A metal foil cross-section for electron backscatter diffraction analysis and a preparation method thereof

Abstract

The present invention discloses a metal foil cross section and preparation method for electron backscatter diffraction analysis, belonging to the field of sample preparation technology. The preparation method comprises the following steps: cutting and fixing a metal foil sheet, placing the sheet in a scanning electron microscope, selecting a target area of the metal foil, and performing electron beam deposition to obtain a metal foil containing an electron beam deposited protective layer; rotating the metal foil containing the electron beam deposited protective layer by 180°, and then performing ion beam deposition under the condition of an ion beam current of 15nA to obtain a metal foil containing an ion beam deposited protective layer; performing tilt compensation on the metal foil containing the ion beam deposited protective layer, and then performing ion beam etching using a focused ion beam under the condition of an ion beam current of 30nA to obtain a metal foil cross section for electron backscatter diffraction analysis. The preparation method of the present invention can perform large-area cross-sectional processing on metal foil, has high preparation efficiency, and can meet the characterization effect of electron backscatter diffraction analysis.

Description

Technical Field

[0001] The present invention relates to the technical field of sample preparation, and more particularly to a metal foil cross section for electron backscatter diffraction analysis and a preparation method thereof. Background Art

[0002] Metal foil, a core material for lithium-ion batteries, printed circuit boards, and chip packaging substrates, is widely used in new energy vehicles, energy storage devices, consumer electronics, and 5G communications. In lithium-ion battery applications, copper foil, for example, not only serves as a carrier for the anode active material but also as a key electron collector, significantly impacting battery performance and current output efficiency. In terms of cost structure, copper foil accounts for approximately 10% of the total weight and 8% of the total cost of a lithium-ion battery, second only to the positive electrode material, negative electrode material, and electrolyte, making it a significant factor influencing battery quality, energy density, and cost. In the printed circuit board (PCB) sector, metal foil primarily serves as the interconnect, conductor, and support for electronic components, with its performance directly impacting signal transmission speed, energy loss, and characteristic impedance. In chip packaging substrate applications, metal foil plays a crucial role in connecting the chip and the packaging substrate, ensuring efficient signal transmission while also providing circuit interconnection and heat dissipation. Furthermore, due to its low surface oxygen content, metal foil can be bonded to a variety of substrates, achieving excellent electromagnetic shielding. This demonstrates the wide range of applications for metal foil.

[0003] The orientation of a metal foil cross section is extremely important because it directly impacts the electrical and mechanical properties of the product. Electrically, grain boundaries of varying orientations can affect conductivity and the loss of high-frequency signal transmission. Mechanically, orientation determines the strength and ductility of the metal foil, impacting the reliability of printed circuit board manufacturing. Orientation is also an important indicator of the level of control over the manufacturing process and can be used to optimize production parameters. This is particularly true in applications such as printed circuit boards and lithium batteries, where high performance requirements for metal foil are crucial. Orientation control is crucial to meet the specific needs of different application scenarios. In addition to measuring the orientation of metal foil using X-ray diffraction techniques, electron backscatter diffraction is often used to obtain more detailed orientation distribution information, or pole figure measurements are used to demonstrate the spatial distribution of crystal orientation. These measurement methods can accurately assess the microstructural characteristics of metal foil, providing an important basis for process optimization and quality control.

[0004] Preparing metal foil cross-sections for electron backscatter diffraction (EBSD) analysis presents unique challenges. Since metal foils are typically only a few to tens of microns thick, they are prone to bending and deformation during cross-section preparation. Obtaining high-quality diffraction patterns typically requires embedding and mounting, followed by mechanical polishing techniques, which are time-consuming, labor-intensive, and complex. Traditional mechanical grinding and polishing processes are prone to step effects and scratches due to the significant hardness difference between the metal foil and the embedding material. Researchers have also used argon ion polishing to prepare cross-sections. While this involves fewer steps than mechanical polishing, it is still relatively time-consuming, taking, for example, 1.5 hours. Furthermore, argon ion polishing prevents real-time observation of the sample's state, making it difficult to accurately determine the polishing endpoint and locate the target area. Furthermore, some researchers have used focused ion beams to prepare cross-sections. However, these processes lack process parameters and the processed area is very small, only a few microns across, failing to reflect the overall texture of the sample cross-section. The surface layer suffers a degree of damage, resulting in a noticeable curtain effect. The processing area of a focused ion beam is severely limited, primarily due to a trade-off between ion beam current and beam spot size. While high currents improve processing efficiency, they reduce precision and increase ion implantation damage. Low currents, on the other hand, slow processing speeds, making large-area processing time-consuming and costly. Therefore, currents of a few nanoamperes or hundreds of picoamperes are typically used for conditional cross-section processing, resulting in processing areas in the micrometer range and making processing large areas extremely time-consuming. Furthermore, using very high currents not only reduces precision but also significantly damages the edges.

[0005] Therefore, it is necessary to provide a preparation method for metal foil that takes into account both efficiency and precision. Summary of the Invention

[0006] In response to the above problems, the present invention provides a metal foil cross-section and preparation method for electron backscatter diffraction analysis. The present invention is based on a dual-beam electron microscope, which can not only perform large-area cross-section processing on metal foil, but also improve efficiency, and ultimately meet the characterization effect of electron backscatter diffraction analysis.

[0007] A first object of the present invention is to provide a method for preparing a metal foil cross section for electron backscatter diffraction analysis, comprising the following steps:

[0008] Cut the metal foil and fix it on the sample holding table to obtain the sample table for holding the metal foil. It should be noted that, taking copper foil as an example, since copper is relatively soft, when the scissors cut the copper foil 1, there is a mechanical deformation area 3 of several microns to more than ten microns on the outermost side of the cross-section tip 2 of the copper foil 1, which needs to be removed by subsequent ion beam etching, such as Figure 3 As shown in the figure, during the experiment, you can cut several areas and select samples with smaller deformation areas for the next processing to improve efficiency. It is also important to note that when the clamping table clamps the sample, the plane of the foil is at a 20° angle to the horizontal plane.

[0009] The sample stage holding the metal foil is placed in a scanning electron microscope, and a target area of the metal foil is selected.

[0010] Performing electron beam deposition on a target area of the metal foil to deposit an electron beam deposited protective layer on a tip of a cross section of the metal foil, thereby obtaining a metal foil containing the electron beam deposited protective layer;

[0011] The sample stage is rotated 180° and tilted so that the ion beam is parallel to the cross-section of the metal foil. Then, ion beam deposition is performed on the electron beam deposition layer under the condition that the ion beam current is 15 nA to obtain an ion beam deposition protective layer, thereby obtaining a metal foil containing an ion beam deposition protective layer. It should be noted that, depending on the manufacturer of the scanning electron microscope, the angle between the sample stage and the horizontal position is different. If the manufacturer is Zeiss, the angle between the sample stage and the horizontal position is 34°. If the manufacturer is Thermo Fisher, the angle between the sample stage and the horizontal position is 32°.

[0012] After tilt compensation is performed on the metal foil containing the ion beam deposited protective layer, ion beam etching is performed using a focused ion beam at an ion beam current of 30 nA, so that a vertical cross-section is generated on the surface of the etched metal foil, thereby obtaining a metal foil cross-section for electron backscatter diffraction analysis.

[0013] The reason for tilt compensation is that a larger ion beam current is used during ion beam etching, and the larger ion beam current causes the processed cross section to have an obvious slope.

[0014] In a preferred embodiment of the present invention, during electron beam deposition, the electron beam voltage is 1 kV, the current is 3 nA, and the deposition time is about 30 s.

[0015] In a preferred embodiment of the present invention, during ion beam deposition, the scan step percentage is 100%.

[0016] In a preferred embodiment of the present invention, the deposition time is 1 min.

[0017] In a preferred embodiment of the present invention, during ion beam etching, the scan step percentage is 5%.

[0018] In a preferred embodiment of the present invention, during tilt compensation, the tilt angle is 2°.

[0019] In a preferred embodiment of the present invention, the target area is an area 5 μm away from the tip of the metal foil cross section to the undeformed area.

[0020] In a preferred embodiment of the present invention, the metal foil is copper foil.

[0021] The second object of the present invention is to provide a cross section of a metal foil produced by the above production method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Compared to traditional inlay-mechanical polishing processes, the present invention offers the simplest, most efficient, and time-saving operation. Compared to argon ion milling, the present invention significantly reduces processing time and allows both processing and characterization to be performed within the same instrument. Compared to conventional focused ion beam processes, the present invention utilizes currents exceeding ten nanoamperes throughout both deposition and etching, resulting in high efficiency and no damage to the upper edge of the cross-section.

[0024] The present invention uses a dual-beam electron microscope equipped with an electron backscatter diffraction system, which performs preparation first and then characterization. For metal foil, it can not only perform large-area cross-sectional processing, but also improve efficiency, and ultimately meet the characterization effect of electron backscatter diffraction, and all the steps from preparation to characterization are carried out in the same device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a preparation diagram of Example 1 of the present invention, wherein a is a structural diagram of the copper foil after shearing in step 1, b is a structural diagram after deposition in step 4, c is a structural diagram after tilting in step 5, and d is a structural diagram of ion beam etching in step 5.

[0026] Figure 2 Schematic diagram of the structure of the sample stage for clamping copper foil.

[0027] Figure 3 Schematic diagram of the structure after copper foil preparation.

[0028] Figure 4 Diagram showing the mechanism of sample tilt during ion beam deposition.

[0029] Figure 5 Schematic diagram of the scanning step percentage mechanism.

[0030] Figure 6 This is a cross-sectional view of the copper foil prepared in Example 1.

[0031] Figure 7 for Figure 6 A partial enlarged view of .

[0032] Figure 8 This is an orientation diagram of the copper foil cross section of Example 1.

[0033] Figure 9 This is a diagram showing the texture analysis results of the copper foil cross section of Example 1.

[0034] Figure 10 This is the inverse pole figure result diagram of the copper foil cross section of Example 1.

[0035] Figure 11This is a cross-sectional scan diagram processed in the prior art.

[0036] Figure 12 Schematic diagram of the structure of each component inside the scanning electron microscope, where a is a schematic diagram of the structure of each component after loading the sample, b is a schematic diagram of the structure of each component during electron beam deposition, c is a schematic diagram of the structure of each component during ion beam deposition, d is a schematic diagram of the structure of each component during focused ion beam cross-section processing, and e is a schematic diagram of the structure of each component during electron backscatter diffraction characterization.

[0037] Figure numerals: 1 - copper foil, 2 - area with prepared cross-section tip, 3 - mechanical deformation area, 4 - clamping table, 5 - ion column, 6 - electron beam and ion beam deposition protective layer, 7 - gas injection system, 8 - scanning electron microscope. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] The present invention provides a method for preparing a copper foil cross section for electron backscatter diffraction analysis. During preparation, the thickness of the sample is approximately within 20 μm. The sample can be copper foil or aluminum foil. The copper foil used in the following embodiments is the copper foil in lithium-ion batteries.

[0040] The clamping table used in the present invention is a sample table used in the transmission Kikuchi diffraction test process.

[0041] Example 1

[0042] This embodiment provides a method for preparing a copper foil cross section for electron backscatter diffraction analysis, such as Figure 1 and Figure 12 As shown, the specific steps include:

[0043] Step 1: Cut a copper foil with a width of about 1mm and a length of about 3mm and place it on the clamping table and fix it with a clamp to obtain a sample table for clamping the copper foil. Figure 2 As shown. At this point, the copper foil is at a 20° angle to the horizontal plane of the clamping table. This allows the finished cross-section to be at a 70° angle to the horizontal plane, meeting the requirement for direct EBSD testing after processing. The copper foil should protrude slightly beyond the clamping plate to ensure smooth subsequent EBSD characterization. Specifically, in this embodiment, only approximately 1 mm of copper foil protrudes beyond the clamping plate after being secured.

[0044] Step 2: Place the sample stage holding the copper foil in a scanning electron microscope. Under the electron microscope, select the tip of the cross section with less deformation as the target area of the metal foil for subsequent deposition.

[0045] This operation can reduce the workload and time of subsequent focused ion beam removal. The area about 5μm from the tip of the cross section to the undeformed part is used as the subsequent target area.

[0046] Step 3: Using a focused ion beam system, the needle tip of the gas deposition system is inserted at a concentric height to perform electron beam deposition on the target area of the metal foil. This deposits an electron beam-deposited protective layer on the tip of the copper foil cross section. The deposited area is approximately 280 μm long and 2 μm wide. Using an electron beam voltage of 1 kV and a current of approximately 3 nA, a protective layer approximately 100 nanometers thick is formed in a few tens of seconds, resulting in a metal foil containing an electron beam-deposited protective layer.

[0047] Step 4: Rotate the sample stage 180° and tilt it to a 34° angle with the horizontal position, aligning the ion beam with the cross-section of the copper foil. Insert the needle tip of the gas deposition system and perform ion beam deposition on the metal foil containing the electron beam deposited protective layer. Deposit an ion beam deposited protective layer approximately 1 μm thick on the tip of the copper foil cross-section, yielding a metal foil containing the ion beam deposited protective layer.

[0048] During ion beam deposition, the beam current was 15nA and the scan step size was 100%. During ion beam deposition, not only was pixel overlap minimized, but defocusing was also necessary. If the defocus value is 0.0 when focused, a defocus value of 0.3 was used here to make ion beam deposition more efficient. Deposition typically took 1 minute, resulting in a copper foil with a protective layer measuring 300μm to 500μm long, 2μm wide, and 1μm thick.

[0049] Step 5: If a large current is used for ion beam processing, the processed cross section will have a slope, forming a structure that is narrow at the top and wide at the bottom, such as Figure 4 As shown in a in . In order to optimize, as Figure 4 As shown in b, in this embodiment, the sample stage is tilted to 36°, and ion beam etching is performed on the metal foil containing the ion beam deposited protective layer. When performing ion beam etching, the ion beam current is 30nA, the scanning step percentage is 5%, the ion beam dose is set according to the film thickness, the processing method is the cross-section processing mode, and the processing time is 5 minutes to obtain the metal foil cross section for electron backscatter diffraction analysis.

[0050] In this step, the sample stage is tilted 2° further because a larger ion beam current is used during ion beam etching. The cross section processed by a larger ion beam current will have a significant slope, such as Figure 4As shown in a in the figure, this is because the ion beam is approximately Gaussian distributed. When the ion beam current is large, the tail of the Gaussian also has a strong processing capability, causing the edge of the cross section to be etched.

[0051] Therefore, tilt compensation is performed in this step, which is very important for generating true vertical sections on the sample surface.

[0052] like Figure 5 As shown in a in Figure 1, in focused ion beam processing, the scan step percentage is usually used to describe the proportional relationship between the distance between adjacent scan points and the size of the processing area when the ion beam scans the sample surface. The calculation formula for the scan step percentage is:

[0053] Scan step percentage = 00%;

[0054] Where S is the step size and D is the beam spot size.

[0055] like Figure 5 As shown in b, the larger the scanning step percentage is, the smaller the pixel overlap is and the rougher the processed contour is. Figure 5 As shown in Figure c, a small scan step percentage results in large aberration overlap, resulting in a very fine machined profile. Considering the high ion beam current used and the significant deviation of the intensity distribution from a Gaussian distribution, a 5% scan step percentage was selected in both the X and Y directions to enhance dose uniformity. Therefore, even with high current machining, the overlap between beam spots in the present invention maintains a very smooth machined profile.

[0056] Furthermore, due to the protective layer of the ion beam deposited in step 4 and the tilted angle in step 5, the edge of the ion beam cannot immediately etch the edge of the cross-section. These factors combine to produce a relatively flat cross-section, comparable to low-current machining. This achieves high-quality machining while retaining the high efficiency of high-current machining.

[0057] Step 6: After the cross-section processing is completed, the sample is rotated 180° again and directly subjected to electron backscatter diffraction analysis.

[0058] Figure 6 This is the cross-sectional effect after deposition and processing of Example 1. The cross-sectional length is close to 300 μm and the thickness is about 15 μm. Figure 7 for Figure 6 From the enlarged partial view, it can be seen that the quality of the processed section is very high. Figures 8 to 10The results of electron backscatter diffraction characterization are an orientation map, a texture statistical map, and an inverse pole figure. The orientation map provides statistical information about the grain size and orientation, the texture statistical map indicates a texture ratio of 44.9%, and the inverse pole figure's X, Y, and Z directions also indicate the preferred orientation of the grains. This shows that the copper foil cross-section obtained using the preparation method of the present invention can effectively characterize the copper foil's crystal orientation and texture.

[0059] In the prior art, Sun Yue et al. published "High-strength copper foil prepared with 2-mercaptothiazoline by direct current electrodeposition" in Electrochimica Acta, Vol. 466, 2023. This paper used a focused ion beam to prepare a cross-section, but the process parameters were not given. Furthermore, the processing area was very small, only a characterization area of 10 to 20 microns.

[0060] Jenn-Ming Song et al. published “Texture and temperature dependence on the mechanical characteristics of copper electrodeposits” in Materials Science and Engineering: A, Vol. 559, 2013; Jenn-Ming Song et al. published “Orientation dependence of the electrochemical corrosion properties of electrodeposited Cu foils” in Corrosion Science, Vol. 74, 2013; Jian Huang et al. published “Electrodeposition, microstructure and characterization of high-strength, low-roughness copper foils with polyethylene glycol additives Electronic supplementary information (ESI) available” in RSC Advances, Vol. 14, No. 51, 2024; Zhichao Dong et al. published “Effects of deformation and applied temperature on the microstructure and performance of industrial ultra-thin rolled Cu” in Journal of Materials Research and Technology, Vol. 23, 2023. foil". In the above articles, researchers used argon ion technology to prepare samples, which took a long time, about 1 hour. Li-ping Wang et al. published "Effect of lowtemperature annealing on microstructure and properties of copper foil" in "Materials Today Communications" (Volume 36, 2023), using the method of inlaying and mechanical polishing to prepare cross-sections, which is time-consuming, labor-intensive and complex.

[0061] According to the method of the present application, a cross-sectional area of 300 μm to 500 μm wide, 10 μm to 20 μm high, and an area of 10,000 μm can be prepared. 2 The ion beam deposition method of the present invention uses a current of 15nA to deposit a thin film 300μm to 500μm long, 2μm wide, and 1μm thick in just 1min to 2min. The etching method of the present invention uses only a current of 30nA, and a larger processing area can be achieved in less than five minutes. From electron beam deposition to ion beam deposition to ion beam etching, it can be completed within 10 minutes, which is very efficient.

[0062] Prior to the present invention, a protective layer 30 μm long, 2 μm wide, and 1 μm high was deposited with a current of 3 nA and took 3 minutes. Then, to etch a cross section 30 μm long and 15 μm wide, ion beam etching used currents of 65 nA, 30 nA, 7 nA, and 1.5 nA, respectively, and took a total of 20 to 30 minutes. Figure 11 As shown, the processed area is very small, which not only takes time to prepare, but also the obtained sample has poor statistics when subjected to electron backscatter diffraction testing.

[0063] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0064] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a metal foil cross-section sample for electron backscatter diffraction analysis, characterized in that: The following steps are involved: Cutting a metal foil piece and fixing it on a sample holding table to obtain a sample table holding the metal foil; Place the sample stage holding the metal foil in a scanning electron microscope and select a target area of the metal foil. Under the electron microscope, select the tip of the cross section with the least deformation as the target area of the metal foil for subsequent deposition. The target area is the area 5 μm away from the tip of the metal foil cross section and the undeformed area. Electron beam deposition is performed on a target area of the metal foil to form an electron beam deposited protective layer at the tip of the metal foil cross section, thereby obtaining a metal foil containing an electron beam deposited protective layer. During the electron beam deposition, the electron beam voltage is 1 kV, the current is 3 nA, and the deposition time is approximately 30 seconds. The deposited area is 280 μm long and 2 μm wide. The thickness of the electron beam deposited protective layer is 100 nanometers. The sample stage is rotated 180 degrees and tilted until the angle between the sample stage and the horizontal position is 34 degrees or 32 degrees, so that the ion beam is parallel to the cross section of the metal foil. Then, ion beam deposition is performed on the electron beam deposited layer under the condition of an ion beam current of 15 nA, and an ion beam deposited protective layer is deposited on the tip of the cross section of the metal foil to obtain a metal foil containing an ion beam deposited protective layer; the deposition time is 1 minute, and the specifications of the protective layer are 300 μm to 500 μm in length, 2 μm in width, and 1 μm in thickness; After performing tilt compensation on the metal foil containing the ion beam deposited protective layer, ion beam etching using a focused ion beam was performed at an ion beam current of 30 nA, so that a vertical cross-section was generated on the surface of the etched metal foil, thereby obtaining a metal foil cross-section sample for electron backscatter diffraction analysis. The length of one side of the prepared vertical cross section is 300 μm to 500 μm, and the length of the other side is 10 μm to 20 μm. During ion beam etching, the processing mode is cross-section processing mode, the processing time is 5 minutes, and the scanning step percentage is 5%. During tilt compensation, the tilt angle continues to be 2°, at which point the angle between the sample stage and the horizontal position is 36° or 34°.

2. The method for preparing a metal foil cross-section sample for electron backscatter diffraction analysis according to claim 1, characterized in that: During ion beam deposition, the scan step percentage is 100%.

3. The method for preparing a metal foil cross-section sample for electron backscatter diffraction analysis according to claim 1, characterized in that: The metal foil is copper foil.

4. A metal foil cross-section sample prepared by the preparation method according to any one of claims 1 to 3.

Images