Preparation method of twin-crystal-free single crystal copper wafer
By depositing Cu(100) on a single crystal sapphire substrate on a side and performing high-temperature annealing, twinless single crystal Cu(111) wafers were successfully prepared, solving the problems of complex preparation and size limitation in the prior art, and achieving efficient and economical wafer preparation.
Patent Information
- Application Number
- CN202510164532.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-14
- Publication Date
- 2025-06-03
AI Technical Summary
The prior art is difficult to prepare twin-free single crystal Cu(111) wafers, especially at the wafer level, and the production process is complex and requires special annealing devices.
A-side single crystal sapphire was used as the substrate, and copper atoms were deposited into Cu(100) thin film by physical vapor deposition method, and high-temperature annealing was performed in a reducing atmosphere, and Cu(100) was rapidly transformed into Cu(111), and twinless single crystal Cu(111) wafer was prepared.
It realizes the preparation of twinless single crystal Cu(111) wafers without special annealing equipment, which shortens the annealing time, improves production efficiency, and reduces energy consumption and costs.
Smart Images
Figure CN120082959A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of single crystal metal wafer preparation, and particularly relates to a method for preparing a twin-free single crystal copper wafer. Background Art
[0002] Two-dimensional materials represented by wafer-scale high-quality single crystal graphene are new materials expected to lead the development of future electronic and optoelectronic devices, with extremely wide application ranges. The process of forming two-dimensional materials is called "growth", and usually requires a substrate as a physical support. The properties of the substrate affect the growth quality, crystal structure and electronic properties of the material. Among them, the ultra-flat twin-free single crystal copper wafer, especially the twin-free single crystal Cu(111) wafer, is an ideal substrate for the directional growth and seamless splicing of graphene into high-quality thin films due to its extremely low lattice mismatch rate with graphene.
[0003] The twin-free single crystal Cu(111) wafer includes a single crystal substrate and a single crystal Cu(111) thin film deposited on the surface of the single crystal substrate. The existing methods for preparing twin-free single crystal Cu(111) wafers include first depositing copper atoms on the surface of an ultra-flat single crystal substrate by Physical Vapor Deposition (PVD) method to form a copper thin film to obtain a copper wafer. Since the crystal structure of c-plane single crystal sapphire is similar to that of Cu(111), copper atoms can directly form a copper thin film with a Cu(111) structure on it. Therefore, c-plane single crystal sapphire (c-Al 2 O 3)As the single-crystal substrate, copper atoms first form a Cu(111) thin film. However, the copper thin film deposited by the PVD method still cannot reach the single-crystal state without twins. Therefore, the prior art still needs to anneal the obtained copper wafer in a reducing atmosphere to cause the rearrangement of copper atoms to form a twin-free single-crystal Cu(111) thin film. However, the size of the twin-free single-crystal Cu(111) prepared by this method still cannot reach the wafer level and is difficult to be compatible with the existing silicon-based wafer preparation process, which limits its processing applications. This is because Cu(111) has two different stacking modes, abc and acb, and on the c-plane sapphire surface with six-fold symmetry, the energies required to form these two stacking modes are very close. Therefore, when copper atoms are deposited on the substrate surface, they will stack in both stacking modes simultaneously, resulting in the formation of twins and twin boundaries in the deposited Cu(111) copper thin film. These twins and twin boundaries are difficult to completely eliminate after annealing and have many disadvantages for the growth of two-dimensional materials such as graphene (such as affecting the nucleation density and the crystal domain orientation of two-dimensional materials) and the subsequent transfer process (such as affecting the integrity and cleanliness of the transfer). In order to avoid the formation of twin Cu(111) thin film after annealing of the Cu(111) thin film, the prior art deposits a polycrystalline Cu thin film on the c-plane sapphire surface and uses the macroscopic circular symmetry of the wafer during annealing and uses a special annealing device for annealing for about one hour or longer: by using a planar heating plate and a graphite gasket, a temperature field with a gradient distribution from the center to the edge of the wafer is constructed, so that Cu(111) crystal nuclei are first formed at the center of the wafer, and then continuously grow and expand under the action of the gradient temperature field and gradually spread to the entire wafer, while suppressing the simultaneous nucleation and growth of grains with different stacking modes on the crystal plane, and finally forming a twin-free single-crystal Cu(111) wafer. However, such a preparation method is relatively complex and requires a special annealing device. Summary of the Invention
[0004] Based on this, the purpose of the present invention is to overcome the defects or deficiencies of the prior art and provide a method for preparing a twin-free single-crystal copper wafer.
[0005] A method for preparing a twin-free single-crystal copper wafer:
[0006] Step S1: Deposit copper atoms on the surface of an a-plane single-crystal sapphire substrate to form a Cu(100) thin film to obtain a copper wafer;
[0007] Step S2: Anneal the copper wafer generated in Step S1 at a high temperature to obtain a twin-free single-crystal copper wafer.
[0008] Compared with the prior art, the method of the present invention uses a-plane single-crystal sapphire as a substrate. In step S1, depositing copper atoms on the surface of the a-plane single-crystal sapphire substrate can directly form a Cu(100) single-crystal thin film or a thin film with a Cu(100) texture similar to a single crystal. Without using special annealing equipment, a twin-free single-crystal copper wafer can be annealed, with higher controllability and shorter time consumption.
[0009] Further, the high-temperature annealing includes heating the copper wafer to an annealing temperature of 800 - 1070 °C, and then maintaining it at the annealing temperature for 5 - 60 minutes.
[0010] Further, the high-temperature annealing includes heating the copper wafer to the annealing temperature at a heating rate of 10 - 25 °C / min.
[0011] Further, the high-temperature annealing includes heating the copper wafer to the annealing temperature at a heating rate of 15 - 23 °C / min, the annealing temperature is 1000 - 1030 °C, and then maintaining it at the annealing temperature for 5 - 35 minutes.
[0012] Further, step S2 is carried out in a reducing atmosphere.
[0013] Further, the reducing atmosphere in step S2 is an environment including an inert gas and hydrogen, where the flow rate of the inert gas is 300 - 800 sccm and the flow rate of hydrogen is 30 - 150 sccm. The inert gas is preferably argon.
[0014] Further, step S1 includes heating the a-plane single-crystal sapphire substrate to 25 - 800 °C, and using physical vapor deposition to deposit copper atoms on the surface of the a-plane single-crystal sapphire substrate to form a copper thin film. Among them, the deposition rate of copper atoms is 1 nm / min - 50 nm / min, and the thickness of the deposited copper thin film is 10 nm - 2000 nm.
[0015] Further, step S1 includes heating the a-plane single-crystal sapphire to 200 - 600 °C, the deposition rate of copper atoms is 20 - 40 nm / min, and the thickness of the deposited copper thin film is 200 - 1500 nm.
[0016] Further, the present invention provides a twin-free single-crystal copper wafer prepared by the above method.
[0017] Further, the present invention provides a twin-free single-crystal copper wafer, including an a-plane single-crystal sapphire substrate and a Cu(111) thin film.
[0018] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings
[0019] Figure 1 XRD test result comparison chart of the copper thin film (a-Al 2 O 3 -Cu) of the copper wafer obtained in step S1 of Example 1 and the a-plane single crystal sapphire (a-Al 2 O 3 ) substrate; the upper part is the peak chart of the a-plane single crystal sapphire (a-Al 2 O 3 ), and the lower part is the peak chart of the copper thin film (a-Al 2 O 3 -Cu) of the copper wafer obtained in step S1 of Example 1;
[0020] Figure 2 XRD test result comparison chart of the copper thin film (a-Al 2 O 3 -Cu) of the twin-free single crystal copper wafer obtained in step S2 of Example 1 and the a-plane single crystal sapphire (a-Al 2 O 3 ) substrate; the upper part is the peak chart of the a-plane single crystal sapphire (a-Al 2 O 3 ), and the lower part is the peak chart of the copper thin film (a-Al 2 O 3 -Cu) of the twin-free single crystal copper wafer obtained in step S2 of Example 1;
[0021] Figure 3 Picture taken of the copper thin film of the twin-free single crystal copper wafer obtained in step S2 of Example 1 under an optical microscope;
[0022] Figure 4 EBSD test result chart of the copper thin film of the twin-free single crystal copper wafer obtained in step S2 of Example 1;
[0023] Figure 5 XRD test result comparison chart of the copper thin film (c-Al 2 O 3 -Cu) of the twin copper wafer obtained in step S2 of Comparative Example 1 and the c-plane single crystal sapphire (c-Al 2 O 3 ) substrate; the upper part is the peak chart of the c-plane single crystal sapphire (c-Al 2 O 3 ), and the lower part is the peak chart of the copper thin film (c-Al 2 O 3 -Cu) of the twin copper wafer obtained in step S2 of Comparative Example 1;
[0024] Figure 6 Picture taken of the copper thin film of the twin copper wafer obtained in step S2 of Comparative Example 1 under an optical microscope;
[0025] Figure 7 It is the EBSD detection result diagram of the copper thin film of the twin copper wafer obtained in step S2 in Comparative Example 1. Specific embodiments
[0026] The present invention attempts to break out of the inherent habits of the prior art and make new attempts from the source. Therefore, the present invention selects different single-crystal substrate materials to prepare wafers and attempts to explore the possibility of using sapphire substrates with other crystal plane characteristics. Single-crystal sapphire usually has several crystal plane types such as a-plane, c-plane, m-plane, r-plane, and v-plane. After observing and analyzing their crystal structures, the sapphire structures of the m-plane, r-plane, and v-plane are relatively complex. Theoretically, copper atoms tend to form copper thin films on their surfaces that are not conducive to the formation of single crystals; while the crystal structure of a-plane sapphire (a-Al 2 O 3 ) has a two-fold symmetry, which is similar to the structure of Cu(100). Therefore, theoretically, copper atoms tend to form Cu(100) thin films on its surface, and Cu(100) has only one stacking mode, which may be conducive to the formation of single-crystal copper thin films. Based on this, the present invention intends to prepare Cu(100) on a-plane sapphire first, and then transform the crystal structure of Cu(100) into Cu(111) by annealing, so as to prepare a twin-free single-crystal Cu(111) wafer.
[0027] Based on the above preparation method, the present invention attempts the idea of using a-plane single-crystal sapphire as a substrate, depositing copper atoms on the substrate surface by physical vapor deposition method, and then annealing to prepare a twin-free single-crystal Cu(111) wafer. The present invention surprisingly discovers that using a-plane single-crystal sapphire, a Cu(100) thin film with a single stacking form can indeed be formed during the deposition process. During the annealing process, only by annealing at an annealing temperature of 800-1070 °C in a reducing atmosphere, Cu(100) can be quickly transformed into Cu(111) with a single stacking mode, and the obtained copper wafer is a twin-free single-crystal Cu(111) wafer. The present invention analyzes the reason that the rapid transformation of Cu(100) is completed under the combined action of the interface energy and the surface energy.
[0028] Furthermore, the present invention also discovers that since it is no longer necessary to first form Cu(111) crystal nuclei in the center of the wafer during the annealing process and then gradually grow and expand to the entire wafer surface, but directly and quickly complete the transformation from Cu(100) to Cu(111), the annealing time can be greatly shortened, and only 5-60 minutes are required to complete the annealing, which is significantly faster than the annealing time of the prior art, improving the production efficiency, reducing the production energy consumption, and helping to control the production cost, save energy and protect the environment.
[0029] The following details the solution of the present invention with reference to the accompanying drawings.
[0030] Example 1
[0031] Step S1: Deposit copper atoms on the surface of an a-plane single-crystal sapphire substrate by physical vapor deposition to form a copper thin film, and obtain a copper wafer:
[0032] Select an a-plane single-crystal sapphire with a size of 2 inches (i.e., wafer-level size) and a crystal orientation of (11-20) as the substrate. After heating the substrate to 300 °C, deposit copper atoms on the surface of the a-plane single-crystal sapphire substrate at a deposition rate of 30 nm / min to form a copper thin film, and deposit until the thickness of the copper thin film reaches 800 nm to obtain a copper wafer. Specifically, in this embodiment, magnetron sputtering is used for copper atom deposition.
[0033] To detect the crystal structure of the copper thin film (a-Al 2 O 3 -Cu) of the copper wafer after step S1, the copper thin film is subjected to structure detection using X-ray Diffraction (XRD) method, and the detection result is compared with the XRD detection result of its substrate - a-plane single-crystal sapphire (a-Al 2 O 3 ). The results are as Figure 1 shown. At this time, in the XRD peak pattern of the copper thin film of the copper wafer, in addition to the same background noise as the a-plane single-crystal sapphire substrate, there is also a peak position of Cu(200), which represents the second-order diffraction peak of Cu(100), indicating that the copper thin film of the copper wafer obtained in step S1 is a Cu(100) thin film, that is, the obtained copper wafer is a Cu(100) wafer.
[0034] Step S2: Place the copper wafer obtained in step S1 in a reducing atmosphere for high-temperature annealing to obtain a twin-free single-crystal copper wafer:
[0035] In this embodiment, the reducing atmosphere is preferably an atmosphere in which argon with a flow rate of 500 sccm and hydrogen with a flow rate of 100 sccm are continuously introduced. Under the reducing atmosphere, the copper wafer obtained in step S1 is heated to the annealing temperature of 1020 °C at a heating rate of 20 °C / min, and annealed at the annealing temperature for 30 minutes. Then, the copper wafer is naturally cooled to room temperature in the reducing atmosphere to obtain a twin-free single-crystal copper wafer.
[0036] To detect the crystal structure of the copper thin film (a-Al 2 O 3 -Cu) of the twin-free single-crystal copper wafer obtained in step S2, the copper thin film is subjected to structure detection using XRD method, and the detection result is compared with the XRD detection result of its substrate - a-plane single-crystal sapphire (a-Al 2 O 3) for comparison with the XRD test results. The results are as Figure 2 shown. At this time, in the peak pattern of the copper film, in addition to the same background noise as that of the a-plane single-crystal sapphire substrate, there is also a peak position of Cu(111) and a peak position of Cu(222), which respectively represent the first-order diffraction peak and the second-order diffraction peak of Cu(111). The above results indicate that the copper film at this time is a Cu(111) film, that is, the obtained twin-free single-crystal copper wafer is a Cu(111) wafer.
[0037] To verify that the copper film of the twin-free single-crystal copper wafer obtained in step S2 is in a twin-free single-crystal state, observe the copper film under an optical microscope at this time: as Figure 3 shown. It can be seen that the surface color of the copper film is uniform, indicating that there are no twins on the surface of the copper film, and the film formation is uniform without obvious defects; also use the Electron Backscatter Diffraction (EBSD) method to detect three inverse pole figures (IPF X, IPF Y, IPF Z) of the copper film: as Figure 4 shown. It can be observed that there are no grain boundaries in the three inverse pole figures, further indicating that the copper film has no twins and is a single-crystal copper film.
[0038] In summary, in Example 1, a Cu(100) wafer was first prepared in step S1, and then a twin-free single-crystal Cu(111) wafer was obtained by annealing in step S2.
[0039] Examples 2, 3, 4, 5, 6
[0040] The differences between Examples 2, 3, 4, 5, and 6 and Example 1 are as follows:
[0041] In step S1, the 2-inch a-plane single-crystal sapphire substrates were respectively heated to 300, 500, 500, 500, and 600 °C, and then copper films were deposited on the substrate surfaces at a rate of 40 nm / min. The deposited copper film thicknesses were 800, 800, 500, 500, and 200 nm respectively, and copper wafers were obtained in this step;
[0042] The reducing atmosphere in step S2 was an atmosphere in which argon with a flow rate of 500 sccm and hydrogen with a flow rate of 50 sccm were continuously introduced. The copper wafers obtained in step S1 were respectively heated to the annealing temperatures of 1020, 1020, 1020, 920, and 970 °C and kept at the annealing temperatures for 5 min, 30 min, 30 min, 30 min, and 60 min respectively to obtain twin-free single-crystal Cu(111) wafers
[0043] The copper film of the twin-free single-crystal Cu(111) wafer obtained after step S2 was detected by XRD, and the results showed that they were all Cu(111) films; by observing the copper film with an optical microscope and detecting it by EBSD, no grain boundaries were observed or detected, indicating that the copper films were all single-crystal copper films. In summary, the wafers finally prepared in Examples 2-6 were twin-free single-crystal Cu(111) wafers.
[0044] Comparative Example 1
[0045] Step S1: Copper atoms were deposited on the surface of a c-plane single-crystal sapphire substrate by physical vapor deposition to form a copper film, and a copper wafer was obtained:
[0046] A c-plane single-crystal sapphire with a size of 2 inches and a crystal orientation of (0001) was selected as the substrate. After heating the substrate to 300 °C, copper atoms were deposited on the surface of the c-plane single-crystal sapphire at a deposition rate of 30 nm / min to form a copper film, and the deposition was continued until the thickness of the copper film reached 800 nm to obtain a copper wafer. Specifically, in this embodiment, the magnetron sputtering method was used for copper atom deposition.
[0047] Step S2: The copper wafer obtained in step S1 was placed in a reducing atmosphere for high-temperature annealing to obtain a twinned copper wafer:
[0048] In this embodiment, the reducing atmosphere was an atmosphere in which argon with a flow rate of 500 sccm and hydrogen with a flow rate of 100 sccm were continuously introduced. Under the reducing atmosphere, the copper wafer obtained in step S1 was heated to the annealing temperature of 1020 °C at a heating rate of 20 °C / min and kept at the annealing temperature for 30 minutes for annealing. Then, the copper wafer was naturally cooled to room temperature in the reducing atmosphere to obtain a twinned copper wafer.
[0049] To detect the crystal structure of the twinned copper wafer (c-Al 2 O 3 -Cu) obtained after step S2, the copper film was structurally detected by the XRD method, and the detection results were compared with the XRD detection results of its substrate - c-plane single-crystal sapphire (c-Al 2 O 3 ). The results are as Figure 5 shown. At this time, in the XRD peak pattern of the copper film of the twinned copper wafer, in addition to the same background noise as the c-plane single-crystal sapphire substrate, there was also a peak position of Cu(111) and a peak position of Cu(222), which respectively represented the first-order diffraction peak and the second-order diffraction peak of Cu(111). The above results indicate that the copper film of the twinned copper wafer obtained in this step S2 is a Cu(111) film, that is, the obtained copper wafer is a Cu(111) wafer.
[0050] To detect the twin situation of the copper thin film on the twin copper wafer obtained in step S2, the copper thin film at this time was observed under an optical microscope: The results are as Figure 6 shown. It can be seen that there are obvious grain boundaries, indicating that twins exist in the copper thin film; further EBSD detection was carried out, and the results are as Figure 7 shown in the three inverse pole figures of
[0051] . It is observed that obvious grain boundaries exist in all three inverse pole figures, further indicating that twins exist in the copper thin film, and it is a twin copper thin film.
[0052] In summary, the final product of Comparative Example 1 is a twin Cu(111) wafer.
[0053] The present invention has the following advantages compared with the prior art:
[0054] 1. The present invention breaks away from the thinking habit of the prior art of using a c-plane single crystal sapphire as a substrate, first depositing a Cu(111) thin film on the substrate surface, and then annealing to obtain a twin-free single crystal Cu(111) wafer. Instead, it selects an a-plane single crystal sapphire as a substrate, first deposits a Cu(100) thin film on the substrate surface, and then anneals to obtain a twin-free single crystal Cu(111) wafer.
[0055] 2. The preparation method of the above concept does not need to use special annealing equipment, reducing the equipment cost; no longer needs to construct a gradient temperature field, improving the controllability and the yield rate.
[0056] 3. When the wafer size and thickness change, it does not require a large amount of time, manpower, and material resources for re-adjustment.
[0057] 4. Since it does not need to wait for the crystal nucleus to expand, but directly makes Cu(100) rapidly transform into Cu(111), the annealing time is shortened compared with the prior art, which can improve production efficiency and reduce energy consumption.
[0058] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. In the description of the present application, for those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.
[0059] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.
Claims
1. A method for preparing a twin-free single crystal copper wafer, characterized in that: Step S1: depositing copper atoms on the surface of the a-plane single crystal sapphire substrate to form a Cu(100) thin film to obtain a copper wafer; Step S2: annealing the copper wafer produced in step S1 at high temperature to obtain a twin-free single crystal copper wafer.
2. The method according to claim 1, characterized in that: The high temperature annealing includes heating the copper wafer to an annealing temperature of 800-1070° C. and maintaining the temperature at the annealing temperature for 5-60 minutes.
3. The method according to claim 1, characterized in that: The high temperature annealing includes heating the copper wafer to an annealing temperature at a heating rate of 10-25° C. / min.
4. The method according to claim 1, characterized in that: The high temperature annealing includes heating the copper wafer to an annealing temperature of 1000-1030° C. at a heating rate of 15-23° C. / min, and then maintaining the annealing temperature for 5-35 minutes.
5. The method according to any one of claims 1 to 4, characterized in that: The step S2 is performed in a reducing atmosphere.
6. The method according to claim 5, characterized in that: The reducing atmosphere in step S2 is an environment including an inert gas and hydrogen, wherein the flow rate of the inert gas is 300-800 sccm, and the flow rate of the hydrogen is 30-150 sccm.
7. The method according to any one of claim 5, characterized in that: The step S1 includes heating the a-plane single crystal sapphire substrate to 25-800° C., and using a physical vapor deposition method to deposit copper atoms onto the surface of the a-plane single crystal sapphire substrate to form a copper film, wherein the deposition rate of the copper atoms is 1nm / min-50nm / min, and the thickness of the deposited copper film is 10nm-2000nm.
8. The method according to claim 7, characterized in that: The step S1 includes heating the a-plane single crystal sapphire substrate to 200-600° C., the deposition rate of copper atoms is 20-40 nm / min, and the thickness of the deposited copper film is 200-1500 nm.
9. A twin-free single crystal copper wafer, characterized in that: Prepared by the method described in claim 8.
10. A twin-free single crystal copper wafer, characterized in that: The invention comprises an a-plane single crystal sapphire substrate and a single crystal Cu (111) film.