Sample preparation method of TEM sample and method for detecting single dislocation in gallium nitride single crystal

Abstract

The application discloses a sample preparation method of a TEM sample and a method for detecting a single dislocation in a gallium nitride single crystal, and the sample preparation method comprises the following steps: performing SEM-CL scanning on a substrate sample surface containing a gallium nitride single crystal, and obtaining a first SEM image and a corresponding cathodoluminescence image; marking a target single dislocation from the first SEM image based on the cathodoluminescence image; marking a first target region where the target single dislocation is located in the first SEM image; performing SEM scanning on the first target region of the substrate sample surface, and obtaining a second SEM image of carbon deposition around the target single dislocation; performing scanning on the second SEM image by using FIB-SEM, and marking a second target region where the carbon deposition is located; and performing etching on the second target region of the substrate sample surface after the carbon deposition, so that a TEM sample is prepared. The single dislocation can be accurately positioned from the substrate sample containing the gallium nitride single crystal, the TEM sample containing the single dislocation is prepared, and then the dislocation type of the single dislocation is determined.

Description

Technical Field

[0001] This invention relates to the field of material defect characterization technology, and in particular to a method for preparing TEM samples based on gallium nitride single crystals and a method for detecting single dislocations in gallium nitride single crystals. Background Technology

[0002] Gallium nitride (GaN) is a novel semiconductor material for developing microelectronic and optoelectronic devices. It possesses a wide direct bandgap, strong atomic bonds, high thermal conductivity, and strong radiation resistance, making it promising for applications in optoelectronics, high-temperature high-power devices, and high-frequency microwave devices. Hydride vapor phase epitaxy (HVPE) is a commonly used method for preparing GaN single crystals. Due to the large lattice mismatch and significant difference in thermal expansion coefficients between the substrate material and GaN, the GaN thin film grown on the substrate exhibits a very high dislocation density, reaching the order of 10⁵. The presence of dislocations acts as non-radiative recombination centers for electron-hole pairs, increasing leakage current and consequently reducing device performance and reliability.

[0003] By studying the properties and behavior of single dislocations in substrate samples containing GaN single crystals, we can reveal the specific mechanisms by which they affect the electrical and optical properties of gallium nitride materials, thus providing a theoretical basis for optimizing device performance. However, the study of single dislocations remains a challenging field. Due to the small size of dislocations and the difficulty in direct observation, it is difficult to locate single dislocations in substrate samples, making accurate characterization and analysis impossible.

[0004] Those skilled in the art can observe dislocations in samples using transmission electron microscopy (TEM). In the prior art, the following methods are commonly used for sample preparation:

[0005] 1. The etching method is used to observe and locate dislocations in the gallium nitride sample to be characterized, and then TEM sample preparation is carried out. However, this will damage the substrate sample. At the same time, due to the complexity of the etching process and the difficulty of the process, it is not only difficult to accurately locate single dislocations for TEM sample preparation, but also cannot guarantee the accuracy of characterization and analysis of single dislocations in gallium nitride samples.

[0006] 2. Another method for preparing TEM samples is ion thinning. First, the gallium nitride sample is sliced ​​into thin sheets. Then, the areas to be observed are joined together to form the TEM sample. Finally, the TEM sample is mounted on a copper ring with a diameter of three millimeters, and ion thinning is performed again. This method requires a high level of experience and skill from the operator. It is difficult to guarantee a high success rate in sample preparation, and it cannot precisely target specific areas for thinning. Similarly, it cannot accurately locate single dislocations.

[0007] This invention solves at least one of the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing TEM samples. This method solves the problems in the prior art where the small size of dislocations makes them difficult to observe directly, making it difficult to locate single dislocations in the substrate sample, thus hindering accurate characterization and analysis, and where etching methods damage the substrate sample. This method can accurately locate single dislocations from a substrate sample containing gallium nitride single crystals and prepare TEM samples containing single dislocations. Compared to traditional etching methods, this method does not damage the substrate sample and enables more accurate characterization and analysis of single dislocations in TEM dual-beam characterization and analysis.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A first aspect of the present invention provides a method for preparing a TEM sample, comprising the following steps:

[0011] The surface of the substrate sample containing the gallium nitride single crystal was scanned by SEM-CL to obtain the first SEM image and its corresponding cathodoluminescence image;

[0012] The target single dislocation is marked from the first SEM image based on the cathodoluminescence image;

[0013] Mark the first target region where the target single dislocation is located in the first SEM image;

[0014] SEM scanning was performed on the first target region on the surface of the substrate sample to obtain a second SEM image of carbon deposition around the target single dislocation.

[0015] The second SEM image was scanned using FIB-SEM to mark the second target area where the carbon deposit was located;

[0016] The second target region on the surface of the substrate sample after carbon deposition is formed is etched to prepare a TEM sample.

[0017] Compared with the prior art, the beneficial effects of the present invention include at least the following: This application uses SEM-CL scanning to mark the target single dislocation from the first SEM image of the substrate sample using the cathodoluminescence image, thereby achieving coarse localization of the target single dislocation in the substrate sample; by performing SEM scanning on the first target region where the target single dislocation is located in the substrate sample, a second SEM image of carbon deposition around the target single dislocation can be obtained, thereby achieving fine localization of the target single dislocation in the substrate sample using carbon deposition; then, the second SEM image is scanned using FIB-SEM to accurately mark the second target region where the carbon deposition is located on the surface of the substrate sample after carbon deposition; by etching the second target region, a TEM sample including the single dislocation can be easily and accurately cut out from the substrate sample. Compared with the traditional etching method, it does not require destroying the substrate sample, and in the application of TEM dual-beam characterization analysis of TEM samples, more accurate characterization and analysis of single dislocations can be achieved.

[0018] In some possible implementations of the first aspect, marking the target single dislocation from the first SEM image based on the cathodoluminescence image includes the following steps:

[0019] All dislocations are determined from the cathodoluminescence image based on a preset contrast threshold;

[0020] Select a single dislocation from all dislocations in the cathodoluminescence image;

[0021] Obtain the registration relationship between the first SEM image and the cathodofluorescence image;

[0022] Based on the registration relationship, the target single dislocation corresponding to the single dislocation is marked from the first SEM image.

[0023] In some possible implementations of the first aspect, marking the first target region where the target single dislocation is located in the first SEM image includes the following steps:

[0024] Obtain the edge contour of the target single dislocation;

[0025] Construct the minimum envelope box of the edge contour;

[0026] The minimum envelope box is marked as the first target region where the target single dislocation is located.

[0027] In some possible embodiments of the first aspect, the method for acquiring the cathodofluorescence image includes the following steps:

[0028] Acquire the cathodoluminescence signal generated by the substrate sample under the SEM-CL scan;

[0029] The cathode fluorescence signal is converted into an electrical signal;

[0030] The cathode fluorescence image is output based on the electrical signal; and / or

[0031] The scanning conditions for the SEM-CL scan include: accelerating voltage of 5–20 kV and beam current of 0.5–1.5 nA.

[0032] In some possible implementations of the first aspect, performing SEM scanning on a first target region on the surface of the substrate sample to obtain a second SEM image of carbon deposition around the target single dislocation includes the following steps:

[0033] The first target region on the surface of the substrate sample is bombarded with an electron beam from a SEM to form carbon deposits around the target single dislocation, thus obtaining a carbon deposit sample.

[0034] The carbon deposit sample was scanned using SEM to obtain the second SEM image; and / or

[0035] The bombardment conditions for the SEM include: accelerating voltage of 5–20 kV, beam current of 0.5–1.5 nA, and bombardment time of 20–30 s; and / or

[0036] The scanning conditions for the SEM scan include: accelerating voltage of 5–20 kV and beam current of 0.5–1.5 nA.

[0037] In some possible embodiments of the first aspect, etching a second target region on the surface of the substrate sample after carbon deposition to prepare a TEM sample includes the following steps:

[0038] Set the etching depth of the ion beam;

[0039] The beam current parameters of the ion beam are determined based on the etching depth;

[0040] Based on the beam parameters, the second target region on the surface of the carbon deposit sample is etched to obtain a TEM sample including the target single dislocation;

[0041] The etching depth of the ion beam is 8–12 μm; and / or

[0042] The beam parameters of the ion beam include: accelerating voltage of 20–30 kV and beam current of 8–10 nA; and / or

[0043] The area of ​​the second target region is at least 10 μm × 10 μm.

[0044] In some possible implementations of the first aspect, the method further includes:

[0045] The TEM sample is thinned using FIB (fiber-optic blotting) so that the thickness of the thinned TEM sample meets a preset thickness detection standard.

[0046] The preset thickness detection standard is less than 100nm.

[0047] A second aspect of the present invention provides a method for detecting a single dislocation in a gallium nitride single crystal, comprising the following steps:

[0048] The above sample preparation method was used to prepare TEM samples;

[0049] The dislocation type of the target single dislocation is obtained by detecting the TEM sample using TEM.

[0050] Technical effect: When the TEM sample prepared using the above method is applied to TEM dual-beam characterization analysis, it can achieve more accurate characterization of single dislocations and accurately analyze the dislocation type of the target single dislocation.

[0051] In some possible embodiments of the second aspect, the TEM includes a grid and an electron gun, and the detection of the TEM sample using the TEM includes the following steps:

[0052] The TEM sample is transferred to the grid.

[0053] The grid is tilted so that the TEM sample on the grid is tilted synchronously.

[0054] The electron gun is used to emit an electron beam so that the electron beam is incident on the surface of the TEM sample along the first zone axis, and the electron diffraction images of the target single dislocation and their corresponding TEM images are obtained under different g vectors.

[0055] The g vector is determined based on the electron diffraction image;

[0056] Based on the standard relationship between the g vector and the Burgers vector b of the dislocation, the dislocation type of the target single dislocation in the TEM image is determined.

[0057] In some possible embodiments of the second aspect, the tilt angle of the carrier net is 0° to 20°; and / or

[0058] The dislocation types include at least one of edge dislocations, screw dislocations, and mixed dislocations. Attached Figure Description

[0059] Figure 1 This application provides an overall flowchart of a method for preparing a TEM sample.

[0060] Figure 2A schematic diagram of the first SEM image provided in an embodiment of this application;

[0061] Figure 3 A flowchart illustrating the steps of a method for acquiring cathodoluminescence images provided in an embodiment of this application;

[0062] Figure 4 A flowchart illustrating the steps for marking a target single dislocation from a first SEM image, as provided in this application embodiment;

[0063] Figure 5 A flowchart illustrating the steps for acquiring the second SEM image provided in this application embodiment;

[0064] Figure 6 A schematic diagram of the second SEM image provided in an embodiment of this application;

[0065] Figure 7 A flowchart illustrating the steps for preparing TEM samples as provided in this application embodiment;

[0066] Figure 8 A flowchart illustrating the steps for marking the first target region provided in this application embodiment;

[0067] Figure 9 This is a flowchart illustrating the overall steps of the method for detecting a single dislocation in a gallium nitride single crystal provided in this application embodiment.

[0068] Figure 10 This is a flowchart illustrating the steps of using TEM to detect TEM samples in an embodiment of this application.

[0069] Figure 11 This is a schematic diagram of electron diffraction images of a single dislocation of a target under different g vectors and their corresponding TEM images, provided in the embodiments of this application. Detailed Implementation

[0070] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided to make the invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore repeated descriptions of them will be omitted.

[0071] In a first aspect, this embodiment provides a method for preparing a TEM sample, in conjunction with an appendix. Figure 1 As shown, it includes the following steps S1-S6.

[0072] Step S1: Perform SEM-CL scanning on the surface of the substrate sample containing gallium nitride single crystal to obtain the first SEM image and its corresponding cathodoluminescence image.

[0073] It should be noted that this method uses gallium nitride single crystal as an example and should not be regarded as a limitation on the materials used in this application.

[0074] The surface of a substrate sample containing gallium nitride single crystals was scanned using SEM (scanning electron microscope)-CL (cathodoluminescence microscope).

[0075] In a SEM, the electron beam emitted by the electron gun is focused into a point source. This point source, under accelerating voltage, forms a high-energy electron beam. This high-energy electron beam is then focused into a tiny spot by two electromagnetic lenses. After passing through a final electromagnetic lens with a scanning coil, the electron beam bombards the substrate sample surface point-by-point in a grating-like scanning manner, simultaneously exciting electron signals at different depths. These electron signals are then received by probes at different signal receivers above the sample, amplified, and synchronously transmitted to a display, forming a real-time imaging record, thus obtaining the first SEM image of the substrate sample. For example, see the appendix for the first SEM image. Figure 2 The left-hand SEM image is shown in the figure.

[0076] During SEM-CL scanning, incident electrons bombard the sample surface and excite various signals, such as Auger electron (AuE) signals, secondary electron (SE) signals, backscattered electron (BSE) signals, X-ray (characteristic X-rays, continuous X-rays) signals, cathodoluminescence (CL) signals, absorbed electron (AE) signals, and transmitted electron signals.

[0077] It should be noted that the scanning conditions for SEM-CL scanning include: accelerating voltage of 5–20 kV and beam current of 0.5–1.5 nA. Within this range, the image quality and signal strength of the first SEM image, especially the signal strength of the cathodoluminescence signal, can be guaranteed, while reducing or even avoiding radiation damage to the sample surface. In this embodiment, preferably, the accelerating voltage is 10 kV and the beam current is 1 nA.

[0078] In some specific implementation methods, in conjunction with the appendix Figure 3 As shown, the method for acquiring cathodoluminescence images includes the following steps S11-S13.

[0079] Step S11: Obtain the cathodoluminescence signal generated by the substrate sample under SEM-CL scanning.

[0080] Step S12: Convert the cathodoluminescence signal into an electrical signal.

[0081] Step S13: Output a cathodoluminescence image based on the electrical signal.

[0082] This allows us to obtain a cathodoluminescence image of the substrate sample. It should be noted that, under SEM-CL scanning, the cathodoluminescence image corresponds to the first SEM image.

[0083] For example, with Figure 2 The corresponding cathodoluminescence image for the SEM image on the left is shown in the appendix. Figure 2 The CL diagram on the right is shown in the figure.

[0084] Step S2: Mark the target single dislocation from the first SEM image based on the cathodoluminescence image.

[0085] Cathodoluminescence images can reveal the luminescence characteristics of different regions of the substrate sample. As nonradiative recombination centers in gallium nitride single crystals, dislocations appear as dark spots in cathodoluminescence images. Therefore, based on the intensity of luminescence in different regions of the substrate sample, dark spots representing dislocations can be identified from the cathodoluminescence images. Since the first SEM image corresponds to the cathodoluminescence image, the target single dislocation can be marked in the first SEM image using the cathodoluminescence image, thus achieving coarse localization of the target single dislocation.

[0086] It should be noted that the target single dislocation is selected through settings, and any one can be selected according to actual needs.

[0087] In some specific implementation methods, in conjunction with the appendix Figure 4 As shown, step S2 includes the following steps S21-S24.

[0088] Step S21: Identify all dislocations from the cathodofluorescence image based on a preset contrast threshold.

[0089] The contrast in a cathodoluminescence image reflects the intensity of light emission in different regions of the substrate sample. Dislocations, as nonradiative recombination centers in gallium nitride single crystals, appear as dark spots in cathodoluminescence images and have a certain contrast range. Therefore, by setting a preset contrast threshold, all dislocations representing all dark spots can be determined from the cathodoluminescence image.

[0090] Step S22: Select a single dislocation from all dislocations in the cathodoluminescence image.

[0091] A single dislocation is selected through a setting, and any one can be chosen according to actual needs.

[0092] Step S23: Obtain the registration relationship between the first SEM image and the cathodoluminescence image.

[0093] For the registration of the first SEM image and the cathodoluminescence image, the common feature points or feature regions of the two are usually aligned in the same coordinate system so that the morphology and luminescence properties of the sample can be analyzed at the same time, and the registration relationship between the two can be constructed. This is a conventional technique and will not be elaborated here.

[0094] Step S24: Based on the registration relationship, mark the target single dislocation corresponding to the single dislocation from the first SEM image.

[0095] By using the above registration relationship, the feature points or feature regions can be made consistent on the same coordinate system, which improves the localization accuracy of the target single dislocation corresponding to the single dislocation marked in the first SEM image, while avoiding the introduction of other dislocations and preventing detection interference.

[0096] Step S3: Mark the first target region where the target single root dislocation is located in the first SEM image.

[0097] Marking the first target region where the target single dislocation is located is a prerequisite for subsequent steps. Theoretically, the target single dislocation only needs to be located in the first target region, so the area of ​​the first target region can be selected according to the requirements.

[0098] Step S4: Perform SEM scanning on the first target area on the substrate sample surface to obtain a second SEM image of carbon deposition around the target single dislocation.

[0099] It should be noted that, due to the adsorption of some hydrocarbons on the surface of the substrate sample, the high-energy electron beam emitted by the electron gun of the SEM will form positively charged carbon ions when it bombards the surface of the substrate sample. The carbon ions generated will become more concentrated in the region as the range of the electron beam decreases. Over time, black areas, i.e., carbon deposition, will form on the surface of the substrate sample.

[0100] In some specific implementation methods, in conjunction with the appendix Figure 5 As shown, step S4 includes steps S41-S42.

[0101] Step S41: Use the electron beam of SEM to bombard the first target area on the surface of the substrate sample to form carbon deposits around the target single dislocation, thereby obtaining a carbon deposit sample.

[0102] When the high-energy electron beam emitted by the electron gun of SEM bombards the first target region, it will form positively charged carbon ions. The carbon ions produced will become more concentrated in the first target region as the range of the electron beam shrinks. As time increases, carbon will be deposited around the target single dislocation, forming a black area in the first target region around the target single dislocation, thus obtaining a carbon deposit sample.

[0103] Furthermore, the bombardment conditions for SEM include: an accelerating voltage of 5–20 kV and a beam current of 0.5–1.5 nA; in this embodiment, preferably, the accelerating voltage is 10 kV and the beam current is 1 nA.

[0104] Furthermore, the bombardment time is 20–30 seconds. Using this time range allows for sufficient carbon buildup in the first target region surrounding the target dislocation, making the black area more prominent and improving the accuracy of locating the target dislocation. In this embodiment, the preferred bombardment time is 25 seconds.

[0105] Step S42: Use SEM to scan the carbon deposit sample to obtain a second SEM image.

[0106] The scanning conditions for SEM scanning include: accelerating voltage of 5–20 kV and beam current of 0.5–1.5 nA;

[0107] In this embodiment, preferably, the accelerating voltage is 10kV and the beam current is 1nA.

[0108] A second SEM image of the carbon deposit sample can be obtained by scanning the surface of the carbon deposit sample with SEM; for example, see the appendix for the second SEM image. Figure 6 As shown.

[0109] In summary, the high-energy electron beam generated by SEM was used to target the first target region where the single dislocation is located.

[0110] The bombardment process generates carbon deposits around the target single dislocation, which are then used to achieve precise localization of the target single dislocation.

[0111] Step S5: Use FIB-SEM to scan the second SEM image and mark the second target area where the carbon deposit is located.

[0112] By scanning the second SEM image using FIB (Focused Ion Beam Microscopy)-SEM, a black region representing the first target area can be identified on the surface of the carbon deposit sample, thereby determining the location of the carbon deposit in the carbon deposit sample.

[0113] It should be noted that the location center of the carbon deposit is the target single dislocation, and thus the location center of the carbon deposit can be used to more accurately characterize the target single dislocation.

[0114] Marking the second target area where carbon deposits are located is a prerequisite for subsequent steps. In theory, as long as the carbon deposits are located in the first target area, it is acceptable. Therefore, the area of ​​the second target area can be selected according to the requirements.

[0115] Furthermore, the area of ​​the second target region is at least 10μm × 10μm. Preferably, in this embodiment, the area of ​​the second target region is 10μm × 10μm. It should be noted that the area of ​​the second target region should conform to the detection standards of the TEM equipment.

[0116] Step S6: Etch the second target region on the surface of the substrate sample after carbon deposition to prepare a TEM sample.

[0117] In some specific implementation methods, in conjunction with the appendix Figure 7 As shown, step S6 includes steps S61-S63.

[0118] Step S61: Set the etching depth of the ion beam.

[0119] The etching depth is 8 to 12 μm. In this embodiment, the preferred etching depth is 10 μm.

[0120] Step S62: Determine the beam current parameters of the ion beam based on the etching depth.

[0121] The beam parameters of the FIB ion beam include an accelerating voltage of 20–30 kV and a beam current of 8–10 nA. In this embodiment, the set etching depth can be achieved within this parameter range. Preferably, the accelerating voltage is 30 kV and the beam current is 9.1 nA.

[0122] Step S63: Based on the beam parameters, etch the second target region on the surface of the carbon deposit sample to obtain a TEM sample including the target single dislocation.

[0123] A focused ion beam is used to etch a second target region on the surface of the carbon deposit sample, etching a region with a size of 10μm×10μm and a depth of 10μm downwards from the surface of the carbon deposit sample along its thickness direction, which facilitates the accurate cutting out of the TEM sample, including single dislocations, from the carbon deposit sample.

[0124] In some specific embodiments of the first aspect, the above-mentioned sample preparation method further includes: using FIB to thin the TEM sample so that the thickness of the thinned TEM sample reaches a preset thickness detection standard.

[0125] It should be noted that the preset thickness detection standard is less than 100nm. In this embodiment, preferably, the thickness of the thinned TEM sample is 80nm.

[0126] The FIB sample preparation method used in this method can not only ensure the success rate of sample preparation, but also accurately specify the area for thinning, thereby more accurately locating single dislocations, taking less time and being more efficient.

[0127] In some specific implementation methods, in conjunction with the appendix Figure 8 As shown, step S3 includes steps 31 to S33.

[0128] Step 31: Obtain the edge profile of the target single dislocation.

[0129] Step 32: Construct the minimum envelope box of the edge profile of the target single dislocation.

[0130] Step 33: Mark the smallest envelope box as the first target region where the target single dislocation is located.

[0131] Combined with step S4, the size of the first target region is precisely planned using the minimum envelope box, which allows the carbon deposits generated around the target single dislocation in the first target region to accumulate sufficiently, further improving the accuracy of locating the target single dislocation, while reducing the bombardment time of the high-energy electron beam.

[0132] A second aspect of this embodiment provides a method for detecting single dislocations in gallium nitride single crystals, in conjunction with the attached... Figure 9 As shown, the method includes the following steps S10-S20.

[0133] Step S10: Provide a TEM sample containing the target single dislocation. The TEM sample is prepared using the sample preparation method described above.

[0134] Step S20: Use TEM to detect the TEM sample and obtain the dislocation type of the target single dislocation.

[0135] TEM includes a grid and an electron gun, combined with an attached... Figure 10 As shown, the detection of TEM samples using TEM includes the following steps S201-S204.

[0136] Step S201: Transfer the TEM sample to the grid.

[0137] Step S202: Tilt the wire mesh to allow the TEM samples on the wire mesh to tilt synchronously.

[0138] It should be noted that, since the TEM sample is prepared according to the crystal orientation, the tilt angle of the grid is set to 0-20 degrees.

[0139] Step S203: Use an electron gun to emit an electron beam so that the electron beam is incident on the surface of the TEM sample along the first zone axis, and obtain the electron diffraction image of the target single dislocation and its corresponding TEM image under different g vectors.

[0140] It should be noted that the first zone axis direction is <1-100>; by tilting the TEM sample, the selected area electron diffraction (SAED) images of the target single dislocation under different g vectors and their corresponding TEM images can be obtained.

[0141] Step S204: Based on the electron diffraction image and its corresponding TEM image, determine the dislocation type of the target single root dislocation in the TEM image.

[0142] After obtaining the electron diffraction images of the target single dislocation under different g vectors and their corresponding TEM images, the TEM image without the target single dislocation is found from all the TEM images (denoted as the target TEM image); the electron diffraction image corresponding to the target TEM image is found (denoted as the target electron diffraction image); the g vector corresponding to the target electron diffraction image is determined (denoted as the target g vector); based on the standard relationship between the target g vector and the Burgers vector b of the dislocation, the dislocation type of the target single dislocation in the TEM image is determined.

[0143] Furthermore, the standard relation refers to the fact that the vector product of the g vector and the Burgh's vector b is 0.

[0144] It should be noted that the dislocation types include at least one of edge dislocations (TED), screw dislocations (TSD), and mixed dislocations (TMD).

[0145] Furthermore, in-situ electrical TEM can be used to observe the evolution behavior of TEM samples under different current conditions.

[0146] For specific methods, please refer to the national standard GB / T44558-2024-Test of dislocation imaging in group III nitride semiconductor materials by transmission electron microscopy, which will not be elaborated here.

[0147] TEM's "double-beam" diffraction contrast technique is a commonly used method for characterizing dislocations. The "double beam" consists of a transmission beam and a diffraction beam. Two different g-vectors are selected to capture the electron diffraction image of a single dislocation and its corresponding diffraction spectrum image. In TEM, the dislocation type can be determined by the extinction rule, i.e., an extinction table is constructed. For a known crystal structure (such as face-centered cubic, body-centered cubic, etc.), the visibility of the dislocation under different g-vectors can be determined according to the extinction rule. By analyzing the visibility of the dislocation under different g-vectors, the Burgers vector b of the dislocation can be further determined, and thus the dislocation type can be determined.

[0148] Under the influence of an electron beam in a TEM, a TEM sample exhibits diffraction contrast. In this method, the electron diffraction image and its corresponding TEM image utilize this diffraction contrast for imaging. The diffraction contrast image of a dislocation is directly determined by the value of g·b. When the Burgers vector b of a dislocation is perpendicular to the operating diffraction vector g, i.e., g·b = 0, the contrast of the dislocation line disappears. This is called dislocation de-image, and therefore, g = 0 is called the dislocation de-image criterion. Since gallium nitride single crystals are typically hexagonal close-packed structures, there are three distinct Burgers vectors in this crystal: 1. Edge dislocation: 1 / 3 <11-20>; 2. Screw dislocation: <0001>; 3. Mixed dislocation: 1 / 3 <11-23>. In transmission electron microscopy, by using the dislocation de-image criterion and selecting an appropriate diffraction vector, specific types of dislocations can be imaged.

[0149] Since the electron diffraction pattern determines the g vector, the g vector and the Burgers vector b are known. Based on the standard relationship between the g vector and the Burgers vector b of the dislocation, the dislocation type of the target single dislocation can be determined.

[0150] For example, with Figure 11 For example, the TEM image (a) and corresponding SAED image (b) are obtained when g=

[0002] , and the TEM image (c) and SAED image (d) are obtained when g=[11-20]. From Figure 11 As can be seen from the TEM image (c), the target single dislocation is not visible, that is, the TEM image (c) is the target TEM image, the SAED image (d) is the target SAED image, the target g vector is [11-20], and using g·b=0, it can be determined that the target single dislocation is an edge dislocation.

[0151] This application utilizes cathodoluminescence microscopy (CFM) to characterize single dislocations in gallium nitride (GaN) single crystals. Compared to the traditional etching method, this approach is simpler, more convenient, and allows for coarse localization of single dislocations without damaging the substrate sample. By using the electron beam of a SEM to locate carbon deposits on the substrate sample surface, the target single dislocation can be precisely located within the sample, making it easier to find during subsequent fibrillation-based lithography (FIB) sample preparation. Accurately pinpointing the target single dislocation facilitates its cutting. Since TEM requires a sample thickness of less than 100 nm, using FIB instruments to prepare TEM samples is also an efficient and convenient method. The transmission electron microscopy method, as per the national standard GB / T44558-2024-Dislocation Imaging Test in Group III Nitride Semiconductor Materials, can more accurately determine the dislocation type of the target single dislocation. Furthermore, because TEM has in-situ capabilities, in-situ electrical testing can be performed, allowing observation of the sample's evolution behavior under different current conditions. The combined use of these methods is crucial and effective for characterizing single dislocations.

[0152] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the invention without departing from the principles and spirit of the invention, and all such changes should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing TEM samples, characterized in that, Includes the following steps: The surface of a substrate sample containing gallium nitride single crystal was scanned by SEM-CL to obtain the first SEM image and its corresponding cathodoluminescence image; Marking a target single dislocation from the first SEM image based on the cathodoluminescence image includes: determining all dislocations from the cathodoluminescence image based on a preset contrast threshold; selecting a single dislocation from all dislocations in the cathodoluminescence image; obtaining the registration relationship between the first SEM image and the cathodoluminescence image; and marking the target single dislocation corresponding to the single dislocation from the first SEM image based on the registration relationship. Mark the first target region where the target single dislocation is located in the first SEM image; SEM scanning was performed on the first target region on the surface of the substrate sample to obtain a second SEM image of carbon deposition around the target single dislocation. The second SEM image was scanned using FIB-SEM to mark the second target area where the carbon deposit was located; The second target region on the surface of the substrate sample after carbon deposition is formed is etched to prepare a TEM sample.

2. The sample preparation method according to claim 1, characterized in that, Marking the first target region where the target single dislocation is located in the first SEM image includes the following steps: Obtain the edge contour of the target single dislocation; Construct the minimum envelope box of the edge contour; The minimum envelope box is marked as the first target region where the target single dislocation is located.

3. The sample preparation method according to claim 1, characterized in that, The method for acquiring the cathodofluorescence image includes the following steps: Acquire the cathodoluminescence signal generated by the substrate sample under the SEM-CL scan; The cathode fluorescence signal is converted into an electrical signal; The cathode fluorescence image is output based on the electrical signal; And / or, the scanning conditions for the SEM-CL scan include: an accelerating voltage of 5 to 20 kV and a beam current of 0.5 to 1.5 nA.

4. The sample preparation method according to claim 1, characterized in that, SEM scanning of the first target region on the surface of the substrate sample to obtain a second SEM image of carbon deposition around the target single dislocation includes the following steps: The first target region on the surface of the substrate sample is bombarded with an electron beam from a SEM to form carbon deposits around the target single dislocation, thus obtaining a carbon deposit sample. The carbon deposit sample was scanned using SEM to obtain the second SEM image; The bombardment conditions of the SEM include: an accelerating voltage of 5–20 kV, a beam current of 0.5–1.5 nA, and a bombardment time of 20–30 s; and / or, the scanning conditions of the SEM scan include: an accelerating voltage of 5–20 kV and a beam current of 0.5–1.5 nA.

5. The sample preparation method according to claim 4, characterized in that, The process of etching the second target region on the surface of the substrate sample after carbon deposition to prepare a TEM sample includes the following steps: Set the etching depth of the ion beam; The beam current parameters of the ion beam are determined based on the etching depth; Based on the beam parameters, the second target region on the surface of the carbon deposit sample is etched to obtain a TEM sample including the target single dislocation; The etching depth of the ion beam is 8–12 μm; and / or The beam parameters of the ion beam include: accelerating voltage of 20-30 kV and beam current of 8-10 nA; and / or The area of ​​the second target region is at least 10 μm × 10 μm.

6. The sample preparation method according to any one of claims 1-5, characterized in that, The sample preparation method further includes: The TEM sample is thinned using FIB (Film-Induced Blotting) to ensure that the thickness of the thinned TEM sample meets the preset thickness detection standard. The preset thickness detection standard is less than 100nm.

7. A method for detecting a single dislocation in a gallium nitride single crystal, characterized in that, Includes the following steps: TEM samples were prepared using the sample preparation method described in any one of claims 1-6; The dislocation type of the target single dislocation is obtained by detecting the TEM sample using TEM.

8. The detection method according to claim 7, characterized in that, The TEM includes a grid and an electron gun, and the detection of the TEM sample using the TEM includes the following steps: The TEM sample is transferred to the grid. The grid is tilted so that the TEM sample on the grid is tilted synchronously. The electron gun is used to emit an electron beam so that the electron beam is incident on the surface of the TEM sample along the first zone axis, and the electron diffraction images of the target single dislocation and their corresponding TEM images are obtained under different g vectors. Based on the electron diffraction image and its corresponding TEM image, determine the dislocation type of the target single root dislocation in the TEM image.

9. The detection method according to claim 8, characterized in that, The tilt angle of the carrier net is 0° to 20°; and / or The dislocation types include at least one of edge dislocations, screw dislocations, and mixed dislocations.

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