TEM (Transmission Electron Microscope) sample preparation method and method for detecting dislocation of single crystal in gallium nitride single crystal

Abstract

The invention discloses a TEM sample preparation method and a method for detecting single dislocation in gallium nitride single crystal, the sample preparation method comprises the following steps: performing SEM-CL scanning on the surface of a substrate sample containing the gallium nitride single crystal to obtain a first SEM image and a cathode fluorescence image corresponding to the first SEM image; marking a target single dislocation from the first SEM image based on the cathode fluorescence image; marking a first target area where the target single dislocation is located in the first SEM image; performing SEM scanning on a first target area on the surface of the substrate sample to obtain a second SEM image of carbon deposition generated by dislocation around a target single root; scanning the second SEM image by using FIB-SEM, and marking a second target area where the deposited carbon is located; and etching the second target area on the surface of the substrate sample after the carbon deposition is generated, and preparing to obtain the TEM sample. According to the method, the single dislocation can be accurately positioned from the substrate sample containing the gallium nitride single crystal, so that the TEM sample containing the single dislocation is prepared, and the dislocation type of the single dislocation is determined.

Description

Technical Field

[0001] The present invention relates to the technical field of material defect characterization, and in particular to a method for preparing a TEM sample based on a gallium nitride single crystal and a method for detecting a single dislocation in the gallium nitride single crystal. Background Art

[0002] GaN (gallium nitride) is a new type of semiconductor material for the development of microelectronic devices and optoelectronic devices. It has wide direct band gap, strong atomic bonds, high thermal conductivity and strong radiation resistance, and has broad prospects in the application of optoelectronics, high-temperature high-power devices and high-frequency microwave devices. HVPE (Hydride Vapor Phase Epitaxy) is a common method for preparing GaN single crystals. Due to the large lattice mismatch and large thermal expansion coefficient difference between the substrate material and GaN, the GaN film grown on the substrate has a very high dislocation density, which can still reach 10 to the fifth power. The existence of dislocations will become non-radiative recombination centers of electron-hole pairs, increase the leakage current of the device, and thus reduce the performance and reliability of the device.

[0003] By deeply studying the properties and behaviors of single dislocations in substrate samples containing GaN single crystals, the specific impact mechanism of single dislocations on the electrical, optical and other properties of GaN materials can be revealed, thereby providing a theoretical basis for optimizing device performance. However, the study of single dislocations is still 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 it impossible to accurately characterize and analyze them.

[0004] A person skilled in the art uses a transmission electron microscope (TEM) ， TEM) method is used to observe the dislocation of the sample. In the prior art, the following method is usually used for sample preparation:

[0005] 1. The etching method is used to observe and locate the dislocation of the GaN sample to be characterized, and then the TEM sample is prepared. However, this will damage the substrate sample. At the same time, due to the complex process conditions and high process difficulty of the etching method, it is not only difficult to accurately locate a single dislocation for TEM sample preparation, but also the accuracy of the characterization and analysis of single dislocations in the GaN sample cannot be guaranteed.

[0006] 2. Another method of preparing TEM samples is ion thinning, which involves first cutting the gallium nitride sample into thin slices, then gluing the areas to be observed together to obtain the TEM sample, and finally mounting the TEM sample on a copper ring with a diameter of three millimeters, and then performing ion thinning. This method requires relatively high operator experience and skills, and it is difficult to guarantee the success rate of sample preparation, and it is also impossible to accurately specify the area for thinning, and it is also impossible to more accurately locate a single dislocation.

[0007] The present invention solves at least one of the above problems. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing TEM samples. The method solves the problem in the prior art that the size of dislocations is small and difficult to directly observe, so it is difficult to locate a single dislocation in a substrate sample, thereby failing to accurately characterize and analyze, and that the etching method destroys the substrate sample. The method can accurately locate a single dislocation from a substrate sample containing a gallium nitride single crystal, and thereby prepare a TEM sample containing the single dislocation. Compared with the traditional etching method, there is no need to destroy the substrate sample. In the TEM sample application TEM double-beam characterization and analysis, more accurate characterization and analysis of the single dislocation can be achieved.

[0009] The purpose of the present invention is achieved by the following technical solutions:

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

[0011] Performing SEM-CL scanning on the surface of the substrate sample containing the gallium nitride single crystal to obtain a first SEM image and a corresponding cathode fluorescence image;

[0012] marking a target single dislocation from the first SEM image based on the cathode fluorescent image;

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

[0014] Performing SEM scanning on a first target area on the surface of the substrate sample to obtain a second SEM image of carbon deposits around the target single dislocation;

[0015] Scanning the second SEM image using FIB-SEM to mark a second target area where the carbon deposits are located;

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

[0017] Compared with the prior art, the beneficial effects of the present invention include at least: the present application uses SEM-CL scanning to mark the target single dislocation from the first SEM image of the substrate sample using the cathode fluorescence image of the substrate sample, thereby achieving rough positioning of the target single dislocation in the substrate sample; by performing SEM scanning on the first target area where the target single dislocation is located in the substrate sample, a second SEM image of carbon deposits generated around the target single dislocation can be obtained, thereby achieving precise positioning of the target single dislocation in the substrate sample using the carbon deposits, and then scanning the second SEM image using FIB-SEM to accurately mark the second target area where the carbon deposits are located on the surface of the substrate sample after the carbon deposits are generated, and by etching the second target area, a TEM sample including the single dislocation can be conveniently and accurately cut out from the substrate sample, and compared with the traditional corrosion method, there is no need to destroy the substrate sample, and in the TEM sample using TEM dual-beam characterization and analysis, more accurate characterization and analysis of the single dislocation can be achieved.

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

[0019] determining all dislocations from the cathode fluorescent image based on a preset contrast threshold;

[0020] Selecting a single dislocation from all dislocations in the cathode fluorescent image;

[0021] Acquiring a registration relationship between the first SEM image and the cathode fluorescent image;

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

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

[0024] Acquiring an edge profile of the target single dislocation;

[0025] Establishing a minimum enveloping 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 implementations of the first aspect, the method for acquiring a cathode fluorescent image comprises the following steps:

[0028] Acquiring a cathode fluorescence signal generated by the substrate sample under the SEM-CL scanning;

[0029] Converting the cathode fluorescent light signal into an electrical signal;

[0030] Outputting the cathode fluorescent image based on the electrical signal; and / or

[0031] The scanning conditions of the SEM-CL scanning include: an acceleration voltage of 5 to 20 kV and a beam current of 0.5 to 1.5 nA.

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

[0033] Bombarding a first target area on the surface of the substrate sample with an electron beam of a SEM, so as to form carbon deposits around the target single dislocation to obtain a carbon deposit sample;

[0034] Performing SEM scanning on the carbon deposit sample to obtain the second SEM image; and / or

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

[0036] The scanning conditions of the SEM scanning include: an acceleration voltage of 5 to 20 kV and a beam current of 0.5 to 1.5 nA.

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

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

[0039] Determining a beam parameter of the ion beam based on the etching depth;

[0040] Etching a second target area on the surface of the carbon deposited sample based on the beam parameters to obtain a TEM sample including the target single dislocation;

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

[0042] The beam parameters of the ion beam include: an acceleration voltage of 20 to 30 kV, a beam current of 8 to 10 nA; and / or

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

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

[0045] Using FIB to thin the TEM sample so that the thickness of the thinned TEM sample reaches a preset thickness detection standard;

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

[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] Providing the above sample preparation method to prepare a TEM sample;

[0049] The TEM sample is tested by using TEM to obtain the dislocation type of the target single dislocation.

[0050] Technical effect: Applying the TEM sample prepared by the above scheme to TEM dual-beam characterization analysis can achieve a more accurate characterization of single dislocations and accurately analyze the dislocation type of the target single dislocation.

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

[0052] transferring the TEM sample to the grid;

[0053] Tilt the grid so that the TEM sample on the grid is tilted synchronously;

[0054] Using the electron gun to emit an electron beam so that the electron beam is incident on the surface of the TEM sample along the first crystal zone axis, and obtaining electron diffraction images of the target single dislocation under different g vectors and corresponding TEM images thereof;

[0055] determining the g vector based on the electron diffraction image;

[0056] The dislocation type of the target single dislocation in the TEM image is determined according to the standard relationship between the g vector and the Burgers vector b of the dislocation.

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

[0058] The dislocation type includes at least one of edge dislocation, screw dislocation and mixed dislocation. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A flowchart of the overall steps of a sample preparation method for a TEM sample is provided for an embodiment of the present application;

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

[0061] Figure 3 A flowchart of the steps of the method for acquiring a cathode fluorescent image provided in an embodiment of the present application;

[0062] Figure 4 A flowchart of the steps of marking a target single dislocation from a first SEM image provided in an embodiment of the present application;

[0063] Figure 5 A flow chart of the steps for obtaining a second SEM image provided in an embodiment of the present application;

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

[0065] Figure 7 A flow chart of the steps for preparing a TEM sample provided in an embodiment of the present application;

[0066] Figure 8 A flowchart of the steps for marking a first target area provided in an embodiment of the present application;

[0067] Fig. 9 A flowchart of the overall steps of a method for detecting a single dislocation in a gallium nitride single crystal provided in an embodiment of the present application;

[0068] Fig.10 A flowchart of the steps of using TEM to detect TEM samples provided in an embodiment of the present application;

[0069] Fig.11 Schematic diagram of the electron diffraction image of a target single dislocation under different g-vectors and its corresponding TEM image provided in an embodiment of the present application. DETAILED DESCRIPTION

[0070] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to make the present invention more comprehensive and complete and to fully convey the concepts of example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar structures, and thus their repeated description will be omitted.

[0071] In a first aspect of this embodiment, a method for preparing a TEM sample is provided, wherein Figure 1 As shown, the process includes the following steps S1 to S6.

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

[0073] It should be noted that this method takes gallium nitride single crystal as an example, which cannot be regarded as a limitation on the materials used in this application.

[0074] The surface of a substrate sample including a gallium nitride single crystal is scanned by SEM (scanning electron microscope)-CL (cathode fluorescence microscope, Cathodoluminescence).

[0075] The electron beam emitted by the electron gun of the SEM is focused and converged into a point light source. The point light source forms a high-energy electron beam under the acceleration voltage. The high-energy electron beam is focused into a light spot with a tiny diameter through two electromagnetic lenses. After passing through the last stage of the electromagnetic lens with a scanning coil, the electron beam bombards the surface of the substrate sample point by point in a raster scanning manner, and stimulates electronic signals at different depths. At this time, the electronic signal will be received by the probes of different signal receivers above the sample, and synchronously transmitted to the display through the amplifier to form a real-time imaging record, thereby obtaining the first SEM image of the substrate sample. For example, the first SEM image is shown in the attached figure. Figure 2 As shown in (a) in .

[0076] During the SEM-CL scanning process, the incident electrons bombard the sample surface and stimulate a variety of signals, such as Auger electron (AuE) signals, secondary electron (SE) signals, backscattered electron (BSE) signals, X-rays (characteristic X-rays, continuous X-rays) signals, cathode fluorescence (CL) signals, absorbed electrons (AE) signals and transmitted electron signals.

[0077] It should be noted that the scanning conditions of the SEM-CL scan include: an acceleration voltage of 5 to 20 kvkv and a beam current of 0.5 to 1.5 nA. Within this condition range, the image quality and signal strength of the first SEM image, especially the signal strength of the cathode fluorescence signal, can be guaranteed, while reducing or even avoiding radiation damage to the sample surface. In this embodiment, preferably, the acceleration voltage is 10 kv and the beam current is 1 nA.

[0078] In some specific embodiments, in combination with Figure 3 As shown, the method for acquiring the cathode fluorescent image includes the following steps S11 to S13.

[0079] Step S11: Acquire the cathode fluorescence signal generated by the substrate sample under SEM-CL scanning.

[0080] Step S12: Convert the cathode fluorescent light signal into an electrical signal.

[0081] Step S13: Outputting a cathode fluorescent image based on the electrical signal.

[0082] Thereby, a cathode fluorescence image of the substrate sample can be obtained. It should be noted that, under SEM-CL scanning, the cathode fluorescence image corresponds to the first SEM image.

[0083] For example, with Figure 2 The corresponding cathode fluorescence image of (a) is shown in the attached Figure 2 As shown in (b) in .

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

[0085] The cathode fluorescence image can reveal the luminescence characteristics of different areas of the substrate sample. Dislocations, as non-radiative recombination centers in gallium nitride single crystals, appear as dark spots on the cathode fluorescence image. Therefore, according to the intensity of luminescence in different areas of the substrate sample, the dark spots representing dislocations can be found from the cathode fluorescence image. Since the first SEM image corresponds to the cathode fluorescence image, the cathode fluorescence image can be used to mark the target single dislocation in the first SEM image, thereby achieving coarse positioning 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 embodiments, in combination with Figure 4 As shown, step S2 includes the following steps S21 to S24.

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

[0089] The contrast on the cathodoluminescence image reflects the intensity of luminescence in different areas of the substrate sample. Dislocations, as non-radiative recombination centers in gallium nitride single crystals, appear as dark spots on the cathodoluminescence image with a certain contrast range. Therefore, all dislocations representing all dark spots can be determined from the cathodoluminescence image through a preset contrast threshold.

[0090] Step S22: selecting a single dislocation from all dislocations in the cathode fluorescent image.

[0091] The single dislocation is selected through settings, and any one can be selected according to actual needs.

[0092] Step S23: Acquire the registration relationship between the first SEM image and the cathode fluorescent image.

[0093] For the registration of the first SEM image and the cathode fluorescence image, the common feature points or feature areas of the two are usually aligned in the same coordinate system so that the morphology and luminescence characteristics of the sample can be analyzed simultaneously, and the registration relationship between the two is constructed thereby. This is a conventional technical means 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] Through the above-mentioned registration relationship, the above-mentioned feature points or feature areas can be made consistent in the same coordinate system, thereby improving the positioning 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: Marking a first target region where a target single 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. In theory, 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 needs.

[0098] Step S4: Performing SEM scanning on the first target area on the surface of the substrate sample to obtain a second SEM image of carbon deposits 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 bombarding the surface of the substrate sample. The generated carbon ions will be more enriched in the area as the range of action of the electron beam decreases. As time goes by, a black area, namely carbon deposition, will form on the surface of the substrate sample.

[0100] In some specific embodiments, in combination with Figure 5 As shown, step S4 includes step S41-step S42.

[0101] Step S41: bombarding a first target area on the surface of a substrate sample with an electron beam of a SEM, so as to form carbon deposits around a target single dislocation to obtain a carbon deposit sample.

[0102] The high-energy electron beam emitted by the electron gun of the SEM will form positively charged carbon ions when bombarding the first target area. The generated carbon ions will be more enriched in the first target area as the range of action of the electron beam decreases. As time goes by, carbon deposits will be generated around the target single dislocation, forming a black area in the first target area around the target single dislocation, thereby obtaining a carbon deposit sample.

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

[0104] Furthermore, the bombardment time is 20 to 30 seconds. With this time range, sufficient carbon deposits can be generated in the first target area around the target single dislocation, so that the black area is more obvious, thereby improving the accuracy of locating the target single dislocation. In this embodiment, preferably, the bombardment time is 25 seconds.

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

[0106] The scanning conditions of the SEM scanning include: an acceleration voltage of 5 to 20 kV and a beam current of 0.5 to 1.5 nA; in this embodiment, preferably, the acceleration voltage is 10 kV and the beam current is 1 nA.

[0107] The second SEM image of the carbon deposit sample can be obtained by scanning the surface of the carbon deposit sample by SEM; for example, the second SEM image is shown in the attached Figure 6 shown.

[0108] In summary, the high-energy electron beam generated by the SEM is used to bombard the first target area where the target single dislocation is located, so that carbon deposits are generated around the target single dislocation, and the carbon deposits are used to achieve precise positioning of the target single dislocation.

[0109] Step S5: Scan the second SEM image using FIB-SEM to mark the second target area where the carbon deposits are located.

[0110] By scanning the second SEM image through FIB (Focused Ion beam)-SEM, a black area 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.

[0111] It should be noted that the position center of the carbon deposit is the target single dislocation, and thus the target single dislocation can be more accurately characterized with the help of the position center of the carbon deposit.

[0112] Marking the second target area where the carbon deposits are located is a prerequisite for the subsequent steps. In theory, as long as the carbon deposits are located in the first target area, the area of ​​the second target area can be selected according to needs.

[0113] Further, the area of ​​the second target region is at least 10 μm×10 μm. Preferably, in this embodiment, the area of ​​the second target region is 10 μm×10 μm. It should be noted that the area of ​​the second target region should meet the detection standard of the TEM equipment.

[0114] Step S6: etching the second target area on the surface of the substrate sample after carbon deposition to prepare a TEM sample.

[0115] In some specific embodiments, in combination with Figure 7 As shown, step S6 includes steps S61 to S63.

[0116] Step S61: setting the etching depth of the ion beam.

[0117] The etching depth is 8-12 μm. In this embodiment, preferably, the etching depth is 10 μm.

[0118] Step S62: determining beam parameters of the ion beam based on the etching depth.

[0119] The beam parameters of the FIB ion beam include: an acceleration 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 acceleration voltage is 30 kV and the beam current is 9.1 nA.

[0120] Step S63: etching the second target area on the surface of the carbon deposited sample based on the beam parameters to obtain a TEM sample including a target single dislocation.

[0121] A focused ion beam is used to etch the second target area on the surface of the carbon deposited sample, and an area with a size of 10μm×10μm and a depth of 10μm is etched downward from the surface of the carbon deposited sample along its thickness direction, so as to facilitate accurate cutting out of the TEM sample including a single dislocation in the carbon deposited sample.

[0122] In some specific embodiments of the first aspect, the sample preparation method further includes: thinning the TEM sample using FIB so that the thickness of the thinned TEM sample reaches a preset thickness detection standard.

[0123] It should be noted that the preset thickness detection standard is less than 100 nm. In this embodiment, preferably, the thickness of the thinned TEM sample is 80 nm.

[0124] The use of FIB sample preparation 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 a single dislocation, taking relatively less time and being more efficient.

[0125] In some specific embodiments, in combination with Figure 8 As shown, step S3 includes step S31 to step S33.

[0126] Step 31: Obtain the edge profile of the target single dislocation.

[0127] Step 32: Establish a minimum envelope box for the edge contour of the target single dislocation.

[0128] Step 33: Mark the minimum envelope box as the first target region where the target single dislocation is located.

[0129] Combined with step S4, the size of the first target area is accurately planned through the minimum envelope box, so that the carbon deposits generated in the first target area around the target single dislocation can be fully gathered, further improving the positioning accuracy of the target single dislocation and reducing the bombardment time of the high-energy electron beam.

[0130] In a second aspect of this embodiment, a method for detecting a single dislocation in a gallium nitride single crystal is provided. Fig. 9 As shown, the method includes the following steps S10-S20.

[0131] Step S10: providing a TEM sample containing a target single dislocation. The TEM sample is prepared by the above-mentioned sample preparation method.

[0132] Step S20: using TEM to detect the TEM sample and obtain the dislocation type of the target single dislocation.

[0133] TEM includes a grid and an electron gun, combined with an attached Fig.10 As shown, using TEM to detect TEM samples includes the following steps S201 to S204.

[0134] Step S201: Transfer the TEM sample to the grid.

[0135] Step S222: Tilt the carrier grid to synchronously tilt the TEM sample on the carrier grid.

[0136] It should be noted that, since the TEM samples were prepared according to a fixed crystal orientation, the tilt angle of the grid was set to 0 to 20 degrees.

[0137] Step S203: using 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 crystal axis, and obtaining electron diffraction images of the target single dislocation under different g vectors and their corresponding TEM images.

[0138] It should be noted that the direction of the first crystal zone axis is <1-100>; by tilting the TEM sample, the electron diffraction (selected area electron diffraction, SAED) image of the target single dislocation under different g vectors and its corresponding TEM image can be obtained.

[0139] Step S204: based on the electron diffraction image and its corresponding TEM image, determine the dislocation type of the target single dislocation in the TEM image.

[0140] After obtaining the electron diffraction images of the target single dislocation under different g vectors and their corresponding TEM images, find the TEM image without the target unit dislocation from all TEM images (referred to as the target TEM image); find the electron diffraction image corresponding to the target TEM image (referred to as the target electron diffraction image); determine the g vector corresponding to the target electron diffraction image (referred to as the target g vector); and judge the dislocation type of the target single dislocation in the TEM image based on the standard relationship between the target g vector and the Burgers vector b of the dislocation.

[0141] Furthermore, the standard relationship means that the vector product of the g vector and the Burgers vector b is 0.

[0142] It should be noted that the dislocation type includes at least one of edge dislocation (TED), screw dislocation (TSD), and mixed dislocation (TMD).

[0143] Furthermore, in-situ electrical TEM can be used to observe the evolution behavior of TEM samples under different current conditions.

[0144] For the specific method, please refer to the national standard GB / T44558-2024-Test transmission electron microscopy method for dislocation imaging in group III nitride semiconductor materials, which will not be repeated here.

[0145] TEM's "double-beam" diffraction imaging technique is a commonly used technical means to characterize dislocations. The "double-beam" is a transmission beam and a diffraction beam. Two different g vectors are selected to take the electron diffraction image of a single dislocation and its corresponding diffraction spectrum image. In TEM, the dislocation type can be judged by the extinction law, that is, an extinction table is made. For known crystal structures (such as face-centered cubic, body-centered cubic, etc.), the visibility of dislocations under different g vectors can be determined according to the extinction law. By analyzing the visibility of dislocations under different g vectors, the Burgers vector b of the dislocation can be further determined, and then the dislocation type can be judged.

[0146] TEM samples will produce diffraction contrast under the action of the electron beam in the TEM. In this method, the electron diffraction image and its corresponding TEM image are imaged using diffraction contrast, and the diffraction contrast image of the dislocation is directly determined by the value of g·b. When the Burgers vector b of the dislocation is perpendicular to the operating diffraction vector g, that is, g·b=0, the contrast of the dislocation line will disappear, which is called dislocation erasure. Therefore, g=0 is called the dislocation erasure criterion. Since gallium nitride single crystals are usually close-packed hexagonal structures. Therefore, the dislocations in the crystal have three obvious Burgers vectors: 1. Edge dislocation: 1 / 3<11-20>; 2. Screw dislocation: <0001>; 3. Mixed dislocation: 1 / 3<11-23>; In the transmission electron microscope, by using the dislocation erasure criterion, by selecting the appropriate diffraction vector, a specific type of dislocation can be imaged.

[0147] Since the electron diffraction image determines the g vector, the g vector and the Burgers vector b are known. According to 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.

[0148] For example, Fig.11 For example, we obtain the TEM image (a) and the corresponding SAED image (b) when g =

[0002] , and obtain the TEM image (c) and SAED image (d) when g = [11-20]. Fig.11 It can be seen from the TEM image (c) that the target single dislocation is invisible, 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 judged that the target single dislocation is an edge dislocation.

[0149] The present application uses a cathode fluorescence microscope to characterize a single dislocation of a gallium nitride single crystal. Compared with the traditional etching method, the method is simple and convenient and can roughly locate a single dislocation without destroying the substrate sample. By using the electron beam of the SEM to locate the carbon deposition produced on the surface of the substrate sample, the target single dislocation can be accurately located in the sample, making it easy to find in the subsequent FIB sample preparation, accurately positioning the target single dislocation, and facilitating the cutting out of the target single dislocation. Since the TEM requires the sample thickness to be less than 100 nm, using a FIB instrument to prepare TEM samples is also an efficient and convenient means. Through the national standard GB / T44558-2024-Dislocation Imaging Test in Group III Nitride Semiconductor Materials, the transmission electron microscopy method can more accurately determine the dislocation type of the target single dislocation. Moreover, since the TEM has an in-situ function, in-situ electrical testing can be performed to observe the evolution behavior of the sample under different current conditions. The sequential combination of the above-mentioned means is very important and effective for the characterization study of single dislocations.

[0150] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, substitute and modify the above embodiments within the scope of the invention without departing from the principles and purpose of the present invention. All such changes should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a TEM sample, characterized in that: The steps include: Performing SEM-CL scanning on the surface of the substrate sample containing the gallium nitride single crystal to obtain a first SEM image and a corresponding cathode fluorescence image; marking a target single dislocation from the first SEM image based on the cathode fluorescent image; Marking a first target region where the target single dislocation is located in the first SEM image; Performing SEM scanning on a first target area on the surface of the substrate sample to obtain a second SEM image of carbon deposits around the target single dislocation; Scanning the second SEM image using FIB-SEM to mark a second target area where the carbon deposits are located; The second target area on the surface of the substrate sample after carbon deposition is etched to prepare a TEM sample.

2. The sample preparation method according to claim 1, characterized in that: Marking a target single dislocation from the first SEM image based on the cathode fluorescent image comprises the following steps: determining all dislocations from the cathode fluorescent image based on a preset contrast threshold; Selecting a single dislocation from all dislocations in the cathode fluorescent image; Acquiring a registration relationship between the first SEM image and the cathode fluorescent image; Based on the registration relationship, a target single dislocation corresponding to the single dislocation is marked in the first SEM image.

3. The sample preparation method according to claim 1, characterized in that: Marking a first target region where the target single dislocation is located in the first SEM image comprises the following steps: Acquiring an edge profile of the target single dislocation; Establishing a minimum enveloping box of the edge contour; The minimum envelope box is marked as the first target region where the target single dislocation is located.

4. The sample preparation method according to claim 1, characterized in that: The method for acquiring the cathode fluorescent image comprises the following steps: Acquiring a cathode fluorescence signal generated by the substrate sample under the SEM-CL scanning; Converting the cathode fluorescent light signal into an electrical signal; outputting the cathode fluorescent image based on the electrical signal; And / or, the scanning conditions of the SEM-CL scanning include: an acceleration voltage of 5 to 20 kV and a beam current of 0.5 to 1.5 nA.

5. The sample preparation method according to claim 1, characterized in that: Performing SEM scanning on a first target area on the surface of the substrate sample to obtain a second SEM image of carbon deposits around the target single dislocation comprises the following steps: Bombarding a first target area on the surface of the substrate sample with an electron beam of a SEM, so as to form carbon deposits around the target single dislocation to obtain a carbon deposit sample; Performing SEM scanning on the carbon deposit sample to obtain the second SEM image; The bombardment conditions of the SEM include: an acceleration voltage of 5 to 20 kV, a beam current of 0.5 to 1.5 nA, and a bombardment time of 20 to 30 s; and / or, the scanning conditions of the SEM scan include: an acceleration voltage of 5 to 20 kV, and a beam current of 0.5 to 1.5 nA.

6. The sample preparation method according to claim 5, characterized in that: Etching the second target area on the surface of the substrate sample after carbon deposition to prepare a TEM sample comprises the following steps: Set the etching depth of the ion beam; Determining a beam parameter of the ion beam based on the etching depth; Etching a second target area on the surface of the carbon deposited sample based on the beam parameters to obtain a TEM sample including the target single dislocation; The etching depth of the ion beam is 8 to 12 μm; and / or The beam parameters of the ion beam include: an acceleration voltage of 20 to 30 kV and a beam current of 8 to 10 nA; and / or The second target region has an area of ​​at least 10 μm×10 μm.

7. The sample preparation method according to claims 1-6, characterized in that: The sample preparation method also includes: Using FIB to thin the TEM sample so that the thickness of the thinned TEM sample reaches a preset thickness detection standard; The preset thickness detection standard is less than 100 nm.

8. A method for detecting a single dislocation in a gallium nitride single crystal, characterized in that: The steps include: A TEM sample is prepared by the sample preparation method according to any one of claims 1 to 7; The TEM sample is tested by using TEM to obtain the dislocation type of the target single dislocation.

9. The detection method according to claim 8, 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: transferring the TEM sample to the grid; Tilt the grid so that the TEM sample on the grid is tilted synchronously; Using the electron gun to emit an electron beam so that the electron beam is incident on the surface of the TEM sample along the first crystal zone axis, and obtaining electron diffraction images of the target single dislocation under different g vectors and corresponding TEM images thereof; Based on the electron diffraction image and its corresponding TEM image, the dislocation type of the target single dislocation in the TEM image is determined.

10. The detection method according to claim 9, characterized in that: The tilt angle of the carrier grid is 0° to 20°; and / or The dislocation type includes at least one of edge dislocation, screw dislocation and mixed dislocation.

Images