Metal foil section for electron back scattering diffraction analysis and preparation method

Abstract

The invention discloses a metal foil section for electron back scattering diffraction analysis and a preparation method, and belongs to the technical field of sample preparation. The preparation method comprises the following steps: shearing a metal foil, fixing the metal foil, placing the metal foil in a scanning electron microscope, selecting a target area of the metal foil, and carrying out electron beam deposition to obtain the metal foil containing an electron beam deposition protective layer; the metal foil containing the electron beam deposition protection layer is rotated by 180 degrees, then ion beam deposition is conducted under the condition that the ion beam current is 15 nA, and the metal foil containing the ion beam deposition protection layer is obtained; and after inclination compensation is carried out on the metal foil containing the ion beam deposition protection layer, etching is carried out by using ion beam etching of a focused ion beam under the condition that the ion beam current is 30nA, and the metal foil section for electron back scattering diffraction analysis is obtained. According to the preparation method, large-area section processing can be carried out on the metal foil, the preparation efficiency is high, and the characterization effect of electron back scattering diffraction analysis can be met.

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] As the core material of lithium-ion batteries, printed circuit boards, and chip packaging substrates, metal foils are widely used in new energy vehicles, energy storage devices, consumer electronics, 5G communication, and other fields. In the application of lithium-ion batteries, taking copper foil as an example, the copper foil not only serves as the carrier of the negative electrode active material but also as the key electron collector, which has an important impact on improving the battery performance and current output efficiency. From the perspective of cost composition, copper foil accounts for about 10% of the total weight and 8% of the total cost of lithium-ion batteries, second only to the positive electrode material, negative electrode material, and electrolyte, and is an important factor affecting the battery quality, energy density, and cost. In the field of printed circuit boards, metal foils are mainly responsible for the interconnection, conduction, and support functions of electronic components, and their performance directly affects the signal transmission speed, energy loss, and characteristic impedance. In the application of chip packaging substrates, metal foils play an important role in connecting chips and packaging substrates, not only ensuring efficient transmission of electrical signals but also providing circuit interconnection and heat dissipation functions. In addition, due to the low oxygen content on the surface of metal foils, they can combine with a variety of substrates to achieve good electromagnetic shielding effects. It can be seen that the application fields of metal foils are very extensive.

[0003] The orientation of the metal foil cross-section is very important because it directly affects the electrical and mechanical properties of the product: electrically, grain boundaries with different orientations will affect the conductivity and the loss of high-frequency signal transmission; mechanically, the orientation determines the strength and ductility of the metal foil, affecting the reliability during the manufacturing process of printed circuit boards. At the same time, the orientation is also an important indicator reflecting the manufacturing process control level, which can be used to optimize production parameters. Especially in application fields with high requirements for the performance of metal foils, such as printed circuit boards and lithium batteries, orientation control is required to meet the specific needs of different application scenarios. In addition to being measured by X-ray diffraction technology, the orientation of metal foils often uses electron backscatter diffraction technology to obtain more detailed orientation distribution information, or uses pole figure measurement to display the spatial distribution of crystal orientations. These measurement methods can accurately evaluate the microstructural characteristics of metal foils and provide an important basis for process optimization and quality control.

[0004] The preparation of electron backscatter diffraction (EBSD) samples of metal foil cross-sections poses special challenges. Since the thickness of metal foil is usually only a few to dozens of micrometers, it is extremely prone to bending and deformation during cross-section preparation. To obtain high-quality diffraction patterns, embedding and mounting are usually required, followed by mechanical polishing techniques, which are time-consuming, laborious, and complex. During traditional mechanical grinding and polishing, due to the large hardness difference between the metal foil and the embedding material, step effects and scratches are likely to occur. Researchers have also used argon ion polishing technology to prepare cross-sections. Although the number of steps is less than that of mechanical polishing, it is still time-consuming, such as taking 1.5 hours. Moreover, argon ion polishing cannot observe the sample state in real time, making it difficult to accurately judge the polishing end point and locate the target area. In addition, some researchers have used focused ion beam to prepare cross-sections. Not only are the process parameters not given, but the processing area is very small, with only a characterization area of one or two tens of micrometers, which cannot reflect the overall texture of the sample cross-section. The surface layer is damaged to a certain extent, and the curtain effect is obvious. The processing area of the focused ion beam is severely limited, mainly because there is a trade-off between the ion beam current and the beam spot size. A large current can improve the processing efficiency but will reduce the processing accuracy and increase ion implantation damage; a small current results in an overly slow processing speed, and large-area processing will consume too much time and be costly. Therefore, a current of several nanoamperes or several hundred picoamperes is usually used for cross-section processing under normal conditions, resulting in a processing area in the micrometer range. If processing a large area, it is very time-consuming. Additionally, if a very high current is used, in addition to reducing the accuracy, the damage to the edge is also more obvious.

[0005] Therefore, a preparation method that takes into account both efficiency and accuracy needs to be provided for metal foil. Summary of the Invention

[0006] In view of the above problems, the present invention provides a metal foil cross-section and a preparation method for electron backscatter diffraction analysis. Based on a dual-beam electron microscope, the present invention can perform large-area cross-section processing on metal foil, improve efficiency, and ultimately meet the characterization effect of electron backscatter diffraction analysis.

[0007] The first object of the present invention is to provide a method for preparing a metal foil cross-section for electron backscatter diffraction analysis, including the following steps: Cut a metal foil piece and fix it on a sample clamping table to obtain a sample table holding the metal foil. It should be noted that taking a copper foil as an example, since copper is relatively soft, when cutting the copper foil 1 with scissors, there is a mechanical deformation area 3 of several to more than a dozen micrometers 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, as Figure 3 shown. During the experiment, several regions can be cut, and samples with smaller deformation regions can be selected for the next step of processing to improve efficiency. It should be noted that when the clamping table holds the sample, the plane where the foil is located forms an angle of 20° with the horizontal plane.

[0008] Place the sample stage holding the metal foil in a scanning electron microscope and select the target area of the metal foil.

[0009] Perform electron beam deposition on the target area of the metal foil to deposit an electron beam deposition protective layer at the tip of the metal foil cross-section, obtaining a metal foil with an electron beam deposition protective layer. Rotate the metal foil with the electron beam deposition protective layer by 180° so that the ion beam is parallel to the cross-section of the metal foil. Then, under the condition that the ion beam current is 15 nA, perform ion beam deposition on the electron beam deposition layer to obtain an ion beam deposition protective layer, obtaining a metal foil with an ion beam deposition protective layer. It should be noted that according to different manufacturers of scanning electron microscopes, 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°, and if the manufacturer is Thermo Fisher, the angle between the sample stage and the horizontal position is 32°.

[0010] After performing tilt compensation on the metal foil with the ion beam deposition protective layer, use ion beam etching of the focused ion beam to etch under the condition that the ion beam current is 30 nA, so that a vertical cross-section is generated on the surface of the etched metal foil, obtaining a metal foil cross-section for electron backscatter diffraction analysis.

[0011] The reason for tilt compensation is that during the ion beam etching process, a relatively large ion beam current is used, and the relatively large ion beam current causes an obvious slope in the processed cross-section.

[0012] 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.

[0013] In a preferred embodiment of the present invention, during ion beam deposition, the scanning step percentage is 100%.

[0014] In a preferred embodiment of the present invention, the deposition time is 1 min.

[0015] In a preferred embodiment of the present invention, during ion beam etching, the scanning step percentage is 5%.

[0016] In a preferred embodiment of the present invention, during tilt compensation, the tilt angle is 2°.

[0017] In a preferred embodiment of the present invention, the target area is an area 5 μm away from the undeformed part at the tip of the metal foil cross-section.

[0018] In a preferred embodiment of the present invention, the metal foil is a copper foil.

[0019] The second object of the present invention is to provide a metal foil cross-section prepared by the above preparation method.

[0020] Compared with the prior art, the present invention has the following beneficial effects: Compared with the traditional inlay-mechanical polishing process, the operation of the present invention is the simplest, most efficient and time-saving. Compared with the argon ion milling process, the present invention effectively reduces the processing time, and the processing and characterization can be realized in the same device. Compared with the conventional focused ion beam process, during the deposition and etching processes of the present invention, currents above ten nanoamperes are all used, which is very efficient and does not damage the upper edge of the cross-section.

[0021] The present invention uses a dual-beam electron microscope equipped with an electron backscatter diffraction system, first prepares and then characterizes. It can not only perform large-area cross-section processing on metal foils, but also improve efficiency, and finally meet the characterization effect of electron backscatter diffraction, and the preparation to characterization is carried out in the same device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a preparation schematic diagram of Embodiment 1 of the present invention. Among them, a is a schematic diagram of the structure of the copper foil after shearing in Step 1, b is a schematic diagram of the structure after the deposition in Step 4, c is a schematic diagram of the structure after tilting in Step 5, and d is a schematic diagram of the structure during ion beam etching in Step 5.

[0023] Figure 2 It is a schematic diagram of the structure of the sample stage for clamping the copper foil.

[0024] Figure 3 It is a schematic diagram of the structure of the copper foil after preparation.

[0025] Figure 4 It is a mechanism diagram of the sample tilting during ion beam deposition.

[0026] Figure 5 It is a mechanism schematic diagram of the scanning step percentage.

[0027] Figure 6 It is a diagram of the cross-section of the copper foil prepared in Embodiment 1.

[0028] Figure 7 For Figure 6 partial enlarged view.

[0029] Figure 8 It is an orientation diagram of the cross-section of the copper foil in Embodiment 1.

[0030] Figure 9 It is a texture analysis result diagram of the cross-section of the copper foil in Embodiment 1.

[0031] Figure 10 It is an inverse pole figure result diagram of the cross-section of the copper foil in Embodiment 1.

[0032] Figure 11 It is a cross-section scanning diagram processed in the prior art.

[0033] Figure 12 It is a schematic structural diagram of each component inside the scanning electron microscope. Among them, a is the schematic structural diagram of each component after loading the sample, b is the schematic structural diagram of each component during electron beam deposition, c is the schematic structural diagram of each component during ion beam deposition, d is the schematic structural diagram of each component during focused ion beam cross-section machining, and e is the schematic structural diagram of each component during electron backscatter diffraction characterization.

[0034] Reference numerals: 1 - copper foil, 2 - area with prepared cross-section tip, 3 - mechanically deformed area, 4 - clamping stage, 5 - ion column, 6 - electron beam and ion beam deposition protective layer, 7 - gas injection system, 8 - scanning electron microscope. Specific embodiments

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] The present invention provides a method for preparing a cross-section of a copper foil for electron backscatter diffraction analysis. During the preparation, the thickness of the sample is about within 20 μm, and the sample can be a copper foil or an aluminum foil. The copper foil used in the following embodiments is the copper foil in a lithium-ion battery.

[0037] The clamping stage used in the present invention is the sample stage used in the transmission Kikuchi diffraction test.

[0038] Embodiment 1 This embodiment provides a method for preparing a cross-section of a copper foil for electron backscatter diffraction analysis. As shown in Figure 1 and Figure 12 , it specifically includes the following steps: Step 1: Cut a copper foil with a width of about 1 mm and a length of about 3 mm and place it on the clamping stage, and fix it with a clamping piece to obtain a sample stage for clamping the copper foil, as shown in Figure 2 . At this time, the copper foil forms an angle of 20° with the horizontal plane of the clamping stage, so that the cross-section after processing forms an angle of 70° with the horizontal plane, meeting the requirement that it can be directly used for electron backscatter diffraction testing after processing. The copper foil should protrude slightly from the clamping piece to ensure the smooth implementation of subsequent electron backscatter diffraction characterization. Specifically, in this embodiment, only about 1 mm long copper foil protrudes from the clamping piece after the copper foil is fixed.

[0039] Step 2: Place the sample stage for clamping the copper foil in the scanning electron microscope, and select the cross-section tip with less deformation as the target area of the metal foil under the electron microscope for subsequent deposition.

[0040] Such an operation can reduce the workload and time for subsequent focused ion beam removal. The area about 5 μm away from the undeformed part at the cross-section tip is used as the subsequent target area.

[0041] Step 3: When operating with a focused ion beam system, insert the tip of the gas deposition system at the concentric height, and perform electron beam deposition on the target area of the metal foil to form an electron beam deposition protective layer at the tip of the copper foil cross-section. The deposited area is approximately 280 μm long and 2 μm wide. Use an electron beam voltage of 1 kV and a current of about 3 nA. It takes about dozens of seconds to form a protective layer with a thickness of about 100 nm, and a metal foil with an electron beam deposition protective layer is obtained.

[0042] Step 4: Rotate the sample stage by 180°. At this time, the angle between the sample stage and the horizontal position is 34°, so that the ion beam is parallel to the cross-section of the copper foil. Then insert the tip of the gas deposition system and perform ion beam deposition on the metal foil with the electron beam deposition protective layer to deposit an ion beam deposition protective layer with a thickness of about 1 μm at the tip of the copper foil cross-section, and a metal foil with an ion beam deposition protective layer is obtained.

[0043] During ion beam deposition, the ion beam current is 15 nA and the scanning step percentage is 100%. During the ion beam deposition process, not only pixel overlap needs to be reduced, but also deliberate defocusing is required. If the defocus amount is 0.0 at normal focus, the defocus amount used here is 0.3 to make the ion beam deposition more efficient. Usually, the deposition time is 1 min, and a copper foil with a protective layer is obtained. The specifications of the protective layer are 300 μm - 500 μm long, 2 μm wide, and 1 μm thick.

[0044] Step 5: If a large current is used for ion beam processing, there will be a slope at the processed cross-section, forming a structure that is narrow at the top and wide at the bottom, as shown in Figure 4 a in Figure 4 To optimize, as shown in

[0045] b in Figure 4 In this embodiment, the sample stage is tilted to 36° and ion beam etching is performed on the metal foil with the ion beam deposition protective layer. During ion beam etching, the ion beam current is 30 nA and 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 min to obtain a metal foil cross-section for electron backscatter diffraction analysis.

[0046] Therefore, tilt compensation is performed in this step, and tilt compensation is very important for generating a true vertical cross-section on the sample surface.

[0047] As Figure 5 shown in a of [], in focused ion beam machining, the scanning step percentage is usually used to describe the proportional relationship between the distance between adjacent scanning points and the size of the machining area when the ion beam scans the sample surface. The calculation formula for the scanning step percentage is: ; where S is the step and D is the beam spot.

[0048] As Figure 5 shown in b of [], a large scanning step percentage results in small pixel overlap and a relatively rough machining profile. As Figure 5 shown in c of [], if the scanning step percentage is small, the aberration overlap is large and the machining profile is very delicate. Considering that the ion beam current used is large and the intensity distribution significantly deviates from the Gaussian distribution, in order to enhance the dose uniformity, a 5% scanning step percentage is selected in both the X direction and the Y direction. Therefore, even when using large-current machining in the present invention, the overlap between beam spots makes the machining profile still very smooth.

[0049] At the same time, due to the protection of the ion beam deposition layer in step 4 and the angular tilt in step 5, the edge of the ion beam cannot immediately etch the edge of the cross-section. Considering these factors comprehensively, the machined cross-section is relatively flat, comparable to the effect of small-current machining. It not only achieves a high-quality machining effect but also retains the high efficiency of large current.

[0050] Step 6: After the cross-section machining is completed, the sample is rotated 180° again and directly subjected to electron backscatter diffraction analysis.

[0051] Figure 6 is the cross-section effect after deposition and machining in Example 1. The cross-section is nearly 300 μm long and about 15 μm thick. Figure 7 is Figure 6 a partial enlarged view of [], and it can be seen that the quality of the machined cross-section is very high. Figures 8 - 10 is the result after electron backscatter diffraction characterization, which are the orientation map, texture statistical chart, and inverse pole figure respectively. The orientation map can provide statistical information on grains and orientations. The texture statistical chart shows that the texture ratio is 44.9%. The X direction, Y direction, and Z direction of the inverse pole figure also show the preferred orientations of grains. It can be seen that the copper foil cross-section obtained by the preparation method of the present invention can effectively characterize the crystal orientation and texture of the copper foil.

[0052] In the prior art, "High-strength copper foil prepared with 2-mercaptothiazoline by directcurrent electrodeposition" published by Sun Yue et al. in Volume 466 of "Electrochimica Acta" in 2023 used a focused ion beam to prepare a cross-section, but did not give the process parameters. Moreover, the processing area is very small, with only a characterization area of one or two tens of microns.

[0053] Jenn-Ming Song et al. published "Texture and temperature dependence on the mechanical characteristics of copper electrodeposits" in "Materials Science and Engineering: A," Volume 559 in 2013. Jenn-Ming Song et al. published "Orientation dependence of the electrochemical corrosion properties of electrodeposited Cu foils" in "Corrosion Science," Volume 74 in 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," Volume 14, Issue 51 in 2024. Zhichao Dong et al. published "Effects of deformation and applied temperature on the microstructure and performance of industrial ultra-thin rolled Cu foil" in "Journal of Materials Research and Technology," Volume 23 in 2023. In these articles mentioned above, the researchers used argon ion technology to prepare samples, which took a relatively long time, about 1 h. In "Effect of low temperature annealing on microstructure and properties of copper foil" published by Li-ping Wang et al. in "Materials Today Communications," Volume 36 in 2023, the method of embedding and mechanical polishing was used to prepare the cross-section, which was time-consuming, laborious, and the process was complex.

[0054] According to the method of the present application, a cross-sectional area of 300 μm to 500 μm in width and 10 μm to 20 μm in height can be prepared, and the area can reach 10000 μm 2 . In the present invention, ion beam deposition uses a current of 15 nA to deposit a thin film with a width of 300 μm to 500 μm, a width of 2 μm, and a thickness of 1 μm, and only requires 1 min to 2 min. The etching in the present invention only uses a current of 30 nA, and a larger processing area can be achieved in less than five minutes. From electron beam deposition, ion beam deposition to ion beam etching, it can be completed within 10 min, which is very efficient.

[0055] Before the present invention, to deposit a protective layer with a length of 30 μm, a width of 2 μm, and a height of 1 μm, a current of 3 nA was required and it took 3 min; then, for etching a cross-section with a length of 30 μm and a width of 15 μm, ion beam etching used currents of 65 nA, 30 nA, 7 nA, and 1.5 nA respectively, and the total time consumption was 20 min to 30 min. As Figure 11 shown, the processed area is very small. Not only is the preparation time-consuming, but also the obtained samples have poor statistics when performing electron backscatter diffraction tests.

[0056] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0057] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing a cross-section of a metal foil for electron backscatter diffraction analysis, characterized in that, Comprising the following steps: Cut a metal foil and fix it on the sample holder to obtain a sample stage with the metal foil clamped; Place the sample stage with the metal foil clamped in a scanning electron microscope and select the target area of the metal foil; Perform electron beam deposition on the target area of the metal foil to deposit an electron beam deposition protection layer at the tip of the metal foil cross-section, obtaining a metal foil with an electron beam deposition protection layer; Rotate the metal foil with the electron beam deposition protection layer by 180° to make the ion beam parallel to the cross-section of the metal foil, and then perform ion beam deposition on the electron beam deposition layer under the condition that the ion beam current is 15 nA to form an ion beam deposition protection layer, obtaining a metal foil with an ion beam deposition protection layer; After performing tilt compensation on the metal foil with the ion beam deposition protection layer, use ion beam etching of the focused ion beam to etch under the condition that the ion beam current is 30 nA, so that a vertical cross-section is generated on the surface of the etched metal foil, obtaining a metal foil cross-section for electron backscatter diffraction analysis; 2. The preparation method of a metal foil cross-section for electron backscatter diffraction analysis according to claim 1, wherein During electron beam deposition, the electron beam voltage is 1 kV and the current is 3 nA; 3. The preparation method of a metal foil cross-section for electron backscatter diffraction analysis according to claim 1, wherein, During ion beam deposition, the scanning step percentage is 100%; 4. A method for preparing a cross-section of a metal foil for electron backscatter diffraction analysis according to claim 1, characterized in that, The deposition time is 1 min; 5. A method for preparing a cross-section of a metal foil for electron backscatter diffraction analysis according to claim 1, characterized in that, During ion beam etching, the scanning step percentage is 5%; 6. The preparation method of a metal foil cross-section for electron backscatter diffraction analysis according to claim 1, characterized in that, During tilt compensation, the tilt angle is 2°; 7. A method for preparing a cross-section of a metal foil for electron backscatter diffraction analysis according to claim 1, characterized in that, The target area is an area 5 μm away from the undeformed part at the tip of the metal foil cross-section; 8. A method for preparing a cross-section of a metal foil for electron backscatter diffraction analysis according to claim 1, characterized in that, The metal foil is a copper foil; 9. A metal foil cross-section prepared by the preparation method according to any one of claims 1-8.

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