JP4895525B2 - Scanning transmission electron microscope - Google Patents

Description

  The present invention converges an electron beam to a sub-nanometer diameter and irradiates the sample, selects all or part of the electron beam diffracted, scattered, or transmitted by the sample, and synchronizes with the scanning of the electron beam probe. The present invention relates to a scanning transmission electron microscope apparatus that detects and forms a scanning transmission image.

  The formation principle and acquisition method of a bright field image using a conventional scanning transmission electron microscope apparatus are disclosed in, for example, (Non-Patent Document 1), (Non-Patent Document 2), (Non-Patent Document 3), and the like. This method is based on the principle of reciprocity between the transmission electron microscope and the scanning transmission electron microscope. The light source in the transmission electron microscope is made to correspond to the detector of the scanning transmission electron microscope, and the objective aperture in the transmission electron microscope is set in the scanning transmission electron microscope. This is a technique that utilizes the fact that an equivalent electron optical system is realized by corresponding to a converging aperture. Here, if the detector of the scanning transmission electron microscope is installed on the optical axis and the detection angle is reduced to about several milliradians, the bright field corresponding to the case where the sample is irradiated with an electron beam in parallel using the transmission electron microscope. An image can be obtained. In addition, if the convergence angle of the electron beam probe of the scanning transmission electron microscope is made smaller than the diffraction angle with respect to a specific crystal plane, the diffraction electron beam corresponding to the specific crystal plane is removed using the objective aperture in the transmission electron microscope. A diffraction contrast image to be formed can be obtained. Conversely, if the convergence angle of the electron probe of the scanning transmission electron microscope is made larger than the diffraction angle with respect to a specific crystal plane, the diffracted electron beam and the transmission electron beam with respect to the specific crystal plane pass through the objective aperture simultaneously in the transmission electron microscope. In this case, a phase contrast image formed can be obtained. When observed at a high magnification of about 3 million times, lattice fringes corresponding to intervals between specific crystal planes can be obtained.

  On the other hand, in the scanning transmission electron microscope, in addition to the bright field image described above, an electron beam scattered at a large angle by the sample is detected and imaged by an annular detector having an opening at the center. Yes. This image is called a dark field image, and the imaging principle and the actually observed image are disclosed in, for example, (Non-Patent Document 4). For example, when an electron beam of 200 kilovolts is used, the detection angle range of the dark field image is generally set to a condition for capturing all the electron beams scattered in an angle range of about 50 milliradians to about 300 milliradians. is there. At such high angles, the intensity of the elastically scattered electron beam decreases, and the intensity of the diffusely scattered electron beam becomes dominant. That is, in the dark field image, image contrast is formed mainly by the intensity of scattering by the substance, and the effects of diffraction and interference of the electron beam by the sample hardly appear as contrast. Also, since the image intensity of a dark field image is often proportional to the atomic number Z empirically, the dark field image is sometimes called a Z contrast image.

Electron Microdiffraction 1992 Plenum Press (New York and London) Paragraphs 169-191

Ultramicroscopy 1990, No. 32, paragraphs 93-102 Ultramicroscopy 2003, 96, paragraphs 239-249 Ultramicroscopy 1991, No. 37, paragraphs 14-38

  In the conventional method for acquiring a bright field image using a scanning transmission electron microscope apparatus, the setting of the convergence angle of the electron beam probe necessary for acquiring the diffraction contrast image and the grating image is different. Therefore, when setting the observation angle of the electron beam probe corresponding to the conditions for obtaining a diffraction contrast image, it is possible to distinguish and observe polycrystalline particles, crystal substrates, and amorphous materials at an appropriate contrast at low magnification. It is impossible to obtain lattice fringes due to electron beam interference at a high magnification, and the original resolution performance of the device cannot be extracted. On the other hand, when the electron beam probe convergence angle corresponding to the conditions for obtaining a crystal lattice image is set and observed, lattice fringes can be observed with an appropriate contrast at a high magnification. Are detected at the same time, the diffraction contrast is lowered in a low-magnification image, and it may be difficult to distinguish and observe a grain boundary with polycrystalline particles or to distinguish between a crystal substrate and an oxide film. For example, under the bright field lattice image observation conditions disclosed in (Non-patent Document 2), the silicon lattice fringes can be observed with high contrast by setting the convergence angle to 27.2 milliradians. However, under this condition, the transmission electron beam and all of the diffracted electron beams from the (111) plane, the (220) plane, the (311) plane, and the (400) plane are detected by the detector. Can't get.

  Therefore, conventionally, in order to obtain a desired contrast at a desired magnification, a method of setting an appropriate convergence angle by changing the hole diameter of the convergence diaphragm according to the observation magnification has been used. However, it was necessary to operate the aperture stop every time the magnification was changed, which hindered rapid observation and analysis. In addition, it is necessary to make the converging aperture coincide with the center of the optical axis. If the adjustment is insufficient, the coma remains and the image resolution may be lowered. Furthermore, the adjustment method for canceling coma aberration is complicated, and even when the operation is automated, it is necessary to wait for the adjustment to be completed each time the magnification is changed. It was.

  Further, in the scanning transmission electron microscope equipped with the spherical aberration corrector disclosed in (Non-Patent Document 3), the third spherical aberration is corrected so that the convergence angle component of the electron beam probe is within 25 milliradians within a constant phase. It can be kept within the shift range. That is, under normal observation conditions, the electron beam convergence angle is set to 25 milliradians, and under the aberration-corrected conditions, the diffraction contrast of the low-magnification bright-field image decreases for the same reason as described above. was there.

In the observation using a dark field image, it is not necessary to change the convergence angle depending on the magnification to be observed. However, since the diffraction contrast cannot be extracted in principle in image formation, the interface position of polycrystalline particles is measured. It cannot be used for the purpose.
In order to solve this problem, electro-optical conditions are set so that diffraction contrast can be extracted efficiently for low-magnification images by simply setting the desired observation magnification without the need to operate the converging aperture. Then, a scanning transmission electron microscope apparatus in which electron optical conditions are set so that the contrast of crystal lattice fringes can be extracted efficiently is required.

  In the present invention, the image magnification is determined by a scanning coil for scanning the electron beam probe on the sample surface, and a part of the transmitted electron beam and diffracted electron beam is detected by the electron beam detector installed on the optical axis downstream from the sample. The focus of the electron beam probe is controlled by changing the image magnification and the excitation of the first-stage convergence lens, the second-stage convergence lens, the front magnetic field objective lens, and the aberration corrector while the convergence diaphragm is fixed. Is always matched with the sample, and when the convergence angle of the electron beam probe is set to a low magnification, the diffraction angle corresponding to a specific crystal plane is made smaller to obtain a diffraction contrast. When setting a high magnification, the diffraction angle corresponding to a specific crystal plane is set larger than that to obtain crystal lattice fringes due to phase contrast.

  According to the present invention, when a bright-field image is acquired with a desired contrast and resolution using a scanning transmission electron microscope apparatus, an operation for changing the convergence angle of the electron beam probe by changing the hole diameter of the focusing aperture is required. As a result, the operability of the apparatus is improved and the time spent for observation and analysis can be shortened. In a scanning transmission electron microscope equipped with an aberration corrector that forms an electron beam probe using a large convergence angle, it is possible to prevent a decrease in diffraction contrast in a low-field bright-field image.

  In a scanning transmission electron microscope device, it is possible to obtain an image obtained by extracting contrast based on electron beam diffraction in a low-magnification bright-field image by simply setting the desired image magnification without changing the aperture diameter of the focusing aperture. The configuration of the apparatus and the electron optical conditions that enable acquisition of crystal lattice fringes due to interference of electron beams with a high-magnification bright-field image will be described. In the following description, an embodiment related to a scanning transmission microscope apparatus using an electron beam will be described. However, the present invention can also be applied to an apparatus using an ion beam.

  FIG. 1 is a view for explaining an irradiation electron optical system of a scanning transmission electron microscope apparatus of the present invention. The electron beam generated from the light source 1 is converged by the first-stage convergence lens 3, the second-stage convergence lens 4, and the front magnetic field objective lens 5 to form an electron beam probe having a sub-nanometer diameter on the sample 6. Each of these lenses may be a magnetic field type or electrostatic type rotationally symmetric lens or a multipole lens. A light source is an actual electron beam spot formed by an electron gun composed of an electron source, an electrostatic or magnetic type electron beam extraction electrode, an electrostatic acceleration electrode, or the like, or a virtual image electron beam spot. This means a virtual light source that is defined as an electron gun, a cold cathode field emission electron gun that emits an electron beam without heating the electron source, or a Schottky type that emits an electron beam by heating the electron source. A method such as an electron gun is conceivable. The focusing diaphragm 7 is used for the purpose of adjusting the convergence angle of the electron beam probe on the sample 6, and in this embodiment, has a round hole shape with a hole diameter of about 500 to 10 microns. Here, the shape of the hole may be not only a round hole but also a rectangular hole.

  Further, in FIG. 1, the position of the converging diaphragm 7 is set between the light source 1 and the first stage converging lens 3, but between the first stage converging lens 3 and the second stage converging lens 4 or the second stage. You may install between the converging lens 4 and the front magnetic field objective lens 5. FIG. The first-stage scanning coil 8 and the second-stage scanning coil 9 have a function of controlling the position of the electron beam probe on the sample 6 by deflecting and separating the electron beam from the optical axis 2. Although not shown in the figure, scanning coils having the same function are disposed at positions rotated by 90 degrees in the same plane as the first-stage scanning coil 8 and the second-stage scanning coil 9, respectively. The electron beam probe can be two-dimensionally scanned on the sample 6 by combining the position control of the electron beam probe. Scanning transmission image formation is performed by detecting an electron beam transmitted through the sample 6 in synchronization with the scanning of the electron beam by a detector (not shown) and displaying it as an image having a dynamic range of about 16 bits. The Control of each lens and the scanning coil is performed by the control mechanism 20 of the optical system. The control mechanism 20 of the optical system includes a drive power supply circuit controlled by a CPU, software, and an interface such as a display, a keyboard, a mouse, and a knob that can be controlled by an operator.

  Next, an image magnification setting method using the scanning transmission electron microscope apparatus of the present invention will be described. The image magnification of the scanning transmission image is defined as the ratio between the off-axis distance of the electron beam probe on the sample 6 and the size of the image display. For example, if the total width of the off-axis distance of the electron beam probe on the sample 6 is 10 micrometers and the image display is 100 millimeters wide, the image magnification is 10,000 times. In FIG. 1, the deflection amount 18 on the sample surface at the time of low-magnification image observation and the deflection amount 19 on the sample surface at the time of high-magnification image observation are defined as distances to the optical axis 2, and the image magnification is determined by this distance. Is determined. If the deflection angle by the first-stage scanning coil 8 is increased with the ratio of the deflection angles of the first-stage scanning coil 8 and the second-stage scanning coil 9 being constant, the off-axis distance of the electron beam probe on the sample 6 is increased. . That is, the image magnification can be set stepwise or arbitrarily by controlling the deflection amount on the sample surface by the deflection angle by the first stage scanning coil 8. Further, the position of the area on the surface of the sample 6 where the scanning transmission image is acquired at a predetermined image magnification can be determined by adding the positioning deflection angle to the scanning deflection angle in the first stage scanning coil 8. In general, the condition that the optical axis 2 and the position of the electron beam probe coincide with each other is often displayed as the center of the scanning transmission image.

  Next, a method for changing the convergence angle of the electron beam probe by linking with the image magnification by the scanning transmission electron microscope apparatus of the present invention will be described. The convergence angle of the electron beam probe on the sample 6 can be changed by combining and changing the excitation conditions of the first-stage convergence lens 3, the second-stage convergence lens 4, and the front magnetic field objective lens 5. An example is shown in FIG. When the image point 12 of the first-stage converging lens at the time of low-magnification image observation and the image point 14 of the second-stage convergence lens at the time of low-magnification image observation are formed as conditions for forming the ray diagram 10 at the time of low-magnification image observation Is assumed. In the light ray diagram at the time of high-magnification image observation, an image point 13 of the first-stage converging lens at the time of high-magnification image observation and an image point 15 of the second-stage convergence lens at the time of high-magnification image observation are formed. The focal lengths of the convergent lens 3 and the second stage convergent lens 4 are changed. At this time, the front magnetic field objective lens 5 is controlled so that the focal point coincides with the sample 6. This electron optical condition is set by increasing the exit angle of the electron beam incident on the front magnetic field objective lens 5 from the image point of the second-stage convergent lens, so that the convergence angle 16 with respect to the sample at the time of low-magnification image observation is set to a high-magnification image. It is an example of the method of changing to the convergence angle 17 with respect to the sample at the time of observation. A method in which only the image point of the second stage converging lens is changed without changing the image point of the first stage converging lens between the low magnification and the high magnification, and the focal point is matched with the sample 6 by the front magnetic field objective lens 5. However, the same effect can be obtained. When the operator sets a desired image magnification from the control system 20 of the optical system, the hardware is controlled by the deflection angle by the first stage scanning coil 8, the first stage convergence lens 3, the second stage convergence lens 4, and the front magnetic field objective. The conditions of the lens 5 are output as one parameter set, and are automatically set in the scanning transmission electron microscope apparatus.

  Next, an electron beam detection mechanism for obtaining a bright field image using the scanning transmission electron microscope of the present invention will be described. FIG. 2 shows a ray diagram of an electron beam on the optical axis 2, that is, an axial electron beam, in the electron optical system of the scanning transmission electron microscope. However, the light source 1, the first-stage converging lens 3 and the converging diaphragm 7 are omitted. The electron beam transmitted through the sample 6 is enlarged or reduced by the rear magnetic field objective lens 21 and the projection lens 23. In FIG. 2, it is assumed that an image point 22 of the rear magnetic field objective lens is formed by the rear magnetic field objective lens 21 and an image point 24 of the projection lens is formed by the projection lens 23. A bright field image detector 26 is installed below the projection lens 23, and converts the intensity of the transmitted electron beam into a current or voltage signal. The detector control and image display mechanism 28 converts the image signal into image data having a gradation of about 16 bits in synchronization with the scanning of the electron beam probe on the sample 6 by the control mechanism 20 of the optical system, and transmits the scanned transmission image. Is displayed.

  The detector control and image display mechanism 28 includes hardware and software for performing not only display of an image but also recording of the image on a medium, correction of a contrast change due to temporal fluctuations in the electron beam probe intensity, and noise removal. is doing. The bright field image detection angle limiting stop 27 is installed on the upper stage of the bright field image detector 26, and is used to select and detect a part of the transmitted electron beam. The bright field image detection angle limiting diaphragm 27 has a round hole shape with a hole diameter of about 1 mm to 0.1 mm. Here, the shape of the bright field image detection angle limiting diaphragm 27 may be not only a round hole but also a rectangular hole. The dark field detector 25 is a mechanism for detecting the intensity of the electron beam scattered by the sample 6 and acquiring it as a scanning transmission image on the same principle as the bright field image.

  Next, the detection angle range of the bright field image in the present invention will be described. In FIG. 2, a light ray diagram 10 at the time of low magnification image observation and a light ray diagram 11 at the time of high magnification image observation, the image point 22 of the rear magnetic field objective lens and the projection lens with the electron beam probe formed on the sample 6 as the object point. Are formed at the same point. Therefore, when the bright field image detection angle limiting diaphragm 27 is used, the electron beam detection angle can be controlled to be constant at an arbitrary image magnification regardless of the convergence angle of the electron beam probe on the sample 6. That is, since the intensity of the scanning transmission image observed when changing from low magnification to high magnification does not change, it is not necessary to adjust the gain and offset of the bright field image detector 26 during image observation. Yes.

  Next, the contrast of the low magnification image and the high magnification image in the scanning transmission electron microscope of the present invention will be described. FIG. 3 shows a ray diagram of an on-axis electron beam and an electron beam diffracted by the sample 6 during low-magnification image observation. The ray diagram 31 of the diffracted electron beam emitted in the direction of the diffraction angle 30 by the sample intersects with the optical axis 2 at the image point 22 of the rear magnetic field objective lens and the image point 24 of the projection lens. Axis. If only the on-axis electron beam that has passed through the sample 6 is set to reach the bright field image detector 26 using the bright field image detection angle limiting diaphragm 27, the electron beam probe is located at the location where the crystal exists in the sample 6. In the case of staying, the intensity of the diffracted electron beam is excluded, so that the signal intensity of the bright field detector is reduced and does not decrease in other places. Therefore, the contrast based on the diffraction of the electron beam is reflected in the image intensity in the portion where the crystal is present and the portion where the crystal is not present in the scanning transmission image. In addition, since the intensity of the diffracted electron beam differs depending on the orientation of the crystal grains and the incident direction of the electron beam probe in the polycrystalline portion, each crystal grain has various contrasts when observed. Observed.

  FIG. 4 shows a ray diagram of an on-axis electron beam and an electron beam diffracted by the sample 6 when observing a high-magnification image. The ray diagram 31 of the diffracted electron beam passes through the same path as in the case of the low-magnification image, but since the convergence angle 17 with respect to the sample at the time of high-magnification image observation is larger than the diffraction angle 30 by the sample, Part of the electron beam will overlap. At this time, when a cold cathode field emission electron gun or the like having high coherence is used, the transmission electron beam and the diffracted electron beam form interference fringes at the overlapping portion. This interference fringe reflects the information of the crystal plane that caused diffraction. Here, when the same bright field image detection angle limiting diaphragm 27 as the condition for observing the low magnification image is used, the intensity of the interference fringes included in the interference region 32 is detected by the bright field image detector 26. Since the intensity of the interference fringes reverses the brightness in synchronization with the period of the crystal plane, if the electron beam probe is scanned on the crystal plane, lattice fringes corresponding to the period of the crystal plane are observed in the scanned transmission image. Become. In the present invention, for example, when a magnification of 2 million times or more, which is an image magnification that can distinguish 0.31 nanometers between crystal planes of a silicon (111) plane, is set, the convergence angle 17 with respect to a sample during high magnification image observation is 200 kilovolts. It is automatically set so that the diffraction angle of the silicon (111) surface with respect to the electron beam is larger than 8 milliradians.

  Next, a method for controlling the optical conditions of the scanning transmission electron microscope of the present invention will be described. FIG. 5 is an example of an embodiment relating to a control method for changing the convergence angle and the probe diameter by linking with the image magnification. FIG. 5 (a) operates the first-stage convergence lens 3, the second-stage convergence lens 4 and the front magnetic field objective lens 5 so that the convergence angle increases in proportion to the image magnification in the electron optical system shown in FIG. It is a thing. In order to increase the convergence angle, the current excitation of the first stage convergence lens 3 is increased and controlled so that the image point of the first stage convergence lens approaches the main surface of the first stage convergence lens 3. At this time, the excitation currents of the second stage converging lens 4 and the front magnetic field objective lens 5 can be selected in such a combination that the convergence angle on the surface of the sample 6 has a desired value and the focal point coincides with the sample 6. In actual scanning transmission image observation, it is necessary to observe a higher image resolution with a higher magnification image, that is, using a smaller electron beam probe diameter. The condition that the probe diameter is reduced by the image magnification is the above-mentioned second-stage convergence lens. 4 and the excitation current condition of the front magnetic field objective lens 5, one combination of the first stage convergence lens 3, the second stage convergence lens 4 and the front magnetic field objective lens 5 is determined.

  FIG. 5 (b) controls the convergence angle as shown in FIG. 5 (a), the scanning transmission electron microscope under the condition that the spherical aberration coefficient of the front magnetic field objective lens 5 is 1.3 millimeters and the acceleration voltage of the electron beam is 200 kilovolts. 2 shows an example of probe diameter control that can be realized when the is operated. From FIG. 5, for example, if a gold crystal is observed at a magnification of 2.5 million times or more, the convergence angle is sufficiently larger than 12.3 milliradians of the diffraction angle of the gold (200) surface for an electron beam of 200 kilovolts, and the diameter of the electron probe Since it is smaller than 0.2 nanometer, the lattice fringes of 0.204 nanometer, which is the crystal plane spacing of the gold (200) plane, can be observed. On the other hand, since the convergence angle is smaller than 12.3 milliradians in the low-magnification image and the medium-magnification image of tens of thousands to several hundred thousand times, it becomes possible to extract the diffraction contrast from the gold (200) plane by the scanning transmission image, so The interface and particle interface can be observed with high contrast. Note that there is no problem because the diameter of the electron beam probe is sufficiently smaller than the size necessary for image observation even when observing a low magnification image.

  Next, a method for controlling the above-described electron optical conditions will be described. FIG. 6 shows an embodiment in which a magnetic lens is used as the first-stage convergence lens 3, the second-stage convergence lens 4 and the front magnetic field objective lens 5. Each lens can vary its focal length by changing the current applied to the coil. When the influence of the saturation of the magnetic circuit is small, there is a characteristic that the focal length is shortened when the excitation current is increased, and in order to realize the optical condition shown in FIG. This can be realized by increasing the energization amount of the stage convergence lens 3 and decreasing the energization amount of the second stage convergence lens 4. The focal length of the front magnetic field objective lens 5 is normally operated with a short focus of about 2 millimeters, and the change amount of the excitation current can be dealt with with respect to the change of the image point of the second stage converging lens. When the image magnification is set, the energization amount of each lens is determined by a data table or a calculation formula and is controlled so as to be automatically set in the scanning transmission electron microscope apparatus. There is no need to adjust. In addition, a plurality of tables or calculation formulas for changing the convergence angle are prepared, and an operator can select a desired contrast according to the sample to be observed. Furthermore, the operator can select whether or not the image magnification link function of the irradiation angle is executed by software or a hardware switch, and the contrast and information desired by the operator can be selected at any magnification. A scanning transmission image including this can be acquired. This control is a control method in which different data tables or calculation formulas are referred to by turning on / off the image magnification link, and also has a function of storing data freely created by the operator.

  Next, FIG. 7 shows examples of low and high magnification images taken using the scanning transmission electron microscope apparatus of the present invention. FIG. 7A is a low-magnification bright-field scanning transmission image observed under electro-optic conditions with a large convergence angle in order to observe crystal lattice fringes at a high magnification. The sample is a silicon device, and polycrystalline tungsten silicide (Poly-WSi) in the wiring part is observed with a black contrast, and the shape can be distinguished, but other components such as a silicon substrate and a silicon oxide film The boundary with (SiO) is not clear and its shape cannot be evaluated. This is a problem of the conventional scanning transmission electron microscope apparatus. In many cases, the problem is solved by adjusting the convergence angle of the electron beam probe by changing the hole diameter of the convergence aperture according to the observation magnification. However, it is necessary to adjust the center position of the converging aperture hole mechanically or electrically so as to coincide with the center of the optical axis, and it is necessary for the operator to perform driving operation and adjustment of the aperture whenever the magnification is changed. This impedes rapid device failure analysis.

  In addition, it is necessary to accurately determine the position of the optical axis when centering the converging aperture. However, it is difficult for a highly skilled operator to determine the exact optical axis position from the scanned transmission image, and the desired image can be obtained. There is a case where the scanning transmission image cannot be observed with the resolution. On the other hand, FIG. 7B is a low-magnification bright-field scanning transmission image obtained by applying the electron optical system of Example 1 shown in FIG. 1 to a scanning transmission electron microscope apparatus. The polycrystalline tungsten silicide (Poly-WSi), polycrystalline silicon (Poly-Si), silicon nitride film (SiN), silicon oxide film (SiO) and silicon substrate (Si-substrate) constituting the device can be identified from the image contrast. In addition, crystal grains are observed at different contrasts in the polycrystalline tungsten silicide (Poly-WSi) and polycrystalline silicon (Poly-Si) parts. it can. Furthermore, FIG. 7 (c) observed the interface portion between the silicon oxide film (SiO) and the silicon substrate (Si-substrate) by performing only the operation of increasing the image magnification without performing the operation of the converging diaphragm. Is. In this image, lattice fringes with an interval of 0.31 nanometers corresponding to the silicon (111) crystal plane are observed, and information on the atomic arrangement at the interface can be obtained.

  Next, a method of changing the convergence angle of the electron beam probe by linking with the image magnification by the scanning transmission electron microscope apparatus when the irradiation electron optical system includes an aberration corrector will be described. FIG. 8 is a diagram showing the first embodiment. In this embodiment, the aberration corrector 40 is disposed between the second stage converging lens 4 and the first stage scanning coil 8, but the aberration corrector 40 includes the first stage converging lens 3 and the second stage converging lens. 4 and the case where it arrange | positions between the light source 1 and the 1st step | paragraph convergent lens 3 are also considered. The aberration corrector 40 is a function for correcting spherical aberration generated in each converging lens and the front magnetic field objective lens 5, a function for correcting chromatic aberration due to the energy distribution of electron beams, and correcting on-axis parasitic aberrations such as astigmatism. It is used for the purpose of improving the image resolution by reducing the electron beam probe to a smaller size. The method of changing the convergence angle of the electron beam probe according to the image magnification is the same as in the embodiment shown in FIG. 1, and the current excitation of the first-stage convergence lens 3 and the second-stage convergence lens 4 is performed by changing the image magnification. To do. Further, the object point of the aberration corrector 40 coincides with the image point 14 of the second stage converging lens 4 at the time of low-magnification image observation during low-magnification image observation, and the object point of the aberration corrector 40 at the time of high-magnification image observation. The aberration corrector 40 is controlled by the control mechanism 20 of the optical system so as to coincide with the image point 15 of the second stage converging lens 4 at the time of low-high magnification image observation.

  Finally, the front magnetic field objective lens so that the image point 41 of the aberration corrector when observing the low magnification image and the image point 42 of the aberration corrector when observing the high magnification image are in focus on the sample 6 under the respective magnification conditions. 5 is controlled by adjusting the excitation condition. Also, the aberration corrector 40 controls the position of the intermediate image point 43 of the aberration corrector to be fixed regardless of the image magnification, and the reduction rate of the electron beam probe by the aberration corrector 40 is constant regardless of the image magnification. 1 can be applied without changing the excitation current control value of each lens used in the embodiment of FIG. In this electro-optical condition, the convergence angle with respect to the sample 6 changes in proportion to the reduction rate of the electron beam probe by the aberration corrector 40. Therefore, the reproduction of the electro-optical condition shown in FIG. This can be realized by setting the reduction ratio of the electron beam probe to 1 time. Further, when the reduction ratio of the electron beam probe by the aberration corrector 40 cannot be set to 1 time, the hole diameter of the converging diaphragm 7 may be changed and fixed without depending on the image magnification.

  Next, an example in which the present invention is applied to a scanning transmission electron microscope apparatus including an aberration corrector will be described. The electron optical conditions set in this embodiment are linked to the image magnification, and the convergence angle of the electron beam probe on the sample 6 is changed by the first stage converging lens, and the image point of the second stage converging lens is fixed. Is. Under this condition, the object point 44 of the aberration corrector is at a constant position regardless of the image magnification, so that it is not necessary to change the driving condition of the aberration corrector 40 in conjunction with the image magnification, and the aberration corrector 40 is operated in a steady state. Therefore, there is an advantage that the aberration correction operation is stabilized. In addition, since it is not necessary to change the condition of the aberration corrector 40 according to the image magnification, the image point 45 of the aberration corrector is always at a fixed position, so that the excitation condition of the front magnetic field objective lens 5 need not be changed according to the magnification. . This is an advantage in the stable operation of the front magnetic field objective lens 5.

The figure showing the off-axis distance and convergence angle of an electron beam at the time of performing low magnification and high magnification image acquisition. The figure showing the detection angle range of the electron beam at the time of the image acquisition of a low magnification and a high magnification. The figure showing the setting method of the position on the detector diaphragm surface of a transmission electron beam and a diffraction electron beam at the time of low-magnification image acquisition, and a detection angle range. The figure showing the setting method of the position on the detector aperture plane of a transmission electron beam and a diffraction electron beam at the time of high magnification image acquisition, and a detection angle range. The figure showing the control method of the convergence angle and electron beam probe diameter in this invention. The figure showing the control method of the convergence lens current and objective lens current in this invention. The figure showing the comparison of the low magnification image in case a convergence angle is large, the low magnification image by this invention, and the high magnification image. The figure showing the off-axis distance and convergence angle of the electron beam in a 1st Example. The figure showing the off-axis distance and convergence angle of the electron beam in a 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Optical axis, 3 ... 1st stage | paragraph convergent lens, 4 ... 2nd stage | paragraph convergent lens, 5 ... Front magnetic field objective lens, 6 ... Sample, 7 * ..Convergent stop, 8... First stage scanning coil, 9... Second stage scanning coil, 10... Ray diagram when observing low magnification image, 11. , 12: Image point of the first-stage converging lens when observing a low-magnification image, 13: Image point of the first-stage converging lens when observing a high-magnification image, 14: 2 when observing a low-magnification image Image point of stage convergence lens, 15... Image point of second stage convergence lens during high magnification image observation, 16... Convergence angle with respect to sample during low magnification image observation, 17. Angle of convergence with respect to the sample at the time, 18... Deflection amount on the sample surface during low magnification image observation, 19... Deflection amount on the sample surface during high magnification image observation, 20. System Mechanism: 21 ... Post magnetic field objective lens, 22 ... Image point of the back magnetic field objective lens, 23 ... Projection lens, 24 ... Image point of the projection lens, 25 ... Dark field image detector, 26 ... Bright field image detector, 27 ... Detection angle limiting stop for bright field image, 28 ... Detector control and image display mechanism, 30 ... Diffraction angle by sample, 31 ... Diffraction electron Ray diagram of line, 32... Interference region, 40... Aberration corrector, 41... Image point of aberration corrector when observing low-magnification image, 42. 43, an intermediate image point of the aberration corrector, 44, an object point of the aberration corrector, 45, an image point of the aberration corrector.

Claims (5)

An electrostatic lens that accelerates the electron beam generated from the electron beam source to a predetermined voltage;
A converging lens that converges the electron beam;
A convergence stop for determining a convergence angle of the electron beam;
A deflection coil for scanning the electron beam;
An objective lens;
An aberration corrector;
An electron beam detecting means for irradiating the sample with the electron beam and detecting a transmitted or diffracted electron beam to form a scanning transmission image;
Display means for displaying the scanning transmission image,
The scanning transmission image in accordance with the image magnification of changing the convergence angle of the electron beam, a scanning transmission electron microscope, characterized in that it comprises means Ru switches the acquisition of diffraction contrast or crystal lattice stripes. The scanning transmission electron microscope apparatus according to claim 1,
Said toggle its means, the condenser aperture the focusing lens in a fixed state, the scanning transmission electron microscope, wherein the is an objective lens, and control means for controlling the excitation condition of the aberration corrector. The scanning transmission electron microscope apparatus according to claim 2,
The control means stores a table or calculation formula with the observation image magnification as a variable as an excitation condition for the convergent lens, objective lens, and aberration corrector. With reference to the table or calculation formula, the convergence lens, objective lens, and A scanning transmission electron microscope apparatus characterized by energizing an aberration corrector. The scanning transmission electron microscope apparatus according to claim 2,
The control means stores a plurality of tables or calculation formulas using the observation image magnification as a variable as excitation conditions for the convergent lens, objective lens, and aberration corrector. Refer to the table or calculation formula selected by the operator. A scanning transmission electron microscope apparatus characterized by energizing the focusing lens, the objective lens, and the aberration corrector. The scanning transmission electron microscope apparatus according to claim 1,
A scanning transmission electron microscope apparatus, wherein the aberration corrector has a function of correcting spherical aberration, chromatic aberration, astigmatism, coma aberration, star aberration, leaf aberration, field curvature aberration, and distortion aberration.