JP5970648B2 - Transmission electron microscope and electron beam interferometry - Google Patents

Description

  The present invention relates to a transmission electron microscope and electron beam interferometry. More specifically, the present invention relates to a transmission electron microscope apparatus and an electron beam interferometry method that obtain an interference microscope image by fine specimen movement.

In order to obtain an interference microscope image using a transmission electron microscope, a method is used in which an electron beam is split into two using an electron biprism, and the two beams are crossed to interfere with each other. A commonly used electron biprism is an electron optical element that has the same action as a Fresnel biprism in optics in an electron beam optical system. A device that uses a potential to deflect an electron beam is called an electric field type biprism, and a device that uses the Lorentz force between a magnetic field and an electron beam is called a magnetic field type electron biprism, and the electric field type is widely used. Yes.
In this specification, a case where an electric field type biprism is used as an electron beam biprism will be described. However, an apparatus that can cause an electron beam to interfere as an electron beam biprism depends on the electric field type and the magnetic field type. However, the present invention is not limited to the electric field type electron biprism used in the following description.

  In addition, as a definition of technical terms used in this specification, a microscope image means a normal image obtained by enlarging, a phase image indicates a phase distribution of an electron beam transmitted through a sample, and an interference microscope image indicates a phase image. It means what is represented by a cos function, that is, what represents a phase distribution as interference fringes.

(Preparation of interference microscope image)
A known electron biprism interferometer using a transmission electron microscope used for producing an interference microscope image will be described.
FIG. 6 is a schematic diagram of a general electric field type electron biprism, and FIG. 7 is a schematic diagram showing an example of an optical system of a conventional electron biprism interferometer.
As shown in FIG. 7, in the electron beam biprism interferometer, the electron beam generated by the electron source or the electron gun 1 is irradiated to the sample 3 via the irradiation optical system 4 on the optical axis 2. The most common electron beam interferometer represented by electron beam holography has an electron beam biprism 90 composed of a center fine wire electrode 91 and a pair of grounded parallel plate type ground electrodes 99 on the optical axis 2. And between the objective lens system 5 and the image plane 71 of the sample 3. Reference numeral 11 denotes a light source image (crossover) formed by the objective lens system 5.

  In the electron optical system, a magnetic field type electromagnetic lens is normally used as the electron lens. Therefore, the path of the electron beam includes rotation about an axis parallel to the optical axis 2 as shown in FIG. The same plane is described as the electron optical system, ignoring the rotation of the electron beam. The same applies to the subsequent optical systems.

  As shown in FIG. 6, the electric field type electron biprism 90 includes a central fine wire electrode 91 at the center and a pair of parallel plate type ground electrodes 99 that are held in parallel and sandwiched between the electrodes. Composed. By applying a positive or negative voltage to the central fine wire electrode 91, the transmitted electrons can be deflected. FIG. 6 shows a case where a positive potential is applied to the central microwire electrode 91, and electron beams passing near the central microwire electrode 91 are deflected in a direction facing each other by the central microwire potential (electrons). Line trajectory 27). A plane 22 is drawn perpendicularly to the electron trajectory 27 in FIG. 6. This is an equiphase surface when expressing the electron beam as a wave, and is generally a plane perpendicular to the electron orbit. Called the wavefront.

  As the distance from the central fine wire electrode 91 increases, the potential acting on the electron beam becomes smaller, but the acting spatial range becomes longer. As a result, the deflection angle of the electron beam does not depend on the incident position. Proportional to applied voltage. That is, only the propagation direction is deflected while the plane wave is a plane wave, and the electron beam biprism 90 is emitted. This is called an electron biprism 90 because it corresponds to the effect of a biprism in which two prisms are optically combined.

  The electron beam biprism 90 has a function of separating the wavefront 22 of one electron beam into two waves and deflecting the wavefront 22 in a direction facing each other, whereby an electron beam that has passed through the electron beam biprism 90 and separated into two waves is The interference fringes 8 are superimposed behind the electron biprism 90 and drawn with a solid line in FIG. Such an electron optical system is generically called an electron beam interference optical system. Further, the interval between the interference fringes 8 observed here is inversely proportional to the voltage applied to the central microwire electrode 91, and in order to obtain a high spatial resolution, it is necessary to use the interference fringes 8 with a fine interval by applying a high voltage. On the other hand, when the interval between the interference fringes 8 is made fine, restrictions on the coherence of the electron beam become conspicuous and the interference fringes 8 are blurred. Therefore, it is necessary to use an appropriate fringe interval. This fringe interval is called a carrier spatial frequency.

  Details of electron beam holography for reproducing electron wave phase information from an interference image are disclosed in Non-Patent Document 1, for example.

  An electron beam transmitted through the sample 3 by applying a positive voltage to the central fine wire electrode 91 (object wave 21: in FIG. 7, the electron beam passing through the left side of the central fine wire electrode 91 is hatched. ) And an electron beam transmitted through the side without the sample 3 (reference wave 23: an electron beam passing through the right side of the central fine wire electrode 91 in FIG. 7) are superposed on each other to obtain an interference microscope image (31 and 8: interference with the sample image 31). An image in which stripes 8 are superimposed is obtained. That is, the phase change that the sample 3 gives to the wavefront of the object wave 21 is recorded as the modulation of the superimposed interference fringe 8. The interference fringes 8 are recorded using a film or a detector such as a two-dimensional CCD camera, and phase information of an electron beam transmitted through the object is extracted by a Fourier transform method or a fringe scanning method described later.

  The positioning of the sample 3 and the central microwire electrode 91 is performed not only by the fine movement mechanism of the sample 3 but also by the moving mechanism and rotating mechanism of the electron biprism 90. Thereby, as shown in FIG. 7, the object wave 21 and the reference wave 23 can be divided on the left and right of the optical axis 2. This operation is one of the general operation tasks for electron beam interference, and is assumed to be performed in the present invention.

  In the one-stage electron biprism interferometer, Fresnel fringes due to the diffracted wave generated at the end of the central fine wire electrode 91 are included on the left and right in the interference microscope image. This is generally the source of artifacts that are most problematic for interference microscopic images because the contrast is generally strong and the fringe spacing is distributed over a wide spatial frequency band from wide to narrow. For this reason, it is desirable that the phase information of the interference image is removed during image processing, or the electron optical system is devised so as not to generate Fresnel fringes. As an example of this contrivance, there is a two-stage electron biprism interference optical system that uses electron biprism 90 in two upper and lower stages. However, since it relates to the basic design of the apparatus, it is necessary to incorporate it from the beginning of the design. It has not spread. A two-stage electron biprism interference optical system capable of almost arbitrarily controlling the interval between the interference fringes 8 and the interference region width is disclosed in detail in Patent Document 1 and Non-Patent Document 2.

(Phase information extraction: Fourier transform method)
Next, a method for extracting phase information recorded in the interference microscope image will be described. As a method for extracting phase information, laser light has been used as a holographic image reproduction method, but with the recent development of computer technology, it has been performed as part of image processing using a computer. Among them, the Fourier transform method in which the reproduction method by the laser optical system is directly transferred to a computer is dominant.

FIG. 8 shows this reproduction procedure. FIG. 8 is a schematic diagram showing images in steps (a) to (f) of the phase reproduction method by the Fourier transform method.
FIG. 8A is an interference microscope image, and FIG. 8B is a Fourier transform image of FIG. In FIG. 8A, the white distribution at the center of the image is the power spectrum 75 of the sample image, and the two sidebands 76 in the direction (left and right) orthogonal to the stripes contain the phase information. (First-order diffracted wave) and its conjugate wave (-1st-order diffracted wave). FIG. 8C shows an image obtained by selecting one of the two side bands 76 and moving it to the center of the image. The inverse Fourier transform of FIG. 8C is performed, and an amplitude distribution image (FIG. 8D) and a phase distribution image (FIG. 8E) can be obtained from the real part and the imaginary part of the calculation result, respectively.

  When a phase distribution image is clearly shown as an interference microscope image, a reference wave 23 is given again to form an interference image, and for example, the phase distribution may be displayed as an equiphase line in another direction as shown in FIG. . In any case, in the Fourier transform method, it is necessary to separate the power spectrum 75 and the sideband 76 of the sample image from the Fourier transform image (FIG. 8B), and the interval between the interference fringes 8 is the reproduced image (amplitude distribution). The spatial resolution of the phase distribution is determined (Non-Patent Document 5). In addition, the reproduction uses a Fourier transform multiple times, which is an obstacle to real-time observation.

(Flying scanning method)
An interference microscope image by an electron beam is composed of an image and interference fringes 8, so that a fringe analysis method can be used. In principle, a phase information extraction method (fringe scanning method, moire method, etc.) different from the Fourier transform method is used. Is possible. In particular, the fringe scanning method that controls the phase of the interference fringe 8 using the relative phase difference between the object wave 21 and the reference wave 23 can increase the resolution in that the spatial resolution of the reproduced image does not depend on the interference fringe interval. Is the method. The fringe scanning method is described in detail in, for example, Patent Document 2, Patent Document 3, Non-Patent Document 3, and Non-Patent Document 4.

  The principle of the fringe scanning method is that M interference microscope images are recorded while shifting the relative phase difference between the object wave 21 and the reference wave 23 by (2π) / M, and the mth intensity distribution of the plurality of images is represented by I ( x, y; m), the phase distribution Φ (x, y) and the amplitude distribution A (x, y) of the object wave 21 are obtained based on the following formulas (1) and (2).

  Since the contrast modulation (sinusoidal curve) accompanying the modulation of the relative phase difference must be determined, the number of images M is limited to 3 or more.

  When the basic interference fringes are present in the image as in the electron beam interference microscope image, the expression (1) is slightly changed to become the following expression (3).

  Here, Rx is a spatial frequency (carrier spatial frequency) of the basic interference fringes, and the interference fringes 8 are assumed to be arranged in the x-axis direction. The basic interference fringes 8 are caused by the relative angles of the two electron waves, and the phase distribution represents a linear inclination in the x-axis direction and can be easily corrected.

Next, the procedure of the fringe scanning method is shown in FIG.
9A shows the first interference microscope image, and FIG. 9B shows the second interference microscope image obtained by shifting the relative phase difference between the object wave 21 and the reference wave 23 by 2π / 3 from the interference image of FIG. (C) is a third interference microscope image in which the relative phase difference is further shifted by 2π / 3 (4π / 3 from (a)) than the interference image of (b). An amplitude distribution image A (x, y) and a phase distribution image Φ (x, y) can be obtained by performing image processing based on the equations (3) and (2) for these three interference microscope images. it can. The number of interference microscope images to be used is the minimum number in the case of three as in the example of FIG. 9, and does not depend on the number of images in the case of three or more. Since the interference microscopic image (FIGS. 9B and 9C) having the interference fringes 8 filling between the interference fringes 8 in FIG. 9A is used, the spatial resolution by this method is interference. High resolution can be achieved without depending on the stripe interval.

FIG. 9 is a schematic diagram showing the positional relationship between the fringes of the first to third interference microscope images acquired by the fringe scanning method.
In the fringe scanning method shown in FIG. 9, the relative phase difference between the object wave 21 and the reference wave 23 must be controlled in the process of creating an interference image, and then the interference microscope image is observed and recorded. Since the phase information is extracted after the relative phase difference is known, the interference microscopic method requires a higher level of work than the Fourier transform method. Therefore, it has not yet spread widely. In particular, in the electron optical system, a method for controlling the relative phase difference between the object wave 21 and the reference wave 23 with high accuracy has not been put into practical use. The electron biprism 90 is connected to the optical axis 2 and the central microwire electrode 91. A method of moving in a direction perpendicular to both directions (in FIG. 7, the left-right direction of the paper) (this is called Conventional Method 1; see Patent Document 3), and the incident angle of the electron beam to the sample 3 is determined by the electron biprism 90. A method of changing the deflection applied to the line in the same plane in terms of electro-optics (this is called the conventional method 2; see Non-Patent Document 3) has been tried.

  In order to realize the fringe scanning method in the electron beam interferometer, a method of modulating only the relative phase difference between the object wave 21 and the reference wave 23 is required. However, although there are methods tried as described above, there is no method that has been put to practical use with high accuracy.

(Conventional method 1)
The electron biprism 90 is moved in a direction perpendicular to both the optical axis 2 and the central fine wire electrode 91. In this method, the electron biprism 90 is required to have the same fine movement accuracy as the sample fine movement mechanism, but a general electron biprism apparatus does not satisfy the required level.

(Conventional method 2)
The incident angle of the electron beam on the sample 3 is changed in the same plane as the deflection that the electron beam biprism 90 applies to the electron beam. This method is based on the premise that the electron beam is shifted from the optical axis 2, and the influence of aberration included in the image differs for each acquired image in high-resolution image observation or the like. For this reason, the method itself is inappropriate depending on the required resolution and the purpose of observation of the interference microscope image. Further, depending on the experimental conditions (high-resolution observation or Lorentz image observation), it is necessary to manipulate the amount of defocus. When using an out-of-focus amount according to the experimental conditions, if the incident electron beam on the sample 3 is tilted, the projection image changes in position, so that image processing for aligning the position of the sample 3 after acquiring the interference image is performed. Is required and lacks real-time capability.

  Further, when the conventional methods (1) and (2) are executed with the conventional electron interferometer shown in FIG. 7, the Fresnel fringes superimposed on the interference image also change at the same time. This is included in the reconstructed image as a new artifact, and has the disadvantage that the accuracy as expected from the principle of the fringe scanning method cannot be obtained.

JP 2005-197165 A International publication WO 01/75394 A1 Japanese Patent Laid-Open No. 11-15359

A. Tonomura: Electron Holography, 2nd ed. (Springer, Heidelberg. Germany, 1999), Chapter 5. Ken Harada, Akira Tonomura, Yoshihiko Togawa, Tetsuya Akashi and Tsuyoshi Matsuda: Applied Physics Letters, "Double-biprism electron interferometry", Vol. 84, (2004), PP 3229-3231 Q. Ru, J. Endo, T. Tanji and A. Tonomura: Applied Physics Letters, "Phase-shifting electron holography by beam tilting", Vol. 59, (1991), PP 2372-2374. Ken Harada, Keiko Ogai and Ryuichi Shimizu: Journal of Electron Microscopy, "The Fringe Scanning Method as Numerical Reconstruction for Electron Holography", Vol. 39, (1990), PP 470-476. Volkl E and Lichte H (1990) Electron holograms for subangstrom point resolution.Ultramicroscopy 32: PP 177-180

  From the above, the actual situation is that a method and means for controlling the relative phase difference between the object wave 21 and the reference wave 23 effective for carrying out the fringe scanning method in the electron beam interferometer and an apparatus therefor have not yet been realized. Met.

  In view of the above-mentioned problems, the present invention can extract the phase of an object wave close to real time, the spatial resolution of the reproduced image can be increased without depending on the interference fringe interval, and the phase can be extracted with high accuracy. A first object is to provide an electron microscope as an electron beam interference device, and a second object is to provide an electron beam interference method.

  In order to achieve the first object, a transmission electron microscope of the present invention includes an electron biprism, a sample holding device capable of finely moving the sample in at least one direction within a plane perpendicular to the optical axis, An electron beam detector comprising a plurality of electron detection elements arranged in a line on a microscope image observation recording surface where an electron beam interference fringe formed by an image and an electron beam biprism is observed A scanning electron microscope that outputs the signal intensity of the electron detection element along an axis determined by the arrangement direction of the element and changes the electron detection element by finely moving the sample by a predetermined distance by a finely movable sample holding device Are sequentially output along with the fine movement of the sample in the direction perpendicular to the axis defined by the element arrangement direction, thereby obtaining a microscopic image as a two-dimensional signal intensity distribution.

In the above configuration, preferably, the image processing apparatus includes an arithmetic device for image processing of a microscope image obtained from the electron beam detector, and a display device for displaying an image processing result.
Preferably, an electron beam interference fringe is formed by superimposing on the sample image by the electron biprism, whereby an interference microscope image is obtained as a microscope image.
Preferably, by using an arithmetic device, a phase distribution image of the electron beam is calculated from the interference microscope image and displayed on the display device.
The fine movement direction of the sample by the sample holding device is preferably perpendicular to the electron detection element array as the moving direction of the sample image on the microscope image observation recording surface.
The electron beam interference fringes formed on the microscopic image observation recording surface are preferably parallel to the element rows constituting the electron detection element device.
Preferably, by providing at least three electron beam detectors in which columns formed by the arrangement of the electron detection elements are parallel to each other on the image observation recording surface, an interference microscope image is individually obtained from each electron beam detector. Can be obtained.
Preferably, by using an arithmetic unit, a phase distribution image of an electron beam is calculated from a plurality of interference microscope images obtained individually from each electron beam detector and displayed on a display device.

  In order to achieve the second object, the electron beam interference method of the present invention includes an electron beam biprism, a sample holding device capable of finely moving the sample in at least one direction within a plane perpendicular to the optical axis, Transmission electron comprising: an electron beam detector comprising a plurality of electron detection elements arranged in a line on a microscope image observation recording surface where an electron beam interference fringe formed by an image and an electron beam biprism is observed An electron beam interference method using a microscope, in which an image of a sample and electron beam interference fringes are superimposed on an image observation recording surface, and the signal intensity of an electron detection element is along an axis determined by the arrangement direction of the element The signal intensity from the electron detection element, which is changed by finely moving the sample by a predetermined distance by a finely movable sample holding device, is sequentially applied along with the fine movement of the sample in the direction perpendicular to the axis defined by the element arrangement direction. To output Ri, characterized in that to obtain an interference microscope image to obtain the two-dimensional signal intensity distribution.

In the above configuration, preferably, an electron microscope phase distribution image is obtained by performing arithmetic processing on the interference microscope image.
Preferably, the image observation recording surface includes at least three electron beam detectors in which columns formed by the arrangement of the electron detection elements are parallel to each other, and an interference microscope image is individually obtained from each electron beam detector. .
Preferably, a phase distribution image of the electron beam that has passed through the material is obtained by arithmetic processing of a plurality of interference microscope images obtained individually using the respective electron beam detectors.

  According to the transmission electron microscope of the present invention, in addition to the biprism in the conventional electron beam biprism interferometer, the sample holding device provided with the sample fine movement mechanism finely moves the sample by a predetermined distance, while By observing the change in the intensity of the interference fringes with the detector, it is possible to obtain an interference microscope image without limiting the resolution due to the carrier spatial frequency and by simply rearranging the obtained data.

  According to the electron beam interferometry of the present invention, when acquiring the interference fringes, the sample position is finely moved with high accuracy, while the one-dimensional detector or the two-dimensional detector on the line is used at a specific location of the interference fringes. Since the intensity is acquired, the relative phase difference between the object wave and the reference wave can be detected with high accuracy.

It is a figure which shows typically the structural example of the transmission electron microscope of this invention. It is a schematic diagram of an interference fringe and a phase image obtained by the interference fringe measuring method of the present invention. It is a schematic diagram of the image recording apparatus used for the interference fringe measuring method of the present invention. It is a figure which shows a series of results of the experiment conducted in the 1st Example of this invention. It is a figure which shows a series of results of the experiment conducted in the 2nd Example of this invention. It is a schematic diagram which shows the relationship between a general electric field type | mold electron biprism and a wave front. It is a schematic diagram which shows the example of the optical system of the conventional electron beam biprism interferometer. It is a schematic diagram which shows the image in each procedure (a)-(f) of the phase reproduction method by a Fourier-transform method. It is a schematic diagram which shows the positional relationship of the fringes of the 1st-3rd interference microscope image acquired by the fringe scanning method.

Embodiments of the present invention will be described below with reference to the drawings.
(Transmission electron microscope)
FIG. 1 is a diagram schematically showing a configuration example of a transmission electron microscope 40 of the present invention.
As shown in FIG. 1, the transmission electron microscope 40 includes an electron source 1, an irradiation optical system 4, an objective lens system 5, an imaging lens system 7, an electron biprism 90, and a sample 3 with an optical axis. 2, a sample holding device 13 capable of fine movement in at least one direction within a plane perpendicular to 2, an electron detection element 36 (see FIG. 3), an image recording device 9, a sample fine movement control device 10, an arithmetic processing device 12, etc. It is configured to include. The transmission electron microscope 40 is an apparatus that is assumed to be used in the electron beam interferometry of the present invention, but the present invention is not limited to the configuration shown in FIG.

  The electron gun serving as the electron source 1 is located at the most upstream part in the direction in which the electron beam flows, and the electron beam irradiates the sample 3 placed on the sample holding device 13 having a fine movement function through the irradiation optical system 4. Is done. The electron beam transmitted through the sample 3 is imaged by the objective lens system 5. This imaging action is taken over by the imaging lens system 7 composed of a plurality of lenses downstream of the objective lens system 5 in the traveling direction of the electron beam, and finally forms an image on the observation recording surface 89 of the electron beam apparatus. . The image is recorded in an image recording device 9 such as a CCD camera. An image of the sample 3 imaged by the imaging lens system 7 is indicated by reference numeral 32.

  The electron detection elements 36 (see FIG. 3) are arranged in a line on the microscope image observation recording surface 89 where the image of the sample 3 and the electron beam interference fringes formed by the electron biprism 90 are observed. If necessary, a plurality of electron detection elements 36 may be provided.

The expression system is used for the irradiation optical system 4, the objective lens system 5, and the imaging lens system 7. However, these optical systems not only have a plurality of lenses, but also provide sufficient optical performance. In this case, there is no problem even if it is composed of a single lens.
Here, in the present invention, examples of the optical axis 2 of the transmission electron microscope 40 are the optical axis of the irradiation optical system 4, the optical axis of the objective lens system 5, and the optical axis of the electron optical system such as the imaging lens system 7. A single axis may be used.

  The electron biprism 90 is located downstream of the objective lens system 5.

  Hereinafter, specific configurations and methods for carrying out the present invention will be described. Here, for convenience of explanation, the discussion will be made assuming that the electron biprism 90 is an electric field type, but this is not related to the essence of the present invention, and there is no problem even if it is a magnetic type. Further, although the discussion proceeds assuming that the electron biprism 90 is a single-stage prism, there is no problem even if there are two or more stages regardless of the essence of the present invention.

Next, the principle of detecting the relative phase difference of the object wave 21 transmitted through the sample 3 with respect to the reference wave 23 by the interference fringe measurement method of the present invention will be specifically described.
In FIG. 1, the sample 3 is held by a finely movable sample holding device 13 while being controlled by the control device 10. In the present invention, the sample 3 is finely moved by using a sample holding device provided with a fine movement mechanism using a piezoelectric element (piezo element). However, any method can be used as long as the apparatus can be finely moved while controlling the sample position. .

  The electron beam emitted from the electron gun 1 is irradiated to an area including the sample 3 after the brightness and parallelism of the electron beam are adjusted by an irradiation optical system 4 including one or more electric or magnetic lenses. Interference fringes 8 (see FIG. 2) are created by one or more electron biprisms 90 magnified by the objective lens system 5 and arranged downstream in the traveling direction of the electron beam. At this time, the interference fringes 8 are appropriately enlarged and projected onto the observation recording surface 89 by the imaging lens system 7 composed of one or more electric or magnetic lenses. Image recording using a one-dimensional electron beam detector 37 composed of a plurality of electron detection elements 36 in which the obtained interference fringes 8 are arranged in a row, or a two-dimensional electron beam detector 38 in which a plurality of columns are arranged. Record by device 9.

  In a specific example to be described later in the embodiment of the present invention, a CCD camera capable of acquiring two-dimensional image data is used as the electron beam detection device, but this is not an essential requirement for the present invention. If it is a detector arranged in a shape, there is no problem.

  By sequentially outputting the signal from the image recording device 9 along with the fine movement of the sample 3, a microscopic image is obtained as a two-dimensional signal intensity distribution. Although the fine movement direction of the sample 3 is a direction perpendicular to the direction of the stripes, the image of the sample 3 is aligned with respect to a component parallel to the fine movement stripes in any direction, and the fine movement stripes are obtained. This can be done in the same way by making the vertical component an effective amount of fine movement.

  The interference microscope images obtained individually from the image recording device 9 are image-processed by the arithmetic processing device 12 and displayed on the display device 14 as a phase distribution image of an electron beam transmitted through the measurement sample 3.

FIG. 2 is a schematic diagram of an interference fringe 8 and a phase image obtained by the interference fringe measuring method of the present invention.
2A to 2D schematically show the interference fringes 8 obtained in FIG. 1 when the sample 3 is finely moved. Further, in this schematic diagram, the sample 3 is finely moved in the direction perpendicular to the direction of the interference fringes 8 (in the horizontal direction of the drawing), and the interference fringes 8 created thereby are represented by black lines. Actually, the intensity of the dark part represented by the black line and the bright part represented between the black lines are not continuously changing from black to white, but continuously changing. Here, the detector detects the intensity on the line.

  Since the phase of the electron beam transmitted through the sample 3 changes depending on the potential or magnetic field of the sample 3, the position of the interference fringes 8 also changes. Since the sample position in the interference fringe 8 is changed by the operation of the fine movement of the sample 3 which is characteristic of the present invention, the position where the fringe is shifted is also displaced in accordance with the fine movement of the sample 3. When the intensity of the obtained interference fringe 8 on an arbitrary column 34 is detected by a one-dimensional detector, the fringe shift occurs at a corresponding position in accordance with the movement of the sample 3, so that the detected intensity changes. By arranging these one-dimensional intensities at positions corresponding to the sample positions, changes in the electron beam phase due to the sample 3 not including fringes of the carrier spatial frequency can be obtained as an interference microscope image represented by equiphase lines. Further, at this time, the phase reproduction by the fringe scanning method can be performed by using the intensity of three or more different rows (35 in FIG. 2) on the interference fringes 8 in total.

This is shown by the following formula. When a plane wave is incident on the sample 3, an electron beam transmitted through the sample 3 (hereinafter referred to as object wave 21) and a wave transmitted through a region other than the sample 3 (hereinafter referred to as reference wave 23) are respectively represented by the following formula (4): , Expressed as equation (5).

Here, the x axis is the direction perpendicular to the stripe, the y axis is the direction parallel to the stripe, φ ₀ and η are the amplitude and phase of the object wave 21, m is the reciprocal of the carrier spatial frequency, and the interference fringe 8 Represents an interval. Since the interference image obtained by the interference fringes 8 shown in FIG. 1 is expressed by the square of the sum of Expression (4) and Expression (5), the following Expression (6) is obtained.

When the object is finely moved in the negative x direction by a predetermined sample displacement amount Δx , the object wave 21 when finely moved n times is expressed by the following equation (7).

  On the other hand, since the reference wave 23 is not affected by the sample fine movement, the intensity when the reference wave 23 is finely moved n times is expressed by the following equation (8).

When the intensity distribution of the interference fringes 8 in FIG. 2 is detected by a detector on a line arranged at an arbitrary x = x ₁ position, the obtained intensity is obtained by substituting x1 for x in the equation (8). It is represented by (9).

  This intensity distribution can be regarded as a function of the fine movement position n and the direction y parallel to the stripes. When the change in the amplitude of the object wave 21 due to the sample 3 can be ignored, the equation (9) is obtained by taking the cosine function of the phase of the object, and an interference microscope in which the isophase surface of the object wave 21 is represented by contour lines. It is a statue. In other words, an interference microscope image is obtained simply by arranging the obtained columnar intensity data for each sample fine movement position, and complicated processing such as Fourier transform is not required, and high-speed processing close to real time is possible. It becomes possible.

  When not an interference microscope image as an equiphase line but a phase and phase distribution are required, the phase distribution can be obtained by taking an inverse function as shown in the following formula (10).

  Since this process only takes an inverse function, it can be performed at high speed and has high real-time characteristics. Even when the amplitude change due to the object cannot be ignored, the phase and amplitude can be obtained by the same processing as the fringe scanning method. Further, in the present invention, since the position resolution obtained is determined by the width of the sample fine movement, high resolution can be obtained even when the interference fringes 8 having a high contrast and a wide width are used. Furthermore, since the intensity on a certain line on the image observation surface is acquired, it is possible to obtain a phase image without being affected by Fresnel fringes.

  When the amplitude change of the object wave 21 is large, it is also possible to obtain a phase image and an amplitude image using a phase recovery method similar to the fringe scanning method. In this case, the intensity is acquired at each sample fine movement position for a plurality of three or more rows on the observation recording surface 89. Since the obtained interference images are images at different sample positions, alignment is performed so that the position of the sample 3 is appropriately the same. Thereafter, the phase image, An amplitude image can be obtained.

FIG. 3 is a schematic diagram of the image recording apparatus 9 used in the interference fringe measurement method of the present invention.
A two-dimensional electron beam detector 38 such as a CCD that is normally used as an image recording apparatus is one in which electron detection elements 36 are two-dimensionally arranged.
In the present invention, one or a plurality of one-dimensional electron beam detectors 37 arranged one-dimensionally in a direction parallel to the interference fringes 8 obtained in FIG. Of course, it is possible to use the image recording apparatus 9 by using the signal of the corresponding column from the signal of the electron detection element 36 of the two-dimensional electron beam detector 38. When performing phase reproduction by the fringe scanning method, a plurality of columns of the one-dimensional electron beam detectors 37 are used, or signals of a plurality of columns of electron detection elements 36 corresponding to the two-dimensional electron beam detectors 38 are used. I can do it.

Example 1
FIG. 4 is a diagram showing a series of results of experiments conducted in the first embodiment of the present invention.
FIG. 4A shows an electron microscope image of the sample 3 to be observed in the first example of the present invention. Sample 3 is a magnesium oxide microcrystal formed when metallic magnesium is burned in the air, has a cubic shape, and has a side length of 12 nm. The strength of the sample 3 is acquired while finely moving the sample 3 in a direction perpendicular to the interference fringes 8 obtained by the electron biprism 90 by a piezo element.
FIG. 4B is an image of the interference fringes 8 at a certain sample position during fine movement. Since a two-dimensional CCD camera is used, a plurality of stripes are recorded. The carrier interference fringe width was 1.17 nm, and the detector pixel size (sample surface conversion) was 0.0585 nm. Further, at the position indicated by 42, it is observed that the interference fringes 8 are shifted due to the phase change caused by the sample 3.

  In the present invention, the sample 3 is finely moved in the direction perpendicular to the stripes, and the columnar data is repeatedly acquired by the detector. For example, FIG. 4C shows an interference microscope image obtained by rearranging data in a row parallel to the stripe at the position indicated by 43 for each position of sample fine movement. The sample fine movement step was acquired at 0.0585 nm which is the same as the detector pixel size in terms of the sample surface. The phase change due to the magnesium oxide microcrystal of Sample 3 is obtained at the position 44.

  FIG. 4D shows a phase image obtained by taking the arc cosine of (c). When the intensity profile of the phase image is taken in the direction parallel to the stripes at the position 45 where the sample 3 is located and the vacuum region 46 in FIG. 4D, the obtained phase image is shown in FIG. 47, 48 and so on. Both the intensity profiles 47 and 48 are slanting, which is due to the drift of the electron biprism 90 during data acquisition and the like, and the difference 49 between these profiles is the phase due to the net magnesium oxide microcrystals. It represents a change.

  FIG. 4 (e) is a phase image obtained by reproducing the same data obtained by the present method by using the fringe scanning method on the image data for one period of the carrier interference fringe, and FIG. The phase profile is shown. Here, 50 represents the particle position, 51 represents the vacuum position, and 52 represents the net phase change due to the particle by the difference in phase change between the particle position and the vacuum position. The phase change due to the detected magnesium oxide microcrystals was 1.1 rad.

  In this embodiment, the fine movement of the sample position can obtain a phase image by a simple process of rearranging the intensities of the columns obtained by obtaining the interference microscope image by changing the voltage to the piezoelectric element. Compared to the Fourier transform method of the interference microscope image as in the example, the resolution can be increased without being limited by the interval of the interference fringes 8. In addition, there is no problem with the conventional fringe scanning method, such as the necessity of high-precision operation and the occurrence of the influence of aberration by the objective lens system 5. Furthermore, since there is no problem that the Fresnel fringes superimposed on the interference image in the one-stage biprism interferometer also change at the same time, a highly accurate reproduced image can be obtained.

(Example 2)
In this embodiment, the problem that the spatial resolution of the obtained phase image depends on the carrier spatial frequency, which is a problem of the conventional fringe scanning method, can be solved, and a highly accurate reproduced image that does not depend on the carrier spatial frequency can be obtained. Indicates that it will be possible.
FIG. 5 is a diagram showing a series of results of experiments conducted in the second embodiment of the present invention.
FIG. 5A shows an electron microscope image of the sample 3 to be observed in the second embodiment of the present invention. Sample 3 is the same as that used in Example 1, which is a magnesium oxide microcrystal formed when metal magnesium is burned in the air, has a cubic shape, and has a side length of 12 nm. FIG. 5B is an image of the interference fringes 8 at a certain scan position. Since a two-dimensional CCD camera is used, a plurality of stripes are recorded. The carrier interference fringe width was 1.75 nm, and the detector pixel size (sample surface conversion) was 0.0591 nm. In addition, it is observed at the position indicated by 42 that the stripes are shifted due to the phase change by the sample 3.

  In the present invention, the columnar data in the image data is used. For example, FIG. 5C shows an interference microscope image obtained by rearranging data in a row parallel to the stripes indicated by 43 for each position of sample fine movement. The sample tremor step was acquired at 0.00591 nm. The phase change due to the magnesium oxide microcrystal of Sample 3 is obtained at the position 44.

  FIG. 5D shows a phase image obtained by inverse cosine (arc cosine) calculation with respect to FIG. When the intensity profile of the phase image is taken in the direction parallel to the stripes at the position 45 where the sample 3 is located and the vacuum region 46 in FIG. 5D, the obtained phase image is shown in FIG. 47, 48 and so on. Both the intensity profiles 47 and 48 are slanting and slightly bent in the middle. This is due to drift of the electron biprism 90 during data acquisition, and the difference 49 between these profiles is oxidized. It shows the phase change due to magnesium microcrystals.

  FIG. 5 (e) is a phase image obtained by reproducing the image data for one period of the carrier interference fringes by the fringe scanning method on the same data obtained by this method, and FIG. A profile, 50 is a particle position, 51 is a vacuum position, 52 is a difference in phase change between the particle position and the vacuum position, and represents a net phase change due to particles. The phase change due to the detected MgO microcrystals was 1.1 rad. The procedure to be performed is exactly the same as in the first embodiment.

1: Electron source or electron gun 2: Optical axis 3: Sample 4: Irradiation optical system 5: Objective lens system 7: Imaging lens system 8: Interference fringe 9: Image recording device 10: Sample fine control device 11: Objective lens system Crossover 12 imaged by: processing unit 13: finely movable sample holding device 14: display device 21: object wave 22: electron beam wavefront 23: reference wave 27: electron beam trajectory 31: by objective lens system The image of the sample formed 32: The image of the sample imaged by the imaging lens system 34: The position 35 of the column used for reproduction 35: The position of the column 36 used for reproduction when performing reproduction by the fringe scanning method: Electronic detection Element 37: One-dimensional electron beam detector 38: Two-dimensional electron beam detector 40: Transmission electron microscope 41: Magnesium oxide microcrystal 42: Displacement of interference fringes due to oxide microcrystal 43: Column position 44 used for reproduction: Regenerated acid Phase change 45 of electron beam due to microcrystals: acquisition position 46 of particle intensity line profile 46 acquisition position 47 of vacuum intensity line profile: intensity line profile 48 of particles of phase image obtained by rearrangement: obtained by rearrangement Intensity line profile 49 of vacuum of phase image obtained: Profile 50 representing phase change caused by particles obtained by subtracting vacuum intensity line profile from intensity line profile of particles of phase image obtained by rearrangement 50: Obtained by fringe scanning method Phase line particle intensity line profile 51: Phase image vacuum intensity line profile obtained by the fringe scanning method 52: Vacuum intensity line profile from phase image particle intensity line profile obtained by the fringe scanning method Profile showing phase change by particles minus 71: Image plane 75 of sample by objective lens system: Power spectrum 76: Side band 89: Observation / recording surface 90: Electron biprism 91: Electron biprism central ultrafine wire electrode 99: Parallel plate type ground electrode

Claims (11)

An electron biprism,
A sample holding device capable of finely moving the sample in at least one direction within a plane perpendicular to the optical axis;
An electron beam detector comprising a plurality of electron detection elements arranged in a row on a microscope image observation recording surface on which an image of the sample and electron beam interference fringes formed by an electron biprism are observed;
A transmission electron microscope comprising:
Forming the electron beam interference fringes on the image of the sample by the electron biprism;
Outputs a signal intensity of the electron beam interference pattern along an axis arrangement direction determined of the electron detector,
The signal intensity from the electron detection element, which is changed by finely moving the sample by a predetermined distance by the finely movable sample holding device, is used to finely move the sample in a direction perpendicular to the axis defined by the arrangement direction of the electron detection elements. with sequentially output,
By arranging the one-dimensional intensity of the signal intensity at a position corresponding to the sample position, the change in the electron beam phase due to the fine movement of the sample is obtained as an interference microscope image represented by an equiphase line. Type electron microscope. An arithmetic device for image processing of the sample image obtained from the electron beam detector and a microscope image on which electron beam interference fringes are superimposed, and a display device for displaying the image processing result. The transmission electron microscope according to claim 1, wherein: The transmission electron microscope according to claim 2 , wherein a phase distribution image of the electron beam is calculated from the interference microscope image and displayed on the display device by using the arithmetic device. Fine movement direction of the sample by the sample holding device, wherein the a device column and the vertical direction of the electron detector as the moving direction of the image of the specimen in the microscope image observation recording surface, any claim 1-3 A transmission electron microscope according to claim 1. The transmission according to any one of claims 1 to 4, wherein the electron beam interference fringes formed on the microscope image observation recording surface are parallel to an element array constituting the electron beam detector. Type electron microscope. By providing at least three electron beam detectors in which columns formed by the arrangement of the electron detection elements are parallel to each other on the image observation recording surface, an interference microscope image is individually obtained from each electron beam detector. The transmission electron microscope according to claim 1 , wherein the transmission electron microscope is obtained. By using the arithmetic unit, a phase distribution image of the electron beam is calculated from the plurality of interference microscope images obtained individually from the respective electron beam detectors, and is displayed on the display device. The transmission electron microscope according to claim 2 or 3 . An electron biprism,
A sample holding device capable of finely moving the sample in at least one direction within a plane perpendicular to the optical axis;
An electron beam detector comprising a plurality of electron detection elements arranged in a row on a microscopic image observation recording surface on which an image of the sample and electron beam interference fringes formed by an electron biprism are observed An electron beam interference method using a transmission electron microscope,
The image of the sample and the electron beam interference fringes are superimposed on the image observation recording surface,
The signal intensity of the electron detection element is output along an axis defined by the arrangement direction of the electron detection element,
The signal intensity from the electron detection element, which is changed by finely moving the sample by a predetermined distance Δx n times by the finely movable sample holding device, is perpendicular to the axis defined by the arrangement direction of the electron detection elements. sequentially output in accordance with the of the fine,
By arranging the one-dimensional intensity of the signal intensity at a position corresponding to the sample position, the change in the electron beam phase due to the fine movement of the sample is expressed by the following equation (9) as an interference microscope image represented by an equiphase line. Electron beam interferometry, characterized by obtaining an intensity distribution .
Here, the x-axis is the direction perpendicular to the stripe, the y-axis is the direction parallel to the stripe, φ ₀ and η are the amplitude and phase of the object wave, m is the reciprocal of the carrier spatial frequency, and the interval between the interference fringes, x ₁ is arbitrary Is the position. Characterized in that to obtain a phase distribution image represented by the following formula (10) of more the electron beam to taking the inverse function of the interference microscope image, electron beam interferometry according to claim 8.
On the image observation recording surface, there are provided at least three electron beam detectors in which columns formed by the arrangement of the electron detection elements are parallel to each other, and interference microscope images are individually obtained from the respective electron beam detectors. Electron beam interferometry according to claim 8 or 9 , characterized in that it is obtained. The processing of the plurality of interference microscope images obtained individually with each of said electron beam detector, and wherein the obtaining a phase distribution image of the transmitted electron beam samples, according to claim 10 Electron beam interferometry.