JP5308903B2 - Crystal orientation identification system and transmission electron microscope - Google Patents

Description

  The present invention relates to a transmission electron microscope and a transmission electron microscope having a crystal orientation identification system for identifying a crystal orientation from an electron diffraction image of a crystalline sample.

  Conventionally, an X-ray diffraction apparatus using X-rays has been used as a method for analyzing the crystal orientation of a crystalline sample.

  Moreover, as a method for analyzing crystal orientation using an electron beam, there are methods of analyzing EBSP (Electron Back-Scattering Pattern) and ECP (Electron Channeling Pattern) in a scanning electron microscope (SEM). In TEM, there are methods for analyzing the Kikuchi pattern, CBED (Convergent Beam Electron Diffraction), and electron diffraction images.

  As an example, the EBSP analysis method is a technique using a pseudo Kikuchi pattern, and since the pseudo Kikuchi pattern reacts sensitively to crystal orientation, it has been used for crystal grain orientation analysis. It is used to analyze the orientation of internal crystal grains of copper wire or steel plate produced by rolling as a sample.

  Further, Patent Document 1 and Patent Document 2 are methods for analyzing an electron beam diffraction image.

JP 2006-258825 A JP 59-163548 A

  In recent years, the miniaturization of materials and devices has progressed, and the crystal orientation of a fine structure has attracted attention. For example, in order to measure the crystal orientation of the HDD magnetic film and the bond angle of crystal grains, it has become necessary to analyze the crystal orientation of particles having a diameter of about 10 nm.

  In TEM, the electron beam can be narrowed (several nm diameter), and is suitable for crystal orientation analysis from the viewpoint of the electron beam diameter. However, in the analysis using the Kikuchi pattern and CBED, there are conditions (sample thickness, orientation, composition) in the samples that can be analyzed, and the crystal orientation cannot be analyzed for all samples.

  In this respect, since the electron beam diffraction image can be observed as long as the sample transmits the electron beam, there are few restrictions on the sample such as the sample thickness like the Kikuchi pattern and CBED. Since an electron diffraction image is also an image reflecting the crystal structure of a sample, it has been used for substance identification together with an elemental analyzer such as EDX (for example, Patent Document 1).

  However, it has been difficult to determine the crystal orientation using electron diffraction images. In the method of Patent Document 1, an electron diffraction image is used to obtain information for substance identification, and no mention is made of crystal orientation. In addition, it is possible to obtain the crystal orientation by taking and analyzing the diffraction image even by the method using the electron diffraction image, but since the diffraction image is taken and analyzed at each point, the crystal orientation It was difficult to analyze the crystal orientation of multiple points necessary for the analysis of the above because of labor and time.

  With the method of Patent Document 2, the orientation (low-order zone axis) of a diffraction pattern with high symmetry can be obtained, but the orientation when the orientation is shifted by, for example, about 5 degrees from the low-order zone axis is also low. It will be calculated as the direction. This is because a deviation of several degrees only changes the intensity of the diffraction spot and does not change its appearance position. Therefore, only a specific crystal orientation can be analyzed, and an accurate crystal orientation cannot be specified.

  The present invention has been made in view of the above situation, and enables the analysis of crystal orientation of minute crystal grains using an electron beam diffraction image, and by automating the analysis, multipoint crystal orientation can be quickly obtained. The purpose is to analyze.

  The present invention relates to a transmission electron microscope that detects transmission electrons by irradiating a sample with an electron beam, wherein the transmission electron microscope includes an electron diffraction image capturing unit that captures an electron diffraction image of the sample, and a composition of the sample. A detection unit for acquiring information, an analysis unit for acquiring information on lattice plane spacing from the electron diffraction image, a substance identification unit for identifying a sample from the acquired composition information and information on the lattice plane spacing, A calculation unit that calculates a diffraction image of the sample from information on the identified sample, and based on the amount of deviation between the calculated diffraction image and the electron diffraction image, the crystal direction of the sample It is characterized by specifying.

  The crystal orientation of a minute region can be automatically and quickly identified using an electron diffraction image. In particular, the crystal orientation can be specified accurately even when it deviates from the low-order zone axis by several degrees.

Explanatory drawing which showed the main processing procedures of the substance identification system by this invention. Explanatory drawing of an electron beam diffraction image. The schematic block diagram of an example of the crystal orientation identification system by this invention. The flowchart which showed the main processing procedures of the crystal orientation identification system by this invention. The schematic diagram which showed the relationship between an Ewald sphere, a reciprocal lattice point, an electron beam, and an electron beam diffraction image when an electron beam injects from a zone zone axis. FIG. 6 is a schematic diagram showing a relationship among an Ewald sphere, a reciprocal lattice point, an electron beam, and an electron beam diffraction image when an electron beam is incident from a position slightly deviated from the zone axis than in the case of FIG. 5. The schematic diagram which showed the positional relationship of the gravity center of an electron beam diffraction image, a transmitted wave spot, and a zone axis. The figure which shows an example of the electron beam diffraction image which showed the intensity | strength gravity center position and the inclination direction. The figure which shows the simulation diffraction image and inclination direction at the time of the zone axis | shaft calculated | required from FIG. The figure which shows the intensity | strength gravity center position of the simulation diffraction image after tilting the sample in the inclination direction by simulation, and the simulation diffraction image of the simulation diffraction image of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

[Example 1]
FIG. 3 is a schematic configuration diagram of an example of a crystal orientation identification system according to the present invention.

  This crystal orientation identification system can create diffraction images by simulation using electron beam device 1, EDX analysis unit 2, electron beam diffraction image analysis unit 3, substance identification unit 4 with crystal structure database, and crystal structure data A crystal orientation analyzer 5 having a function is provided.

  The electron beam apparatus 1 includes an electron gun 12, a condenser lens 13, an objective lens 14, and a projection lens 24. Between the condenser lens 13 and the objective lens 14, a scanning coil 27 that is fed from a scanning power source 18 under the control of the electron beam apparatus control unit 19 is disposed. The objective lens 14 has two lens actions of a front magnetic field 14a and a rear magnetic field 14b by strong excitation, and a sample holder 25 movable between the front magnetic field 14a and the rear magnetic field 14b of the objective lens 14 by a sample fine movement device 26. The mounted sample 15 is inserted.

  The secondary electron detector 6 is disposed above the sample 15 and below the scanning coil 27. An annular dark field image detector 8 is disposed below the projection lens 24, and a bright field image detector 7 is installed below the dark field image detector 8 so as to be able to enter and leave the optical axis. The detectors 6, 7, and 8 are connected to a scanning image display unit 17 such as a CRT via signal amplifiers 16, 20, and 21, respectively. A scanning signal from the scanning power source 18 is also input to the scanning image display unit 17. An electron diffraction image detector 10 is disposed below the bright field image detector 7. The electron beam diffraction image detector 10 is connected to the electron beam diffraction image display monitor 11 via the electron beam diffraction image analyzer 3.

  The electron beam analysis image analysis unit 3 is connected to the electron beam apparatus control unit 19 and the crystal orientation analysis unit 5 so as to be able to communicate data. Further, an EDX detector 9 for detecting characteristic X-rays generated from the sample by electron beam irradiation is disposed above the objective lens 14, and the EDX detector 9 is connected to the EDX analyzer 2. Yes. The electron beam device control unit 19, the EDX analysis unit 2, the crystal orientation analysis unit 5, and the electron beam diffraction image analysis unit 3 are connected to each other so as to be able to communicate data with the substance identification unit 4.

FIG. 1 is an explanatory diagram showing the main processing procedure of the crystal orientation identification system.
(1) First, the electron beam apparatus 1 irradiates the measurement region of the sample with an electron beam, and the shape and structure of the sample are secondary by the secondary electron detector 6, the bright field image detector 7 or the dark field image detector 8. Observe electronic, bright-field, or dark-field images. The result is stored in the electron beam apparatus controller 19.
(2) The scanning electron beam is stopped in the region to be measured on the sample. The electron beam diffraction image formed at this time is captured by the electron beam diffraction image detector 10. The diffraction image observation result is displayed on the electron diffraction image display monitor 11. The diffraction image observation record is stored in the electron beam diffraction image analysis unit 3. Simultaneously with the storage, the image file name or image data is input to the substance identification unit 4.

Next, the measured value R is obtained from the electron diffraction image, and the lattice spacing d of the crystal is obtained. FIG. 2 is an example of an electron beam diffraction image. Here, the measured value R indicates the distance between the transmitted wave spot and the diffracted wave spot. The lattice spacing d is given by d = Lλ / R. Since L is the camera length, λ is the wavelength of the electron beam, and Lλ is a constant, if Lλ is determined in advance using d and R of a known substance, the lattice spacing d is calculated from the measured value R. be able to. The calculated lattice spacing value of the crystal is stored in the electron diffraction image analysis unit 3, and the data is input to the substance identification unit 4.
(2 ') EDX analysis is started simultaneously with electron beam diffraction image photography. The obtained EDX spectrum is stored in the EDX analyzer 2. Simultaneously with the storage, the file name or EDX spectrum data is input to the substance identification unit 4.

The constituent elements of the sample in the electron beam irradiation region are determined from the EDX spectrum. The obtained composition data is stored in the EDX analysis unit 2 and simultaneously input to the substance identification unit 4.
(3) The substance identification unit 4 collates the lattice spacing data of the crystal obtained above and the composition data obtained above, and retrieves the corresponding substance from the crystal structure database. The search result is stored in the substance identification unit 4, and the crystal structure data is input to the electron diffraction image analysis unit 3 and the crystal orientation analysis unit 5.
(4) The electron beam diffraction image analyzer 3 collates the lattice spacing data d with the crystal structure data obtained above, and obtains the low-order zone axis of the electron beam diffraction image. The zone axis refers to a group of planes parallel to a certain direction in a crystal as a zone and refers to that direction. Here, the lower-order (smaller u, v, w) of the zone axis [uvw] is called the lower-order zone axis. The collation result is stored in the electron beam diffraction image analysis unit 3 and input to the crystal orientation analysis unit (diffraction image calculation unit) 5.
(5) The crystal orientation analysis unit 5 draws a simulation diffraction image from the crystal structure data obtained above and the crystal zone axis data obtained above. The simulation diffraction image is stored in the crystal orientation analysis unit 5.
(6) The electron beam diffraction image analysis unit 3 calculates a pixel intensity barycentric position for the transmitted wave spot position and the entire diffraction image from the electron beam diffraction image. The calculation result is stored in the electron diffraction image analyzer 3 and input to the crystal orientation analyzer 5.

Further, the electron beam diffraction image analysis unit 3 obtains the tilt direction 104 from the pixel intensity gravity center position 102 and the transmitted wave spot position 100 of the electron beam diffraction image. The crystal orientation analysis unit 5 draws a simulation diffraction image in which the sample is tilted in the tilt direction 104. If the tilted simulation diffraction image is equal to the electron beam diffraction image, the tilt angle of the sample, that is, the crystal orientation is read from the simulation diffraction image. The obtained crystal orientation is stored in the crystal orientation analyzer 5.
(7) The crystal orientation analyzer 5 stores the crystal orientation and the series of data with a unique label indicating the analysis location.

  FIG. 4 is a more detailed flowchart for explaining the procedure of the crystal orientation analysis system.

The sample is irradiated with an electron beam by the electron beam apparatus 1, and an electron beam diffraction image _Im is observed (S1). The diffraction image observation result is stored in the electron beam diffraction image analysis unit 3. FIG. 2 is an example of an observed electron beam diffraction image. The center point is the transmitted wave spot 100 and the regularly arranged points around it are the diffracted wave spot 101. The electron diffraction image captured here is generally from an unspecified crystal orientation.

  Here, it is preferable to have a mechanism for photographing and storing so that the bright field image or dark field image observed in advance and the observed electron beam diffraction image are the same in the vertical and horizontal directions.

To set the criteria for simulation crystal orientation analysis, determine the lower order of the zone axis A from I _m (S2). There are various methods, for example, a method of identifying the crystal structure from the lattice spacing, constituent elements, and crystal structure data, and calculating the crystal zone axis from the plane index of each spot.

The identification of the crystal structure is detailed in Patent Document 1. The method, first, actual measurement value R from the electron beam diffraction image I _m, to calculate the lattice spacing d. Here, the measured value R is the distance between the transmitted wave spot and the diffracted wave spot (FIG. 2), and the lattice spacing d is given by d = Lλ / R. Since L is the camera length, λ is the wavelength of the electron beam, and Lλ is a constant, the lattice spacing d can be obtained from the measured value R if Lλ is obtained in advance using a known substance.

  Next, the constituent elements of the sample in the electron beam irradiation region are specified by elemental analysis such as EDX.

  Next, crystal structure data such as a JCPDS card is compared with lattice spacing data and composition data to identify a crystal that matches the measured value.

  The low-order zone axis A [uvw] can be calculated using, for example, the plane indices (h1 k1 l1) and (h2 k2 l2) of the two diffracted waves and Equation 1.

Here, (a ^* b ^* c ^* ) is a basic vector in the inverse space.

  Further, the counterclockwise direction is from (h1 k1 l1) to (h2 k2 l2).

Therefore, the obtained zone axis A [uvw] is [uvw] = [k1 * l2-l1 * k2 l1 * h2-h1 * l2
h1 * k2-k1 * h2]
It becomes. Here, * indicates a product.

  It is preferable to previously create and store a crystal structure data such as a JCPDS card such as a lattice constant, a space group, a zone axis, and an atomic position.

A diffraction image corresponding to the zone axis A of the crystal system obtained in the previous section is drawn by simulation (S3). The simulation conditions are set to match shooting conditions (acceleration voltage, the camera length) of a diffraction image I _m and. As each spot of the diffracted wave spot and I _s near transmission wave spot of the electron beam diffraction image I _m is matched, to perform the rotational operation automatically in the simulation. Drawing the simulated diffraction image I _s is saved in the crystal orientation analysis unit.

From pixel intensity distribution of the transmitted wave spot and a diffraction wave spot of the electron beam diffraction image I _m seeking pixel intensity gravity center position of the diffraction image (S4). At this time, the center of gravity of the entire diffraction image may be obtained, or the center of gravity of the diffraction image excluding HOLZ may be obtained. Further, since the transmitted wave always has center information, the center of gravity of the diffraction image excluding the transmitted wave may be obtained. The merit except for HOLZ and transmitted waves is that the tilt of the crystal can be detected sensitively.

The intensity center of gravity of the electron beam diffraction image I _m and P _m. There are various methods for obtaining P _m . For example, if the coordinates of the pixel x are represented by (i, j) and the pixel intensity of the pixel x is w _ij , P (p, q) is calculated using Equation 2. be able to.

Then, the electron beam diffraction image I _m is to ascertain whether it is the zone axis, determines the difference of the transmitted wave spot O _m and intensity gravity center position P _m (S5).

  5 and 6 show the relationship between the electron beam, the reciprocal lattice, and the diffraction image. When the Ewald sphere 200 and the reciprocal lattice point 201 of the surface intersect, this surface satisfies the Bragg condition, and the diffracted wave spot 101 exists at this location. A reciprocal lattice is a collection of regularly arranged points, and an Ewald sphere passes through them, so that reciprocal lattice points that intersect with the Ewald sphere are projected onto a plane in a circular shape. The intensity of the diffracted wave spot is determined by the deviation from the Ewald sphere.

Here, when the orientation of the sample is the low-order zone axis A (FIG. 5A), the reciprocal lattice points intersecting the Ewald sphere are arranged concentrically, and the diffracted wave spot is in contrast to the transmitted wave spot. Distributed (FIG. 5B). Therefore, the intensity distribution centroid position of the diffraction pattern is equal to the transmitted wave spot (P _m = O _m ).

If the orientation of the sample is slightly inclined from the above case (FIG. 6A), the intersection of the Ewald sphere and the reciprocal lattice point is deviated from the above case. However, in TEM, the position of the diffraction spot does not change so much, so it becomes an image similar to the diffraction image at the zone axis A, the intensity distribution of the diffraction spot changes, and there is a spot excited in an arc shape. (FIG. 6B). In this case, the intensity gravity center position of the diffraction pattern does not coincide with the transmitted wave spot (P _m ≠ O _m ). At this time, a low-order zone axis exists on the extended line connecting the intensity gravity center position and the transmitted wave spot (FIG. 7).

Since the coordinates of P _m have already been obtained, the coordinates of the transmitted wave spot O _m are obtained next. Although there are various methods, for example, since a spot that exists even if the sample is finely moved is a transmitted wave spot, the coordinates thereof are stored. As another method, since the position of the transmitted wave spot depends on the scanning coil 27, an electron beam is scanned in advance by the scanning coil 27, and the position of the transmitted wave spot and the current value of the scanning coil are recorded together. At this time, the position of the transmitted wave spot may be calculated backward from the current value of the scanning coil.

Next, the difference between the transmitted wave spot O _m and the center of gravity position P _m is determined to examine the positional relationship between the transmitted wave spot and the center of gravity position. If O _m −P _m = 0, the center of gravity P _m overlaps the transmitted wave spot (S5). On the other hand, if O _m −P _m ≠ 0, the barycentric position and the transmitted wave spot position are different (S5).

If the transmitted wave spot and the center of gravity position are different, the electron beam diffraction image I _m is offset from the zone axis A. In order to obtain the crystal orientation of the sample, the sample of the simulation diffraction image is tilted to coincide with the electron diffraction image.

The method first draws a line connecting P _m and O _m (FIG. 8). The straight line P _m O _m is superimposed on the simulation diffraction image created in S3 (FIG. 9). The sample is tilted in the P _m O _m direction on the simulation. The tilted simulation diffraction image I _s ′ is plotted (S6) (FIG. 10).

After tilting, the difference O _s -P _s between the transmission spot O _s and the center of gravity P _s of the simulated diffraction image I _s ′ is compared with the difference O _m -P _m between the transmission spot O _m and the center of gravity P _m . An error range is arbitrarily set, and S6 is repeated until it becomes equal within the range (S7).

If equal in O _s -P _s and O _m -P _m error range, comparing the simulated diffraction image I _s and the electron beam diffraction image I _m, which is inclined. Were arbitrarily set the error range, I _s is to be matched with the I _m and the error range, obtains a different zone axis, it performs the same processing (S8). If the positions of the diffraction spots coincide within an arbitrarily set error range, the simulation diffraction image and the electron beam diffraction image are regarded as equal (S8). The simulation diffraction image can be created, for example, from the smaller of u, v, and w of the zone axis [uvw].

When comparing I _s and I _m, may be performed entire comparison, but the diffraction spot of the actual measurement results, got a neighborhood information, or contain unrelated diffracted wave, diffraction spots Ideally It may not be a typical round spot. In order to eliminate such measurement errors, each diffraction spot is regarded as a two-dimensional distribution and arranged in an m × n matrix, and the diffraction intensity for each diffraction spot is assigned to each matrix element as Im (m, n). In the same manner, the simulation is assigned as Is (m, n), and Im (m, n) and Is (m, n) are compared. By doing so, it becomes possible to eliminate irrelevant diffracted wave information and to capture only the intensity even if the diffraction spot is not round.

Load the specimen rotation angle of I _s, is it the crystal orientation of the sample (S9). The read crystal orientation may be indicated by, for example, three rotation angles of the x-axis, y-axis, and z-axis. For example, the rotation of the two axes of the x-axis, z-axis, and x-axis is similar to the Euler angle. It may be indicated by a corner.

[Example 2]
In Example 1, an example was given for the azimuth analysis at one location. Next, an example of a method for setting an analysis area and acquiring an orientation distribution image of the analysis area will be introduced.

  The focused electron beam diffraction image display monitor 11 is scanned on the sample surface using the scanning coil 27. The analysis area is arbitrarily designated from the bright field image or dark field image observed in (1) of FIG. At each point in the analysis area, the electron beam diffraction image is automatically analyzed by the method shown in the first embodiment. The automatically analyzed data is stored in the crystal orientation analysis unit 5 using a unique label indicating the analysis location, for example, the pixel coordinates of the analysis area.

  The acquired crystal orientation data may be color-coded according to the orientation, for example, to create a crystal orientation two-dimensional distribution image of the analysis area.

DESCRIPTION OF SYMBOLS 1 Electron beam apparatus 2 EDX analysis part 3 Electron beam diffraction image analysis part 4 Material identification part 5 Crystal orientation analysis part (Diffraction image calculation part)
6 Secondary electron detector 7 Bright field image detector 8 Dark field image detector 9 EDX detector 10 Electron diffraction image detector 11 Electron diffraction image display monitor 12 Electron gun 13 Condenser lens 14 Objective lens 15 Samples 16 and 20 , 21 Signal amplifier 17 Scanned image display unit 18 Scanning power source 19 Electron beam device controller 22 Electron beam 23 Display unit 24 Projection lens 25 Sample holder 26 Sample fine movement device 27 Scan coil 100 Transmitted wave spot 101 Diffracted wave spot 102 Pixel intensity center of gravity position 103 Low-order zone axis 104 Inclination direction (OP direction)
105 Distance between transmitted wave spot of electron diffraction image and intensity center of gravity (O _m -P _m )
106 Distance (O _s −P _s ) between transmitted wave spot and intensity centroid position of simulation diffraction image
200 Ewald sphere 201 Reciprocal lattice point

Claims (8)

In a transmission electron microscope that detects transmission electrons by irradiating a sample with an electron beam,
The transmission electron microscope includes an electron diffraction image capturing unit that captures an electron diffraction image of the sample;
A detection unit for acquiring composition information of the sample;
An analysis unit for obtaining information on the lattice spacing from the electron diffraction image;
A substance identifying unit for identifying a sample from the acquired composition information and information on the lattice spacing; a computing unit for calculating a diffraction image of the sample from the identified sample information;
Have
A transmission electron microscope characterized in that the crystal direction of the sample is specified based on a deviation amount between the calculated diffraction image and the electron beam diffraction image. In claim 1,
A transmission electron microscope characterized in that composition information of the sample is acquired by an EDX detector. In claim 1,
A transmission electron microscope characterized in that the calculated diffraction image is acquired in consideration of a position deviation direction and a size of a diffraction spot of the electron beam diffraction image and a transmitted wave spot.   The transmission electron microscope characterized in that the calculated diffraction image is calculated from a smaller index of the zone axis of the sample. An electron diffraction image capturing unit that captures an electron diffraction image obtained by irradiating the sample with an electron beam;
A detection unit for acquiring composition information of the sample;
An analysis unit for obtaining information on the lattice spacing from the electron diffraction image;
A substance identifying unit for identifying a sample from the acquired composition information and information on the lattice spacing; a computing unit for calculating a diffraction image of the sample from the identified sample information;
Have
An analysis system characterized in that a crystal direction of the sample is specified based on a deviation amount between the calculated diffraction image and the electron beam diffraction image. In claim 5,
An analysis system characterized in that composition information of the sample is acquired by an EDX detector. In claim 5,
The analysis system characterized in that the calculated diffraction image is acquired in consideration of the position deviation direction and the size of the diffraction spot of the electron beam diffraction image and the transmitted wave spot. In claim 5,
The calculated diffraction image is calculated from a smaller index of the zone axis of the sample.

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