A silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer and a preparation method thereof

Abstract

The present invention provides a silicon-based single-crystalline two-dimensional material epitaxial wafer based on an alumina buffer layer and a preparation method thereof, belonging to the field of semiconductor technology. The method comprises the following steps: preparing an alumina substrate with an active layer; bonding a pre-cleaned silicon-based substrate and the alumina substrate; peeling off the alumina active layer to obtain a composite substrate; and depositing a two-dimensional material on the composite substrate to obtain a silicon-based single-crystalline two-dimensional material based on an alumina buffer layer. By this method, a two-dimensional semiconductor material can be directly epitaxially grown on a silicon-based substrate, avoiding the transfer process of the two-dimensional semiconductor material, which not only reduces the production cost of the two-dimensional semiconductor material but also improves its quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductors, and particularly relates to the technical field of two-dimensional semiconductor material epitaxial wafers. Specifically, it relates to a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer and a preparation method thereof. Background Art

[0002] Two-dimensional semiconductors are considered to be the most competitive channel materials for continuing the miniaturization of device sizes to the 1nm node. However, the high-quality growth of two-dimensional semiconductor materials is severely limited by the substrate. Currently, the large-scale preparation of mature single-crystal two-dimensional semiconductor materials usually uses metals or Al2O3 as substrates and is epitaxially grown by chemical vapor deposition (CVD). Both of these substrates can prepare large-area single crystals. The reported single-crystal graphene can reach 6 inches or even 8 inches, and single-crystal h-BN (hexagonal boron nitride) and molybdenum disulfide can reach 2 - 4 inches. However, it is very difficult to prepare single-crystal two-dimensional semiconductor materials using silicon as a substrate. There is usually an oxide layer on the silicon-based substrate, and this amorphous SiO2 cannot provide a suitable lattice for the nucleation and directional epitaxy of two-dimensional semiconductor materials. Therefore, it is difficult to directly epitaxially grow single-crystal two-dimensional materials on its surface. That is, the large lattice mismatch between the silicon-based substrate and the two-dimensional material and the amorphous oxide layer both result in the difficulty of forming wafer-level single crystals of two-dimensional atomic layers on its surface, thereby severely restricting the application and development of two-dimensional materials in the semiconductor field.

[0003] In order to apply two-dimensional graphene and two-dimensional transition metal sulfides in the silicon-based integration field, it is necessary to first prepare two-dimensional materials on other substrates and then transfer them to silicon-based substrates, and then complete the preparation of highly integrated devices through mature CMOS processes. For two-dimensional materials grown on metal substrates, the currently relatively mature process for transferring them to silicon-based substrates is wet transfer. It etches the metal substrate with a metal etching solution, and then repeatedly cleans the etched surface with acid and alkali solutions to completely remove the metal; then transfers the two-dimensional material to the target silicon-based substrate; then performs process steps such as cleaning, drying, and annealing on its surface, and finally achieves the purpose of transferring the two-dimensional material to the silicon-based substrate. Since two-dimensional materials are only a few atomic layers thick, during the wet transfer process, it is very easy to generate defects such as wrinkles and cracks, which seriously affect the material performance.

[0004] "Large-area integration of two-dimensional materials and their heterostructures by wafer bonding" (https: / / doi.org / 10.1038 / s41467-021-21136-0) discloses a bonding device for supporting two-dimensional materials, which directly bonds two-dimensional materials on a Si substrate using an adhesive. Different bonding parameters are changed for different two-dimensional materials to achieve the silicon-based integration of various two-dimensional materials. In this literature, through material analysis of the whole transferred wafer, the conclusion is that this method can achieve wafer-level silicon-based two-dimensional material integration without damaging the materials; at the same time, a transistor array of the whole wafer is also fabricated to verify the material performance and its uniformity. The wafer-level transfer of two-dimensional materials by the bonding method largely preserves the excellent properties of the materials; however, there are still problems such as the introduction of impurities and the appearance of wrinkles during the removal process of the original substrate, and the very strict precision requirements of two-dimensional materials for automated equipment. Therefore, the cost of developing highly integrated and automated transfer equipment is also very high.

[0005] Large-area single-crystal two-dimensional material epitaxial growth can also be achieved on non-insulating substrates such as sapphire substrates. Furthermore, III-V semiconductors can be continuously grown on two-dimensional materials by van der Waals epitaxy, and high-performance LED devices can be fabricated. Alternatively, by the transfer method, the grown two-dimensional materials are transferred from the sapphire substrate to the silicon-based substrate to realize the integrated application of some optoelectronic devices. However, the heat dissipation performance of the sapphire substrate is much worse than that of the silicon-based substrate or the silicon carbide substrate, and the heat dissipation performance directly affects the performance and lifespan of the device and even the entire chip. Therefore, this technical solution cannot be used in many power devices or video devices.

[0006] Based on the above problems, it is necessary to develop a technology for directly epitaxially growing two-dimensional semiconductor materials on a silicon-based substrate with good heat dissipation performance. Summary of the Invention

[0007] To solve the above problems, the present invention provides a method for preparing a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer. This method can directly epitaxially grow two-dimensional semiconductor materials on a silicon-based substrate, avoiding the process of using material transfer and greatly improving the quality of two-dimensional semiconductor materials.

[0008] Specifically, the present invention adopts the following technical solutions to achieve the above purpose:

[0009] A method for preparing a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer, comprising the following steps:

[0010] S1. Preparation of an alumina substrate with an active layer: Activate the surface of alumina by high-energy ion implantation technology to form an active layer on the alumina surface that is easy to peel off; the crystal form of the alumina is single crystal, and the surface crystal plane is the C plane;

[0011] S2. Bonding of the silicon-based substrate and the alumina substrate: Bond the alumina substrate with the active layer prepared in step S1 to the pre-cleaned silicon-based substrate;

[0012] S3. Peeling off the alumina active layer: Peeling off the alumina substrate with the active layer along the active layer by heat treatment, and then annealing and polishing to obtain a composite substrate bonded by alumina and silicon-based;

[0013] S4. Preparation of single-crystal two-dimensional material: Deposit a two-dimensional material on the surface of the composite substrate to obtain a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer.

[0014] In a preferred embodiment, the distance between the active layer in step S1 and the surface of the alumina substrate for bonding with the silicon-based substrate is 100 - 300 nm.

[0015] In a preferred embodiment, the bonding in step S2 uses surface activation bonding technology or polymer wafer bonding technology.

[0016] In a further preferred embodiment, the surface activation bonding technology uses rapid atom bombardment to activate the surfaces of the alumina substrate with the active layer and the silicon-based substrate. The specific parameters are: the vacuum degree is 1×10 -6 Pa, the bombardment voltage is 1.5 kV, the current is 100 mA, the argon gas flow rate is 10 - 15 sccm, and the radiation time is 20 - 40 s.

[0017] In a further preferred embodiment, the polymer wafer bonding technology uses benzocyclobutene as the bonding material, bakes at 100 °C for 5 minutes, and then heats to 150 - 300 °C in an inert atmosphere and holds for 20 - 60 minutes; the pressure during the bonding process is 300 - 400 kPa, and the vacuum degree is 10 -3 mbar.

[0018] In a further preferred embodiment, the thickness of the coated bonding material is 30 - 50 nm.

[0019] In a further preferred embodiment, the heating rate during heating is 1 - 10 °C / min.

[0020] In a preferred embodiment, the high-energy ion implantation technology uses hydrogen ion and helium ion implantation.

[0021] In a further preferred embodiment, the implantation energy of hydrogen ions is 60 keV, and the implantation dose is 1×10 17 cm -2 .

[0022] In a further preferred embodiment, the implantation energy of helium ions is 75 keV, and the implantation dose is 3.5×10 17 cm -2 .

[0023] In a preferred embodiment, the heat treatment in step S3 refers to maintaining the structure obtained after bonding in step S2 in an inert atmosphere at 500 - 550 °C for 2 h; the annealing refers to annealing the alumina substrate after peeling off the active layer in an inert atmosphere at 800 °C for 2 - 3 h.

[0024] In a preferred embodiment, the two-dimensional material is one of graphene, hexagonal boron nitride, and transition metal sulfides. The transition metal sulfide is preferably molybdenum disulfide.

[0025] The present invention also provides a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer prepared by the method according to any one of the above. When the single-crystal two-dimensional material is graphene or hexagonal boron nitride, its thickness is 0.34 nm; when the single-crystal two-dimensional material is a transition metal sulfide, its thickness is 0.65 - 0.66 nm.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) In the present invention, the method of compounding an alumina substrate and a silicon-based substrate is adopted to achieve the purpose of directly epitaxially growing a two-dimensional material on the silicon-based substrate, avoiding the process of transferring the two-dimensional material, with a simpler technical path and lower industrialization difficulty, which not only reduces the production cost of the two-dimensional material but also improves the quality of the two-dimensional material. (2) Since the heat dissipation performance of the silicon-based substrate is better than that of the sapphire substrate, the thermal conductivity of the composite substrate is also better than that of a single sapphire substrate. (3) In the present invention, the alumina substrate is cut into multiple thin alumina layers, greatly improving the utilization rate of the sapphire substrate, reducing the usage amount of the sapphire substrate, and reducing the raw material cost from another aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flowchart for preparing a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer in Example 1;

[0028] Figure 2 is a flowchart for preparing a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer in Example 4;

[0029] Figure 3 is a schematic structural diagram of a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer prepared in Examples 1 - 3;

[0030] Figure 4 Schematic structural diagram of the silicon-based single-crystal two-dimensional material epitaxial wafer based on the alumina buffer layer prepared in Examples 4-6.

[0031] In the figure: 11, alumina substrate; 12, alumina substrate with an active layer; 13, alumina substrate after the active layer is peeled off; 2, active layer; 3, silicon-based substrate; 31, silicon dioxide layer; 32, silicon-based; 4, single-crystal two-dimensional material layer; 5, adhesive layer. Detailed implementation manners

[0032] The following content describes the technical solutions of the present invention clearly and completely in combination with the embodiments, so that those skilled in the art can fully understand the present invention. Obviously, the described embodiments are only some preferred embodiments of the present invention, rather than all embodiments. Any equivalent transformation or substitution made to the following embodiments by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Example 1

[0034] As Figure 1 shown, this embodiment provides a method for preparing a silicon-based single-crystal graphene epitaxial wafer based on an alumina buffer layer, including the following steps:

[0035] S1. Prepare an alumina substrate with an active layer

[0036] Prepare an alumina substrate 11 with the same size as the silicon-based substrate, with a crystal form of α-Al2O3 and a surface crystal plane of the C plane. Use the high-energy ion implantation technology to implant H / He ions into the surface of the alumina substrate 11. Among them, the implantation energy of hydrogen ions is 60 keV, and the implantation dose is 1×10 17 cm -2 ; the implantation energy of helium ions is 75 keV, and the implantation dose is 3.5×10 17 cm -2 . A peelable active layer 2 is formed at a depth of 200 nm from the surface of the alumina substrate 11 used for bonding with the silicon-based substrate 3, that is, an alumina substrate 12 with an active layer is obtained.

[0037] S2. Bond the silicon-based substrate and the alumina substrate

[0038] Clean the silicon-based substrate 3, and clean the surface of the silicon-based substrate with acetone, isopropyl alcohol, and deionized water respectively to remove the residual surface contaminants. After cleaning, purge the surface of the silicon-based substrate with N2 to make it dry and clean. The structure of the silicon-based substrate 3 is a composite structure with a silicon dioxide layer 31 deposited on the silicon-based 32.

[0039] The alumina substrate with an active layer obtained in step S1 is bonded to the cleaned silicon-based substrate by using a surface-activated bonding (SAB) wafer bonding process. The specific process is as follows: First, the surface of the alumina substrate 12 with an active layer and the surface of the silicon-based substrate 3 are irradiated by Ar rapid atomic bombardment (Ar-FAB) to generate ions on both surfaces. The process parameters are: the vacuum degree is 1×10 -6 Pa, the bombardment voltage is 1.5 kV, the current is 100 mA, the argon gas flow rate is 12 sccm, and the radiation time is 30 s. After bombardment, keep it in a vacuum environment and immediately make the activated surface of the alumina substrate 12 with an active layer and the activated surface of the silicon-based substrate 3 contact the whole surface and apply a pressure of 10 5 N for 10 s to complete the bonding.

[0040] S3. Stripping the alumina active layer

[0041] The structure obtained in step S2 is placed in a nitrogen atmosphere and annealed at 530 °C for 2 h. The alumina substrate 12 with an active layer is peeled along the active layer 2 to obtain the alumina substrate 13 after the active layer is peeled. Then, it is annealed in a nitrogen atmosphere at 800 °C for 2.5 h. The peeled surface is polished by using a standard chemical mechanical polishing (CMP) process to reduce the roughness of the peeled surface, complete the bonding of the C-plane single-crystal Al2O3 thin film on the silicon-based substrate 3, and obtain a composite substrate bonded by the alumina substrate 13 after the active layer is peeled and the silicon-based substrate 3.

[0042] S4. Preparing single-crystal two-dimensional materials

[0043] By using the chemical vapor deposition (CVD) method, methane is used as a precursor, and hydrogen / argon is used as a carrier gas. Keep the gas pressure before growth at 100 mtorr, heat up to 1080 °C, and keep the inlet flow rates of argon and hydrogen at 300 sccm and 10 sccm respectively. At 1080 °C, 20 sccm of methane is introduced and kept for 10 minutes. Subsequently, stop introducing methane and hydrogen, quickly cool down (100 °C / min) to 300 °C, and finally slowly cool down to room temperature to complete the deposition of the single-crystal two-dimensional material layer 4 (single-crystal graphene layer), and obtain the Figure 3 shown silicon-based single-crystal two-dimensional material epitaxial wafer (graphene wafer) based on an alumina buffer layer. The thickness of the single-crystal two-dimensional material layer 4 is 0.34 nm.

[0044] Example 2

[0045] The method for preparing a silicon-based single-crystal hexagonal boron nitride epitaxial wafer based on an alumina buffer layer in this example is basically the same as that in Example 1, except that:

[0046] In step S1, a peelable active layer 2 is formed at a depth of 100 nm from the surface of the alumina substrate 11 for bonding with the silicon-based substrate 3( Figure 1 ), and thus the alumina substrate 12 with the active layer is obtained.

[0047] The process parameters in step S2 are as follows: the vacuum degree is 1×10 -6 Pa, the bombardment voltage is 1.5 kV, the current is 100 mA, the argon gas flow rate is 10 sccm, and the radiation time is 40 s.

[0048] In step S3, the structure obtained in step S2 is placed in a nitrogen atmosphere and annealed at 500 °C for 2 h, and the alumina substrate with the active layer is peeled along the active ion implantation layer. Then, it is annealed in a nitrogen atmosphere at 800 °C for 3 h.

[0049] In step S4, borane ammonia powder is used as a precursor, 300 sccm of argon gas is introduced as a carrier gas, 30 sccm of hydrogen gas is used as a protective gas, and growth is carried out at 1050 °C for 40 minutes. Subsequently, the temperature is rapidly decreased (100 °C / min) to 300 °C, and finally, it is naturally cooled to room temperature to complete the deposition of the single-crystal two-dimensional material layer 4 (single-crystal hexagonal boron nitride layer), and the silicon-based single-crystal two-dimensional material epitaxial wafer (hexagonal boron nitride wafer) based on the alumina buffer layer as shown in Figure 3 is obtained. The thickness of the single-crystal two-dimensional material layer 4 is 0.34 nm.

[0050] Example 3

[0051] In this example, the method for preparing a silicon-based single-crystal molybdenum disulfide epitaxial wafer based on an alumina buffer layer is basically the same as that in Example 1, except that:

[0052] In step S1, a peelable active layer 2 is formed at a depth of 300 nm from the surface of the alumina substrate 11 for bonding with the silicon-based substrate 3( Figure 1 ), and thus the alumina substrate 12 with the active layer is obtained.

[0053] The process parameters in step S2 are as follows: the vacuum degree is 1×10 -6 Pa, the bombardment voltage is 1.5 kV, the current is 100 mA, the argon gas flow rate is 15 sccm, and the radiation time is 20 s.

[0054] In step S3, the structure obtained in step S2 is placed in a nitrogen atmosphere and annealed at 550 °C for 2 h, and the alumina substrate with the active layer is peeled along the active ion implantation layer. Then, it is annealed in a nitrogen atmosphere at 800 °C for 2 h.

[0055] In step S4, sulfur powder is used as the sulfur source and MoO3 is used as the molybdenum source. The sulfur powder is heated to 200 °C and introduced into the reaction chamber through 300 sccm of argon carrier gas. MoO3 is introduced into the reaction chamber through 3 sccm of oxygen and 100 sccm of argon carrier gas, heated to 950 °C, grown at this temperature for 60 minutes, and then slowly cooled (50 °C / min) to room temperature to complete the deposition of the single-crystal two-dimensional material layer 4 (single-crystal molybdenum disulfide layer), obtaining Figure 3 the silicon-based single-crystal two-dimensional material epitaxial wafer (molybdenum disulfide wafer) based on the alumina buffer layer as shown, and the thickness of the single-crystal two-dimensional material layer 4 is 0.65 - 0.66 nm.

[0056] Example 4

[0057] As Figure 2 shown, the difference between the method for preparing the silicon-based single-crystal graphene epitaxial wafer based on the alumina buffer layer in this example and that in Example 1 lies in:

[0058] S2. Bonding the silicon-based substrate and the alumina buffer material

[0059] The silicon-based substrate 3 is cleaned. The surface of the silicon-based substrate is cleaned with acetone, isopropyl alcohol, and deionized water respectively to remove the residual surface contaminants. After cleaning, the surface of the silicon-based substrate is purged with N2 to make it dry and clean.

[0060] The alumina substrate 12 with the active layer obtained in step S1 is bonded to the cleaned silicon-based substrate 3 by using the polymer wafer bonding process. The specific process is as follows: A 40-nm-thick adhesive layer 5 is spin-coated on the silicon-based substrate 3, and the polymer benzocyclobutene (BCB) is used as the adhesive material. After baking at 100 °C for 5 minutes, the solvent evaporation and the curing of the adhesive layer 5 are completed. Subsequently, it is heated in a nitrogen atmosphere with a heating rate of 5 °C / min, the temperature is raised to 200 °C and maintained for 50 minutes, and then taken out after cooling to complete the bonding. The bonding pressure during the bonding process is 350 kPa, and the chamber vacuum degree is 10 -3 mbar.

[0061] The structure of the silicon-based single-crystal two-dimensional material epitaxial wafer based on the alumina buffer layer obtained in this example is as Figure 4 shown.

[0062] Example 5

[0063] The method for preparing the silicon-based single-crystal graphene epitaxial wafer based on the alumina buffer layer in this example is basically the same as that in Example 4, and the difference lies in:

[0064] In step S2, the thickness of the adhesive layer 5 is 30 nm. The heating rate is 1 °C / min, the temperature is raised to 150 °C and maintained for 60 minutes. The bonding pressure during the bonding process is 300 kPa.

[0065] Example 6

[0066] The method for preparing the silicon-based single-crystal graphene epitaxial wafer based on the alumina buffer layer in this example is basically the same as that in Example 4, except that:

[0067] In step S2, the thickness of the bonding layer 5 is 50 nm. The heating rate is 10 °C / min, and the temperature is raised to 300 °C and held for 20 minutes. The bonding pressure during the bonding process is 400 kPa.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. For any person skilled in the art, the present invention can have various changes and modifications. Any simple equivalent changes and modifications made according to the protection scope of the present invention application and the content of the specification shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer, characterized in that, It includes the following steps: S1. Prepare an alumina substrate with an active layer: Activate the alumina surface through high-energy ion implantation technology to form an active layer on the alumina surface that is easy to peel off; the crystal form of the alumina is single crystal, and the surface crystal plane is the C plane; the high-energy ion implantation technology uses hydrogen ions and helium ions for implantation, the implantation energy of the hydrogen ions is 60 keV, and the implantation dose is 1×10 17 cm -2 , the implantation energy of the helium ions is 75 keV, and the implantation dose is 3.5×10 17 cm -2 ; S2. Bond the silicon-based substrate and the alumina substrate: Bond the alumina substrate with an active layer prepared in step S1 to the pre-cleaned silicon-based substrate; the bonding uses surface activation bonding technology or polymer wafer bonding technology; S3. Strip the alumina active layer: Strip the alumina substrate with the active layer along the active layer by means of heat treatment, and then perform annealing and polishing to obtain a composite substrate with alumina and silicon-based bonding; S4. Prepare a single-crystal two-dimensional material: Deposit a two-dimensional material on the surface of the composite substrate to obtain a silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer.

2. The preparation method according to claim 1, characterized in that, The surface activation bonding technology uses fast atom bombardment to activate the surfaces of the alumina substrate with an active layer and the silicon-based substrate. The specific parameters are as follows: the vacuum degree is 1×10 -6 Pa, the bombardment voltage is 1.5 kV, the current is 100 mA, the argon gas flow rate is 10 - 15 sccm, and the radiation time is 20 - 40 s.

3. The preparation method according to claim 1, characterized in that, The polymer wafer bonding technology uses benzocyclobutene as the bonding material, bakes at 100 °C for 5 minutes, and then heats to 150 - 300 °C in an inert atmosphere and holds for 20 - 60 minutes; the pressure during the bonding process is 300 - 400 kPa, and the vacuum degree is 10 -3 mbar.

4. The preparation method according to claim 3, wherein, The heating rate during heating is 1-10 °C / min.

5. The preparation method according to claim 1, characterized in that, The heat treatment in step S3 refers to placing the structure obtained after bonding in step S2 in an inert atmosphere at 500-550 °C for 2 h; the annealing refers to annealing the alumina substrate after stripping the active layer in an inert atmosphere at 800 °C for 2-3 h.

6. The preparation method according to claim 1, wherein The two-dimensional material is one of graphene, hexagonal boron nitride, and transition metal sulfides.

7. A silicon-based single-crystal two-dimensional material epitaxial wafer based on an alumina buffer layer prepared by the preparation method according to any one of claims 1-6.

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