CN119779788A - Sample preparation method of TEM sample and detection method of single dislocation in gallium nitride monocrystal - Google Patents
Sample preparation method of TEM sample and detection method of single dislocation in gallium nitride monocrystal Download PDFInfo
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Abstract
本发明公开一种TEM样品的制样方法及氮化镓单晶中单根位错的检测方法，该制样方法包括如下步骤：对包含氮化镓单晶的衬底样品表面进行SEM‑CL扫描，获取第一SEM图像及其对应的阴极荧光图像；基于阴极荧光图像从第一SEM图像中标记出目标单根位错；在第一SEM图像中标记出目标单根位错所在的第一目标区域；对衬底样品表面的第一目标区域进行SEM扫描，获取围绕目标单根位错产生积碳的第二SEM图像；利用FIB‑SEM对第二SEM图像进行扫描，标记出积碳所在的第二目标区域；对产生积碳后的衬底样品表面的第二目标区域进行刻蚀，制备得到TEM样品。本发明可以从包含氮化镓单晶的衬底样品精确地定位出单根位错，并以此制备出包括单根位错的TEM样品，进而确定出单根位错的位错类型。
The present invention discloses a method for preparing a TEM sample and a method for detecting a single dislocation in a gallium nitride single crystal. The method comprises the following steps: 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 thereof; 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 the first target area on the surface of the substrate sample to obtain a second SEM image where carbon deposits are generated around the target single dislocation; scanning the second SEM image using a FIB-SEM to mark a second target area where carbon deposits are located; etching the second target area on the surface of the substrate sample after carbon deposits are generated to prepare a TEM sample. The present invention can accurately locate a single dislocation from a substrate sample containing a gallium nitride single crystal, and thereby prepare a TEM sample including a single dislocation, and further determine the dislocation type of the single dislocation.
Description
Technical Field
The invention relates to the technical field of material defect characterization, in particular to a sample preparation method of a TEM sample based on gallium nitride single crystal and a detection method of single dislocation in the gallium nitride single crystal.
Background
GaN (gallium nitride) is a novel semiconductor material for developing microelectronic devices and optoelectronic devices. The material has the properties of wide direct band gap, strong atomic bond, high heat conductivity and the like, and strong irradiation resistance, and has wide prospect in the application fields of photoelectrons, high-temperature high-power devices and high-frequency microwave devices. HVPE (Hydride Vapor Phase Epitaxy ) is a common method for preparing GaN single crystals, and because of the large lattice mismatch and large thermal expansion coefficient difference between the substrate material and GaN, the GaN film growing on the substrate has high dislocation density, still can reach the order of 5 times of 10, and the existence of dislocation can become a non-radiative recombination center of electron hole pairs, thereby increasing the leakage current of the device and further reducing the performance and reliability of the device.
Through intensive research on the properties and behaviors of single dislocation in a substrate sample containing GaN single crystals, specific influence mechanisms of the single dislocation on the electrical, optical and other performances of a gallium nitride material can be revealed, so that theoretical basis is provided for optimizing the performance of a device, however, the research on the single dislocation is still a challenging field, and the single dislocation in the substrate sample is difficult to position because the size of the dislocation is small and is difficult to directly observe, so that accurate characterization and analysis cannot be performed.
Dislocation observation of the sample by a transmission electron microscope (Transmission Electron Microscope , TEM) is performed by a person skilled in the art, and in the prior art, the following methods are generally used for sample preparation:
1. The gallium nitride sample to be characterized is observed and positioned by adopting a corrosion method, and then the sample preparation of the TEM sample is carried out, but the substrate sample is damaged in this way, meanwhile, the process condition control of the corrosion method is complex, the process difficulty is high, the sample preparation of the TEM sample is difficult to accurately position single dislocation, and the accuracy of the single dislocation characterization and analysis in the gallium nitride sample cannot be ensured.
2. Another sample preparation method of the TEM sample is ion thinning, firstly slicing a gallium nitride sample, then sticking the observed area pairs together to obtain the TEM sample, finally embedding the TEM sample on a copper ring with the diameter of three millimeters, and then carrying out ion thinning. The method has high experience and technical requirements on operators, is difficult to ensure the success rate of sample preparation, cannot accurately designate the area for thinning, and cannot more accurately position single dislocation.
The present invention solves at least one of the above problems.
Disclosure of Invention
The invention aims to provide a sample preparation method of a TEM sample, which solves the problems that in the prior art, the size of dislocation is small and direct observation is difficult, so that single dislocation in a substrate sample is difficult to position, accurate characterization and analysis cannot be performed, and a corrosion method sample is not used for damaging the substrate sample, single dislocation can be accurately positioned from the substrate sample containing gallium nitride monocrystal, and the TEM sample containing the single dislocation can be prepared by the method.
The invention adopts the following technical scheme:
in a first aspect of the present invention, there is provided a sample preparation method for a TEM sample, comprising the steps of:
Carrying out SEM-CL scanning on the surface of a substrate sample containing the gallium nitride monocrystal 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;
SEM scanning is carried out on a first target area of the surface of the substrate sample, and a second SEM image of carbon deposit generated around the target single dislocation is obtained;
scanning the second SEM image by using an FIB-SEM to mark a second target area where the carbon deposit is located;
And etching a second target area on the surface of the substrate sample after carbon deposition is generated, and preparing the TEM sample.
Compared with the prior art, the method has the advantages that the method marks the target single dislocation from the first SEM image by scanning SEM-CL and utilizes the cathode fluorescence image of the substrate sample, so that coarse positioning of the target single dislocation is realized in the substrate sample, the second SEM image which surrounds the target single dislocation and generates carbon deposit can be obtained by scanning SEM on the first target area where the target single dislocation is positioned in the substrate sample, so that fine positioning of the target single dislocation in the substrate sample is realized by utilizing the carbon deposit, then scanning is performed on the second SEM image by utilizing FIB-SEM, and the second target area where the carbon deposit is accurately marked on the surface of the substrate sample after the carbon deposit is generated.
In some possible embodiments of the first aspect, marking the target single dislocation from the first SEM image based on the cathode fluorescence image comprises the steps of:
Determining all dislocations from the cathode fluorescence image based on a preset contrast threshold;
selecting a single dislocation from all dislocations in the cathode fluorescence image;
acquiring a registration relationship between the first SEM image and the cathode fluorescence image;
and marking a target single dislocation corresponding to the single dislocation from the first SEM image based on the registration relation.
In some possible embodiments of the first aspect, marking the first target region where the target single dislocation is located in the first SEM image includes the steps of:
acquiring the edge contour of the target single dislocation;
establishing a minimum envelope box of the edge profile;
And marking the minimum envelope box as a first target area where the target single dislocation is located.
In some possible embodiments of the first aspect, the method for obtaining a cathode fluorescence image includes the following steps:
Acquiring a cathode fluorescence signal generated by the substrate sample under the SEM-CL scanning;
converting the cathode fluorescence signal into an electrical signal;
outputting the cathode fluorescence image based on the electrical signal, and/or
Scanning conditions of SEM-CL scanning include an acceleration voltage of 5-20 kv and a beam current of 0.5-1.5 nA.
In some possible embodiments of the first aspect, SEM scanning is performed on a first target region of the surface of the substrate sample, and obtaining a second SEM image of carbon deposition around the target single dislocation includes the steps of:
Bombarding a first target area on the surface of the substrate sample by using an electron beam of SEM so as to form carbon deposition around the target single dislocation to obtain a carbon deposition sample;
Scanning the carbon deposit sample by SEM to obtain a second SEM image, and/or
The bombardment conditions of the SEM comprise acceleration voltage of 5-20 kv, beam current of 0.5-1.5 nA, bombardment time of 20-30 s, and/or
Scanning conditions of SEM scanning comprise an acceleration voltage of 5-20 kv and a beam current of 0.5-1.5 nA.
In some possible embodiments of the first aspect, etching the second target area on the surface of the substrate sample after carbon deposition is generated, and preparing the TEM sample includes the following steps:
setting the etching depth of the ion beam;
determining beam parameters of the ion beam based on the etching depth;
Etching a second target area on the surface of the carbon deposit sample based on the beam parameters to obtain a TEM sample comprising the target single dislocation;
the etching depth of the ion beam is 8-12 mu m, and/or
The beam parameters of the ion beam comprise an acceleration voltage of 20-30 kv and a beam current of 8-10 nA, and/or
The area of the second target region is at least 10 μm×10 μm.
In some possible implementations of the first aspect, the method further includes:
thinning the TEM sample by using an FIB (fiber reinforced plastic) to ensure that the thickness of the thinned TEM sample reaches a preset thickness detection standard;
the preset thickness detection standard is less than 100nm.
In a second aspect of the present invention, there is provided a method for detecting single dislocation in gallium nitride single crystal, comprising the steps of:
providing the sample preparation method to prepare a TEM sample;
And detecting the TEM sample by using a TEM to obtain the dislocation type of the target single dislocation.
The technical effect is that the TEM sample prepared by the scheme is applied to TEM double-beam characterization analysis, so that more accurate characterization of single dislocation can be realized, and the dislocation type of the target single dislocation can be accurately analyzed.
In some possible embodiments of the second aspect, the TEM includes a carrier grid and an electron gun, and the detecting the TEM sample with the TEM includes the steps of:
transferring the TEM sample onto the carrier web;
Tilting the carrier web to synchronize tilting of the TEM samples on the carrier web;
Emitting an electron beam by using the electron gun, so that the electron beam is incident on the surface of the TEM sample along a first crystal band axis, and obtaining electron diffraction images of the single dislocation of the target and corresponding TEM images thereof under different g vectors;
determining the g-vector based on the electron diffraction image;
and judging the dislocation type of the target single dislocation in the TEM image according to the standard relation between the g vector and the Boss vector b of the dislocation.
In some possible embodiments of the second aspect, the tilting angle of the carrier web is 0-20 degrees, and/or
The dislocation type at least comprises one of edge dislocation, screw dislocation and mixed dislocation.
Drawings
FIG. 1 is a flowchart showing the overall steps of a sample preparation method for a TEM sample according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a first SEM image provided according to an embodiment of the present application;
FIG. 3 is a flowchart illustrating steps of a method for acquiring a cathode fluorescence image according to an embodiment of the present application;
FIG. 4 is a flowchart illustrating steps for marking a target single dislocation from a first SEM image according to an embodiment of the present application;
FIG. 5 is a flowchart illustrating a second SEM image acquisition step according to an embodiment of the present application;
FIG. 6 is a schematic diagram of a second SEM image provided according to an embodiment of the present application;
FIG. 7 is a flowchart showing steps for preparing a TEM sample according to an embodiment of the present application;
FIG. 8 is a flowchart illustrating steps for marking a first target area according to an embodiment of the present application;
FIG. 9 is a flowchart showing the overall steps of a method for detecting single dislocations in a gallium nitride single crystal according to an embodiment of the present application;
FIG. 10 is a flowchart illustrating steps for detecting a TEM sample using a TEM according to an embodiment of the present application;
fig. 11 is a schematic diagram of an electron diffraction image of a single dislocation of a target and a TEM image corresponding thereto under different g vectors according to an embodiment of the present application.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. However, the exemplary embodiments can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather, these embodiments are provided so that this disclosure will be thorough and complete, and will 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 thus a repetitive description thereof will be omitted.
In a first aspect of the present embodiment, a method for preparing a TEM sample is provided, and as shown in fig. 1, the method includes the following steps S1 to S6.
And S1, carrying out SEM-CL scanning on the surface of a substrate sample containing gallium nitride monocrystal to obtain a first SEM image and a cathode fluorescence image corresponding to the first SEM image.
The present method is exemplified by gallium nitride single crystal, and is not to be construed as limiting the material used in the present application.
The surface of the substrate sample containing gallium nitride single crystal was scanned by SEM (scanning electron microscope ) -CL (cathode fluorescence microscope, cathodoluminescence).
The electron beams emitted by the electron gun of the SEM are focused to form point light sources, the point light sources form high-energy electron beams under the accelerating voltage, the high-energy electron beams are focused to light spots with small diameters through two electromagnetic lenses, and after passing through the electromagnetic lens with a scanning coil at the last stage, the electron beams bombard the surface of a substrate sample point by point in a raster scanning mode, and meanwhile, electron signals with different depths are excited. At this time, the electronic signals are received by probes of different signal receivers above the sample, and are synchronously transmitted to the display through the amplifier to form a real-time imaging record, so that a first SEM image of the substrate sample is obtained. For example, the first SEM image is shown in (a) of fig. 2.
During SEM-CL scanning, incident electrons bombard the sample surface to excite various signals, such as auger electron (Au E) signals, secondary Electron (SE) signals, back Scattered Electron (BSE) signals, X-ray (characteristic X-ray, continuous X-ray) signals, cathode fluorescence (CL) signals, absorption Electron (AE) signals, and transmission electron signals.
The scanning conditions of SEM-CL scanning include an acceleration voltage of 5-20 kvkv and a beam current of 0.5-1.5 nA. Within this range of conditions, the image quality of the first SEM image and the signal intensity, in particular of the cathode fluorescence signal, can be ensured while reducing or even avoiding radiation damage of the sample surface. In this embodiment, the acceleration voltage is preferably 10kv and the beam current is preferably 1nA.
In some specific embodiments, as shown in fig. 3, the method for acquiring a cathode fluorescence image includes the following steps S11 to S13.
Step S11, acquiring a cathode fluorescence signal generated by the substrate sample under SEM-CL scanning.
And step S12, converting the cathode fluorescence signal into an electric signal.
And step S13, outputting a cathode fluorescence image based on the electric signal.
Thus, a cathode fluorescence image can be obtained with the substrate sample, it being noted that the cathode fluorescence image corresponds to the first SEM image under SEM-CL scanning.
For example, a cathode fluorescence image corresponding to (a) of fig. 2 is shown in (b) of fig. 2.
And S2, marking a target single dislocation from the first SEM image based on the cathode fluorescence image.
The cathode fluorescence image can reveal the luminescence characteristics of different areas of the substrate sample, dislocation is taken as a non-radiative recombination center in the gallium nitride monocrystal, and the dislocation appears as a dark point on the cathode fluorescence image, so that the dark point representing the dislocation can be found out from the cathode fluorescence image according to the intensity of luminescence of different areas of the substrate sample, and the first SEM image corresponds to the cathode fluorescence image, so that the target single dislocation can be marked in the first SEM image by utilizing the cathode fluorescence image, and coarse positioning of the target single dislocation is realized.
It should be noted that the target single dislocation is selected by setting, and any one can be selected according to actual requirements.
In some specific embodiments, as shown in connection with fig. 4, step S2 includes the following steps S21-S24.
And S21, determining all dislocations from the cathode fluorescence image based on a preset contrast threshold.
The contrast on the cathode fluorescence image reflects the intensity of light emitted by different areas of the substrate sample, dislocation is taken as a non-radiative recombination center in the gallium nitride monocrystal, dark spots are displayed on the cathode fluorescence image, and a certain contrast range is provided, so that all the dislocation representing all the dark spots can be determined from the cathode fluorescence image through a preset contrast threshold value.
And S22, selecting a single dislocation from all the dislocations in the cathode fluorescence image.
The single dislocation is selected by setting, and any dislocation can be selected according to actual requirements.
Step S23, the registration relation between the first SEM image and the cathode fluorescence image is acquired.
For the registration of the first SEM image and the cathode fluorescence image, the feature points or feature regions shared by the first SEM image and the cathode fluorescence image are usually aligned in the same coordinate system, so that the morphology and the luminescence characteristics of the sample can be analyzed simultaneously, and a registration relationship between the first SEM image and the cathode fluorescence image is constructed, which is a conventional technical means and is not described herein.
And step S24, marking a target single dislocation corresponding to the single dislocation from the first SEM image based on the registration relation.
Through the registration relationship, the characteristic points or the characteristic areas can be consistent on the same coordinate system, the positioning accuracy of the target single dislocation corresponding to the single dislocation marked from the first SEM image is improved, the introduction of other dislocations is avoided, and detection interference is prevented.
And S3, marking a first target area where the target single dislocation is located in the first SEM image.
The first target area where the target single dislocation is marked is a precondition for the subsequent step, and theoretically, the target single dislocation is only required to be located in the first target area, so the area of the first target area can be selected according to the requirement.
And S4, carrying out SEM scanning on a first target area of the surface of the substrate sample, and acquiring a second SEM image of carbon deposit generated around the target single dislocation.
It should be noted that, because some hydrocarbons will be adsorbed 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, and the generated carbon ions will be more enriched in this region along with the reduction of the action range of the electron beam, and as time increases, a black region, i.e. a carbon deposition phenomenon, will be formed on the surface of the substrate sample.
In some embodiments, as shown in connection with fig. 5, step S4 includes steps S41-S42.
And S41, bombarding a first target area on the surface of the substrate sample by utilizing an electron beam of the SEM so as to form carbon deposition around a target single dislocation to obtain a carbon deposition sample.
The high-energy electron beam emitted by the electron gun of the SEM can form positively charged carbon ions when bombarding the first target area, the generated carbon ions can be more enriched in the first target area along with the reduction of the action range of the electron beam, carbon deposition can be generated around the single dislocation of the target along with the increase of time, and the first target area around the single dislocation of the target forms a black area, so that a carbon deposition sample is obtained.
Further, the bombardment conditions of the SEM include an acceleration voltage of 5-20 kv and a beam current of 0.5-1.5 nA, and in this embodiment, the acceleration voltage is preferably 10kv and the beam current is preferably 1nA.
Further, the bombardment time is 20-30 s, and by adopting the time range, enough carbon deposition can be generated in a first target area surrounding the single dislocation of the target, so that the black area is more obvious, and the positioning accuracy of the single dislocation of the target is improved. In this embodiment, the bombardment time is preferably 25s.
And S42, carrying out SEM scanning on the carbon deposit sample by utilizing an SEM to obtain a second SEM image.
Scanning conditions of SEM scanning include an acceleration voltage of 5-20 kv and a beam current of 0.5-1.5 nA, and in this embodiment, the acceleration voltage is preferably 10kv and the beam current is preferably 1nA.
A second SEM image of the carbon deposit sample may be obtained by SEM scanning the surface of the carbon deposit sample, for example, as shown in fig. 6.
In summary, the high-energy electron beam generated by SEM is used to bombard the first target area where the target single dislocation is located, carbon deposition is generated around the target single dislocation, and the fine positioning of the target single dislocation is realized by using the carbon deposition.
And S5, scanning the second SEM image by using the FIB-SEM to mark a second target area where carbon deposition is located.
By scanning the second SEM image by FIB (Focused Ion beam microscope) -SEM, a black region representing the first target region can be identified on the surface of the carbon deposit sample, thereby determining the position of the carbon deposit in the carbon deposit sample.
It should be noted that the position center of the carbon deposit is the target single dislocation, so that the target single dislocation can be more accurately represented by means of the position center of the carbon deposit.
The second target area where the carbon deposit is marked is a precondition for the subsequent step, and theoretically, the carbon deposit may be located in the first target area, so the area of the second target area may be selected according to the requirement.
Further, the area of the second target region is at least 10 μm×10 μm, and 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 device.
And S6, etching a second target area on the surface of the substrate sample after carbon deposition is generated, and preparing a TEM sample.
In some embodiments, as shown in connection with fig. 7, step S6 includes steps S61-S63.
Step S61, setting etching depth of the ion beam.
The etching depth is 8-12 μm, and in this embodiment, the etching depth is preferably 10 μm.
Step S62, determining beam parameters of the ion beam based on the etching depth.
The beam parameters of the FIB ion beam include an acceleration voltage of 20-30 kv and a beam current of 8-10 nA, and in this embodiment, the set etching depth can be reached under the parameter range. Preferably, the acceleration voltage is 30kv and the beam current is 9.1nA.
And step S63, etching a second target area on the surface of the carbon deposition sample based on the beam parameters to obtain a TEM sample comprising the target single dislocation.
And etching a second target area on the surface of the carbon deposition sample by using the focused ion beam, and etching an area with the size of 10 mu m multiplied by 10 mu m and the depth of 10 mu m downwards from the surface of the carbon deposition sample along the thickness direction of the area, so that a TEM sample comprising single dislocation can be conveniently and accurately cut out from the carbon deposition sample.
In some specific embodiments of the first aspect, the sample preparation method further includes thinning the TEM sample by FIB, so that the thinned TEM sample thickness reaches a preset thickness detection standard.
It should be noted that, the preset thickness detection standard is less than 100nm, in this embodiment, the thickness of the thinned TEM sample is preferably 80nm.
The method adopts FIB sample preparation, which not only can ensure the success rate of sample preparation, but also can accurately designate the area for thinning, thereby more accurately positioning single dislocation, having relatively short time and higher efficiency.
In some embodiments, as shown in connection with fig. 8, step S3 includes steps 31-S33.
And step 31, acquiring the edge contour of the target single dislocation.
Step 32, establishing a minimum envelope box of the edge profile of the target single dislocation.
And step 33, marking the minimum envelope box as a first target area where the target single dislocation is located.
And in combination with the step S4, the area size of the first target area is accurately planned through the minimum envelope box, so that carbon deposition generated in the first target area around the single dislocation of the target can be fully gathered, the positioning accuracy of the single dislocation of the target is further improved, and meanwhile, the bombardment time of the high-energy electron beam is reduced.
In a second aspect of this embodiment, a method for detecting a single dislocation in a gallium nitride single crystal is provided, which includes the following steps S10 to S20, in combination with fig. 9.
Step S10, providing a TEM sample containing the target single dislocation. The TEM sample is prepared by the sample preparation method.
And step S20, detecting a TEM sample by using a TEM to obtain the dislocation type of the target single dislocation.
The TEM includes a carrier grid and an electron gun, and as shown in fig. 10, the detection of the TEM sample by the TEM includes the following steps S201 to S204.
Step S201, transferring the TEM sample onto a carrier net.
Step S222, tilting the carrying net so as to enable the TEM sample on the carrying net to synchronously tilt.
The TEM sample was prepared according to a fixed crystal orientation, and the tilt angle of the carrier web was set to 0 to 20 degrees.
And S203, emitting an electron beam by using an electron gun so that the electron beam is incident on the surface of the TEM sample along a first crystal band axis, and acquiring electron diffraction images of single dislocation of the target and corresponding TEM images thereof under different g vectors.
The first crystal band axis direction is <1-100>, and electron diffraction (SELECTED AREA electron diffraction, SAED) images of a single dislocation of the target and corresponding TEM images thereof at different g vectors can be obtained by tilting the TEM sample.
Step S204, judging the dislocation type of the target single dislocation in the TEM image based on the electron diffraction image and the corresponding TEM image.
After obtaining electron diffraction images of single dislocation of a target under different g vectors and TEM images corresponding to the electron diffraction images, finding TEM images (marked as target TEM images) without target unit dislocation from all TEM images, finding electron diffraction images (marked as target electron diffraction images) corresponding to the target TEM images, determining g vectors (marked as target g vectors) corresponding to the target electron diffraction images, and judging dislocation types of the single dislocation of the target in the TEM images according to the standard relation between the g vectors of the target and the Boss vector b of the dislocation.
Further, the standard relationship means that the vector product of the g vector and the berkovich vector b is 0.
The dislocation type includes at least one of edge dislocation (TED), screw dislocation (TSD), and mixed dislocation (TMD).
Furthermore, in-situ electrical TEM can be utilized, and the evolution behavior of a TEM sample under different current conditions can be observed.
For a specific method, please refer to the test transmission electron microscope method for bit-oriented imaging in the national standard GB/T44558-2024-III nitride semiconductor material, and the description thereof will not be repeated here.
The 'double beam' diffraction contrast image technology of TEM is a common technical means for representing dislocation, the 'double beam' is a beam of transmission beam and a beam of diffraction beam, two different g vectors are selected to shoot electron diffraction images of single dislocation and corresponding diffraction spectrum images thereof respectively, the dislocation type in TEM can be judged through extinction rules, namely an extinction table is manufactured, for a known crystal structure (such as face-centered cube, body-centered cube and the like), the dislocation visibility under different g vectors can be determined according to the extinction rules, the Boehringer vector b of dislocation can be further determined by analyzing the dislocation visibility under different g vectors, and the dislocation type can be judged.
The electron diffraction image and its corresponding TEM image in the method are imaged by using the diffraction contrast, and the diffraction contrast image of dislocation is directly determined by g.b. When the berkovich vector b of dislocation is perpendicular to the operational diffraction vector g, i.e., g·b=0, the contrast of dislocation lines disappears, which is called dislocation resolution, and therefore, g=0 is called dislocation resolution criterion. Since gallium nitride single crystals are typically close-packed hexagonal structures. The dislocation in the crystal has three obvious Ber vectors, namely 1, edge dislocation, 1/3<11-20>, 2, screw dislocation, 0001, 3, mixed dislocation, 1/3<11-23>, and the dislocation can be imaged by selecting proper diffraction vectors in a transmission electron microscope by utilizing dislocation imaging criteria.
Since the electron diffraction image determines the g-vector, the g-vector and the berkovich vector b are known, and the dislocation type of the target single dislocation can be determined from the standard relationship of the g-vector and the berkovich vector b of the dislocation.
For example, taking fig. 11 as an example, a TEM image (a) and a corresponding SAED image (b) when g= [0002] are acquired, and a TEM image (c) and a SAED image (d) of g= [11-20] are acquired. As can be seen from the TEM image (c) of fig. 11, 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 the target single dislocation can be judged as an edge dislocation by g·b=0.
According to the application, the single dislocation of the gallium nitride monocrystal is represented by utilizing the cathode fluorescence microscope, compared with a traditional corrosion method, the single dislocation can be roughly located without damaging a substrate sample, the target single dislocation can be precisely located in the sample by utilizing the electron beam of the SEM to locate carbon deposition generated on the surface of the substrate sample, so that the target single dislocation can be easily found in a subsequent FIB preparation sample, the position of the target single dislocation is convenient to cut out, the TEM sample is prepared by utilizing a FIB instrument because the thickness requirement of the TEM on the sample is less than 100nm, the method is also an efficient and convenient means, the dislocation type of the target single dislocation can be more accurately judged by utilizing a test transmission electron microscope method of dislocation imaging in national standard GB/T44558-2024-III nitride semiconductor material, in-situ electrical test can be carried out by utilizing the TEM, the evolution behavior of the sample under different current conditions can be observed, and the single dislocation is very important and effective for research and research on single dislocation by combining the means.
While embodiments of the present invention have been shown and described, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that changes, modifications, substitutions and alterations may be made therein by those of ordinary skill in the art without departing from the spirit and scope of the invention, all such changes being within the scope of the appended claims.
Claims (10)
1. A method for preparing a TEM sample, comprising the steps of:
Carrying out SEM-CL scanning on the surface of a substrate sample containing the gallium nitride monocrystal 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;
SEM scanning is carried out on a first target area of the surface of the substrate sample, and a second SEM image of carbon deposit generated around the target single dislocation is obtained;
scanning the second SEM image by using an FIB-SEM to mark a second target area where the carbon deposit is located;
And etching a second target area on the surface of the substrate sample after carbon deposition is generated, and preparing the TEM sample.
2. The sample preparation method according to claim 1, wherein marking the target single dislocation from the first SEM image based on the cathode fluorescence image comprises the steps of:
Determining all dislocations from the cathode fluorescence image based on a preset contrast threshold;
selecting a single dislocation from all dislocations in the cathode fluorescence image;
acquiring a registration relationship between the first SEM image and the cathode fluorescence image;
and marking a target single dislocation corresponding to the single dislocation from the first SEM image based on the registration relation.
3. The sample preparation method according to claim 1, wherein marking the first target region where the target single dislocation is located in the first SEM image comprises the steps of:
acquiring the edge contour of the target single dislocation;
establishing a minimum envelope box of the edge profile;
And marking the minimum envelope box as a first target area where the target single dislocation is located.
4. The sample preparation method according to claim 1, wherein the method for acquiring a cathode fluorescence image comprises the steps of:
Acquiring a cathode fluorescence signal generated by the substrate sample under the SEM-CL scanning;
converting the cathode fluorescence signal into an electrical signal;
outputting the cathode fluorescence image based on the electrical signal;
And/or scanning conditions of SEM-CL scanning comprise an acceleration voltage of 5-20 kv and a beam current of 0.5-1.5 nA.
5. The sample preparation method according to claim 1, wherein SEM scanning of the first target region of the substrate sample surface to obtain a second SEM image of carbon deposition around the target single dislocation comprises the steps of:
Bombarding a first target area on the surface of the substrate sample by using an electron beam of SEM so as to form carbon deposition around the target single dislocation to obtain a carbon deposition sample;
SEM scanning is carried out on the carbon deposit sample, and the second SEM image is obtained;
The SEM bombardment conditions comprise an acceleration 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 comprise an acceleration voltage of 5-20 kv and a beam current of 0.5-1.5 nA.
6. The method of claim 5, wherein etching the second target region of the surface of the substrate sample after carbon deposition is generated, and preparing the TEM sample comprises the steps of:
setting the etching depth of the ion beam;
determining beam parameters of the ion beam based on the etching depth;
Etching a second target area on the surface of the carbon deposit sample based on the beam parameters to obtain a TEM sample comprising the target single dislocation;
the etching depth of the ion beam is 8-12 mu m, and/or
The beam parameters of the ion beam comprise an acceleration voltage of 20-30 kv and a beam current of 8-10 nA, and/or
The area of the second target region is at least 10 μm×10 μm.
7. The sample preparation method according to claim 1 to 6, further comprising:
thinning the TEM sample by using an FIB (fiber reinforced plastic) to ensure that the thickness of the thinned TEM sample reaches a preset thickness detection standard;
the preset thickness detection standard is less than 100nm.
8. The method for detecting single dislocation in gallium nitride monocrystal is characterized by comprising the following steps:
preparing a TEM sample using the sample preparation method of any one of claims 1 to 7;
And detecting the TEM sample by using a TEM to obtain the dislocation type of the target single dislocation.
9. The method according to claim 8, wherein said TEM comprises a grid and an electron gun, and said detecting said TEM sample with said TEM comprises the steps of:
transferring the TEM sample onto the carrier web;
Tilting the carrier web to synchronize tilting of the TEM samples on the carrier web;
Emitting an electron beam by using the electron gun, so that the electron beam is incident on the surface of the TEM sample along a first crystal band axis, and obtaining electron diffraction images of the single dislocation of the target and corresponding TEM images thereof under different g vectors;
And judging the dislocation type of the target single dislocation in the TEM image based on the electron diffraction image and the corresponding TEM image.
10. The detection method according to claim 9, wherein the tilting angle of the carrier web is 0-20 degrees and/or
The dislocation type at least comprises one of edge dislocation, screw dislocation and mixed dislocation.
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