A three-dimensional atom probe with high ion detection efficiency

Abstract

The present invention discloses a three-dimensional atom probe with high ion detection efficiency. The three-dimensional atom probe comprises a needle tip sample, a surface treatment material evaporation source and an ion detector; the ion detector comprises a microchannel plate group with expanded opening after surface evaporation treatment and a position-sensitive anode; the process of the surface evaporation treatment is: the ion detector and the evaporation source are installed in the three-dimensional atom probe, and the evaporation source is heated after vacuuming to excite the low work function material therein to perform surface evaporation treatment on the ion detector for 1 to 10 minutes. Based on the synergistic effect between the components, the three-dimensional atom probe effectively improves the emission coefficient of secondary electrons generated by ion collision, greatly improves the ion conversion efficiency and the detection accuracy of the three-dimensional atom probe. After testing, the detector of the three-dimensional atom probe has a detection efficiency of ≥95% for ions, and the overall detection efficiency for ions reaches more than 90%. Compared with the prior art, the overall detection efficiency is improved by about 20%.

Description

Technical Field

[0001] The invention relates to a three-dimensional atom probe, in particular to a three-dimensional atom probe with high ion detection efficiency, and belongs to the technical field of three-dimensional atom probe analysis. Background Art

[0002] The three-dimensional atom probe is a method that can reconstruct and image materials in three dimensions at the atomic scale. Its main principle is to apply high voltage to a needle-shaped sample with a radius of curvature less than hundreds of nanometers, so that an ultra-strong electric field is formed near the tip of the sample. This ultra-strong electric field will cause the atoms in the outermost layer of the sample tip and the point with the largest curvature to be severely polarized until a certain moment, and they will lose electrons and fly away from the sample along the direction of the electric lines (i.e., ionization and evaporation), and finally be detected by a two-dimensional position-sensitive detector. According to the two-dimensional position of the ion falling on the detector, the position of the ion on the surface of the sample tip can be inverted. The charge-to-mass ratio of the ion can be determined by its flight time, and then the type of the ion can be determined. According to the evaporation order of the ions, the inversion algorithm is used to calculate and reconstruct the three-dimensional atomic distribution of the sample.

[0003] The three-dimensional atom probe has a very wide range of applications in the field of microscopic analysis. It can obtain analytical data that is different from test methods such as TEM, and has unique advantages in the field of detection. The use of a three-dimensional atom probe can help us understand the problem of uneven distribution of different alloying elements in micro-regions in metal materials; it can help us understand the segregated distribution of alloying elements at various interfaces and crystal defects; it can help us understand the process when only dozens of different atoms agglomerate at the beginning of microstructural changes. The three-dimensional atom probe is currently the most microscopic analytical instrument that can perform quantitative analysis of components and can play an important role in studying many problems of metal materials. The industry fields in which the three-dimensional atom probe is applied include traditional metal materials, new metal materials, new energy materials, electronic information materials and their devices, storage media, advanced materials (nanowires, quantum wells), LED chips, photovoltaic materials, composite materials and integrated devices, and other multidisciplinary research fields such as materials, physics, and chemistry.

[0004] With the development of science and technology, various fields have higher and higher requirements for the precision of microscopic detection, especially in the microscopic detection of semiconductor chip devices. As the feature size becomes smaller and smaller, the detection accuracy is also getting higher and higher. The requirements for the ion detection efficiency of the three-dimensional atom probe instrument are also getting higher and higher. The conventional three-dimensional atom probe has an ion detection efficiency of 60%~80%, which means that at least 20% of the ions evaporated from the sample to be tested are lost and cannot be detected. This has a certain impact on the detection and analysis of the sample, especially the detection of trace doping on the microscopic size of the chip sample, which affects the detection of the sample and the judgment of the results. Therefore, it is necessary to further improve the detection efficiency of the three-dimensional atom probe for sample ions in order to obtain higher detection accuracy. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a three-dimensional atom probe with high ion detection efficiency. The three-dimensional atom probe is based on the synergy between the components, especially the synergy between the surface evaporation treatment expanded microchannel plate group and the position-sensitive anode, which effectively improves the emission coefficient of secondary electrons from ion collisions, greatly improves the ion conversion efficiency, and solves the technical problem that a part of ions cannot be converted into electrons that can be effectively multiplied from the probability distribution due to too low conversion efficiency, thereby more accurately reflecting the atomic distribution on the surface of the sample to be tested and improving the detection accuracy of the three-dimensional atom probe.

[0006] In order to achieve the above technical objectives, the present invention provides a three-dimensional atom probe with high ion detection efficiency, including a needle tip sample, a surface treatment material evaporation source and an ion detector; the ion detector includes a microchannel plate group with expanded openings after surface evaporation treatment and a position-sensitive anode;

[0007] The process of the surface evaporation treatment is as follows: installing the ion detector and the evaporation source in the three-dimensional atom probe, heating the evaporation source after evacuation to excite the low work function material therein to perform surface evaporation treatment on the ion detector for 1 to 10 minutes;

[0008] The expanded microchannel plate group is composed of 2 to 3 stacked microchannel plates, wherein the first microchannel plate is an expanded microchannel plate with a functional film layer coated on the input surface, the expanded area is ≥90%, the expanded depth is 0.5 to 2.0D, and D is the microchannel aperture.

[0009] One of the key technical features of the three-dimensional atomic probe provided by the present invention is that the ion detector adopts an expanded microchannel plate group that has been subjected to surface evaporation treatment. By evaporating low work function materials on the surface of the expanded microchannel plate group, the emission coefficient of secondary electrons produced by ion collisions can be effectively improved. When the emission coefficient of secondary electrons is larger, the probability of ions being detected will also increase significantly, thereby effectively improving the detection accuracy of the three-dimensional atomic probe.

[0010] As a preferred solution, the expanded microchannel plate group is composed of 2 to 3 stacked microchannel plates, wherein the first microchannel plate is an expanded microchannel plate with a functional film layer coated on the input surface, the expanded area is ≥90%, the expanded depth is 0.5~2.0D, and D is the microchannel aperture.

[0011] The flared microchannel plate assembly provided by the present invention must be strictly implemented in accordance with the above requirements. When the flared area is too small, it will directly affect the proportion of the effective ion detection area, thereby reducing the ion detection efficiency; when the flared depth is too shallow, it will cause the electrons generated on the inclined surface of the flared to rebound in the opposite direction, resulting in the inability to achieve effective ion detection, thereby reducing the ion detection efficiency.

[0012] As a preferred solution, the functional film layer is at least one of beryllium oxide, aluminum oxide, magnesium oxide and silicon oxide.

[0013] As a preferred solution, the thickness of the functional film layer is 10-30 nm, the coating depth is ≥0.5D, and the coating range is 0.5-2.0D.

[0014] The functional film layer provided by the present invention must be implemented strictly in accordance with the above requirements. If the first microchannel plate has no functional film layer on the input surface, secondary electrons cannot be generated when ions collide with the electrode material, resulting in loss of ion information and lowering the ion detection efficiency. If the functional film layer is too thin, the number and probability of secondary electrons generated when ions collide with the film layer will be too low, affecting the detection efficiency. If the functional film layer is too thick, the poor conductivity of the film layer will affect the electron replenishment capacity, thus affecting the detection efficiency.

[0015] As a preferred solution, the outer diameter of the microchannel plate ranges from 80 to 120 mm, the pore size ranges from 6 to 25 μm, and the aspect ratio is 40 to 80:1.

[0016] As a preferred solution, the microchannels of the microchannel plate are one of circular holes and hexagonal holes, and the distribution between the channels is hexagonal close packing.

[0017] As a preferred solution, the preparation process of the expanded microchannel plate group is as follows: expand the input surface of the first microchannel plate and then vacuum evaporate the functional film layer, and then stack and combine it with the remaining microchannel plates to obtain the expanded microchannel plate group; assemble the expanded microchannel plate group and the delay line position-sensitive anode to obtain an ion detector.

[0018] As a preferred solution, a NiCr electrode is sandwiched between the functional membrane layer and the microchannel plate substrate on the input surface of the first microchannel plate; the NiCr electrode extends from the input surface to a depth of 0.3-0.6D in the microchannel.

[0019] As a preferred solution, the low work function material is at least one of lithium, beryllium, sodium, magnesium, potassium, rubidium and cesium; and the vacuum degree after evacuation is ≤1E-6Pa.

[0020] As a preferred solution, the surface of the ion detector needs to be evaporated again after the vacuum is broken at any stage of the three-dimensional atomic probe.

[0021] Breaking the vacuum at any stage of the three-dimensional atom probe will cause the low work function material on the surface of the ion detector to fall off or fail, thereby exposing the functional film layer with a larger surface work function, thereby reducing the emission coefficient of secondary electrons produced by ion collisions, thereby affecting the probability of ions being detected. Therefore, in order to ensure the detection accuracy of the three-dimensional atom probe, the surface of the ion detector needs to be re-evaporated after breaking the vacuum at any stage.

[0022] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are:

[0023] 1) The three-dimensional atom probe provided by the present invention is based on the synergistic effect between various components, especially the synergistic effect between the surface evaporation treatment expanded microchannel plate group and the position-sensitive anode, which effectively improves the emission coefficient of secondary electrons produced by ion collisions, greatly improves the ion conversion efficiency, and solves the technical problem that a part of ions cannot be converted into electrons that can be effectively multiplied from the probability distribution due to too low conversion efficiency, thereby more accurately reflecting the atomic distribution on the surface of the sample to be tested and improving the detection accuracy of the three-dimensional atom probe.

[0024] 2) In the technical solution provided by the present invention, after the input surface of the first microchannel plate is expanded to an opening area ≥ 90%, a functional film layer with high ion conversion efficiency is vacuum evaporated, and then it is stacked with the remaining conventional microchannel plates to form an expanded microchannel plate group; this method has simple process steps, is easy to operate, has high expansion processing accuracy, and is convenient for large-scale industrial production.

[0025] 3) In the technical solution provided by the present invention, based on the excellent detection accuracy of the above-mentioned ion detector, the detection efficiency of ions in the three-dimensional atom probe can be greatly improved. After testing, when the three-dimensional atom probe using the ion detector is used for detection, the detection efficiency of the detector for ions is ≥95%, and the overall detection efficiency of the three-dimensional atom probe for ions reaches more than 90%. Compared with the existing technology, the overall detection efficiency is improved by about 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the structure of a three-dimensional atom probe provided in Example 1 of the present invention;

[0027] Figure 2 1 is a schematic diagram comparing a vertical cross section of the surface of the first microchannel plate in the ion detector provided in Example 1 of the present invention and a vertical cross section of the surface of a conventional microchannel plate in Comparative Example 1;

[0028] Figure 3 is a schematic diagram of the vertical cross-section microstructure of the surface of the first microchannel plate in the ion detector provided in Example 1 of the present invention;

[0029] Figure 4is a schematic diagram of the microscopic structure of the cross-section of the surface of the first microchannel plate in the ion detector provided in Embodiment 1 and Embodiment 2 of the present invention;

[0030] Figure 5 This is a SEM image of the surface cross section of the first microchannel plate in the ion detector provided in Example 1 of the present invention;

[0031] Figure 6 It is a schematic diagram of the three-dimensional atom probe imaging results performed by the ion probe provided in Example 1 of the present invention and the three-dimensional atom probe imaging results performed by the conventional ion probe in Comparative Example 1;

[0032] Among them, 1-needle tip sample; 2-surface treatment material evaporation source; 3-microchannel plate group; 4-position sensitive anode; 5-ions that can be effectively detected and their movement trajectories; 6-the first microchannel plate of the expanded microchannel plate group; 7-ions that cannot be effectively detected and their movement trajectories; 8-conventional microchannel plate; 9-surface structure of high ion detection efficiency microchannel plate; 10-NiCr electrode on the input surface; 11-high electron yield ion conversion membrane on the input surface; 12-microchannel plate glass substrate; 13-schematic diagram of the top view structure of the hexagonal aperture large opening area ratio microchannel plate input surface; 14-schematic diagram of the top view structure of the circular aperture large opening area ratio microchannel plate input surface; 15-schematic diagram of high ion detection efficiency three-dimensional atom probe imaging results; 16-empty positions that cannot be detected due to low ion detection efficiency; 17-schematic diagram of conventional three-dimensional atom probe imaging results. DETAILED DESCRIPTION

[0033] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0034] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed by the present invention are not limited to any implementation. In addition, some aspects disclosed by the present invention can be used alone or in any appropriate combination with other aspects disclosed by the present invention.

[0035] Example 1

[0036] This embodiment provides a three-dimensional atom probe with high ion detection efficiency, and the specific process is as follows:

[0037] 1. Coating treatment of the expanded microchannel plate

[0038] A flared microchannel plate was selected, with an outer diameter range of 106 mm, an aperture of 21 μm, an aspect ratio of 60:1, a circular hole in the shape of the microchannel, a hexagonal close-packed channel distribution, an opening area ratio of more than 90%, a flaring depth of 1.0D (D is the channel aperture), and an electrode depth of 0.5D; the input surface of the flared microchannel plate was coated with silicon oxide, the coating material was silicon oxide, the surface film thickness was 25 nm, and the coating depth was 1.5D.

[0039] 2. Ion detector production

[0040] Two MCPs are stacked and used, wherein the first microchannel plate adopts the above-mentioned processed expanded MCP, and the second microchannel plate adopts a conventional non-expanded microchannel plate of the same size and aperture specification, without additional coating treatment; after the MCPs are stacked, they are assembled with the delay line position-sensitive anode to obtain the result.

[0041] 3. 3D Atom Probe Assembly

[0042] The above-mentioned ion detector was installed in a three-dimensional atom probe, and the evaporation source was installed at the oblique side of the ion detector. There were two evaporation sources with a distance of 15 cm. The evaporation source was a potassium source. After the installation was completed, vacuum was drawn. After the vacuum degree reached 1E-6Pa, the input surface of the MCP in the ion detector was processed: the evaporation source was heated to evaporate the gaseous substance potassium required for surface treatment. The processing time was 5 minutes.

[0043] In order to verify the detection efficiency of the three-dimensional atom probe provided in this embodiment, a standard sample was transferred into the test chamber through the transfer chamber for calibration test; the test results showed that the overall ion detection efficiency of the three-dimensional atom probe reached 93%.

[0044] Example 2

[0045] This embodiment is exactly the same as the embodiment 1, except that the shape of the microchannel is a regular hexagon.

[0046] Comparative Example 1

[0047] This comparative example is exactly the same as Example 1, except that a conventional ion detector is used to assemble a three-dimensional atom probe, and its surface vertical section is as follows: Figure 2 The standard sample is transferred into the test chamber through the transfer chamber for calibration test; the test results show that the verification efficiency of the three-dimensional atom probe is 78%.

[0048] From the above description, it can be seen that the ion detection efficiency of the three-dimensional atom probe provided by Example 1 of the present invention is significantly improved compared with the three-dimensional atom probe provided in Comparative Example 1, and the improvement is as high as 19.2%. Figure 6It can be seen that according to the test results of Example 1, the number of missing atoms in the restored three-dimensional structure is relatively small, and the test accuracy and restoration accuracy of the overall structure of the sample to be tested are relatively high. This technical effect is due to the synergistic effect between the low work function material and the functional film layer on the surface evaporation treatment expanded microchannel plate group. The functional film layer can ensure that the ions collide with the electrode material to produce enough secondary electrons, and the low work function material can effectively improve the emission coefficient of secondary electrons produced by ion collision, significantly increasing the probability of ions being detected, thereby effectively improving the detection accuracy of the three-dimensional atomic probe.

Claims

1. A three-dimensional atom probe with high ion detection efficiency, characterized in that: It includes a needle tip sample, a surface treatment material evaporation source and an ion detector; the ion detector includes a microchannel plate group with expanded opening after surface evaporation treatment and a position-sensitive anode; The process of the surface evaporation treatment is as follows: installing the ion detector and the evaporation source in the three-dimensional atom probe, heating the evaporation source after evacuation to excite the low work function material therein to perform surface evaporation treatment on the ion detector for 1 to 10 minutes; The expanded microchannel plate group is composed of 2 to 3 stacked microchannel plates, wherein the first microchannel plate is an expanded microchannel plate with a functional film layer coated on the input surface, the expanded area is ≥90%, the expanded depth is 0.5 to 2.0D, and D is the microchannel aperture; After the three-dimensional atom probe breaks vacuum at any stage, the surface of the ion detector needs to be evaporated again; The low work function material is at least one of lithium, beryllium, sodium, magnesium, potassium, rubidium and cesium.

2. A three-dimensional atom probe with high ion detection efficiency according to claim 1, characterized in that: The functional film layer is at least one of beryllium oxide, aluminum oxide, magnesium oxide and silicon oxide; the thickness of the functional film layer is 10-30 nm, the coating depth is ≥0.5D, and the coating range is 0.5-2.0D.

3. A three-dimensional atom probe with high ion detection efficiency according to claim 1, characterized in that: The outer diameter of the microchannel plate ranges from 80 to 120 mm, the pore size ranges from 6 to 25 μm, and the aspect ratio is 40 to 80:

1.

4. A three-dimensional atom probe with high ion detection efficiency according to claim 1, characterized in that: The microchannels of the microchannel plate are one of circular holes and hexagonal holes, and the distribution mode between the channels is hexagonal close packing.

5. A three-dimensional atom probe with high ion detection efficiency according to claim 1, characterized in that: The preparation process of the expanded microchannel plate group is as follows: expanding the input surface of the first microchannel plate, vacuum evaporating a functional film layer, and then stacking and combining it with the remaining microchannel plates to obtain the expanded microchannel plate group; assembling the expanded microchannel plate group and the delay line position sensitive anode to obtain an ion detector.

6. A three-dimensional atom probe with high ion detection efficiency according to claim 1, characterized in that: A NiCr electrode is sandwiched between the functional membrane layer and the microchannel plate substrate on the input surface of the first microchannel plate; the NiCr electrode extends from the input surface to the microchannel to a depth of 0.3-0.6D.

7. A three-dimensional atom probe with high ion detection efficiency according to claim 1, characterized in that: The vacuum degree after evacuation is ≤1E-6Pa.

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