Method for producing a twinned-free single crystal metal wafer

Abstract

The application provides a preparation method of a twin-free single crystal metal wafer. A certain thickness of metal film is sputtered on a sapphire single crystal wafer substrate by a magnetron sputtering method. The sputtered metal / sapphire wafer is placed on a flat heating plate, and a graphite gasket with a certain size is placed between the metal wafer and the heating plate. The graphite gasket is located directly below the center of the metal wafer, so that the metal wafer is located in a temperature field with a gradient distribution from the center to the edge during the temperature rising process of the flat heating plate to perform annealing and single crystallization. By adjusting the size of the graphite gasket and the temperature of the heating plate, the in-plane twin density of the single crystal metal wafer can be significantly reduced. The application solves the in-plane twin problem existing in the single crystallization process of the existing metal wafer, and can realize the controllable preparation of the twin-free single crystal metal wafer.

Description

Technical Field

[0001] This invention belongs to the field of single-crystal metal wafer preparation, and specifically relates to a method for preparing a twin-free single-crystal metal wafer. Background Technology

[0002] Single-crystal wafer materials are the cornerstone of the modern semiconductor industry. Taking single-crystal silicon wafers as an example, their excellent electrical, optical, and doping properties make them the most widely used chip materials. In recent years, two-dimensional nanomaterials, represented by graphene, have attracted worldwide attention due to their superior physicochemical properties and are considered key to leading the development of future electronic and optoelectronic devices. Graphene films prepared by traditional chemical vapor deposition methods often face structural defects such as point defects, grain boundaries, and wrinkles, significantly affecting their excellent intrinsic properties. Therefore, the controllable preparation of wafer-level single-crystal graphene wafers is not only beneficial for improving the physicochemical properties and uniformity of graphene materials, but also compatible with current mature silicon-based wafer fabrication processes, facilitating the processing and application of wafer-level graphene devices.

[0003] The fabrication of single-crystal metal wafers is crucial for graphene wafer growth. On one hand, single-crystal metal wafers can serve as epitaxial substrates, enabling oriented growth and seamless splicing of graphene domains, thereby reducing grain boundary formation. On the other hand, they can act as catalysts, lowering the energy barrier for carbon source precursor decomposition and graphitization, and improving the crystallinity quality of graphene films.

[0004] However, the fabrication of large-size single-crystal metal wafers currently faces bottlenecks, with in-plane twinning being a key issue. Typically, single-crystal metal wafers are obtained through solid-state epitaxy and annealing recrystallization on a single-crystal substrate (such as sapphire). During this process, metals often exhibit equivalent stacking modes; for example, fcc metals like Cu can have both abc and acb stacking modes, and the formation energies of these modes are similar. This results in similar nuclei formation profiles for different stacking modes during annealing and recrystallization, leading to in-plane twinning after subsequent grain growth and splicing. Due to the absence of metal atoms and structural instability at in-plane twin sites, twin boundaries form during high-temperature annealing and graphene growth. This not only affects the domain orientation and nucleation density of graphene but also the integrity and cleanliness of subsequent graphene film transfer, negatively impacting the fabrication of graphene wafer devices. Therefore, there is an urgent need to develop methods for fabricating twin-free single-crystal metal wafers. Summary of the Invention

[0005] Considering the symmetry of wafers, a gradient temperature field can be constructed from the center to the edge of the wafer, allowing the central grain to nucleate, grow, and gradually migrate across the entire wafer. The presence of this gradient temperature field effectively suppresses the simultaneous nucleation and growth of grains with different stacking patterns on the crystal surface, thus significantly reducing the twin density of single-crystal metal wafers. To achieve the construction of this gradient temperature field, this invention employs a combination of a planar heating plate and graphite pads. The planar heating plate acts as a heat source, providing the energy required for the single-crystalization of the metal during annealing. The graphite pads possess excellent thermal conductivity, ensuring effective temperature conduction within their contact area. Therefore, by changing the dimensions of the graphite pads, such as their height and diameter, and the temperature and heating rate of the planar heating plate, a gradient temperature field can be constructed for metal wafers of different sizes.

[0006] In summary, by employing a central temperature gradient annealing method, initial single-crystal grains are introduced into the central region of a metal wafer using the excellent thermal conductivity of graphite pads. Then, by adjusting the size of the graphite pads and setting the temperature of the planar heating plate to construct a suitable temperature gradient field, abnormal grain growth and grain boundary migration within the wafer can be achieved, thus enabling the fabrication of twin-free single-crystal metal wafers. This method is significant for clarifying the mechanisms of single-crystalization and twin formation in metal thin films, and for promoting the controllable fabrication and commercial application of single-crystal metal wafers. Simultaneously, this method can also provide a good epitaxial and catalytic substrate for the wafer-level growth of two-dimensional nanomaterials, such as graphene, contributing to the construction and application of wafer-level devices using two-dimensional nanomaterials.

[0007] The purpose of this invention is to provide a method for preparing a twin-free single-crystal metal wafer. Specifically, it includes the following steps:

[0008] 1) Metal atoms are sputtered onto the surface of a single-crystal sapphire wafer with a c-plane orientation by magnetron sputtering to prepare a metal thin film of a certain thickness.

[0009] 2) Place the magnetron sputtered metal / sapphire wafer on a flat heating plate, and place a cylindrical graphite pad of a certain size between the metal wafer and the flat heating plate for annealing; the graphite pad is located directly below the center of the metal wafer, and the diameter of the sapphire wafer is larger than the diameter of the graphite pad.

[0010] 3) After annealing the metal wafer, the temperature of the heating plate is reduced to room temperature under the original atmosphere, and a sample is taken to obtain a single crystal metal wafer without twins.

[0011] According to one embodiment of the present invention, the ratio of the diameter of the graphite gasket to the diameter of the sapphire is 1 / 10 to 1 / 5.

[0012] According to one embodiment of the present invention, the sapphire wafer has a diameter of 2 to 6 inches and a thickness of 450 to 1000 μm; the graphite pad has a diameter of 2 to 100 mm and a thickness of 0.5 to 20 mm.

[0013] According to one embodiment of the present invention, the sapphire wafer has a diameter of 2 inches and a thickness of 450 mm; the graphite pad has a diameter of 5 mm and a thickness of 1 mm.

[0014] According to one embodiment of the present invention, the temperature during the annealing process is 900-1100°C, the heating rate is 10-200°C / min, and the annealing time is 0.5-3h.

[0015] According to one embodiment of the present invention, the annealing temperature is 1000-1015℃; the heating rate is 50℃ / min when the temperature is 25-500℃ and 30℃ / min when the temperature is 500-1015℃.

[0016] According to one embodiment of the present invention, the system pressure during the annealing process is 200-2000 Pa, the gas types are argon and hydrogen, and the gas flow rates are 50-1000 sccm for hydrogen and 200-1000 sccm for argon.

[0017] According to one embodiment of the present invention, the pressure during the annealing process is 500-1000 Pa, the gas type is argon and hydrogen, and the gas flow rate is 500 sccm for hydrogen and 500 sccm for argon.

[0018] According to one embodiment of the present invention, the metal thin film is a Cu thin film or a CuNi alloy thin film; the film thickness is 500-1000 nm; the magnetron sputtering rate is 0.2-1.0 nm / s; and the sputtering temperature is 25-200 °C.

[0019] In another aspect, the present invention provides an application of the non-twinned single-crystal metal wafer prepared by the above preparation method in the preparation of graphene films.

[0020] The method for preparing twin-free single-crystal metal wafers provided by this invention includes the following steps:

[0021] 1) Metal atoms are sputtered from a high-purity metal target onto the surface of a single-crystal sapphire wafer by magnetron sputtering at a certain sputtering rate and sputtering temperature to prepare a metal thin film of a certain thickness.

[0022] 2) Place the magnetron sputtered metal / sapphire wafer on a flat heating plate, and place a circular graphite pad of a certain size between the metal wafer and the heating plate, with the graphite pad located directly below the center of the metal wafer;

[0023] 3) By adjusting the size of the graphite pad, the heating rate and temperature of the planar heating plate, a temperature gradient field is constructed from the center to the edge of the metal wafer, which promotes the metal wafer to start the single crystallization process from the center point and migrate to the grain boundary at the edge;

[0024] 4) By adjusting parameters such as gas type, flow rate and pressure during the single crystallization process of metal wafers, volatilization and surface reconstruction during the high-temperature annealing process of metal wafers can be suppressed, thereby improving the flatness of the metal wafer surface.

[0025] 5) After annealing the metal wafer, the temperature of the heating plate is reduced to room temperature under the original atmosphere, and a sample is taken to obtain a single crystal metal wafer without twins.

[0026] In the above method, a metal thin film is prepared by magnetron sputtering using a high-purity metal target on the surface of a single-crystal sapphire wafer; the sapphire size is 2 inches, 4 inches, and 6 inches, the thickness is 450 μm, 500 μm, and 1000 μm, and the crystal plane orientation is c-plane; the metal thin film prepared by magnetron sputtering can be a Cu thin film or a CuNi alloy thin film, with a film thickness of 500-1000 nm; the magnetron sputtering rate is 0.2-1.0 nm / s, and the sputtering temperature is 25-200℃.

[0027] In the above method, a temperature field with a gradient distribution from the center to the edge of the metal wafer is constructed by adjusting the size of the graphite pad, the heating rate and temperature of the planar heating plate; the thickness of the graphite pad is 0.5-20 mm, and the diameter of the graphite pad is 2-100 mm; the temperature of the heating plate is 900-1100 °C; the heating rate of the heating stage is 10-200 °C / min; and the size of the annealed wafer needs to be larger than the size of the graphite pad.

[0028] In the above method, the flatness of the wafer surface is improved by adjusting parameters such as gas type, flow rate, and pressure during the metal wafer annealing process; the system pressure is 200-2000 Pa, the gas type is hydrogen and argon, and the gas flow rate is 50-1000 sccm for hydrogen and 200-1000 sccm for argon. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the fabrication process for twinless single-crystal copper wafers.

[0030] Figure 2 This is a schematic diagram of the fabrication apparatus for twinless single-crystal copper wafers.

[0031] Figure 3 These are the results of the single crystallinity characterization of a 2-inch non-twinned copper wafer.

[0032] Figure 4 This is a schematic diagram of the fabrication process for a twinless single-crystal copper-nickel wafer.

[0033] Figure 5 These are the results of the single crystallinity characterization of a 2-inch non-twinned copper-nickel wafer.

[0034] Figure 6 This is the result of characterizing the single crystallization of twinned copper wafers.

[0035] Figure 7 This is the result of characterizing the single crystallinity of twinned copper-nickel wafers.

[0036] Figure 8 This is a schematic diagram of a method for fabricating twinless single-crystal metal wafers. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods described are conventional methods. Unless otherwise specified, the raw materials are all available from publicly available commercial sources.

[0038] Example 1: The preparation of a twinless Cu(111) single-crystal metal wafer was carried out through the following steps:

[0039] Step 1: Place a 2-inch, 450μm thick sapphire single crystal wafer with c-plane orientation into the magnetron sputtering chamber, heat the substrate to 120°C, and deposit a 500nm copper thin film at a sputtering rate of 0.5nm / s.

[0040] Step 2: Place the sputtered copper / sapphire wafer on the flat heating plate of the annealing chamber. Place a graphite pad with a thickness of 1 mm and a diameter of 5 mm between the copper wafer and the heating plate. The graphite pad is located directly below the center of the wafer.

[0041] Step 3: Evacuate the annealing chamber to a vacuum and set the annealing parameters for the metal wafers inside the chamber. Specifically, the heating rate is 50℃ / min for 25-500℃ and 30℃ / min for 500-1000℃. When the heating plate starts heating, introduce 500 sccm of Ar and 500 sccm of H2, maintain the system pressure at 600 Pa, and heat for 30 min. The annealing temperature is 1000℃ and the time is 60 min.

[0042] Step 4: After annealing, reduce the temperature of the heating plate to room temperature under the annealing atmosphere, stop the gas supply, break the vacuum in the chamber and take a sample to obtain a non-twinned single-crystal Cu(111) wafer.

[0043] Figure 1This is a schematic diagram of the fabrication process for a 2-inch twinless single-crystal copper wafer. Copper atoms are sputtered from a high-purity copper target onto a sapphire single-crystal wafer with a c-plane orientation using magnetron sputtering to obtain a smooth copper film. The twinless single-crystal copper wafer is then fabricated through high-temperature annealing.

[0044] Figure 2 This is a schematic diagram of the apparatus for fabricating a twinless single-crystal copper wafer. By placing graphite pads of appropriate height and size on a planar heating plate, a suitable gradient temperature field can be established on the copper wafer, thereby obtaining a twinless single-crystal copper wafer.

[0045] Figure 3 The characterization results are for a 2-inch non-twinned single-crystal copper wafer. Characterization by electron backscatter diffraction and X-ray diffraction shows that the prepared single-crystal copper wafer not only has good out-of-plane orientation consistency, but also has only three peaks spaced 120° apart in-plane, with no twin formation.

[0046] Example 2: The preparation of a twinless CuNi(111) single-crystal metal wafer was carried out through the following steps:

[0047] Step 1: Place a 2-inch, 450μm thick sapphire single crystal wafer with c-plane orientation into the magnetron sputtering chamber. Heat the substrate to 120°C and perform thin film deposition at a sputtering rate of 0.5nm / s. Use high-purity copper and high-purity nickel as targets to deposit 450nm copper and 50nm nickel simultaneously.

[0048] Step 2: Place the sputtered copper-nickel / sapphire wafer on the flat heating plate of the annealing chamber. Place a graphite pad with a thickness of 1 mm and a diameter of 5 mm between the copper-nickel wafer and the heating plate. The graphite pad is located directly below the center of the wafer.

[0049] Step 3: Evacuate the annealing chamber to a vacuum and set the annealing parameters for the metal wafers inside the chamber. Specifically, the heating rate is 50℃ / min for the 25-500℃ range and 30℃ / min for the 500-1015℃ range. When the heating plate begins to heat up, introduce 500 sccm of Ar and 500 sccm of H2, maintain the system pressure at 600 Pa, heat for 30 min, and anneal at 1015℃ for 60 min.

[0050] Step 4: After annealing, reduce the temperature of the heating plate to room temperature under the annealing atmosphere, stop the gas supply, break the vacuum in the chamber and take a sample to obtain a twin-free single-crystal CuNi(111) wafer.

[0051] Figure 4This is a schematic diagram of the fabrication process for a 2-inch non-twinned single-crystal copper-nickel wafer. Copper and nickel atoms are co-sputtered from a high-purity target onto a sapphire single-crystal wafer with a c-plane orientation using magnetron sputtering, resulting in a smooth alloy film. The non-twinned single-crystal copper-nickel wafer is then fabricated through high-temperature annealing.

[0052] Figure 5 The characterization results are for a 2-inch twin-free single-crystal copper-nickel wafer. Characterization by electron backscatter diffraction and X-ray diffraction shows that the prepared single-crystal copper-nickel wafer not only has good out-of-plane orientation consistency, but also has only three peaks spaced 120° apart in-plane, with no twin formation.

[0053] Comparative Example 1: Other experimental conditions were the same as in Example 1, except that graphite pads were not used.

[0054] Figure 6 The characterization results are for the twinned copper wafers obtained without using graphite pads. Electron backscatter diffraction characterization shows that the prepared copper wafers have intraplane twins. X-ray diffraction characterization also shows six peaks spaced 60° apart, indicating twin formation.

[0055] Comparative Example 2: Other experimental conditions were the same as in Example 2, except that graphite pads were not used.

[0056] Figure 7 The characterization results are for the twinned copper-nickel wafers obtained without using graphite pads. Electron backscatter diffraction characterization shows that the prepared copper-nickel wafers have intraplane twins. X-ray diffraction characterization also shows six peaks spaced 60° apart, indicating twin formation.

[0057] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0058] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A method for preparing a twinless single-crystal metal wafer, characterized in that, Includes the following steps: 1) A polycrystalline metal thin film of a certain thickness is prepared by sputtering metal atoms onto the surface of a single-crystal sapphire wafer with the crystal plane orientation of c-plane using magnetron sputtering. 2) Place the magnetron sputtered metal / sapphire wafer on a flat heating plate, and place a circular graphite pad of a certain size between the metal wafer and the flat heating plate for annealing; the graphite pad is located directly below the center of the metal wafer, and the diameter of the sapphire wafer is larger than the diameter of the graphite pad; 3) After the metal wafer is annealed, the temperature of the heating plate is reduced to room temperature under the original atmosphere, and a sample is taken to obtain a twin-free single-crystal metal wafer; The graphite pad has a diameter that is 1 / 10 to 1 / 5 the diameter of the sapphire wafer, and a thickness that is 1 to 5 the thickness of the sapphire wafer. The sapphire wafer has a diameter of 1 to 6 inches and a thickness of 200 to 1000 μm. The graphite pad has a diameter of 2 to 100 mm and a thickness of 0.5 to 20 mm. The annealing process involves a temperature of 900~1100℃, a heating rate of 10~200℃ / min, and an annealing time of 0.5-3h.

2. The preparation method according to claim 1, characterized in that, The sapphire wafer has a diameter of 2-6 inches and a thickness of 400-1000 μm; the graphite pad has a diameter of 2-10 mm and a thickness of 0.5-2 mm.

3. The preparation method according to claim 2, characterized in that, The sapphire wafer has a diameter of 2 inches and a thickness of 450 μm; the graphite pad has a diameter of 5 mm and a thickness of 1 mm.

4. The preparation method according to claim 1, characterized in that, The annealing temperature is 1000-1015℃, and the heating rate is 40-60℃ / min when the temperature is 25-500℃ and 20-40℃ / min when the temperature is 500-1015℃.

5. The preparation method according to claim 4, characterized in that, The heating rate is 50℃ / min in the range of 25-500℃ and 30℃ / min in the range of 500-1015℃.

6. The preparation method according to claim 1, characterized in that, During the annealing process, the system pressure is 200-2000 Pa, the gas types are argon and hydrogen, and the gas flow rates are 50-1000 sccm for hydrogen and 200-1000 sccm for argon.

7. The preparation method according to claim 6, characterized in that, The pressure during the annealing process is 600 Pa, the gas types are argon and hydrogen, and the gas flow rates are 500 sccm for hydrogen and 500 sccm for argon.

8. The preparation method according to claim 1, characterized in that, The metal thin film is a Cu thin film or a CuNi alloy thin film; the film thickness is 500-1000 nm; the magnetron sputtering rate is 0.2-1.0 nm / s; and the sputtering temperature is 25-200 ℃.

9. The application of the non-twinned single-crystal metal wafer prepared by the preparation method according to any one of claims 1-8 in the preparation of graphene films.

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