A method for preparing APT samples and APT samples

Abstract

This invention discloses a method for preparing APT samples, comprising: selecting a block sample containing dislocations; preparing a TEM thin-film sample suitable for TEM detection; observing the dislocations in the TEM thin-film sample using TEM to obtain a dislocation image on the TEM thin-film sample; and, based on the dislocation image on the TEM thin-film sample, performing ring milling around the location of the dislocation using a fibrillation element (FIB) to prepare the TEM thin-film sample into a needle-shaped APT sample. The APT sample prepared by the method of this invention ensures the presence of a dislocation within the sample, thus providing a reliable research sample for studying the atomic distribution on the dislocation.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for fabricating APT samples. Background Technology

[0002] Dislocations, also known as differential packings, are microscopic defects within crystalline materials in materials science, representing localized irregular arrangements of atoms (crystallographic defects). Geometrically, dislocations are line defects, acting as the boundary between slipped and unslipped portions of a crystal. Their presence significantly impacts the physical properties of materials. In the active region of a silicon substrate, the presence of such anomalies—where line defects of dislocations are located precisely within the active region of a device—can cause "junction puncture," often affecting the device's electrical performance and leading to electrical failures. The degree of leakage current caused by this "junction puncture" is directly proportional to the dislocation density and depth.

[0003] Semiconductor materials such as Si, SiC, and GaN are widely used in the fabrication of high-performance integrated circuits, field-effect transistors, detectors, and other optoelectronic devices. Large-size, high-integrity single crystals are the primary goal in preparing these materials. The preparation of such single crystals mainly involves melt growth methods, including the Czochralski method, Bridgman process, vertical gradient solidification, moving heater method, and zone melting method. To improve the growth quality of the crystals, these methods also employ techniques such as applying magnetic fields, high pressure, accelerating crucible rotation, vapor pressure control, and microgravity to optimize the temperature field and melt convection field. Dislocations are one of the unavoidable defects in the melt-directed solidification process of single crystal growth, especially for compound semiconductors. Due to the high growth temperature, low thermal conductivity, and relatively small critical shear stress, the crystal is more prone to plastic deformation under thermal stress, resulting in high-density dislocations. During the melt crystal growth process, dislocations are generated due to: (1) thermal stress caused by axial and radial temperature gradients; (2) for crystal-crucible contact growth systems, the different thermal expansion coefficients of the crystal and crucible also cause thermal stress; (3) defects such as vacancies, impurity segregation, and precipitates cause lattice mismatch, resulting in local stress concentration. Thermal stress is the main factor in dislocation generation. Under the action of stress, dislocations will move and multiply.

[0004] Currently, the most common methods for physical observation of dislocations include:

[0005] Transmission electron microscopy (TEM) allows direct observation of dislocations in the microsurface structure of materials. The first step in TEM observation is to fabricate the sample into a thin film through which an electron beam can pass. In regions without dislocations, electrons will diffract as they pass through the regularly spaced crystal planes. The diffraction angle, interplanar spacing, and electron wavelength satisfy Bragg's law. However, near the location of dislocations, the crystal lattice is distorted, thus changing the diffraction intensity. Consequently, the image formed near the dislocation will have a contrast with the surrounding area. This is the basic principle of observing dislocations with TEM, and the contrast difference caused by this is called diffraction contrast. This method obtains the true surface information of dislocations, but its limitation is that it still observes from the surface; the true depth information of the dislocations cannot actually be obtained.

[0006] Atomic probe chromatography (APT) can identify the types of atoms and visually reconstruct their spatial positions, realistically displaying the three-dimensional spatial distribution of different elements in a material, thus becoming a high-resolution analytical testing method. As shown in the recent progress and applications of APT published by Liu Wenqing et al., APT can be used to detect shallow dislocation information in materials. APT has relatively high sample requirements; generally, the sample needs to be prepared into a needle shape with a tip radius of less than 100 nm. Currently, the main method for preparing APT samples is electrochemical polishing. However, electrochemical polishing cannot locate defects and its accuracy is not easily sufficient to meet the high requirements of APT sample preparation, thus leading to the problem of inaccurate detection of dislocation information.

[0007] In summary, it can be seen that how to prepare APT samples containing dislocations and use them for APT detection is a problem that needs to be solved. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides an APT sample preparation method that ensures that the prepared APT sample contains at least one dislocation, thereby enabling APT detection technology to correctly reconstruct the three-dimensional spatial distribution of atoms at the dislocation.

[0009] A method for preparing an APT sample according to the present invention, for preparing an APT sample containing at least one dislocation, includes the following steps:

[0010] S1: Select a blocky sample containing dislocations;

[0011] S2: The block sample is subjected to corrosion treatment, and the corrosion pits formed by corrosion are used as the basis for determining the location of dislocations. The middle position of one of the corrosion pits is selected and marked as the dislocation center.

[0012] S3: Using the dislocation center as a reference, prepare a TEM thin-film sample suitable for TEM detection;

[0013] S4: Use TEM to observe the dislocations in the TEM thin film sample and obtain a dislocation image on the TEM thin film sample;

[0014] S5: Based on the dislocation image on the TEM thin film sample, deposit a first protective layer on the surface of the TEM thin film sample;

[0015] S7: Fix the thin film sample with the first protective layer deposited on the APT sample stage;

[0016] S8: Use FIB to perform ring milling around the location of the dislocation in the TEM sheet sample to make the TEM sheet sample into a needle-shaped APT sample.

[0017] Preferably, before depositing the first protective layer on the front and rear surfaces of the TEM sheet sample, the method further includes depositing at least two marker lines on the TEM sheet sample, the intersection of the two marker lines being located on the dislocation line observed in the TEM image.

[0018] Preferably, when depositing the first protective layer on the surface, the deposition area of ​​the first protective layer is obtained with the intersection of the two marked lines as the center; wherein the distance between the boundary of the deposition area of ​​the first protective layer and the intersection is 2-3 μm.

[0019] Preferably, the specific steps of step S3 are as follows:

[0020] S31: Deposit a second protective layer on the surface of the corrosion pits of the block sample;

[0021] S32: A first groove and a second groove are etched from the outside towards the edge of the second protective layer on the block sample. The first groove and the second groove are located on the upper and lower sides of the second protective layer, respectively. The lower side of the first groove and the upper side of the second groove are then trimmed to obtain the TEM sheet sample. The thickness of the TEM sheet sample is the same as the width of the second protective layer.

[0022] S33: Perform a U-shaped cut on the TEM thin-film sample;

[0023] S34: Extract the TEM thin-film sample from the bulk sample;

[0024] S35: Fix the TEM thin-film sample onto a copper grid;

[0025] S36: The front and rear parts of the TEM thin film sample are thinned to reduce the thickness of the TEM thin film sample to 0.1-0.3 μm.

[0026] Preferably, the specific steps of step S33 are as follows: cut off the bottom and one side of the TEM thin film sample, separate the TEM thin film sample from the block sample, the side becomes the free end of the thin film sample, and the other side is cut off from bottom to top to form the fixed end of the thin film sample.

[0027] The specific steps of step S34 are as follows: First, bring the extraction probe close to the free end of the TEM thin film sample; then, deposit welding material at the position where the extraction probe contacts the free end of the TEM thin film sample to fix the extraction probe to the free end of the TEM thin film sample; then cut off the fixed end of the TEM thin film sample; and slowly extract the TEM thin film sample.

[0028] The specific steps of step S35 are as follows: Position the copper mesh vertically and cut an L-shaped plane on one side of the copper mesh; Place the side of the TEM thin film sample not fixed to the extraction probe into contact with the vertical surface of the L-shaped plane on the copper mesh; deposit welding material on the contact surface to weld the TEM thin film sample to the copper mesh; and separate the TEM thin film sample from the extraction probe.

[0029] Preferably, the specific steps of step S36 are as follows:

[0030] S361: Use 30kV FIB to coarsely thin the front and rear parts of the TEM thin film sample to about 2μm;

[0031] S362: The front and rear parts of the TEM thin film sample are finely thinned using FIB with gradually decreasing voltage to a thickness of 0.1μm-0.3μm; and the tilt angle of the ion beam increases accordingly during the voltage reduction process.

[0032] The gradual voltage reduction method includes thinning the TEM sample with a 15kV FIB and compensating for the ion beam tilt angle by -1.5° to +1.5°; thinning the TEM sample with a 5kV FIB and compensating for the ion beam tilt angle by -3° to +3°; and thinning the TEM sample with a 2kV FIB and compensating for the ion beam tilt angle by -5° to +5°.

[0033] Preferably, the first protective layer or the second protective layer is one of platinum, carbon, and tungsten; and the first protective layer and the marking line are made of different materials.

[0034] Preferably, in step S32, the size of the first groove and the second groove is larger than the size of the second protective layer.

[0035] Preferably, the specific steps of step S7 are as follows:

[0036] S71: The TEM thin film sample is transferred to the APT sample stage using an extraction probe, with the bottom of the TEM thin film sample in contact with the APT sample stage, and the intersection of the marker lines deposited on the TEM thin film sample is located at the center of the APT sample stage;

[0037] S72: Deposit welding material on the contact surface between the bottom of the TEM thin film sample and the APT sample stage to fix the TEM thin film sample on the APT sample stage.

[0038] According to another objective of the present invention, an APT sample is prepared using the APT sample preparation method described above. The APT sample is needle-shaped, with a height of 50 nm to 200 nm and a diameter of less than 100 nm. The distance between the needle tip and the intersection of the marking line is about 100 nm. The APT sample includes at least one dislocation.

[0039] The beneficial effects of this invention are as follows: First, this invention uses an etching solution to determine the location of dislocations in a bulk sample. Then, it prepares a TEM thin-film sample suitable for TEM detection based on these locations. Next, it uses TEM to detect the dislocation information in the thin-film sample and deposits marker lines at the dislocation locations. Finally, the areas of the thin-film sample with deposited marker lines are used to prepare a sample suitable for ATP detection. This solves the problem that APT cannot guarantee the preservation of at least one intact dislocation in the sample during sample preparation. Furthermore, during the preparation of the TEM thin-film sample, a gradually decreasing voltage is used to reduce the possibility of sample structural deformation caused by atomic compression due to excessive electron beam bombardment energy. A corresponding tilt angle of the ion beam is also set to compensate for defects caused by ion beam dispersion. This invention also finds that when the thin-film sample is thinned to 0.1 μm-0.3 μm using the above method, the thickness of the amorphous layer can also be reduced, making the amorphous layer thickness less than 35% of the total thickness. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a blocky sample with a second protective layer deposited on it.

[0041] Figure 2 This is a schematic diagram of the block sample after the first and second grooves have been removed.

[0042] Figure 3 This is a schematic diagram of a thin-film sample being cut in a U-shape.

[0043] Figure 4 This is a schematic diagram of the extraction probe in contact with the thin-film sample.

[0044] Figure 5 This is a schematic diagram of the extraction of a thin-slice sample.

[0045] Figure 6 This is a schematic diagram of fixing a thin sheet sample onto a copper mesh.

[0046] Figure 7 This is a schematic diagram of a thin-film sample.

[0047] Figure 8 This is a diagram showing the structural deformation of a sample caused by atomic compression after bombardment with an electron beam.

[0048] Figure 9 This is a schematic diagram showing the location of dislocations obtained from TEM dislocation images of samples observed using a transmission electron microscope.

[0049] Figure 10 This is a schematic diagram of depositing two marker lines at the location of a dislocation based on a TEM dislocation image.

[0050] Figure 11 This is a schematic diagram of the deposition of the first protective layer before and after the dislocation.

[0051] Figure 12 This is a schematic diagram of placing a thin-film sample on an APT sample stage.

[0052] Figure 13 This is a schematic diagram of cutting a thin sheet sample into a cylindrical sample.

[0053] Figure 14 This is a schematic diagram of cutting a columnar sample into a frustum-shaped sample.

[0054] Figure 15 This is a schematic diagram of a needle-shaped sample.

[0055] Marker explanation:

[0056] 10. Block samples

[0057] 11. Thin-film sample

[0058] 12. Columnar sample

[0059] 13. Frustum-shaped sample

[0060] 14. Needle-shaped sample

[0061] 20. First protective layer

[0062] 21. Second protective layer

[0063] 30. First tank

[0064] 31. Second slot

[0065] 40. Extract the probe

[0066] 50. Copper mesh

[0067] 60. Dislocation

[0068] 70. Marking lines

[0069] 80. APT Sample Stage Detailed Implementation

[0070] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0071] The method described in this embodiment addresses the problem that current techniques for preparing APT samples cannot detect dislocations within the samples, thus failing to fully preserve dislocations during sample preparation and affecting the comprehensiveness of dislocation information detection. This invention utilizes TEM-assisted detection technology in the APT sample preparation process. First, a thin-film sample suitable for TEM detection is prepared; second, TEM is used to detect dislocations in the sample and determine their locations; then, the dislocation locations are marked in the sample, and a protective layer is deposited at the dislocation sites; finally, a fibrillated metallized iron (FIB) is used to perform ring milling around the dislocation locations, shaping the sample into a needle-like form. Compared to existing technologies, the method described in this invention provides more comprehensive and efficient dislocation detection.

[0072] The main steps of the method for preparing APT samples containing dislocations are as follows:

[0073] S1: Select 10 block samples containing dislocations;

[0074] S2: Use an etching solution to etch the surface of the block sample 10 to form an etching pit, the center of which is the dislocation center;

[0075] Preferably, the etching solution comprises: 50 ml HF, 30 ml HNO3, 15 g CrO3 (solid), 2 g Cu(NO3)2 (solid), 60 ml H2O, and 60 ml CH,COOH. Etching the dislocation sites with the etching solution will form etching pits; the center of the largest etching pit is selected as the dislocation center.

[0076] S3: Using the line where the dislocation center is located as the axis, symmetrically thin the block sample to make a thin sheet sample 11 suitable for TEM detection;

[0077] S31: As Figure 1As shown, a second protective layer 21 is deposited on the surface of the corrosion pits in the bulk sample 10 to prevent the selected area from being consumed during subsequent FIB thinning. This protects the integrity of the target structure during sample preparation and ensures the fabrication of a complete tip structure. In this embodiment, a 10 μm × 2 μm region is selected for illustration, and a 2 μm thick second protective layer 21 is deposited in an ion beam at 30 kV. The deposited protective layer is generally a platinum protective layer, but tungsten or carbon protective layers can also be used. The deposition process takes approximately 2–3 minutes.

[0078] S32: The sample is coarsely cut to obtain thin-slice sample 11. The selected area is separated from the block sample 10 and pre-processed into thin-slice sample 11. For example... Figure 2 As shown, a larger focused ion beam is used to hollow out both sides of the thin film to be processed. The size of the groove etched during hollowing should be much larger than the selected area to facilitate the complete separation of the thin film sample from the bulk sample later. For example, a first groove 30 and a second groove 31 with a size of 18μm × 9μm are etched under 30kV parameters. The first groove 30 is located above the selected area, and the second groove 31 is located below the selected area. The etching direction is from the outside to the edge of the second protective layer 21, maintaining a distance of 0.5μm to 1μm. The etching depth should be deeper than the depth of the thin film sample to be processed, generally about 2μm more. The sample stage is tilted to 54° and 50° respectively. A smaller FIB is used to trim the upper and lower sides of the thin film sample 11 to be processed. Under 30kV parameters, the thinner layer is further thinned towards the edge of the second protective layer 21.

[0079] S33: Perform a U-shaped cut on the thin-film sample. Rotate the sample stage to 0° and use FIB at 30kV to completely cut off the bottom and one side of the thin-film sample 11. This side forms the free end of the thin-film sample. Cut a portion from bottom to top to form the fixed end of the thin-film sample, as shown. Figure 3 As shown. The cutting depth is generally 0.1μm to 5μm.

[0080] S34: Extract the sheet sample 11 from the block sample 10. First, as... Figure 4 As shown, the extraction probe 40 is inserted into and close to the free end of the thin film sample 11. Platinum is deposited at the contact point between the extraction probe 40 and the free end of the thin film sample 11 using a FIB with parameters of 30 kV, thus fixing the extraction probe 40 and the thin film sample 11 together. Next, as... Figure 5 As shown, the fixed end of the thin sheet sample 11 is cut off using a FIB with a parameter of 30kV, so that the thin sheet sample 11 is completely separated from the block sample 10, and the thin sheet sample 11 is slowly extracted.

[0081] S35: Fix the thin sheet sample 11 onto the copper mesh 50. For example... Figure 6As shown, first, the copper mesh 50 is placed in a vertical position, and an L-shaped plane is cut out on one side of the copper mesh 50 using FIB. Second, the side of the cut thin sample 11 that is not welded to the extraction probe 40 is brought into contact with the vertical surface of the L-shaped plane on the copper mesh 50, and platinum is deposited on the contact surface using 30kV FIB to weld the thin sample 11 to the copper mesh 50. Finally, the thin sample 11 is separated from the extraction probe 40, and the extraction probe 40 is slowly extracted.

[0082] S36: Reduce the thickness of sheet sample 11 to 0.1–0.3 μm. Use a 30 kV FIB to coarsely thin the front and rear parts of sheet sample 11 to approximately 2 μm; then use a 15 kV FIB to finely thin the front and rear parts of sheet sample 11, tilting the ion beam at an angle of -1.5 to +1.5 degrees to compensate for ion beam dispersion defects; then reduce the voltage to 5 kV, at which point the ion beam dispersion is more severe, requiring tilting the ion beam at -3 to +3 degrees; finally, use a 2 kV FIB tilted at -5 to +5 degrees to thin sheet sample 11 to a thickness of 0.1 μm–0.3 μm. A schematic diagram of sheet sample 11 is shown below. Figure 7 As shown, in this embodiment, a thin sheet sample 11 with a thickness of 0.2 μm, a length of 8 μm, and a depth of 5 μm is selected for illustration. If a 30 kV FIB is used to thin the thin sheet sample 11 to 0.1 μm to 0.3 μm, the sample structure may be deformed due to atomic compression caused by excessive electron beam bombardment energy. Figure 8 As shown. Reducing the electron beam bombardment energy can cause defects such as ion beam dispersion. Therefore, this invention compensates for the defects caused by ion beam dispersion by gradually reducing the voltage and correspondingly setting the tilt angle of the ion beam. At the same time, this invention also found that when the thin sheet sample is thinned to 0.1μm-0.3μm using the above method, the thickness of the amorphous layer can also be reduced, making the thickness of the amorphous layer less than 35% of the total thickness. The thickness of the amorphous layer is a defect caused by the ion beam (e.g., Ga ions) in the FIB bombarding the material layer. The further the amorphous layer is, the more difficult it is to observe the information of the material itself in the prepared TEM sample.

[0083] The existing FIB has an angle of 52° between the ion beam and the sample stage. When the tilt angle of the ion beam needs to be compensated from -3° to +3°, the angle between the ion beam and the sample stage is 49° to 55°.

[0084] S4: Use TEM to detect dislocation 60 in thin-film sample 11 and obtain TEM images of the dislocations; such as Figure 9As shown, a TEM image containing dislocation information 60 was obtained by observing the thin-film sample 11 using a transmission electron microscope. The precision of TEM can reach 0.1 nm. Compared with AFM, TEM is more favorable for dislocation information, and the preparation of APT samples requires the needle tip to be as sharp as possible. Therefore, TEM is theoretically the best choice.

[0085] S5: As Figure 10 As shown, based on the TEM dislocation image, at least two marker lines 70 are deposited on the thin-film sample 11, the intersection of the two marker lines 70 being located on the dislocation line observed in the TEM image. The marker lines 70 are deposited at a parameter of 30 kV, and the material of the marker lines 70 is either tungsten or carbon.

[0086] S6: Centered on the intersection of the marking lines 70, deposit a first protective layer 20 on the surface of the thin-film sample. During deposition, the front and rear surfaces can be deposited simultaneously, or only the front surface can be deposited. At a parameter of 30 kV, deposit the first protective layer 20 before and after the dislocation 60, as follows: Figure 11 As shown. The first protective layer is made of a different material than the marker line 70. The deposited first protective layer 20 is generally a platinum protective layer, but it can also be a tungsten or carbon protective layer.

[0087] S7: Transfer the thin film sample with the first protective layer 20 deposited onto the APT sample stage 80.

[0088] S71: As Figure 12 As shown, the thin film sample 11 is placed on the APT sample stage 80 using the extraction probe 40, with the bottom of the thin film sample in contact with the APT sample stage 80, and the intersection of the marker lines 70 deposited on the thin film sample 11 is located at the center of the APT sample stage 80.

[0089] S72: Pt is deposited on the contact surface between the bottom of the sheet sample 11 and the APT sample stage 80 using FIB, in order to fix the sheet sample 11 on the APT sample stage 80.

[0090] S8: Use FIB to perform ring milling around the location of the dislocation to make the sample into a needle-like shape.

[0091] S81: As Figure 13As shown, the thin-film sample 11 is square-cut. First, the side lengths of the inner and outer square rings are determined. Then, the sample between the inner and outer square rings is removed using a 30kV FIB cut. The side length of the inner square ring is 0.1μm to 3μm, and the side length of the outer square ring is 0.1μm to 10μm. In this embodiment, the side length of the inner square ring is 0.2μm, and the side length of the outer square ring is 10μm. The structure within the inner ring is protected by the protective layer and will not be cut by the ion beam. The structure between the inner and outer rings will be completely removed, resulting in a columnar sample 12. The first protective layer 20 deposited before and after the dislocation will be cut during this operation.

[0092] S82: As Figure 14 As shown, the columnar sample 12 is cut into rings. First, the diameters of the inner and outer rings are determined, and then the sample between the inner and outer rings is removed using a 30kV FIB cut. In this embodiment, the diameters of the inner and outer rings can be determined based on the dimensions of the columnar sample 12. In this embodiment, the inner ring diameter is selected as 0.1μm and the outer ring diameter as 0.2μm. During the cutting of the columnar sample 12, the structure within the inner ring area is protected from being cut by the ion beam, and the structure between the inner and outer rings is completely removed. By controlling the scattering of the ion beam, a frustum-shaped sample 13 is finally obtained.

[0093] S83: Perform closed-loop cutting on the frustum-shaped sample 13. During the closed-loop cutting process, the frustum-shaped sample 13 is completely exposed to the ion beam, and the second protective layer 21 at the top of the sample and the entire frustum-shaped sample 13 are simultaneously cut by the ion beam. The closed-loop diameter can be determined comprehensively based on factors such as the volume of the frustum-shaped sample 13 and the condition of the focused ion beam equipment. In this embodiment, a closed-loop diameter of 5 μm is selected. A focused ion beam of 5 kV-2 kV cuts the frustum-shaped sample 13 within a 5 μm annular region. During this step, the second protective layer 21 at the top becomes thinner and thinner, while the tip diameter continuously decreases. When the remaining portion of the second protective layer 21 at the top of the cone or when the second protective layer 21 is cut off, the FIB cutting is stopped. Figure 15 As shown, the final needle-like sample 14 is obtained at this point. The height of the needle-like sample 14 is 50 nm to 200 nm, and its diameter is less than 100 nm. Furthermore, the intersection of the needle tip and the marking line 70 after cutting the needle-like sample 14 is within 100 nm above and below to ensure that the dislocation is within the range of the APT sample. The final needle-like sample 14 retains a second protective layer 21 at its tip, which is beneficial for positioning the needle tip during APT testing. Because the material used for this protective layer is easily evaporated in the field, it is evaporated first during the APT testing process and will not interfere with the test results.

[0094] In TEM observation of dislocations, it is crucial to avoid sample deformation due to improper clamping or other handling. When sample deformation occurs due to clamping, TEM observations often reveal equiclinal fringes or numerous long, nearly parallel dislocations caused by deformation. These dislocations can be easily confused with the actual dislocation distribution in the sample. To eliminate long, straight dislocations introduced by clamping, a protective film can be deposited on the sample surface, and the sample should be handled with care during clamping. Dislocation configurations that constitute a large proportion of the observed field of view should be selected as typical configurations to ensure more accurate and reliable observation results.

[0095] The quality of the APT sample tip determines the accuracy of the experimental data. Generally, APT samples must meet the following requirements: (1) tip radius less than 100 nm; (2) tip shape must be symmetrical to avoid elliptical shapes; (3) tip cone angle cannot be too large; (4) the column body must avoid microcracks; (5) no other tips or micro-tips should appear within 100 μm of the tip. Applying a large DC bias (5-20 V) to a needle-shaped sample with a radius of curvature less than 100 nm will generate a very large electrostatic field (tens of V / nm) at the tip due to its extremely small radius of curvature. Under the influence of this high electrostatic field, atoms at the tip will ionize and evaporate from the surface. The APT sample prepared by the APT sample preparation method of the present invention is needle-shaped with a height of 50nm to 200nm and a diameter of less than 100nm. The intersection of the needle tip and the marking line is about 100nm, which well meets the parameter requirements of the APT sample. Furthermore, the present invention can ensure that the prepared APT sample includes at least one dislocation.

[0096] The working principle of APT detection is as follows: During data acquisition, the sample analysis chamber must reach an ultra-high vacuum (generally less than 10). -8The vacuum level is controlled to avoid interference signals caused by field-evaporated ions colliding with gas molecules. The sample is then cooled to a low temperature (20-80K, depending on sample properties) to reduce thermal vibrations of atoms. A 1-15kV positive voltage is applied to the sample as the anode, placing the atoms at the sample tip in a state of ionization. After a pulsed voltage or pulsed laser is applied to the sample tip, its surface atoms are ionized, evaporated, and strike the detector. Between each pulse, almost only a single layer of the diaphragm is field-evaporated, and the tip radius becomes increasingly larger as the experiment progresses. Therefore, the applied positive voltage must be gradually increased to maintain the evaporation rate. The time difference between the pulse and the detector yields the particle's flight time. A time-of-flight mass spectrometer is used to determine the mass / charge ratio of the evaporated ions, thus obtaining the mass spectral peak to identify the element. A position-sensitive probe records the two-dimensional coordinates of the flying ions on the sample tip surface. By accumulating the ions layer by layer in the longitudinal direction, the longitudinal coordinates of the ions are determined, providing a three-dimensional spatial distribution image of different element atoms.

[0097] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing an APT sample, characterized in that: To prepare an APT sample containing at least one dislocation, the following steps are included: S1: Select a blocky sample containing dislocations; S2: The block sample is subjected to corrosion treatment, and the corrosion pits formed by corrosion are used as the basis for determining the location of dislocations. The middle position of one of the corrosion pits is selected and marked as the dislocation center. S3: Using the dislocation center as a reference, prepare a TEM thin-film sample suitable for TEM detection; S4: Use TEM to observe the dislocations in the TEM thin film sample and obtain a dislocation image on the TEM thin film sample; S5: Based on the dislocation image on the TEM thin film sample, at least two marker lines are deposited on the TEM thin film sample, the intersection of the two marker lines is located on the dislocation line observed in the TEM image; with the intersection point as the center, a first protective layer is deposited on the surface of the TEM thin film sample, the first protective layer being disposed on the front surface of the TEM thin film sample. S7: Fix the thin film sample with the first protective layer deposited on the APT sample stage, and the intersection of the marker lines deposited on the TEM thin film sample is located at the center of the APT sample stage; S8: Use FIB to perform circumferential milling around the location of the dislocation in the TEM sheet sample to form a needle-shaped APT sample; wherein the APT sample contains complete dislocations.

2. The APT sample preparation method according to claim 1, characterized in that: The distance between the boundary of the deposition area of ​​the first protective layer and the intersection point is 2-3 μm.

3. The APT sample preparation method according to claim 1, characterized in that: The specific steps of step S3 are as follows: S31: Deposit a second protective layer on the surface of the corrosion pits of the block sample; S32: A first groove and a second groove are etched from the outside towards the edge of the second protective layer on the block sample. The first groove and the second groove are located on the upper and lower sides of the second protective layer, respectively. The lower side of the first groove and the upper side of the second groove are then trimmed to obtain the TEM sheet sample. The thickness of the TEM sheet sample is the same as the width of the second protective layer. S33: Perform a U-shaped cut on the TEM thin-film sample; S34: Extract the TEM thin-film sample from the bulk sample; S35: Fix the TEM thin-film sample onto a copper grid; S36: The front and rear parts of the TEM thin film sample are thinned to reduce the thickness of the TEM thin film sample to 0.1-0.3 μm.

4. The APT sample preparation method according to claim 3, characterized in that: The specific steps of step S33 are as follows: cut off the bottom and one side of the TEM thin film sample, separate the TEM thin film sample from the block sample, and form the free end of the thin film sample from this side. Cut off a portion of the other side from bottom to top to form the fixed end of the thin film sample. The specific steps of step S34 are as follows: First, the extraction probe is brought close to the free end of the TEM thin film sample; then, a welding material is deposited at the position where the extraction probe contacts the free end of the TEM thin film sample to fix the extraction probe to the free end of the TEM thin film sample; then, the fixed end of the TEM thin film sample is cut off. The TEM thin-film sample was then slowly extracted. The specific steps of step S35 are as follows: Position the copper mesh vertically and cut an L-shaped plane on one side of the copper mesh; Place the side of the TEM thin film sample not fixed to the extraction probe into contact with the vertical surface of the L-shaped plane on the copper mesh; deposit welding material on the contact surface to weld the TEM thin film sample to the copper mesh; and separate the TEM thin film sample from the extraction probe.

5. The APT sample preparation method according to claim 3, characterized in that: The specific steps of step S36 are as follows: S361: Use 30kV FIB to coarsely thin the front and rear parts of the TEM thin film sample to about 2μm; S362: The front and rear parts of the TEM thin film sample are finely thinned using FIB with gradually decreasing voltage to a thickness of 0.1μm-0.3μm; and the tilt angle of the ion beam increases accordingly during the voltage reduction process. The gradual voltage reduction method includes thinning the TEM sheet sample with a 15kV FIB and compensating for the ion beam tilt angle by -1.5° to +1.5°; thinning the TEM sheet sample with a 5kV FIB and compensating for the ion beam tilt angle by -3° to +3°; and thinning the TEM sheet sample with a 2kV FIB and compensating for the ion beam tilt angle by -5° to +5°.

6. The APT sample preparation method according to claim 3, characterized in that: The first protective layer or the second protective layer is one of platinum, carbon, and tungsten; and the first protective layer and the marking line are made of different materials.

7. The APT sample preparation method according to claim 3, characterized in that: In step S32, the size of the first groove and the second groove is greater than the size of the second protective layer.

8. The APT sample preparation method according to claim 1, characterized in that: The specific steps of step S7 are as follows: S71: The TEM thin-film sample is transferred to the APT sample stage using an extraction probe, with the bottom of the TEM thin-film sample in contact with the APT sample stage; S72: Deposit welding material on the contact surface between the bottom of the TEM thin film sample and the APT sample stage to fix the TEM thin film sample on the APT sample stage.

9. An APT sample, characterized in that: The APT sample is prepared using the APT sample preparation method according to any one of claims 1-8. The APT sample is needle-shaped with a height of 50 nm to 200 nm and a diameter of less than 100 nm. The intersection of the needle tip and the marking line is about 100 nm. The APT sample includes at least one complete dislocation.

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