. 2F shows the positions where the standard moving deviation difference profile gives an extreme value as boundaries 113, 114 of the structure boundary region 105 on the model image 101.

[0026] Although details will be described later, in the model image 101 of the thin film sample shown in FIG. 2A, the appearance of the structure boundary surface changes depending on the relationship between the structure boundary surface between the phases 103 and 104 and the optical axis of the electron beam. When the structure boundary surface between the phases 103 and 104 and the optical axis of the electron beam coincide with each other, the structure boundary width W of the structure boundary region 105 is minimum, and the greater the degree of mismatch, the larger the structure boundary width W of the structure boundary region 105 becomes. In this embodiment, since the structure boundary position and structure boundary width of the microscope image can be determined based on numerical values, information for performing highly accurate sample orientation can be obtained without relying on the TEM / STEM operation skill of the operator. In addition, by performing both the processes of FIG. 1A and B, both the structure boundary position and the structure boundary width can be determined, but it is also possible to determine only one of the structure boundary position and the structure boundary width, and in this case, the procedure related to only the determination of the structure boundary position or the structure boundary width that is not required to be determined can be omitted.

[0027] In this example, the evaluation area 102 is set in order to calculate the luminance at a pixel position as the average luminance of multiple pixels in order to reduce the influence of noise, but if such averaging is not performed, it is not necessary to set the evaluation area 102, and it is sufficient to specify the direction in which the luminance profile is to be obtained in step S02. The direction specified at this time needs to intersect with the direction in which the boundary between phases 103 and 104 extends, but it does not have to be perpendicular.

[0028] The above is an example of processing for a simple model image 101, but the same processing can be performed on actual microscope images. FIG. 3A shows an example of an actual TEM image. For the TEM image 121, an evaluation region 122 is set. The TEM image 121 is a TEM image of a thin film sample having a structure composed of a first phase 123, a second phase 124, and a third phase 125. Hereinafter, an example of obtaining the structural boundary position and the structural boundary width at the boundary between the phase 124 and the phase 125 will be shown. FIG. 3B is a luminance profile calculated for the evaluation region 122. FIG. 3C shows a moving standard deviation profile of luminance calculated by setting four calculation widths A to D (where A < B < C < D) for the evaluation region 122. Depending on the difference in the size of the calculation width, a difference similar to that in the case of the model image 101 appears in the convex waveform shape for each calculation width. In the case of the calculation width D, a waveform with a plurality of peaks is observed in one convex waveform that did not exist in the example of the model image 101. This is considered to be because the calculation width D is too large and the moving standard deviation is calculated including the luminance information of the three phases. Based on the moving standard deviation profile in FIG. 3C, the calculation width B is specified as the calculation width for specifying the structural boundary position and the structural boundary width. FIG. 3D shows only the moving standard deviation profile of luminance calculated with the calculation width B extracted from FIG. 3C. The structural boundary position at the boundary between the phase 124 and the phase 125 is determined as the position of the peak p of the moving standard deviation graph in FIG. 3D. FIG. 3E is a moving standard deviation difference profile of luminance calculated with the calculation width B. A set of a maximum point 126 and a minimum point 127 is shown in the moving standard deviation difference profile. The structural boundary width W can be calculated from the difference in the positions giving extreme values in the standard moving deviation difference profile. FIG. 3F shows the position where the peak of the convex waveform in the case of the calculation width B exists as the structural boundary position 128 on the TEM image 121, and the positions giving extreme values in the standard moving deviation difference profile as the boundaries 129 and 130 of the structural boundary region on the TEM image 121.

[0029] The relationship between the structure boundary surface in the sample structure and the structure boundary area appearing in the TEM image will be described with reference to FIG. 5. FIG. 5 shows a cross section of a thin film sample 201. The thin film sample 201 is composed of three phases, an A phase 202, a B phase 203, and a C phase 204. A structure boundary surface 205 between the A phase 202 and the B phase 203 and a structure boundary surface 206 between the B phase 203 and the C phase 204 are formed in the thin film sample 201. A TEM image 211 is obtained by irradiating the surface of the thin film sample 201 with an electron beam from a direction perpendicular to the surface (z direction). In the TEM image 211, a structure boundary area 215 with a structure boundary width W1 is observed between the A phase 212 and the B phase 213, and a structure boundary area 216 with a structure boundary width W2 is observed between the B phase 213 and the C phase 214. In the example of FIG. 5, the structure boundary width W1>the structure boundary width W2, which indicates that the greater the inclination of the structure boundary surface with respect to the electron beam incidence angle, the greater the structure boundary width in the microscope image. Using this relationship, the thin film sample is tilted so that the structure boundary width W becomes minimal, thereby aligning the sample orientation.

[0030] FIG. 6 shows a flow of adjusting the sample tilt for sample orientation alignment using the structure boundary width W of the microscope image. First, the sample 21 is placed on the sample stage 22 (S21). In the initial position, the surface of the sample 21 is placed so as to be perpendicular to the optical axis of the primary electron beam of the STEM 51. A microscope image is acquired in this state (S22). The boundary and direction of the structure to be analyzed are specified (S23). In the following, the longitudinal direction of the structure boundary region used for sample orientation alignment is defined as the y-axis direction, the direction parallel to the surface of the sample 21 and perpendicular to the y-axis direction is defined as the x-axis direction, and the direction perpendicular to the surface of the sample 21 is defined as the z-axis direction. Next, the flow described with reference to FIGS. 1A and 1B is applied to calculate the structure boundary width for the specified structure boundary region (S24). After that, the sample 21 is tilted by the sample stage 22 (S25), a microscope image is acquired (S26), and the structure boundary width is calculated for the specified structure boundary region for the acquired microscope image (S24). This process is repeated while changing the sample tilt angle.

[0031] FIG. 7 shows the information on the structure boundary area obtained by the above process (structure boundary width W ai(where \(i = 1\) to \(7\)) is schematically shown. The sample has a first phase 302 and a second phase 303, and the structural interface between the first phase 302 and the second phase 303 is the object of analysis. The sample is tilted about the y-axis parallel to the longitudinal direction of the structural boundary region, as shown by the coordinate axes 301. Here, when the sign of the z-coordinate is +, the sample tilt angle \(a_i\) is positive; when the z-coordinate is 0, the sample tilt angle \(a_i\) is 0; when the sign of the z-coordinate is -, the sample tilt angle \(a_i\) is negative, and it is defined that \(a_1 < a_2 < a_3 < a_4 < a_5 < a_6 < a_7\). In this way, the size of the structural boundary width changes according to the sample tilt angle. Here, for clarity, the sample has been described as being tilted about the y-axis parallel to the longitudinal direction of its structural boundary region, but even when the central axis for changing the sample tilt angle is not parallel to the longitudinal direction of the structural boundary region, the relationship as shown in Fig. 7 can be extracted.

[0032] Return to the description of Fig. 6. According to the information on the structural boundary region obtained in this way, the relationship between the sample tilt angle \(a_i\) and the structural boundary width \(W\) ai is graphed and displayed on the output device 414 (S27). The sample tilt angle \(a_i\) / structural boundary width \(W\) graph corresponding to Fig. 7 ai is shown in Fig. 8. From the sample tilt angle \(a_i\) / structural boundary width \(W\) ai graph, the point that gives the minimum value to the structural boundary width is extracted (S28). In the example of Fig. 8, if the structural boundary width \(W\) in the case of the sample tilt angle \(a_5\) a5 is a sufficiently small value, the sample tilt angle \(a_5\) is extracted as the point that gives the minimum value. Alternatively, from the sample tilt angle \(a_i\) / structural boundary width \(W\) ai graph, a function is obtained by fitting with the sample tilt angle \(a_i\) as the explanatory variable and the structural boundary width \(W\) ai as the objective variable, and the explanatory variable that minimizes the objective variable may be specified from the function. The sample tilt angle \(a_i\) obtained in this way is determined as the tilt parameter of the sample (S29), and the sample is tilted (S30). Thereby, the sample alignment is completed.

[0033] In this way, whether the structure boundary surface is perpendicular to the optical axis of the primary electron beam, i.e., whether the structure boundary width in the microscope image is narrow or not, can be determined numerically, not by human eyes, so that the variation in observation conditions that depends on the TEM / STEM operator can be reduced, and automation becomes possible. Furthermore, the adjustment method of this embodiment makes it possible to adjust the structure orientation of the target portion not only for samples with single crystal regions and samples without single crystal regions as exemplified, but also for samples with curved thin film surfaces.

[0034] (Modification) In the above embodiment, an example of determining the structure boundary position and the structure boundary width based on a one-dimensional luminance profile has been shown. In contrast, it is also possible to determine the structure boundary position and the structure boundary width by expanding to two dimensions. When calculating the moving standard deviation of luminance at each pixel position of the evaluation area, for example, when the calculation width is set to 7 pixels, the standard deviation of pixel position (i, j) is determined for each pixel position as the standard deviation of luminance in a region including a total of 7×7 pixel positions, including (i-3) pixel to (i+3) pixel in the x direction and (j-3) pixel to (j+3) pixel in the y direction. Since a peak of the moving standard deviation of luminance appears two-dimensionally at the position where the phase boundary exists, it is possible to determine the two-dimensional distribution of the structure boundary region in the evaluation area. Note that, although an example is shown in which the calculation width in the x direction and the calculation width in the y direction are the same, different calculation widths may be used. FIG. 9 shows a schematic diagram of the structure boundary position 901 and the structure boundary width W determined in the evaluation area 900 when expanded to two dimensions. Here, the length and width of the microscope image are represented as the y direction and the x direction, respectively, and the evaluation area 900 is the area surrounded by coordinates (x1, y1), (x2, y1), (x1, y2), and (x2, y2).

[0035] The structure boundary position 901 is obtained as follows. In the section (y1-y2) of the evaluation area 900, a moving standard deviation profile along the x direction is obtained, and the peak of the convex waveform included in each moving standard deviation profile is extracted. In addition, in the section (x1-x2) of the evaluation area 900, a moving standard deviation profile along the y direction is obtained, and the peak of the convex waveform included in each moving standard deviation profile is extracted. When determining the structure boundary position 901, the size of the area when calculating the moving standard deviation for each pixel position may be arbitrary as long as a waveform in which the peak of the convex waveform is clear is obtained. For both the moving standard deviation profile along the x direction and the moving standard deviation profile along the y direction, the pixel position (x, y) that gives the peak of the convex waveform included in them is the structure boundary position 901. The line obtained by connecting the structure boundary positions 901 is called the structure boundary line.

[0036] Next, the structure boundary width W is calculated as follows. The calculation method is the same as in the embodiment, but is characterized in that a brightness profile, a moving standard deviation profile, a moving standard deviation difference profile, or a moving standard deviation differential profile along a direction perpendicular to the structure boundary line is used. Specifically, the method is as follows.

[0037] First, for an arbitrary structure boundary position, a luminance profile along a direction perpendicular to the structure boundary line is obtained, and a moving standard deviation of the luminance profile is calculated using multiple calculation widths to obtain a moving standard deviation profile. In FIG. 9, for a structure boundary position 905, the direction perpendicular to the structure boundary line is shown as direction 902 (direction o, however, this direction differs for each structure boundary position 901 on the structure boundary line). Next, for each moving standard deviation profile calculated using multiple calculation widths, a half-width of a convex waveform included in the moving standard deviation profile is calculated. Next, a calculation width of a moving standard deviation profile in which the convex waveform has a peak and the half-width of the convex waveform is narrowest is specified among the multiple moving standard deviation profiles.

[0038] Next, for each position along the o direction, an element difference or derivative of the moving standard deviation profile calculated using the identified calculation width is calculated to obtain a moving standard deviation difference profile or a moving standard deviation differential profile. Next, a pair of a first position 903 having a maximum value and a second position 904 having a minimum value is identified from the moving standard deviation difference profile or the moving standard deviation differential profile. Next, the distance between the first position 903 and the second position 904 is determined as the structure boundary width W. This process is performed for each structure boundary position 901 on the structure boundary line.

[0039] The present invention is not limited to the above-mentioned embodiment, and includes various modified examples. The above-mentioned embodiment has been described in detail to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all of the described configurations. For example, for the sake of simplicity, the direction in which the luminance profile is obtained is the x direction of the microscope image in FIG. 2A, but this direction is not limited to this direction. If the direction in which the luminance profile is obtained, including the o direction in the modified example, is different from the x direction or y direction of the microscope image, the luminance at the position where the luminance profile is obtained may be obtained by interpolating the luminance of nearby pixels. Furthermore, it is possible to add, delete, or replace other configurations with respect to part of the configuration of the embodiment. Furthermore, the image processing method of the present invention is not limited to TEM images, and can also be applied to images obtained by a scanning electron microscope (SEM). [Explanation of symbols]

[0040] 1: electron beam source, 2: extraction electrode, 11: condenser lens, 12: condenser aperture, 13: axis adjustment deflector, 14: astigmatism correction device, 15: scan deflector, 20: objective lens, 21: sample, 22: sample stage, 23: objective aperture, 24: axis adjustment deflector, 25: limited area aperture, 30: imaging lens, 31: detector, 40: control device, 41: computer, 42: control system, 51: STEM, 101: model image, 102: evaluation area, 103: first phase, 104: second phase, 105: structure boundary area, 110: maximum point, 111: minimum point, 112: structure boundary position, 113, 114: boundary, 121: TEM image, 122: evaluation area, 123: first phase, 1 24: second phase, 125: third phase, 126: maximum point, 127: minimum point, 128: structure boundary position, 129, 130: boundary, 201: thin film sample, 202: phase A, 203: phase B, 204: phase C, 205, 206: structure boundary surface, 211: TEM image, 212: phase A, 213: phase B, 214: phase C, 215, 216: structure boundary area, 301: coordinate axis, 302: first phase, 303: second phase, 411: processor, 412: memory, 413: auxiliary storage device, 414: output device, 415: input device, 416: communication interface, 417: bus, 900: evaluation area, 901, 905: structure boundary position, 902: direction, 903: first position, 904: second position.

Claims

1. 1. An image processing method for determining a structural boundary position between a first phase and a second phase in a microscopic image of a sample, the first phase and the second phase being in contact with each other at a structural boundary region, the method comprising: a first step of specifying a second direction in the microscope image that includes the structure boundary region and intersects with a first direction that is a longitudinal direction of the structure boundary region; a second step of determining a luminance profile along the second direction; a third step of calculating a moving standard deviation of the luminance profile using a plurality of calculation widths to obtain a moving standard deviation profile; a fourth step of calculating a half-width of a convex waveform included in each of the moving standard deviation profiles calculated using a plurality of the calculation widths; a fifth step of identifying a calculation width of a moving standard deviation profile in which the convex waveform has a peak and a half-width of the convex waveform is narrowest, among the plurality of moving standard deviation profiles; and a sixth step of determining, as the structure boundary position, a peak position of a moving standard deviation profile calculated using the specified calculation width.

2. In claim 1, In the first step, the second direction is defined so as to be perpendicular to the first direction, and a belt-shaped evaluation area extending in the first direction and the second direction is specified; An image processing method in which, in the second step, an average value of luminance at a plurality of positions along the first direction with respect to a position in the evaluation area is used as the luminance at the position for which the luminance profile is to be obtained.

3. In claim 1, An image processing method for displaying the determined structure boundary position superimposed on the microscope image.

4. 1. An image processing method for determining a structure boundary width, which is a width of a structure boundary region in a microscopic image of a sample, in which a first phase and a second phase contact each other at the structure boundary region, comprising: a first step of specifying a second direction in the microscope image that includes the structure boundary region and intersects with a first direction that is a longitudinal direction of the structure boundary region; a second step of determining a luminance profile along the second direction; a third step of calculating a moving standard deviation of the luminance profile using a plurality of calculation widths to obtain a moving standard deviation profile; a fourth step of calculating a half-width of a convex waveform included in each of the moving standard deviation profiles calculated using a plurality of the calculation widths; a fifth step of identifying a calculation width of a moving standard deviation profile in which the convex waveform has a peak and a half-width of the convex waveform is narrowest, among the plurality of moving standard deviation profiles; a sixth step of calculating an element difference or derivative of the moving standard deviation profile calculated using the specified calculation width to obtain a moving standard deviation difference profile or a moving standard deviation derivative profile; a seventh step of identifying a pair of a first position having a maximum value and a second position having a minimum value from the moving standard deviation difference profile or the moving standard deviation differential profile; and an eighth step of determining the distance between the first position and the second position as the structure boundary width.

5. In claim 4, In the first step, the second direction is defined so as to be perpendicular to the first direction, and a belt-shaped evaluation area extending in the first direction and the second direction is specified; An image processing method in which, in the second step, an average value of luminance at a plurality of positions along the first direction with respect to a position in the evaluation area is used as the luminance at the position for which the luminance profile is to be obtained.

6. In claim 4, An image processing method for displaying the first position and the second position superimposed on the microscope image.

7. In claim 4, As the microscope image, a plurality of transmission electron microscope images are captured by a transmission electron microscope or a scanning transmission electron microscope while changing the tilt angle of the sample with respect to the optical axis of a primary electron beam; an image processing method for determining, based on the structure boundary width determined for each of the plurality of transmission electron microscope images, the tilt angle that minimizes the structure boundary width as the tilt angle when observing the sample with the transmission electron microscope or the scanning transmission electron microscope.

8. an electron microscope that irradiates a sample with a primary electron beam and forms an image of electrons transmitted through or diffracted by the sample on a detector; a control system for controlling the electron microscope; the control system acquires a plurality of electron microscope images by changing a tilt angle of the sample with respect to an optical axis of the primary electron beam using the electron microscope; In each of the plurality of electron microscope images, a first phase and a second phase are in contact with each other at a structural boundary region, the control system determines a structure boundary width, which is a width of the structure boundary region, for each of the plurality of electron microscope images; The control system determines, based on the structure boundary width determined for each of the multiple electron microscope images, the tilt angle that minimizes the structure boundary width as the tilt angle when observing the sample with the electron microscope.

9. In claim 8, the control system determines the structure boundary width by performing steps 1 to 8 for each of the plurality of electron microscope images; the first step is a step of specifying, in the electron microscope image, a second direction that includes the structure boundary region and intersects with a first direction that is a longitudinal direction of the structure boundary region; The second step is a step of obtaining a luminance profile along the second direction, the third step is a step of calculating a moving standard deviation of the luminance profile using a plurality of calculation widths to obtain a moving standard deviation profile; the fourth step is a step of calculating a half-width of a convex waveform included in each of the moving standard deviation profiles calculated using a plurality of the calculation widths, the fifth step is a step of identifying a calculation width of a moving standard deviation profile in which the convex waveform has a peak and a half-width of the convex waveform is narrowest, among the plurality of moving standard deviation profiles; the sixth step is a step of calculating an element difference or a derivative of the moving standard deviation profile calculated using the specified calculation width to obtain a moving standard deviation difference profile or a moving standard deviation derivative profile, the seventh step is a step of identifying a pair of a first position having a maximum value and a second position having a minimum value from the moving standard deviation difference profile or the moving standard deviation differential profile, The eighth step is a step of determining the distance between the first position and the second position as the structure boundary width.

10. In claim 9, The control system includes: In the first step, the second direction is defined so as to be perpendicular to the first direction, and a belt-shaped evaluation area extending in the first direction and the second direction is specified; An electron microscope system in which, in the second step, an average value of brightnesses at a plurality of positions along the first direction in the evaluation area with respect to a position for which the brightness profile is to be obtained is used as the brightness at that position.

11. In claim 8, The control system calculates a function with the tilt angle as an explanatory variable and the structural boundary width as a target variable based on the structural boundary width determined for each of the plurality of electron microscope images, and determines the tilt angle that minimizes the structural boundary width as the tilt angle when observing the sample with the electron microscope.

12. In claim 8, The electron microscope is an electron microscope system that scans the primary electron beam on the sample.

13. 1. An image processing method for determining a structural boundary position between a first phase and a second phase in a microscopic image of a sample, the first phase and the second phase being in contact with each other at a structural boundary region, the method comprising: a first step of specifying an evaluation area in the microscope image, the evaluation area including the structure boundary area and extending in a first direction and a second direction perpendicular to the first direction; a second step of calculating a moving standard deviation of an area specified by a first calculation width in the first direction and a second calculation width in the second direction for each position included in the evaluation area, and determining a first moving standard deviation profile along the first direction and a second moving standard deviation profile along the second direction; and a third step of determining, as the structure boundary position, a position giving a peak of a first convex waveform included in the first moving standard deviation profile and a peak of a second convex waveform included in the second moving standard deviation profile.

14. In claim 13, a fourth step of obtaining a luminance profile along a third direction that passes through the structure boundary positions and is perpendicular to a structure boundary line obtained by connecting the structure boundary positions, and calculating a moving standard deviation of the luminance profile using a plurality of third calculation widths to obtain a third moving standard deviation profile; a fifth step of calculating a half-width of a third convex waveform included in each of the third moving standard deviation profiles calculated using the third calculation widths; a sixth step of identifying a third calculation width of a moving standard deviation profile in which the third convex waveform has a peak and the half-width of the third convex waveform is narrowest, among the plurality of third moving standard deviation profiles; a seventh step of calculating an element difference or a derivative of the moving standard deviation profile calculated using the specified third calculation width to obtain a moving standard deviation difference profile or a moving standard deviation derivative profile; an eighth step of identifying a pair of a first position having a maximum value and a second position having a minimum value from the moving standard deviation difference profile or the moving standard deviation differential profile; and a ninth step of determining a distance between the first position and the second position as a structure boundary width.

15. In claim 13, An image processing method in which the area specified by the first calculation width and the second calculation width is set with the position included in the evaluation area as the center.

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