Dielectric layer assisted graphene patterning method

Abstract

The invention belongs to the technical field of semiconductor processing, and particularly relates to a dielectric layer assisted graphene patterning method. The method comprises the following steps: transferring a two-dimensional material (graphene, hexagonal boron nitride or molybdenum disulfide) to a substrate, depositing a dielectric layer (Si3N4, Al2O3, boron nitride or SiO2), then coating photoresist and performing patterning, removing the dielectric layer which is not patterned and the two-dimensional material below through etching, and finally removing the photoresist. Residue, wrinkles and cracks of photoresist on the surface of the two-dimensional material film after traditional photoetching patterning can be effectively avoided, surface defects of the two-dimensional material are reduced, meanwhile, the introduced dielectric layer can serve as a protection layer of the two-dimensional material, the problems of oxidation and doping of the two-dimensional material in a high-temperature environment are avoided, and the performance of the two-dimensional material is improved. And the consistency and the stability of a sensor prepared from the composite material are obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor processing, and in particular relates to a dielectric layer-assisted graphene patterning method. Background Art

[0002] Graphene is a two-dimensional material composed of a single layer of carbon atoms, with excellent mechanical strength, high electrical conductivity, high thermal conductivity and other properties. With these unique properties, graphene has shown wide application potential in many fields such as electronic devices, sensors, energy storage devices and biomedicine.

[0003] However, in the actual application of graphene, in order to achieve specific functions, it is usually necessary to use photoresist to pattern graphene. The photoresist mask used in the traditional photolithography process will inevitably leave organic residues on the graphene surface, and the exposed graphene is easily oxidized and easily affected by H2O and other impurities, which significantly reduces the electrical performance and stability of graphene-based devices.

[0004] In order to solve these problems, some new methods have been proposed in the prior art. For example, aluminum (Al) material is used as a sacrificial layer to separate graphene and photoresist. Although this method is low in cost, simple in process, and can pattern graphene over a large area, when the aluminum mask is removed, the bubbles generated may cause the graphene to break and increase the roughness of the graphene surface, thereby affecting the performance of the device. Metal yttrium has also been reported to be used as a sacrificial layer, but due to the stable chemical and physical properties of yttrium, it is difficult to be completely removed in the etching process, and yttrium is a rare element, scarce and expensive. In addition, these methods usually require additional deposition and removal steps, making the manufacturing process more complicated. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a dielectric layer-assisted graphene patterning method, which effectively avoids the residual, wrinkles and cracks of the photoresist on the surface of the two-dimensional material film after traditional photolithography patterning, reduces the surface defects of the two-dimensional material, and at the same time, the introduced dielectric layer can also serve as a protective layer for the two-dimensional material, avoiding oxidation and doping problems in high temperature environments, improving the consistency and stability of the sensors prepared therewith, and does not require an additional removal step to remove the dielectric layer, thereby simplifying the preparation process.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a dielectric layer-assisted graphene patterning method, comprising the following steps:

[0008] Depositing a dielectric layer on the substrate with the two-dimensional material to cover the two-dimensional material to obtain a dielectric layer / two-dimensional material / substrate composite film;

[0009] Coat a photoresist to cover the surface of the dielectric layer to form a photoresist layer, obtaining a composite film of photoresist layer / dielectric layer / two-dimensional material / substrate;

[0010] After patterning the photoresist layer, etch away the dielectric layer and the underlying two-dimensional material in the unpatterned area;

[0011] Clean and remove the photoresist layer to obtain a patterned composite film of dielectric layer / two-dimensional material / substrate;

[0012] The two-dimensional material includes graphene, hexagonal boron nitride, or molybdenum disulfide;

[0013] The material of the dielectric layer includes Si3N4, Al2O3, boron nitride, or SiO2.

[0014] Preferably, the substrate is a Si3N4 / Si substrate; the Si3N4 / Si substrate is a Si substrate covered with a Si3N4 thin film, and the two-dimensional material is in contact with the Si3N4 thin film on the Si3N4 / Si substrate.

[0015] Preferably, the method for preparing the substrate with the attached two-dimensional material is: transfer the two-dimensional material onto the substrate; the transfer method is wet transfer or dry transfer; the wet transfer is polymethyl methacrylate wet transfer.

[0016] Preferably, the thickness of the dielectric layer is 5 - 45 nm.

[0017] Preferably, the method for depositing a dielectric layer is plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition, or high-density plasma chemical vapor deposition.

[0018] Preferably, the photoresist is AZ5214 positive photoresist or AZP4620 positive photoresist.

[0019] Preferably, the coating is spin coating; the spin coating includes low-speed spin coating and high-speed spin coating performed in sequence; the rotation speed of the low-speed spin coating is 400 - 600 r / min; the rotation speed of the high-speed spin coating is 3000 - 4500 r / min.

[0020] Preferably, the thickness of the photoresist layer is 1 - 2 μm.

[0021] Preferably, the cleaning is performed by water bath in acetone and absolute ethanol in sequence.

[0022] The present invention also provides an application of the method for patterning graphene assisted by the dielectric layer as described in the above technical solution in the preparation of sensors.

[0023] The present invention provides a method for patterning graphene assisted by a dielectric layer, comprising the following steps: depositing a dielectric layer on a substrate with a two-dimensional material attached thereto to cover the two-dimensional material, obtaining a dielectric layer / two-dimensional material / substrate composite film; coating a photoresist to cover the surface of the dielectric layer to form a photoresist layer, obtaining a photoresist layer / dielectric layer / two-dimensional material / substrate composite film; after patterning the photoresist layer, removing the dielectric layer in the unpatterned area and the underlying two-dimensional material by etching; cleaning to remove the photoresist layer, obtaining a patterned dielectric layer / two-dimensional material / substrate composite film; the two-dimensional material includes graphene, hexagonal boron nitride or molybdenum disulfide; the material of the dielectric layer includes Si3N4, Al2O3, boron nitride or SiO2.

[0024] The method of the present invention for patterning two-dimensional materials assisted by a dielectric layer has the roughness of the obtained patterned two-dimensional materials close to that of the bare two-dimensional material film, which can effectively avoid the photoresist residue on the surface of two-dimensional materials caused by traditional photolithographic patterning methods and avoid the cracking and damage of two-dimensional materials. The dielectric layer used in the present invention can not only serve as a mask layer for two-dimensional materials but also as a protective layer. By this method, it is possible to isolate other contaminants such as O2 and H2O, prevent unintentional impurity doping, significantly reduce the risk of two-dimensional material contamination, thereby further improving the performance of sensors prepared from two-dimensional materials, and no additional removal step is required to remove the dielectric layer, simplifying the preparation process. Compared with traditional photolithographic patterning methods, the sensors prepared from two-dimensional materials patterned by the dielectric layer assisted patterning method used in the present invention show excellent results in electrical performance and stability tests: the standard deviation of the resistance of the sensors is reduced by 29.56%, and the stability in harsh environments such as high oxygen and high temperature is improved by more than 59.4%, with excellent consistency and stability. Description of the Drawings

[0025] Figure 1 It is a schematic flow chart of the method for patterning graphene assisted by a dielectric layer in an embodiment of the present invention;

[0026] Figure 2 It is a schematic flow chart of the traditional photolithographic patterning method (a) and the method for patterning graphene assisted by using an Si3N4 film as a dielectric layer (b);

[0027] Figure 3 It is a surface quality test result diagram of the PR-Gr sample prepared in Comparative Example 1 and the Si3N4-Gr sample prepared in Example 1, wherein (a) is the OM image of the PR-Gr sample, (b) is the OM image of the Si3N4-Gr sample, (c) is the SEM image of the PR-Gr sample, and (d) is the SEM image of the Si3N4-Gr sample;

[0028] Figure 4AFM images of bare graphene film (a), PR-Gr sample prepared in Comparative Example 1 (b), and Si3N4-Gr sample prepared in Example 1 (c);

[0029] Figure 5 Electrical measurement result graph of the sensor prepared from the Si3N4-Gr sample prepared in Example 3;

[0030] Figure 6 Test result graph of the ability to resist the external environment after 10 days of the sensors prepared using the Si3N4-Gr sample prepared in Example 3 and the PR-Gr sample prepared in Comparative Example 1;

[0031] Figure 7 Test result graph of the ability to resist the external environment after 30 days of the sensors prepared using the Si3N4-Gr sample prepared in Example 3 and the PR-Gr sample prepared in Comparative Example 1. Detailed implementation manners

[0032] The present invention provides a method for patterning graphene assisted by a dielectric layer, comprising the following steps:

[0033] Deposit a dielectric layer on a substrate with a two-dimensional material attached thereto to cover the two-dimensional material, obtaining a dielectric layer / two-dimensional material / substrate composite film;

[0034] Coat a photoresist to cover the surface of the dielectric layer, forming a photoresist layer, obtaining a photoresist layer / dielectric layer / two-dimensional material / substrate composite film;

[0035] After patterning the photoresist layer, remove the dielectric layer in the unpatterned area and the two-dimensional material thereunder by etching;

[0036] Clean and remove the photoresist layer, obtaining a patterned dielectric layer / two-dimensional material / substrate composite film;

[0037] The two-dimensional material includes graphene, hexagonal boron nitride or molybdenum disulfide;

[0038] The material of the dielectric layer includes Si3N4, Al2O3, boron nitride or SiO2.

[0039] Unless otherwise specified, the present invention has no special requirements for the sources of the raw materials used, and commercially available products well-known to those skilled in the art can be adopted.

[0040] The present invention deposits a dielectric layer on a substrate with a two-dimensional material attached thereto to cover the two-dimensional material, obtaining a dielectric layer / two-dimensional material / substrate composite film.

[0041] As an implementation manner, the two-dimensional material includes graphene, hexagonal boron nitride (h-BN) or molybdenum disulfide (MoS2), and in a specific embodiment, it is graphene or hexagonal boron nitride.

[0042] As an implementation manner, the substrate is a Si3N4 / Si substrate; the Si3N4 / Si substrate is a Si3N4 thin film covered on a Si substrate, and the two-dimensional material is in contact with the Si3N4 thin film on the Si3N4 / Si substrate.

[0043] As an implementation manner, the preparation method of the substrate with the two-dimensional material attached is: transferring the two-dimensional material onto the substrate; the transfer method is wet transfer or dry transfer, and in a specific embodiment, it is wet transfer; the wet transfer is polymethyl methacrylate (PMMA) wet transfer to minimize wrinkles and impurity residues on the surface of the two-dimensional material.

[0044] As an implementation manner, the PMMA wet transfer includes the following steps:

[0045] Coating PMMA onto the two-dimensional material grown on a metal substrate, curing to form a PMMA support layer;

[0046] Floating the metal base surface of the obtained PMMA support layer / two-dimensional material / metal substrate composite film downward in an etching solution for etching to remove the metal substrate and obtain a PMMA support layer / two-dimensional material composite film;

[0047] After cleaning the PMMA support layer / two-dimensional material composite film to remove metal impurities, fishing up the cleaned PMMA support layer / two-dimensional material composite film with the substrate, drying after the substrate is in contact with the two-dimensional material, and finally removing the PMMA support layer to obtain the substrate with the two-dimensional material attached.

[0048] As an implementation manner, the PMMA is PMMA-A4 glue, and the manufacturer is Kayaku Advanced Materials, Inc.; the metal substrate is copper foil.

[0049] As an implementation method, the preparation method of the two-dimensional material grown on the metal substrate is: depositing the two-dimensional material on the metal substrate by chemical vapor deposition (CVD). As an implementation method, the steps of the chemical vapor deposition are: under a reducing gas and a protective gas, after performing a reduction reaction on the metal substrate, depositing the two-dimensional material on the metal substrate after the reduction reaction under a reaction gas to obtain the two-dimensional material grown on the metal substrate; the reducing gas is hydrogen; the protective gas is argon or nitrogen, specifically argon in a specific embodiment; when the two-dimensional material is graphene, the reaction gas is a carbon source gas; the carbon source gas is methane; when the two-dimensional material is h-BN, the reaction gas is trimethylamine borane; the temperature of the reduction reaction is 900-1100 °C, specifically 1000 °C in a specific embodiment; the time of the reduction reaction is 18-22 min, specifically 20 min in a specific embodiment; the temperature of the deposition is 900-1100 °C, specifically 1000 °C in a specific embodiment; the time of the deposition is 25-33 min, specifically 30 min in a specific embodiment; after the deposition is completed, it further includes: introducing a protective gas to exhaust the carbon source gas, and until the metal substrate on which the two-dimensional material is deposited cools to room temperature in the environment of the protective gas, taking out the metal substrate on which the two-dimensional material is deposited to obtain the two-dimensional material grown on the metal substrate.

[0050] As an implementation method, the thickness of the PMMA support layer is 400-600 nm, specifically 500 nm in a specific embodiment; the coating is spin coating; the equipment used for spin coating is a spin coater; the specific steps of the spin coating are: fixing the two-dimensional material grown on the metal substrate on a wafer spacer and placing it on the spin coater for spin coating of PMMA; the spin coating is two-stage spin coating; the two-stage spin coating is sequentially performing low-speed spin coating, low-temperature curing, high-speed spin coating, and high-temperature curing; the rotation speed of the low-speed spin coating is 600-800 r / s, specifically 700 r / s in a specific embodiment; the time of the low-speed spin coating is 7-9 s, specifically 9 s in a specific embodiment; the rotation speed of the high-speed spin coating is 2600-3200 r / s, specifically 3000 r / s in a specific embodiment; the time of the high-speed spin coating is 35-40 s, specifically 40 s in a specific embodiment; both the low-temperature curing and the high-temperature curing are baking on a hot plate; when performing low-temperature curing, the temperature of the hot plate is 70-90 °C, specifically 80 °C in a specific embodiment, and the baking time is 3-6 min, specifically 5 min in a specific embodiment; when performing high-temperature curing, the temperature of the hot plate is 160-190 °C, specifically 180 °C in a specific embodiment, and the baking time is 2-4 min, specifically 2 min in a specific embodiment.

[0051] As an implementation manner, the etching solution includes CuSO4, HCl, and H2O; CuSO4:HCl:H2O = 16 g:10 mL:100 mL; the HCl is a 15 wt% hydrochloric acid solution; the etching is carried out under static conditions; the static time is 10 to 24 h, specifically 24 h in specific embodiments. In the present invention, the static time is set within the above range to ensure the complete dissolution of the metal substrate.

[0052] As an implementation manner, the cleaning method used is an improved RCA cleaning method; the steps of the improved RCA cleaning method are: successively floating the PMMA support layer / two-dimensional material composite film with the two-dimensional material facing down in a mixed solution of H2O:H2O2:NH4OH, deionized water, a mixed solution of H2O:H2O2:HCl, and deionized water for cleaning; the cleaning time for each reagent is 5 to 10 min, specifically 5 min in specific embodiments; the volume ratio of H2O:H2O2:NH4OH is 20:1:1; the volume ratio of H2O:H2O2:HCl is 20:1:1; the H2O2 is a 45 wt% hydrogen peroxide solution; the NH4OH is a 25 wt% ammonia water; the HCl is a 15 wt% hydrochloric acid solution.

[0053] As an implementation manner, the drying is carried out by natural air drying in a vertical position and then baking with a hot plate; the time for natural air drying in a vertical position is 1.5 to 2.5 h, specifically 2 h in specific embodiments; the temperature of the hot plate is 75 to 90 °C, specifically 85 °C in specific embodiments; the baking time is 15 to 20 min, specifically 18 min in specific embodiments. In the present invention, baking with a hot plate is used to enhance the adhesion between the two-dimensional material and the substrate.

[0054] As an implementation manner, the method for removing the PMMA support layer is: successively carrying out water baths of the dried PMMA support layer / two-dimensional material composite film in acetone and absolute ethanol; the temperature for the water bath in acetone is 45 to 55 °C, specifically 50 °C in specific embodiments; the number of water baths in acetone is 2 to 3 times, specifically 2 times in specific embodiments; the time for each water bath in acetone is 5 to 7 min, specifically 5 min in specific embodiments; the temperature for the water bath in absolute ethanol is 45 to 55 °C, specifically 50 °C in specific embodiments; the time for the water bath in absolute ethanol is 5 to 7 min, specifically 5 min in specific embodiments.

[0055] As an implementation manner, the material of the dielectric layer includes Si3N4, Al2O3, boron nitride (BN), or SiO2, specifically Si3N4 or SiO2 in specific embodiments; the thickness of the dielectric layer is 5 to 45 nm, specifically 20 nm in specific embodiments.

[0056] As an implementation manner, the method for depositing a dielectric layer is plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD) or high density plasma chemical vapor deposition (HDP-CVD), and in a specific embodiment, it is plasma enhanced chemical vapor deposition.

[0057] As an implementation manner, the steps of the plasma enhanced chemical vapor deposition are as follows: Place the substrate with two-dimensional material in the four-inch circular groove of the deposition table. After preheating, turn on the mechanical pump and molecular pump to evacuate the chamber, and then fill the reaction gas into the gas inlet for deposition; the temperature of the preheating is 200-300 °C, and in a specific embodiment, it is 250 °C; the time of the preheating is 0.8-1.2 h, and in a specific embodiment, it is 1 h; evacuate to a vacuum degree of 10 -4 ~10 - 7 Pa, and in a specific embodiment, it is 10 -6 Pa; the reaction temperature during the deposition process is 200-400 °C, and in a specific embodiment, it is 300 °C; the pressure during the deposition process is 60-90 Pa, and in a specific embodiment, it is 80 Pa; the deposition rate is 12-16 nm / min, and in a specific embodiment, it is 15 nm / min; when the material of the dielectric layer is SiO2, the reaction gas used for the deposition is a mixed gas of SiH4 and N2O; the flow rate of SiH4 during the deposition process is 10-15 sccm, and in a specific embodiment, it is 13 sccm, and the flow rate of N2O is 190-220 sccm, and in a specific embodiment, it is 210 sccm; when the material of the dielectric layer is Si3N4, the reaction gas used for the deposition is a mixed gas of SiH4, N2 and NH3; the flow rate of SiH4 during the deposition process is 10-15 sccm, and in a specific embodiment, it is 11 sccm, the flow rate of N2 is 190-230 sccm, and in a specific embodiment, it is 205 sccm, and the flow rate of NH3 is 16-24 sccm, and in a specific embodiment, it is 20 sccm.

[0058] In the present invention, the dielectric layer can not only be used as a mask layer for graphene patterning, effectively isolating the photoresist and two-dimensional material to prevent photoresist residue from contaminating the two-dimensional material film, but also can be used as a protective layer during the subsequent etching process to isolate other impurities such as O2 and H2O and prevent damage to the two-dimensional material.

[0059] After obtaining the dielectric layer, the present invention coats a photoresist to cover the surface of the dielectric layer to form a photoresist layer, and obtains a photoresist layer / dielectric layer / two-dimensional material / substrate composite film.

[0060] As an implementation manner, the photoresist is AZ5214 positive photoresist or AZP4620 positive photoresist, and in a specific embodiment, it is AZ5214 positive photoresist; the coating is spin coating; the equipment used for spin coating is a semi-automatic spin coater.

[0061] As an implementation manner, the spin coating includes low-speed spin coating and high-speed spin coating carried out in sequence; the rotation speed of the low-speed spin coating is 400 - 600 r / min, and in a specific embodiment, it is 500 r / min; the time of the low-speed spin coating is 5 - 8 s, and in a specific embodiment, it is 5 s; the rotation speed of the high-speed spin coating is 3000 - 4500 r / min, and in a specific embodiment, it is 4000 r / min; the time of the high-speed spin coating is 26 - 35 s, and in a specific embodiment, it is 30 s; the thickness of the photoresist layer is 1 - 2 μm, and in a specific embodiment, it is 2 μm.

[0062] As an implementation manner, the equipment used for spin coating is a semi-automatic spin coater; the specific steps for spin coating with a semi-automatic spin coater are: placing the dielectric layer / two-dimensional material / substrate composite film on the spin coater turntable of the semi-automatic spin coater and turning on the vacuum adsorption, first running at a low speed to evenly spread the photoresist, and then running at a high speed to control the spin coating thickness of the photoresist.

[0063] Bubbles should be avoided during spin coating of the photoresist. If bubbles appear, they should be removed in a timely manner to ensure the quality of spin coating.

[0064] After obtaining the photoresist layer, in the present invention, after patterning the photoresist layer, the dielectric layer and the two-dimensional material below it in the unpatterned area are removed by etching;

[0065] As an implementation manner, the method of patterning is photolithography technology; the steps of the photolithography technology include: pre-baking treatment, exposure treatment, development treatment, post-baking treatment, and primer film treatment carried out in sequence.

[0066] As an implementation manner, the pre-baking treatment is to bake the photoresist layer / dielectric layer / two-dimensional material / substrate composite film on a hot plate to cure the photoresist; the temperature of the hot plate is 80 - 100 °C, and in a specific embodiment, it is 95 °C; the baking time is 80 - 100 s, and in a specific embodiment, it is 90 s.

[0067] As an implementation manner, the exposure treatment is to use a lithography machine to project the pattern on the photomask onto the surface of the photoresist layer for exposure; the lithography machine is MA6 lithography machine; the exposure time is 3.2 - 3.9 s, and in a specific embodiment, it is 3.7 s;

[0068] As an implementation manner, the development process is to use a developer to remove the exposed areas in the photoresist layer to obtain a developed pattern; the developer is a 3038 developer, and the main component of the 3038 developer is 1-5 wt% of tetramethylammonium hydroxide, specifically 2.38 wt% of tetramethylammonium hydroxide in a specific embodiment; the development time is 35-45 s, specifically 40 s in a specific embodiment; after development, it further includes: fixing; the fixing is to soak the developed photoresist layer / dielectric layer / two-dimensional material / substrate composite film in deionized water; the soaking time is 1-2 min, specifically 1 min in a specific embodiment. The present invention removes the residual developer through fixing.

[0069] As an implementation manner, the post-baking process is: baking the developed photoresist layer / dielectric layer / two-dimensional material / substrate composite film on a hot plate to complete the film hardening process before etching; the temperature of the hot plate is 100-130 °C, specifically 110 °C in a specific embodiment; the baking time is 2-3 min, specifically 2 min in a specific embodiment.

[0070] As an implementation manner, the underlayer film treatment is: using a spin coater to remove the residual photoresist on the developed pattern, and the set parameters of the underlayer film treatment are: the flow rate of O2 is 120-160 sccm, specifically 150 sccm in a specific embodiment; the power is 180-230 W, specifically 200 W in a specific embodiment; the treatment time is 2-4 min, specifically 2 min in a specific embodiment.

[0071] As an implementation manner, the etching method is reactive ion etching (RIE), ion beam etching (IBE), oxygen plasma etching (OISE) or inductively coupled plasma etching (ICP), specifically reactive ion etching or ion beam etching in a specific embodiment.

[0072] As an implementation manner, the equipment used for reactive ion etching is an ion etcher; the parameters of the reactive ion etching include: the chamber pressure is 1200-1600 mTor, specifically 1500 mTor in a specific embodiment; the etching power is 180-220 W, specifically 200 W in a specific embodiment; the etching rate is 90-120 nm / min, specifically 100 nm / min in a specific embodiment; when the material of the dielectric layer is Si3N4, the introduced gases include CFH3, CF6 and He, where the flow rate of CFH3 is 6-13 sccm, specifically 10 sccm in a specific embodiment, the flow rate of CF6 is 5-10 sccm, specifically 8 sccm in a specific embodiment, and the flow rate of He is 120-170 sccm, specifically 150 sccm in a specific embodiment.

[0073] As an implementation manner, the parameters of the oxygen plasma etching (OISE) include: the flow rate of oxygen introduced is 40 - 60 sccm, specifically 50 sccm in a specific embodiment; the plasma power is 550 - 650 W, specifically 600 W in a specific embodiment; the chamber pressure is 140 - 160 mTorr, specifically 150 mTorr in a specific embodiment; the temperature is 90 - 110 °C, specifically 100 °C in a specific embodiment; the time is 75 - 85 s, specifically 80 s in a specific embodiment.

[0074] As an implementation manner, the specific steps of the ion beam etching (IBE) are as follows: fix the substrate on the sample stage, ensure the levelness, evacuate to the base pressure to avoid interference of residual gas with etching; then introduce the working gas, start the ion source, set the beam energy and the incident angle, gradually increase the anode voltage to be stable, and after controlling the chamber pressure, carry out the ion beam etching.

[0075] As an implementation manner, the base pressure is 3×10 -6 ~8×10 -6 Torr, specifically 5×10 -6 Torr in a specific embodiment; the working gas is Ar; the flow rate of the working gas is 12 - 17 sccm, specifically 15 sccm in a specific embodiment; the beam energy is 380 - 420 eV, specifically 400 eV in a specific embodiment; the incident angle is 0°; the chamber pressure during the ion beam etching process is 2×10 -4 ~4×10 -4 Torr, specifically 3×10 -4 Torr in a specific embodiment. In the present invention, the sample stage needs to have good thermal contact.

[0076] After the etching, the present invention removes the photoresist layer by cleaning to obtain the patterned two-dimensional material / medium layer / substrate composite film.

[0077] As an implementation manner, the cleaning is carried out in a water bath with acetone and absolute ethanol; the temperature of the water bath in acetone is 40 - 50 °C, specifically 45 °C in a specific embodiment; the number of times of the water bath in acetone is 2 - 3 times, specifically 2 times in a specific embodiment; the time of each water bath in acetone is 5 - 8 min, specifically 6 min in a specific embodiment; the temperature of the water bath in absolute ethanol is 40 - 50 °C, specifically 45 °C in a specific embodiment; the number of times of the water bath in absolute ethanol is 1 - 2 times, specifically 1 time in a specific embodiment; the time of each water bath in absolute ethanol is 5 - 8 min, specifically 5 min in a specific embodiment. The present invention removes the remaining photoresist by carrying out a water bath in acetone and absolute ethanol to ensure that the surface of the patterned two-dimensional material is clean and not contaminated.

[0078] Figure 1Schematic flow chart of the method for medium layer-assisted graphene patterning in an embodiment of the present invention. As Figure 1 shown, in the present invention, graphene is transferred onto a substrate, a medium layer is deposited on the transferred graphene film, a photoresist layer is patterned using lithography technology, the unpatterned medium layer is etched, and at the same time, the underlying graphene is removed, and the photoresist is etched away to complete patterning.

[0079] In the present invention, the medium layer can effectively isolate the photoresist from the two-dimensional material, avoid the photoresist remaining on the surface of the two-dimensional material, and at the same time provide an additional protective layer, avoiding damage to the two-dimensional material film during the etching process, greatly improving the surface quality of the two-dimensional material film, and contributing to improving the durability of the sensor prepared therefrom.

[0080] The present invention also provides an application of the above-mentioned medium layer-assisted graphene patterning method in the preparation of a sensor.

[0081] As an implementation method, the preparation method of the sensor is: depositing a metal electrode by magnetron sputtering on the two-dimensional material prepared by the above-mentioned medium layer-assisted graphene patterning method; the metal electrode is an Au electrode; the deposited thickness is 15-30 nm, specifically 20-25 nm in specific embodiments; the power of the magnetron sputtering is 0.4-0.6 kW, specifically 0.5 kW in specific embodiments; the sputtering rate of the magnetron sputtering is 2.2-2.6 nm / s, specifically 2.4 nm / s in specific embodiments.

[0082] The present invention connects the metal electrode with the two-dimensional material film to form the main structural part of the sensor.

[0083] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention, but they cannot be understood as limiting the protection scope of the present invention.

[0084] Embodiment 1

[0085] In Embodiment 1 of the present invention, an Si3N4 film is used as the medium layer to assist graphene patterning, and a photoresist (AZ5214) is used. As Figure 2 shown, Figure 2 in (b) shows the method flow of using an Si3N4 film as the medium layer to assist graphene patterning. The specific steps are as follows:

[0086] Step 1: Transfer the graphene film onto the Si3N4 / Si substrate by wet transfer using polymethyl methacrylate (PMMA), and remove the PMMA support layer (500 nm);

[0087] The specific process of PMMA wet transfer is as follows: Cut a 2-inch sample from the graphene copper foil grown by chemical vapor deposition (CVD), and use tape to fix it on the wafer gasket for subsequent operations;

[0088] CVD step: Put the copper foil into the furnace, introduce the reducing gas hydrogen and the protective gas argon, heat to 1000 °C, stabilize the temperature, and maintain for 20 min for the reduction reaction; then stop introducing hydrogen and argon, change to introduce methane gas for 30 min. After the deposition is completed, cut off the power supply, close the methane gas, and then introduce argon to exhaust the methane gas. Under the environment of argon, wait until the copper foil with deposited graphene cools to room temperature, take out the copper foil with deposited graphene, and obtain graphene on the copper foil;

[0089] Spin-coat PMMA-A4 glue (manufactured by Kayaku Advanced Materials, Inc.) on a spin coater. Use a two-stage spin coating to form a uniform film of PMMA on the graphene surface. First, spin-coat at 700 r / s for 9 s, place the sample on a hot plate (80 °C) and bake for 5 min. Then, spin-coat at 3000 r / s for 40 s, and then place the sample on a hot plate (180 °C) and bake for 2 min to complete the curing of PMMA;

[0090] Subsequently, corrode the copper substrate. Float the sample with the Cu side down in the etching solution with a specific ratio (CuSO4:HCl:H2O = 16 g:10 mL:100 mL, HCl is a 15 wt% hydrochloric acid solution), and let it stand for 24 h to ensure that the copper is completely dissolved, obtaining a PMMA support layer / graphene composite film;

[0091] After the corrosion is completed, use an improved RCA cleaning method to remove metal impurities: Float the PMMA support layer / graphene composite film in turn in the mixed solution of H2O:H2O2:NH4OH (volume ratio 20:1:1, H2O2 is a 45 wt% hydrogen peroxide solution, NH4OH is a 25 wt% ammonia water), deionized water, the mixed solution of H2O:H2O2:HCl (volume ratio 20:1:1, H2O2 is a 45 wt% hydrogen peroxide solution, HCl is a 15 wt% hydrochloric acid solution) and deionized water for cleaning, and each step lasts for 5 min;

[0092] After cleaning, use the target Si3N4 / Si substrate to fish out the PMMA support layer / graphene composite film from the water. The Si3N4 / Si substrate is a Si3N4 thin film covered on the Si substrate, and the graphene contacts the Si3N4 thin film on the Si3N4 / Si substrate. Then place the sample vertically for 2 h to dry naturally, and then bake on a hot plate at 85 °C for 18 min to enhance the adhesion between the graphene and the substrate;

[0093] Finally, successively perform water baths in acetone at 50 °C (twice, 5 min each) and in absolute ethanol at 50 °C (5 min) to remove the PMMA support layer, obtaining a high-quality bare graphene film;

[0094] Step 2: Use plasma-enhanced chemical vapor deposition (PECVD) technology to deposit Si3N4 (with a thickness of 20 nm) on the transferred graphene film, obtaining a Si3N4 dielectric layer / graphene / Si3N4 / Si composite film;

[0095] The specific process of growing Si3N4 by PECVD is as follows: Place the graphene / Si3N4 / Si wafer in the four-inch circular groove of the deposition stage, and preheat the graphene / Si3N4 / Si wafer at a temperature of 250 °C for 1 h; then turn on the mechanical pump and the molecular pump to evacuate to a chamber vacuum of 10 -6 Pa, and then fill the inlet with a mixed gas of SiH4, N2, and NH3. The reaction temperature is 300 °C, the SiH4 flow rate is 11 sccm, the N2 flow rate is 205 sccm, the NH3 flow rate is 20 sccm, the pressure is 80 Pa, and the deposition rate is 15 nm / min;

[0096] Step 3: Spin-coat a photoresist (AZ5214) on the Si3N4 dielectric layer to form a photoresist layer, and pattern the photoresist layer through photolithography technology to form the required structure;

[0097] The specific steps of patterning using standard photolithography technology are as follows:

[0098] Photoresist spin coating: Use a semi-automatic spin coater for photoresist coating. Use AZ5214 positive photoresist. Place the Si3N4 dielectric layer / graphene / Si3N4 / Si composite film on the spin coater turntable and turn on the vacuum adsorption. First, run at a low speed of 600 r / min for 5 s to spread the photoresist evenly, and then run at a high speed of 4000 r / min for 30 s to control the photoresist thickness. The spin coating thickness is 2 μm. Avoid generating bubbles when dropping the photoresist. If bubbles appear, they should be removed in time to ensure the quality of spin coating;

[0099] Pre-baking treatment: Bake the silicon wafer coated with photoresist on a hot plate at 95 °C for 90 s to cure the photoresist, obtaining a photoresist layer / Si3N4 dielectric layer / graphene / Si3N4 / Si composite film;

[0100] Exposure treatment: Use a MA6 mask aligner for exposure, select a photomask, and set the exposure duration to 3.7 s;

[0101] Development process: The development was carried out using a 3038 developer solution, the main component of which is 2.38 wt% of tetramethylammonium hydroxide. The development time was 40 s. After development, the photoresist layer / Si3N4 dielectric layer / graphene / Si3N4 / Si composite film was soaked in deionized water for 1 min for fixing to remove the residual developer solution;

[0102] Post-baking process: The silicon wafer was baked on a hot plate at 110 °C for 2 min to complete the hardening process before etching;

[0103] Priming film process: The spin coater was used to remove the residual photoresist on the developed pattern. The set parameters were: O2 flow rate 150 sccm, power 200 W, and processing time 2 min;

[0104] Step 4: The unpatterned Si3N4 dielectric layer region was etched using the reactive ion etching (RIE) method, and at the same time, the underlying graphene was removed. The photoresist layer was removed by cleaning to obtain the Si3N4-graphene composite film (Si3N4-Gr);

[0105] The specific process of RIE etching was as follows: In the ion etching machine, trifluoromethane (CFH3) with a flow rate of 10 sccm, CF6 with a flow rate of 8 sccm, and He with a flow rate of 150 sccm were introduced; the chamber pressure was set to 1500 mTor; the etching power was set to 200 W; the etching rate was controlled to be 100 nm / min;

[0106] The remaining photoresist was removed by water bath in acetone at 45 °C (twice, 6 min each) and water bath in absolute ethanol at 45 °C (5 min) to ensure that the surface of the patterned graphene was clean and not contaminated.

[0107] Comparative Example 1

[0108] To verify the improvement of the graphene surface quality by the dielectric layer-assisted graphene patterning method proposed in the present invention, Example 1 was selected for comparison with the traditional photolithography patterning method. Figure 2 (a) in it describes the traditional photolithography process flow. The specific steps are as follows:

[0109] Step 1: The graphene thin film was transferred to the substrate by PMMA wet transfer, and the PMMA support layer was removed (this step is the same as that in Example 1 and will not be elaborated here);

[0110] Step 2: A photoresist (AZ5214 positive photoresist) was spin-coated on the bare graphene thin film to form a photoresist layer. The photoresist layer was patterned by photolithography technology to form the required structure;

[0111] The specific process of spin coating is as follows: Use a semi-automatic spin coater to coat the photoresist. Use AZ5214 positive photoresist. Place the silicon wafer on the spin coater turntable and turn on the vacuum adsorption. First, run at a low speed of 600 r / min for 5 s to evenly spread the photoresist, and then run at a high speed of 4000 r / min for 30 s to control the thickness of the photoresist. The thickness of the spin-coated photoresist is 2 μm.

[0112] The pre-baking treatment, exposure treatment, development treatment, post-baking treatment, and bottom film treatment are the same as those in Example 1, and will not be elaborated here.

[0113] Step 3: Etch the unpatterned area through oxygen plasma, and clean and remove the photoresist layer to obtain U-shaped strip-like graphene (PR-Gr).

[0114] The specific process of oxygen plasma etching is as follows: The oxygen flow rate is 50 sccm, the plasma power is set at 600 W, the chamber pressure is 150 mTorr, the temperature is controlled at 100 °C, and the time is set at 80 s.

[0115] The step of cleaning and removing the photoresist layer is the same as that in Example 1, and will not be elaborated here.

[0116] Performance test:

[0117] (1) Figure 3 Figures (a) to (d) respectively show the surface quality of the samples PR-Gr and Si3N4-Gr processed by using two methods of traditional lithography process and Si3N4 dielectric layer-assisted patterning. The morphology of the samples was observed and compared through an optical microscope (OM) and a scanning electron microscope (SEM).

[0118] As Figure 3 shown in the OM image of the (a) PR-Gr sample in, the U-shaped strip area is graphene.

[0119] As Figure 3 shown in the OM image of the (b) Si3N4-Gr sample in, the yellow area is the Si3N4 / Gr layer structure, and the width of the strip where the U-shaped strip-like graphene contacts the metal electrode is 30 μm.

[0120] As Figure 3 shown in the SEM image of the (c) PR-Gr sample in, it is observed that the area of the U-shaped strip-like graphene is uneven in light and dark. This is because in the traditional lithography process, the photoresist in contact with the surface of the graphene film could not be completely removed by acetone and other cleaning agents, resulting in obvious residues left on the surface of the graphene film.

[0121] As Figure 3As shown in the SEM image of the (d) Si3N4-Gr sample, the area of the U-shaped strip graphene is observed to have a uniform color because the Si3N4 dielectric layer effectively isolates the photoresist (AZ5214) and the graphene film, avoiding the residue of contaminants.

[0122] As Figure 3 shown, it indicates that using the Si3N4 film as a dielectric layer to assist graphene patterning can effectively isolate the photoresist and graphene, prevent photoresist residue, and show superiority compared to the traditional photolithography process.

[0123] (2) The roughness of the bare graphene film, PR-Gr sample, and Si3N4-Gr sample was measured using an atomic force microscope (AFM), and the results are as Figure 4 shown.

[0124] As Figure 4 shown in (a), the root mean square roughness (R q ) of the bare graphene film transferred to the substrate is 1.29 nm, and the average roughness (R a ) is 0.928 nm, which is mainly caused by surface wrinkling and PMMA residues.

[0125] As Figure 4 shown in (b), the AFM 3D image of the PR-Gr sample shows the aggregation of white columns, the root mean square roughness (R q ) is 4.04 nm, and the average roughness (R a ) is 1.91 nm, mainly due to photoresist residue and impurity particles.

[0126] As Figure 4 shown in (c), the root mean square roughness (R q ) of the Si3N4-Gr sample after using the Si3N4 film as a dielectric layer to assist graphene patterning is 1.40 nm, and the average roughness (R a ) is 1.04 nm, which is close to the roughness of the bare graphene film.

[0127] Through the roughness comparison of the AFM images, it is further proved that using the Si3N4 film as a dielectric layer to assist graphene patterning can avoid photoresist residue and show better effects than the traditional photolithography process.

[0128] In summary, in Example 1 of the present invention, using Si3N4 as a dielectric layer to assist graphene patterning can isolate and protect graphene from the photoresist (AZ5214). And through morphological characterization, it is confirmed that the Si3N4 film as a dielectric layer can completely prevent the residue of the photoresist (AZ5214), significantly reduce the contamination of the photoresist (AZ5214), and do not introduce additional defects.

[0129] Example 2

[0130] In Example 2 of the present invention, SiO2 is used as the dielectric layer to assist in the patterning of h-BN. This method effectively solves the problems of damage and pollution that may be caused to the h-BN material in traditional patterning techniques.

[0131] Step 1: Transfer the h-BN thin film onto the Si3N4 / Si substrate using the standard wet transfer technique (PMMA wet transfer). During the transfer process, ensure that the h-BN thin film evenly and smoothly covers the Si3N4 / Si substrate.

[0132] The specific process of PMMA wet transfer is as follows: Cut a 2-inch sample from the CVD-grown h-BN copper foil and fix it on the wafer spacer using tape for subsequent operations.

[0133] CVD step: Place the copper foil in the furnace, introduce the reducing gas hydrogen and the protective gas argon, heat to 1000 °C, stabilize the temperature, and maintain for 20 min for the reduction reaction; then stop introducing hydrogen and argon, and change to introduce trimethylamine borane gas for 30 min. After the deposition is completed, cut off the power supply, close the trimethylamine borane gas, and then introduce argon to exhaust the methane gas. Under the argon environment, wait until the copper foil deposited with h-BN cools to room temperature, and take out the copper foil deposited with h-BN to obtain h-BN on the copper foil.

[0134] Spin-coat PMMA-A4 glue (manufactured by Kayaku Advanced Materials, Inc.) on a spin coater. Use a two-stage spin coating to form a uniform thin film of PMMA on the surface of h-BN. First, spin-coat at 700 r / s for 9 s, place the sample on a hot plate (80 °C) and bake for 5 min. Then, spin-coat at 3000 r / s for 40 s and place the sample on a hot plate (180 °C) and bake for 2 min to complete the curing of PMMA, forming a PMMA support layer (500 nm).

[0135] Subsequently, corrode the copper substrate. Float the sample with the Cu side down in the etching solution with a specific ratio (CuSO4:HCl:H2O = 16 g:10 mL:100 mL, HCl is a 15 wt% hydrochloric acid solution), and let it stand for 24 h to ensure that the copper is completely dissolved, obtaining a PMMA support layer / h-BN composite film.

[0136] After the corrosion is completed, an improved RCA cleaning method is used to remove metal impurities: the PMMA support layer / h-BN composite film is successively floated in solutions of H2O:H2O2:NH4OH (volume ratio 20:1:1, H2O2 is a 45wt% hydrogen peroxide solution, NH4OH is a 25wt% ammonia water solution), deionized water, H2O:H2O2:HCl (volume ratio 20:1:1, H2O2 is a 45wt% hydrogen peroxide solution, HCl is a 15wt% hydrochloric acid solution) and deionized water for cleaning, and each step lasts for 5 min;

[0137] After cleaning, the target Si3N4 / Si substrate is used to fish out the PMMA support layer / h-BN composite film from the water. The Si3N4 / Si substrate is a Si substrate covered with a Si3N4 thin film, and h-BN contacts the Si3N4 thin film on the Si3N4 / Si substrate. Then the sample is placed vertically for 2 h to dry naturally, and then baked on a hot plate at 85 °C for 18 min to enhance the adhesion between h-BN and the substrate;

[0138] Finally, the PMMA support layer is removed by water bath in acetone at 50 °C (twice, 5 min each) and water bath in absolute ethanol at 50 °C (5 min) to obtain a high-quality bare h-BN thin film;

[0139] Step 2: Use plasma-enhanced chemical vapor deposition (PECVD) technology to deposit a SiO2 dielectric layer with a thickness of 20 nm on the transferred h-BN thin film to obtain a SiO2 dielectric layer / h-BN / Si3N4 / Si composite film. As a dielectric layer, SiO2 can not only effectively isolate the photoresist and h-BN to prevent photoresist residue from contaminating the h-BN thin film, but also serve as a protective layer during the subsequent etching process to prevent damage to the h-BN material;

[0140] The specific process of PECVD growth of SiO2 is as follows: the h-BN / Si3N4 / Si wafer is placed in a four-inch circular groove on the deposition stage and preheated at a temperature of 250 °C for 1 h; then the mechanical pump and the molecular pump are turned on to pump the vacuum until the chamber vacuum reaches 10 -6 Pa, and then a mixed gas of SiH4 and N2O is filled into the intake port. The reaction temperature is 300 °C, the SiH4 flow rate is 13 sccm, the N2O flow rate is 210 sccm, the pressure is 80 Pa, and the deposition rate is 15 nm / min;

[0141] Step 3: Spin-coat a layer of photoresist uniformly on the surface of the SiO2 dielectric layer, and the photoresist layer will be patterned through lithography technology to form the required structure;

[0142] The specific steps of using standard lithography technology for patterning are as follows:

[0143] Photoresist spin coating: A semi-automatic spin coater is used for photoresist coating. AZ5214 positive photoresist is used. The SiO2 dielectric layer / h-BN / Si3N4 / Si composite film is placed on the spin coater turntable and vacuum adsorption is turned on. First, it runs at a low speed of 600 r / min for 5 s to spread the photoresist evenly, and then runs at a high speed of 4000 r / min for 30 s to control the photoresist thickness. The spin coating thickness is 2 μm. Bubbles should be avoided when dropping the photoresist. If bubbles appear, they should be removed in time to ensure the quality of spin coating;

[0144] Pre-baking treatment: The silicon wafer coated with photoresist is baked on a hot plate at 95 °C for 90 s to cure the photoresist;

[0145] Exposure treatment: A MA6 mask aligner is used for exposure. A photomask is selected, and the exposure duration is set to 3.7 s;

[0146] Development treatment: 3038 developer is used for development. Its main component is 2.38 wt% tetramethylammonium hydroxide. The development time is 40 s. After development, the photoresist layer / SiO2 dielectric layer / h-BN / Si3N4 / Si composite film is soaked in deionized water for 1 min for fixing to remove the residual developer;

[0147] Post-baking treatment: The photoresist layer / SiO2 dielectric layer / h-BN / Si3N4 / Si composite film is baked on a hot plate at 110 °C for 2 min to complete the hardening film treatment before etching;

[0148] Priming film treatment: A glue coater is used to remove the residual photoresist on the developed pattern. The set parameters are: O2 flow rate 150 sccm, power 200 W, treatment time 2 min;

[0149] The patterned photoresist layer will be used for the subsequent etching process to ensure the accurate patterning of SiO2 and h-BN;

[0150] Step 4: The unpatterned SiO2 dielectric layer region is etched using the ion beam etching (IBE) method, and at the same time, the underlying h-BN thin film region is removed. The photoresist layer is cleaned and removed. During the etching process, the SiO2 layer provides protection to avoid damage to the h-BN thin film during etching. This step ensures that the h-BN thin film region is accurately etched and the required structure is formed;

[0151] The specific process of IBE etching is as follows: The substrate is fixed on the sample stage (good thermal contact is required), the levelness is ensured, and the vacuum is pumped to the base pressure of 5×10 -6Torr to avoid residual gas interference in etching; introduce working gas Ar with a flow rate of 15 sccm, start the ion source, with a beam current energy of 400 eV and an incident angle of 0°, gradually increase the anode voltage until it stabilizes; control the chamber pressure at 3×10 - 4 Torr;

[0152] Remove the remaining photoresist by water bath in acetone at 45 °C (twice, 6 min each) and water bath in absolute ethanol at 45 °C (5 min) to ensure the surface of the patterned h-BN is clean and not contaminated;

[0153] On the patterned h-BN thin film, deposit metal electrode Au (20 nm) by magnetron sputtering, with a sputtering power of 0.5 kW and a sputtering rate of 2.4 nm / s. The electrode is connected to the h-BN thin film to form the main structural part of the device.

[0154] In Example 2 of the present invention, SiO2 is used as the dielectric layer to assist in h-BN patterning, which can isolate the h-BN from the photoresist and provide protection, avoiding damage to the h-BN thin film during the etching process and greatly improving the surface quality of the h-BN thin film.

[0155] Example 3

[0156] In Example 3 of the present invention, by applying the dielectric layer-assisted graphene patterning method to the preparation of pressure sensors, the improvement of the sensor performance and stability by this method is demonstrated.

[0157] Step 1: Transfer graphene to the Si3N4 / Si substrate by wet transfer (such as using a PMMA support layer) and remove the PMMA support layer;

[0158] The specific process of PMMA wet transfer is as follows: Cut a 2-inch sample from the graphene copper foil grown by CVD, and use tape to fix it on the wafer spacer for subsequent operations;

[0159] CVD step: Put the copper foil into the furnace, introduce reduction gas hydrogen and protective gas argon, heat to 1000 °C, stabilize the temperature, and maintain for 20 min for the reduction reaction; then stop introducing hydrogen and argon, change to introduce methane gas for 30 min. After the deposition is completed; cut off the power supply, close the methane gas, and then introduce argon to exhaust the methane gas. Under the environment of argon, wait until the copper foil deposited with graphene cools to room temperature, take out the copper foil deposited with graphene to obtain graphene on the copper foil;

[0160] Spin coating of PMMA-A4 glue (manufactured by Kayaku Advanced Materials, Inc.) was carried out on a spin coater. A two-stage spin coating method was used to form a uniform thin film of PMMA on the surface of graphene. First, spin coat at 700 r / s for 9 s, place the sample on a hot plate (80 °C) and bake for 5 min. Then, spin coat at 3000 r / s for 40 s, and then place the sample on a hot plate at 180 °C and bake for 2 min to complete the curing of PMMA, forming a PMMA support layer (500 nm).

[0161] Subsequently, the copper substrate was corroded. The sample was floated with the Cu side down in an etching solution with a specific ratio (CuSO4:HCl:H2O = 16 g:10 mL:100 mL, HCl is a 15 wt% hydrochloric acid solution), and left standing for 24 h to ensure complete dissolution of copper, obtaining a PMMA support layer / graphene composite film.

[0162] After corrosion, an improved RCA cleaning method was used to remove metal impurities: sequentially float the PMMA support layer / graphene composite film in a mixed solution of H2O:H2O2:NH4OH (volume ratio 20:1:1, H2O2 is a 45 wt% hydrogen peroxide solution, NH4OH is a 25 wt% ammonia water), deionized water, a mixed solution of H2O:H2O2:HCl (volume ratio 20:1:1, H2O2 is a 45 wt% hydrogen peroxide solution, HCl is a 15 wt% hydrochloric acid solution) and deionized water for cleaning, and each step lasts for 5 min to minimize the retention of wrinkles and impurities on the graphene surface.

[0163] After cleaning, use the target Si3N4 / Si substrate to fish out the PMMA support layer / graphene composite film from water. The Si3N4 / Si substrate is a Si3N4 thin film covered on a Si substrate, and graphene contacts the Si3N4 thin film on the Si3N4 / Si substrate. Then place the sample vertically for 2 h to dry naturally, and then bake on a hot plate at 85 °C for 20 min to enhance the adhesion between graphene and the substrate.

[0164] Finally, remove the PMMA support layer by water bath in acetone at 50 °C (twice, 5 min each) and water bath in absolute ethanol at 50 °C (5 min) in sequence to obtain a high-quality bare graphene thin film.

[0165] Step 2: On the transferred graphene surface, deposit a 20-nm-thick Si3N4 dielectric layer using PECVD technology to obtain a Si3N4 dielectric layer / graphene / Si3N4 / Si composite film. Si3N4 as the dielectric layer can effectively isolate the photoresist from graphene, avoid photoresist residues on the graphene surface, and at the same time provide an additional protective layer, which helps to improve the durability of the sensor.

[0166] The specific process of growing Si3N4 by PECVD is as follows: Place the graphene / Si3N4 / Si wafer in the four-inch circular groove of the deposition stage and preheat the graphene / Si3N4 / Si wafer at a temperature of 300 °C for 1 h. Then, turn on the mechanical pump and the molecular pump to evacuate the chamber until the chamber vacuum reaches 10 -6 Pa. After that, fill the inlet with a mixed gas of SiH4, N2, and NH3. The reaction temperature is 300 °C, the flow rate of SiH4 is 11 sccm, the flow rate of N2 is 205 sccm, the flow rate of NH3 is 20 sccm, the pressure is 80 Pa, and the deposition rate is 15 nm / min.

[0167] Step 3: Spin-coat a layer of photoresist on the surface of the Si3N4 dielectric layer to evenly cover the entire surface. Using standard photolithography technology, through exposure and development, pattern the photoresist to form the required graphene pattern structure.

[0168] The specific steps of the standard photolithography technology are as follows:

[0169] Photoresist spin-coating: Use a semi-automatic spin coater to coat the photoresist. Use AZ5214 positive photoresist. Place the Si3N4 dielectric layer / graphene / Si3N4 / Si composite film on the spin coater turntable and turn on the vacuum adsorption. First, run at a low speed of 600 r / min for 5 s to evenly spread the photoresist, and then run at a high speed of 4000 r / min for 30 s to control the thickness of the photoresist. The thickness of the spin-coated photoresist is 2 μm. When dropping the photoresist, avoid generating bubbles. If bubbles appear, they should be removed in time to ensure the quality of the spin-coated photoresist.

[0170] Pre-baking treatment: Bake the Si3N4 dielectric layer / graphene / Si3N4 / Si composite film coated with photoresist on a hot plate at 95 °C for 90 s to cure the photoresist and obtain the photoresist layer / Si3N4 dielectric layer / graphene / Si3N4 / Si composite film.

[0171] Exposure treatment: Use a MA6 lithography machine for exposure. Select a photomask, and set the exposure time to 3.7 s.

[0172] Development treatment: Use 3038 developer for development. Its main component is 2.38 wt% tetramethylammonium hydroxide. The development time is 40 s. After development, soak the photoresist layer / Si3N4 dielectric layer / graphene / Si3N4 / Si composite film in deionized water for 1 min for fixing to remove the residual developer.

[0173] Post-baking treatment: Bake the photoresist layer / Si3N4 dielectric layer / graphene / Si3N4 / Si composite film on a hot plate at 110 °C for 2 min to complete the hardening treatment before etching.

[0174] Priming film treatment: Use a gluing machine to remove the residual photoresist on the developed pattern. Set the parameters as follows: O2 flow rate is 150 sccm, power is 200 W, and treatment time is 2 min;

[0175] Step 4: Use the reactive ion etching (RIE) method to etch the unpatterned Si3N4 dielectric layer region, and at the same time remove the underlying graphene region. Clean and remove the photoresist layer, and retain the formed graphene sensor structure;

[0176] The specific process of RIE etching is as follows: The flow rate of CFH3 is 10 sccm; the flow rate of CF6 is 8 sccm; the flow rate of He is 150 sccm; set the chamber pressure to 1500 mTor; the etching power is 200 W; the etching rate is 100 nm / min;

[0177] Use water bath in acetone at 45 °C (twice, 6 min each) and water bath in absolute ethanol at 45 °C (5 min) to remove the remaining photoresist, ensure that the sensor surface is smooth and free of contaminants, and obtain the Si3N4-Gr sample;

[0178] On the patterned graphene surface, deposit the metal electrode Au (20 nm) by magnetron sputtering. The sputtering power is 0.5 kW and the sputtering rate is 2.4 nm / s, so that the electrode forms good electrical contact with the graphene layer, and the basic structure of the pressure sensor is completed.

[0179] Performance test:

[0180] As Figure 5 shown, electrical measurements were carried out on the sensors prepared with the Si3N4-Gr samples prepared in Example 3. Set the applied voltage to -50 to 100 mV, and measure the I-V curve of the sensors prepared using Si3N4 as the dielectric layer, showing good linearity, indicating that the sensors prepared with the Si3N4-Gr samples have superior consistency and stability.

[0181] As Figure 6 and Figure 7 shown, the sensors prepared with the Si3N4-Gr samples prepared in Example 3 and the PR-Gr samples prepared by the traditional photolithography process in Comparative Example 1 were used to test the ability to resist the external environment. Among them Figure 6 is the stability test result after 10 days, Figure 7 is the stability test result after 30 days.

[0182] As Figure 6 and Figure 7As shown, the device fabricated from the Si3N4-Gr sample was more stable during the long-term stability test. From the figure, the normalized resistance (R / R0) can be seen, where R and R0 are the real-time resistance and the original resistance of the device. Due to the doping of graphene by moisture and air, the resistance of the PR-Gr device decreased within the first 6 days, and then it increased sharply over time, with a relative resistance change of 12.5%. In contrast, the resistance of the Si3N4-Gr device changed slightly, with a relative change of only 1.92%. Over time, the resistance of the PR-Gr device increased significantly, which can be attributed to the oxidation and contamination of the graphene film. After 30 days, the relative resistance change reached 68.5%. The Si3N4-Gr device remained stable because the Si3N4-Gr film prevented the contamination of impurity particles (such as H2O, O2, and dust) in the external environment compared to the PR-Gr sample.

[0183] In Example 3 of the present invention, the sensor fabricated with the Si3N4-Gr sample demonstrated the ability to isolate air and water and inhibit oxidation during electrical and stability tests. The standard deviation of the resistance of the fabricated device decreased by 29.56%, and the ability of the device to resist the external environment increased by more than 59.4%, showing excellent consistency and long-term stability.

[0184] The dielectric layer used in the present invention can effectively isolate the residue of the photoresist, prevent environmental doping, reduce the risk of contamination, and at the same time, as a protective layer, effectively improve the stability of two-dimensional materials such as graphene or h-BN in a complex environment, thereby significantly improving the consistency and stability of the device.

[0185] The dielectric layer materials used in the present invention include Si3N4, Al2O3, BN, SiO2, etc., and the patterned two-dimensional materials include graphene, h-BN, MoS2, etc. Based on the principle of the present invention, the embodiments can be subject to various changes, modifications, substitutions, and variations, and all these changes are within the protection scope of the present invention.

[0186] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention rather than all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and all these embodiments belong to the protection scope of the present invention.

Claims

1. A method for patterning graphene assisted by a dielectric layer, characterized in that It includes the following steps: Deposit a dielectric layer on the substrate with the two-dimensional material attached to cover the two-dimensional material, obtaining a dielectric layer / two-dimensional material / substrate composite film; Coat a photoresist to cover the surface of the dielectric layer, forming a photoresist layer, obtaining a photoresist layer / dielectric layer / two-dimensional material / substrate composite film; After patterning the photoresist layer, remove the dielectric layer in the unpatterned area and the underlying two-dimensional material by etching; Clean and remove the photoresist layer, obtaining a patterned dielectric layer / two-dimensional material / substrate composite film; The two-dimensional material includes graphene, hexagonal boron nitride or molybdenum disulfide; The material of the dielectric layer includes Si3N4, Al2O3, boron nitride or SiO2.

2. The graphene patterning method according to claim 1, wherein, The substrate is a Si3N4 / Si substrate; the Si3N4 / Si substrate has a Si3N4 thin film covered on the Si substrate, and the two-dimensional material is in contact with the Si3N4 thin film on the Si3N4 / Si substrate.

3. The graphene patterning method according to claim 1, wherein The preparation method of the substrate with the two-dimensional material attached is: transfer the two-dimensional material to the substrate; the transfer method is wet transfer or dry transfer; the wet transfer is polymethyl methacrylate wet transfer.

4. The graphene patterning method according to claim 1, wherein The thickness of the dielectric layer is 5-45 nm.

5. The graphene patterning method according to claim 1, characterized in that The method of depositing a dielectric layer is plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition or high-density plasma chemical vapor deposition.

6. The graphene patterning method according to claim 1, wherein The photoresist is AZ5214 positive photoresist or AZP4620 positive photoresist.

7. The graphene patterning method according to claim 1, wherein The coating is spin coating; the spin coating includes low-speed spin coating and high-speed spin coating performed in sequence; the rotation speed of the low-speed spin coating is 400-600 r / min; the rotation speed of the high-speed spin coating is 3000-4500 r / min.

8. The graphene patterning method according to claim 1 or 7, characterized in that The thickness of the photoresist layer is 1-2 μm.

9. The graphene patterning method according to claim 1, wherein The cleaning is to perform a water bath in acetone and absolute ethanol in sequence.

10. Application of the method for patterning graphene assisted by the dielectric layer according to any one of claims 1 to 9 in the preparation of a sensor.

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