Electronic microscope for three-dimensional imaging and three-dimensional imaging method

Abstract

The invention provides an electron microscope for three-dimensional imaging and a three-dimensional imaging method, and relates to the technical field of electron microscopes, the electron microscope for three-dimensional imaging comprises an ion gun, a sample table and a baffle plate located between the ion gun and the sample table, the position of the sample table and / or the baffle plate can be adjusted in parallel, and the sample table and / or the baffle plate can be adjusted in parallel. Therefore, the baffle can adjustably shield an ion beam emitted by the ion gun to a sample on the sample table. Thus, an ion beam emitted by the ion gun bombards the part, not shielded by the baffle, of the sample to form a plane, after plane imaging is finished, a new unshielded part is formed on the sample by adjusting the position of the sample table and / or the baffle in parallel, bombardment continues to be conducted through the ion beam, a new plane is formed on the sample, and then imaging of the plane is completed. The new plane is parallel to the last plane, and the steps are repeated to stack the images of the plurality of planes to form three-dimensional imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of electron microscopes, and in particular to an electron microscope for three-dimensional imaging and a three-dimensional imaging method. Background Art

[0002] An electron microscope (EM) uses an electron beam as a light source to irradiate solid materials and uses the electrons scattered by the electron beam as signals. It is mainly used for high-resolution imaging of the surface or internal structure and morphology of sample materials to analyze the microstructural characteristics of the material.

[0003] Traditionally, electron microscopes, like conventional optical microscopes, present two-dimensional images. However, for actual research objects, more information exists in the three-dimensional structure of the sample. In order to seek the three-dimensional structural information of the sample, volume electron microscope technology has emerged.

[0004] At present, the working principle of volume electron microscopy technology based on scanning electron microscope (SEM) imaging is: use mechanical or ion beam to slice or peel the sample layer by layer to obtain a new section, and take pictures layer by layer, finally obtain a series of images aligned in the thickness direction, and then superimpose them into a three-dimensional image through computing software. It can include the following two types: one is to use diamond knife slicing technology, including the ultra-thin slicer outside the electron microscope to make serial slices (Array Tomography) and the ultra-thin slice installed inside the electron microscope sample chamber. Serial block-face imaging, referred to as SBFI; the other is to use focused ion beam technology, including the focused ion beam (FIB) using a metal gallium source and the plasma focused ion beam (PFIB) using a gas source to remove the sample surface layer by layer.

[0005] Taking common life science samples as an example, when using diamond knife slicing technology, the serial slicing technology (ArrayTomography) requires a special slicer to cut the sample into a series of continuous slices. SBFI miniaturizes the design of the external slicer and places it on the sample stage inside the electron microscope chamber to scrape the sample layer by layer. Each time a layer is scraped off, the SEM is imaged once, and then the multiple layers of images are stacked to form a three-dimensional model. When using focused ion beam technology, FIB or PFIB needs to use a focused ion beam to bombard the sample with ion beams to remove the cut surface layer by layer. When the structure of interest appears, the ion beam sectioning and imaging are repeated to form a three-dimensional model of the sample area.

[0006] The above-mentioned diamond knife slicing technology requires a highly stable continuous slicer, which is expensive and difficult to maintain whether installed outside or inside the electron microscope. Moreover, due to the large limitations of the diamond knife's blade thickness, mechanical movement accuracy, and sample mechanical strength, it is difficult to continuously and stably cut out serial slices with a thickness of less than 30nm, making it difficult to improve the analysis accuracy of the sample in the thickness direction to within 20nm. In addition, the diamond knife itself is easily damaged as a consumable, and the thin slices prepared by diamond knife slicing are also prone to deformation, making it difficult to align the image. The beam spot diameter of the focused ion beam technology is less than 1μm, and can only form a three-dimensional model of the sample within a small range of about tens of microns, and cannot perform three-dimensional imaging of samples in a large range of millimeters. Summary of the invention

[0007] The present invention aims to provide an electron microscope for three-dimensional imaging and a three-dimensional imaging method, in order to at least partially solve at least one of the above-mentioned technical problems.

[0008] To solve the above technical problems, the first aspect of the present invention provides an electron microscope for three-dimensional imaging, comprising: an ion gun, a sample stage, and a baffle located between the ion gun and the sample stage, wherein the positions of the sample stage and / or the baffle can be adjusted in parallel so that the baffle can adjustably block the ion beam emitted by the ion gun to the sample on the sample stage.

[0009] According to a preferred embodiment of the present invention, the parallel adjustment refers to multiple movements of a predetermined distance along the same adjustment direction; the adjustment direction is any direction within the plane where the baffle is located.

[0010] According to a preferred embodiment of the present invention, the sample stage can be raised and lowered;

[0011] Alternatively, the baffle can be raised or lowered;

[0012] Alternatively, both the sample stage and the baffle can be raised and lowered.

[0013] According to a preferred embodiment of the present invention, the sample stage is a sample lifting stage, and the baffle is arranged on the baffle lifting stage;

[0014] The sample lifting platform is adjacent to the baffle lifting platform, and both are arranged on the electron microscope sample moving platform.

[0015] According to a preferred embodiment of the present invention, the apparatus further comprises a shell, wherein the ion gun passes through a side wall of the shell and emits an ion beam to a baffle and a sample on a sample lifting platform.

[0016] According to a preferred embodiment of the present invention, the sample stage can move in the horizontal direction of the plane where the baffle plate is located;

[0017] Alternatively, the baffle may be movable in a horizontal direction along the plane where the baffle is located;

[0018] Alternatively, both the sample stage and the baffle can move in a horizontal direction along the plane where the baffle is located.

[0019] According to a preferred embodiment of the present invention, the sample stage is adjacent to the baffle stage, and is arranged on the electron microscope sample moving stage via a sliding structure that can move in a horizontal direction along the plane where the baffle is located.

[0020] According to a preferred embodiment of the present invention, the beam spot diameter of the ion beam generated by the ion gun is greater than or equal to 100 μm.

[0021] In order to solve the above technical problems, the second aspect of the present invention provides a three-dimensional imaging method generally applicable to electron microscopes, the method comprising:

[0022] S1. Place the sample to be tested on the sample stage and reset the baffle and / or the sample stage;

[0023] S2, controlling the ion gun to emit an ion beam to bombard the portion of the sample on the sample stage that is not blocked by the baffle to form a first plane, and controlling the electron microscope to image the first plane to obtain a first plane image;

[0024] S3, adjusting the position of the sample stage and / or the baffle in parallel according to the adjustment direction to form a new unblocked portion on the sample;

[0025] S4, looping through steps S2 and S3, stacking the obtained images of multiple parallel planes to form a three-dimensional image.

[0026] In summary, the electron microscope and three-dimensional imaging method of the present invention, by setting a baffle between the ion gun and the sample stage, and making the position of the sample stage and / or the baffle adjustable in parallel, so that the baffle can adjustably block the ion beam emitted by the ion gun to the sample on the sample stage; in this way, the ion beam emitted by the ion gun will bombard the part of the sample not blocked by the baffle to form a plane, and after imaging this plane, the position of the sample stage and / or the baffle can be adjusted in parallel to form a new unblocked part on the sample, and continue to bombard with the ion beam to form a new plane on the sample parallel to the previous plane, and so on, the cycle is repeated, and the images of multiple planes are stacked to form a three-dimensional image. Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] 1. High precision: Avoid mechanical slicing operations, damage to the sample section caused by physical damage to the tool, and reduce the error in the thickness direction of the sample mechanical slicing process; improve the accuracy of three-dimensional imaging.

[0028] 2. Low cost: no expensive slicer is required, which greatly saves costs.

[0029] 3. Wide imaging range: The spot diameter of the ion beam exceeds 100μm, which can form a large imaging processing area, overcoming the disadvantage that the focused ion beam technology can only perform three-dimensional imaging on a small area of ​​the sample.

[0030] 4. Simple operation: just adjust the workbench and / or baffle position several times. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of an electron microscope for three-dimensional imaging provided in Embodiment 1 of the present invention;

[0032] Figure 2 It is a schematic diagram of bombarding a sample with an ion gun in an electron microscope for three-dimensional imaging provided in the first embodiment of the present invention;

[0033] Figure 3 is a schematic flow chart of a three-dimensional imaging method for an electron microscope provided in Embodiment 2 of the present invention;

[0034] Among them: 1-ion gun, 2-baffle, 21-baffle lifting platform, 3-sample stage, 4-electron microscope sample moving stage, 6-connecting flange. DETAILED DESCRIPTION

[0035] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and Examples. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention.

[0036] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0037] Embodiment 1

[0038] refer to Figure 1 and 2 , Embodiment 1 of the present invention provides an electron microscope for three-dimensional imaging, comprising: a shell (not shown in the figure), an ion gun 1 is penetrated through the side wall of the shell, a sample stage 3 and a baffle 2 are arranged in the bottom of the shell, and the baffle 2 is located between the ion gun 1 and the sample stage 3, and the ion beam generated by the ion gun 1 can be emitted to the baffle 2 and the sample on the sample stage 3. Wherein: the position of the sample stage 3 and / or the baffle 2 can be adjusted in parallel, so that the baffle 2 can be adjusted to block the ion beam emitted by the ion gun 1 to the sample on the sample stage 3. Wherein: parallel adjustment refers to multiple movements of a predetermined distance along the same adjustment direction, and the predetermined distance of each movement can be the same or different. The adjustment direction can be any direction in the plane where the baffle 2 is located (for example: vertical direction, horizontal direction of the plane where the baffle is located, etc.). In this way, if Figure 2 The ion beam emitted by the ion gun 1 will bombard the part of the sample that is not blocked by the baffle to form a plane. After imaging this plane, the position of the sample stage 3 and / or the baffle 2 can be adjusted to form a new unblocked part on the sample, and the ion beam bombardment is continued to form a new plane on the sample. Since the position of the sample stage 3 and / or the baffle 2 is adjusted in parallel, the new plane is parallel to the previous plane. This cycle is repeated to stack the images of multiple parallel planes to form a three-dimensional image.

[0039] In this embodiment, the ion beam generated by the ion gun 1 is a defocused ion beam rather than a focused ion beam. Preferably, a defocused ion beam with a beam spot diameter greater than or equal to 100 μm can be used instead of a focused ion beam with a diameter less than 1 μm currently used in the market. In this way, a large flat cutting surface can be obtained at the same time. The role of the ion beam can be similar to that of a tool, scraping off the part of the sample that is not blocked by the baffle to form a new plane. Furthermore, the outside of the shell can be connected to other devices through the flange of the electron microscope (such as a scanning electron microscope) cavity.

[0040] For example, during the three-dimensional imaging process, the position of the sample stage 3 and / or the baffle 2 can be moved up and down in the vertical direction to obtain images of multiple parallel planes. Then, the sample stage 3 can be set as a liftable structure; wherein: the lift structure can be integrated with the sample stage 3, that is, the sample lift table is directly used as the sample stage, and the lift structure can be separated from the sample stage 3, for example: the sample stage 3 is fixed on the lift structure.

[0041] Alternatively, only the baffle 2 can be set as a liftable structure; wherein: the lift structure can be integrated with the baffle 2, that is, the lift structure has the baffle 2, and the lift structure can be separated from the baffle 2, for example: the baffle 2 is fixed to the lift structure. Exemplarily, the baffle 2 can be a flat plate, and the plane where the flat plate is located is perpendicular to the direction in which the ion gun 1 emits the ion beam. The material of the baffle 2 can be selected from hard materials to withstand the attack of the ion beam, so that the part of the sample blocked by the baffle is not bombarded by the ion beam.

[0042] Alternatively, the sample stage 3 and the baffle 2 may both be configured as liftable structures. Figure 1 and 2 In the figure, the sample stage 3 is integrated with the lifting structure to form a sample lifting platform, and the baffle 2 is arranged on the baffle lifting platform 21, wherein: the baffle lifting platform 21 includes a lifting structure; in this way, the relative height of the sample and the baffle 2 can be adjusted by the baffle lifting platform 21 and / or the sample lifting platform. Optionally, the baffle lifting platform 21 and the sample lifting platform can be made of piezoelectric ceramics or mechanical structures. Part of the ion beam can be blocked by the baffle 2 to form a parabolic plane. Furthermore, in order to save the internal space of the shell, the sample lifting platform and the baffle lifting platform 21 can be arranged adjacent to each other. In addition, an electron microscope sample moving platform 4 can be arranged at the bottom of the shell, and the sample lifting platform and the baffle lifting platform 21 can be fixed on the electron microscope sample moving platform 4. Among them: the electron microscope sample motion stage 4 can provide overall movement in five directions of XYZRT for the sample, baffle 2, sample lifting platform, and baffle lifting platform 21 thereon, so that the sample or the device carrying the sample can be moved to a specified position; further, a connecting flange 5 can be set on the side of the electron microscope sample motion stage 4 as an interface for connecting the driving motor of the electron microscope sample motion stage 4.

[0043] In this example, the lifting structure can be implemented by using an existing mechanical structure that can be lifted and lowered gradually, or it can be implemented by using materials such as piezoelectric ceramics to achieve lifting and lowering of a specific value under the control of the user, for example, 10 nm at a time.

[0044] In another example, during the three-dimensional imaging process, the position of the sample stage 3 and / or the baffle 2 can be moved in the horizontal direction of the plane where the baffle 2 is located to obtain images of multiple parallel planes. Then, only the sample stage 3 can be set to be movable in the horizontal direction of the plane where the baffle 2 is located; for example, a sliding structure that can move in the horizontal direction of the plane where the baffle 2 is located can be set at the bottom of the sample stage 3 and the bottom of the shell.

[0045] Alternatively, the baffle 2 may be configured to be movable in the horizontal direction along the plane where the baffle 2 is located; for example, sliding structures movable in the horizontal direction along the plane where the baffle 2 is located may be provided at the bottom of the baffle 2 and the bottom of the shell, respectively.

[0046] Alternatively, the sample stage 3 and the baffle 2 can be both arranged to be movable in the horizontal direction of the plane where the baffle 2 is located; a sliding structure that can be movable in the horizontal direction of the plane where the baffle 2 is located can be arranged at the bottom of the sample stage 3, the bottom of the baffle 2, and the bottom of the shell, respectively. In this way, the relative position of the sample and the baffle 2 in the horizontal direction of the plane where the baffle 2 is located can be adjusted by the baffle 2 and / or the sample stage 3, and part of the ion beam can be shielded by the baffle 2 to form a parabolic plane. Furthermore, in order to save the internal space of the shell, the sample stage 3 and the baffle 2 can be arranged adjacent to each other. In addition, an electron microscope sample moving stage 4 can be arranged at the bottom of the shell, and a sliding structure that can be movable in the horizontal direction of the plane where the baffle 2 is located can be arranged on the electron microscope sample moving stage 4.

[0047] In this example, the sliding structure may include: a slide rail and a slider. A plurality of clamps that can be rotated to the inside of the slider can be arranged on the outside of the slider. When the slider moves to a certain clamp position, the clamp is rotated to the inside of the slide rail to fix the slider, and then the ion beam bombardment is turned on to form a new plane on the sample. Among them: the slider can be arranged on the baffle 2 and / or the sample stage 3, and the slide rail is arranged at the bottom of the shell; or, the slider can be arranged at the bottom of the shell, and the slide rail is arranged on the baffle 2 and / or the sample stage 3. In addition, materials such as piezoelectric ceramics can also be used to achieve horizontal movement of a specific value under the control of the user, for example, 10nm each time.

[0048] The above only illustrates examples of achieving parallel adjustment of the baffle 2 and / or the sample stage 3 along the vertical direction and the horizontal direction of the plane where the baffle 2 is located. Based on the above examples, a person skilled in the art can expand the implementation methods of parallel adjustment of the baffle 2 and / or the sample stage 3 along any direction within the plane where the baffle 2 is located, which will not be repeated here.

[0049] Embodiment 2

[0050] Based on any electron microscope for three-dimensional imaging in the first embodiment, the second embodiment of the present invention provides a three-dimensional imaging method for an electron microscope, such as Figure 2 As shown, the method includes:

[0051] S1, placing the sample to be tested on the sample stage 3, and resetting the baffle 2 and / or the sample stage 3;

[0052] In this embodiment, the sample is an object that the user needs to perform three-dimensional imaging of the electron microscope. Among them: the baffle 2 can be adjusted alone, and the baffle 2 needs to be restored to the initial position (i.e., reset), and the sample stage 3 can be adjusted alone, and the sample stage 3 needs to be reset; the baffle 2 and the sample stage 3 can also be adjusted at the same time, and the baffle 2 and the sample stage 3 need to be reset at the same time.

[0053] The adjustable baffle 2 and / or the sample stage 3 both have preset initial positions. For example: when only the position of the baffle 2 can be adjusted parallelly in the vertical direction, the lowest position of the baffle 2 can be set as the initial position; when only the position of the sample stage 3 can be adjusted parallelly in the horizontal direction, the position of one end of the sample stage 3 in this horizontal direction can be set as the initial position, and so on. Other situations can be inferred by analogy.

[0054] S2. Control the ion gun 1 to emit an ion beam to bombard the unobstructed part of the sample on the sample stage 3 to form a first plane, and control the electron microscope to image the first plane to obtain a first plane image.

[0055] S3. Adjust the position of the sample stage 3 and / or the baffle 2 parallelly according to the adjustment direction to form a new unobstructed part on the sample.

[0056] In this embodiment, the adjustment direction can be any direction within the plane of the baffle 2. For example Figure 1 in the case where the ion gun 1 penetrates the side wall of the housing, the adjustment direction can be any direction within the plane of the baffle 2 (i.e., the plane perpendicular to the plane where the ion beam emitted by the ion gun 1 is located). The parallel adjustment means moving along the same adjustment direction (such as: vertically upward, vertically downward, horizontally left within the plane of the baffle 2, inclined 45 degrees upward within the plane of the baffle 2, etc.).

[0057] The specific adjustment direction can be determined according to the structure of the electron microscope used for three-dimensional imaging. For example Figure 1 in the case where the positions of the sample stage 3 and the baffle 2 can both be adjusted in the vertically upward or vertically downward direction, in this step, the heights of the sample stage 3 and the baffle 2 can be adjusted simultaneously in the opposite direction, or the sample stage 3 can be adjusted alone in the first direction, or the baffle 2 can be adjusted alone in the second direction, where: the first direction can be vertically upward, then the second direction is vertically downward; the first direction can also be vertically downward, then the second direction is vertically upward.

[0058] S4. Loop and execute steps S2 and S3, stack the images of the obtained multiple parallel planes to form a three-dimensional image.

[0059] In this embodiment, since the positions of the sample stage 3 and / or the baffle 2 are adjusted parallelly, the new plane is parallel to the previous plane. In this way, by looping and stacking the images of the obtained multiple parallel planes, a three-dimensional image is formed.

[0060] Specifically, a predetermined number of loops m can be set. When the number of imaging times N≥m, stack the images of the obtained multiple parallel planes to form a three-dimensional image. When the number of imaging times N<m, loop and execute steps S2 and S3.

[0061] In summary, the electron microscope and three-dimensional imaging method of the present invention, by setting a baffle 2 between the ion gun 1 and the sample stage 3, and making the position of the sample stage 3 and / or the baffle 2 adjustable in parallel, so that the baffle 2 can be adjusted to block the ion beam emitted by the ion gun 1 to the sample on the sample stage 3; in this way, the ion beam emitted by the ion gun 1 will bombard the part of the sample not blocked by the baffle to form a plane, and after imaging this plane, the position of the sample stage 3 and / or the baffle 2 can be adjusted in parallel to form a new unblocked part on the sample, and continue to bombard with the ion beam to form a new plane on the sample parallel to the previous plane, and so on, the cycle is repeated, and the images of multiple planes are stacked to form a three-dimensional image. Compared with the prior art, the present invention has at least the following beneficial effects:

[0062] 1. High precision: Avoid mechanical slicing operations, damage to the sample section caused by physical damage to the tool, and reduce the error in the thickness direction of the sample mechanical slicing process; improve the accuracy of three-dimensional imaging.

[0063] 2. Low cost: no expensive slicer is required, which greatly saves costs.

[0064] 3. Wide imaging range: The spot diameter of the ion beam exceeds 100μm, which can form a large imaging processing area, overcoming the disadvantage that the focused ion beam technology can only perform three-dimensional imaging on a small area of ​​the sample.

[0065] 4. Simple operation: just adjust the workbench and / or baffle position several times.

[0066] It should be clear that the present invention is not limited to the specific structures and processes described above and shown in the figures. For the sake of simplicity, a detailed description of known structures is omitted here. In the above embodiments, several specific structures are described and shown as examples. However, the electron microscope for three-dimensional imaging of the present invention is not limited to the specific structures described and shown, and those skilled in the art can make various changes, modifications and additions, or change the installation positions between structures after understanding the spirit of the present invention.

[0067] The above is only a specific implementation of the present invention. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process of the above-described structure, module and unit can refer to the corresponding process in the aforementioned embodiment, and will not be repeated here. It should be understood that the protection scope of the present invention is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be covered within the protection scope of the present invention.

Claims

1. An electron microscope for three-dimensional imaging, characterized in that: include: An ion gun, a sample stage, and a baffle located between the ion gun and the sample stage. The positions of the sample stage and / or the baffle can be adjusted in parallel so that the baffle can adjustably block the ion beam emitted by the ion gun to the sample on the sample stage.

2. The electron microscope for three-dimensional imaging according to claim 1, characterized in that: The parallel adjustment refers to moving a predetermined distance multiple times along the same adjustment direction; the adjustment direction is any direction within the plane where the baffle is located.

3. The electron microscope for three-dimensional imaging according to claim 2, characterized in that: The sample stage can be raised and lowered; Alternatively, the baffle can be raised or lowered; Alternatively, both the sample stage and the baffle can be raised and lowered.

4. The electron microscope for three-dimensional imaging according to claim 3, characterized in that: The sample platform is a sample lifting platform, and the baffle is arranged on the baffle lifting platform; The sample lifting platform is adjacent to the baffle lifting platform, and both are arranged on the electron microscope sample moving platform.

5. The electron microscope for three-dimensional imaging according to claim 4, characterized in that: The invention also includes a housing, wherein the ion gun passes through a side wall of the housing and emits an ion beam to a baffle and a sample on a sample lifting table.

6. The electron microscope for three-dimensional imaging according to claim 2, characterized in that: The sample stage can move in the horizontal direction along the plane where the baffle plate is located; Alternatively, the baffle may be movable in a horizontal direction along the plane where the baffle is located; Alternatively, both the sample stage and the baffle can move in a horizontal direction along the plane where the baffle is located.

7. The electron microscope for three-dimensional imaging according to claim 6, characterized in that: The sample stage is adjacent to the baffle stage and is arranged on the electron microscope sample moving stage via a sliding structure that can move in a horizontal direction along the plane where the baffle is located.

8. The electron microscope for three-dimensional imaging according to claim 1, characterized in that: The ion gun generates an ion beam with a spot diameter greater than or equal to 100 μm.

9. A three-dimensional imaging method commonly used in electron microscopes, characterized in that: The method comprises: S1. Place the sample to be tested on the sample stage and reset the baffle and / or the sample stage; S2, controlling the ion gun to emit an ion beam to bombard the portion of the sample on the sample stage that is not blocked by the baffle to form a first plane, and controlling the electron microscope to image the first plane to obtain a first plane image; S3, adjusting the position of the sample stage and / or the baffle in parallel according to the adjustment direction to form a new unblocked portion on the sample; S4, looping through steps S2 and S3, stacking the obtained images of multiple parallel planes to form a three-dimensional image.

Images