Transmission electron microscope and its operating method

Abstract

The present invention provides a transmission electron microscope and a method of operating the same, which allows for arbitrary adjustment of the illumination intensity to any pixel of the image sensor and reduces the intensity of the center spot. [Solution] The transmission electron microscope according to this embodiment comprises a beam irradiation unit, a first lens system located downstream thereof, a holder located downstream thereof for mounting a sample, a second lens system located downstream thereof, a detection mechanism located downstream thereof, and a control unit. The detection mechanism comprises a scintillator for detecting electron beams, a light propagation unit for propagating the light converted in the scintillator, and an image sensor for receiving the light propagated by the light propagation unit. Furthermore, the light propagation unit is provided with an element that can change the transmittance of light. The control unit generates first light intensity data from a signal obtained by detecting the light transmitted through this element with the image sensor.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a transmission electron microscope and a method for operating the same. [Background technology]

[0002] Nano-beam electron diffraction (NBD) and electron energy-loss spectroscopy (EELS) using transmission electron microscopy (TEM) are well-known methods. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6546933 [Patent Document 2] Japanese Patent Publication No. 2023-11409 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In conventional TEMs, when strong light is shone on various locations (pixels) of the image sensor, the output signal saturates in locations (pixels) where the light exceeds the dynamic range, making it impossible to measure the actual intensity. When light exceeding the dynamic range is shone, adjusting the light intensity can be considered. However, since the light source is common, if the light intensity is adjusted so that the dynamic range is not exceeded in some locations (pixels) of the image sensor, the light intensity in other locations (pixels) of the image sensor will also decrease, resulting in a weaker output signal.

[0005] Also, when acquiring a diffraction pattern in a TEM, the intensity of the center spot is more than one order of magnitude stronger compared to others. When using a beam stopper to avoid damaging the TEM, the intensity and position of the center spot become unknown. Also, in EELS, the intensity of the zero loss peak is more than one order of magnitude stronger compared to others.

[0006] The problem to be solved by the embodiment is to provide a transmission electron microscope and its operating method that can arbitrarily adjust the irradiation intensity to any pixel of an imaging device and can reduce the intensity of the beam irradiated to a portion (pixel) corresponding to the center spot in NBD or the zero loss peak in EELS.

Means for Solving the Problem

[0007] The transmission electron microscope according to the embodiment includes a beam irradiation unit, a first lens system downstream thereof, a holder on which a sample is mounted downstream thereof, a second lens system downstream thereof, a detection mechanism downstream thereof, and a control unit. The detection mechanism includes a scintillator that detects an electron beam, an optical propagation unit that propagates the light converted in the scintillator, and an imaging device that receives the light propagated by the optical propagation unit. Further, the optical propagation unit includes an element capable of changing the transmittance of light. The control unit generates first light intensity data from a signal obtained by detecting the light transmitted through this element with the imaging device.

Brief Description of the Drawings

[0008] [Figure 1] Configuration diagram of a transmission electron microscope according to the first embodiment. [Figure 2] Configuration diagram of an electron beam detector applied to a transmission electron microscope according to the first embodiment. [Figure 3A] Plan view of a liquid crystal panel applied to a transmission electron microscope according to the first embodiment. [Figure 3B] Schematic diagram for explaining the relationship between the liquid crystal control voltage and the position of the liquid crystal cell in a liquid crystal panel applied to a transmission electron microscope according to the first embodiment. < [Figure 3C] A schematic diagram explaining the relationship between the light intensity that passes through and is detected by a liquid crystal cell and the position of the liquid crystal cell in a liquid crystal panel applied to a transmission electron microscope according to the first embodiment. [Figure 4] A flowchart explaining the operation method of a transmission electron microscope according to the first embodiment when the light transmittance of a liquid crystal element is defined as 1%. [Figure 5] A flowchart explaining the operation method of a transmission electron microscope according to the first embodiment. [Figure 6A] A configuration diagram of a transmission electron microscope according to the second embodiment. [Figure 6B] Configuration example 1 of a frame mechanism applied to a transmission electron microscope according to the second embodiment. [Figure 6C] Configuration example 2 of a frame mechanism applied to a transmission electron microscope according to the second embodiment. [Figure 6D] Configuration example 3 of a frame mechanism applied to a transmission electron microscope according to the second embodiment. [Figure 7] A flowchart explaining the operation method of a transmission electron microscope according to the second embodiment.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments will be described with reference to the drawings. In the following description, the same or similar members are denoted by the same reference numerals, and the description of the members once described will be omitted as appropriate. In the following description, the direction perpendicular to the liquid crystal panel extending in the XY plane is the Z direction, the first direction of the arrangement of the liquid crystal cells is the X direction, and the second direction of the arrangement of the liquid crystal cells, which is perpendicular to the Z direction and the X direction, is the Y direction. Also, the minus Z direction from the beam irradiation unit 11 toward the detection mechanism 22 is defined as the downstream, and the plus Z direction is defined as the upstream. Also, for convenience of explanation, the detection mechanism 22 may be referred to as an electron beam detector. Also, the element 60 may be referred to as a liquid crystal element, a liquid crystal panel, or a liquid crystal cell.

[0010] Hereinafter, embodiments will be described with reference to the drawings. (Configuration of Transmission Electron Microscope) Figure 1 is a diagram showing the configuration of a transmission electron microscope 1 according to the first embodiment.

[0011] As shown in Figure 1, the transmission electron microscope 1 according to the first embodiment includes a beam irradiation unit 11, a first lens system 100 located downstream thereof, a holder 31 located downstream thereof for mounting a sample, a second lens system 200 located downstream thereof, a dark-field detector 21 located downstream thereof, a detection mechanism 22 located downstream thereof, and a control unit 40.

[0012] The first lens system 100 comprises a condenser lens 12, a scan coil 13, and an objective lens 14. The second lens system 200 comprises an intermediate lens 15, a descan coil 16, and a projection lens 17. The lens system may also be referred to as a lens mechanism, coil system, or illumination system.

[0013] The beam irradiation unit 11 includes a field emission electron gun 111, which is an electron source that emits an electron beam 10, and an acceleration unit 112 that accelerates the emitted electron beam 10. The condenser lens 12 focuses the electron beam 10 accelerated in the acceleration unit 112. The scan coil 13 scans the irradiation position of the electron beam 10 on the surface of the sample in the X direction and / or the Y direction. The objective lens 14 further focuses the electron beam 10 to form an extremely small electron beam (nanobeam).

[0014] The intermediate lens 15 magnifies the electron diffraction pattern created by the objective lens 14 and projects it onto the object plane of the subsequent projection lens 17. The descan coil 16 corrects the positional shift of the electron beam 10 from the optical axis caused by the scan coil 13 back to the optical axis. The irradiation position of the electron beam 10 can be corrected by shifting the irradiation position of the electron beam 10 in the opposite direction by the amount by which the irradiation position of the electron beam 10 was shifted from the optical axis of the condenser lens 12 by the scan coil 13.

[0015] The projection lens 17 further magnifies the electron diffraction image magnified by the intermediate lens 15 and forms an image on the dark-field detector 21 and the electron beam detector 22.

[0016] The dark-field detector 21 is a ring-shaped electron beam detector with an aperture formed in its central part. It detects electrons that have passed through the sample and have been scattered and diffracted at high angles. The electron diffraction pattern detected by the dark-field detector 21 is a dark-field image. The detection mechanism 22 detects electrons that have passed through the aperture of the dark-field detector 21 among the electrons that have passed through the sample. The electron diffraction pattern detected by the detection mechanism 22 is a diffraction pattern.

[0017] The control unit 40 includes a central processing unit (CPU) 401 as a processor and random access memory (RAM) 402.

[0018] The CPU 401 operates according to a program stored in memory (not shown) and has a control function that controls the operation and settings of each part that makes up the transmission electron microscope (beam irradiation unit 11, condenser lens 12, scan coil 13, objective lens 14, intermediate lens 15, descan coil 16, projection lens 17, etc.). It also has a data analysis function that analyzes electron diffraction patterns output from the dark-field detector 21 and electron beam detector 22. In other words, it analyzes electron diffraction patterns input from the dark-field detector 21 and electron beam detector 22. For example, if the sample is a crystal, it identifies the crystal orientation of the target region.

[0019] Furthermore, the CPU 401 controls the voltage supplied to the voltage supply unit of the liquid crystal panel. The CPU 401 also calculates the second light intensity data OP2 before attenuation from the first light intensity data OP1 after attenuation.

[0020] RAM402 stores the data after analysis and various settings. RAM402 may also store a database used for matching the measured electron diffraction pattern, for example, to determine the crystal orientation.

[0021] Furthermore, RAM402 records the relationship between the liquid crystal control voltage and transmittance, as well as the obtained image. RAM402 also stores characteristic information showing the relationship between the liquid crystal control voltage and transmittance of the liquid crystal cell.

[0022] (Electron beam detector) Figure 2 is a diagram showing the configuration of a detection mechanism 22 applied to a transmission electron microscope 1 according to the first embodiment. The detection mechanism 22 is an electron beam detector.

[0023] As shown in Figure 2, the electron beam detector 22 comprises a scintillator 25 for detecting the electron beam 10, an optical propagation unit 80 for propagating the light converted in the scintillator 25, and an image sensor 70 for receiving the light propagated by the optical propagation unit 80. Multiple optical fiber bundles 82 are bundled together in the optical propagation unit 80. The image sensor 70 is mounted on a heat sink 75. The image sensor 70 can be a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0024] As shown in Figure 2, the transmission electron microscope 1 according to the first embodiment includes an element 60 in the light propagation section 80 that can change the transmittance of light.

[0025] Element 60 comprises a liquid crystal element whose transmittance can be changed according to the supplied voltage, and a voltage supply unit that supplies the voltage. In Figure 2, element 60 is shown as an example of a liquid crystal element divided into multiple parts. The voltage supply unit is a wiring mechanism for supplying voltage to the liquid crystal element. The light converted in the scintillator 25 propagates through the light propagation unit 80 as shown by the arrows in Figure 2, passes through the liquid crystal element 60, and is incident on the image sensor 70. The spacing between the liquid crystal cells of the liquid crystal element 60 is shown, schematically illustrating that the liquid crystal element 60 is divided. The wiring mechanism is formed between liquid crystal cells and across liquid crystal cells, so it is not shown in the figure.

[0026] Another example of element 60 is a sol-gel element. Since the turbidity of a sol-gel element can be changed by temperature control, the light transmittance can be changed by combining it with a heater element.

[0027] (Liquid crystal panel) In the transmission electron microscope 1 according to the first embodiment, an example of using a liquid crystal panel 60 as an element capable of changing the light transmittance will be described below.

[0028] FIG. 3A is a plan view of the liquid crystal panel 60 applied to the transmission electron microscope 1 according to the first embodiment. As shown in FIG. 3A, the liquid crystal elements constituting the liquid crystal panel 60 are arranged with the liquid crystal cells 60 ij laid out and arranged. A wiring mechanism (not shown) for supplying a liquid crystal control voltage applied to the liquid crystal cells 60 arranged in the XY direction is connected to the liquid crystal panel 60. In FIG. 3A, depending on the positions X1, X2, X3, X4, X5, X6 of the liquid crystal cells in the X direction, for example, the liquid crystal cells arranged in the j-th column in the Y direction are 60 ij 、60 1j 、60 2j 、60 3j 、60 4j 、60 5j 、60 6j represented by. Here, i is an integer from X = 1 to 6, and j is an integer from Y = 1 to 6.

[0029] In the example of FIG. 3A, it is shown as a matrix of 6×6 elements with 6 cells arranged in the X direction and 6 cells arranged in the Y direction, but this number is not limited. Specific numerical examples will be described later. For example, when one liquid crystal element is placed on a 4×4 pixel imaging element, about 1024 liquid crystal elements are arranged vertically and horizontally.

[0030] FIG. 3B is a schematic diagram for explaining the relationship between the liquid crystal control voltage VC and the position X of the liquid crystal cell in the X direction in the liquid crystal panel 60. *

[0031] FIG. 3C is a schematic diagram for explaining the relationship between the light intensity OP transmitted through and detected by the liquid crystal cell 60 and the position X of the liquid crystal cell in the X direction in the liquid crystal panel ij 60.

[0032] The liquid crystal panel 60 can change the light transmittance at an arbitrary position. Each of the liquid crystal cells 60 divided into a plurality ijBy changing the liquid crystal control voltage VC applied to each liquid crystal cell 60, the light transmittance can be continuously changed. ij From the relationship between the liquid crystal control voltage VC applied to the liquid crystal and the transmittance, each liquid crystal cell 60 during measurement ij By recording the liquid crystal control voltage VC, it is possible to determine the value before the light attenuation occurs.

[0033] Here, each liquid crystal cell 60 ij The liquid crystal control voltage VC is recorded in the RAM 402 located in the control unit 40. For example, a personal computer PC can be used as the CPU 401 located in the control unit 40. Using the CPU 401, each liquid crystal cell 60 of the liquid crystal panel 60 ij By changing the liquid crystal control voltage VC to each liquid crystal cell 60 of the liquid crystal panel 60 ij The transmittance can be changed.

[0034] Furthermore, the transmittance is measured by the image sensor 70. That is, each liquid crystal cell 60 of the liquid crystal panel 60 ij The transmittance can be measured at each pixel of the image sensor 70. ij Ideally, there should be a one-to-one correspondence between the image sensor 70 and the pixels of the liquid crystal cell, but a correspondence of approximately 3x3 to 4x4 pixels per liquid crystal cell is also acceptable.

[0035] Each of the 60 liquid crystal cells is divided into multiple sections. ij The control unit 40 for changing the liquid crystal control voltage VC applied to each liquid crystal cell 60 may include, for example, a scanning unit in the XY direction. ij The control unit 40 controls how much liquid crystal control voltage VC is applied to each liquid crystal cell. This allows the transmittance of each liquid crystal cell to be changed. Furthermore, by changing the liquid crystal control voltage VC applied to the liquid crystal cells, the light transmittance can be continuously changed.

[0036] In the transmission electron microscope 1 according to the first embodiment, the liquid crystal element 60 is divided into at least a first region and a second region, and the voltage supply unit can change the light transmittance at any position by supplying an arbitrary voltage to the first region and the second region.

[0037] Changing the light transmittance at an arbitrary position means that, in a liquid crystal element divided into multiple sections and arranged in the XY direction, the light transmittance can be changed by applying a voltage to some or all of the elements. For example, the transmittance can be reduced in areas where "strong light" hits. Here, as an example, "strong light" can be defined as the point at which the image sensor reaches the upper limit of its 16-bit = 65536-level dynamic range (saturation), which is the detection limit of the image sensor.

[0038] As shown in Figure 3C, the liquid crystal cell 60 1j , 60 2j Therefore, the detected light intensity is lower than the first light intensity data OP1. As shown in Figure 3B, the liquid crystal control voltage VC is sufficiently lower than VC1 and is at zero level. Similarly, as shown in Figure 3C, the liquid crystal cell 60 5j , 60 6j Therefore, the detected light intensity is lower than the first light intensity data OP1. As shown in Figure 3B, here too the liquid crystal control voltage VC is sufficiently lower than VC1 and is at zero level. In contrast, as shown in Figure 3C, the liquid crystal cell 60 3j , 60 4j Therefore, the light intensity to be detected is the level of the second light intensity data OP2. As shown in Figure 3B, by setting the value of the liquid crystal control voltage VC to VC1, the liquid crystal cell 60 3j , 60 4j This reduces the light transmittance.

[0039] In the transmission electron microscope 1 according to the first embodiment, the control unit 40 controls the first liquid crystal cell 60 of the liquid crystal element 60 ij and the second LCD cell 60 i-1j The liquid crystal control voltage VC applied to each is gradually increased, and the first liquid crystal cell 60 ij and the second LCD cell 60 i-1jIn each case, the liquid crystal control voltage VC1 obtained when data within the dynamic range is acquired is stored in the RAM 402. Based on the stored liquid crystal control voltage VC1, the beam irradiation unit 11 performs irradiation and generates the attenuated first light intensity data OP1. In other words, the control unit 40 can generate the attenuated first light intensity data OP1 from the signal obtained by detecting the light transmitted through the liquid crystal element 60 with the image sensor 70.

[0040] In the transmission electron microscope 1 according to the first embodiment, the control unit 40 controls the first liquid crystal cell 60 of the liquid crystal element 60 ij and the second LCD cell 60 i-1j Each component further includes a RAM 402 that stores characteristic information showing the relationship between the liquid crystal control voltage and transmittance, and a CPU 401 that calculates the second light intensity data OP2 before attenuation, corresponding to the intensity of received light, from the first light intensity data OP1 after attenuation, based on this characteristic information. Here, the characteristic information showing the relationship between the liquid crystal control voltage VC and transmittance is represented by the sum of the original transmittance before the application of the liquid crystal control voltage VC and the change in transmittance after the application of the liquid crystal control voltage VC.

[0041] The following explanation can be given using the examples in Figures 3B and 3C.

[0042] The control unit 40 controls the first liquid crystal cell 60 of the liquid crystal element 60 4j and the second LCD cell 60 3j The liquid crystal control voltage VC applied to each is gradually increased, and the first liquid crystal cell 60 4j and the second LCD cell 60 3j In each case, the liquid crystal control voltage VC1 (Figure 3B) obtained when data within the dynamic range is stored in the RAM 402. Based on the stored liquid crystal control voltage VC1, the CPU 401 performs irradiation with the beam irradiation unit 11 and generates the attenuated first light intensity data OP1 (Figure 3C).

[0043] RAM402 is the first liquid crystal cell 60 4j and the second LCD cell 60 3jFor each, characteristic information showing the relationship between the liquid crystal control voltage VC and transmittance is stored. Based on this characteristic information, the CPU 401 calculates the second light intensity data OP2 (Figure 3C) before attenuation, which corresponds to the intensity of the received light, from the first light intensity data OP1 (Figure 3C) after attenuation.

[0044] (Response speed) In the transmission electron microscope 1 according to the first embodiment, the response speed between the liquid crystal control voltage and the light transmittance is several tens of milliseconds or less. Therefore, the liquid crystal element can be applied without any problems in the operation of the TEM camera.

[0045] (The arrangement of the liquid crystal cell, optical fiber bundle, and image sensor) This section explains the coupling between the liquid crystal cell and the optical fiber bundle, as well as the arrangement relationship with the image sensor.

[0046] To control the intensity at the individual image sensor unit (pixel) level using a liquid crystal panel, it is desirable that the number of divisions in the liquid crystal panel correspond to the number of image sensor units (pixels). In other words, it is desirable to have a one-to-one correspondence between the number of liquid crystal cells and the number of pixels in the image sensor. For example, the pixel size of an image sensor is approximately 15 μm square, while the liquid crystal cell size of a liquid crystal panel is approximately 40 μm square or larger. Therefore, in practice, one liquid crystal cell is mounted on multiple image sensors (approximately 3 x 3 to 4 x 4 pixels). The optical fiber bundle 82 consists of bundled optical fibers. Each optical fiber is smaller than an image sensor.

[0047] (Center spot, LCD cell, image sensor size) The correspondence between the planar size of the center spot and the number of liquid crystal cells in the XY direction, and the correspondence between the number of liquid crystal cells and the number of pixels on the image sensor, will be explained using an example of a camera that acquires a spot image.

[0048] The pixel size of an image sensor is, for example, a square with sides of approximately 15 μm. Approximately 4096 of these pixels are arranged vertically and horizontally. Therefore, the overall size of the camera's image sensor is approximately 61 mm square. While the size of each liquid crystal cell in a liquid crystal panel is ideally a square of approximately 15 μm, in reality, they are typically around 40 μm to 80 μm square. For this reason, as mentioned above, one liquid crystal element is mounted on multiple image sensors (approximately 3x3 to 4x4 pixels). For example, if one liquid crystal element is mounted on a 4x4 pixel image sensor, approximately 1024 liquid crystal elements will be arranged vertically and horizontally. The size of the center spot is, for example, approximately 200 x 200 pixels, which corresponds to approximately 3 mm x 3 mm on the image sensor. The number of cells in the liquid crystal panel would be approximately 50 x 50.

[0049] (Current at which the image sensor saturates) This explains the current value at which one pixel of the image sensor saturates. Assume the optical integration time is 0.1 seconds. Assume that the scintillator generates 46 counts when struck by one electron. Since each pixel has a 16-bit grayscale range, it can count up to 65536 counts. Therefore, the number of electrons that can be counted theoretically is 65536 / 46 = 1425. The current value at that time is 1425 × 1.6 × 10⁻¹⁵. -19 / 0.1 = 2fA. If more than 2fA of electrons are incident on a single pixel, that pixel of the image sensor will saturate and become uncountable. This value is easily reached, for example, by transmitted electrons in EELS (Electron Energy Loss Spectroscopy) or NBD (Nanobeam Electron Diffraction). In the transmission electron microscope 1 according to the first embodiment, by attenuating the light transmitted through the multiple divided liquid crystal cells, the current level at which the image sensor saturates can be avoided, and the irradiation intensity to any pixel of the image sensor can be arbitrarily adjusted on the camera.

[0050] (Zero-loss peak intensity) This section explains why recording the liquid crystal control voltage of each liquid crystal cell is necessary to determine the value before light attenuation occurs. The following explanation uses EELS (Electron Energy Loss Spectroscopy) as an example. Transmission electron microscopes use thin sections (generally less than 100 nm) that are thin enough for the electron beam to penetrate. The strongest zero-loss peak in EELS varies depending on the thickness of the thin section being observed. This intensity can be used to estimate the thickness of the thin section. Furthermore, determining the zero-loss peak intensity requires appropriately determining the background, making the zero-loss peak intensity crucial. Thus, because knowing the zero-loss peak intensity provides valuable information, it is necessary to determine the value before attenuation.

[0051] (Flowchart for determining the relationship between liquid crystal control voltage and transmittance) Before measuring the first light intensity data OP1 after attenuation, it is necessary to determine the relationship between the liquid crystal control voltage VC applied to the liquid crystal element and the transmittance (attenuation rate). Here, the liquid crystal control voltage VC applied to the liquid crystal element is supplied by the control unit 40. The transmittance (attenuation rate) is measured at the image sensor 70.

[0052] Figure 4 is a flowchart for determining the relationship between liquid crystal control voltage and transmittance. It is a flowchart of the operation method of a transmission electron microscope according to an embodiment, where the light transmittance of the liquid crystal element is defined as 1%. The operation flowchart in Figure 4 allows for the detection of the liquid crystal control voltage VC and image when the light transmittance (attenuation rate) is 1%, i.e., the shielding rate is 99%.

[0053] (A) First, in step S1, the electron beam 10 is irradiated onto the electron beam detector 22 by the control of the control unit 40.

[0054] (B) Next, in step S2, the electron beam detector 22 (camera) takes an image, and the liquid crystal control voltage VC applied to the liquid crystal element and the obtained image are recorded in the RAM 402 in the control unit 40.

[0055] (C) Next, in step S3, it is determined whether the measured transmittance (light attenuation rate) of the image sensor 70 is 1% (shielding rate is 99%).

[0056] (D) If the judgment result is NO, the process proceeds to step S4, where the control unit 40 changes the liquid crystal control voltage VC applied to the liquid crystal element, and the process returns to step S2.

[0057] (E) If the result of the judgment in step S3 is YES, the process ends.

[0058] The above operation flow allows us to determine the relationship between the liquid crystal control voltage VC applied to the liquid crystal element and its transmittance (light attenuation rate).

[0059] (Flowchart showing how a transmission electron microscope works) Figure 5 is a flowchart showing the operation method of a transmission electron microscope.

[0060] The flowchart for determining the relationship between the liquid crystal control voltage VC applied to the liquid crystal element and the transmittance (light attenuation rate) is the same as in Figure 4.

[0061] (F) Next, if the judgment result in step S3 is YES, the process proceeds to step S5, where the sample is observed, the liquid crystal control voltage VC applied to the liquid crystal element and the obtained image are recorded in the RAM 402 in the control unit 40, and the attenuated first light intensity data OP1 is generated.

[0062] (G) Next, the process moves to step S6, where the CPU 401 calculates the second light intensity data OP2 before attenuation using the transmittance (attenuation rate) recorded in RAM 402 from the liquid crystal control voltage VC of each liquid crystal element.

[0063] (H) Next, the process moves to step S6, where the calculation of the second light intensity data OP2 before attenuation is displayed on the image. Since the liquid crystal control voltage applied to each liquid crystal element is recorded during measurement, and the attenuation rate of each liquid crystal element is known, the second light intensity data OP2 before attenuation can be calculated and displayed on the image.

[0064] Following the above operation flow, the second light intensity data OP2 before attenuation can be calculated from the measurement result of the first light intensity data OP1 after attenuation and displayed on the image.

[0065] According to the transmission electron microscope of the first embodiment, in EELS (electron energy loss spectroscopy), the spectral count can be increased by adjusting the intensity.

[0066] According to the transmission electron microscope of the first embodiment, in NBD (nanobeam electron diffraction), weaker spots and halo patterns can be clearly obtained by adjusting the intensity.

[0067] According to the transmission electron microscope of the first embodiment, the intensity of the center spot can be reduced by adjusting the intensity, so the position of the center spot can be determined. Furthermore, since the degree of reduction can be calculated, it is possible to obtain a bright-field image by calculation, and the position in real space can also be determined.

[0068] (Effects of the first embodiment) According to the first embodiment, a transmission electron microscope and a method of operating the same can be provided, which allows for arbitrary adjustment of the illumination intensity to any pixel of the image sensor and reduces the intensity of the center spot.

[0069] (Second Embodiment) (Configuration of a transmission electron microscope) Figure 6A is a diagram showing the configuration of the transmission electron microscope 2 according to the second embodiment. The differences from the first embodiment will be explained below, and redundant explanations will be omitted.

[0070] As shown in Figure 6A, the transmission electron microscope 2 according to the second embodiment comprises a beam irradiation unit 11, a first lens system 100 located downstream thereof, a holder 31 located downstream thereof for mounting a sample, a second lens system 200 located downstream thereof, a dark-field detector 21 located downstream thereof, a detection mechanism 22 located downstream thereof, and a control unit 40.

[0071] The detection mechanism 22 includes a scintillator 25, a light propagation unit 80 that propagates the light converted in the scintillator 25, and an image sensor 70 that receives the light propagated by the light propagation unit 80. In the transmission electron microscope 2 according to the second embodiment, unlike the first embodiment, it is not necessary to provide the element 60 inside the detection mechanism 22.

[0072] The transmission electron microscope 2 according to the second embodiment includes a film 24 provided downstream of the second lens system 200 and between it and the detection mechanism 22, which reduces the amount of electrons incident on the detection mechanism 22. Alternatively, the film 24 may be provided upstream of the detection mechanism 22, or between the second lens system 200 and the dark-field detector 21. The film 24 can be positioned to overlap with the center spot, allowing the detection mechanism 22 to acquire the diffraction pattern.

[0073] Film 24 is an electron beam attenuation type (semi-transmissive type) beam stopper film. A semi-transmissive beam stopper film is capable of achieving, for example, an electron beam semi-transmittance of approximately 1% to approximately 99%. The thickness of film 24 is, for example, approximately 100 nm to 1 μm.

[0074] The film 24 can be a carbon (C) film or a silicon nitride (SiN) film. Other examples include amorphous silicon (a-Si), amorphous germanium (a-Ge), polyvinyl formal, or nitrocellulose.

[0075] The film 24 may also be equipped with a mechanism that allows for the arbitrary reduction of the amount of electrons incident on the detection mechanism 22 by inserting multiple films into the center spot.

[0076] For example, carbon films of different thicknesses may be prepared, resulting in films 24 with electron beam semitransmittances of 25%, 50%, and 75%, which can then be combined. Alternatively, multiple identical films 24 may be combined.

[0077] (Frame mechanism) Figure 6B shows a first configuration example of the frame mechanism applied to the transmission electron microscope 2 according to the second embodiment. Figure 6C shows a second configuration example of the frame mechanism applied to the transmission electron microscope 2 according to the second embodiment. Figure 6D shows a third configuration example of the frame mechanism applied to the transmission electron microscope 2 according to the second embodiment. In the first configuration example, the frame 23A is circular. In the second configuration example, the frame 23A is elliptical or oblong. In the third configuration example, the frame 23A is rectangular. The shape of the frame 23A is not limited to the above examples. It is sufficient that it can cover the center spot, and it may be triangular, a polygon with 5 or more sides, cloud-shaped, etc.

[0078] The film 24 is held by a frame 23A, as shown in Figures 6B to 6D. A frame bar 23B is connected to the frame 23A. Examples of materials that can be used for the frame 23A and frame bar 23B include copper (Cu), molybdenum (Mo), or aluminum (Al). It is desirable that the frame 23A and frame bar 23B be physically small. For this reason, it is preferable to use a hard and easily workable metal. Also, due to the characteristics of the transmission electron microscope 2, it is desirable that they be conductive. In the example in Figure 6B, the diameter of the frame 23A is about 3 mm.

[0079] The frame mechanism 23 must be located downstream of all electromagnetic lenses and upstream of the electron beam detector 22 due to the configuration of the device. The mechanism for positioning the frame mechanism 23 is the mechanism for moving the frame bar 23B attached to frame 23A. In the example shown in Figure 6A, the frame mechanism 23 is located upstream of the dark-field detector 21, but it is not limited to this. It only needs to be located upstream of the electron beam detector 22, and may be located upstream of the electron beam detector 22 and downstream of the dark-field detector 21.

[0080] (Flowchart showing how a transmission electron microscope works) Figure 7 is a flowchart showing the operation method of the transmission electron microscope 2 according to the second embodiment.

[0081] (A) First, in step S11, the observation area on the sample is specified and the exposure time is set. Here, the exposure time may be the minimum exposure time. The value of the minimum exposure time is, for example, about 0.001 seconds.

[0082] (B) Next, in step S12, the electron beam 10 is irradiated onto the sample under the control of the control unit 40, and the diffraction pattern is acquired by the detection mechanism 22.

[0083] (C) Next, in step S13, the film 24 held by the frame mechanism 23 is placed in a predetermined position corresponding to the center spot. The center spot is a spot irradiated by a relatively strong electron beam. Here, the predetermined position is located between the downstream of the second lens system 200 and the upstream of the detection mechanism 22, and reduces the amount of electrons incident on the detection mechanism 22. It is also a position between the second lens system 200 and the dark-field detector 21 that reduces the amount of electrons incident on the detection mechanism 22. The film 24 is a film that overlaps with the center spot and allows the detection mechanism 22 to acquire a diffraction pattern.

[0084] (D) Next, in step S14, the electron beam 10 is irradiated onto the sample under the control of the control unit 40, and the diffraction pattern is acquired by the detection mechanism 22.

[0085] (E) Next, in step S15, it is determined whether the signal intensity obtained by the detection mechanism 22 is 90% or more of the saturation level. Here, the saturation level is the signal intensity value at which the signal intensity does not change even if the exposure time is extended. For example, it is a value close to zero where the time derivative of the signal intensity is below a certain threshold level. The saturation level may also be defined as a specific upper limit of the signal intensity. In this case, in step S15, it is determined whether the signal intensity obtained by the detection mechanism 22 is 90% or more of the specific upper limit.

[0086] (F) Next, if the answer in step S15 is NO, the process proceeds to step S16, the exposure time is extended, and the process returns to step S14.

[0087] (G) Next, if the answer in step S15 is YES, the diffraction pattern is acquired for the extended exposure time and the process is terminated. Specifically, for example, if the signal intensity obtained by the detection mechanism 22 in step S15 of the (n+1)th exposure time is 90% or more of a specific upper limit compared to step S15 of the (n)th exposure time, the diffraction pattern is acquired for the (n+1)th extended exposure time and the process is terminated.

[0088] The results of observing a cross-section of a MOS device using a transmission electron microscope 2 according to the second embodiment are described below. The polysilicon, silicon (Si), and silicon oxide film (SiO2) portions were observed.

[0089] For silicon (Si), NBD mapping (pseudo-bright-field imaging) was created using a center spot, and the diffraction pattern of a Si single crystal was observed. However, this method cannot be used if a beam stopper that blocks the center spot is employed.

[0090] For polysilicon, NBD mapping (pseudo-bright-field imaging) was created using a center spot, and the diffraction pattern of polycrystalline polysilicon was observed. However, this method cannot be used if a beam stopper that blocks the center spot is employed.

[0091] For silicon oxide (SiO2) films, NBD mapping (pseudo-bright-field imaging) was created using a center spot, and the diffraction pattern of amorphous (SiO2) was observed. Again, this method cannot be used if a beam stopper that blocks the center spot is employed. In the example of the diffraction pattern for amorphous (SiO2), a halo pattern was observed around the center spot because it is not crystalline.

[0092] Based on the observations above, a comparison of the beam intensity at the center spot reveals a tendency for the beam intensity to be stronger in the order of Si single crystal < polycrystalline polysilicon < amorphous (SiO2). The intensity of the diffraction pattern can be considered as the intensity of the bright-field image at each point. In Si single crystals, the beam intensity is dispersed by the crystal diffraction pattern around the center spot, resulting in a decrease in the beam intensity at the center spot. In polycrystalline polysilicon, the beam intensity is dispersed by the diffraction pattern of the polycrystalline portion around the center spot, resulting in a decrease in the beam intensity at the center spot. In contrast, in amorphous (SiO2), the beam intensity is not dispersed by the diffraction pattern. Therefore, a relatively strong beam intensity is observed at the center spot. In Si single crystals, the upper limit of the count of the center spot in the diffraction pattern is 65,536 counts in 16 bits, which is approximately 60,000 counts. In contrast, the diffraction spot has approximately 2,000 counts, and the halo pattern has approximately 400 counts.

[0093] (Effects of the second embodiment) According to the transmission electron microscope of the second embodiment, weak-intensity spots can be acquired without damaging the camera or causing saturation. Furthermore, since the position of the center spot can be determined, crystal structure analysis becomes easier.

[0094] According to the transmission electron microscope of the second embodiment, only the intensity of the strong spots can be attenuated, and as a result, weak spots can be acquired in the same region as the strong spots without damaging the camera (without saturation).

[0095] According to the second embodiment, a transmission electron microscope and a method of operating the same can be provided, which allows adjustment of only the intensity of the center spot and acquisition of a diffraction pattern including the center spot with the same camera.

[0096] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0097] 1, 2...Transmission electron microscope 10… Electron beam 11...Beam irradiation section 12...Condenser lens 13... Scan Coil 14…Objective lens 15…Intermediate lens 16...Descan Coil 17…Projection lens 21... Dark-field detector 22…Detection mechanism (electron beam detector) 23... Frame mechanism 23A...frame 23B... Frame bar 24...Membrane 25... Scintillator 31... Holder 40... Control Unit 50...Display section 60... elements (liquid crystal elements, liquid crystal panels, liquid crystal cells) 70…Image sensor 75… Heatsink 80...Optical propagation section 82… Fiber optic bundle 100...First lens system 111... Field emission electron gun 112...Acceleration section 200...Second lens system 401…CPU 402…RAM

Claims

1. The beam irradiation section, A first lens system provided downstream of the beam irradiation section, A holder for mounting a sample is provided downstream of the first lens system, A second lens system provided downstream of the holder, A detection mechanism provided downstream of the second lens system, It includes a control unit, The aforementioned detection mechanism is A scintillator that detects electron beams, A light propagation unit that propagates the light converted in the scintillator, The system comprises an image sensor that receives light propagated by the aforementioned light propagation unit, The light propagation section includes an element that can change the transmittance of light, The control unit, A transmission electron microscope that generates first light intensity data from a signal obtained by detecting light transmitted through the aforementioned element with the image sensor.

2. The transmission electron microscope according to claim 1, wherein the element comprises a liquid crystal element capable of changing its transmittance according to a supplied liquid crystal control voltage, and a voltage supply unit that supplies the liquid crystal control voltage.

3. The transmission electron microscope according to claim 2, wherein the liquid crystal element is divided into at least a first region and a second region, and the voltage supply unit can change the light transmittance at any position by supplying an arbitrary liquid crystal control voltage to the first region and the second region.

4. The control unit, A storage unit for storing characteristic information showing the relationship between the liquid crystal control voltage and transmittance for each of the first and second regions, The transmission electron microscope according to claim 3, further comprising a calculation unit that calculates a second light intensity data corresponding to the intensity of received light from the first light intensity data based on the characteristic information.

5. The control unit, The liquid crystal control voltage applied to the first region and the second region is gradually increased. In the first and second regions, the liquid crystal control voltage obtained when data within the dynamic range is stored in the storage unit. Based on the stored liquid crystal control voltage, the beam irradiation unit performs irradiation. The transmission electron microscope according to claim 4, which generates the first light intensity data.

6. Downstream of the second lens system, a film is provided between it and the detection mechanism to reduce the amount of electrons incident on the detection mechanism. The transmission electron microscope according to claim 1, wherein the film overlaps with the center spot, and the diffraction pattern can be acquired by the detection mechanism.

7. The beam irradiation section, A first lens system provided downstream of the beam irradiation section, A holder for mounting a sample is provided downstream of the first lens system, A second lens system provided downstream of the holder, A detection mechanism provided downstream of the second lens system, It includes a control unit, The aforementioned detection mechanism is A scintillator that detects electron beams, A light propagation unit that propagates the light converted in the scintillator, The system comprises an image sensor that receives light propagated by the aforementioned light propagation unit, Downstream of the second lens system, a film is provided between it and the detection mechanism to reduce the amount of electrons incident on the detection mechanism. A transmission electron microscope in which the aforementioned film overlaps with the center spot, and the diffraction pattern can be acquired by the detection mechanism.

8. The transmission electron microscope according to claim 6 or 7, wherein the film is a semi-transmissive beam stopper film.

9. The transmission electron microscope according to claim 6 or 7, wherein the film is provided with a mechanism that allows the amount of electrons incident on the detection mechanism to be arbitrarily reduced by inserting multiple films into the center spot.

10. The transmission electron microscope according to claim 6 or 7, wherein the film can be a carbon (C) film or a silicon nitride (SiN) film.

11. The liquid crystal control voltage applied to the first and second liquid crystal cells of the liquid crystal panel is gradually increased. Characteristic information showing the relationship between the liquid crystal control voltage and transmittance when data within the dynamic range is obtained in each of the first liquid crystal cell and the second liquid crystal cell is stored in the memory unit. Based on the stored liquid crystal control voltage, the beam irradiation unit performs irradiation. Based on the stored liquid crystal control voltage, the attenuated first light intensity data is generated. A method for operating a transmission electron microscope, comprising calculating a second light intensity data before attenuation, corresponding to the intensity of received light, from the first light intensity data based on the characteristic information.

12. Specify the observation area on the sample, set the exposure time, An electron beam is irradiated onto the sample, and a diffraction pattern is acquired in the detection mechanism. A membrane is placed in the position corresponding to the center spot. The electron beam is irradiated onto the sample, and the diffraction pattern is acquired in the detection mechanism. A method for operating a transmission electron microscope, comprising: determining whether the signal intensity obtained in the detection mechanism is 90% or more of a specific upper limit; if it is less than 90%, extending the exposure time; and if it is 90% or more, acquiring a diffraction pattern during the extended exposure time.

Images