A method for patterning suspended heterogeneous films and a method for preparing pressure sensors

Abstract

The present invention discloses a method for patterning suspended heterogeneous films and a method for preparing pressure sensors. All steps of the method are fully compatible with current CMOS processes. Without the need for additional customized equipment, large-scale wafer preparation and cost reduction of suspended two-dimensional material structures can be achieved. During the implementation of the method, the two-dimensional material is supported and protected by a polymer support material throughout the entire process, effectively avoiding damage to the two-dimensional material during implementation.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure sensors, and in particular to a method for patterning a suspended heterogeneous film and a method for preparing a pressure sensor. Background Art

[0002] Atoms within a two-dimensional material layer are bonded by extremely strong covalent bonds, and the layers are attracted to each other by weak van der Waals (vdWs) forces, allowing for the exfoliation of stable two-dimensional layers as thin as one or a few atomic layers. Currently, the main discovered two-dimensional materials include graphene, hexagonal boron nitride (h-BN, also known as white graphene), transition metal dichachogenides (TMDs) (such as molybdenum disulfide (MoS2), WS2, and WSe2), silicene, black phosphorus, and layered superconducting oxides (such as NbSe2 and BSCCO). This constitutes a comprehensive two-dimensional material system, providing a new material framework for the research of new nanoelectromechanical resonators. Take graphene, for example. Graphene is only one or more carbon atoms thick and boasts extremely high mechanical strength, excellent electrical properties, a large surface area, and good thermal conductivity, making it a promising alternative to silicon in the post-silicon era. Suspended graphene maximizes the preservation of graphene's intrinsic physical properties. Its piezoresistive pressure sensor boasts a sensitivity 20 times greater than that of conventional silicon piezoresistive sensors.

[0003] A key challenge hindering the application of suspended graphene is the severe damage to suspended atomic-scale monolayer / few-layer 2D films, resulting in extremely low yields. Furthermore, a key challenge in the application of polymer-2D heterofilms is how to pattern these composite films. For example, PMMA-graphene (abbreviated as Gra) heterofilms are incompatible with traditional UV lithography processes because PMMA is an electron beam photoresist. Using electron beam lithography, the high cost and low efficiency of fabrication make it impossible to meet the market demand for low-cost pressure sensors. Summary of the Invention

[0004] The present invention provides a method for patterning a suspended heterogeneous film and a method for preparing a pressure sensor, which are used to overcome the defects of the prior art such as easy breakage, low yield and high cost of suspended two-dimensional materials.

[0005] To achieve the above object, the present invention provides a method for patterning a suspended heterogeneous film, comprising the following steps:

[0006] S1: Take a substrate of suitable size and grow a single layer or a few layers of two-dimensional material.

[0007] S2: Fix the substrate on a suitable supporting platform, and fix the supporting platform on a coating machine.

[0008] S3: spin-coating a layer of polymer support material on the two-dimensional material of the substrate.

[0009] S4: Remove the base and trim the edges of the base.

[0010] S5: placing the substrate in a substrate etching solution, etching and removing the substrate on which the two-dimensional material is grown, and obtaining a composite heterogeneous thin film floating on the surface of the etching solution.

[0011] S6: cleaning the composite heterogeneous film to remove organic pollutants and metal pollutants on the surface of the two-dimensional material in the composite heterogeneous film.

[0012] The cleaning method is to rinse with deionized water multiple times, then transfer to a 20:1:1 volume ratio of H2O:H2O2:HCl solution for about 15 minutes, transfer to a 20:1:1 volume ratio of H2O:H2O2:NH4OH solution for about 15 minutes. The above two steps are referred to as the mRCA cleaning method, and finally transfer to deionized water for multiple rinses;

[0013] S7: Using a pre-prepared substrate with a cavity to fish out the composite heterogeneous film from deionized water, and tilting the substrate with the cavity with the composite heterogeneous film to stand still for natural dehydration and drying.

[0014] S8: In order to remove the trace moisture remaining at the interface between the film and the substrate and make the film adhere more firmly to the substrate, the substrate with the cavity from which the composite heterogeneous film was taken out after drying was heated to obtain a suspended composite heterogeneous film sample.

[0015] S9: Spin-coat a layer of LOR (lift-off resist, stripping photoresist) and a layer of conventional photoresist compatible with LOR on the surface of the thin film sample in sequence.

[0016] S10: exposing the pattern of the thin film sample to be etched, immersing the thin film sample in a developer of the conventional photoresist to develop and expose the area to be etched.

[0017] S11: Select corresponding plasma according to the type of the two-dimensional material, and use the plasma to etch the area to be etched of the thin film sample.

[0018] S12: Immerse the thin film sample in the conventional photoresist developer again to dissolve the LOR layer.

[0019] S13: After the LOR layer is completely dissolved, the sample is gently shaken to completely peel off the conventional photoresist layer on the original LOR layer, releasing the patterned composite heterogeneous film.

[0020] S14: The patterned composite heterogeneous film is transferred to deionized water for cleaning, and then transferred to a low surface tension solution for cleaning and taken out, and blown dry with nitrogen to obtain a patterned film.

[0021] Preferably, in step S1, the two-dimensional material is one of graphene, boron nitride, molybdenum disulfide and other transition metal sulfur compounds, black phosphorus, graphite phase carbon nitride, layered metal oxides, layered double hydroxides, layered metal carbides, metal nitrides or metal nitride oxide composite two-dimensional materials, metal organic framework materials, covalent organic framework materials, perovskite materials, noble metal transition metal sulfides, tellurene, selenene, silicene, and borophene.

[0022] Preferably, in step S1, the substrate is one of a copper substrate, a nickel substrate, a silicon oxide substrate, a quartz substrate, a glass substrate, a silicon substrate, a silicon carbide substrate, a silicon nitride substrate, and a sapphire substrate.

[0023] Preferably, in step S3, the polymer support material is one of poly(methylmethacrylate, abbreviated as PMMA), polypropylene carbonate (abbreviated as PPC), polycarbonate (abbreviated as PC), ethylene-vinyl acetate (abbreviated as EVA), and polydimethylsiloxane (abbreviated as PDMS).

[0024] Preferably, in step S5, if the substrate is a copper substrate or a nickel substrate, the substrate etching solution is FeCl3, Fe(NO3)3 or (NH4)2S2O8 solution;

[0025] Preferably, in step S5, if the substrate is a silicon oxide substrate, silicon nitride substrate, quartz substrate, or glass substrate, the substrate etching solution is a mixed solution of NH4F:HF in a ratio of 7:1 (referred to as BOE solution), or a mixed solution of HF:HCl in a ratio of 1:1, or a 49% HF solution;

[0026] Preferably, in step S5, if the substrate is a silicon substrate, the substrate etching solution is a KOH solution;

[0027] Preferably, in step S5, if the substrate is a sapphire substrate, the substrate etching solution is an NH4OH:H2O2:H2O solution; preferably, in step S7, the substrate with a cavity can be a silicon substrate, a silicon / silicon oxide substrate, a quartz substrate, a glass substrate, a silicon carbide substrate, a silicon nitride, a sapphire substrate, a polydimethylsiloxane (PDMS) substrate, a polyethylene terephthalate (PET) substrate, a polyimide (PI) substrate, a polyethylene (PE) substrate and a polyurethane (PU) substrate, and the cavity can penetrate the substrate or not penetrate and have a certain depth.

[0028] Preferably, in step S8, the heating treatment is specifically:

[0029] Heat from room temperature to 40-60°C at a heating rate of 0.1-10°C / min, and keep at 40-60°C for 10-20 minutes;

[0030] The temperature is raised from 40 to 60°C at a heating rate of 0.1 to 10°C / min to near the glass critical temperature of the polymer support material in the composite heterogeneous film;

[0031] Cool down to room temperature at a cooling rate of 0.1~10℃ / min.

[0032] Preferably, in step S11, if the two-dimensional material is graphene, the plasma is oxygen plasma; preferably, in step S11, if the two-dimensional material is boron nitride, molybdenum disulfide or other transition metal sulfide compounds, black phosphorus, graphite phase carbon nitride, layered metal oxides, layered double hydroxides, layered metal carbides, metal nitrides or metal oxynitride composite two-dimensional materials, metal organic framework materials, covalent organic framework materials, perovskite materials, noble metal transition metal sulfides, tellurene, selenene, silicene, boronene, the plasma is CHF3 / O2 mixed atmosphere plasma or SF6 / Ar mixed atmosphere plasma;

[0033] Preferably, in step S14, the low surface tension solution is a n-hexane solution or a methoxynonafluorobutane solution (referred to as fluorinated solution).

[0034] To achieve the above object, the present invention further provides a method for preparing a pressure sensor, including the above-mentioned patterning method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] All steps of the patterning method of suspended heterogeneous films provided by the present invention are fully compatible with the current CMOS process. Without the need for additional customized equipment, large-scale wafer preparation and cost reduction of suspended two-dimensional material structures can be achieved. During the implementation of the method, the two-dimensional material is supported and protected by the polymer support material throughout the process, effectively avoiding damage to the two-dimensional material during the implementation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0038] Figure 1 Flowchart of the method for patterning a suspended heterogeneous film in Example 1;

[0039] Figure 2 Schematic diagram of a single layer or a few layers of two-dimensional material grown on a substrate cut to a suitable size in Example 1;

[0040] Figure 3 Schematic diagram of using tape to stick the two-dimensional material to the glass slide in Example 1;

[0041] Figure 4 Schematic diagram of the spin-coated polymer support material in Example 1;

[0042] Figure 5 Schematic diagram of edge cutting after glue leveling in Example 1;

[0043] Figure 6 Schematic diagram of substrate etching in Example 1;

[0044] Figure 7 Schematic diagram of cleaning the 2DMat / SP composite heterogeneous film in Example 1;

[0045] Figure 8 Schematic diagram of scooping out the 2DMat / SP composite heterogeneous film from the cavity substrate in Example 1;

[0046] Figure 9 This is a schematic diagram of temperature-controlled baking in Example 1;

[0047] Figure 10 Schematic diagram of spin coating LOR and conventional photoresist in Example 1;

[0048] Figure 11 Schematic diagram of exposure and development of LOR and conventional photoresist in Example 1;

[0049] Figure 12 Schematic diagram of the graphical etching of two-dimensional materials in Example 1;

[0050] Figure 13 Schematic diagram of the patterned two-dimensional material after removing LOR and conventional photoresist in Example 1.

[0051] Figure numerals: 1. Substrate with a single layer or a few layers of two-dimensional material; 2. Two-dimensional material; 3. Substrate; 4. Tape; 5. Glass slide; 6. Polymer material; 7. 2DMat / SP composite heterojunction film; 8. Substrate with cavity; 9. Cavity; 10. Conventional photoresist; 11. LOR.

[0052] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0054] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0055] Unless otherwise specified, all drugs / reagents used were commercially available.

[0056] Example 1

[0057] This embodiment provides a method for patterning a suspended heterogeneous film, such as Figure 1 As shown, taking graphene as an example, the specific steps include:

[0058] (1) If Figure 2 As shown, use scissors to cut the copper substrate graphene 1 into appropriate sizes, where 2 represents graphene and 3 represents the copper substrate;

[0059] (2) Use tape to fix the copper-based graphene 1 along the edge of the substrate on a suitable support platform (the support platform is a clean flat platform suitable for loading into a coating machine, such as a glass slide). Figure 3 As shown, 4 represents tape and 5 represents a glass slide. The copper-based graphene carrier is fixed on a spin coater and prepared for spin coating;

[0060] (3) By controlling the concentration of the polymer solution and the spin coating speed, ultrathin polymer materials (SP) with a thickness ranging from a few nanometers to tens of nanometers are evenly spin-coated on graphene, such as Figure 4 As shown, for graphene, in this embodiment, polymethyl methacrylate (PMMA) is selected as the polymer material with a molecular weight of 950,000, the solvent is ether with a concentration of 2%, the spin coating speed is 50 rpm, and the spin coating thickness is about 50 nm;

[0061] (4) Reverse the tape application sequence, use tweezers to carefully peel off the tape along the edge, and then use clean scissors to remove the edge of the copper substrate, such as Figure 5 As shown;

[0062] (5) Placing the copper substrate in a substrate etching solution to etch away the substrate on which the two-dimensional material is grown, e.g. Figure 6 As shown, a nanoscale 2DMat / SP film is obtained. In this embodiment, the copper substrate on which the graphene is grown is etched away by placing the film in a copper substrate etching solution to obtain a nanoscale Gra / SP film.

[0063] (6) Cleaning the 2DMat / SP film 7 to remove organic and metal contaminants on the surface of the two-dimensional material in the 2DMat / SP film. In this embodiment, the Gra / SP film is cleaned to remove organic and metal contaminants on the surface of the graphene in the Gra / SP film, such as Figure 7 As shown;

[0064] (7) Using a pre-prepared cavity substrate 8, a 2DMat / SP composite heterogeneous film is collected from deionized water (DIW). In this embodiment, a Gra / SP composite heterogeneous film is collected. The sample substrate with the composite heterogeneous film collected is tilted and allowed to stand for natural dehydration and drying at low temperature. Figure 8 As shown, the cavity 9 is shown in the figure;

[0065] (8) Sample temperature control baking: During the heating process, first slowly heat it to around 50 degrees Celsius for soft baking; then continue to slowly heat it to around the glass critical temperature of the thin film polymer material; during the cooling process, slowly cool it down to room temperature, and do not cool it down to room temperature quickly, such as Figure 9 As shown;

[0066] (9) Spin-coat a layer of LOR 11 on the sample surface, and then spin-coat a layer of conventional photoresist 10 compatible with LOR. In this embodiment, the conventional photoresist selected is AZ5214 photoresist, such as Figure 10 As shown;

[0067] (10) Expose the Gra / SP composite heterojunction film pattern to be etched and immerse it in a conventional photoresist developer compatible with LOR. In this embodiment, AZ photoresist developer PD238 is used to develop and expose the Gra / SP composite heterojunction film area to be etched, such as Figure 11 As shown;

[0068] (11) According to the type of two-dimensional material, the corresponding plasma is selected to etch the 2DMat / SP composite heterojunction film in the development area. In this embodiment, oxygen plasma is selected for graphene etching, and oxygen plasma etches the Gra / SP composite heterojunction film in the development area, such as Figure 12 As shown;

[0069] (12) After the plasma etching is completed, the sample is immersed in a conventional photoresist developer compatible with LOR again to dissolve the LOR sacrificial layer. In this embodiment, the AZ photoresist developer PD238 is selected;

[0070] (13) After the LOR sacrificial layer is dissolved, the sample is gently shaken to completely peel off the conventional photoresist layer on the original LOR sacrificial layer, and the patterned Gra / SP composite heterojunction film is released. Figure 13 As shown;

[0071] (14) The sample was transferred to DIW for cleaning, then transferred to a low surface tension solution for cleaning and removed, and dried with nitrogen to obtain a patterned suspended two-dimensional material film.

[0072] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for patterning a suspended heterogeneous film, characterized in that: The following steps are involved: S1: Take a substrate of suitable size and grow a single layer or a few layers of two-dimensional material; S2: Fix the substrate on a suitable support platform, and fix the support platform on a coating machine; S3: spin coating a layer of polymer support material on the two-dimensional material of the substrate; S4: remove the substrate and remove the edges of the substrate; S5: placing the substrate in a substrate etching solution, etching and removing the substrate on which the two-dimensional material is grown, and obtaining a composite heterogeneous film floating on the surface of the etching solution; S6: cleaning the composite heterogeneous film to remove organic pollutants and metal pollutants on the surface of the two-dimensional material in the composite heterogeneous film; S7: using a pre-prepared substrate with a cavity to fish out the composite heterogeneous film from deionized water, and tilting the substrate with the cavity with the composite heterogeneous film to stand still and naturally dehydrate and dry; S8: heating the dried substrate with the cavity and the composite heterogeneous film to obtain a film sample; S9: Spin-coat a LOR layer and a conventional photoresist layer compatible with LOR on the surface of the film sample in sequence; S10: exposing the pattern of the thin film sample to be etched, immersing the thin film sample in the developer of the conventional photoresist to develop and expose the area to be etched; S11: selecting a corresponding plasma according to the type of the two-dimensional material, and etching the area to be etched of the thin film sample using the plasma; S12: immersing the film sample in the developer of the conventional photoresist again to dissolve the LOR layer; S13: After the LOR layer is completely dissolved, the sample is gently shaken to completely peel off the conventional photoresist layer on the original LOR layer, releasing the patterned composite heterogeneous film; S14: The patterned composite heterogeneous film is transferred to deionized water for cleaning, and then transferred to a low surface tension solution for cleaning and taken out, and blown dry with nitrogen to obtain a patterned film.

2. The graphical method according to claim 1, wherein: In step S1, the two-dimensional material is one of transition metal sulfide compounds, black phosphorus, graphite phase carbon nitride, layered metal oxides, layered double hydroxides, layered metal carbides, metal nitrides or metal nitride oxide composite two-dimensional materials, metal organic framework materials, covalent organic framework materials, perovskite materials, noble metal transition metal sulfides, tellurene, selenene, silicene and borophene.

3. The graphical method according to claim 1, wherein: In step S1 , the substrate is one of a copper substrate, a nickel substrate, a silicon oxide substrate, a quartz substrate, a glass substrate, a silicon substrate, a silicon carbide substrate, a silicon nitride substrate and a sapphire substrate.

4. The graphical method according to claim 1, wherein: In step S3, the polymer support material is one of methyl methacrylate, polymethyl ethylene carbonate, polycarbonate, and polydimethylsiloxane.

5. The graphical method according to claim 1, wherein: In step S5, if the substrate is a copper substrate or a nickel substrate, the substrate etching solution is FeCl3, Fe(NO3)3 or (NH4)2S2O8 solution.

6. The graphical method according to claim 1, wherein: In step S5, if the substrate is a silicon oxide substrate, silicon nitride substrate, quartz substrate, or glass substrate, the substrate etching solution is a 49% HF solution.

7. The graphical method according to claim 1, wherein: In step S5, if the substrate is a sapphire substrate, the substrate etching solution is an NH4OH:H2O2:H2O solution.

8. The graphical method according to claim 1, wherein: In step S8, the heating process is specifically as follows: Heat from room temperature to 40-60°C at a heating rate of 0.1-10°C / min, and keep at 40-60°C for 10-20 minutes; The temperature is raised from 40 to 60°C at a heating rate of 0.1 to 10°C / min to near the glass critical temperature of the polymer support material in the composite heterogeneous film; Cool down to room temperature at a cooling rate of 0.1~10℃ / min.

9. The graphical method according to claim 1, wherein: In step S14, the low surface tension solution is a n-hexane solution or a methoxynonafluorobutane solution.

10. A method for preparing a pressure sensor, characterized in that: The method comprises the graphical method according to any one of claims 1 to 9.

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