A system and method for improving the accuracy of three-dimensional atom probe image reconstruction

Abstract

The present invention belongs to the field of atom probe tomography technology and relates to a system and method for improving the accuracy of three-dimensional atom probe image reconstruction. The system comprises: an APT sample rotation device for placing an APT sample and driving the APT sample to rotate about its axis; a focused electron beam generator for generating a focused electron beam that irradiates the APT sample; an electron beam deflection device for adjusting the focused electron beam; the deflected focused electron beam irradiates the APT sample at a predetermined angle, generating a backscattered electron signal; and a backscattered electron detector for collecting the backscattered electron signal. The backscattered electron detector is disposed between the focused electron beam generator and the electron beam deflection device, and has a through-hole at its center for a focusing resistor to pass through. The backscattered electron detector can monitor the surface topography of the APT sample in situ during the APT test and obtain the corresponding electric field distribution. During the reconstruction process, the results can be corrected based on the surface topography and the corresponding electric field distribution, thereby improving reconstruction accuracy.

Description

Technical Field

[0001] The present invention relates to a system and method for improving the reconstruction accuracy of three-dimensional atom probe images, and belongs to the technical field of atom probe tomography. Background Art

[0002] Three-Dimensional Atom Probe (3DAP; also known as atom probe tomography or atom probe tomography, APT) is a nanoscale material analysis technique that can provide near-atomic-scale three-dimensional spatial imaging of APT samples and highly sensitive chemical composition measurements. The basic working principle of APT is to prepare the APT sample to be analyzed into a rod or wedge shape with a diameter of 20–100 nm and a smooth pointed tip; use the APT sample as the positive electrode and place it close to a hollow micro-negative electrode, forming an ultra-strong (~10 10 V / m) electric field. This extremely strong electric field causes atoms in the outermost layer of the APT sample tip, where the curvature is greatest, to become severely polarized until they lose electrons and are ejected along the electric field lines (i.e., ionized and evaporated). The evaporated ions travel through a small hole in the center of the negative electrode, continuing their flight and impacting a two-dimensional position-sensitive detector. By applying a narrow pulse width (~ns) and low repetition rate (0.02–1 MHz) of voltage or laser pulses (to heat the tip) to the APT sample, the ion's flight time can be measured, its mass-to-charge ratio determined, and thus its species. The ion's two-dimensional position (and the electric field distribution) upon the detector allows the ion's orientation on the APT sample tip surface to be inferred. With this information, combined with the order of ion evaporation, an inversion algorithm can be used to reconstruct the layer-by-layer stacking of individual atoms on the APT sample.

[0003] Existing APT devices, whether commercial or laboratory-built, do not have a 100% collection rate for evaporated ions; some devices even collect less than 50%. This means that the device's detector only collects a portion of the ions evaporated from the APT sample. Furthermore, certain types of APT samples also evaporate large amounts of atomic or neutral molecular fragments. The delay line microchannel plate detectors currently used in APT devices are insensitive to atomic or neutral molecular fragments, resulting in a significant loss of information during the test process. Using only the ions collected by the detector to invert the three-dimensional distribution of atoms in the entire APT sample is bound to introduce errors. To reduce reconstruction errors, the current approach is simply to compensate for the lack of ion collection efficiency through algorithms. This approach still results in significant errors.

[0004] Furthermore, as the APT sample atoms evaporate, the surface morphology changes, and the electric field near the sample also changes accordingly. This change occurs in real time as the atoms evaporate. This changing electric field causes the ion trajectory to deviate from the ideal one, resulting in a decrease in the positional accuracy in the X and Y directions. Summary of the Invention

[0005] To address these issues, the present invention provides a system and method for improving the accuracy of three-dimensional atom probe image reconstruction. This system enables in-situ monitoring of the surface topography of an APT sample during an APT test and derives the corresponding electric field distribution. The reconstruction process can then calibrate the results based on the surface topography and the corresponding electric field distribution, thereby improving reconstruction accuracy.

[0006] To achieve the above-mentioned objectives, the present invention proposes the following technical solutions: a system for improving the accuracy of three-dimensional atom probe image reconstruction, comprising: an APT sample rotation device, a focused electron beam generating device, an electron beam deflecting device and a backscattered electron detection device; the APT sample rotation device is used to place the APT sample and drive the APT sample to rotate around an axis; the focused electron beam generating device is used to generate a focused electron beam for irradiating the APT sample; the electron beam deflecting device is used to adjust the focused electron beam; the deflected focused electron beam irradiates the APT sample at a predetermined angle to form a backscattered electron signal, and the backscattered electron detection device is used to collect the backscattered electron signal; the backscattered electron detection device is arranged between the focused electron beam generating device and the electron beam deflecting device, and a through hole for the focused electron beam to pass through is arranged at its center.

[0007] Furthermore, the rotation angle of the APT sample rotating device each time is obtained by dividing 360° by the number of sampling times.

[0008] The present invention also discloses a method for improving the accuracy of three-dimensional atom probe image reconstruction, which uses any of the above-mentioned systems for improving the accuracy of three-dimensional atom probe image reconstruction, including the following steps: before the imaging process begins, the voltage applied to the APT sample is slowly reduced to 0V, and then grounded; when imaging begins, the focused electron beam generating device, the electron beam deflection device and the backscattered electron detection device are adjusted to the initial angle; the focused electron beam is adjusted by the electron beam deflection device to scan the APT sample tip area point by point and line by line; the backscattered electron detector detects the generated backscattered electrons to obtain the APT sample morphology at the initial position; the APT sample rotation device rotates a preset angle, and the above steps are repeated until the APT sample morphology at all angles is obtained.

[0009] The present invention also discloses a system for improving the accuracy of three-dimensional atom probe image reconstruction, which is characterized in that it includes: a plurality of image reconstruction units, which are evenly arranged around the APT sample according to the number of times of collection required, and the image reconstruction units include a focused electron beam generating device, an electron beam deflecting device and a backscattered electron detection device; the focused electron beam generating device is used to generate a focused electron beam for irradiating the APT sample; the electron beam deflecting device is used to deflect the focused electron beam; the focused electron beam after deflection irradiates the APT sample at a predetermined angle to form a backscattered electron signal, and the backscattered electron detection device is used to collect the backscattered electron signal; the backscattered electron detection device is arranged between the focused electron beam generating device and the electron beam deflecting device, and a through hole for the focusing resistor to pass through is arranged at its center.

[0010] Furthermore, the angle set by the image reconstruction unit is obtained by dividing 360° by the number of sampling times.

[0011] Furthermore, there are three image reconstruction units, with one image reconstruction unit provided every 120°.

[0012] The present invention also discloses a method for improving the accuracy of three-dimensional atom probe image reconstruction. The system for improving the accuracy of three-dimensional atom probe image reconstruction adopts any of the above-mentioned methods, including the following steps: before the imaging process begins, the voltage applied to the APT sample is slowly reduced to 0V, and then grounded; when imaging begins, the first image reconstruction unit is started, and the focused electron beam is adjusted by the electron beam deflection device to scan the APT sample tip area point by point and line by line; the backscattered electron detector detects the generated backscattered electrons to obtain the APT sample morphology at the initial position; the second image reconstruction unit is started to obtain the APT sample morphology at the second position; the image reconstruction unit at each position is started in turn to obtain the APT sample morphology at each position until all image reconstruction units are exhausted.

[0013] Furthermore, when any one of the image reconstruction units is started, the other image reconstruction units are grounded.

[0014] Furthermore, based on the APT sample morphology at each position, the three-dimensional morphology at the APT sample tip is inverted using a three-dimensional reconstruction algorithm.

[0015] The technical solution of the present invention has at least the following technical effects or advantages: it can monitor the surface morphology of an APT sample in situ during the APT test process and obtain the corresponding electric field distribution. The reconstruction process can correct the results based on the surface morphology and the corresponding electric field distribution, thereby improving reconstruction accuracy. During the test process, the APT sample is imaged in situ without affecting the APT test process. Using a low-energy focused electron beam, the imaging process does not destroy the atomic structure of the APT sample, enabling non-destructive imaging of the APT sample tip at the nanometer level. The electric field distribution near the APT sample tip can be obtained based on the APT sample morphology, which facilitates correction of the reconstruction process and improves reconstruction accuracy. This method is particularly suitable for significantly improving the position reconstruction accuracy in the X and Y directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A system for improving the accuracy of three-dimensional atom probe image reconstruction in one embodiment of the present invention;

[0017] Figure 2 This is another embodiment of the system for improving the accuracy of three-dimensional atom probe image reconstruction in the present invention. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail through specific embodiments. However, it should be understood that the specific embodiments are provided only for a better understanding of the present invention and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terms used are for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0019] In order to solve the problem that the delay line microchannel plate detector widely used in the APT device in the prior art is insensitive to atoms or neutral molecular fragments, resulting in a lot of information being missed during the test process. Using only the ions collected by the detector to invert the three-dimensional distribution of the atoms of the entire APT sample is bound to introduce errors. The present invention proposes a system and method for improving the accuracy of three-dimensional atomic probe image reconstruction. During the APT sample test process, a low-energy focused electron beam 2 is used to perform in-situ scanning of the APT sample tip at intervals. The precise three-dimensional morphology of the APT sample tip is obtained by measuring the backscattered electrons or secondary electrons at each scanning point, and then the corresponding electric field distribution is obtained. During data reconstruction, the results are corrected in combination with the precise three-dimensional morphology and electric field distribution, thereby improving the reconstruction accuracy. The scheme of the present invention is described in detail below through examples in conjunction with the accompanying drawings.

[0020] Example 1

[0021] This embodiment discloses a system for improving the accuracy of three-dimensional atom probe image reconstruction. Figure 1As shown, the system includes an APT sample rotation device, a focused electron beam generator, an electron beam deflection device 4, and a backscattered electron detector 3. The APT sample rotation device is used to place the APT sample 1 and drive the APT sample 1 to rotate about its axis. The focused electron beam generator is used to generate a focused electron beam 2 that irradiates the APT sample 1. The electron beam deflection device 4 is used to adjust the focused electron beam 2. After deflection, the focused electron beam 2 irradiates the APT sample 1 at a predetermined angle, generating a backscattered electron signal. The backscattered electron detector 3 is used to collect the backscattered electron signal. The backscattered electron detector 3 is disposed between the focused electron beam generator and the electron beam deflection device 4. A through hole is provided at its center for the focused electron beam to pass through. This allows in-situ monitoring of the surface morphology of the APT sample 1 during the APT test and to obtain the corresponding electric field distribution. The reconstruction process can correct the results based on the surface morphology and the corresponding electric field distribution, thereby improving reconstruction accuracy.

[0022] This image reconstruction precision system only uses a set of low-energy focused electron beams 2. By rotating the APT sample 1, scanning imaging of the APT sample 1 tip in different orientations is achieved. Using a set of focused electron beams 2, scanning imaging of the APT sample 1 tip morphology in multiple orientations can be achieved, and the scanning orientation can be easily and arbitrarily increased.

[0023] In this embodiment, the rotation angle of the APT sample 1 rotating device each time is obtained by dividing 360° by the number of sampling times. The sampling times can be rotated at any angle. The more angles there are, the higher the reconstruction accuracy.

[0024] Example 2

[0025] Based on the same inventive concept, this embodiment discloses a method for improving the accuracy of three-dimensional atom probe image reconstruction. Using any of the above-mentioned systems for improving the accuracy of three-dimensional atom probe image reconstruction, the electric field strength near the needle tip during the test of APT sample 1 needs to reach tens of V / nm. This electric field will seriously affect the flight trajectory of low-energy electrons. At the same time, if the electron beam deflection device 4 is charged during the ionization evaporation process, it will also affect the flight trajectory of the ionized evaporated atoms, thereby affecting the experimental results. Therefore, the electron beam deflection device 4 needs to be as far away from the needle tip of APT sample 1 as possible; the two test processes need to be carried out at intervals, that is, during the ionization evaporation test, all electron beam deflection devices 4 need to be powered off; when imaging the needle tip morphology of APT sample 1, the voltage applied to APT sample 1 should first be set to 0 V and then grounded to prevent the accumulation of charge at the needle tip during the electron beam scanning process. The following describes the method using the example of rotating the APT sample 1 120° each time, which includes the following steps:

[0026] Before the imaging process begins, the voltage applied to APT sample 1 is slowly reduced to 0V and then grounded. At the start of imaging, the focused electron beam generator, electron beam deflection device 4, and backscattered electron detector 3 are adjusted to their initial angles. The electron beam deflection device 4 adjusts the focused electron beam 2 to scan the tip area of ​​APT sample 1 point by point and line by line. The backscattered electron detector detects the generated backscattered electrons, obtaining the morphology of APT sample 1 at the initial position. The APT sample 1 rotation device is then set to its initial position. Subsequently, the APT sample 1 is rotated 120° about its axis, and the tip area of ​​APT sample 1 is scanned point by point and line by line to obtain the morphology of APT sample 1 at a second angle. The APT sample 1 is then rotated again 120° about its axis, and the tip area of ​​APT sample 1 is scanned point by point and line by line to obtain the morphology of APT sample 1 at a third position. Finally, the APT sample 1 is rotated 120° about its axis and returned to its initial position. The morphology of APT sample 1 scanned at these three angles is used to invert the three-dimensional morphology of the tip of APT sample 1 using a three-dimensional reconstruction algorithm for electric field calculation and APT inversion correction.

[0027] Example 3

[0028] Based on the same inventive concept, this embodiment discloses a system for improving the accuracy of three-dimensional atom probe image reconstruction, such as Figure 2 As shown, it includes: a plurality of image reconstruction units, which are evenly arranged around the APT sample 1 according to the number of times of collection required, and the image reconstruction units include a focused electron beam generating device, an electron beam deflecting device 3 and a backscattered electron detecting device 4; the focused electron beam generating device is used to generate a focused electron beam 2 for irradiating the APT sample 1; the electron beam deflecting device 3 is used to deflect the focused electron beam 2; the focused electron beam after deflection irradiates the APT sample 1 at a predetermined angle to form a backscattered electron signal, and the backscattered electron detecting device 4 is used to collect the backscattered electron signal; the backscattered electron detecting device 4 is arranged between the focused electron beam generating device and the electron beam deflecting device 3, and a through hole for the focusing resistor to pass through is set at the center thereof.

[0029] In this example, the tip of an APT sample (1) is fixed in place. Multiple low-energy focused electron beams (2) are used to scan the tip from different directions. The backscattered electrons are measured to determine the tip's topography in each direction. A 3D reconstruction algorithm is then used to invert the 3D topography and calculate the corresponding electric field distribution. The greater the number of electron beams used, the more accurate the resulting 3D topography.

[0030] In this embodiment, the angle at which the image reconstruction unit is set is obtained by dividing 360° by the sampling position. This is not preferred. More sampling positions lead to better accuracy, but fewer sampling positions can reduce costs. There are three image reconstruction units, one at every 120°.

[0031] In this embodiment, the algorithm for reconstructing the three-dimensional shape of an object is an important research direction in the field of computer vision and image processing, which aims to restore the three-dimensional shape and surface information of an object from a two-dimensional image or other related data. The three-dimensional shape reconstruction algorithm can adopt a stereo vision algorithm, which uses multiple cameras to shoot the same object from different angles, and then calculates the parallax between the images to obtain the depth information of the object, thereby reconstructing the three-dimensional shape. For example, in autonomous driving, three-dimensional information of the surrounding environment can be obtained by installing multiple cameras on the vehicle to help the vehicle identify obstacles and plan paths. Alternatively, deep learning-based algorithms use deep neural networks to learn reconstruction patterns from a large number of two-dimensional images and corresponding three-dimensional model data. For example, some algorithms based on convolutional neural networks (CNNs) can directly predict the three-dimensional shape of an object from a single image.

[0032] Example 4

[0033] Based on the same inventive concept, this embodiment discloses a method for improving the accuracy of three-dimensional atom probe image reconstruction. The system for improving the accuracy of three-dimensional atom probe image reconstruction adopts any of the above-mentioned methods, including the following steps: before the imaging process starts, the voltage applied to the APT sample 1 is slowly reduced to 0V and then grounded; when the imaging starts, the first image reconstruction unit is started, and the focused electron beam 2 is adjusted by the electron beam deflection device 3 to scan the needle tip area of ​​the APT sample 1 point by point and line by line; the backscattered electron detector detects the generated backscattered electrons to obtain the morphology of the APT sample 1 at the initial position. During this process, the second electron beam deflection device 3 and the third electron beam deflection device 3 are grounded. Subsequently, the second image reconstruction unit is activated, and the focused electron beam 2 is adjusted through the electron beam deflection device 3 to scan the tip area of ​​the APT sample 1 point by point and line by line. The backscattered electron detector detects the generated backscattered electrons to obtain the morphology of the APT sample 1 at the initial position. During this process, the first electron beam deflection device 3 and the third electron beam deflection device 343 are grounded. The second image reconstruction unit is activated, and the focused electron beam 2 is adjusted through the electron beam deflection device 3 to scan the tip area of ​​the APT sample 1 point by point and line by line. The backscattered electron detector detects the generated backscattered electrons. During this process, the first electron beam deflection device 3 and the second electron beam deflection device 3 are grounded. Finally, the morphology of the APT sample 1 scanned at these three angles is used to invert the three-dimensional morphology at the tip of the APT sample 1 using a three-dimensional reconstruction algorithm for electric field calculation and APT inversion correction.

[0034] During the testing of APT sample 1, a low-energy focused electron beam 2 is used to perform in-situ scanning and imaging of the surface of APT sample 1, obtaining the surface topography of APT sample 1 and, subsequently, the corresponding electric field distribution. The measured surface topography and corresponding electric field distribution of APT sample 1 are used to correct the reconstruction process, improving reconstruction accuracy. In-situ imaging of APT sample 1 during the testing process does not affect the APT testing process. Using a low-energy focused electron beam 2, the imaging process does not destroy the atomic structure of APT sample 1, enabling non-destructive nanometer-level imaging of the tip of APT sample 1. The electric field distribution near the tip of APT sample 1 can be derived from the topography of APT sample 1, facilitating correction of the reconstruction process and improving reconstruction accuracy. This method is particularly suitable for significantly improving the accuracy of position reconstruction in the X and Y directions.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific embodiments of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be included within the scope of protection of the claims of the present invention. The above content is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art who can easily think of changes or replacements within the technical scope disclosed by the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A system for improving the accuracy of three-dimensional atom probe image reconstruction, characterized in that: include: APT sample rotation device, focused electron beam generation device, electron beam deflection device and backscattered electron detection device; The APT sample rotating device is used to place the APT sample and drive the APT sample to rotate around the axis; The focused electron beam generating device is used to generate a focused electron beam for irradiating the APT sample; The electron beam deflection device is used to adjust the focused electron beam; The deflected focused electron beam irradiates the APT sample at a predetermined angle to form a backscattered electron signal, and the backscattered electron detection device is used to collect the backscattered electron signal; The backscattered electron detection device is arranged between the focused electron beam generating device and the electron beam deflecting device, and a through hole for the focused electron beam to pass through is arranged at the center of the backscattered electron detection device.

2. The system for improving the accuracy of three-dimensional atom probe image reconstruction according to claim 1, wherein: The rotation angle of the APT sample rotating device each time is obtained by dividing 360° by the number of sampling times.

3. A method for improving the accuracy of three-dimensional atom probe image reconstruction, characterized in that: The system for improving the accuracy of three-dimensional atom probe image reconstruction according to claim 1 or 2 comprises the following steps: Before the imaging process begins, the voltage applied to the APT sample is slowly reduced to 0 V and then grounded. At the beginning of imaging, the focused electron beam generating device, the electron beam deflecting device and the backscattered electron detecting device are adjusted to the initial angles; The electron beam deflection device is used to adjust the focused electron beam and scan the APT sample tip area point by point and line by line; The backscattered electron detector detects the generated backscattered electrons and obtains the APT sample morphology at the initial position; The APT sample rotating device rotates the preset angle, and the above steps are repeated until the APT sample morphology at all angles is obtained.

4. A system for improving the accuracy of three-dimensional atom probe image reconstruction, characterized in that: include: Several image reconstruction units are evenly arranged around the APT sample according to the number of acquisitions required, and the image reconstruction units include a focused electron beam generating device, an electron beam deflecting device and a backscattered electron detecting device; The focused electron beam generating device is used to generate a focused electron beam for irradiating the APT sample; The electron beam deflection device is used to deflect the focused electron beam; The deflected focused electron beam irradiates the APT sample at a predetermined angle to generate a backscattered electron signal, and the backscattered electron detection device is used to collect the backscattered electron signal; The backscattered electron detection device is arranged between the focused electron beam generating device and the electron beam deflecting device, and a through hole for the focused electron beam to pass through is arranged at the center of the backscattered electron detection device.

5. The system for improving the accuracy of three-dimensional atom probe image reconstruction according to claim 4, wherein: The angle set by the image reconstruction unit is obtained by dividing 360° by the number of sampling times.

6. The system for improving the accuracy of three-dimensional atom probe image reconstruction according to claim 5, wherein: There are three image reconstruction units, and one image reconstruction unit is set every 120 degrees.

7. A method for improving the accuracy of three-dimensional atom probe image reconstruction, characterized in that: The system for improving the accuracy of three-dimensional atom probe image reconstruction according to any one of claims 4 to 6 comprises the following steps: Before the imaging process begins, the voltage applied to the APT sample is slowly reduced to 0 V and then grounded. At the beginning of imaging, the first image reconstruction unit is activated, and the electron beam deflection device is used to adjust the focused electron beam to scan the APT sample tip area point by point and line by line. The backscattered electron detector detects the generated backscattered electrons to obtain the APT sample morphology at the initial position. Start the second image reconstruction unit to obtain the APT sample morphology at the second position; start the image reconstruction unit at each position in turn to obtain the APT sample morphology at each position until all image reconstruction units are exhausted.

8. The method for improving the accuracy of three-dimensional atom probe image reconstruction according to claim 7, wherein: When any one of the image reconstruction units is started, the other image reconstruction units are grounded.

9. The method for improving the accuracy of three-dimensional atom probe image reconstruction according to claim 7, wherein: According to the APT sample morphology at each position, the three-dimensional morphology of the APT sample tip is inverted through a three-dimensional reconstruction algorithm.

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