A method for controlling the wrinkle orientation of graphene single-crystal wafers

Abstract

This invention discloses a method for controlling the wrinkle orientation of graphene single-crystal wafers. The method includes the following steps: A single-crystal sapphire substrate with a chamfered angle on its C-plane and A-plane is pretreated by high-temperature annealing. A copper thin film is deposited on its surface using a high-purity copper target via magnetron sputtering. A copper thin film / chamfered sapphire wafer constructed by magnetron sputtering is placed as a graphene growth substrate in a CVD tube furnace. After high-temperature annealing, graphene is grown on the surface of the single-crystal sapphire substrate. After graphene growth, while maintaining the graphene growth atmosphere, the temperature of the CVD tube furnace system is slowly reduced to allow the graphene film to fully release stress, forming a graphene wrinkle array. The temperature of the CVD tube furnace is then reduced to room temperature, and a sample is taken to obtain a graphene single-crystal wafer with uniform wrinkle orientation. This invention is of great significance for promoting the development of graphene single-crystal wafer materials in novel electronic and optoelectronic devices and in the field of remote epitaxial substrates.

Description

Technical Field

[0001] This invention belongs to the field of graphene film preparation, specifically relating to a method for controlling the orientation of wrinkles in graphene single-crystal wafers. Background Technology

[0002] Single-crystal wafers are a crucial foundation of the semiconductor industry. In recent years, the emergence of two-dimensional nanomaterials, represented by graphene, has brought new hope for the continuation of Moore's Law. As a representative of this field, the controllable preparation of high-quality graphene single-crystal wafers via chemical vapor deposition (CVD) is a vital prerequisite for the construction of high-performance electronic devices and the manufacturing of large-scale integrated circuits. However, during CVD preparation, significant thermal mismatch stress exists between graphene and the growing metal substrate, leading to severe wrinkling on the graphene surface after cooling. An ideal solution has yet to be found. Wrinkles, as a type of line defect structure, significantly reduce the excellent intrinsic mechanical, electrical, and thermal properties of graphene and affect the yield of subsequent applications. However, effectively controlling and eliminating wrinkles faces numerous challenges: on the one hand, the complex surface morphology of the metal substrate results in random distribution of graphene wrinkle orientation, making effective control difficult; on the other hand, the high CVD growth temperature of graphene and its tight bonding with the metal substrate further exacerbate the thermal mismatch problem and stress transfer, making it difficult to fundamentally eliminate graphene wrinkles.

[0003] Specifically, regarding graphene single-crystal wafer fabrication systems, although current literature indicates that highly flat Cu(111) / sapphire single-crystal wafer substrates with good single-crystal properties can suppress wrinkle formation to some extent through strong bonding with graphene, in reality, Cu(111) inevitably undergoes surface reconstruction and forms different step structures. This causes the graphene to be affected by the surface undulations of the substrate during the cooling stage, ultimately forming a triangular network structure with an angle of approximately 120°. Under the influence of this interwoven wrinkled network, the proportion of flat regions that best reflect the intrinsic properties of graphene is significantly reduced, typically only on the order of tens of micrometers, severely limiting the usable area of ​​graphene single-crystal wafers. Therefore, effectively utilizing the interaction force between the growth substrate and graphene, and fully leveraging the substrate's role in regulating the distribution of graphene wrinkles, transforming the originally dense and random wrinkled network into a directional, adjustable-spacing wrinkled array, thereby increasing the proportion of flat regions in graphene and the yield of subsequent devices, has significant application value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling the wrinkle orientation of graphene single-crystal wafers. The method uses obliquely cut sapphire single-crystal wafer substrates with different angles between the C-plane and the A-plane. By utilizing the parallel steps on the surface of the substrate parallel to the <10-10> cut edge, the copper thin film sputtered by magnetron sputtering is prompted to replicate the step structure of the sapphire substrate during high-temperature annealing. This introduces periodic parallel steps on the surface of the Cu(111) growth substrate, restricts the stress release of graphene along the direction perpendicular to the steps, and ultimately transforms the original disordered triangular network of graphene wrinkles into a co-oriented wrinkle array.

[0005] The method of this invention is of great significance for investigating the stress release behavior and wrinkle formation process of graphene films. Furthermore, this method enables the controllable fabrication of large-area wrinkle-free graphene single-crystal strips and co-oriented graphene wrinkled arrays, and has significant application prospects in the construction of large-area electronic and optoelectronic devices, as well as the remote epitaxial growth of III-V semiconductor materials.

[0006] The method for controlling the wrinkle orientation of graphene single-crystal wafers provided by this invention includes the following steps:

[0007] S1. After high-temperature annealing pretreatment, a single-crystal sapphire substrate with a C-plane biased to an A-plane with a slanted cutting angle is deposited on its surface by magnetron sputtering using a high-purity copper target.

[0008] S2. A copper thin film / oblique-cut sapphire wafer constructed by the magnetron sputtering method is placed in a CVD tube furnace as a graphene growth substrate. After high-temperature annealing, graphene is grown on the surface of the single-crystal sapphire substrate.

[0009] S3. After the graphene growth is completed, under the condition of maintaining the graphene growth atmosphere, the temperature of the CVD tube furnace system is slowly reduced to allow the graphene film to fully release stress and form a graphene wrinkle array.

[0010] S4. Lower the temperature of the CVD tube furnace to room temperature, and after sampling, a graphene single crystal wafer with uniform wrinkle orientation can be obtained.

[0011] In the method of the present invention, the bevel angle of the single crystal sapphire substrate is less than 4 degrees, such as 1 degree, 2 degrees and 4 degrees.

[0012] In the method of the present invention, the size of the single crystal sapphire substrate is 2-6 inches, preferably 4 inches and 6 inches; the thickness of the single crystal sapphire substrate is 400-1200 μm, preferably 650 μm and 1000 μm.

[0013] In the method of the present invention, the conditions for the high-temperature annealing pretreatment in step S1 are as follows:

[0014] The atmosphere is a pure oxygen atmosphere at normal pressure, the temperature is 1000-1100℃, and the annealing time is 3-12h.

[0015] In the method of this invention, the conditions for magnetron sputtering are as follows:

[0016] The substrate temperature is 120-200℃; the deposition rate is 0.2-1.0nm / s.

[0017] In the method of the present invention, the deposition thickness of the copper thin film is 300-1000 nm.

[0018] In the method of the present invention, the conditions for high-temperature annealing in step S2 are as follows:

[0019] The annealing temperature is 970-1020℃; the system pressure during the annealing process is 65-100kPa; the annealing time is 10-60min; the atmosphere during the annealing process is argon and hydrogen, with gas flow rates of 20-200sccm for hydrogen and 200-3000sccm for argon.

[0020] In the method of the present invention, in step S2, the carbon source for growing the graphene is methane diluted with argon gas at a flow rate of 10-50 sccm; the growth time of the graphene is 6-26 h.

[0021] In the method of the present invention, in step S3, the cooling rate after the graphene growth is completed is 2-200℃ / min.

[0022] The graphene single-crystal wafer folded array with consistent orientation prepared by the method of this invention is also within the scope of protection of this invention.

[0023] The method of this invention uses obliquely cut sapphire to control the surface morphology of annealed copper thin films, and utilizes the stepped structure of the copper substrate to achieve the directional alignment and controllable spacing of wrinkles in graphene single-crystal wafers. This method is of great significance for promoting the development of graphene single-crystal wafer materials in novel electronic and optoelectronic devices, as well as their application in remote epitaxial substrates. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the adjustment of graphene wrinkle orientation using obliquely cut sapphire.

[0025] Figure 2 The graphene wrinkle size is as shown in Examples 1-3.

[0026] Figure 3 The results are optical and Raman characterizations of the sample transferred to a Si / SiO2 substrate in Example 2.

[0027] Figure 4 This is the atomic force microscopy characterization of the graphene wrinkle array in Example 2.

[0028] Figure 5 This is the graphene wrinkle morphology of Comparative Example 1. Detailed Implementation

[0029] 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.

[0030] In the following examples and comparative examples, CA-1°, 2°, and 4° beveled sapphire refer to the angles of offset from the C-plane (0001) to the A-plane (11-20) of the sapphire during the wafer slicing process, which are 1°, 2°, and 4° respectively.

[0031] Example 1: Growth and wrinkle orientation control of graphene films on Cu / CA-1° ​​obliquely cut sapphire.

[0032] Step 1: After high-temperature oxygen annealing pretreatment, a CA-1° ​​sapphire single crystal wafer with a diameter of 4 inches and a thickness of 650 μm is placed in a magnetron sputtering chamber. After heating the substrate to 150°C, a 500 nm copper thin film is deposited at a sputtering rate of 0.5 nm / s.

[0033] Step 2: Place the copper / sapphire wafer in the CVD tube furnace system, pump the system to low pressure with a vacuum pump, fill it with argon gas to atmospheric pressure, and then introduce 2200 sccm of argon gas and 40 sccm of hydrogen gas. Anneal at 1000℃ for 45 min to prepare Cu(111) single crystal wafer.

[0034] Step 3: Pass 18 sccm of diluted methane (0.1% argon dilution) into the CVD tube furnace to grow graphene single crystal wafers for 9 hours;

[0035] Step 4: Stop heating, maintain the existing gas flow, and cool the CVD system to room temperature. Sampling will yield a graphene single-crystal wafer with uniformly oriented wrinkles. The wrinkle width is approximately 100 nm, and the height is approximately 2 nm.

[0036] Example 2: Growth and wrinkle orientation control of graphene films on Cu / CA-2° obliquely cut sapphire.

[0037] Step 1: After high-temperature oxygen annealing pretreatment, a CA-2° sapphire single crystal wafer with a diameter of 4 inches and a thickness of 650 μm is placed in a magnetron sputtering chamber. After heating the substrate to 150°C, a 500 nm copper thin film is deposited at a sputtering rate of 0.5 nm / s.

[0038] Step 2: Place the copper / sapphire wafer in the CVD tube furnace system, pump the system to low pressure with a vacuum pump, fill it with argon gas to atmospheric pressure, and then introduce 2200 sccm of argon gas and 40 sccm of hydrogen gas. Anneal at 1000℃ for 45 min to prepare Cu(111) single crystal wafer.

[0039] Step 3: Pass 18 sccm of diluted methane (0.1% argon dilution) into the CVD tube furnace to grow graphene single crystal wafers for 9 hours;

[0040] Step 4: Stop heating, maintain the existing gas flow, and cool the CVD system to room temperature. Sampling will yield a graphene single-crystal wafer with uniformly oriented wrinkles. The wrinkle width is approximately 150 nm, and the height is approximately 10 nm.

[0041] Example 3: Growth and wrinkle orientation control of graphene films on Cu / CA-4° beveled sapphire.

[0042] Step 1: After high-temperature oxygen annealing pretreatment, a CA-4° sapphire single crystal wafer with a diameter of 4 inches and a thickness of 650 μm is placed in a magnetron sputtering chamber. After heating the substrate to 150°C, a 500 nm copper thin film is deposited at a sputtering rate of 0.5 nm / s.

[0043] Step 2: Place the copper / sapphire wafer in the CVD tube furnace system, pump the system to low pressure with a vacuum pump, fill it with argon gas to atmospheric pressure, and then introduce 2200 sccm of argon gas and 40 sccm of hydrogen gas. Anneal at 1000℃ for 45 min to prepare Cu(111) single crystal wafer.

[0044] Step 3: Pass 18 sccm of diluted methane (0.1% argon dilution) into the CVD tube furnace to grow graphene single crystal wafers for 9 hours;

[0045] Step 4: Stop heating, maintain the existing gas flow, and cool the CVD system to room temperature. Sampling will yield a graphene single-crystal wafer with uniformly oriented wrinkles. The wrinkle width is approximately 200 nm, and the height is approximately 20 nm.

[0046] Comparative Example 1: Observation of the growth and wrinkle orientation of graphene films on Cu / C sapphire surfaces

[0047] Step 1: After pre-treatment with high-temperature oxygen annealing, a 4-inch diameter, 650μm thick C-plane sapphire single crystal wafer is placed in a magnetron sputtering chamber. After heating the substrate to 150°C, a 500nm copper thin film is deposited at a sputtering rate of 0.5nm / s.

[0048] Step 2: Place the copper / sapphire wafer in the CVD tube furnace system, pump the system to low pressure with a vacuum pump, fill it with argon gas to atmospheric pressure, and then introduce 2200 sccm of argon gas and 40 sccm of hydrogen gas. Anneal at 1000℃ for 45 min to prepare Cu(111) single crystal wafer.

[0049] Step 3: Pass 18 sccm of diluted methane (0.1% argon dilution) into the CVD tube furnace to grow graphene single crystal wafers for 9 hours;

[0050] Step 4: Stop heating, maintain the existing gas flow, and cool the CVD system to room temperature. Samples can then be taken to obtain graphene single-crystal wafers. Observation of the graphene wrinkle orientation using optical and atomic force microscopy revealed that the graphene wrinkles exhibit a nearly 120° triangular network structure.

[0051] Figure 1 This diagram illustrates the orientation of graphene wrinkles adjusted by beveled sapphire. On a conventional Cu / C sapphire wafer, the graphene wrinkles exhibit a nearly 120° triangular network structure. Using beveled sapphire with a stepped structure as a sputtering substrate introduces a periodic stepped structure onto the surface of the Cu(111) film after high-temperature annealing, causing the graphene film to form wrinkles in a single direction perpendicular to the copper steps.

[0052] Figure 2 The graphene wrinkle dimensions are shown in Examples 1-3 of this invention. As the bevel angle increases, the width and height of the graphene wrinkles also increase.

[0053] Figure 3 The optical and Raman characterization results for the graphene transferred to a Si / SiO2 substrate in Example 2 of this invention are shown. Optical microscope images reveal that the spacing between graphene wrinkles on the obliquely cut substrate is on the order of hundreds of micrometers, and no fine wrinkles are present between the wrinkles. Raman spectral comparison results show that the graphene film in the wrinkle-free region has higher quality and no D peak. In the wrinkled region, due to graphene folding, the 2D peak is significantly reduced, while a weak D peak remains. Raman surface scanning of the wrinkle-sensitive graphene G peak reveals a uniform color distribution, further verifying the absence of fine wrinkles between the wrinkles.

[0054] Figure 4 The atomic force microscopy characterization of the graphene wrinkle array in Embodiment 2 of the present invention shows that the graphene wrinkles are large-area wrinkle-free graphene single-crystal films.

[0055] Figure 5 The graphene wrinkle morphology is shown in Comparative Example 1. The morphology distribution of graphene wrinkles is greatly affected by the substrate. On the Cu / C sapphire wafer surface, graphene wrinkles generally exhibit a triangular network structure with a radius of nearly 120°.

[0056] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0057] 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 controlling the wrinkle orientation of a graphene single-crystal wafer, comprising the following steps: S1. After high-temperature annealing pretreatment, a single-crystal sapphire substrate with a C-plane biased to an A-plane with a slanted cutting angle is deposited on its surface by magnetron sputtering using a high-purity copper target. S2. A copper thin film / oblique-cut sapphire wafer constructed by the magnetron sputtering method is placed in a CVD tube furnace as a graphene growth substrate. After high-temperature annealing, graphene is grown on the surface of the single-crystal sapphire substrate. S3. After the graphene growth is completed, under the condition of maintaining the graphene growth atmosphere, the temperature of the CVD tube furnace system is slowly reduced to allow the graphene film to fully release stress and form a graphene wrinkle array. S4. Lower the temperature of the CVD tube furnace to room temperature, and after sampling, a graphene single crystal wafer with uniform wrinkle orientation can be obtained.

2. The method according to claim 1, characterized in that: The bevel angle of the single-crystal sapphire substrate is less than 4 degrees.

3. The method according to claim 1 or 2, characterized in that: The single-crystal sapphire substrate has a size of 2-6 inches and a thickness of 400-1200 μm.

4. The method according to any one of claims 1-3, characterized in that: In step S1, the conditions for the high-temperature annealing pretreatment are as follows: The atmosphere is a pure oxygen atmosphere at normal pressure, the temperature is 1000-1100℃, and the annealing time is 3-12h.

5. The method according to any one of claims 1-4, characterized in that: The conditions for magnetron sputtering are as follows: The substrate temperature is 120-200℃; the deposition rate is 0.2-1.0nm / s.

6. The method according to any one of claims 1-5, characterized in that: The copper thin film has a deposition thickness of 300-1000 nm.

7. The method according to any one of claims 1-6, characterized in that: In step S2, the conditions for high-temperature annealing are as follows: The annealing temperature is 970-1020℃; the system pressure during the annealing process is 65-100kPa; the annealing time is 10-60min; the atmosphere during the annealing process is argon and hydrogen, and the gas flow rate is 20-200sccm for hydrogen and 200-3000sccm for argon.

8. The method according to any one of claims 1-7, characterized in that: In step S2, the carbon source for growing the graphene is methane diluted with argon gas at a flow rate of 10-50 sccm; the growth time of the graphene is 6-26 h.

9. The method according to any one of claims 1-8, characterized in that: In step S3, the cooling rate after the graphene growth is completed is 2-200℃ / min.

10. A graphene single-crystal wafer folded array with consistent orientation prepared by the method of any one of claims 1-9.

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