Preparation method of nitride film material plane TEM sample
By using a wedge grinding and dynamic ion thinning strategy to prepare nitride thin film TEM samples, the problems of sample fragility and high cost were solved, and TEM sample preparation with large thin area, low damage and high positioning accuracy was achieved, thus improving the TEM imaging effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUZHOU INST OF NANO TECH & NANO BIONICS CHINESE ACEDEMY OF SCI
- Filing Date
- 2026-03-16
- Publication Date
- 2026-04-28
AI Technical Summary
Existing technologies make it difficult to prepare high-quality planar TEM samples of nitride thin film materials, especially since they are prone to breakage and warping during the thinning process, and the equipment costs are high and the operation threshold is high.
By employing a wedge-shaped grinding stress release combined with a dynamic ion thinning strategy, and through mechanical grinding and ion beam processing, and using equal-thickness stripes to monitor the material layer, sample preparation with large thin areas, low damage, and high positioning accuracy is achieved.
It enables large-scale observation and high-image-quality TEM sample preparation, reduces equipment costs and operational difficulty, and improves the imaging resolution and clarity of transmission electron microscopy.
Smart Images
Figure CN121933332A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of transmission electron microscopy sample technology, specifically relating to a method for preparing planar TEM samples of nitride thin film materials. Background Technology
[0002] During the epitaxial growth of nitride semiconductor materials, lattice and thermal mismatches with the substrate material accumulate significant stress, introducing numerous crystal defects such as dislocations and stacking faults into the epitaxial layer, directly impacting device performance. Planar transmission electron microscopy (TEM) samples can perform in-plane atomic-level characterization of these defects, making it an important tool for semiconductor material research.
[0003] Currently, the methods for preparing cross-sectional samples of this type of material are relatively mature. High-quality cross-sectional TEM samples can be prepared by first cutting a thick block cross-section using focused ion beam (FIB) technology, and then thinning it from both sides towards the center to a thickness of less than 100 nm. Alternatively, mechanical grinding combined with ion beam thinning can be used. However, planar samples still present certain challenges. The difficulties lie in: 1. Most epitaxial layers of nitride materials are heteroepitaxial films, typically ranging from tens to hundreds of nanometers in thickness. The residual stress in the epitaxial layer is high. When using FIB processing or conventional ion beam thinning, the sample is prone to bending, breakage, or surface lattice damage. During processing, it is necessary to reduce the voltage and beam current to minimize bombardment stress and precisely control the thinning endpoint to the ideal range of 50-100 nm.
[0004] For heteroepitaxial nitride thin film materials on sapphire substrates, such as GaN, InN, AlN and their ternary compounds InGaN and AlGaN, existing planar TEM sample preparation methods are all based on conventional FIB or ion beam thinning schemes. When applied to the above-mentioned semiconductor thin film materials with high stress, they are prone to breakage and warping during the thinning process, resulting in sample preparation failure. Summary of the Invention
[0005] The purpose of this invention is to provide a method for preparing planar TEM samples of nitride thin film materials, which can achieve sample preparation with large thin areas, low damage, and high positioning accuracy, while reducing equipment costs and operating threshold.
[0006] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:
[0007] A method for preparing a planar TEM sample of a nitride thin film material, the method comprising the following steps:
[0008] Cut the sample into strips, place the sample with the substrate facing up, and attach it side by side with the silicon wafer on the stage;
[0009] Grind the sample to a thickness of 10μm~20μm;
[0010] The stage is tilted along one side of the silicon wafer to grind the sample on one side of the silicon wafer into a wedge-shaped structure;
[0011] The dual ion gun angle was set to +4°~+8°, and the energy was 3.5keV~4.0keV to perform ion thinning on the sample;
[0012] After the substrate of the sample shows equal thickness stripes, continue ion thinning until the epitaxial layer of the sample shows equal thickness stripes. If the area to be measured is located on the surface of the epitaxial layer, keep the angle of the dual ion gun at +4° to +8° until the sample is thinned to form a hole. If the area to be measured is located in the middle area of the epitaxial layer, set the angle of the dual ion gun to one positive and one negative until the sample is thinned to form a hole.
[0013] The sample was cleaned to obtain a planar TEM sample of nitride thin film material.
[0014] In one or more embodiments of the present invention, the tilt angle of the stage is 1° to 3°.
[0015] In one or more embodiments of the present invention, the cleaning operation is as follows: the angle of the dual ion gun is set to one positive and one negative, the angle is 6°~10°, the energy is 1.0keV~1.2keV, and the time is 10min~20min.
[0016] In one or more embodiments of the present invention, the sample structure includes a substrate, on which at least a buffer layer and an epitaxial layer are disposed.
[0017] In one or more embodiments of the present invention, the buffer layer is a GaN buffer layer.
[0018] In one or more embodiments of the present invention, the epitaxial layer is a GaN epitaxial layer, an AlN layer, an InGaN epitaxial layer, or an AlGaN epitaxial layer.
[0019] In one or more embodiments of the present invention, the sample is cut into strips with a length of 2 mm to 3 mm and a width of 0.5 mm to 1.5 mm.
[0020] In one or more embodiments of the present invention, the sample is ground to a thickness of 10μm to 20μm using diamond sandpaper with a grit size of 3μm to 30μm; the sample is ground to a wedge-shaped structure using diamond sandpaper with a grit size of 1μm to 2μm.
[0021] In one or more embodiments of the present invention, the ion gun is a Ga ion gun.
[0022] Compared with the prior art, the present invention has the following beneficial effects:
[0023] 1. Large thin-area coverage, suitable for large-scale observation, minimal surface damage, and high image quality. Wedge grinding pre-releases film stress, combined with a two-stage ion thinning strategy (high-energy perforation + low-energy cleaning), effectively removing the surface amorphous damage layer and contaminants introduced by high-energy ion bombardment while ensuring efficiency, thus improving the atomic resolution and clarity of transmission electron microscopy.
[0024] 2. High positioning accuracy, especially suitable for thin-layer epitaxial materials. This invention proposes to determine the thinning progress of different material layers (substrate and epitaxial layer) based on the changes in equal-thickness fringes, and dynamically adjust the angle and energy of the ion gun based on the depth position of the area to be measured in the epitaxial layer. When the area to be measured is located on the surface, a double positive angle is used; when it is located in the middle, a single positive and a single negative angle are used. This effectively controls the thinning endpoint and accurately preserves the thin area at the target observation position, solving the problem of ultra-thin epitaxial layer samples being easily worn through or difficult to position.
[0025] 3. Lower cost and wider equipment availability. This method mainly relies on mechanical grinders and general-purpose ion thinners. Compared with FIB equipment, the cost of sample preparation equipment and consumables is significantly reduced, and the relevant equipment is available in most materials analysis laboratories, making it easy to promote. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a flowchart of a method for preparing a planar TEM sample of a nitride thin film material according to an embodiment of the present invention;
[0028] Figure 2 This is an optical mirror image of the InGaN planar TEM sample in Embodiment 1 of the present invention;
[0029] Figure 3 This is a scanning transmission annular dark-field image of the InGaN planar TEM sample in Embodiment 1 of the present invention;
[0030] Figure 4 This is a high-resolution image of a V-shaped defect in an InGaN planar TEM sample from Embodiment 1 of the present invention. Detailed Implementation
[0031] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.
[0032] Currently, common drawbacks of using FIB technology to prepare nitride thin film TEM planar samples include: small thin area, with the FIB processing area typically limited to the micrometer scale, which is unfavorable for large-scale observation when the defect concentration in the sample is low; significant surface damage, with high-energy ion beams easily introducing amorphous layers or lattice distortion; and high cost. In conventional mechanical polishing followed by ion thinning processes, residual stress can easily cause sample fragmentation during polishing, and it is difficult to accurately locate specific depth regions within the epitaxial layer.
[0033] Therefore, this invention addresses the preparation of planar TEM samples of nitride semiconductor thin films by using wedge grinding to release stress and dynamic ion thinning control to achieve sample preparation with large thin areas, low damage, and high positioning accuracy, while reducing equipment costs and operating barriers.
[0034] A specific embodiment of the present invention provides a method for preparing a planar TEM sample of a nitride thin film material, such as... Figure 1 As shown, the specific steps include the following:
[0035] Step 1, Sample pretreatment.
[0036] Specifically, such as Figure 1 In (a), the sample structure is: a sapphire substrate with a GaN buffer layer, and a heteroepitaxial nitride film (specifically GaN, AlN, InN, InGaN or AlGaN) on the substrate, with an epitaxial layer thickness of tens to hundreds of nanometers.
[0037] The thin film sample was cut into narrow strips of 2mm-3mm in diameter and 0.5mm-1.5mm in width using a wire EDM machine. A Si wafer was taken, and the sample was placed side-by-side with the epitaxial layer surface facing down and the substrate surface facing down. It was then adhered to the copper ring with a circular hole using epoxy resin adhesive. (Specific details are as follows...) Figure 1 (b) The size of the Si substrate is not specifically limited, as long as it does not exceed the size of the copper ring after being attached to the sample.
[0038] Step 2, mechanical grinding.
[0039] Specifically, a copper ring is attached to the stage, and diamond abrasive paper with grit sizes of 30μm, 9μm, and 3μm is used sequentially to grind the entire sample, starting from the substrate surface, until a thickness of 10μm~20μm is achieved. Then, the stage is tilted along one side of the Si wafer at an angle of 1°~3°. Using 1μm diamond abrasive paper, the sample on the Si wafer side is ground into a wedge-shaped structure, as shown below. Figure 1 (c) In this process, the sample thickness can be referenced by the degree of red light transmission of the Si substrate under the bottom light of the microscope. If the Si substrate can clearly transmit red light and uniformly glow red under the bottom light of the microscope, then the overall thickness of the sample is 10μm~20μm. When it is ground into a wedge-shaped structure, the Si substrate at the tip of the wedge has very bright and extremely strong red light transmission under the bottom light of the microscope.
[0040] In this step, a two-stage mechanical grinding process is adopted. First, the sample is thinned to ≤20μm, and then it is tilted and ground into a wedge shape for stress release and expansion of the thin area. This step is the key pretreatment to achieve a large-scale, controllable thin area.
[0041] Step 3, ion thinning.
[0042] Specifically, the sample, along with the copper ring, is immersed in an acetone solution, and then the sample, along with the copper ring, is fixed on the clamp of the thinning instrument, which can be a Gatan PIPs or other similar ion thinning instrument.
[0043] During the thinning process, the angle of the dual ion gun is set to +4° to +8° and the energy is 3.5 keV to 4.0 keV. During the thinning process, the changes in the colored equal thickness stripes are observed through a microscope.
[0044] Specifically, such as Figure 1 In (d), (e), and (f), the substrate material first shows equal-thickness stripes on the sample, and the range of the equal-thickness stripes gradually expands as the thinning process proceeds. Then, the epitaxial layer shows equal-thickness stripes. The angle and energy of the ion gun of the thinning instrument are adjusted according to the position of the area to be measured in the epitaxial layer. If the area to be measured is located on the outermost surface of the epitaxial layer, the positive angle of the ion gun is kept at +4° to +8° until the sample is thinned to form a hole. If the area to be measured is located in the middle region of the epitaxial layer, the angles of the dual ion guns are set to one positive and one negative, and the angles remain unchanged until the sample is thinned to form a hole.
[0045] In this step, a material layer thinning monitoring and dynamic control method based on isothickness stripe observation is adopted. This involves observing the appearance, changes, and extent of isothickness stripes on the sample under a microscope to determine the timing of substrate material thinning and epitaxial layer thinning. Simultaneously, an ion gun angle combination strategy based on the depth of the test area is employed. Depending on whether the test area is located at the outermost or middle region of the epitaxial film, two positive angles or one positive and one negative angle are used during the sample perforation stage. This is the core logic for achieving precise positioning and thinning.
[0046] Step 4: Clean the sample.
[0047] Specifically, after the sample is thinned and the pores are formed, the angle of the ion gun is adjusted to one positive and one negative, with an angle of 6°~10°, an energy of 1.0KeV~1.2KeV, and a time of 10min~20min to clean the damaged layer and dirt on the sample surface.
[0048] The present invention will be further described in detail below with reference to specific embodiments.
[0049] Example 1
[0050] The method for preparing the planar TEM sample of the nitride thin film material in this embodiment is as follows:
[0051] Take a sample; the epitaxial layer in the sample is InGaN. Use a wire cutter to cut the thin film sample into narrow strips of 3mm × 1mm. Take a 3mm × 1mm Si wafer and place the sample and the Si wafer side by side with the epitaxial layer surface facing down and the substrate surface facing up. Then, attach them to the copper ring with a circular hole using epoxy resin adhesive.
[0052] A copper ring was attached to the stage, and the sample was ground to a thickness of 15 μm using diamond sandpaper with grits of 30 μm, 9 μm, and 3 μm in sequence. The stage was tilted at an angle of 2° along one side of the Si wafer, and the sample on the Si wafer side was ground to a wedge-shaped structure using diamond sandpaper with a grit of 1 μm.
[0053] The sample, along with the copper ring, was immersed in acetone solution, and then fixed onto the clamp of the thinning instrument. The angle of the dual Ga ion gun was set to +5° on both sides, and the energy was 4.0 keV. Ion thinning was then performed, and the changes in the colored isothight stripes were observed under a microscope during the thinning process.
[0054] First, uniform thickness stripes of the substrate material appear on the sample, and the range of these stripes gradually expands as the thinning process proceeds. Subsequently, uniform thickness stripes of the epitaxial layer appear. The ion gun angle is adjusted to alternate between positive and negative, while maintaining the same angle, until the sample is thinned to create a hole.
[0055] After the sample was thinned to form a hole, the ion gun angle was adjusted to one positive and one negative, with an angle of 6°, an energy of 1.0 keV, and a time of 15 min. The surface damage layer and dirt were cleaned, and an InGaN planar TEM sample was prepared after the process.
[0056] The optical micrograph of the sample obtained in this embodiment is as follows: Figure 2 As shown in the figure, two rings of colored patterns can be seen. The outer ring consists of equal-thickness stripes of the substrate, while the rings around the small hole in the middle consist of equal-thickness stripes of the epitaxial layer. Figure 3 This is a scanning transmission annular dark-field image of an InGaN planar TEM sample. Figure 4 This is a high-resolution image of V-type defects in an InGaN planar TEM sample. It can be seen that the planar sample was accurately thinned to the middle region of the InGaN epitaxial film. The distribution of V-type defects and dislocations in InGaN can be seen. The thin region is large and uniform in thickness, with little surface damage and clear atomic images.
[0057] Example 2
[0058] The method for preparing the planar TEM sample of the nitride thin film material in this embodiment is as follows:
[0059] Take a sample; the epitaxial layer in the sample is InGaN. Use a wire cutter to cut the thin film sample into narrow strips of 3mm × 1mm. Take a 3mm × 1mm Si wafer and place the sample and the Si wafer side by side with the epitaxial layer surface facing down and the substrate surface facing up. Then, attach them to the copper ring with a circular hole using epoxy resin adhesive.
[0060] A copper ring was attached to the stage, and the sample was ground to a thickness of 15 μm using diamond sandpaper with grits of 30 μm, 9 μm, and 3 μm in sequence. The stage was tilted at an angle of 1° along one side of the Si wafer, and the sample on the Si wafer side was ground to a wedge-shaped structure using diamond sandpaper with a grit of 1 μm.
[0061] The sample, along with the copper ring, was immersed in acetone solution, and then fixed onto the clamp of the thinning instrument. The angle of the dual Ga ion gun was set to +4° on both sides, and the energy was 3.5 keV. Ion thinning was then performed, and the changes in the colored isothight stripes were observed under a microscope during the thinning process.
[0062] First, uniform thickness stripes of the substrate material appear on the sample, and the range of these stripes gradually expands as the thinning process continues. Subsequently, uniform thickness stripes of the epitaxial layer appear. The dual ion gun is kept at a positive angle of +4° until the sample is thinned to create a hole.
[0063] After the sample was thinned to form a hole, the ion gun angle was adjusted to one positive and one negative, with an angle of 8°, an energy of 1.1 keV, and a time of 18 min. The surface damage layer and dirt were cleaned, and an InGaN planar TEM sample was prepared after the process.
[0064] Example 3
[0065] The method for preparing the planar TEM sample of the nitride thin film material in this embodiment is as follows:
[0066] Take a sample; the epitaxial layer in the sample is InGaN. Use a wire cutter to cut the thin film sample into narrow strips of 3mm × 1mm. Take a 3mm × 1mm Si wafer and place the sample and the Si wafer side by side with the epitaxial layer surface facing down and the substrate surface facing up. Then, attach them to the copper ring with a circular hole using epoxy resin adhesive.
[0067] A copper ring was attached to the stage, and the sample was ground to a thickness of 15 μm using diamond sandpaper with grits of 30 μm, 9 μm, and 3 μm in sequence. The stage was tilted at an angle of 3° along one side of the Si wafer, and the sample on the Si wafer side was ground to a wedge-shaped structure using diamond sandpaper with a grit of 1 μm.
[0068] The sample, along with the copper ring, was immersed in acetone solution, and then fixed onto the clamp of the thinning instrument. The angle of the dual Ga ion gun was set to +8° on both sides, and the energy was 4.0 keV. Ion thinning was then performed, and the changes in the colored equal-thickness stripes were observed under a microscope during the thinning process.
[0069] First, uniform thickness stripes of the substrate material appear on the sample, and the range of these stripes gradually expands as the thinning process proceeds. Subsequently, uniform thickness stripes of the epitaxial layer appear. The ion gun angle is adjusted to alternate between positive and negative, while maintaining the same angle, until the sample is thinned to create a hole.
[0070] After the sample was thinned to form a hole, the ion gun angle was adjusted to one positive and one negative, with an angle of 10°, an energy of 1.0 keV, and a time of 20 min. The surface damage layer and dirt were cleaned, and an InGaN planar TEM sample was prepared after the process.
[0071] The samples obtained in Examples 2 and 3, upon observation, all exhibited the advantages of large thin-area coverage, minimal surface damage, and high image quality.
[0072] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.
[0073] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A method for preparing a planar TEM sample of a nitride thin film material, characterized in that, The preparation method includes the following steps: Cut the sample into strips, place the sample with the substrate facing up, and attach it side by side with the silicon wafer on the stage; Grind the sample to a thickness of 10μm~20μm; The stage is tilted along one side of the silicon wafer to grind the sample on one side of the silicon wafer into a wedge-shaped structure; The dual ion gun angle was set to +4°~+8°, and the energy was 3.5keV~4.0keV to perform ion thinning on the sample; After the substrate of the sample shows equal thickness stripes, continue ion thinning until the epitaxial layer of the sample shows equal thickness stripes. If the area to be measured is located on the surface of the epitaxial layer, keep the angle of the dual ion gun at +4° to +8° until the sample is thinned to form a hole. If the area to be measured is located in the middle area of the epitaxial layer, set the angle of the dual ion gun to one positive and one negative until the sample is thinned to form a hole. The sample was cleaned to obtain a planar TEM sample of nitride thin film material.
2. The method for preparing a planar TEM sample of a nitride thin film material according to claim 1, characterized in that, The tilt angle of the platform is 1° to 3°.
3. The method for preparing a planar TEM sample of a nitride thin film material according to claim 1, characterized in that, The cleaning operation is as follows: the dual ion guns are set to one positive and one negative angle, with an angle of 6°~10°, an energy of 1.0 keV~1.2 keV, and a time of 10 min~20 min.
4. The method for preparing a planar TEM sample of a nitride thin film material according to claim 1, characterized in that, The sample structure includes a substrate, on which at least a buffer layer and an epitaxial layer are disposed.
5. The method for preparing a planar TEM sample of a nitride thin film material according to claim 4, characterized in that, The buffer layer is a GaN buffer layer.
6. The method for preparing a planar TEM sample of a nitride thin film material according to claim 4, characterized in that, The epitaxial layer is a GaN epitaxial layer, an AlN layer, an InGaN epitaxial layer, or an AlGaN epitaxial layer.
7. The method for preparing a planar TEM sample of a nitride thin film material according to claim 1, characterized in that, Cut the sample into strips with a length of 2mm to 3mm and a width of 0.5mm to 1.5mm.
8. The method for preparing a planar TEM sample of a nitride thin film material according to claim 1, characterized in that, The sample was ground to a thickness of 10μm to 20μm using diamond sandpaper with a grit size of 3μm to 30μm; the sample was then ground to a wedge-shaped structure using diamond sandpaper with a grit size of 1μm to 2μm.
9. The method for preparing a planar TEM sample of a nitride thin film material according to claim 1, characterized in that, The ion gun is a Ga ion gun.