JP2010186614A - Detection method of periodical pattern, and photographing method of sample image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detection method of a periodical pattern for detecting a position of a periodical pattern having a known profile in high precision, and a photographing method of a sample image using this detection method. <P>SOLUTION: The detection method of a periodical pattern and the photographing method of a sample image, are structured of a process 1 forming an periodical and artificial pattern with calibration already carried out, a process 2 carrying out template matching between the artificial pattern and a captured image, a process 3 cutting out a part containing each peak of a correlation image with template matching carried out then overlapping with each other, a process 4 searching a single peak which is emphasized of the obtained peak by lamination in an integrated image, and a process 5 obtaining all peak positions in the correlation image by rearranging the peak position which is detected in this way and only emphasized into each unit lattice in the correlation image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a periodic pattern detection method and a sample image capturing method. More specifically, the present invention can stably detect a position where a periodic pattern having a known parameter exists in an image even when the S / N ratio is low. The present invention relates to a periodic pattern detection method and a sample image photographing method using this method. Specifically, the present invention relates to the field of performing stage movement automatically using a transmission electron microscope (TEM) or the field of semiconductor inspection using a scanning electron microscope (SEM).

  Conventionally, normalized correlation has been used as a method of detecting the position of a pattern having a known shape existing in an image. While this has the advantage that image processing can be performed at high speed using Fourier transform, there is a problem that the success rate is low in a noisy image. For example, in the field of observing a biological sample that is vulnerable to electron beam irradiation with a TEM, a carbon thin film that supports the sample may be used in which periodic holes are opened. It is extremely difficult to detect a hole by a normal normalization correlation in an automatic system that detects a sample and images a sample embedded in the hole.

  This is shown in FIG. (A) is an image of a virus fixed to a carbon thin film in which circular holes are periodically opened. The diameter of the hole is about 2 μm. Here, a comparatively negative contrast-stained sample (a sample with a white sample and a black sample around it) was used. For the purpose of detecting the positions of individual holes in this image, When an artificial hole picture as shown in () is made and the normalized correlation between (a) and (b) is calculated, an image as shown in (c) is obtained. Although a bright peak can be observed at each position of (c) corresponding to the center position of each hole of (a), it cannot be detected well because it is blurred. (D) is a three-dimensional representation of (c), but it can be seen that the individual peaks are small ones buried in gentle bumps.

  Furthermore, when observing an ice-embedded sample without staining as shown in FIG. 6 (a), the correlation image is further blurred and individual peaks cannot be detected. This is not limited to the TEM image, and the same applies to the field of inspecting periodic semiconductor patterns.

  As a conventional device of this type, a sample is prepared using holey carbon, inserted into a TEM to obtain a lens suitable for observation, and an image formed by an imaging system is captured by a digital camera, and the captured image is captured. In addition, the circles arranged in a grid pattern at equal intervals are displayed as a schematic diagram of the hole, superimposed on the image, and the schematic diagram is actually displayed using the buttons etc. displayed around the displayed image. There is known a technique for calculating the center of distortion and the magnitude of the distortion when the schematic diagram is fitted to the actual hole, and storing the center of distortion and the magnitude of the distortion (for example, Patent Document 1).

JP 2008-171756 A (paragraphs 0016 to 0021, FIGS. 1 and 2)

  As described above, with the conventional technology, the correlation image is blurred even if the normalized correlation between the artificial pattern and the read image is taken, so the position of the periodic pattern with periodic holes in the carbon thin film is accurately detected with high accuracy. There was a problem that could not be done.

  The present invention has been made in view of such problems, and uses a periodic pattern detection method capable of detecting a position of a periodic pattern having a known shape with high accuracy, and the detection method. It aims at providing the imaging | photography method of a sample image.

  (1) The invention according to claim 1 performs the step 1 of creating a calibrated periodic artificial pattern, the step 2 of performing template matching between the artificial pattern and the captured image, and the template matching. Step 3 for cutting out and superimposing portions including individual peaks of the correlation image, Step 4 for searching for a single peak in which the peak obtained by the superposition is emphasized in the integrated image, and detection in this way And the step 5 of relocating the only emphasized peak positions to each unit cell in the correlation image to obtain all the peak positions in the correlation image.

(2) The invention described in claim 2 is characterized in that the template matching is a normalized correlation operation between the artificial pattern and the captured image.
(3) The invention according to claim 3 is a step 1 in which a sample is prepared using a carbon thin film having a periodically circular hole, and is inserted into a transmission electron microscope to obtain a lens state suitable for observation; Step 2 for starting the automatic data collection software, Step 3 for capturing an image from the digital camera, Step 4 for calibrating the hole diameter, the hole inclination, and the interval between adjacent holes, and the automatic data collection software The step 5 of moving the sample stage sequentially to each position where data on the sample is to be acquired, the step 6 of capturing an image from a digital camera, and the image photographed in the step 6 are individually processed by the method described in claim 1. Step 7 for detecting the position of each hole, Step 8 for moving the stage to the position of each hole detected in Step 7, and Step 9 for taking an image of the embedded sample inside the hole by increasing the magnification. A step 10 of checking whether treated with all the pores, the process 11 of the determination of whether finished all positions, characterized in that it is composed of.

  (1) According to the first aspect of the invention, the peak matching is further emphasized by cutting out and superimposing and superimposing a portion including individual template-matched peaks, and the obtained peak position is assigned to each unit cell in the correlation image. By re-arranging, since the peak position of the captured image can be detected even for an image having a lot of noise, the sample stage can be accurately moved.

(2) According to the invention described in claim 2, a matching image can be obtained by performing normalized correlation calculation as template matching.
(3) According to the invention described in claim 3, each sample can be accurately positioned and a sample image in the hole of the carbon thin film can be obtained.

It is a figure which shows the system configuration example which implements this invention. It is a figure which shows the operation | movement flow of the system using this invention. FIG. 8 is a diagram illustrating a normalized correlation obtained using a schematic diagram of an artificial hole arrangement with respect to the image of FIG. It is a figure which shows integration | accumulation of a correlation image. It is a figure which shows the integrated peak position and the hole detected based on it. A TEM image (a) of an ice-embedded sample, a state (b) in which individual holes are manually detected, a result (c) detected by the present invention, and a result (d) designated from a simple normalized correlation peak position FIG. It is a figure which shows the example (c) and (d) which calculated the normalization correlation with the image (a) of the sample fixed to the perforated carbon film, the schematic diagram (b) of the artificial hole.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a diagram showing a system configuration example for carrying out the present invention. In the figure, 1 is a transmission electron microscope (TEM), 4 is a digital camera that takes a TEM image, 3 is a computer having an interface for capturing an image of the digital camera, and 2 is connected between the digital camera 4 and the computer 3. An image capturing cable 5 is a cable for communication between the TEM 1 and the computer 3. The operation of the method of the present invention will be described using such a configuration.

FIG. 2 is a diagram showing an operation flow of a system using the present invention. Hereinafter, processing up to image capturing will be described using this operation flow.
1. Step S1: Preparation of Sample The operator periodically prepares a sample using a carbon thin film having a circular hole, and inserts the sample into the TEM 1 to obtain a lens state suitable for observation.

2. Step S2: Start the automatic software The operator starts the automatic data collection software in the computer 3. The method of the present invention is incorporated into this software.

3. Step S3: Image Capture from Digital Camera The automatic data collection software captures an image from the digital camera 4 via the image capture cable 2 and displays the captured image. In the displayed image, it is assumed that several holes are periodically shown as shown in FIG.

4). Step S4: Calibration The operator calibrates the diameter of the holes, the inclination of the hole array, and the interval between adjacent holes while interacting with the automatic data collection software. Here, calibration refers to determining the diameter of the holes, the inclination of the hole arrangement, and the interval between adjacent holes. This calibration can be performed in the same manner as the distortion calibration as shown in Patent Document 1.

5). Step S5: Stage movement The automatic data collection software moves the sample stage to each position where data on the TEM sample is desired to be acquired.

6). Step S6: Capture an image from the digital camera The automatic data collection software captures an image from the digital camera 4 under the same optical conditions as in step S3 after moving in step S5.

7). Step S7: Detection According to the Present Invention The position of each hole is detected by performing a normalized correlation between the image photographed in step S6 and the artificial pattern prepared in advance (details will be described later).

8). Step S8: Move to each hole The stage is moved to the position of each hole detected in Step S7. Here, the resolution of the stage movement is, for example, about 0.2 μm.

9. Step S9: Photographing at high magnification The magnification is increased and an image of the sample embedded in the hole is photographed. This shooting can be performed on a film, or can be taken from a digital camera and stored on a hard disk.

10. Step S10: Determination of whether or not processing has been performed for all holes It is determined whether or not photographing has been performed for all of the holes detected in step S7. If there is a hole that has not been photographed yet, the process returns to step S8.

11. Step S11: Determination of whether or not photographing of all positions has been completed. It is determined whether or not the operations of Steps S6 to S10 have been performed on all positions for which data on the TEM sample is desired to be acquired. If not, the process returns to step S5.

As described above, according to the method of the present invention, each sample can be accurately positioned and a sample image in the hole of the carbon thin film can be obtained.
Next, the detection method according to the present invention will be described. Here, the details of the detection method according to the present invention will be described using the perforated carbon thin film sample as described in step S1 to step S11 as an example. The same processing can be performed even when a regular pattern of another shape is used as in the case of application to semiconductor inspection.

  As described above, even if a schematic diagram of one hole (FIG. 7B) is made and the normalized correlation is calculated, the peak position here is blurred and is difficult to detect. Therefore, in the present invention, a periodic artificial pattern as shown in FIG. In this case, not only the size of the hole but also the inclination and interval of the periodic pattern are already calibrated as described in the above operation example. When a normalized correlation with the image shown in FIG. 7A is calculated using such a periodic reference image, a result shown in FIG. 3B is obtained. It can be seen that the individual peaks are easier to identify than the result of FIG. Here, the peak indicates the center position of the hole.

  In the present invention, the correlation image obtained in this way also uses the fact that the peaks should be periodically arranged in the same manner as the original image, and cuts out and superimposes the portions including individual peaks. Match. In this case, in the original image shown in FIG. 7A, the holes form a two-dimensional square lattice, and the lattice constant and inclination are known. In FIG. 3B, each peak should be present on a square lattice having the same parameters, so that it is cut out for each unit lattice.

  The original normalized correlation has multiple peaks corresponding to multiple holes, whereas each individual unit cell that is cut has a single peak in the same position, each corresponding to a single hole. Should be. Therefore, if these are integrated, the peak is emphasized at that position. This enhanced single peak may be searched in the integrated image.

FIG. 4 shows a state where the unit cell of the correlation image is cut out and integrated. The first piece should be set at the center of the correlation image, and the unit cell should be cut out so as to be adjacent to it.
If the positions of the only emphasized peaks detected in this way are rearranged in each unit cell in the correlation image, the positions of all the peaks in the correlation image can be obtained. FIG. 5 shows the peak positions obtained by such calculation and the holes detected based on the peak positions. (A) shows a correlation image, and (b) shows a hole detected based on the correlation image. It should be noted that a hole partially protruding from the image was not detected.

  According to the present invention, the peak matching is further emphasized by cutting out and superimposing a portion including individual peaks subjected to template matching, and the obtained peak position is rearranged in each unit cell in the correlation image, thereby reducing noise. Even in the case of an image with many images, the peak position of the captured image can be detected, so that the sample stage can be accurately moved.

  FIG. 6 shows the results for an ice-embedded sample without staining. (A) is a photographed image, (b) is an individual hole extracted manually, (c) is an image automatically detected by the present invention, (e) is a peak position calculated by normal normalization correlation. Is what we asked for. In such an image with a very low signal-to-noise ratio (S / N ratio), it can be seen that individual holes that can hardly be detected by the conventional method can be detected with high accuracy by the method of the present invention.

  In the above-described embodiment, the case where the normalized correlation is taken as the template matching is taken as an example. However, the present invention is not limited to this method, and the present invention can be realized using other template matching.

  When the position of the hole can be identified in this way, when the sample in the target hole is imaged, the sample stage can be moved to the target position and the sample in the hole can be imaged. As described above, according to the present invention, the position of a pattern having a known periodicity can be detected with high accuracy even in an image having a very low signal-to-noise ratio.

1 Transmission Electron Microscope 2 Image Capture Cable 3 Computer 4 Digital Camera 5 Communication Cable

Claims (3)

Step 1 of creating a calibrated periodic artificial pattern;
Step 2 for performing template matching between the artificial pattern and the captured image;
A step 3 of cutting out and superposing portions including individual peaks of the correlation image subjected to the template matching;
Searching for a single peak in which the peak obtained by the superposition is emphasized in the integrated image; and
Step 5 relocating the only emphasized peak position detected in this way to each unit cell in the correlation image to obtain all peak positions in the correlation image;
A method of detecting a periodic pattern, comprising:   The periodic pattern detection method according to claim 1, wherein the template matching is a normalized correlation calculation between the artificial pattern and the captured image. A sample is prepared using a carbon thin film having periodically circular holes, and is inserted into a transmission electron microscope to obtain a lens state suitable for observation;
Step 2 of starting the automatic data collection software;
Step 3 for capturing images from a digital camera;
Step 4 for calibrating the diameter of the hole, the inclination of the hole and the interval between adjacent holes;
The automatic data collection software moves the sample stage in order to each position where the data on the TEM sample is to be acquired,
Step 6 for capturing an image from a digital camera;
Step 7 for detecting the position of each hole by the method described in claim 1 for the image taken in Step 6;
Step 8 for moving the stage to the position of each hole detected in Step 7;
Step 9 of increasing the magnification and taking an image of the embedded sample inside the hole;
Step 10 for checking whether all holes have been treated,
Step 11 for determining whether all positions have been completed;
A method for taking a sample image comprising: