JPH07282769A - Electron beam diffracting device - Google Patents

Abstract

PURPOSE:To provide an accurate distribution image of a crystal without requiring selection of a characteristic diffraction spot from a diffraction pattern by providing specific constitution in an electron beam diffracting device to find a distribution image of a crystal of a sample surface by the diffraction pattern obtained by radiating a scanning electron beam to a sample. CONSTITUTION:An electron beam diffracting device has an image pickup device 7 to pick up an image of a diffraction pattern, an image memory 14 to store a reference pattern and an image processing device 13 to find a resemblance degree of both diffraction patterns by comparing the diffraction pattern obtained by the image pickup device 7 and the diffraction pattern stored in the image memory 14, and a distribution image in a crystal condition of a sample surface is found according to this resemblance degree.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam diffractometer for observing a crystalline state on the surface of a sample by observing a diffraction image obtained by irradiating the sample with an electron beam.

[0002]

2. Description of the Related Art As a method for observing the crystalline state of a sample surface, a scanning reflection electron diffraction apparatus (scanning RHEED) for observing a diffraction image obtained by irradiating a sample with an electron beam is known. For example, in the conventional scanning backscattered electron diffraction apparatus of FIG. 12, the primary electron beam 4 emitted from the electron gun 2 is focused on the surface of the sample 3 in the vacuum container 1 and on the surface of the sample 3. To be scanned. Then, the secondary electron intensity emitted from the sample 3 is converted into a brightness modulation signal by a secondary electron detector (not shown), and a scanning image is displayed on the CRT 12. When observing the crystal state of the sample surface in this conventional electron beam diffractometer, first, the place where the target crystal grain of the sample 3 is to be analyzed is selected, and the primary electron beam 4 is fixedly irradiated to this analysis point. Reflected diffraction line 5 obtained by
Are formed as a diffraction pattern on the fluorescent screen 6. Then, a characteristic diffraction spot is selected from the diffraction spots forming this diffraction pattern through an optical system or an aperture (not shown), and the brightness of the diffraction spot is determined by using a photoelectric conversion element 9 such as a photomultiplier. The scanning image is observed as.

[0003]

However, the above-mentioned conventional electron beam diffractometer has a problem that it is necessary to select characteristic diffraction spots from the diffraction pattern, and a part of the diffraction pattern is required. Since the scanning image of the crystalline state is obtained only by the brightness of the area, there is a problem that the distribution of the crystalline state cannot be represented accurately. FIG.
FIG. 4 is a diagram for obtaining a luminance signal from a diffraction pattern of a conventional electron beam diffractometer. For example, the region under observation is crystalline state A
And the crystalline state B, the crystalline patterns of the crystalline state A and the crystalline state B are different when scanning along the scanning line (arrow in the figure), and thus the obtained diffraction patterns are different. Therefore, characteristic diffraction spots are determined from the obtained diffraction pattern, the luminance signal of the diffraction spots is obtained, and the distribution of the crystalline state is observed by this. Here, the observation point P _A in a crystalline state A, and in each of the diffraction pattern to be obtained from the observation point P _B crystalline state B,
When the positions of the selected characteristic diffraction spots (indicated by ●) match, the same luminance signal is sent despite the difference in the diffraction pattern, and similarly for different crystalline states on the CRT. It is displayed and it is difficult to distinguish the crystalline states.

Conventionally, in order to solve the above-mentioned problems, an electron beam diffraction apparatus has been proposed in which a plurality of diffraction spots are selected from a diffraction pattern and a product of signal intensities indicating the brightness thereof is used as a luminance signal of a CRT. However, it has not been fully effective.

Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional electron beam diffractometer and to provide an electron beam diffractometer capable of accurately expressing the distribution of the crystalline state. Another object of the present invention is to provide an electron diffraction apparatus which does not require selection of characteristic diffraction spots from a diffraction pattern.

[0006]

According to the present invention, a diffraction pattern is imaged in an electron diffraction apparatus for obtaining a distribution image of a crystalline state on the surface of a sample by a diffraction pattern obtained by irradiating a sample with a scanned electron beam. An image pickup device, an image memory that stores a reference diffraction pattern, and an image processing device that obtains the similarity between both diffraction patterns by comparing the diffraction pattern obtained by the image pickup device and the diffraction pattern stored in the image memory, The above object is achieved by obtaining a distribution image of the crystalline state on the sample surface based on the degree of similarity.

The reference diffraction pattern of the present invention is information for specifying a diffraction pattern representing a reference crystal state, and can be used as a parameter of a diffraction pattern image itself or a diffraction spot for specifying the diffraction pattern. Further, the similarity of the present invention serves as a reference for comparison between diffraction patterns, and using the parameters of the diffraction spots that specify the diffraction pattern image itself or the diffraction pattern, the reference diffraction pattern and the measured diffraction pattern are compared. It is possible to show relevance.

[0008]

With the above structure, the electron beam diffractometer irradiates the sample with the electron beam while scanning the sample and obtains a diffraction pattern image formed by the electron beam obtained by diffracting the sample. Then, this diffraction pattern image is picked up by an image pickup device. In the image processing measurement, the diffraction pattern imaged by this imaging device is compared with the reference diffraction pattern in the image memory to obtain the similarity between both diffraction patterns, and based on this similarity, the distribution of the crystalline state of the sample surface Ask for a statue.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. [Configuration of Embodiment] The configuration of the electron beam diffractometer of the present invention will be described with reference to the block diagram of the electron beam diffractometer of the present invention shown in FIG. In FIG. 1, an electron gun 2 is provided in a vacuum container 1, and an electron beam 4 from the electron gun 2 is irradiated onto the surface of a sample 3 in the vacuum container 1 at an acute angle and scans the surface of the sample 3. . The scanning of the electron beam 2 on the sample surface is performed by controlling the electron beam 2 by the scanning signal generation circuit 10. A magnification adjusting circuit 11 is connected between the scanning signal generating circuit 10 and the electron gun 4. The scanning electron beam is reflected and diffracted on the surface of the sample 3 to become a reflected diffracted electron beam 5, which projects a diffraction pattern on the fluorescent screen 6. The crystal state such as the crystal structure or the geometrical structure of the surface of the sample 3 is different at each position on the sample surface, and when the irradiation position is moved on the sample surface by the scanning of the electron beam,
The diffraction pattern changes according to the scanning. Then, the diffraction pattern projected on the fluorescent screen 6 is imaged by the imaging device 7, the image signal processing is performed by the image processing device 13, and then the crystal state of the sample surface is displayed by the CRT 12. The image signal processing in the image processing device 13 is to obtain the degree of similarity of the diffraction pattern by comparing the diffraction pattern input from the imaging device 7 with the reference diffraction pattern. Therefore, the image processing device 1
An image memory 14 for storing a reference diffraction pattern is connected to 3. The image memory 14 can store the reference diffraction pattern itself for obtaining the degree of similarity, or a parameter thereof, and also stores the diffraction pattern from the image pickup device 7, the processing result of the image processing device 13, and the like. It can also be configured. A shade is provided between the image pickup device 7 and the fluorescent screen 6 to improve the image pickup sensitivity. Further, the CRT 12 receives the scanning signal from the scanning signal generation circuit 10 and is synchronized with the signal of the scanned diffraction pattern from the imaging device 7.

[Operation of Embodiment] Next, the operation of the embodiment of the present invention will be described. FIG. 2 is a diagram for explaining the function of the diffraction pattern comparison processing according to the embodiment of the present invention. FIG. 2A shows a part of the surface of the sample 3, which is formed by a crystalline state A (a downward-sloping oblique line portion in the drawing) and a crystalline state B (a downward-sloping oblique line portion in the drawing). It has been done.

In the case of comparing and observing the crystal states of the two, in the embodiment of the present invention, the diffraction pattern obtained by scanning the sample surface along the scanning line of the arrow is imaged by the image pickup device 7, and the image processing device 13 is used. Send to. For example, the measurement point P _A
It is assumed that images are taken at (the crystalline state A) and at the measurement point P _B (the crystalline state B), and the diffraction patterns shown in FIG. 2B are obtained. The pattern comparison means 20 in the image processing device 13 compares the captured diffraction pattern with the reference diffraction pattern in the image memory 14,
The degree of similarity to the reference diffraction pattern is obtained, and the crystal state of the sample is displayed on a display means such as a CRT based on this degree of similarity signal. The display of the crystal state according to the degree of similarity and the degree of similarity will be described later. Note that, in FIG. 2B, the same diffraction pattern as the diffraction pattern of the measurement point P _B is shown as the reference diffraction pattern in the image memory, but this reference diffraction pattern is an example, and the diffraction pattern of the measurement point P _A is shown. It can also be a pattern or other diffraction pattern. As the reference diffraction pattern stored in the image memory 14, a diffraction pattern imaged by an imaging device during scanning can be used. In this case, there is an effect that the same crystalline state distribution as that of the specific portion under observation can be obtained. As the reference diffraction pattern stored in the image memory 14, a known diffraction pattern stored in advance can be used instead of the diffraction pattern from the image pickup device. In this case, there is an effect that the distribution of the known crystal state on the sample surface can be obtained.

(Output Display Based on Similarity) Next, the display of the crystal state according to the similarity in the electron beam diffractometer of the present invention will be described. As described above, in the electron beam diffractometer of the present invention, the similarity obtained by comparing the diffraction patterns is used to obtain the distribution image of the crystalline state on the sample surface. FIG. 3 is a diagram for explaining the degree of similarity used in the electron beam diffractometer of the present invention, in which the sample surface has a crystalline state A.
And a crystal state B are shown. The similarity A is obtained by comparing the diffraction pattern obtained along the scanning line with the reference diffraction pattern of the crystalline state A, and the similarity B is obtained by comparing the diffraction pattern with the reference diffraction pattern of the crystalline state B. . As shown in the graph, the similarity A and the similarity B greatly change at the boundary of the crystalline state. Obtaining this similarity for each scan,
A two-dimensional crystal state can be output and displayed. In addition,
The output display shown in the figure is an example in which the degree of similarity is obtained by a plurality of threshold values. In this case, a minute change due to an angle change or the like can be displayed in a similar crystal state.
It should be noted that in the figure, minute changes are shown with different shaded densities, but they can also be represented by color changes on the CRT.

(Similarity Calculation Example 1) Next, calculation of the similarity in the electron diffraction apparatus of the present invention will be described with reference to FIG. In this first calculation example, the output of each pixel that captures a diffraction pattern is used, and the degree of similarity is determined by the number of pixels whose output states match. Although FIG. 4 illustrates the case of 18 pixels, the number of pixels is arbitrary and can be determined according to the imaging device or the processing circuit. When the imaging device is composed of a plurality of pixels, the magnitude of the output intensity of each pixel changes according to the brightness of the diffraction spot of the diffraction pattern. When the output intensity of this pixel is binarized by a certain threshold value,
For example, as shown in FIG. 4, a distribution pattern formed in two types of pixel states can be obtained. For example, in the figure, a pixel that produces a large output corresponding to a bright diffraction spot is represented by a pattern ground. Further, in the drawing, each pixel is represented by a combination of numbers 1 to 6 in the horizontal direction and symbols a to c in the vertical direction. In comparing the diffraction patterns, for example, comparing the measured diffraction pattern a with the reference diffraction pattern, the diffraction spots corresponding to the pixels represented by 1a, 1c, 3b, 5a, and 5c in both diffraction patterns are bright, and The diffraction spots corresponding to are dark, and the output states of all pixels match.

Therefore, if the similarity is determined by, for example, similarity = {(number of pixels whose output states match) / (total number of pixels)} × 100%, the similarity of the measured diffraction pattern a is
(18/18) × 100% = 100%. In addition, comparing the measured diffraction pattern b with the reference diffraction pattern, 3
The brightness of the diffraction spots corresponding to the pixel b is different, and the brightness of the diffraction spots corresponding to the other pixels are the same. Therefore, the similarity of the measured diffraction pattern b in this case is
(17/18) × 100% = 94%. Further, when the measured diffraction pattern c is compared with the reference diffraction pattern, the brightness of the diffraction spots corresponding to all the pixels is different, and the similarity of the measured diffraction pattern b in this case is (0/18) ×
100% = 0%. The calculation of the degree of similarity can be performed by the pattern comparison means in the image processing measurement 13. Then, the reference diffraction pattern can be read out from the image memory 14 at the time of pattern comparison and used, and the reference diffraction pattern can be a measured diffraction pattern or a known diffraction pattern. The degree of similarity can be adjusted by adjusting the threshold value for binarization. For example, the higher the threshold value, the tighter the similarity can be set, and the lower the threshold value, the lower the similarity.

(Similarity Calculation Example 2) Next, a second similarity calculation example in the electron beam diffractometer of the present invention will be described with reference to FIGS. The second calculation example is an example in which the parameters of the diffraction pattern are used as the comparison reference of the diffraction pattern, not the image of the diffraction pattern. In FIG. 6, the parameters of the diffraction spots indicating the features of the reference diffraction pattern are obtained in advance and stored in the memory 21, and the parameters of the diffraction spots are read from the memory 21,
The degree of similarity is obtained by comparing with the corresponding diffraction spots in the measured diffraction pattern. This processing can be performed by the signal strength measuring means 22 and the comparing means 20.
For example, in FIG. 5, the parameters of the position (x, y) of the diffraction spot indicating the feature in the reference diffraction pattern and the diffraction signal intensity I are stored in the memory 21. Then, the parameters of the diffraction spot position (x _n , y _n ) and the diffraction signal intensity I _n are read from the memory 21, and the diffraction signal intensity I corresponding to the diffraction spot position (x _n , y _n ) of the measured diffraction pattern is read.
_{N is obtained} by the signal strength measuring means 22. Then, the ratio of the obtained diffraction signal intensity I _{N to} the diffraction signal intensity I _n is obtained by the comparison means 20, and the similarity as shown below can be determined. Similarity = (I _N / I _n ) × 100% The definition of the similarity is an example, and another definition such as determining the similarity by the degree of positional deviation of diffraction spots with respect to the same diffraction signal intensity is used. It can also be set by.

(Similarity Calculation Example 3) Next, a third example of similarity calculation in the electron diffraction apparatus of the present invention will be described with reference to FIGS. The third calculation example is an example in which the degree of similarity is obtained using the parameters of the diffraction pattern in the same manner as the second calculation example. In FIG. 8, the parameters of the diffraction spots showing the features of the reference diffraction pattern are obtained in advance and stored in the memory 21.
A parameter of a certain diffraction spot is read from the comparison means 20 and compared with the corresponding diffraction spot in the measured diffraction pattern to obtain the degree of similarity. For example, in FIG. 7, the distance d ₁ between the diffraction spots showing the features in the reference diffraction pattern,
The d ₂ and the angle θ formed by the diffraction spots are stored in the memory 21 as parameters. Then, the parameters of the distances d ₁ and d ₂ between the diffraction spots and the angle θ formed by the diffraction spots are read out from the memory 21, and the distances D ₁ and D ₂ between the diffraction spots of the measured diffraction pattern and the diffraction spots are read. Comparison means 20 for comparing with the formed angle Θ
In step 1, the degree of similarity is calculated. As for this similarity,
Similarity function f (D _1M / d _1n , D _2M / d _2n , Θ _M / θ _n )
And the value of the similarity function can be calculated for the diffraction spots of the reference diffraction pattern and the measured diffraction pattern. This similarity function f (D _1M / d _1n , D _2M / d _2n , Θ
_{As M} / θ _n ), for example, a function for averaging the similarity of each parameter can be used as in the following equation.

F = {(D _1M / d _1n + D _2M / d _2n + Θ _M /
θ _n ) / 3} × 100% The definition of the similarity function is an example, and if the definition of the similarity function according to the similarity of each parameter is determined according to the measurement experiment or the specific gravity to be applied to the parameters is different. It can be set by other definitions, such as

(Setting of Reference Diffraction Pattern) Next, regarding the setting of the reference diffraction pattern to be stored in the image memory 14,
This will be described with reference to FIG. FIG. 9A is a diagram for explaining the first setting of the reference diffraction pattern. The first setting is to input the diffraction pattern from the imaging device 7 to the image memory 14 via the image processing device 13 and store it as a reference diffraction pattern. The signal flow of this diffraction pattern is
It is indicated by a broken line in the figure. Therefore, in setting the reference diffraction pattern, the diffraction pattern in a specific crystal state obtained during measurement of the sample surface can be used as the reference diffraction pattern. The diffraction pattern stored in the image memory 14 is read out again to the image processing device 13,
A comparison is made with another diffraction pattern obtained from the imaging device 7.

FIG. 9B is a diagram for explaining the second setting of the reference diffraction pattern. The second setting is to store the parameters of the known reference diffraction pattern in the image memory 14 via the input means (not shown). As described above, the position of the diffraction spot and the diffraction signal intensity, or the distance and angle between the diffraction spots can be used as this parameter. The parameters can be directly input to the image memory 14 or can be input via the parameter forming means 23. When the parameter forming means 23 is used, data relating to the substance and surface condition of the sample are input to the parameter forming means 23, parameters based on the data are obtained, and the parameters are input to the image memory 14. In this case, in the parameter forming means 23, it is possible to carry out by storing the parameters for the data regarding the substance and surface state of the sample in the memory. The flow of parameters of this diffraction pattern is shown by the broken line in the figure. Therefore, in setting the reference diffraction pattern, a known crystal state can be searched for by simply setting parameters on the sample surface. The diffraction pattern read from the image memory 14 by inputting the parameters is compared with the diffraction pattern obtained from the image pickup device in the image processing device 13.

(Comparison with a plurality of reference patterns) Next, in the electron beam diffractometer of the present invention, a case of comparison with a plurality of reference patterns will be described with reference to FIGS. 10 and 11. FIG. 10 shows a case where a plurality of image memories are used for comparison with a plurality of reference patterns.
A plurality of image memories 31 to 3n are connected to the reference numeral 3, and reference diffraction patterns 1 to n are stored in the respective image memories 31 to 3n. When the measurement diffraction pattern is input from the image pickup device 7, the image processing device 13 receives each of the image memories 31 to 3n.
Then, the reference diffraction patterns 1 to n are sequentially read out and compared with the measured diffraction pattern to obtain the degree of similarity. With this configuration, a plurality of crystal states on the sample surface can be analyzed and displayed. Further, FIG. 11 shows a case where a plurality of sets of image processing measurement and image memory are used to compare with a plurality of reference patterns, and image memories 31 to 3n are connected to the image processing devices 41 to 4n, respectively. Each image memory 31 to 3n
Stores reference diffraction patterns 1 to n. When the measurement diffraction pattern is input from the image pickup device 7, the image processing devices 41 to 4n receive the image memories 31 to 3n.
The reference diffraction patterns 1 to n are sequentially read from n, and the degree of similarity is obtained by comparing with the measured diffraction pattern. With this configuration, a plurality of crystal states on the sample surface can be analyzed and displayed.

A plurality of image memories can be connected to each of the image processing devices 41 to 4n, and a different process can be set for each image processing device.

(Embodiment of the Invention) A first embodiment of the electron beam diffractometer of the present invention is characterized in that an image memory stores a diffraction pattern imaged by an image pickup device. The embodiment has an effect that a distribution image of a crystalline state can be obtained with reference to an arbitrary crystalline state of a sample. A second embodiment of the electron diffraction apparatus of the present invention is characterized in that the image memory stores a known diffraction pattern, and this embodiment searches for a crystal state to be obtained from the sample surface. There is an effect that can be. A third embodiment of the electron beam diffractometer of the present invention is characterized in that the image memory stores the parameters of the diffraction pattern, and this embodiment searches for the crystal state to be obtained from the sample surface. There is an effect that can be. A fourth embodiment of the electron diffraction apparatus of the present invention is characterized in that the image memory has a function of storing a plurality of reference diffraction patterns. In this embodiment, a plurality of diffraction patterns are stored. There is an effect that the comparison can be performed.

The function can be realized by installing a plurality of image memories or forming a plurality of storage areas in the image memories. A fifth embodiment of the electron beam diffractometer of the present invention is characterized in that the image processing device compares diffraction patterns in pixel units,
This embodiment has an effect that the pixel signal of the image pickup device can be effectively used. Sixth of the electron diffraction device of the present invention
This embodiment is characterized in that the image processing device compares the parameters of the diffraction patterns, and this embodiment has the effect of improving the comparison calculation speed.

[0024]

As described above, according to the present invention,
It is possible to provide an electron diffraction apparatus capable of accurately expressing the distribution of crystalline states. Further, it is possible to provide an electron beam diffraction apparatus which does not require selection of characteristic diffraction spots from the diffraction pattern.

[Brief description of drawings]

FIG. 1 is a block diagram of an electron beam diffraction apparatus of the present invention.

FIG. 2 is a diagram illustrating a function of a diffraction pattern comparison process according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating the degree of similarity used in the electron beam diffractometer of the present invention.

FIG. 4 is a diagram illustrating calculation of similarity in the electron beam diffractometer of the present invention.

FIG. 5 shows a second similarity degree in the electron diffraction apparatus of the present invention.
It is a figure explaining the example of calculation of.

FIG. 6 shows a second similarity degree in the electron diffraction apparatus of the present invention.
It is a figure explaining the example of calculation of.

FIG. 7 shows a third similarity degree in the electron diffraction apparatus of the present invention.
It is a figure explaining the example of calculation of.

FIG. 8 shows a third similarity degree in the electron diffraction apparatus of the present invention.
It is a figure explaining the example of calculation of.

FIG. 9 is a diagram illustrating setting of a reference diffraction pattern of the electron diffraction apparatus of the present invention.

FIG. 10 is a diagram illustrating a comparative example of the electron diffraction apparatus of the present invention with a plurality of reference patterns.

FIG. 11 is a diagram illustrating a comparative example of the electron diffraction apparatus of the present invention with a plurality of reference patterns.

FIG. 12 is a conventional scanning reflection electron diffraction apparatus.

FIG. 13 is a diagram for obtaining a luminance signal from a diffraction pattern of a conventional electron beam diffractometer.

[Explanation of symbols]

1 ... Vacuum container, 2 ... Electron gun, 3 ... Sample, 4 ... Electron beam, 5
... reflection diffracted electron beam, 6 ... fluorescent screen, 7 ... imaging device, 10 ... scanning signal generating circuit, 11 ... magnification adjusting circuit, 1
2 ... CRT, 13, 41-4n ... Image processing device, 14 ...
Image memory, 20 ... Comparing means, 21, 31-3n ... Memory, 22 ... Signal strength measuring means, 23 ... Parameter forming means

Claims (1)

[Claims] 1. An electron beam diffraction apparatus for obtaining a distribution image of a crystalline state on a sample surface by a diffraction pattern obtained by irradiating a sample with a scanned electron beam, and an image pickup apparatus for picking up the diffraction pattern, and a reference diffraction pattern. And an image processing device that obtains the similarity between both diffraction patterns by comparing the diffraction pattern obtained by the image pickup device with the diffraction pattern stored in the image memory, based on the similarity. An electron beam diffractometer characterized by obtaining a distribution image of the crystalline state on the surface of the sample.