Electron microscope analysis system

Abstract

The present invention maximally obtains information about a sample while suppressing, to a minimum level, damage to the sample due to electron irradiation. This electron microscope analysis system is provided with a detector, such as a CCD camera, for capturing an electron microscopy image which, by irradiating an observation sample with an electron beam, is formed on a detection surface by the electron beam having passed through the sample. By forming a linear rotary body that is a set of electrons having wave motions of de Broglie waves, grasping electrons individually is enabled unlike an entry of a plane wave, charge conservation is satisfied, and interaction with the sample occurring within the sample can be calculated. In addition, since indication is performed as a detection point on the detection surface, comparison with actual measurement data can be easily made in a state where the number of electrons is small, damage to the sample due to the electron beam can be reduced, and information about the sample can be easily obtained at a stage where the irradiation amount is small.

Description

[Technical Field]

[0001] The present invention relates to an electron microscope analysis system, and more particularly to a low-dose electron microscope analysis technique using generalized trajectory calculations. [Background technology]

[0002] Currently, various devices are widely used to investigate the properties and structure of materials using electrons accelerated to energy levels ranging from several tens of keV to 1,000 keV. Among these, electron microscopes, inspired by optical microscopes and using electron beams, can obtain magnified transmission images of samples, secondary electron images, and diffraction patterns. By incorporating various analytical devices, various physical quantities can be evaluated and observed, such as analyzing the energy of electron beams that have interacted with samples, forming images using energy-selected electrons, and observing the electromagnetic fields inside and around samples.

[0003] In structural analysis of materials using electron beams, the interpretation of high-magnification transmission images and diffraction patterns of the sample is based on the wave function used in quantum mechanics, which expresses electrons as waves and compares the phase-modulated waves with the wave function of the sample due to the interaction with the electromagnetic field created by the assumed structure of the material. electromagnetic The structure is confirmed and identified by comparing the interference image or electron diffraction pattern between the waves that have passed through without being affected by the field with the image or electron diffraction pattern of the assumed structure. - The electron beam is a particle (point) with a certain electric charge, and its trajectory is controlled by the electrostatic lens, magnetic lens, deflection system, etc. of the irradiation system so that the sample is irradiated with the electron beam at an appropriate irradiation angle and electron beam density (see Non-Patent Document 1).

[0004] When obtaining an image with a relatively low magnification, the analysis and evaluation of the image is carried out by calculating and evaluating the particle trajectories of electrons scattered by the sample for each electron beam irradiation condition. However, in the case of a high-magnification transmission image, the contrast of the image is calculated by replacing the electrons incident on the sample with plane waves at the point of incidence, assuming that the image is mainly dependent on the phase rather than the amplitude of the electron beam (see Non-Patent Document 2). That is, as shown in Figure 1(a), the particle trajectories of electrons are calculated and evaluated up to the crossover directly above the sample (Speci), but electronic Electrons are treated as spherical waves from the source or the crossover directly above the sample, and as plane waves on the sample surface located far enough away, they can be approximated as plane waves.

[0005] In this way, electrons, which are the same elementary particles, are sometimes treated as particles and sometimes as wave functions. Experiments conducted so far on the interference of electron beams have demonstrated that the detection points of individual electrons accumulate on the detection surface to form an interference image (see Non-Patent Document 3), and the detector detects individual electrons, not their existence probability.

[0006] As another example, electron holography has been used to observe the disturbances in the electric field that occur when a sample is irradiated with an electron beam and the electrons emitted from the sample stay around the sample or return to the sample surface (see Non-Patent Document 4). Therefore, each electron is electronic It is thought that electrons can be treated as individual electrons from the source to the detection surface, and it is assumed that the wave nature of electrons is involved in their trajectories. For example, as shown in (a) and (b) of Figure 2, a typical example of an electron's trajectory is that the direction of the electron's travel is selected to be a state and direction (stable state) where there is no change in the phase of the de Broglie wave (hereafter referred to as the de Broglie wave). In other words, in (a) of the same figure, the electron's trajectory is a de Broglie wave. wavelength In (b), the optical path difference is de Broglie. wavelength It moves in a direction that is an integer multiple of λ. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Dr. Walter Glaser, “Grundlagen der Elektronenoptik”, Wien Springer-Verlag, 1952 [Non-patent document 2] JMCowley, and AFMoodie, “The Scattering of Electrons by Atoms and Crystals, IA New Theoretical Approach”, ActaCryst (1957), 10, 609 [Non-patent document 3] A. Tonomura, et.al, “Demonstration of single-electron buildup of an interference pattern”, American Journal of Physics 57, 117 (1989) [Non-patent document 4] Takafumi Sato, et al, “Electron Holography Study of Secondary Electron Distribution around Charged Epoxy Resin”, MATERIALS TRANSACTIONS, Volume 60 (2019) Issue 10, pp.2114-2119 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, current simulations of high-magnification sample images using electron microscopes and the like treat the electrons irradiating the sample as de Broglie plane waves, using the wave function of quantum mechanics. Specifically, a plane wave enters the sample and is split into a wave that passes through as is and a wave that is diffracted by the sample's electromagnetic field. These two waves are then superimposed on the image plane by the objective lens, causing interference and forming an image (Non-Patent Document 2). The image or diffraction pattern is expressed as |Ψ| using the wave function 〈Ψ| 2 The probability of electron presence, i.e., the position distribution of the probability of electron detection, is calculated as follows. However, in actual image detection, the position of each electron that passes through the electron trajectory 11 and reaches the detection surface is detected and integrated to form an image on the detection surface. Therefore, as shown in Figures 3(a) and 3(b), in order to compare the diffraction pattern or image of the sample generated by the actually detected electrons with the simulated diffraction pattern or image, a large amount of electron beam irradiation is required until a continuous, smooth contrast is achieved. For this reason, with samples that are prone to severe damage from irradiated electrons, such as polymer samples or biological polymer samples, the sample is often destroyed before the irradiation dose required to obtain reliable sample information is reached.

[0009] In view of the above facts, the problem to be solved by the present invention is to make it possible to obtain maximum information about a sample while minimizing sample damage caused by electron irradiation by using a simulation and an electron microscope analysis system based on the simulation, which is consistent with the actual detection situation, and which makes it easy to compare with detection data and obtain sample information even at a stage when the amount of current irradiating the sample is small, rather than treating electrons incident on a sample and electrons that interact with the sample and reach the detection surface in terms of existence probability using a wave function. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides an electron microscope analysis system that compares and analyzes a detected image obtained by an electron microscope equipped with a detection unit that irradiates an observation sample with an electron beam, passes it through, and detects the electron microscope image formed on the detection surface, with a simulated image obtained by an electronic model of a rotating linear material wave, and the above-mentioned unique electronic model makes it possible to compare the detected image with the electron image even when the electron irradiation dose is low.

[0011] That is, in this invention, in order to resolve the contradiction between the electron positions obtained only as a distribution of existence probability and the existence of clear detection positions in actual electron detection and to be able to explain the movement of electrons, electrons are not represented by wave functions, but are considered to be linearly distributed electric charges rotating at high speed (corresponding to a spin angular momentum h / 4π), as shown in Figure 9, and the electron position is represented by the center point of the line, and is considered to be a rotating linear matter wave (de Broglie wave).With such electrons, each electron position is detected as the center of a rotating linear matter wave, which matches the actual detection state, making it possible to compare simulations and actual measurements even under low irradiation dose conditions.

[0012] Furthermore, the electron microscope analysis system of the present invention is capable of controlling single electron irradiation using the photoelectric effect. electron source (electron gun) and diffraction pattern, specimen image simulation software, ) The electron microscope is configured to be able to be controlled using a microscope, and the number of incident electrons is controlled while irradiating a sample held in a sample holder, and the obtained diffraction pattern is compared with an image simulation, making it possible to perform analysis while checking for sample damage caused by the irradiation. [Effects of the Invention]

[0013] According to the present invention, electrons incident on a sample are treated as linear bodies of revolution with de Broglie waves, and unlike plane wave incidence, they can be treated as individual electrons, satisfying the law of conservation of charge and making it possible to calculate the interaction between electrons and the sample inside the sample. probabilitySince the measured data is expressed as detection points rather than evaluated as a whole, it is easier to compare it with actual measurement data even when the number of electrons is small, sample damage caused by the electron beam can be reduced, and sample information can be obtained more easily even when the irradiation dose is low. [Brief explanation of the drawings]

[0014] [Figure 1] 1A and 1B are diagrams for explaining the difference between the conventional diffraction patterns and the simulation of the image of the present invention. [Figure 2] FIG. 1 is a diagram for explaining the orbit and direction of travel of an electron. [Figure 3] 10A and 10B are diagrams for explaining the difference between the simulation result images of the conventional technology and the present invention. [Figure 4] FIG. 1 is a diagram showing an example of the configuration of a low-dose electron microscope analysis system according to a first embodiment. [Figure 5] FIG. 2 is a diagram showing a configuration example of a secondary electronic manipulator according to the first embodiment. [Figure 6] 4A and 4B are diagrams for explaining the difference between the conventional method and the first embodiment of the present invention in terms of incident wave on the sample. [Figure 7] 10A and 10B are diagrams showing interference fringes obtained by simulation results and actual measurements according to the first embodiment. [Figure 8] FIG. 10 is a diagram for explaining a conventional simulation. [Figure 9] 1A and 1B are diagrams for explaining a simulation using a rotating linear matter wave according to the present invention. [Figure 10] FIG. 2 is a diagram showing an example of a comparative analysis procedure of the low dose electron microscope analysis system according to the first embodiment. [Figure 11] A diagram showing the relationship between the incident electron beam and the biprism wire. [Figure 12] A comparison of the intensity cross-sections of the observed and calculated interference fringes. [Figure 13] A diagram showing the parameters and constants used in the simulation. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in order with reference to the drawings. [Example]

[0016] Example 1 is an example of an electron microscope analysis system, which includes a detector that irradiates an electron beam onto a sample, transmits the electron beam, and captures an electron microscope image formed on a detection surface, and analyzes the electron beam that forms the electron microscope image using an electron model having a linear matter wave (de Broglie wave) that rotates around a predetermined point on the irradiation line.

[0017] FIG. 4 shows an example of the system configuration of this embodiment. That is, it is an electron microscope analysis system, This is an electron microscope analysis system in which a biprism and a joint holder are installed in a transmission electron microscope, and it is possible to approach the sample surface while checking the accumulation of secondary electrons using the amplitude contrast image of the biprism.

[0018] In the figure, electrons emitted from an electron source and passing through an irradiation system are irradiated onto a sample held in a sample holder 41, and are detected by a two-dimensional detector 42 via an imaging system including a biprism etc. The detection signal is Irradiation electron source control system 43 The image information is then converted into image information as appropriate and displayed on the monitor 44. Irradiation electron source control system 43 As described above, the comparison is made between the simulation by IT and the data from the two-dimensional detector 42.

[0019] FIG. 10 is a diagram showing an example of a comparative analysis procedure of the low-dose electron microscope analysis system according to the first embodiment. The electron microscope analysis system outputs irradiation beam data and an image detection signal from a camera or the like (S102). The irradiation beam data output, together with sample data input, is used to perform a detection plane (image plane) intensity distribution simulation (S101). The image detection signal and data are compared for small, medium, and large irradiation doses (S103 to S105), and the results are output. As shown in (b) of the same figure, in the data comparison, the integrated value of the distance between the simulation point and the closest detection point is calculated and evaluated. Then, based on the results, irradiation system setting data is output (S106), and the irradiation conditions are reset (S107).

[0020] In this way, Irradiation electron source control system 43 By controlling the accelerating (high voltage) power supply and pulsed light source, the required electron emission and acceleration control is performed. In other words, by referring to the comparison results, feedback is provided to the pulsed light source and accelerating power supply, and the amount of irradiated beam is controlled, allowing sample information to be obtained while minimizing sample damage.

[0021] FIG. 5 shows an example of the configuration of a secondary electron manipulator according to this embodiment. A sample 51 is irradiated with an electron beam at the tip of a two-dimensional manipulator 52, which can be moved along the X-axis by a three-axis control piezoelectric element 53. Using this type of two-dimensional manipulator, it is possible to observe the accumulation of secondary electrons at the Y-shaped tip of an insulating sample. For example, by simultaneously configuring a biprism and a two-terminal holder in a transmission electron microscope, the Y-shaped insulating sample can be fixed to one terminal of the two-terminal holder and the sample can be fixed to the other terminal, thereby constructing a manipulator with a protrusion several tens of nanometers in diameter that densely collects secondary electrons (0 to several tens of eV). This can be brought close to the sample surface to observe changes in the sample's physical properties, making it a useful measurement method for measuring physical properties by bringing it close to the surface of a semiconductor or other material.

[0022] 6(b) shows the difference between the conventional and present embodiment in the incident wave to the sample, and as shown in Fig. 6(b), the incident wave to the sample in this embodiment is a rotating linear material wave 61 that travels along the Z axis (optical axis) and is incident on the sample. As a result, as shown in Fig. 6(c), n rotating linear material waves cross the sample surface, and as n approaches infinity, they become equivalent to a plane wave.

[0023] FIG. 7 shows the simulation results of this embodiment and the interference fringes obtained by actual measurement, where (a) in the figure shows the simulation results of this embodiment (black dots), and (b) in the figure shows the experimental results (white dots) disclosed in Non-Patent Document 3. In both cases, the interference fringes become clearer as the number of dots increases. In this way, Non-Patent Document 3 demonstrates that the detection points of individual electrons accumulate on the detection surface to form an interference image, and the detector detects individual electrons.

[0024] Furthermore, Non-Patent Document 4 observes that when a sample is irradiated with an electron beam, electrons that have passed through the sample become trapped around the sample or circulate around the sample surface, causing disturbances in the electric field.

[0025] The individual electrons in the electron beam are electronic It is thought that electrons can be treated as individual electrons from the source to the detection surface, and the electron trajectories are thought to involve the wave nature of electrons.

[0026] Next, the differences between the conventional diffraction patterns and the simulation of the image in this embodiment will be explained using equations with reference to Figures 8 and 9. Figure 8 is a diagram for explaining the conventional simulation, and Figure 9 is a diagram for explaining the simulation using a rotating linear matter wave in this embodiment.

[0027] First, we will explain the conventional treatment of incident electrons shown in Figure 8 using equations (1), (2), and (3). Equation (1) shows the wave function according to the conventional treatment, and equation (2) shows its transmission function. Here, σ is the interaction constant determined by the wavelength and accelerating voltage, φ(x, y) is the potential distribution of the sample, and Δt is the sample thickness. Equation (3) shows the scattering (diffraction) intensity of electrons that have passed through the sample.

[0028]

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[0029]

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[0030]

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[0031] On the other hand, equation (4) shows the wave function of the rotating linear matter wave in this example. Here, l1 indicates the linear region on the sample. As shown in Figure 9, in this example, the linear charge rotates at the speed of light level, and it can be considered that there is a charge at the center. This electron model is used to interpret the electron diffraction pattern and electron wave interference image of the material. The transmission function in equation (4) is as shown in equation (2). Equation (5) shows the scattering (diffraction) intensity in this example.

[0032] In this example, the direction in which a single electron is scattered (diffracted) corresponds to the direction in which the shape of the matter wave is maintained. This is treated as an evaluation of the degree of wave interference in the line segment where the linear matter wave intersects with the sample, i.e., the interference and diffraction effects through the wave function.

[0033]

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[0034]

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[0035] The interference fringes of an electron hologram can also be treated in the same way as in Figure 9. The calculation in Figure 3(b) is for the case where a biprism wire is placed at the sample position in Figure 6(b). In the conventional model, a plane wave passes through the surface of this wire, and the electric field of the wire tilts the wavefront relative to the optical axis, causing fringes to appear in the tilt direction of the wavefront. In the electronic model in Figure 3(b), the existence of a broadened wave on the detection surface probability Since the measured data is expressed as detection points rather than evaluated as a whole, it is easier to compare it with actual measurement data even when the number of electrons is small, sample damage caused by the electron beam can be reduced, and sample information can be obtained more easily even when the irradiation dose is low.

[0036] In this electron model, each electron rotates in a random direction while passing through the wire surface and reaches the hologram surface (equivalent to the detection surface). angle As mentioned above, it can be treated as an evaluation of the interference and diffraction effects using the wave function for the line segment region where the linear material wave intersects with the wire surface.

[0037] Figure 11 shows the relationship between the incident electron beam and the biprism wire. It shows a portion of the intensity cross-sectional interference fringes on the observation plane when a rotating linear wave cuts the wire surface perpendicularly. Figures 12(a) to 12(e) show the simulation results of the interference fringes caused by the linear rotating wave described above. Figure 12(a) plots the simulated results of 20 linear rotating waves randomly cutting the wire surface and 20 electron positions detected on the observation plane corresponding to each linear rotating wave.

[0038] According to equation (6), the probability of detecting 20 electrons on the image plane can be estimated and plotted by tracing the random path of the rotating linear wave. Figures 12(b), (c), and (d) show the results for the case where the number of electrons, n, is 2x10. 2 , 2x10 3 , 2x10 4 The interference fringes become clearer as the incident electron beam increases, just as in the experimental observation.

[0039]

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[0040] Figure 12(e) is a graph plotting the number of detected electrons integrated along the Y-axis as a relative value on the vertical axis in the simulation of Figure 12(d). This matches well with the intensity distribution calculated using a plane wave shown in Figure 12(f), and it can be said that this electron model is consistent with previous experimental results and can also explain actual detection behavior (detection of individual electrons). Note that all calculations described here use the parameters shown in Figure 13.

[0041] The above-described embodiments have been described in detail to facilitate a better understanding of the present invention, and are not necessarily limited to those having all of the described configurations. Furthermore, while the above-described configurations, functions, systems, etc. have been described primarily as examples of creating programs that realize some or all of them, it goes without saying that some or all of them may be realized in hardware, for example, by designing them as integrated circuits. In other words, all or part of the functions of the processing unit may be realized by integrated circuits, such as ASICs (Application Specific Integrated Circuits) and FPGAs (Field Programmable Gate Arrays), instead of programs.

[0042] According to the present invention as described above, a microscope image can be obtained with a small amount of electron beam irradiation, and a particularly effective technique can be provided for observation samples that are sensitive to electron beam irradiation, such as polymer samples and biological samples.

[0043] The inventions disclosed in this specification include not only the inventions described in the claims but also numerous other inventions, some of which are listed below.

[0044] <List 1> An electron microscope analysis system, comprising: An electron microscope analysis system that interprets the behavior of electrons using an electron model based on rotating, linear matter waves (de Broglie waves).

[0045] <List 2> The electron microscope analysis system according to List 1, An electron microscope analysis system characterized by using the electron model to analyze the interaction between an electron beam incident on a sample and the sample, and the behavior of electrons emitted from the sample.

[0046] <List 3> The electron microscope analysis system according to List 1, A biprism and a joint holder are configured in the transmission electron microscope, and it is possible to approach the sample surface while checking the accumulation of secondary electrons in the amplitude contrast image of the biprism. Electron microscope analysis system characterized by:

[0047] <List 4> The electron microscope analysis system according to List 1, Using the electron model, an electron diffraction pattern or an electron wave interference pattern of the material is interpreted. Electron microscope analysis system characterized by:

[0048] <List 5> The electron microscope analysis system according to List 1, In an apparatus for obtaining electron diffraction patterns and electron microscope images from a sample using an electron beam, the obtained results are analyzed based on the interpretation of the electron model, and the structure, constituent atoms, etc. of the sample are simulated. Electron microscope analysis system characterized by:

[0049] <List 6> The electron microscope analysis system according to List 1, obtaining microstructural information of the portion of the sample irradiated with the electron beam by comparing a simulation of an electron diffraction pattern or an electron microscope image using the electron model with an actually obtained electron diffraction pattern or an electron microscope image; Electron microscope analysis system characterized by:

[0050] <List 7> The electron microscope analysis system according to List 1, By comparing the simulation of electron diffraction patterns and electron microscope images using the electron model with the electron diffraction patterns and electron microscope images that are actually obtained, information on the irradiation of the sample with a low electron dose can be obtained. Electron microscope analysis system characterized by: [Explanation of symbols]

[0051] 11 Electron Orbitals 31 Route (Trajectory) 41 Sample holder 42 2D detector 43 Irradiation electron source control system 44 monitors 51 Samples 52 2D Manipulator 53 Two-dimensional control piezoelectric element 61 Rotating Linear Material Waves

Claims

1. An electron microscope analysis system, comprising: an electron source that emits an electron beam; an irradiation system that irradiates the sample with the electron beam; a detector that captures an electron microscope image formed on a detection surface by the electron beam that has passed through the sample through an imaging system; an irradiation light source control system for controlling irradiation conditions of the electron beam, the irradiation light source control system analyzes the electron beam forming the electron microscope image using an electron model having a linear matter wave (de Broglie wave) rotating around a predetermined point on the irradiation line; Electron microscope analysis system characterized by:

2. 2. The electron microscope analysis system according to claim 1, a transmission electron microscope including the electron source, the illumination system, the imaging system, and the detector; The transmission electron microscope is provided with a biprism and a sample holder having a secondary electron manipulator. Electron microscope analysis system characterized by:

3. 2. The electron microscope analysis system according to claim 1, the illumination light source control system compares a simulation of an electron diffraction pattern or an electron microscope image using the electron model with the electron diffraction pattern or the electron microscope image of the sample obtained by the detector; Electron microscope analysis system characterized by:

Images