A clean transfer method for wafer-level two-dimensional materials

Abstract

The present invention relates to a method for clean transfer of wafer-level two-dimensional materials, and belongs to the technical field of two-dimensional material transfer. The specific method is: spin coating on a copper layer to prepare a polymer film, and then using an electrochemical method to separate the polymer film, and then using a copper foil / two-dimensional material substrate to scoop it out to obtain a polymer film / two-dimensional material / copper foil, and then using an etching method to remove the copper foil and scoop it out with a target substrate to obtain a polymer film / two-dimensional material / target substrate, and finally using a silicone film to physically adhere and remove the polymer film to obtain a two-dimensional material / target substrate, thereby achieving a clean transfer of the two-dimensional material. The method uses an acrylic polymer containing a large side functional group as a transfer medium, and by prefabricating a polymer film and physically removing the polymer film with a silicone film, the interaction force between the polymer film and the two-dimensional material is weakened, and the polymer residue on the surface of the two-dimensional material is avoided. The transferred two-dimensional material has the characteristics of a clean surface, uniform and complete, and less polymer residue.

Description

Technical Field

[0001] The invention belongs to the technical field of two-dimensional material transfer and relates to a clean transfer method of wafer-level two-dimensional material. Background Art

[0002] Two-dimensional materials such as graphene and boron nitride have broad application prospects in high-end electronic and optoelectronic devices due to their excellent electrical and optical properties. At present, chemical vapor deposition (CVD) is mostly used to prepare two-dimensional thin film materials on metal substrates. The prepared materials have the advantages of high quality, large area, and controllable number of layers. In order to achieve its subsequent functional application, it is usually necessary to transfer the two-dimensional thin film material on the metal substrate to the target functional substrate. However, large-area two-dimensional thin film materials will inevitably produce problems such as damage, wrinkles and contamination during the transfer process, which seriously affects its properties after transfer. Therefore, how to achieve large-area non-destructive and clean transfer of two-dimensional materials is still a bottleneck in the research technology in the field of two-dimensional material applications and needs to be solved urgently.

[0003] The mainstream transfer method in the prior art is liquid phase etching, in which the medium used to transfer the two-dimensional material includes polymers such as polymethyl methacrylate (PMMA), thermal release tape (TRT), polydimethylsiloxane (PDMS), ethylene vinyl acetate (EVA), rosin (Rosin), paraffin, naphthalene, camphor, polycarbonate (PC), etc. Among them, PMMA is mostly used as the transfer medium. However, due to the strong interaction between these polymers and the two-dimensional material and the difficulty in dissolving in the solvent, the two-dimensional material after transfer is easily damaged and a large amount of polymers remain on the surface, which not only reduces the photoelectric performance of the two-dimensional material, but also greatly increases its surface roughness. For example, the surface roughness of a single layer of graphene after PMMA transfer can reach hundreds of nanometers. Therefore, in order to adapt to the industrial development of two-dimensional material optoelectronic devices, it is urgent to further deepen the problems encountered in the transfer link of two-dimensional materials to achieve non-damage and non-contamination transfer of wafer-level two-dimensional materials. Summary of the invention

[0004] In view of this, one of the objectives of the present invention is to provide a clean transfer method of wafer-level two-dimensional materials.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] 1. A clean transfer method for wafer-level two-dimensional materials, the method comprising the following steps:

[0007] S1: copper is plated on the flat surface of the inorganic substrate to form a copper layer with a thickness of 100 to 300 nm;

[0008] S2: Spin-coating the polymer solution on the copper layer in step S1, and then drying at 60-120° C. for 10-50 min to form a polymer film on the copper layer to obtain an inorganic substrate / copper layer / polymer film; the polymer in the polymer solution is any one of polybornyl acrylate or polytert-butyl acrylate;

[0009] S3: Separating the inorganic substrate / copper layer / polymer film in step S2 by electrochemical method to obtain a mixture, wherein a polymer film with a thickness of 20 to 80 nm in the mixture floats on the water surface;

[0010] S4: adding the copper foil / two-dimensional material substrate to the mixture in step S3 to scoop out the polymer film, taking it out and drying it to obtain the polymer film / two-dimensional material / copper foil;

[0011] S5: etching the surface of the copper foil in the polymer film / two-dimensional material / copper foil in step S4 to remove the copper foil, and rinsing with deionized water to obtain an aqueous solution of the polymer film / two-dimensional material;

[0012] S6: adding the target substrate to the aqueous solution of the polymer film / two-dimensional material in step S5, scooping out the polymer film / two-dimensional material, taking it out and drying it to obtain the polymer film / two-dimensional material / target substrate;

[0013] S7: adhering a silicone film to the surface of the polymer film in the polymer film / two-dimensional material / target substrate in step S6, and then degassing at 0.2-1.5 MPa to obtain a silicone film / polymer film / two-dimensional material / target substrate;

[0014] S8: The two-dimensional material / target substrate can be obtained by removing the silicone film / polymer film in the silicone film / polymer film / two-dimensional material / target substrate in step S7.

[0015] Preferably, the inorganic substrate in step S1 is any one of quartz, sapphire, mica or silicon wafer.

[0016] Preferably, the copper plating method in step S1 is any one of magnetron sputtering or thermal evaporation.

[0017] Preferably, the solvent in the polymer solution in step S2 is any one of ethyl acetate, butyl acetate, N,N-dimethylformamide, acetone, butanone or toluene.

[0018] Preferably, the spin coating in step S2 has a rotation speed of 500 to 3000 rpm and a time of 10 to 40 s.

[0019] Preferably, in the electrochemical method in step S3, the voltage is 0.5 to 3.5 V and the electrolyte is 0.2 to 2 mol / L sodium hydroxide solution.

[0020] Preferably, the two-dimensional material in the copper foil / two-dimensional material substrate in step S4 is any one of graphene, boron nitride, molybdenum sulfide or molybdenum selenide.

[0021] Preferably, the etching solution in the etching method in step S5 is any one of ammonium persulfate solution or ferric nitrate solution.

[0022] Preferably, the target substrate in step S6 is any one of silicon wafer, quartz or sapphire.

[0023] The beneficial effect of the present invention is that the present invention provides a method for clean transfer of wafer-level two-dimensional materials. The specific method is: copper plating on an inorganic substrate - preparing a polymer film on the surface of the copper layer - separating the polymer film by electrochemical method - preparing a polymer film / two-dimensional material / copper foil - etching the copper foil - preparing a polymer film / two-dimensional material / target substrate - preparing a silicone film / polymer film / two-dimensional material / target substrate - peeling off the silicone film / polymer film. The two-dimensional material / target substrate is prepared by this method, thereby achieving clean transfer of the two-dimensional material. This method has the following advantages: ① Using acrylic polymers containing large side functional groups instead of traditional high molecular weight materials such as polymethyl methacrylate (PMMA), polymethyl methacrylate (PMMA) or rosin as transfer media helps to weaken the interaction between the polymer film and the two-dimensional material, and avoids the polymer residue on the surface of the two-dimensional material during the transfer process; ② Preparing a polymer film on the surface of the copper layer, and then separating the polymer film to preform the polymer film. When the preformed polymer film is attached to the surface of the two-dimensional material, the interaction between the two can be further weakened; ③ Using a physical separation method to remove the polymer film through a silica gel membrane helps to further avoid the residue of the polymer on the surface of the two-dimensional material. The surface of the two-dimensional material transferred by the transfer method of this application is clean, uniform and complete, and there is little polymer residue.

[0024] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 This is a flow chart of wafer-level graphene clean transfer in Example 1;

[0027] Figure 2 This is an appearance diagram of graphene being transferred onto a silicon wafer substrate using the method in Example 1;

[0028] Figure 3 for Figure 2 Optical microscope images of the formed graphene in different regions, wherein (a) is an optical microscope image of region 1, (b) is an optical microscope image of region 2, (c) is an optical microscope image of region 3, and (d) is an optical microscope image of region 4;

[0029] Figure 4 : This is the Raman mapping diagram of graphene transferred by the method in Example 1, wherein (a) is the intensity ratio of the D peak to the G peak, and (b) is the intensity ratio of the G peak to the 2D peak. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0031] Example 1

[0032] A clean transfer method for wafer-level two-dimensional materials, the specific transfer method is as follows:

[0033] S1: copper is plated on the flat surface of the quartz substrate by magnetron sputtering to form a copper layer with a thickness of 100 nm;

[0034] S2: Spin-coat the ethyl acetate solution of poly(tert-butyl acrylate) on the copper layer in step S1 at a rotation speed of 1000 rpm, and place the solution on a constant temperature electric hot plate at a temperature of 100° C. after spin-coating for 25 seconds, and keep the temperature for 10 minutes to obtain a quartz substrate / copper layer / poly(tert-butyl acrylate) film;

[0035] S3: using Pt foil as an anode and the quartz substrate / copper layer / polytert-butyl acrylate film in step S2 as a cathode, then placing the anode and the cathode in a 1 mol / L sodium hydroxide solution at a constant voltage of 2.4 V to cause an electrochemical reaction, and after the reaction is completed, a polytert-butyl acrylate film with a thickness of 40 nm floating on the water surface is obtained;

[0036] S4: using the copper foil / graphene substrate to fish out the poly(tert-butyl acrylate) film in step S3, taking it out and letting it stand to dry, and then placing it on a hot plate at a temperature of 150° C. and keeping it warm for 30 minutes to further remove moisture to obtain the poly(tert-butyl acrylate) film / graphene / copper foil;

[0037] S5: placing the poly(tert-butyl acrylate) film / graphene / copper foil in step S4 in a 2 mol / L ammonium persulfate solution for wet etching to remove the copper foil to obtain a transparent film, and then rinsing the transparent film with deionized water for 3 times to obtain an aqueous solution of the poly(tert-butyl acrylate) film / graphene;

[0038] S6: adding the silicon wafer substrate to the aqueous solution of tert-butyl acrylate film / graphene in step S5, scooping the tert-butyl acrylate film / graphene to the surface of the silicon wafer substrate, taking it out and letting it stand to dry, and then placing it on a constant temperature electric heating plate at a temperature of 120° C., keeping it warm for 20 minutes to further remove moisture to obtain the tert-butyl acrylate film / graphene / silicon wafer substrate;

[0039] S7: adhering the silicone film to the surface of the tert-butyl acrylate film in the tert-butyl acrylate film / graphene / silicon wafer substrate in step S6, and degassing at 0.5 MPa to make the silicone film tightly adhere to the tert-butyl acrylate film to obtain the silicone film / tert-butyl acrylate film / graphene / silicon wafer substrate;

[0040] S8: The graphene / silicon wafer substrate is obtained by peeling off the silicone film and the tert-butyl acrylate film adhered thereto in the silicone film / tert-butyl acrylate film / graphene / silicon wafer substrate in step S7.

[0041] The flow chart of wafer-level graphene clean transfer in Example 1 is as follows: Figure 1 As shown. Figure 1 It can be seen that the realization of clean transfer of graphene includes eight processes: copper plating - preparing a polymer film on the surface of the copper layer - separating the polymer film by electrochemical method - preparing polymer film / graphene / copper foil - etching copper foil - preparing polymer film / graphene / target substrate - preparing silicone film / polymer film / graphene / target substrate - peeling off the silicone film / polymer film.

[0042] Figure 2 This is an appearance diagram of graphene being transferred to a silicon wafer substrate using the method in Example 1. Figure 2 It can be seen that the graphene surface transferred by the method of the present invention is clean and has less polymer residue.

[0043] Figure 3 for Figure 2Optical microscope images of the formed graphene in different regions, where (a) is an optical microscope image of region 1, (b) is an optical microscope image of region 2, (c) is an optical microscope image of region 3, and (d) is an optical microscope image of region 4. Figure 3 It can be seen that the graphene transferred by the method of the present invention has good integrity in all regions and almost no polymer residue.

[0044] Figure 4 The Raman mapping diagram of graphene after transfer using the method in Example 1, where (a) is the intensity ratio of the D peak to the G peak, and (b) is the intensity ratio of the G peak to the 2D peak. The intensity ratio of D / G represents the defects of graphene. The larger the ratio, the more defects there are. Figure 4 In (a), we can see that the D / G ratio is very small, indicating that graphene has few defects; the intensity ratio of G / 2D represents the number of graphene layers. Figure 4 It can be seen from (b) that the G / 2D ratio is below 0.4, indicating that the graphene is a single layer. That is, the graphene transferred by the method of the present invention is very uniform.

[0045] In summary, the present invention provides a method for clean transfer of wafer-level two-dimensional materials. The transfer method includes 8 processes. Among them, an acrylate polymer containing a large side functional group is used instead of traditional high molecular weight substances such as polymethyl methacrylate, polymethyl methacrylate or rosin as a transfer medium, and the prefabricated polymer film is formed and the polymer film is removed through a silicone film by a physical method, which helps to weaken the interaction between the polymer film and the two-dimensional material, thereby avoiding the residue of polymer on the surface of the two-dimensional material during the transfer process. The surface of the two-dimensional material transferred by the transfer method of the present application is clean, uniform and complete, with little polymer residue.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A clean transfer method for wafer-level two-dimensional materials, characterized in that: The method comprises the following steps: S1: copper is plated on the flat surface of the inorganic substrate to form a copper layer with a thickness of 100 to 300 nm; S2: Spin-coating the polymer solution on the copper layer in step S1, and then drying at 60-120° C. for 10-50 min to form a polymer film on the copper layer to obtain an inorganic substrate / copper layer / polymer film; the polymer in the polymer solution is any one of polybornyl acrylate or polytert-butyl acrylate; S3: Separating the inorganic substrate / copper layer / polymer film in step S2 by electrochemical method to obtain a mixture, wherein a polymer film with a thickness of 20 to 80 nm in the mixture floats on the water surface; S4: adding the copper foil / two-dimensional material substrate to the mixture in step S3 to scoop out the polymer film, taking it out and drying it to obtain the polymer film / two-dimensional material / copper foil; S5: etching the surface of the copper foil in the polymer film / two-dimensional material / copper foil in step S4 to remove the copper foil, and rinsing with deionized water to obtain an aqueous solution of the polymer film / two-dimensional material; S6: adding the target substrate to the aqueous solution of the polymer film / two-dimensional material in step S5, scooping out the polymer film / two-dimensional material, taking it out and drying it to obtain the polymer film / two-dimensional material / target substrate; S7: adhering a silicone film to the surface of the polymer film in the polymer film / two-dimensional material / target substrate in step S6, and then degassing at 0.2-1.5 MPa to obtain a silicone film / polymer film / two-dimensional material / target substrate; S8: The two-dimensional material / target substrate can be obtained by removing the silicone film / polymer film in the silicone film / polymer film / two-dimensional material / target substrate in step S7.

2. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: The inorganic substrate in step S1 is any one of quartz, sapphire, mica or silicon wafer.

3. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: The copper plating method in step S1 is any one of magnetron sputtering or thermal evaporation.

4. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: The solvent in the polymer solution in step S2 is any one of ethyl acetate, butyl acetate, N,N-dimethylformamide, acetone, butanone or toluene.

5. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: The spin coating in step S2 has a rotation speed of 500 to 3000 rpm and a time of 10 to 40 seconds.

6. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: In the electrochemical method in step S3, the voltage is 0.5 to 3.5 V and the electrolyte is 0.2 to 2 mol / L sodium hydroxide solution.

7. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: The two-dimensional material in the copper foil / two-dimensional material substrate in step S4 is any one of graphene, boron nitride, molybdenum sulfide or molybdenum selenide.

8. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: The etching solution in the etching method in step S5 is any one of ammonium persulfate solution or ferric nitrate solution.

9. The clean transfer method of wafer-level two-dimensional materials according to claim 1, characterized in that: In step S6, the target substrate is any one of silicon wafer, quartz or sapphire.

Images