Cheap and simple method for preparing single crystal copper foil

Abstract

The invention discloses a cheap and simple method for preparing a single crystal copper foil. The method comprises the following steps: (1) pretreating a polycrystalline copper foil; (2) putting the pretreated polycrystalline copper foil on a high-temperature-resistant substrate, and then stably pushing the whole structure into a tubular furnace; (3) detecting the air tightness of the tubular furnace; (4) gas washing: injecting reducing gas into the tubular furnace to ensure that oxygen in the tubular furnace is thoroughly cleaned; and (5) continuously introducing reducing gas into the tubular furnace, heating the copper foil to a surface melting temperature, keeping for 10-30 minutes, then cooling to an annealing temperature, preserving heat, and naturally cooling the copper foil to room temperature along with the furnace after the heat preservation stage is ended, thereby obtaining the copper foil. Rotation of crystal lattices and migration of crystal boundaries are promoted through heat treatment, and therefore the single crystal copper foil with the lowest exposed Gibbs free energy is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of single crystal copper foil preparation, and in particular to a method for preparing single crystal copper foil inexpensively and simply. Background Art

[0002] Single crystal material is an excellent functional material. Due to its smooth grain-free surface and strong anisotropy, it exhibits special physical, chemical and optical properties. Single crystal copper foil is a self-supporting two-dimensional copper crystal film composed of a single grain. Its electrical conductivity, thermal conductivity and mechanical properties have been significantly improved. Single crystal copper has high electrical conductivity, thermal conductivity and good solderability. Single crystal copper wire can improve the conductivity of about 10% compared with ordinary copper wire, and can play an important role in electronic devices. In addition, in the structure of single crystal materials, electrons can pass more easily in single crystal materials, with less scattering and lower resistivity. Cables use single crystal copper as the core. The resistance of single crystal copper is 8% to 13% lower than that of ordinary copper, and it has extremely high toughness. Ordinary copper breaks after 16 turns of twisting, while single crystal copper can be twisted 116 times. In the field of high-fidelity audio and video cables, various audio and video signals will produce reflection, refraction and other phenomena when passing through grain boundaries during transmission, causing signal deformation, distortion and attenuation. The few or no grain boundaries of single crystal copper fundamentally improve the transmission quality. What is important is that in recent years, studies have found that atomically flat single-crystalline copper foil has a uniform surface orientation and a certain catalytic effect, so it is often used as a growth substrate for some two-dimensional materials (such as graphene, h-BN) and surface catalytic research materials.

[0003] There are two conventional methods for preparing single crystals, the single crystal pulling method and the Bridgman method. The advantages of both methods are simple operation and easy observation of growth conditions, but impurities are easily introduced during the preparation process, resulting in internal defects in the single crystal, and the expensive bulk single crystals need to be cut, ground, polished and other additional processes, which increases the preparation cost. The high price and small size of single crystal copper foil on the current market are gradually becoming a bottleneck restricting its widespread application, and it is difficult to fully meet the society's growing demand for high-quality single crystal copper foil. Therefore, a simple and affordable preparation method is urgently needed.

[0004] Nankai University and others invented and disclosed a method and equipment for preparing large-area single-crystal copper foil in 2023. First, the polycrystalline copper foil with the oxide layer removed after pretreatment is placed on carbon paper or carbon cloth, and placed in a three-zone tubular furnace with a quartz plate as support; then the interior of the three-zone tubular furnace is evacuated to a vacuum, and a reducing gas is introduced. The reducing gas is a hydrogen-argon mixture, with a hydrogen ratio of 10%-50% and a gas flow rate of 100-600sccm; finally, under the condition of continuous introduction of reducing gas, the copper foil is heated to maintain a temperature difference of 2-100 degrees Celsius in the three temperature zones where the copper foil is located, and the highest temperature at the copper foil position is heated to 1000-1070 degrees Celsius, kept warm for 6-10 hours, and naturally cooled to room temperature to obtain (111) single crystal copper foil. This method uses a three-zone tubular furnace, which has high requirements for equipment; it is connected to a high-temperature resistant transmission device, and the preparation process is complicated; the preparation process requires a large gas flow rate, a high experimental temperature, and a long time. Summary of the invention

[0005] Based on the problems existing in the background technology, the present invention provides a cheap and simple method for preparing large-sized single crystal copper foil, which promotes the rotation of the lattice and the migration of the grain boundaries through heat treatment, thereby obtaining a single crystal copper foil that exposes the crystal plane with the lowest Gibbs free energy.

[0006] The present invention is implemented by the following technical solutions:

[0007] A method for preparing single crystal copper foil inexpensively and simply comprises the following steps:

[0008] (1) Pretreatment of polycrystalline copper foil;

[0009] (2) placing the pretreated polycrystalline copper foil on a high temperature resistant substrate, and then smoothly pushing the entire structure into a tube furnace;

[0010] (3) Check the air tightness of the tube furnace;

[0011] (4) Gas washing: inject reducing gas into the tube furnace to ensure that the oxygen in the tube furnace is thoroughly cleaned;

[0012] (5) continuously introducing reducing gas into the tubular furnace, heating the copper foil to the surface melting temperature, maintaining the temperature for 10 to 30 minutes, then cooling to the annealing temperature, and maintaining the temperature. After the heat preservation stage, the copper foil is naturally cooled to room temperature along with the furnace.

[0013] Furthermore, the specific operation of step (1) pre-treating the polycrystalline copper foil is as follows: first, ultrasonic cleaning is performed with acetone and alcohol, and then, a matching polishing liquid is poured into the automatic polishing machine and evenly distributed on the grinding disc, the rotation speed is 100 rpm, clockwise, polishing for 5-15 seconds, and rinsing with deionized water to remove all residual substances; finally, the copper foil is blown dry with nitrogen to ensure that its surface is clean and free of moisture. The polishing treatment can remove impurities and uneven layers on the surface during the preparation of the single crystal copper foil, improve the surface roughness of the copper foil, and create good conditions for grain growth during the annealing process.

[0014] Furthermore, in step (2), the high temperature resistant substrate is a quartz sheet or an alumina ceramic sheet.

[0015] Furthermore, in step (2), the overall structure is pushed away from the main temperature zone by 1.5-3 cm in the tube furnace.

[0016] Furthermore, when a copper foil with a thickness of 30 μm is prepared, the overall structure is pushed 1.5 cm away from the main temperature zone.

[0017] Furthermore, when a copper foil with a thickness of 50 μm is prepared, the entire structure is pushed 3 cm away from the main temperature zone.

[0018] Furthermore, the specific operation for testing the airtightness of the tubular furnace is: first close the valve at the gas outlet end of the furnace tube, then fill in inert gas until the pressure gauge indicates 0.04MPa; maintain this state for 5-10 minutes, during which the pressure gauge value should remain unchanged. This operating procedure can confirm that the airtightness in the furnace is in good condition.

[0019] Furthermore, in steps (4) and (5), the reducing gas is a mixture of hydrogen and argon, the hydrogen accounts for 10-30%, and the gas flow rate is 100-500 sccm.

[0020] Furthermore, in step (5), the surface melting temperature is 1030-1050°C.

[0021] Furthermore, in step (5), the cooling rate is 3-5°C / min.

[0022] Furthermore, in step (5), the annealing temperature is 1000-1030° C., and the holding time is 2-6 h.

[0023] Beneficial effects of the present invention:

[0024] 1. The original commercial polycrystalline copper foil used in the preparation method of the present invention is easy to obtain, cheap and abundant. The tubular furnace required for the preparation process is a single-temperature zone tubular furnace, which has low equipment requirements. The single crystallization process is simple to operate and has a short preparation cycle, showing significant industrial application potential. Compared with the traditional pulling method, it reduces energy consumption and reduces pollution introduced from the outside during the preparation process.

[0025] 2. Single crystal growth usually relies on directional solidification, that is, the gradual transition from liquid phase to solid phase. In the present invention, the overall structure is pushed away from the main temperature zone to cause a temperature difference on the surface of the sample. Crystal growth will preferentially occur in the area with lower temperature (cold end) and gradually extend to the area with higher temperature (hot end). By controlling the cooling rate and temperature distribution of the melt, the crystal can be made to grow in a specific direction to avoid the formation of irregular polycrystals or miscellaneous crystals. This technical solution is beneficial to the stable and complete growth of single crystals by stabilizing the liquid-solid interface and promoting preferential oriented growth during the single crystal growth process, and significantly improves the purity and performance of single crystal materials.

[0026] 3. The preparation method of the present invention introduces a surface melting process before the annealing step. This operation ensures that when the copper foil is kept at the melting temperature, its surface can meet the thermodynamic conditions for the transformation from solid to liquid. Copper atoms in the liquid state show a faster diffusion rate, which creates more favorable conditions for the preparation of single crystal copper foil, thereby improving the preparation efficiency and quality of single crystal copper foil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide further explanation of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 This is an optical image of the single crystal copper foil of Example 1, and its size is 4.5*2.5 cm;

[0029] Figure 2 (a) is the EBSD image of the original polycrystalline copper foil in Example 1. Figure 2 (b) is the EBSD image of the single crystal copper foil prepared in Example 1;

[0030] Figure 3 This is an optical image of the single crystal copper foil of Example 2, and its size is 8*2.5 cm;

[0031] Figure 4 This is the EBSD image of the single crystal copper foil prepared in Example 2;

[0032] Figure 5 This is an optical image of the single crystal copper foil of Example 3, and its size is 4.5*2.5cm;

[0033] Figure 6 This is the EBSD image of the single crystal copper foil prepared in Example 3. DETAILED DESCRIPTION

[0034] The present invention is further described in detail with reference to specific embodiments. The methods are conventional methods unless otherwise specified. The raw materials can be obtained from public commercial channels unless otherwise specified.

[0035] The polycrystalline copper foil used in the present invention is purchased from Anhui Zhengying Metal Materials Co., Ltd.

[0036] Example 1

[0037] A method for preparing single crystal copper foil inexpensively and simply comprises the following steps:

[0038] (1) Pretreatment of polycrystalline copper foil: First, ultrasonically clean a polycrystalline copper foil (thickness 30 μm) with a size of 4.5*2.5 cm using acetone and then alcohol. Then, use an automatic polishing machine to pour the matching polishing liquid evenly on the grinding disc, rotate at 100 rpm, and polish in a clockwise direction for 10 seconds. Rinse with deionized water to remove all residual substances. Finally, blow dry the copper foil with nitrogen to ensure that its surface is clean and free of moisture.

[0039] (2) Place the pretreated polycrystalline copper foil on a flat ceramic sheet, and then push the whole structure smoothly into the tube furnace, with the whole structure pushed 1.5 cm away from the main temperature zone;

[0040] (3) Check the air tightness of the tube furnace: first close the valve at the outlet of the furnace tube, then fill it with inert gas until the pressure gauge indicates 0.04MPa; maintain this state for 5-10 minutes, during which the pressure gauge value should remain unchanged;

[0041] (4) Gas washing: inject reducing gas (argon: hydrogen at 200 sccm:50 sccm) into the tube furnace to ensure that the oxygen in the tube furnace is thoroughly cleaned;

[0042] (5) Surface melting: the copper foil was heated to 1050°C in an atmosphere of argon:hydrogen (200 sccm:20 sccm) within 2 h, and kept at this temperature for 20 min; then the temperature was lowered to 1020°C annealing temperature at a cooling rate of 5°C / min and kept at this temperature for another 3 h. After the insulation was completed, it was cooled to room temperature in the furnace, and a single crystal copper foil was successfully prepared.

[0043] Figure 1 This is an optical image of a single crystal copper foil, with a size of 4.5*2.5cm;

[0044] Figure 2 (a) Original polycrystalline copper foil and Figure 2 (b) EBSD image of single crystal copper foil. It can be seen from the figure that this method successfully prepared single crystal copper foil with uniform surface orientation.

[0045] Example 2

[0046] A method for preparing single crystal copper foil inexpensively and simply comprises the following steps:

[0047] (1) Pretreatment of polycrystalline copper foil: First, ultrasonically clean a polycrystalline copper foil (30 μm thick) with a size of 8*2.5 cm using acetone and then alcohol. Then, use an automatic polishing machine to pour the matching polishing liquid evenly on the grinding disc, rotate at 100 rpm, and polish in a clockwise direction for 10 seconds. Rinse with deionized water to remove all residual substances. Finally, blow dry the copper foil with nitrogen to ensure that its surface is clean and free of moisture.

[0048] (2) Place the pretreated polycrystalline copper foil on a flat ceramic sheet, and then push the whole structure smoothly into the tube furnace, with the whole structure pushed 1.5 cm away from the main temperature zone;

[0049] (3) Check the air tightness of the tube furnace: first close the valve at the outlet of the furnace tube, then fill it with inert gas until the pressure gauge indicates 0.04MPa; maintain this state for 5-10 minutes, during which the pressure gauge value should remain unchanged;

[0050] (4) Gas washing: inject reducing gas (argon: hydrogen at 300 sccm:50 sccm) into the tube furnace to ensure that the oxygen in the tube furnace is thoroughly cleaned;

[0051] (5) Surface melting: the copper foil was heated to 1050°C in an atmosphere of argon and hydrogen with a ratio of 300 sccm:50 sccm within 2 h, and kept at this temperature for 20 min; then the temperature was lowered to 1020°C annealing temperature at a cooling rate of 5°C / min and kept at this temperature for another 4 h. After the insulation was completed, it was cooled to room temperature in the furnace, and a single crystal copper foil was successfully prepared.

[0052] Figure 3 This is an optical image of a single crystal copper foil, with a size of 8*2.5cm;

[0053] Figure 4 This is the EBSD image of a single crystal copper foil. From the figure, it can be seen that the surface orientation of the single crystal copper foil prepared by this method is uniform.

[0054] Example 3

[0055] A method for preparing single crystal copper foil inexpensively and simply comprises the following steps:

[0056] (1) Pretreatment of polycrystalline copper foil: First, ultrasonically clean a polycrystalline copper foil (50 μm thick) with a size of 4.5*2.5 using acetone and then alcohol. Then, use an automatic polishing machine to pour the matching polishing liquid evenly on the grinding disc, rotate at 100 rpm, and polish in a clockwise direction for 10 seconds. Rinse with deionized water to remove all residual substances. Finally, blow dry the copper foil with nitrogen to ensure that its surface is clean and free of moisture.

[0057] (2) Place the pretreated polycrystalline copper foil on a flat ceramic sheet, and then push the whole structure smoothly into the tube furnace, 3 cm away from the main temperature zone;

[0058] (3) Check the air tightness of the tube furnace: first close the valve at the outlet of the furnace tube, then fill it with inert gas until the pressure gauge indicates 0.04MPa; maintain this state for 5-10 minutes, during which the pressure gauge value should remain unchanged;

[0059] (4) Gas washing: inject reducing gas (argon: hydrogen at 300 sccm: 60 sccm) into the tube furnace to ensure that the oxygen in the tube furnace is thoroughly cleaned;

[0060] (5) Surface melting: the copper foil was heated to 1050°C in an atmosphere of argon and hydrogen with a ratio of 300 sccm:60 sccm within 2 h, and kept at this temperature for 20 min; then the temperature was lowered to 1025°C annealing temperature at a cooling rate of 5°C / min and kept at this temperature for another 6 h. After the insulation was completed, it was cooled to room temperature in the furnace, and a single crystal copper foil was successfully prepared.

[0061] Figure 5 This is an optical image of a single crystal copper foil, with a size of 4.5*2.5 cm.

[0062] Figure 6 This is the EBSD image of single crystal copper foil.

[0063] In one embodiment, the specific steps of detecting the airtightness of the tube furnace in step (3) are as follows:

[0064] The tube furnace is dried and cleaned, and after the drying and cleaning requirements are met, an inflation device is connected to the air inlet valve of the tube furnace, wherein the inflation device includes an inflation source, an inflation hole, a plurality of air flow control valves and a flow sensor, wherein the plurality of air flow control valves are arranged in the connecting pipe, and the flow sensor is used to detect the air flow of the connecting pipe;

[0065] Before testing the air tightness of the tube furnace, close the valve at the air inlet end, fill the inert gas at the air filling source, and open the air flow control valves in the connecting pipes in sequence. Each time an air flow control valve is opened, test the air tightness of the corresponding part of the connecting pipe, and seal the connecting pipe according to the test results until the air tightness of the connecting pipe meets the requirements;

[0066] After the air tightness of the connecting pipe meets the requirements, open the air inlet valve to fill the furnace body of the tubular furnace with inert gas until the pressure gauge in the furnace body indicates 0.04MPa, then close the air inlet valve, and continuously detect the value of the pressure gauge within the next 5-10 minutes to determine whether the change range of the value of the pressure gauge is within the preset range;

[0067] If yes, make sure the air tightness of the tube furnace meets the requirements;

[0068] Otherwise, it is determined that there is leakage in the furnace body of the tube furnace, the leakage amount is determined based on the change amplitude of the value of the pressure gauge, the leakage area is determined based on the leakage amount, and the furnace body detection accuracy is selected based on the leakage area to detect and repair the furnace body of the tube furnace;

[0069] When the air tightness of the tube furnace body meets the requirements, the air tightness of the preparation environment of the tube furnace body is verified based on the test of polycrystalline copper foil, and the tube furnace body is processed according to the verification result.

[0070] In this embodiment, the connecting pipe is sealed according to the detection result until the air tightness of the connecting pipe meets the requirement. Specifically, when the monitoring result does not meet the air tightness requirement, the connecting pipe is sealed with a sealant.

[0071] In this embodiment, the smaller the gas leakage amount, the smaller the corresponding gas leakage area, and the greater the furnace body detection accuracy.

[0072] The beneficial effects of the above design scheme are: providing a suitable testing environment for air tightness detection by drying and cleaning the tube furnace, providing a high-quality testing device for air tightness detection of the furnace body of the tube furnace by first checking the air tightness of the device for detecting air tightness, and performing air tightness detection on the furnace body of the tube furnace after completing the above steps. After determining that there is air leakage in the furnace body of the tube furnace, the amount of leakage is determined based on the amplitude of change of the value of the pressure gauge, and the leakage area is determined based on the amount of leakage, and the furnace body of the tube furnace is detected and repaired based on the furnace body detection accuracy selected based on the leakage area, so as to achieve targeted detection and repair of the furnace body and improve the repair efficiency. Finally, after the air tightness of the furnace body meets the requirements, the air tightness of the preparation environment of the furnace body of the tube furnace is verified by testing the polycrystalline copper foil, and according to the verification result, the furnace body of the tube furnace is processed to ensure that the furnace body of the tube furnace after the final processing provides a good preparation environment for the preparation of polycrystalline copper foil.

[0073] In one embodiment, the air tightness of the preparation environment of the furnace body of the tube furnace is verified based on the test polycrystalline copper wafer, and the furnace body of the tube furnace is processed according to the verification result, including:

[0074] Transferring the test polycrystalline copper wafer to a furnace body of a tube furnace, depositing a dielectric layer on the polycrystalline copper wafer, obtaining a thickness and a fitting degree value of the dielectric layer, and determining whether the thickness and the fitting degree value of the dielectric layer meet the fitting requirements under standard air tightness;

[0075] If yes, make sure that the furnace preparation environment of the tube furnace meets the preparation requirements of single crystal copper foil;

[0076] Otherwise, the furnace preparation environment of the duct furnace does not meet the preparation requirements of the single crystal copper foil, and the ambient temperature of the furnace body of the duct furnace and the components of the duct furnace are corrected.

[0077] The beneficial effect of the above design scheme is: after the air tightness of the furnace body meets the requirements, the air tightness of the preparation environment of the tube furnace body is verified by testing the polycrystalline copper foil, and according to the verification results, the tube furnace body is treated to ensure that the tube furnace body after the final treatment provides a good preparation environment for the preparation of polycrystalline copper foil.

[0078] Finally, it should be noted that the above-mentioned embodiments only express several implementation methods of the present invention and are not intended to limit the invention. For those skilled in the art, any modification, equivalent replacement, improvement, etc. made without departing from the concept of the present invention should be included in the protection scope of the invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A cheap and simple method for preparing single crystal copper foil, characterized in that: The following steps are involved: (1) Pretreatment of polycrystalline copper foil; (2) placing the pretreated polycrystalline copper foil on a high temperature resistant substrate, and then smoothly pushing the entire structure into a tube furnace; (3) Check the air tightness of the tube furnace; (4) Gas washing: inject reducing gas into the tube furnace to ensure that the oxygen in the tube furnace is thoroughly cleaned; (5) continuously introducing reducing gas into the tubular furnace, heating the copper foil to the surface melting temperature, maintaining the temperature for 10 to 30 minutes, then cooling to the annealing temperature, and keeping the temperature. After the heat preservation stage, the copper foil is naturally cooled to room temperature along with the furnace.

2. The method for preparing single crystal copper foil inexpensively and simply according to claim 1, characterized in that: Step (1) pre-treating the polycrystalline copper foil is specifically performed as follows: first, ultrasonic cleaning is performed with acetone and then alcohol, and then, a matching polishing liquid is poured into an automatic polishing machine and evenly distributed on the grinding disc, the speed is 100 rpm, and the polishing is performed in a clockwise direction for 5-15 seconds, and then the copper foil is rinsed with deionized water to remove all residual substances; finally, the copper foil is blown dry with nitrogen to ensure that its surface is clean and free of moisture.

3. The method for preparing single crystal copper foil inexpensively and simply according to claim 1, characterized in that: In step (2), the high temperature resistant substrate is a quartz sheet or an alumina ceramic sheet.

4. The method for preparing single crystal copper foil inexpensively and simply according to claim 1, characterized in that: In step (2), the whole structure is pushed away from the main temperature zone by 1.5-3 cm in the tube furnace.

5. The method for preparing single crystal copper foil inexpensively and simply according to claim 4, characterized in that: When a copper foil with a thickness of 30 μm was prepared, the overall structure was pushed 1.5 cm away from the main temperature zone.

6. The method for preparing single crystal copper foil inexpensively and simply according to claim 4, characterized in that: When a copper foil with a thickness of 50 μm is prepared, the entire structure is pushed 3 cm away from the main temperature zone.

7. The method for preparing single crystal copper foil inexpensively and simply according to claim 1, characterized in that: In steps (4) and (5), the reducing gas is a mixture of hydrogen and argon, with the hydrogen accounting for 10-30% and the gas flow rate being 100-500 sccm.

8. The method for preparing single crystal copper foil inexpensively and simply according to claim 1, characterized in that: The surface melting temperature in step (5) is 1030-1050°C.

9. The method for preparing single crystal copper foil inexpensively and simply according to claim 1, characterized in that: The cooling rate in step (5) is 3-5°C / min.

10. The method for preparing single crystal copper foil inexpensively and simply according to claim 1, characterized in that: In step (5), the annealing temperature is 1000-1030° C. and the holding time is 2-6 h.

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