JP3224277B2 - Apparatus and method for evaluating strain using focused electron diffraction pattern - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaluation apparatus for evaluating distortion of a material, and more particularly to an evaluation apparatus suitable for evaluating a material in which distortion of a minute portion is a problem.

[0002]

2. Description of the Related Art The crystal structure of a material is one of the important characteristics that characterize the material. In general, the crystal structure of a material shows a different crystal system depending on the growth conditions, or the growth direction differs even with the same crystal system. Further, depending on crystal growth conditions and material processing conditions, distortion may occur in a certain direction of the crystal structure. The physical properties of a material having an anisotropic crystal structure and a material having a strain show different characteristics depending on the direction of the crystal. Therefore, investigating the crystal structure and distortion state of the material of the material and optimizing the growth conditions and processing conditions according to the purpose of use are regarded as important in the development of high-performance products and materials. . Heretofore, generally known methods such as X-ray diffraction and Raman spectroscopy have been used as methods for examining the distortion of the crystal structure of a material.

[0003]

In recent years, the development of minute elements having an internal structure of an nm unit such as an LSI element has been rapidly progressing. Along with this, it is necessary to evaluate the crystal structure and strain of the material constituting the fine internal structure of the element. However, the conventional evaluation methods such as the X-ray diffraction method and the Raman spectroscopy have insufficient spatial resolution, so that it is not possible to perform measurement using such a material in nm units as a sample. Therefore, under the same conditions, there is no method other than preparing a measurement sample having a size of mm unit which can be measured by the conventional measurement method and performing the measurement to infer the actual state of the element having a fine structure. However, there is a limit in estimating the crystal structure of a material in nm units from the measurement results of a sample in mm units, and almost no evaluation can be made on crystal distortion.

An object of the present invention is to provide an evaluation apparatus capable of evaluating the distortion of the crystal structure of a fine sample.

[0005]

According to the present invention, there is provided a converging lens system for converging an electron beam on a sample, and a convergent electron beam diffraction for forming an image of the electron beam transmitted through the sample. An objective lens for forming a figure, image capturing means for capturing the convergent electron beam diffraction pattern, display means,
Input means, calculating means for approximately calculating the trajectories of a plurality of Holtz lines of a theoretical convergent electron beam diffraction pattern when the sample has no distortion in the crystal structure, and the image capturing device Image processing means for generating an image in which the convergent electron beam diffraction pattern and the trajectory of the Holtz line calculated by the calculation means are superimposed, wherein the display means displays the image generated by the image processing means, The input means, among the plurality of Holtz lines calculated by the calculation means, a Holtz line which does not match the Holtz line shown in the convergent electron beam diffraction pattern captured by the image capturing device, on the image of the display device. Receiving an external input specified in, the calculating means obtains a lattice plane of the crystal of the sample corresponding to the externally specified Holtz line received by the input means,
A distortion evaluation device using a convergent electron beam diffraction pattern, which is displayed on the display means, is provided.

[0006]

An electron beam is converged on a sample by a converging lens system, and an electron beam transmitted through the sample is imaged by an objective lens to form a convergent electron beam diffraction pattern. In general, an electron beam can be converged in units of nm. The image capturing device captures a focused electron beam diffraction pattern. Next, the calculating means approximately calculates the trajectories of a plurality of Holtz lines in a theoretical convergent electron beam diffraction pattern when the sample has no distortion in the crystal structure.

[0007] The image processing means generates an image in which the convergent electron beam diffraction pattern of the sample is superimposed on the trajectory of the Holtz line obtained by the above calculation, and displays the image on the display means. The user
Of the plurality of Holtz lines obtained by the calculation, a Holtz line that does not match the Holtz line shown in the convergent electron beam diffraction pattern is input from the input means on the screen. The calculation means determines which lattice plane of the crystal of the sample is the input Holtz line. Then, the display means displays the sample in which the lattice plane has distortion.

As described above, according to the present invention, since the electron beam is converged on the sample, the distortion can be evaluated if the sample has a size in nm unit capable of converging the electron beam.

[0009]

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

As shown in FIG. 1, the distortion evaluation apparatus using a convergent electron beam diffraction pattern according to the present invention comprises: an electron microscope 1; an image capturing device 7 for capturing a diffraction pattern of a sample 4 obtained by the electron microscope 1; An image storage device 8, a processing device 9 for processing a captured image, calculating a Holtz line of an approximate diffraction pattern, and controlling an electron microscope, and a display device 1
1 is provided. An electron microscope 1 includes a converging lens system 3 for converging an electron beam 2 on a sample 4 to about 10 nmφ.
And an objective lens 5 for imaging the electron beam diffracted by the sample 4
And a control device 6 for controlling the exciting current of the converging lens system 3. Further, the processing device 9 is connected to an input device 10 having a two-dimensional position specifying device 10a for allowing a user to input parameters and calculation conditions for calculating an approximate diffraction pattern. The control device 6 is connected to the processing device 9.

In the evaluation apparatus using a focused electron beam diffraction pattern of this embodiment, an electron beam 2 incident from an electron beam generator (not shown) is converged by a converging lens system 3 to evaluate the distortion of a sample 4. It is incident on the desired part. The electron beam transmitted through the sample 4 is imaged by the objective lens 5, and forms an electron diffraction pattern called a convergent electron diffraction pattern on the image capturing device 7. The electron diffraction pattern captured by the image capturing device 7 is stored in the image storage device 8 and processed by the processing device 9.
Is input to The electron diffraction pattern image-processed by the processing device 9 is displayed on the display device 11. Also, the input device 1
Based on the information input from 0, an approximate electron diffraction pattern calculated using a program built in the processing device 9 is also displayed on the display device 11.

Next, an evaluation procedure of the evaluation apparatus using the convergent electron beam diffraction pattern of this embodiment will be described with reference to FIG. The evaluation device of this embodiment is a device for examining the direction in which the crystal of the sample 4 has a distortion. First, the processing device 9
Instruct the image capturing device 7 to capture a diffraction pattern of a portion of the sample 4 to be evaluated from the electron microscope 1 (step 1).
09). Next, the processing apparatus 9 obtains a Holtz line of a theoretical diffraction pattern without distortion of the above-described portion of the sample 4 by an approximate calculation (step 110). Next, the processing device 9 compares the line figure fetched in Step 109 with Step 110
The Holtz line for the case where there is no distortion calculated by approximation is superimposed and displayed (step 111). The user uses the two-dimensional position specification device 10a to specify a Holtz line that does not match (step 112). The processing device 9 calculates the index of the designated Holtz line and displays it on the display device 11 to indicate that the direction is distorted (step 115).

Next, regarding the above step 109,
This will be described in more detail. First, the processing device 9 instructs the image capturing device 7 to capture, from the electron microscope 1, a diffraction pattern of a portion of the sample 4 to be evaluated. FIG. 2 schematically shows an example of a display result of the display device 11 in this case. A display area 91 on the left side of the display device 11 includes an image capturing device 7.
Shows the captured electron diffraction pattern. In the right display area 92, the processing device 9 displays the calculation result of the electron diffraction pattern by the built-in program. In this case, since the processing device 9 has not yet calculated the diffraction pattern, No calculation result is displayed in the display area 92. In the diffraction pattern shown in FIG. 2, the opening angle of the electron beam is small, the center disk displayed in the display area 91 is small, and the Holtz line 12 is not suitable for analysis.
Therefore, the processing device 9 binarizes the convergent electron diffraction pattern displayed in the image display area 91 by the diffraction intensity of the electron beam, thereby obtaining the radius of the disk, that is, the opening angle r of the electron beam.
Then, the distance between the disks, ie, the angle R of electron diffraction, is calculated. Next, a convergence condition of the converging lens system 3 for making R and 2r substantially the same is calculated. Then, the control unit 6 is instructed to an excitation current for setting the converging lens system 3 to the convergence condition. The control device 6 adjusts the exciting current of the converging lens system 3. Accordingly, even if the operator does not adjust the exciting current of the converging lens system 3 by trial and error, the photographing conditions of the electron diffraction pattern are optimally adjusted by image capturing and calculation processing. In the display area 91 on the left side of FIG. 3, the electron diffraction pattern adjusted as described above is displayed. The adjusted diffraction pattern is stored in the storage device 8.

Next, the procedure for calculating a distortion-free Holtz line in step 110 of FIG. 7 will be described with reference to FIG. H
It is known that the trajectory of the OLZ line can be calculated from the length of the crystal axis of the sample, that is, the lattice constant, the angle of the crystal axis, the accelerating voltage of the electron microscope, and the direction of incidence of the electron beam on the sample. explain. First, the user inputs the lattice type (for example, a face-centered cubic lattice or a diamond structure) of the crystal of the sample 4 and the lattice constants (a, b, c) using the input device 10 (step 124). The processing device 9 calculates an existing reciprocal lattice point based on the lattice type of the crystal of the sample 4 input from the input device 10 and the lattice constants (a, b, c) (step 125). Next, the user uses the input device 10 to operate the electron microscope 1 as operating conditions.
The wavelength λ of the electron beam, the incident direction of the electron beam, the opening angle of the electron beam, and the camera constant L are input (step 126). These operating conditions are stored in the storage device 8. Step 12
The excitation error range is calculated from the opening angle of No. 6 and step 125
A reciprocal lattice point within the excitation error range is selected from the reciprocal lattice points calculated in (1) (step 127). For each reciprocal lattice point selected in step 127, a Holtz line is drawn according to the following equations 1 to 4 (step 128). The Holtz line image is stored in the storage device 8.

[0015]

(Equation 1)

[0016]

(Equation 2)

[0017]

(Equation 3)

[0018]

(Equation 4)

Here, λ is the wavelength of the electron beam and can be obtained from the acceleration voltage E of the electron beam using λ = 1.22 / √E. In the above equations 1 to 4, hkl is HO
Since there are many combinations of what is called an LZ line index, there are a plurality of HOLZ lines to be drawn. For example, if the crystal is orthorhombic and incident along the crystal axis [001],
The locus (X, Y) of the HOLZ line is displayed in the display area 9 on the right side of FIG.
It is shown in FIG.

Next, the procedure for superimposing the diffraction pattern shown in step 111 of FIG. 7 with the calculated Holtz line will be described in more detail with reference to FIG. The diffraction pattern captured in step 109 in FIG. 7 described above is captured from the storage device 8 (and 120 in FIG. 9). Next, the values of the opening angle of the electron beam and the camera constant input in step 126 of FIG. 10 are read again from the storage device 8 (step 12).
1). Next, the Holtz line calculated in step 128 of FIG. 10 is fetched from the storage device 8 (step 122).
The diffraction pattern and the Holtz line obtained by calculation are superimposed by matching the camera constant and the center position of the disc, and are displayed in the display area 91 on the left side of the display device 11 as shown in FIG. 5 (step 123). .

The user designates the Holtz line of the diffraction pattern of the sample 4 and the Holtz line obtained by calculation which does not match by using the two-dimensional position designation device 10a by arrows as shown in FIG. (Step 112 in FIG. 7). The processing device 9 refers to the designated Holtz line to the calculation result of step 128 in FIG.
Find the direction of the Holtz line. Then, as shown in FIG. 5, the user is notified of the direction of the distortion by displaying the direction as “Δd distortion exists in the (H, K, L) direction” 93 (step 115 in FIG. 7).

In the above-described embodiment, only the direction of the distortion is shown, but the distortion amount Δd can be quantitatively obtained.
When obtaining the distortion amount Δd, the above-described steps 109 to 111 are executed as shown in FIG. Thereafter, the user designates, using the two-dimensional position designation device 10a, non-matching Holtz lines for both the Holtz line of the acquired diffraction pattern and the calculated Holtz line as shown in FIG. The processing device 9 obtains the shift amount Δx on the screen of the Holtz line that does not match from the output of the two-dimensional position specifying device 10a. The processing device reads the camera constant L, the wavelength λ of the electron beam, and the angle R of the electron diffraction at the time of capturing the image from the storage device 8 and calculates the distortion amount Δd from Equations 5 and 6, and the same as Step 115 in FIG. (H, K, L) are obtained (step 213) and displayed on the display device 11 (step 2).
14). As a result, the amount of distortion Δd is determined quantitatively,
Can be displayed.

[0023]

(Equation 5)

[0024]

(Equation 6)

Further, the distortion amount Δd obtained in step 213 is added to the data of the Holtz line obtained in the calculation, the Holtz line is calculated again, and steps 109 to 111 and steps 212 to 214 are obtained. By repeating until the line and the calculated Holtz line completely match, more detailed distortion can be obtained.

As still another embodiment, the difference between the image intensities of the two Holtz lines in order to display the degree of coincidence between the Holtz lines of the acquired diffraction pattern and the calculated Holtz lines in a manner that is easy for the user to understand. The quantity can be displayed. In this case, the Holtz line of the acquired diffraction pattern is a dark line (a region having a low intensity), so that the dark line is binarized with the intensity 0 and the portion brighter than the Holtz line is binarized with 1, and the Holtz line obtained by calculation is also It is preferable that the intensity of the Holtz line is 0 and the intensity of the portion other than the Holtz line is 1, and the difference between the acquired diffraction pattern and the calculated Holtz line is good. In addition, the degree of matching can be estimated with higher accuracy by having the user limit the difference area.

In the above embodiment, the electron diffraction pattern captured by the image capturing device is directly compared with the calculation result. However, the electron diffraction pattern may be differentiated and then compared. As a result, the HOLZ line can be clearly observed, and can be compared with the calculation result more clearly.

As another embodiment, when a convergent electron diffraction pattern is photographed from an arbitrary incident direction, the calculation result of the HOLZ line in a typical incident direction is simultaneously displayed on a display device, and the closest figure is displayed. By selecting this, even when the incident direction of the electron beam with respect to the sample is not known at all, the distortion can be evaluated in the incident direction.

As described above, the evaluation apparatus using the convergent electron beam diffraction pattern of this embodiment uses electron beam diffraction. Since the electron beam can sufficiently converge to a size of about 10 nmφ as in this embodiment, the size of the sample 4 is reduced to 10 nm.
The direction of the distortion can be checked even for a small degree. Further, in the present embodiment, the Holtz line determined by calculation,
By displaying an image superimposed on the actually acquired diffraction image, the user can easily specify the Holtz line that does not match,
You can know the direction of distortion. Therefore, even if the user does not know the analysis method of the Holtz line figure, it is possible to provide an easy-to-use evaluation device that can easily evaluate the distortion of the minute material. In addition, it is possible to omit the photographing of an unnecessary part of a figure and a complicated operation. An electron microscope capable of quickly adjusting the opening angle r of an electron beam to an optimum value even when the incident direction of an electron beam or the type of a sample changes and the angle R of electron diffraction changes.

In the above-described embodiment, a configuration is used in which the user inputs the electron beam wavelength λ, the incident direction, the opening angle, and the camera constant as the operating conditions of the electron microscope in step 126 in FIG. However, the information may be inputted online from the control device of the electron microscope to the processing device. In this case, the acceleration voltage E is input from the control device, and the wavelength λ is calculated by the processing device 9 from λ = 1.22 / √E.

In the above-described embodiment, the processing device 9
The display device 11 displays the diffraction pattern captured by the image capturing device 7 so as to be superimposed on the calculated Holtz line. However, the input unit 10 allows the user to move the diffraction pattern or Holtz line on the screen. It is also possible to provide further means. The processing device 9 moves the image on the display device 11 according to the instruction means. As a result, the user can finely adjust the superposition of the images, and can easily specify a Holtz line that does not match.

Further, the distortion evaluation apparatus using the focused electron beam diffraction pattern of the present embodiment can be used not only as a distortion evaluation apparatus but also as a conventional electron microscope capable of observing a focused electron beam diffraction pattern. Further, when a lens system for irradiating a parallel beam of an electron beam onto a sample is provided, it is of course possible to use it as an electron microscope for general-purpose high-resolution image observation.

[0033]

As described above, the distortion evaluation apparatus using a convergent electron beam diffraction pattern of the present invention can evaluate the distortion of a very small portion of a fine sample by using an electron microscope.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is an explanatory view showing a display example of an electron diffraction pattern of a sample.

FIG. 3 is an explanatory diagram showing a display example of an electron diffraction pattern of a sample and Holtz lines obtained by calculation.

FIG. 4 is an explanatory diagram showing a display example of an electron diffraction pattern of a sample and Holtz lines obtained by calculation.

FIG. 5 is an explanatory view showing an electron diffraction pattern of a sample, a Holtz line obtained by calculation, and a display example showing a direction with distortion.

FIG. 6 is an explanatory view showing a display example of an electron diffraction pattern of a sample and Holtz lines obtained by calculation.

FIG. 7 is a flowchart illustrating a procedure of distortion evaluation according to an embodiment of the present invention.

FIG. 8 is a flowchart illustrating a procedure of distortion evaluation according to another embodiment of the present invention.

FIG. 9 is a flowchart showing a more detailed procedure of superposition in the procedure shown in FIG. 7;

FIG. 10 is a flowchart showing a more detailed procedure of calculating a Holtz line among the procedures shown in FIG. 7;

[Explanation of symbols]

1. Electron microscope 2. Electron beam 3. Convergent lens system 4.
Sample 5 Objective lens 6 Control device 7 Image capturing device 8 Image storage device 9 Processing device 10 Input device 11 Display device 12 HOLZ line

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 23/00-23/227 H01J 37/26-37/295 H01J 37/22

Claims (2)

(57) [Claims] 1. The method according to claim 1, wherein a plurality of Holtz-line trajectories of a theoretical convergent electron beam diffraction pattern in a case where the sample has no distortion in the crystal structure are approximately calculated. Superimposed on the trajectory of the Holtz line determined by the calculation, of the plurality of Holtz lines determined by the calculation, of the crystal of the sample of the Holtz line that does not match the Holtz line appearing in the convergent electron diffraction pattern A distortion evaluation method using a convergent electron beam diffraction pattern for determining a lattice plane and evaluating that the sample has distortion in the lattice plane. 2. An image capturing means for capturing a focused electron beam diffraction pattern of a sample, a display means, an input means, and a theoretical focused electron beam diffraction pattern when the sample has no distortion in the crystal structure. Calculating means for approximately calculating the trajectories of a plurality of Holtz lines; and image processing means for generating an image in which the convergent electron beam diffraction pattern captured by the image capturing device and the trajectories of the Holtz lines calculated by the calculating means are superimposed. Wherein the display means displays an image generated by the image processing means, and the input means comprises a converging electron beam captured by the image capturing device among a plurality of Holtz lines calculated by the calculation means. An input from the outside that designates a Holtz line that does not match the Holtz line appearing in the diffraction pattern on an image of the display device is received, and the calculating unit receives the external input received by the input unit. A lattice plane of the crystal of the sample corresponding to the Holtz line specified by the method, and displaying the lattice plane on the display means.