JP3870141B2 - electronic microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electron microscope in which a sample image is obtained based on electrons transmitted through a sample, electrons reflected from the sample surface, and electrons generated by secondary excitation of the sample by irradiating the sample with a primary electron beam.
[0002]
[Prior art]
In an electron microscope, an electron beam generated and accelerated from an electron gun is finely focused on a sample by a condenser lens and an objective lens. Electrons transmitted and scattered through the sample are imaged by an intermediate lens and a projection lens, and a fluorescent screen is disposed at the imaging position, and an image enlarged and projected on the fluorescent screen is observed. Further, instead of the fluorescent plate, a TV camera such as a CCD camera is arranged at the image forming position, an image projected on the screen of the TV camera is converted into a video signal, and this video signal is supplied to a display device such as a cathode ray tube. An image is also observed with a display device.
[0003]
In another type of electron microscope, that is, a scanning transmission electron microscope, an electron beam generated from an electron gun and accelerated is finely focused on a sample by a condenser lens and an objective lens, and a predetermined range on the sample is electron-controlled. The beam is scanned. Electrons transmitted through the sample are detected by irradiating the sample with an electron beam, and this detection signal is supplied to the display in accordance with the scanning of the primary electron beam to display a scanning transmission electron microscope image of the sample. .
[0004]
Furthermore, in a scanning transmission electron microscope, a scanning secondary electron image and a reflected electron image of a sample can be obtained. In this case, the electron beam generated from the electron gun and accelerated is finely focused on the sample by the condenser lens and the objective lens, and a predetermined range on the sample is scanned with the electron beam. If secondary electrons generated from the sample are detected by secondary excitation generated by irradiating the sample with the primary electron beam, and this detection signal is supplied to the display according to the scanning of the primary electron beam, the sample is scanned. A secondary electron image can be displayed. Further, if the reflected electrons reflected from the sample are detected and this detection signal is supplied to the display according to the scanning of the primary electron beam, the scanning reflected electron image of the sample can be displayed.
[0005]
In such a scanning transmission electron microscope, three stops are mainly used. This diaphragm is basically arranged so as to allow only electrons along the observation purpose to pass and to block signals of electrons that have an adverse effect on the observation purpose. The types of these three diaphragms will be briefly described from the diaphragm arranged from the upper stage of the electron optical system.
[0006]
First, a condenser lens diaphragm is disposed between the condenser lens and the sample. This condenser lens diaphragm restricts electrons incident on the sample with a large opening angle among the electrons generated from the electron gun.
[0007]
Next, an objective lens diaphragm is usually disposed between the sample and the lower pole of the objective lens pole piece in the objective lens. The objective lens stop is provided to selectively pass only electrons having a specific scattering angle among electrons transmitted through the sample in order to observe a bright field image and a dark field image.
[0008]
Next, a limited field stop is usually disposed between the objective lens and the intermediate lens. This limited field stop is used to obtain a diffraction pattern from an arbitrary region of the sample.
[0009]
Each of these diaphragms is provided with a plurality of circular diaphragm holes of different sizes. Depending on the observation mode of the scanning transmission electron microscope, the magnification of the acquired image in each observation mode, etc., the diaphragm holes of different diameters are provided. It is necessary to select and arrange the selected aperture hole at a predetermined position.
[0010]
In each of these diaphragms, an appropriate diaphragm hole is selected according to the observation mode to be performed, magnification, and the like. In many cases, selection of this diaphragm hole (movement of the diaphragm position) is performed manually by an operator. Has been done by. However, in recent years, an apparatus that uses an electric motor to select and position the aperture has been developed.
[0011]
[Problems to be solved by the invention]
In each of the apertures described above, an appropriate aperture is selected each time the observation conditions such as the electron beam irradiation conditions, magnification, and field of view are changed, and the selected aperture is accurately placed at the specified position. I have to let it. Therefore, the diaphragms are often moved frequently, which is one factor that complicates the operation of the electron microscope.
[0012]
In particular, when a high resolution is required or when it is necessary to obtain information with high accuracy, the diaphragm must be accurately positioned. For an operator who is not familiar with the operation of an electron microscope, this positioning operation is one of difficult operations. If the position of the stop is greatly shifted and the stop hole with the selected diameter is greatly deviated from the optical axis, it will be very difficult to find the stop hole again.
[0013]
As described above, an apparatus has been developed that uses an electric motor to move the aperture for selecting and positioning the aperture. When such movement of the diaphragm is performed by an electric motor, the selected diaphragm hole can be moved close to the required position, but the center of the diaphragm hole cannot be placed at the exact set position, and the motor After the movement of the diaphragm by means of, the diaphragm positioning work is required manually.
[0014]
In order to obtain a movement amount as accurate as possible, it is also possible to detect the position of the diaphragm with a potentiometer and control the movement of the diaphragm with the electric motor according to the movement amount obtained by the potentiometer. Has been tried. However, there are backlash of a moving feed screw and a backlash of a gear used in the diaphragm movement mechanism, and it is difficult to position the diaphragm hole in the μm order.
[0015]
In addition, for the mechanism that reads the current value of the aperture position, the actual movement amount cannot be directly read, and the movement amount of the diaphragm is estimated by the movement amount and rotation amount of the mechanical elements on the motor and the diaphragm feed mechanism. In such a configuration, it is difficult to accurately detect the movement amount and the diaphragm position of the diaphragm.
[0016]
The present invention has been made in view of such a point, and an object thereof is to realize an electron microscope capable of accurately positioning a selected aperture hole at a predetermined position.
[0017]
[Means for Solving the Problems]
An electron microscope according to the present invention is an electron microscope that observes a sample image on the basis of electrons transmitted through the sample or electrons generated from the sample surface by irradiating the sample with a primary electron beam, and an electron optical system thereof In an electron microscope in which a diaphragm having a plurality of diaphragm holes having different diameters is arranged in a part of the diaphragm, another diaphragm hole is predetermined from each diaphragm hole for each diaphragm hole arranged at a predetermined position. The coordinate value of the diaphragm at the time of arranging at the position is obtained and stored, and when the diaphragm hole having a desired diameter is set at a predetermined position, the coordinate value stored from the stored coordinate value is A feature is that a diaphragm coordinate value for selecting a diaphragm hole having a desired diameter and setting it at a predetermined position is read, and the diaphragm is moved based on the read coordinate value.
[0018]
In the invention based on claim 1, in order to select and set another diaphragm hole at a predetermined position for each of the plurality of diaphragm holes provided in the diaphragm, the coordinate values of the diaphragm are stored in a matrix, When exchanging holes, the coordinate value applied when exchanging the old restrictor hole to the new restrictor hole is read out from the coordinate values stored in a matrix, and the movement of the restrictor is performed based on this coordinate value. Then, a new aperture is arranged at a predetermined position such as on the optical axis.
[0019]
In the invention based on claim 2, when an error occurs in the coordinate value of the aperture position, the shift amount is obtained for a specific aperture hole, and the other aperture position coordinates are corrected based on the obtained shift amount.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of a scanning transmission electron microscope according to the present invention. In this microscope, an electron beam is scanned on a sample, and a scanning electron microscope image based on secondary electrons from the sample surface is also shown. A scanning transmission electron microscope image based on electrons transmitted through the sample by scanning the beam and a transmission electron microscope image based on electrons transmitted through the sample without scanning the electron beam can be selectively observed. It is configured to be able to.
[0021]
In the figure, an electron beam EB generated from an electron gun 2 disposed on the top of an electron microscope column 1 is accelerated by an acceleration tube 3. The electron beam accelerated to, for example, 50 kV by the accelerating tube 3 is focused by the first condenser lens 4 and the second condenser lens 5.
[0022]
The central portion of the electron beam focused by the condenser lenses 4 and 5 passes through the aperture of the condenser lens aperture 6, and a portion with large aberration outside the electron beam is shielded by the aperture 5. The condenser lens diaphragm 6 is provided with a plurality of openings having different diameters, and is configured such that any appropriate diameter opening is arranged on the optical axis in accordance with various modes of the microscope. Yes. Between the accelerating tube 3 and the condenser lens 4, a pair of alignment coils 7 and 8 are arranged for correcting an axial deviation of the electron beam generated from the electron gun 2 and accelerated by the accelerating tube 3.
[0023]
The electron beam that has passed through the aperture of the condenser lens aperture 6 is finely adjusted by the condenser mini-lens 9 and then irradiated onto the sample 11 disposed in the magnetic field of the objective lens 10. Between the condenser lens diaphragm 6 and the sample 11, an astigmatism correction lens 13 for correcting the astigmatism of the condenser lens, and an axis deviation of the electron beam focused by the condenser lenses 4 and 5 are corrected. Alignment coils 14 and 15 are arranged. The alignment coils 14 and 15 also operate as two-dimensional scanning coils for electron beams in the scanning image observation mode.
[0024]
The front magnetic field of the sample 11 by the objective lens 10 contributes to the focus of the electron beam, and the rear magnetic field of the sample 11 constitutes an imaging lens system by the intermediate lenses 16, 17, 18 and the projection lens 19 in the subsequent stage. In addition, an objective lens stop 20 is disposed in front of the objective lens 10, and a portion with large aberration outside the electron beam is shielded by the stop 20.
[0025]
The objective lens stop 20 is provided with a plurality of apertures having different diameters, and any appropriate aperture is arranged on the optical axis according to various modes of the microscope. Yes. Further, an objective mini lens 22 for finely adjusting the magnetic field of the objective lens 10 is disposed between the objective lens 10 and the field limiting aperture 21.
[0026]
Further, an astigmatism correction lens 23 and image shift coils 24 and 25 for correcting astigmatism of the objective lens 10 are provided below the objective lens aperture 20. In addition, an alignment coil 26 for axial alignment of the electron beam is disposed after the projection lens 19.
[0027]
A secondary electron detector 27 is provided on the top of the sample 11. This secondary electron detector is operated in the scanning electron microscope image observation mode. For example, a detector composed of a scintillator and a photomultiplier tube is used to accelerate secondary electrons from the sample. And led to the scintillator.
[0028]
Further, in the subsequent stage of the imaging lens system, in order from the top, the first TV camera 28 such as a CCD camera, the dark field image observation detector 29, the bright field image observation detector 30, and the CCD camera. Two TV cameras 31 are arranged. The first TV camera 28 is configured to be detachable on the optical axis by the drive mechanism 32. The dark field image observation detector 29 and the bright field image observation detector 30 are configured to be detachable on the optical axis by drive mechanisms 33 and 34, respectively. Further, the second TV camera 31 is configured to be detachable on the optical axis by the drive mechanism 35.
[0029]
Lenses in the column 1, that is, condenser lenses 4 and 5, condenser lens minilens 9, objective lens 10, objective lens minilens 22, intermediate lenses 16, 17 and 18, projection lens 19 and astigmatism correction lenses 13 and 23. An excitation current is supplied from the lens power source 36. A desired high voltage is applied to the electron gun 2 and the acceleration tube 3 from a high voltage power source 37.
[0030]
Further, a desired current is supplied from the alignment power source 38 to the electron gun alignment coils 7 and 8, the condenser lens alignment coils 14 and 15, the image shift coils 24 and 25, and the projection lens alignment coil 26. Due to the magnetic field generated by, the axial deviation of the electron beam is corrected as appropriate and the position of the image is moved.
[0031]
Further, the drive mechanism 32 of the secondary electron detector 27, the drive mechanism 33a of the first TV camera 28, the drive mechanism 34 of the dark field image observation detector 29, the drive mechanism 35 of the bright field image observation detector 30, The drive mechanism 33b of the second TV camera 31 is selectively driven by the drive voltage from the detector drive power supply 39 so that only a specific detector is arranged on the optical axis or brought close to the optical axis. It is configured.
[0032]
Further, a TV power source 40 for acquiring transmission electron microscope image signals from the first TV camera 28 and the second TV camera 31 is provided, and the secondary electron detector 27 and detection for dark field image observation are provided. The scanning image signal from the detector 29 and the bright field image observation detector 30 is supplied to the amplifier 41.
[0033]
The diaphragms 6, 20, and 21 arranged along the optical axis in the column 1 are driven by a diaphragm driving power source 42, and the size of the aperture of each diaphragm on the optical axis is selected to be optimum.
[0034]
The lens power source 36, high voltage power source 37, alignment power source 38, detector position driving power source 39, TV camera power source 40, detector signal amplifier 41, and aperture driving power source 42 are connected to a computer 44 via an interface 43. Yes. As a result, the lens power source 36, the high voltage power source 37, the alignment power source 38, the detector driving power source 39, the TV camera power source 40, the signal amplifier 41, and the aperture driving power source 42 are controlled by the computer 44.
[0035]
A memory 45 is connected to the computer 44. The memory 45 includes information such as the intensity of each lens, the selection of a detector, the selection of the aperture of an aperture, the observation mode of the electron microscope, the acceleration voltage and magnification of the electron gun. Is stored in the form of a table.
[0036]
For example, when the acceleration voltage of the electron gun is changed, the electron beam is optimally focused on the sample 11 with the selected acceleration voltage, and the electron image transmitted through the sample has a specified magnification, for example. Each lens intensity that is optimally projected onto the screen of one TV camera 28 is stored in advance.
[0037]
A keyboard 46, a mouse 47, a control panel 48, and a display 49 are connected to the computer 44. The keyboard 44 and the mouse 47 are configured so that commands to the computer 44 and various conditions can be set. . On the screen of the display 49, an image display area 50, a GUI (graphic user interface) 51 for controlling the apparatus, and a pointer 52 that moves on the screen by a mouse 47 and a keyboard 46 are displayed. As a matter of course, the computer 44 is provided with software 53 for controlling various components of the electron microscope in accordance with designated modes and conditions. The operation of such a configuration will be described next.
[0038]
The scanning transmission electron microscope shown in FIG. 1 can perform observation of a transmission electron microscope (TEM) image, observation of a scanning electron microscope image, and observation of a transmission scanning electron microscope image. When observing a transmission electron microscope image, the keyboard 52 and the mouse 47 are used to position the pointer 52 in, for example, the area where TEM is displayed in the GUI 51 displayed on the display 49, and click the mouse 47. Etc. to select the TEM mode.
[0039]
When the TEM mode is selected, the computer 44 controls the detector driving power source 39, the driving mechanism 32 retracts the secondary electron detector 27 away from the optical axis, and the driving mechanism 34 causes the dark field image detector 29 to move. The bright field image detector 30 is retracted from the optical axis by the drive mechanism 35. Then, either one of the first TV camera 28 or the second TV camera 31 is disposed on the optical axis and the other is retracted from the optical axis by the driving mechanisms 33a and 33b.
[0040]
The first TV camera 28 is mainly used when observing an image with a relatively low magnification for wide-field observation, and is disposed at a position close to the projection lens 19. The second TV camera 31 is a high-resolution TV camera and is used when observing an image at a relatively high magnification. Which of these two types of TV cameras is used can be selected by the GUI 51 of the display 49 of the computer 44.
[0041]
For example, when observing a wide-field electron microscope image, the first TV camera 28 is arranged on the optical axis, and the second TV camera 31 is retracted from the optical axis. In this state, the computer 44 controls the excitation currents of the condenser lenses 4 and 5 and the objective lens 10 so as to irradiate the sample 11 with a probe having a relatively thick diameter (1 nm). Further, the excitation currents of the intermediate lenses 16 to 18 and the projection lens 19 are controlled so that an image of electrons transmitted through the sample 11 is formed on the screen of the first TV camera 28.
[0042]
Thus, when each lens is controlled and the sample 11 is irradiated with the electron beam from the electron gun 2, a transmission electron microscope image of a specific wide field of view of the sample is projected on the screen of the first TV camera 28. The image projected on the screen of the TV camera 28 is read out as a video signal and sent to the computer 44 through the TV power source 40 for acquiring a transmission electron microscope image. The video signal supplied to the computer 44 is supplied to the display 49, and on the image display area 50 of the screen of the display 49, a transmission electron microscope image having a relatively low magnification is displayed.
[0043]
When observing a high-resolution transmission electron microscope image having a relatively high magnification, the first TV camera 28 is retracted from the optical axis by the drive mechanism 33a, and the second TV camera 31 is retracted by the drive mechanism 33b. Is arranged on the optical axis. At that time, the lens intensities of the intermediate lenses 16 to 18 and the projection lens 19 are adjusted, and control is performed so that an electronic image is formed on the screen of the second TV camera 31 disposed below the column 1. The
[0044]
The image projected on the screen of the TV camera 31 is read out as a video signal and sent to the computer 44 via the TV power source 40 for acquiring a transmission electron microscope image. The video signal supplied to the computer 44 is supplied to the display 49, and a high-resolution transmission electron microscope image with high magnification is displayed on the image display area 50 of the screen of the display 49. Note that the image obtained using the first TV camera 28 is used for searching the field of view of the sample, and the image obtained using the second TV camera 31 is the desired sample obtained as a result of searching the field of view. A high resolution image of the region.
[0045]
Next, operations for observing a scanning secondary electron microscope (SEM) image and a transmission scanning electron microscope (SEM) image will be described. When observing a scanning electron microscope image or a scanning transmission electron microscope image, the pointer 52 is moved to an area where, for example, SEM or STEM is displayed in the GUI 51 displayed on the display 49 using the keyboard 46 or the mouse 47. Select the SEM or STEM mode, for example by clicking the mouse 47.
[0046]
When this SEM mode is selected, the computer 44 controls the detector driving power source 39 and moves the secondary electron detector 27 to a position close to the optical axis by the driving mechanism 32, and the dark field image detector 29, bright field The image detector 30 is retracted from the optical axis. Then, the first TV camera 28 and the second TV camera 31 are also retracted from the optical axis.
[0047]
In this state, the computer 44 controls the excitation currents of the condenser lenses 4 and 5 and the objective lens 10 so as to irradiate the sample 11 with a probe having a relatively small diameter (about 0.2 nm). In this way, by controlling each lens to irradiate the sample 11 with the electron beam from the electron gun 2 and supplying a two-dimensional scanning signal of the electron beam to the condenser lens alignment coils 14 and 15, a predetermined region of the sample 11 can be obtained. The electron beam is scanned two-dimensionally.
[0048]
Secondary electrons generated from the surface of the sample 11 based on the two-dimensional scanning of the electron beam on the sample are guided to the secondary electron detector 27 and detected. The detected secondary electron signal is supplied to the computer 44 through the amplifier 41 as a video signal. The video signal supplied to the computer 44 is supplied to the display 49, and as a result, a scanning electron microscope image is displayed in the image display area 50.
[0049]
Next, when the STEM mode is selected, the computer 44 controls the detector driving power source 39, moves the secondary electron detector 27 away from the optical axis by the driving mechanism 32, and drives the driving mechanisms 33a and 33b. One of the dark field image detector 29 and the bright field image detector 30 is disposed on the optical axis, and the other is retracted from the optical axis. Then, the first TV camera 28 and the second TV camera 31 are also retracted from the optical axis.
[0050]
In this state, the computer 44 controls the excitation currents of the condenser lenses 4 and 5 and the objective lens 10 so as to irradiate the sample 11 with a probe having a relatively small diameter (about 0.2 nm). In this way, by controlling each lens to irradiate the sample 11 with the electron beam from the electron gun 2 and supplying a two-dimensional scanning signal of the electron beam to the condenser lens alignment coils 14 and 15, a predetermined region of the sample 11 can be obtained. The electron beam is scanned two-dimensionally.
[0051]
The electrons transmitted through the sample 11 based on the two-dimensional scanning of the electron beam on the sample are detected by either the dark field image detector 29 or the bright field image detector 30 arranged on the optical axis. The detected transmission electron signal is supplied to the computer 44 through the amplifier 41 as a video signal. The video signal supplied to the computer 44 is supplied to the display 49, and as a result, a bright transmission field or a dark field scanning transmission electron microscope image is displayed in the image display area 50.
[0052]
FIG. 2 shows each lens intensity and optical path in the TEM mode, SEM, and STEM mode for reference. In FIG. 2, the solid line indicates the lens intensity and the optical path when in the TEM mode, and the dotted line indicates the lens intensity and the optical path when in the SEM and STEM modes. In the figure, CL is a condenser lens, and the two-stage condenser lens of the apparatus of FIG. OLpre indicates the front magnetic field of the sample by the objective lens 10, and OLpost indicates the rear magnetic field of the sample by the objective lens 10.
[0053]
Further, IL1 is an intermediate lens, and the two-stage intermediate lens of the apparatus shown in FIG. IL2 + PL indicates a combined lens of the third stage intermediate lens and the projection lens in FIG. As is clear from this figure, in the SEM / STEM mode, the lens intensity of the objective lens 10 is increased and the lens intensity of the intermediate lens system is decreased compared to the TEM mode.
[0054]
As described above, the apparatus of FIG. 1 can observe a transmission electron microscope image, a scanning electron microscope image, and a scanning transmission electron microscope image. FIG. 3 shows a specific example of the structure of each of the diaphragms 6, 20, and 21 used in FIG. The mechanisms for selecting the respective apertures and aperture holes have almost the same configuration, and FIG. 3 shows the structure of the condenser lens aperture 6 as a representative.
[0055]
The aperture 6 is attached to the tip of an aperture support rod 60, and the aperture 6 is formed with a plurality of aperture holes 6a, 6b, 6c. The plurality of throttle holes have different diameters, and the centers of the holes are aligned in the X direction. Reference numeral 61 denotes an X drive mechanism for moving the diaphragm 6 in the X direction via the diaphragm support rod 60. The motor 64 rotates the gear 62 via the pinion 63, and the X drive shaft rotates as the gear 62 rotates. 65, a pinion 66 that is rotated by the rotation of the gear 62, a potentiometer 67 that generates a signal corresponding to the rotation amount of the pinion 66, and a fixing member 68 that is screwed to the X drive shaft 65.
[0056]
In such an X drive mechanism 61, when the motor 64 is driven based on the drive signal in the X direction from the aperture drive power supply 42, the gear 62 is rotated via the pinion 63. As the gear 62 rotates, the X drive shaft 65 rotates. The surface of the X drive shaft 65 is threaded, and the inside of the opening (not shown) of the fixing member 68 through which the X drive shaft 65 passes is engaged with the screw outside the X drive shaft 65. Screws are provided.
[0057]
Thus, if the pinion 62 is rotated by the motor 64 and the X drive shaft 65 is rotated, the X drive shaft 65 is moved in the X direction, and as a result, is provided in contact with the tip of the X drive shaft 65. The diaphragm support bar 60 is moved according to the movement of the X drive shaft 65, and the diaphragm 6 provided at the tip of the support bar 60 also moves in the X direction. Although not shown, the diaphragm support rod 60 is applied with a force in the direction of the X drive rod 65. If the X drive shaft 65 is moved in the left direction in the figure, the diaphragm 6 is also moved in the left direction. A smaller diameter aperture is selected and placed on the optical axis.
[0058]
On the other hand, if the motor 64 is rotated in the reverse direction and the X drive shaft 65 is moved in the right direction in the figure, the diaphragm 6 is also moved in the right direction, and a larger diameter aperture hole is selected and placed on the optical axis. Be placed. As described above, when the control software 53 supports the selection of the aperture, the aperture X movement signal is supplied to the aperture drive power supply 42 so that the selected aperture is arranged on the optical axis. The motor 64 is driven.
[0059]
The aperture support rod 60 is moved in the X direction by the rotation of the motor 64, and the amount of movement of the aperture indicating rod is detected by a potentiometer 67, and the detection signal is supplied to the control software 53. The control software 53 compares the designated aperture movement amount with the actual movement amount, and if there is a difference between them, the X drive shaft 65 is further rotated to finely adjust the position of the aperture support rod 60. adjust.
[0060]
The width of the gear 62 is selected so as not to be disengaged from the pinions 63 and 66 even when the gear 62 moves in the axial direction.
Reference numeral 71 denotes a Y drive mechanism for moving the diaphragm 6 in the Y direction via the diaphragm support bar 60. The motor 74 rotates the gear 73 via the pinion 72, and the Y drive shaft rotates with the rotation of the gear 73. 75, a pinion 76 that meshes with the pinion 72 and rotates in synchronization with the gear 73, a potentiometer 77 that generates a signal in accordance with the amount of rotation of the pinion 76, and a Y position controller that is screwed with the Y drive shaft 75 and whose rotation is restricted. 78.
[0061]
In such a diaphragm Y drive mechanism 71, when the motor 74 is driven based on a drive signal in the Y direction from the diaphragm drive power supply 42, the pinion 73 is rotated via the pinion 72. As the gear 73 rotates, the Y drive shaft 75 rotates. The surface of the Y drive shaft 75 is threaded, and inside the opening (not shown) of the Y position control body 78 through which the Y drive shaft 75 penetrates, a screw outside the Y drive shaft 75 and Intermeshing screws are provided.
[0062]
Thereby, if the gear 73 is rotated by the motor 74 and the Y drive shaft 75 is rotated, the Y position control body 78 is moved in the Y direction. The tip of the Y moving shaft 75 is in contact with a predetermined position of the aperture support rod 60. As a result, when the Y position controller 78 is moved, the aperture support rod 60 also moves in the same direction.
[0063]
Accordingly, the diaphragm 6 provided at the tip of the Y diaphragm support rod 60 also moves in the Y direction. Although not shown, the diaphragm 6 is applied with a force downward in the figure, and if the Y position controller 78 is moved downward in the figure, the diaphragm 6 is also moved downward and selected. The position of the aperture hole in the Y direction is adjusted. The width of the gear 73 is also selected so as not to be disengaged from the pinion 72 due to its axial movement.
[0064]
As described above, when the control software 53 supports the selection of the aperture, the aperture X movement signal is supplied to the aperture drive power supply 42 so that the selected aperture is arranged on the optical axis. The motor 64 is driven. The aperture indicator bar 60 is moved in the X and Y directions by the rotation of the motor 64. The position of the aperture indicator bar in the Y direction is detected by a potentiometer 77, and the detection signal is supplied to the control software 53. The control software 53 compares the Y-direction position of the designated aperture hole with the Y-direction position actually measured by the potentiometer 77. If there is a difference between them, the control software 53 further rotates the Y drive shaft 75. Then, the position of the aperture support rod 60 is finely adjusted.
[0065]
The above-described diaphragm control mechanism has been described by taking the condenser lens diaphragm 6 as an example, but the objective lens diaphragm 20 and the field limiting diaphragm 21 have the same mechanism. Here, when performing microscopic observation in a desired mode, the keyboard 46, mouse 47, and GUI 51 are used to select the type of aperture suitable for the observation mode and the apertures of different diameters formed in the aperture.
[0066]
In this case, the control software 53 reads the aperture number currently set on the optical axis for the selected aperture 6 via the aperture drive power source 42 and the interface 43. The control software 53 reads information on the selected diaphragm type and diaphragm hole diameter (numbers of a plurality of diaphragm holes provided in the diaphragm). In the example of FIG. 3, the aperture 6 has four aperture holes A1, A2, A3, and A4 having different diameters. For example, the control software 53 sets the aperture hole currently set on the optical axis. Reads A1.
[0067]
On the other hand, in the memory 45, as shown in FIG. 4, the vertical axis is the number of the aperture hole that is currently set, and the horizontal axis is the number of the aperture hole to be set next, and is currently set. Coordinate values for moving the aperture from the aperture to the aperture to be set next are stored.
[0068]
For example, when the aperture hole currently set on the optical axis is A1, and the aperture hole A3 is moved on the optical axis, the control software 53 stores the coordinates in the table of FIG. Read the value. For example, the coordinate value (X) stored at the position where the vertical axis is A1 and the horizontal axis is A3. ₁₃ , Y ₁₃ ). Based on the read coordinate value, the control software 53 controls the aperture drive power source 42 via the interface 43 to set the aperture 6 to the coordinate value (X ₁₃ , Y ₁₃ ).
[0069]
The movement of the diaphragm 6 to this coordinate value drives the motors 64 and 74 shown in FIG. 3, moves the X-axis drive shaft 65 in the X direction using the rack and pinion mechanism, and moves in the Y direction. Is performed by moving the Y position controller 78 in the Y direction. The amount of movement of the diaphragm 6 (the coordinate values in the X and Y directions) is measured by potentiometers 67 and 77, and the diaphragm 6 is accurately coordinated (X ₁₃ , Y ₁₃ ) And the aperture A3 is accurately set on the optical axis. This coordinate value is an absolute coordinate value read from a measuring instrument such as a potentiometer.
[0070]
When the currently set aperture is A2, and a new aperture A3 is to be selected, the moving coordinate value used when selecting a new aperture A3 from the currently set aperture A1. (X ₁₃ , Y ₁₃ ) Cannot be used. This is because there is an error in the output value with respect to the input value due to the backlash of the feed screw or gear included in the moving mechanism shown in FIG.
[0071]
In addition, regarding the mechanism for reading the current value, the desired part cannot be directly read as movement amount information, and it must be dealt with by reading the feed amount with the movement amount or rotation amount of the machine element on the motor or feed mechanism. There are many cases where this is not possible, and an error in position detection due to this factor occurs. Therefore, when the aperture hole A3 is selected and set on the optical axis from the state where the aperture hole A2 is set on the optical axis, the movement coordinate value (X when the aperture holes A1 to A3 are selected) ₁₃ , Y ₁₃ ) Cannot be used.
[0072]
Therefore, when the aperture hole A3 is selected and set on the optical axis from the state where the aperture hole A2 is set on the optical axis, the current aperture number A2 in the table shown in FIG. The coordinates of the part where the destination aperture number A3 intersects (X _{twenty three} , Y _{twenty three} ) And the diaphragm 6 is moved to this coordinate value.
[0073]
As described above, when selecting a throttle hole having a different hole diameter, coordinate values are set in advance in a matrix for each of the currently selected throttle hole and the next selected throttle hole, and a new throttle hole is selected. When making a selection, the diaphragm is moved based on the coordinate positions of the individual diaphragms set for the current and next selected diaphragm holes. As described above, since the coordinate value is obtained in advance and the diaphragm is moved based on the coordinate value, any of the above-described diaphragm feeding mechanism and diaphragm position detecting mechanism may include an error. The diaphragm can be moved to the correct position.
[0074]
In the embodiment of FIG. 3, the example in which the reading of the potentiometer is converted into the coordinate is shown, but the reading of the potentiometer itself is also possible. Even if the measurement position and method such as a linear gauge are different, it is possible to use another measuring device by setting the reading of the coordinate value itself of the movement destination.
[0075]
By the way, when a deviation occurs in the set aperture, the GUI 51, the mouse 47, the keyboard 46, the control panel 48, etc. while viewing the observation screen of the sample image such as the scanning electron microscope image or the transmission electron microscope image. Then, the aperture position is moved to correct the displacement of the aperture. The correction of the displacement of the aperture position is performed by the currently set aperture hole. When the aperture movement operation is completed, the corrected coordinate position information is immediately sent to the memory 45, and the table of FIG. Each coordinate value of is rewritten.
[0076]
Note that the coordinate values shown in the table of FIG. 4 need only be set once in all cases. Due to changes in the surrounding environment, an error may occur in the coordinates shown in the table of FIG. The main error component in that case is the expansion and contraction of the portion of the bar being pushed to move the diaphragm.
[0077]
For this reason, the positions of the respective apertures are displaced by the same amount in the same direction. If the amount of deviation at this time is ΔX and ΔY, this value may be added to each coordinate value. For example, when the aperture is moved from A2 to A4, the coordinate value of the portion where A2 and A4 intersect is (X _{twenty four} + ΔX, Y _{twenty four} + ΔY).
[0078]
Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various modifications are possible. For example, the control of the condenser lens diaphragm of the transmission electron microscope has been described, but the present invention can also be applied to operations of other diaphragms, for example, an objective lens diaphragm and a field limiting diaphragm.
[0079]
【The invention's effect】
In the invention based on claim 1, in order to select and set another diaphragm hole at a predetermined position for each of the plurality of diaphragm holes provided in the diaphragm, the coordinate values of the diaphragm are stored in a matrix, When exchanging holes, the coordinate value applied when exchanging the old restrictor hole to the new restrictor hole is read out from the coordinate values stored in a matrix, and the movement of the restrictor is performed based on this coordinate value. The new aperture was arranged at a predetermined position such as on the optical axis. As a result, the diaphragm feed (selection of the aperture) can be managed by coordinates, and an appropriate aperture is selected each time the observation conditions change, such as the electron beam irradiation conditions, magnification, and field of view. The selected aperture can be accurately placed at a predetermined position.
[0080]
Further, it is not necessary to frequently move each aperture, and it is possible to easily select the aperture that was one factor that complicates the operation of the electron microscope. Especially when high resolution is required or when it is necessary to obtain information with high accuracy, the aperture must be accurately positioned. However, this operation is difficult for operators who are not familiar with electron microscope operations. However, anyone can easily perform this operation.
[0081]
In the invention based on claim 2, when an error occurs in the coordinate value of the aperture position, the displacement amount is obtained for the specific aperture hole, and the other aperture position coordinates are corrected by the obtained displacement amount. The value correction work can be simplified.
[Brief description of the drawings]
FIG. 1 shows a scanning transmission electron microscope as an example of an electron microscope for implementing a method according to the present invention.
FIG. 2 is a diagram showing lens strength and optical paths in SEM mode and TEM mode.
FIG. 3 is a diagram illustrating an example of an aperture driving mechanism.
FIG. 4 is a table showing the coordinate values of apertures stored in a memory.
[Explanation of symbols]
1 column
2 electron gun
3 Accelerating tube
6, 20, 21 Aperture
7, 8 Electron gun alignment coil
10 Objective lens
11 samples
13, 23 Astigmatism correction lens
14, 15 Condenser lens alignment coil
16, 17, 18 Intermediate lens
19 Projection lens
24, 25 Image shift coil
26 Projection lens alignment coil
27, 29, 30 Detector
28, 31 TV camera
32a, 32b TV camera drive mechanism
33, 34, 35 Detector drive mechanism
36 Lens power supply
37 High voltage power supply
38 Power supply for alignment coil
39 Detector drive power supply
40 TV power supply for TEM images
41 Scanning image signal amplifier
42 Aperture drive power supply
43 Interface
44 computers
45 memory
46 keyboard
47 mouse
48 Control Panel
49 display
50 image display area
51 GUI
52 pointer
60 Aperture support rod
61 X drive mechanism
71 Y drive mechanism

Claims (2)

An electron microscope that irradiates a sample with a primary electron beam and observes a sample image based on electrons transmitted through the sample or electrons generated from the surface of the sample. In an electron microscope in which a diaphragm having a diaphragm having a diameter is arranged, a diaphragm for arranging another diaphragm hole from each diaphragm hole at a predetermined position for each diaphragm hole disposed at a predetermined position. The coordinate value is stored in the storage means, and when the throttle hole with the desired diameter is set at a predetermined position, the throttle hole with the desired diameter is set from the currently set throttle hole and the throttle with the desired diameter. An electron microscope which reads out the coordinate value of the diaphragm for selecting and setting at a predetermined position from the storage means, and moves the diaphragm based on the read coordinate value. The electron microscope according to claim 1, wherein when an error occurs in the coordinate value of the aperture position, an amount of deviation is obtained for a specific aperture hole, and the other aperture position coordinates are corrected by the obtained amount of deviation.

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