Method for rapidly and nondestructively cleaning and transferring wafer-level two-dimensional material and device construction method

Abstract

The invention discloses a method for rapidly, losslessly and cleanly transferring a wafer-level two-dimensional material, which utilizes strong binding force between modifier molecules and a growth substrate to form covalent bonds and construct a stable and regular self-assembled monomolecular layer, and the monomolecular layer effectively reduces the surface energy of the growth substrate, so that the surface energy of the growth substrate is effectively reduced. The interaction force between the growth substrate and the two-dimensional material which are in close contact originally is obviously weakened, and the growth substrate is convenient to remove; secondly, PDMS with low viscosity is used as a transfer medium; the low-viscosity PDMS not only can provide proper adhesive force and ensure that the two-dimensional material cannot fall off due to insufficient adhesive force in the transfer process, but also cannot be damaged or remained due to too strong adhesive force; and after the transfer is completed, the low-viscosity PDMS is more easily stripped from the target substrate, so that residues and bubbles are reduced, transfer defects are reduced, and the original electrical and optical characteristics of the two-dimensional material are effectively maintained.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor technology, and in particular relates to a method for quickly and non-destructively cleaning and transferring wafer-level two-dimensional materials. Background Art

[0002] Two-dimensional materials play an important role in many fields such as chip computing, superconductivity, the Internet of Things, and wearable devices due to their excellent optoelectronic properties, adjustable band structure, and atomic-level thickness. In the field of optoelectronic devices, transistors and their logic circuits built on the basis of two-dimensional materials have the advantages of high computing efficiency, high responsiveness, and ultra-lightness. Therefore, two-dimensional field-effect transistors have become one of the most promising candidates to replace silicon-based semiconductor devices. In the process of large-scale application of two-dimensional materials, researchers usually need to rely on transfer processes to realize the design and construction of devices. However, the immature transfer process has severely restricted the development of the two-dimensional semiconductor industry.

[0003] There are two main types of transfer schemes that have been reported so far: the first is wet transfer, including PMMA (polymethyl methacrylate) assisted transfer and surface energy assisted transfer; the second is dry transfer, including viscoelastic dry transfer and van der Waals force pickup transfer. However, these methods all have certain limitations. In wet transfer, acidic and alkaline etchants can seriously damage the crystallization quality of the material, thereby affecting the performance of optoelectronic devices. Existing dry transfer processes are generally only applicable to top-down mechanical stripping preparation methods, which limits their large-scale application. In addition, these two methods have slow transfer speeds and low yields. After transfer, wrinkles, breakage, and transfer medium residues are prone to form on the surface of the material, which seriously affects the performance of two-dimensional optoelectronic devices.

[0004] Moreover, when applying the above transfer method, the two-dimensional material often has a strong chemical or physical adsorption effect with the substrate during the growth process, which makes it difficult to completely peel the two-dimensional material from the substrate, which can easily cause material damage or destroy the structural integrity of the material. Therefore, in order to address the above problems, it is of great significance to develop a method for fast, non-destructive and clean transfer of wafer-level two-dimensional materials. Summary of the invention

[0005] In view of this, the present invention discloses a method for quickly and non-destructively cleaning and transferring wafer-level two-dimensional materials. The method has the advantages of fast transfer speed, high surface cleanliness, good transfer integrity, and high crystal quality after transfer.

[0006] To this end, the present invention adopts the following technical solutions: A method for rapid and non-destructive clean transfer of wafer-level two-dimensional materials comprises the following steps: 1) First, the growth substrate is treated with oxygen plasma, and then methyltrichlorosilane is drop-coated on the surface of the growth substrate and transferred to an environment with a pressure of 0.1-0.2 MPa and a temperature of 100-120° C. for modification for 1-2 hours. After being taken out, ultrasonic washing is performed in chloroform, isopropanol, and deionized water for 10-15 minutes, and the substrate is placed on a hot plate at 100-120° C. for drying and annealing for 5-15 minutes, and cooled to room temperature to obtain a methyltrichlorosilane-modified growth substrate. The treatment pressure of the oxygen plasma is 0.2-0.6 mbar, the treatment power is 40-60 W, and the treatment time is 1-5 minutes. The growth substrate is any one of quartz, sapphire or silicon wafer. 2) growing a two-dimensional material on the methyltrichlorosilane modified growth substrate prepared in step 1) by a CVD method to obtain a composite structure of a two-dimensional material / growth substrate; the two-dimensional material is any one of molybdenum disulfide, molybdenum diselenide, tungsten sulfide or tungsten selenide; 3) Mix the main agent and curing agent of PDMS in a mass ratio of 5:1-8:1, then drop the mixture on the silicon wafer, cure it at 60-90°C for 10-60 minutes, and slowly peel it off to obtain a PDMS film; 4) flatly laminating the PDMS film prepared in step 3) onto the composite structure prepared in step 2) to obtain a composite structure of PDMS / two-dimensional material / growth substrate; 5) immersing the composite structure prepared in step 4) in deionized water, removing the growth substrate, and obtaining a composite structure of PDMS / two-dimensional material; 6) Flattening the composite structure prepared in step 5) onto a target substrate to obtain a composite structure of PDMS / two-dimensional material / target substrate; the target substrate is any one of a silicon wafer, a heavily doped silicon wafer, quartz or sapphire; 7) Physically peeling off the PDMS film in the composite structure prepared in step 6) to obtain a composite structure of two-dimensional material / target substrate.

[0007] The core mechanism of wafer-level two-dimensional material transfer of the present invention is as follows: First, the rapid, non-destructive and clean transfer of wafer-level two-dimensional materials is achieved by modifying the growth substrate. Specifically, this method uses the strong binding force between the modifier molecules and the growth substrate to form covalent bonds and construct a stable and regular self-assembled monolayer. The existence of this monolayer effectively reduces the surface energy of the growth substrate, significantly weakening the interaction force between the growth substrate and the two-dimensional material that were originally in close contact, making it easier to remove the growth substrate. Secondly, the present invention selects low-viscosity PDMS as the transfer medium. Low-viscosity PDMS can not only provide appropriate adhesion to ensure that the two-dimensional material will not fall off due to insufficient adhesion during the transfer process, nor will it be damaged or leave residue due to excessive adhesion; and after the transfer is completed, the low-viscosity PDMS is easier to peel off from the target substrate, thereby reducing the generation of residues and bubbles, reducing transfer defects, and effectively maintaining the original electrical, optical and other properties of the two-dimensional material. In contrast, the interaction between high-viscosity PDMS and the two-dimensional material is too strong, resulting in material breakage and cracking, and high-viscosity PDMS is more difficult to completely remove, and is prone to leaving residues and bubbles, ultimately reducing device performance.

[0008] The beneficial effects of the present invention are as follows: (1) The method of the present invention has a fast transfer speed, and the entire transfer process takes less than 30 seconds, which greatly saves time costs and improves production efficiency; (2) The method of the present invention can achieve extremely high surface cleanliness. Since only deionized water is used as the transfer medium during the entire transfer process, and PDMS has low viscosity and few residual impurities, it ensures that the material surface reaches excellent cleanliness standards and prevents the introduction of other impurities. It is particularly suitable for application scenarios with extremely high requirements for surface purity. After the transfer, there are no bubbles on the interface and the average roughness is as low as 0.27nm; (3) The method of the present invention has a high transfer integrity. The transfer integrity of 5*5 cm wafer-level two-dimensional materials is about 99%, which can effectively avoid material damage or performance degradation during the transfer process, thereby maintaining the original properties of the two-dimensional material; (4) The method of the present invention can effectively maintain the crystal quality of wafer-level two-dimensional materials after transfer. In the key step of peeling, by introducing a modification layer, the integrity of the crystal structure during the transfer process is ensured while retaining the original growth epitaxial relationship, achieving higher crystallinity and flatness. Compared with traditional methods, this technology effectively avoids common defects and damage problems; (5) The optoelectronic devices prepared by the method of the present invention exhibit excellent electrical properties. Compared with the traditional method, the method of the present invention can effectively avoid the introduction of wrinkles, damage and residues, ensure the high quality of the two-dimensional material and the contact surface, and thus significantly improve the overall performance of the device. It has excellent performance in terms of response speed, stability and energy consumption, laying a solid foundation for the development of high-performance optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG1 is a flow chart of the method for rapid and non-destructive clean transfer of wafer-level two-dimensional materials of the present invention.

[0010] Figure 2 Optical microscope images after transfer; (a) Optical microscope image after transfer by Example 1. The inset is the optical image after transfer, (b) Optical microscope image after transfer by Comparative Example 1.

[0011] FIG3 Atomic force microscope (AFM) images after transfer; (a) AFM image after transfer through Example 1, (b) AFM image after transfer through Comparative Example 1.

[0012] FIG4 is a scanning electron microscope (SEM) image after transfer; (a) a scanning electron microscope image after transfer through Example 1, (b) a scanning electron microscope image after transfer through Comparative Example 1.

[0013] FIG. 5 is a Raman spectrum diagram of Example 1 and Comparative Example 1 after transfer.

[0014] FIG6 is a photoluminescence spectrum diagram of Example 1 and Comparative Example 1 after transfer.

[0015] Figure 7 Transfer curves of MoS2 field effect transistors prepared in Example 1 and Comparative Example 1, V ds =1V. DETAILED DESCRIPTION

[0016] The present invention is described in detail below through specific embodiments.

[0017] Example 1 like Figure 1 As shown, the transfer method of the molybdenum disulfide semiconductor layer in this embodiment is as follows: (1) A 5*5 cm sapphire substrate was used as the growth substrate, and the sapphire substrate was treated with oxygen plasma. The treatment pressure was 0.4 mbar, the treatment power was 50 W, and the treatment time was 5 minutes. The methyltrichlorosilane modifier molecules were adhered to the surface of the treated sapphire substrate by drop coating or dip coating. The treated sapphire substrate was then placed in an oven to be modified with methyltrichlorosilane. The vacuum pressure of the oven was 0.1 MPa, the modification temperature was 120°C, and the modification time was 120 minutes. The modified sapphire substrate was ultrasonically washed in chloroform, isopropanol, and deionized water for 10 minutes in turn, and then placed on a hot plate set at 120°C for drying and annealing for 10 minutes, and then cooled to room temperature. (2) growing a molybdenum disulfide semiconductor layer on the modified sapphire substrate prepared in step (1) by a CVD method; The growth process is as follows: a tube furnace is used, S (sulfur) powder and MoO3 (molybdenum trioxide) powder are used as growth precursors, the mass ratio is 8:1 to 10:1, and the temperature range is 150-250°C; the growth substrate is placed in the temperature range of 700-1000°C, Ar / O2 is used as carrier gas, the Ar flow rate is 90-120sccm, the O2 flow rate is 1-5sccm, the growth pressure is 1-10torr, and the reaction time is 10-40min; (3) The main agent and curing agent of PDMS (Dow Corning SYLGARD 184) were mixed in a mass ratio of 8:1, and then the mixture was drop-coated on a silicon wafer, cured at 90 °C for 10 min, and slowly peeled off to obtain a PDMS film; (4) flatly laminating the PDMS prepared in step (3) to the surface of the molybdenum disulfide semiconductor layer grown and prepared in step (2) to obtain a composite structure of PDMS / molybdenum disulfide / sapphire; (5) placing the composite structure obtained in step (4) in deionized water, and slightly shaking the composite structure with a small amplitude to allow water molecules to enter the interface gap between the two-dimensional material and the growth substrate. Using tweezers to lift the edge of the growth substrate, the water molecules fully penetrate into the interface between the two-dimensional material and the growth substrate, causing the sapphire to automatically detach, thereby obtaining a PDMS / molybdenum disulfide composite structure; (6) The structure obtained in step (5) is evenly bonded to the target substrate (a 500 μm thick heavily doped silicon wafer with 300 nm silicon dioxide), and is slowly lowered from one end to prevent the air between the PDMS and the target substrate from being trapped in the middle and generating bubbles due to excessive transfer speed or uneven bonding pressure. Slight pressure is applied with tweezers to ensure full contact between the two-dimensional material and the target substrate, and then allowed to stand for 1-2 hours to allow sufficient time for the PDMS, the two-dimensional material, and the target substrate to release stress and establish a state of minimum energy, so that a uniform and complete van der Waals interaction is formed between the two-dimensional material and the target substrate, thereby obtaining a composite structure of PDMS / molybdenum disulfide / target substrate; 7) Slowly peeling off the PDMS film in the composite structure prepared in step 6) with tweezers to obtain a composite structure of two-dimensional material / target substrate; 8) The composite structure prepared in step 7) was deposited by thermal deposition (evaporation rate of 0.1 Å / s, vacuum degree of 4×10 -4 Pa) Use a metal mask to deposit 20nm of gold as source and drain electrodes on the molybdenum disulfide semiconductor layer, use 500 µm thick heavily doped silicon as the gate, and 300 nm silicon dioxide as the dielectric layer to obtain a molybdenum disulfide field effect transistor device.

[0018] Comparative Example 1 (1) A MoS2 semiconductor layer was grown on an unmodified 5×5 cm sapphire substrate by CVD. (2) The main agent and curing agent of PDMS (Dow Corning SYLGARD 184) were mixed in a mass ratio of 10:1, and then the mixture was drop-coated on a silicon wafer, cured at 90 °C for 10 min, and slowly peeled off to obtain a PDMS film; (3) flatly bonding the PDMS obtained in step (2) to the surface of the grown molybdenum disulfide to obtain a composite structure of PDMS / molybdenum disulfide / sapphire; (4) placing the composite structure obtained in step (3) in deionized water to separate the sapphire and obtain a PDMS / molybdenum disulfide composite structure; (5) The structure obtained in step (4) is evenly bonded to a 500 μm thick heavily doped silicon wafer with 300 nm of silicon dioxide to obtain a PDMS / molybdenum disulfide / silicon wafer structure; (6) slowly peeling off the PDMS in the structure obtained in step (5) from the silicon wafer to obtain a molybdenum disulfide / silicon wafer structure; (7) The composite structure prepared in step (6) is subjected to a thermal deposition method using a metal mask to deposit 20 nm of gold as source and drain electrodes on the molybdenum disulfide semiconductor layer, with 500 µm thick heavily doped silicon as a gate and 300 nm silicon dioxide as a dielectric layer to obtain a molybdenum disulfide field effect transistor device.

[0019] The following further illustrates the method of the present invention for achieving rapid, non-destructive and clean transfer of wafer-level two-dimensional materials using a growth substrate modification layer and low-viscosity PDMS by analyzing the surface morphology, crystal quality and electrical properties of the embodiments and comparative examples.

[0020] 1. Surface morphology characterization To verify the integrity and cleanliness of the transferred MoS2, 3D confocal microscopy ( Figure 2 ) The morphology of the molybdenum disulfide transferred on the silicon wafer was observed. The optical microscope image of the molybdenum disulfide transferred in Example 1 is as follows: Figure 2 a, wherein the top illustration is the optical image after transfer, and the optical microscope image of molybdenum disulfide transferred in comparative example 1 is as follows Figure 2 As shown in b. Figure 2 It can be observed that the surface of the molybdenum disulfide transferred by the growth substrate modification layer and low-viscosity PDMS in Example 1 is smooth, has fewer defects such as pores, cracks, and fissures, and has high transfer integrity.

[0021] Using atomic force microscopy ( Figure 3 ) and scanning electron microscopy ( Figure 4 ) The morphology of the molybdenum disulfide transferred on the silicon wafer was further characterized. The image of the molybdenum disulfide transferred in Example 1 is as follows Figure 3 a, 4a, the image of molybdenum disulfide transferred in comparative example 1 is as follows Figure 3b, as shown in 4b. Figure 3 and Figure 4 It can be observed that the surface of molybdenum disulfide transferred by the growth substrate modification layer and low-viscosity PDMS in Example 1 is flatter, with an average roughness of 0.27 nm, no isolated bright spots or dark spots, fewer bubbles and residues, better flatness, and high transfer cleanliness.

[0022] 2. Crystallization quality characterization In order to verify the quality of the transferred MoS2 crystals, Raman spectroscopy was used ( Figure 5 ) and photoluminescence spectra ( Figure 6 ) to compare the crystalline quality of MoS2 transferred onto silicon wafers. Figure 5 and Figure 6 It can be observed that in the decoupling transfer method shown in Example 1, 1 2g The peak is closer to the intrinsic position 383cm -1 , while A 1g The peak is closer to the theoretical value of 408 cm -1 , the spectral intensity is stronger, and the half-peak width of the photoluminescence fingerprint peak is narrower. It is observed that the molybdenum disulfide transferred by the growth substrate modification layer and low-viscosity PDMS in Example 1 reduces crystal stress, defects and impurities, and the crystals are more regular and the crystallization quality is higher.

[0023] 3. Electrical performance characterization In order to verify the electrical performance of the optoelectronic devices prepared by different transfer methods, the electrical performance of the molybdenum disulfide field effect transistor prepared in Example 1 and the molybdenum disulfide field effect transistor prepared in Comparative Example 1 were tested. The transfer characteristic curves of the two are shown in FIG. Figure 7 As shown. Figure 7 It can be seen that the electrical performance of the molybdenum disulfide field effect transistor prepared by the growth substrate modification layer and low-viscosity PDMS in Example 1 is significantly stronger. It can be found that there is less internal damage due to stress during the transfer process, and the complete internal structure can ensure the continuity and stability of the electron transmission path, thereby ensuring the high performance of the molybdenum disulfide field effect transistor.

Claims

1. A method for rapid and non-destructive clean transfer of wafer-level two-dimensional materials, characterized in that: The following steps are involved: 1) First, the growth substrate is treated with oxygen plasma, and then methyltrichlorosilane is drop-coated on the surface of the growth substrate and transferred to an environment with a pressure of 0.1-0.2 MPa and a temperature of 100-120°C for modification for 1-2 hours. After being taken out, ultrasonic washing is performed in chloroform, isopropanol, and deionized water for 10-15 minutes in sequence, and then placed on a hot plate at 100-120°C for drying and annealing for 5-15 minutes, and then cooled to room temperature to obtain a methyltrichlorosilane-modified growth substrate; 2) growing a two-dimensional material on the methyltrichlorosilane-modified growth substrate prepared in step 1) by a CVD method to obtain a composite structure of a two-dimensional material / growth substrate; 3) Mix the main agent and curing agent of PDMS in a mass ratio of 5:1-8:1, then drop the mixture on the silicon wafer, cure it at 60-90°C for 10-60 minutes, and slowly peel it off to obtain a PDMS film; 4) flatly laminating the PDMS film prepared in step 3) onto the composite structure prepared in step 2) to obtain a composite structure of PDMS / two-dimensional material / growth substrate; 5) immersing the composite structure prepared in step 4) in deionized water, removing the growth substrate, and obtaining a composite structure of PDMS / two-dimensional material; 6) Flattening the composite structure prepared in step 5) onto the target substrate to obtain a composite structure of PDMS / two-dimensional material / target substrate; 7) Physically peeling off the PDMS film in the composite structure prepared in step 6) to obtain a composite structure of two-dimensional material / target substrate.

2. A method for rapid and non-destructive cleaning and transfer of wafer-level two-dimensional materials as claimed in claim 1, characterized in that: In step 1), the treatment pressure of oxygen plasma is 0.2-0.6 mbar, the treatment power is 40-60 W, and the treatment time is 1-5 min.

3. A method for rapid and non-destructive cleaning and transfer of wafer-level two-dimensional materials as claimed in claim 1, characterized in that: In step 1), the growth substrate is any one of quartz, sapphire or silicon wafer.

4. A method for rapid and non-destructive cleaning and transfer of wafer-level two-dimensional materials as claimed in claim 1, characterized in that: In step 2), the two-dimensional material is any one of molybdenum disulfide, molybdenum diselenide, tungsten sulfide or tungsten selenide.

5. A method for rapid and non-destructive cleaning and transfer of wafer-level two-dimensional materials as claimed in claim 1, characterized in that: In step 6), the target substrate is any one of a silicon wafer, a heavily doped silicon wafer, quartz or sapphire.

6. A device construction method based on wafer-level two-dimensional materials, characterized in that: Including the transfer method described in any one of claims 1 to 5, the construction method also includes: after achieving wafer-level transfer of the two-dimensional material, depositing metal gold on the upper surface of the two-dimensional material as a source and drain electrode.

Images