Charged particle beam device

Abstract

To provide a charged particle beam device capable of suppressing degradation in image quality of an observation image obtained using a diaphragm-type holder.SOLUTION: A charged particle beam device includes an electron source that irradiates a diaphragm-type holder with an electron beam, a deflector that changes the angle of incidence of the electron beam, a camera that is exposed to the electron beam that passes through the diaphragm-type holder, and a control unit that controls the electron source, the deflector, and the camera, and the control unit continuously exposes the camera to obtain an exposure image while changing the angle of incidence of the electron beam focused on any one of a first layer, a second layer, or a third layer included in the diaphragm-type holder.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a charged particle beam device.

Background Art

[0002] A charged particle beam device typified by a transmission electron microscope is a device that obtains an observation image of a sample by irradiating the sample with an electron beam accelerated at a high voltage. In a charged particle beam device, it is common to observe a sample placed in a vacuum. However, in order to elucidate the reaction mechanism of a catalyst used in a fuel cell or the like, it is necessary to observe a sample placed in a gas or a liquid.

[0003] Patent Document 1 discloses enclosing a gas or a liquid in a diaphragm-type holder having a sealed space formed by a diaphragm and observing a sample placed in the gas or the liquid.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Document 1, no consideration is given to the influence of the diaphragm forming the sealed space on the observation image. Since the electron beam irradiated on the sample passes through not only the sample but also the diaphragms above and below the sample, the observation image includes signals derived from the diaphragm as well as signals derived from the sample, and the signals derived from the diaphragm may deteriorate the image quality of the observation image.

[0006] Therefore, an object of the present invention is to provide a charged particle beam device capable of suppressing a deterioration in the image quality of an observation image obtained using a diaphragm-type holder.

Means for Solving the Problems

[0007] In order to achieve the above object, the present invention provides a charged particle beam apparatus including an electron source that irradiates an electron beam onto a diaphragm type holder, a deflector that changes the incident angle of the electron beam, a camera on which the electron beam passing through the diaphragm type holder is exposed, and a control unit that controls the electron source, the deflector, and the camera. The control unit is characterized in that while changing the incident angle of the electron beam focused on any one of a first layer, a second layer, and a third layer included in the diaphragm type holder, it continuously exposes the camera to obtain an exposure image.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a charged particle beam apparatus capable of suppressing a decrease in the image quality of an observation image obtained using a diaphragm type holder.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, with reference to the drawings, the charged particle beam device of the present invention will be described. The charged particle beam device is a transmission electron microscope, a scanning electron microscope, a focused ion beam device, etc. that generate an observation image of a sample by irradiating the sample with a charged particle beam such as an electron beam. Hereinafter, a transmission electron microscope will be described as an example of the charged particle beam device. In the following description and the accompanying drawings, components having the same functional configuration are denoted by the same reference numerals, and redundant description is omitted. In addition, an XYZ coordinate system is added to each figure to indicate the orientation of each figure.

Examples

[0011] The transmission electron microscope 1 of Example 1 will be described with reference to FIG. 1. The transmission electron microscope 1 includes an electron source 4, a focusing lens 5, a deflector 6, an objective lens 7, an imaging lens 8, a fluorescent plate 9, a camera 10, a goniometer 11, an image display unit 14, and a control unit 2. A sample holder 12 having a diaphragm-type holder 13 at its tip is inserted into the goniometer 11. The structure of the diaphragm-type holder 13 will be described later with reference to FIG. 2.

[0012] The electron source 4 includes a cathode that emits an electron beam 3 irradiated onto the diaphragm-type holder 13 and an accelerating tube that accelerates the electron beam 3. The focusing lens 5 is a lens that adjusts the size of the electron beam 3 irradiated onto the diaphragm-type holder 13. The deflector 6 changes the incident angle of the electron beam 3 irradiated onto the diaphragm-type holder 13. The objective lens 7 is a lens that adjusts the focus of the electron beam 3 irradiated onto the diaphragm-type holder 13. The imaging lens 8 is a lens that forms an image of the electrons transmitted through the diaphragm-type holder 13 on the fluorescent plate 9 or the camera 10. The fluorescent plate 9 is a plate that emits fluorescence when electrons passing through the imaging lens 8 are incident thereon. The camera 10 images the fluorescence emitted by the fluorescent plate 9 and the electrons passing through the imaging lens 8. The goniometer 11 is a mechanism that moves the inserted sample holder 12 in the X-axis direction or rotates it around an axis parallel to the X-axis. Note that the goniometer 11 is not essential, and an insertion hole into which the sample holder 12 is inserted may be provided instead of the goniometer 11. The image display unit 14 is a liquid crystal display or the like that displays the observation image captured by the camera 10. The control unit 2 is a device that controls each part and is a so-called computer.

[0013] The diaphragm-type holder 13 will be described with reference to FIG. 2. The diaphragm-type holder 13 has an upper diaphragm 21 and a lower diaphragm 22, encloses a gas or a liquid in a sealed space formed by the upper diaphragm 21 and the lower diaphragm 22, and holds the sample 20. Since the electron beam 3 irradiated onto the diaphragm-type holder 13 passes through not only the sample 20 but also the upper diaphragm 21 and the lower diaphragm 22, the observation image displayed on the image display unit 14 includes signals derived from the upper diaphragm 21 and the lower diaphragm 22 as well as signals derived from the sample 20. When observing the sample 20, the signals derived from the upper diaphragm 21 and the lower diaphragm 22 are noise and degrade the image quality of the observation image of the sample 20.

[0014] Therefore, in Example 1, while changing the incident angle of the electron beam 3 focused on the sample 20, the camera 10 is continuously exposed, so as to disperse the noise signals derived from the upper diaphragm 21 and the lower diaphragm 22 and suppress the deterioration of the image quality of the observation image of the sample 20. Note that the upper diaphragm 21 may be referred to as the first layer, the sample 20 as the second layer, and the lower diaphragm 22 as the third layer.

[0015] With reference to FIG. 3, an example of the processing flow of Example 1 will be described step by step.

[0016] (S301) The operator sets the electron beam tilt conditions. For setting the electron beam tilt conditions, for example, a tilt condition setting screen 40 shown in FIG. 4 is used. The tilt condition setting screen 40 has an incident angle range setting unit 41, an azimuth angle setting unit 42, an exposure time setting unit 43, and a camera button 44.

[0017] In the incident angle range setting unit 41, the range in which the incident angle of the electron beam 3 changes is set. The incident angle is the angle with respect to the electron beam 3 when the input signal to the deflector 6 is zero, and is the angle θ formed by the tilted electron beam 50 and the electron beam 3 illustrated in FIG. 5A. By inputting the start angle and the end angle into the incident angle range setting unit 41, the range in which the incident angle changes is set.

[0018] In the azimuth angle setting unit 42, the azimuth angle indicating the direction in which the incident angle changes is set. The azimuth angle is the angle with respect to a predetermined direction, and is, for example, the angle φ formed by the Y-axis direction and the tilted electron beam 50 as illustrated in FIG. 5B.

[0019] In the exposure time setting unit 43, the time for continuously exposing the camera 10 is set. The camera button 44 is pressed when starting or ending the continuous exposure by the camera 10.

[0020] (S302) The operator adjusts the focus of the electron beam 3 so that it coincides with the sample 20. By aligning the focus with the sample 20, even when the incident angle of the electron beam 3 changes, the position where the observation image of the sample 20 is formed can be kept from moving. Note that the focus of the electron beam 3 may be adjusted to match the upper diaphragm 21 or the lower diaphragm 22. Also, an autofocus function may be used for focus adjustment.

[0021] (S303) The control unit 2 starts continuous exposure by the camera 10. For example, when the pressing of the camera button 44 is detected, continuous exposure starts.

[0022] (S304) The control unit 2 controls the incident angle of the electron beam 3 based on the electron beam tilt condition set in S301. An example of the electron beam tilt condition will be described with reference to FIG. 6. In FIG. 6, when the camera exposure becomes ON at time t1, the electron beam irradiation also becomes ON, and while the azimuth angle is maintained at φ0, the incident angle is changed at a constant speed from θs to θe, and at time t2, the camera exposure and the electron beam irradiation become OFF. Note that since aberration may occur due to the change in the incident angle of the electron beam, it is preferable that the aberration is corrected according to the incident angle.

[0023] (S305) The control unit 2 ends the continuous exposure by the camera 10. For example, when the time set by the exposure time setting unit 43 has elapsed since the camera button 44 was pressed in S303, the continuous exposure ends. Note that even if the pressing of the camera button 44 is detected before the set exposure time has elapsed, the continuous exposure also ends.

[0024] (S306) The control unit 2 causes the image display unit 14 to display the exposure image captured by the continuous exposure of the camera 10. On the image display unit 14, for example, an image display screen 70 shown in FIG. 7 is displayed. The image display screen 70 has an exposure image display unit 71 and an azimuth angle display unit 72.

[0025] An exposure image is displayed on the exposure image display unit 71. The exposure image illustrated in FIG. 7 is an observation image of the end portion of the sample 20, and is obtained by changing the incident angle of the electron beam 3 based on the electron beam tilt condition of FIG. 6 from the start of continuous exposure in S303 to the end of continuous exposure in S305. The dark region in the upper left is the region where the electron beam has passed through the sample 20, the upper diaphragm 21, and the lower diaphragm 22, and the bright region in the lower right is the region where the electron beam has passed through the upper diaphragm 21 and the lower diaphragm 22. Since the exposure image of FIG. 7 is an image obtained by continuous exposure while changing the incident angle, although a large number of streaks derived from the diaphragm can be seen parallel to the direction in which the incident angle changes, the noise signal derived from the diaphragm is dispersed and averaged, so there is no obstacle to observing the sample 20 in the dark region.

[0026] In the azimuth angle display unit 72, the direction of the azimuth angle set in S301 is indicated by a line segment. By showing the direction of the azimuth angle together with the exposure image, the operator can determine whether a large number of streaks in the exposure image are due to changes in the incident angle.

[0027] According to the processing flow illustrated in FIG. 3, by continuously exposing the camera 10 while changing the incident angle of the electron beam focused on the sample 20, an exposure image in which the noise signals derived from the upper diaphragm 21 and the lower diaphragm 22 are dispersed can be obtained. Although the obtained exposure image includes a large number of streaks derived from the diaphragm due to the change in the incident angle, the sample 20 can be clearly observed. Note that an image equivalent to the exposure image can be obtained by synthesizing the observation images captured at different incident angles, but according to the continuous exposure while changing the incident angle, the process of synthesizing the observation images for each different incident angle can be made unnecessary. Also, the electron beam tilt condition is not limited to that illustrated in FIG. 6.

[0028] Using FIG. 8, another example of the electron beam tilt condition will be described. In FIG. 8, when the camera exposure becomes ON at time t1, the electron beam irradiation also becomes ON, and the incident angle is changed at a constant speed from θs to θe while the azimuth angle is kept constant until time t3. Then, at times t3, t4, and t5, the azimuth angle is switched, and the incident angle is changed at a constant speed from θs to θe until the azimuth angle is switched. According to the electron beam tilt condition of FIG. 8, since there are a plurality of directions in which the incident angle of the electron beam changes, a large number of streaks resulting from the change in the incident angle are dispersed and averaged in the directions of a plurality of azimuth angles, thereby improving the image quality of the exposure image.

[0029] Using FIG. 9, another example of the electron beam tilt condition will be described. FIG. 9 shows the case where Example 1 is applied to the time-resolved electron microscopy method. That is, while the camera exposure from time t1 to t2 is ON and the incident angle is changed at a constant speed from θs to θe while the azimuth angle is kept at φ0, the electron beam is pulse-irradiated by the delay time td with respect to the trigger signal emitted at the period T0. The trigger signal is emitted based on the timing at which gas or liquid is supplied to the diaphragm-type holder 13, light is irradiated to the sample 20, or voltage is applied. The exposure image obtained under the electron beam tilt condition of FIG. 9 is generated by superimposing the transmitted electrons when the electron beam is pulse-irradiated. Then, while the electron beam is pulse-irradiated, the incident angle of the electron beam is changing, so an exposure image in which the noise signal derived from the diaphragm is dispersed is obtained.

[0030] Using FIG. 10, another example of the electron beam tilt condition will be described. FIG. 10 shows the case where Example 1 is applied to the time-resolved electron microscopy method in the same manner as FIG. 9. However, in FIG. 10, the incident angle is changed at a constant speed from θs to θe in each section where the electron beam is pulse-irradiated. According to the electron beam tilt condition of FIG. 10, since the range in which the incident angle changes in each section where the electron beam is pulse-irradiated is wider than that in FIG. 9, the noise signal derived from the diaphragm is dispersed, and the image quality of the exposure image is improved.

[0031] Note that Example 1 is also applicable to charged particle beam devices other than the transmission electron microscope 1 shown in FIG. 1. The transmission electron microscope for electron beam holography will be described with reference to FIG. 11. The transmission electron microscope 1 illustrated in FIG. 11 is obtained by adding an electron biprism 110 and a retarding deflector 111 to the configuration of FIG. 1.

[0032] The electron biprism 110 obtains a hologram image by causing interference between the object wave that has passed through the object and the reference wave that has passed through the vacuum. Note that the position of the electron biprism 110 is not limited to the position shown in FIG. 11, and it may be below the deflector 6.

[0033] The retarding deflector 111 deflects the electron beam so that the electron beam is incident on the electron biprism 110 even when the incident angle of the electron beam changes. That is, the retarding deflector 111 is disposed between the deflector 6 and the electron biprism 110 and operates in conjunction with the operation of the deflector 6.

[0034] By applying Example 1 to the transmission electron microscope for electron beam holography, a hologram image with a reduced noise signal derived from the diaphragm can be obtained.

Example

[0035] In Example 1, it was described that an exposure image in which the noise signal derived from the diaphragm was dispersed was obtained by continuously exposing the camera 10 while changing the incident angle of the electron beam 3 focused on the sample 20. The exposure image obtained in Example 1 includes a number of streaks derived from the diaphragm due to the change in the incident angle. In Example 2, it will be described how a number of streaks derived from the diaphragm are reduced by image processing. For the same configurations as in Example 1, the description will be simplified by assigning the same reference numerals.

[0036] An example of the processing flow of Example 2 will be described step by step with reference to FIG. 12.

[0037] (S1201) The operator sets the electron beam tilt condition and the image processing method. For setting the electron beam tilt condition and the image processing method, for example, the setting screen 130 shown in FIG. 13 is used. The setting screen 130 illustrated in FIG. 13 is obtained by adding an image processing setting section 131 to the tilt condition setting screen 40 in FIG. 4. In the image processing setting section 131, the method of image processing to be performed on the exposure image is selected from the options. Note that in the image processing setting section 131 of FIG. 13, options of "FFT + mask processing" and "machine learning processing" are shown, and "FFT + mask processing" is selected.

[0038] (S1202)~(S1205) It is the same as S302 to S305 in FIG. 3. Note that in S1205, while changing the incident angle of the electron beam 3, an exposure image obtained by continuous exposure by the camera 10 is acquired.

[0039] (S1206) The control unit 2 performs the image processing selected in S1201 on the exposure image acquired in S1205.

[0040] Using FIG. 14, "FFT + mask processing" will be described. The exposure image acquired in S1205 includes a large number of streaks derived from the diaphragm due to the change in the incident angle. Therefore, an FFT (Fast Fourier Transform) image is generated by performing FFT processing on the exposure image, and the streaks corresponding to the streaks are made apparent.

[0041] The FFT image is an image representing the intensity of the spatial frequency by the luminance, the horizontal axis is the spatial frequency in the horizontal direction, the vertical axis is the spatial frequency in the vertical direction, the center coordinate is that the spatial frequency is zero, and the spatial frequency increases toward the edge. In the FFT image of FIG. 14, streaks corresponding to a large number of streaks included in the exposure image appear from the upper left to the lower right around the center coordinate.

[0042] Next, by performing mask processing to apply a mask to the FFT image, streaks corresponding to a large number of streaks included in the exposure image are deleted from the FFT image, and a masked image is generated. In the masked image of FIG. 14, a plurality of black circles superimposed on the streaks are shown as masks.

[0043] Then, by performing inverse FFT processing on the masked image, an inverse FFT image with a large number of streaks derived from the diaphragm reduced is generated. In the inverse FFT image of FIG. 14, a large number of streaks included in the exposure image are reduced.

[0044] When "machine learning processing" is selected in S1201, noise signals derived from the diaphragm are reduced from the exposure image by a machine learning processing unit that is generated in advance by learning a large number of teacher images. Note that, as the teacher image used for the generation of the machine learning processing unit, an image obtained by synthesizing an observation image of the sample 20 disposed in a vacuum and an observation image of the diaphragm type holder 13 not including the sample 20 is used. Further, the noise signal derived from the diaphragm may be reduced from the exposure image by a machine learning processing unit generated by learning without a teacher image.

[0045] The image obtained by "machine learning processing" has higher image quality than the image obtained by "FFT + mask processing". On the other hand, in "FFT + mask processing", since it is not necessary to generate a machine learning processing unit in advance, the capacity of the storage device can be saved.

[0046] (S1207) The control unit 2 causes the image display unit 14 to display the image on which the image processing has been performed in S1206.

[0047] According to the processing flow illustrated in FIG. 12, a large number of streaks derived from the diaphragm included in the exposure image obtained by continuous exposure while changing the incident angle of the electron beam are reduced by image processing. As a result, the sample 20 can be observed more clearly.

[0048] The above describes a plurality of embodiments of the present invention. The present invention is not limited to the above embodiments, and components can be modified and embodied without departing from the gist of the invention. Also, a plurality of components disclosed in the above embodiments may be appropriately combined. Furthermore, some components may be deleted from all the components shown in the above embodiments.

Explanation of Reference Numerals

[0049] 1: Transmission electron microscope, 2: Control unit, 3: Electron beam, 4: Electron source, 5: Focusing lens, 6: Deflector, 7: Objective lens, 8: Imaging lens, 9: Fluorescent plate, 10: Camera, 11: Goniometer, 12: Sample holder, 13: Diaphragm-type holder, 14: Image display unit, 20: Sample, 21: Upper diaphragm, 22: Lower diaphragm, 40: Tilt condition setting screen, 41: Incident angle range setting unit, 42: Azimuth angle setting unit, 43: Exposure time setting unit, 44: Camera button, 50: Tilted electron beam, 70: Image display screen, 71: Exposure image display unit, 72: Azimuth angle display unit, 110: Electron beam biprism, 111: Return deflector, 130: Setting screen, 131: Image processing setting unit.

Claims

1. A charged particle beam device comprising an electron source that irradiates an electron beam onto a diaphragm-type holder, a deflector that changes the incident angle of the electron beam, a camera that exposes the electron beam transmitted through the diaphragm-type holder, and a control unit that controls the electron source, the deflector, and the camera, wherein the control unit obtains an exposure image by continuously exposing the camera while changing the incident angle of the electron beam focused on any one of a first layer, a second layer, and a third layer included in the diaphragm-type holder. A charged particle beam device characterized by that.

2. The charged particle beam device according to claim 1, wherein the control unit performs image processing on the exposure image. A charged particle beam device characterized by that.

3. The charged particle beam device according to claim 2, wherein the control unit generates an FFT image by performing a Fourier transform process on the exposure image, generates a masked image by performing a mask process on the FFT image, and generates an inverse FFT image by performing an inverse Fourier transform process on the masked image. A charged particle beam device characterized by that.

4. The charged particle beam device according to claim 2, wherein the control unit generates an image with reduced noise signals derived from the diaphragm by performing a machine learning process on the exposure image. A charged particle beam device characterized by that.

5. The charged particle beam device according to claim 4, wherein the machine learning process is performed by a machine learning processing unit generated by learning, as a teacher image, an image in which an observation image of a sample arranged in a vacuum and an observation image of the diaphragm-type holder are combined. A charged particle beam device characterized by that.

6. The charged particle beam device according to claim 1, wherein the control unit displays an azimuth angle indicating the direction in which the incident angle is changed, together with the exposure image. A charged particle beam device characterized by that.

7. The charged particle beam device according to claim 1, wherein the control unit sets a plurality of azimuth angles indicating the direction in which the incident angle is changed, and obtains the exposure image by changing the incident angle for each azimuth angle. A charged particle beam device characterized by that.

8. The charged particle beam device according to claim 1, wherein the control unit pulse-irradiates the electron beam based on a periodically emitted trigger signal, and obtains the exposure image by changing the incident angle from a start angle to an end angle in each section where the electron beam is pulse-irradiated. A charged particle beam device characterized by that.

9. A charged particle beam apparatus according to claim 1, further comprising an electron biprism that obtains a hologram image by interfering an object wave that has passed through an object and a reference wave that has passed through a vacuum. The charged particle beam apparatus is characterized by this.

Images