A graphene film cutting method based on sapphire substrate

Abstract

The present invention discloses a graphene film cutting method based on a sapphire substrate. Before cutting, the method first uses PMMA to pre-treat a graphene wafer, then uses EBL to complete shaping of the graphene wafer and expose a cutting track, then removes the PMMA coating and graphene on the cutting track, and finally cuts the graphene wafer according to the cutting track. The method provided by the present invention performs EBL etching on the graphene wafer, destroys the adhesion of PMMA and graphene at the cut part, so that the graphene in the target area can maintain its complete performance during the cutting process. The method can achieve efficient and low-loss cutting of a single-layer graphene based on a sapphire substrate, and can be applied to the large-scale graphene device preparation process.

Description

Technical Field

[0001] The invention relates to the technical field of graphene film cutting, in particular to a graphene film cutting method based on a sapphire substrate. Background Art

[0002] Since Andre Geim and Konstantin Novoselov separated graphene by mechanical exfoliation in 2004, graphene has been widely used in the design and production of optoelectronic devices such as absorbers and modulators due to its high carrier mobility, electrical tunability and high absorbance, and has played a huge role in military and civilian fields. With the continuous deepening of graphene research, the technology of large-scale production of graphene wafers using chemical vapor deposition (CVD) has become very mature. In current research, a feasible method for preparing optoelectronic modulator devices is to transfer graphene to a standard substrate for preparation. The graphene transfer process has problems such as introducing more chemical impurities into the sample, complex transfer process and low success rate. Directly cutting the grown graphene wafer and then preparing optoelectronic devices can undoubtedly greatly improve the production efficiency of graphene optoelectronic devices and reduce the pollution caused by the graphene transfer process. However, due to the inability to efficiently and non-destructively cut graphene wafers, the large-scale preparation of graphene optoelectronic devices in experiments and production is limited.

[0003] At present, the method of cutting wafers with sapphire as substrate is relatively mature, and there are three main cutting methods: laser cutting, water jet cutting and mechanical cutting. Laser cutting has higher cutting accuracy, but the cutting result of this method is greatly affected by the laser power and laser cutting speed, and it is easy to cause thermal damage, which has a serious impact on product quality. The high-pressure water jet cutting method has the disadvantages of slow speed, low precision and expensive equipment. The earliest mechanical cutting technology used diamond scratching cutting, which has been eliminated because it cannot obtain a complete cutting seam and will produce cracks. The latest cutting method is ultra-thin diamond scribing cutting, which is the most mature and has the advantages of high precision, low cost and high efficiency. It is widely used in sapphire substrate wafer cutting at this stage. However, if this method is directly applied to sapphire substrate graphene wafer cutting, it is easy to damage the graphene on the surface of the sample during the cutting process and cannot be applied on a large scale. Summary of the invention

[0004] The present invention provides a graphene film cutting method based on a sapphire substrate, which is used to overcome the defects of the prior art such as graphene that is easily damaged on the surface of a sample.

[0005] To achieve the above object, the present invention provides a graphene film cutting method based on a sapphire substrate, comprising the following steps:

[0006] S1: pre-treating the graphene wafer using PMMA (polymethyl methacrylate) to form a PMMA coating layer on the graphene wafer;

[0007] S2: Electron Beam Lithography (EBL) is performed on the graphene wafer after S1 to expose a pattern to be cut on the graphene wafer to obtain a cutting track;

[0008] S3: pre-treating the graphene wafer after S2, and then removing the PMMA coating on the graphene wafer;

[0009] S4: removing graphene on the cutting track of the graphene wafer;

[0010] S5: cutting the graphene wafer along the cutting track to obtain a graphene film of the pattern exposed in S2.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The present invention provides a graphene film cutting method based on a sapphire substrate. Before cutting, the method first uses PMMA to pre-treat the graphene wafer, then uses EBL to complete the shaping of the graphene wafer and expose the cutting track, then removes the PMMA coating and the graphene on the cutting track, and finally cuts the graphene wafer according to the cutting track. The method provided by the present invention performs EBL etching on the graphene wafer on the basis of traditional diamond scribing cutting, destroys the adhesion of PMMA and graphene in the cut part, so that the graphene in the target area can maintain its complete performance during the cutting process. The method can achieve efficient and low-loss cutting of single-layer graphene based on sapphire substrate, effectively avoiding the disadvantages of difficult control of laser cutting parameters and introduction of thermal damage, and the slow cutting speed and low precision of high-pressure water jet method, as well as the problem that single-layer graphene is difficult to fully preserve during ordinary mechanical cutting. The method can be applied to the preparation process of large-scale graphene devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0014] Figure 1 This is a physical picture of the graphene wafer used in Example 1;

[0015] Figure 2 The graphene wafer based on the sapphire substrate cut in Example 1;

[0016] Figure 3a This is the imaging result of the graphene wafer under AFM before cutting in Example 1;

[0017] Figure 3b This is the imaging result of the graphene wafer after cutting under AFM in Example 1;

[0018] Figure 4a This is the laser micro-Raman spectrum of the graphene wafer before cutting;

[0019] Figure 4b This is the laser micro-Raman spectrum of the graphene wafer after cutting;

[0020] Figure 5a This is a sample image of a sapphire with a thickness of 0.5 mm after laser cutting using Laser MicroJet in Comparative Example 2;

[0021] Figure 5b This is the image of the cut surface under an optical microscope after laser cutting of 0.5 mm thick sapphire using Laser MicroJet in Comparative Example 2.

[0022] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] 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 the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0025] Unless otherwise specified, all drugs / reagents used were commercially available.

[0026] The present invention provides a graphene film cutting method based on a sapphire substrate, comprising the following steps:

[0027] S1: pre-treating the graphene wafer using PMMA to form a PMMA coating layer on the graphene wafer;

[0028] S2: performing electron beam exposure on the graphene wafer after S1 to expose a pattern to be cut on the graphene wafer, thereby obtaining a cutting track;

[0029] S3: pre-treating the graphene wafer after S2, and then removing the PMMA coating on the graphene wafer;

[0030] S4: removing graphene on the cutting track of the graphene wafer;

[0031] S5: cutting the graphene wafer along the cutting track to obtain the graphene film of the pattern exposed in S2. During the cutting process, since a cutting channel has been reserved, the blade does not cause damage to the graphene on the surface of the graphene wafer due to contact during the cutting process.

[0032] The present invention provides a novel graphene film cutting method, which uses PMMA to protect the graphene wafer before using traditional ultra-thin diamond scriber for cutting, and then uses electron beam exposure to expose the cutting track. Compared with the currently commonly used cutting method, this method can effectively shorten the cutting time of graphene wafers based on sapphire substrates, improve the success rate of graphene wafer cutting, and obtain high-quality samples.

[0033] Preferably, step S1 specifically includes:

[0034] PMMA is spin-coated on the graphene wafer at a rotation speed of 3500-4500 r / min and allowed to stand to obtain a graphene wafer with a PMMA coating.

[0035] PMMA has the characteristics of easy peeling and low price, and is suitable as a protective film to protect graphene.

[0036] Preferably, the molecular weight of the PMMA is 950K, and the thickness of the PMMA coating is 420nm. PMMA that is too thin or too thick or uses different molecular weights cannot better implement the subsequent electron beam exposure step and cannot achieve the best electron beam exposure effect.

[0037] Preferably, in step S2, the electron beam exposure time is 4 to 5 hours. The electron beam exposure time is determined by the required exposure area, the complexity of the exposure pattern and the instrument used.

[0038] Preferably, in step S2, the graphene wafer with PMMA coating is exposed by electron beam exposure of model EBPG5000Plus. The main function of electron beam exposure is to protect the graphene wafer and to shape the graphene sample by electron beam exposure so as to remove the graphene and PMMA on the cutting path, so that the phenomenon of large pieces of graphene being taken away by PMMA in the direct cutting method will not occur during cutting.

[0039] During the sapphire substrate graphene wafer dicing process, the interface interaction energy between graphene grown directly on Al2O3 and sapphire is 1.47 Jm -2 The interfacial interaction energy of graphene transferred to sapphire surface is 0.66 Jm -2 After high temperature training, the interface interaction energy between the transferred surface graphene and sapphire can reach 1.25 Jm -2 . This shows that in addition to the van der Waals force between the surfaces of sapphire and graphene, CO-AL bonds are also formed between the sapphire surface and the carbon atoms in graphene at high temperatures. Nevertheless, due to the van der Waals epitaxial characteristics, covalent bonds are formed between the PMMA layer and graphene. Whether it is graphene grown directly on sapphire or transferred graphene after high-temperature tempering, the force between it and the surface of the sapphire substrate is still nearly two orders of magnitude smaller than the covalent bond force, resulting in the interaction force between graphene and PMMA being significantly higher than the interaction force between graphene and sapphire. Therefore, during ordinary mechanical cutting, at the high rotation speed of the diamond dicing knife, the cooling water flow will not only wash away the spin-coated PMMA layer, but also the graphene layer with a stronger interaction force with PMMA, which will lead to cutting failure.

[0040] Preferably, in step S3, the pre-processing is specifically:

[0041] Place the graphene wafer after S2 in water for 20 to 40 seconds, take it out and blow it dry to remove static electricity, then place the graphene wafer in gold etching solution for 1 to 3 minutes to remove the gold left during the electron beam exposure process, wash it with water, and blow it dry with nitrogen.

[0042] Preferably, in step S3, removing the PMMA coating on the graphene wafer is specifically performed by:

[0043] The pre-treated graphene wafer is immersed in a mixed solution of 1:3 methyl isobutyl ketone and isopropyl alcohol for 40 to 70 seconds, and then immersed in isopropyl alcohol for 40 to 70 seconds to remove the PMMA coating on the graphene wafer.

[0044] Preferably, step S4 is specifically:

[0045] The graphene wafer was placed in a reactive ion etcher and treated with oxygen plasma for 15 seconds to etch the graphene on the cutting tracks of the graphene wafer, and then the etched graphene residues were blown away.

[0046] Preferably, in step S5, the cutting is performed using a DISCO cutting machine with a blade model of NBC ZB1050.

[0047] Preferably, the graphene wafer is a single-layer graphene 4-inch wafer directly grown on a sapphire insulating substrate with a thickness of 0.5 mm.

[0048] Example 1

[0049] This embodiment provides a graphene film cutting method based on a sapphire substrate, comprising the following steps:

[0050] S1: Spin-coat PMMA on the graphene wafer at a rotation speed of 3500-4500 r / min, let it stand, and obtain a graphene wafer with a PMMA coating; the molecular weight of PMMA is 950K, and the thickness of the PMMA coating is 420 nm.

[0051] The graphene wafer is a 4-inch single-layer graphene wafer grown directly on a 0.5 mm thick sapphire insulating substrate. Figure 1 shown.

[0052] S2: The graphene wafer after S1 is subjected to electron beam exposure for 20 to 40 seconds (model: EBPG5000Plus) to expose a pattern to be cut on the graphene wafer to obtain a cutting track;

[0053] S3: Place the graphene wafer after S2 in water for 20 to 40 seconds, take it out and blow dry it to remove static electricity, then place the graphene wafer in gold etching solution for 1 to 3 minutes to remove the gold left during the electron beam exposure process, wash it with water, and blow dry it with nitrogen;

[0054] The pre-treated graphene wafer is immersed in a mixed solution of 1:3 methyl isobutyl ketone and isopropyl alcohol for 40 to 70 seconds, and then immersed in isopropyl alcohol for 40 to 70 seconds to remove the PMMA coating on the graphene wafer.

[0055] S4: placing the graphene wafer into a reactive ion etcher, treating it with oxygen plasma for 15 seconds to etch the graphene on the cutting track of the graphene wafer, and then blowing off the etched graphene residue.

[0056] S5: Cutting the graphene wafer along the cutting track to obtain a 1 cm×1 cm graphene film.

[0057] The graphene wafer based on the sapphire substrate cut in this embodiment is as follows: Figure 2As shown in the figure, there is no obvious damage on the surface compared with that before cutting. The graphene wafer based on sapphire substrate after cutting was characterized by atomic force microscopy (AFM) and Raman spectrometer. The results are shown in the figure. Figure 3a , Figure 3b , Figure 4a and Figure 4b shown. Figure 3a This is the imaging result of graphene wafer under AFM before cutting. Figure 3b The following is the imaging result of the graphene wafer under AFM after cutting. By comparison, it is found that although a lot of residues left over from the cutting process are generated on the graphene wafer (the white dots in Figure 3 (b)), the stepped morphology of the sapphire surface after hydrogen etching generated in the CVD production process and the boundaries between crystals formed during the cooling process due to the different thermal expansion coefficients of graphene and sapphire are clearly visible before and after cutting, and the overall characteristics of the sample are completely preserved. Figure 4a This is the laser micro-Raman spectrum of the graphene wafer before cutting. Figure 4b This is the laser micro Raman spectrum of the graphene wafer after cutting. The G peak and 2D peak are the main characteristic peaks of graphene. The two important features of graphene appear in the Raman spectrum before and after cutting. The G peak and 2D peak before cutting appear at 1589cm -1 and 1589cm -1 After cutting, the G peak and 2D peak appear at 1584cm -1 and 2699cm -1 The G peak and 2D peak of standard single-layer graphene are at 1582cm -1 Nearby and 2700cm -1 It appears nearby. After comparing the characteristic peak position of the cut sample with that of the standard single-layer graphene, it is found that the characteristic peak position has not shifted, and the G peak position after cutting has not shifted to a high wave number as the Cohen anomaly effect weakens.

[0058] The intensity ratio between the G peak and the D peak is an important parameter for characterizing the defect density in graphene. D / I G , using formulas (1) and (2), the average distance L between two zero-dimensional point defects in graphene can be calculated: D , and then the defect density n of the graphene sample is obtained D , where E L The laser energy.

[0059]

[0060]

[0061] In this embodiment, a Horiba LabRAM HR laser with a wavelength of 514 nm and an energy of 2.41 eV is used. D / I G is 0.674. After calculation, the distance between the two defect points is 11.49nm to 15.69nm, and the defect density is 1.16×10 11 cm -2 to 2.16×10 11 cm -2 The defect density of the graphene sample after cutting is low, indicating that the cutting process does not change the defect density of the sample. By comparing the Raman signal of the graphene sample before cutting, the sample after cutting retains the high-quality single-layer graphene characteristics.

[0062] Comparative Example 1

[0063] This comparative example provides a direct cutting method for graphene film based on sapphire substrate, using the graphene wafer in Example 1. This cutting method requires continuous use of flowing water to cool the blade, and a large amount of splashing pollutants will be generated during the cutting process. Therefore, the graphene wafer needs to be spin-coated for protection before cutting, specifically, PMMA is spin-coated on the graphene wafer at a speed of 3500-4500r / min, and the obtained graphene wafer with PMMA coating is left to stand. The molecular weight of PMMA is 950K, and the thickness of the PMMA coating is 420nm. Then the graphene wafer is directly cut by diamond scribing. After cutting, it was found that the graphene wafer was damaged and the cutting experiment failed. This is because the adhesion between graphene and PMMA is greater than the adhesion between graphene and sapphire. In the process of cooling the blade, the running water washed away the PMMA and the graphene attached to PMMA, resulting in sample damage.

[0064] Comparative Example 2

[0065] This comparative example provides a method for laser cutting of a graphene film based on a sapphire substrate, firstly using a laser to groove a graphene wafer, and then using a blade to separate the graphene wafer. Figure 5a During the experiment, it was found that the laser cutting method requires experiments with different laser modes. It is difficult to control the cutting parameters during the experiment. It is easy to have problems such as too short laser grooving time resulting in too narrow grooves or too many grooving iterations resulting in thermal damage to the sample near the groove. Figure 5b This is an image of the laser cutting section under an optical microscope. The light-colored cutting grooves are narrow and discontinuous, while the samples near the black cutting grooves are damaged. In addition, the laser cutting method requires more iterations and a longer time.

[0066] 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 changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A graphene film cutting method based on a sapphire substrate, characterized in that: The following steps are involved: S1: pre-treating the graphene wafer using PMMA to form a PMMA coating layer on the graphene wafer; S2: performing electron beam exposure on the graphene wafer after S1 to expose a pattern to be cut on the graphene wafer, thereby obtaining a cutting track; S3: pre-treating the graphene wafer after S2, and then removing the PMMA coating on the graphene wafer; the molecular weight of the PMMA is 950K, and the thickness of the PMMA coating is 420nm; S4: removing graphene on the cutting track of the graphene wafer; S5: cutting the graphene wafer along the cutting track to obtain a graphene film of the pattern exposed in S2; The graphene wafer is a 4-inch single-layer graphene wafer directly grown on a sapphire insulating substrate with a thickness of 0.5 mm.

2. The graphene film cutting method according to claim 1, characterized in that: Step S1 is specifically as follows: PMMA is spin-coated on the graphene wafer at a rotation speed of 3500-4500 r / min and allowed to stand to obtain a graphene wafer with a PMMA coating.

3. The graphene film cutting method according to claim 1, characterized in that: In step S2, the electron beam exposure time is 4 to 5 hours.

4. The graphene film cutting method according to claim 1 or 3, characterized in that: In step S2, the graphene wafer with the PMMA coating is exposed using an electron beam exposure machine model EBPG5000Plus.

5. The graphene film cutting method according to claim 1, characterized in that: In step S3, the pre-processing is specifically as follows: Place the graphene wafer after S2 in water for 20 to 40 seconds, take it out and blow it dry to remove static electricity, then place the graphene wafer in gold etching solution for 1 to 3 minutes to remove the gold left during the electron beam exposure process, wash it with water, and blow it dry with nitrogen.

6. The graphene film cutting method according to claim 1, characterized in that: In step S3, removing the PMMA coating on the graphene wafer is specifically as follows: The pre-treated graphene wafer is immersed in a mixed solution of 1:3 methyl isobutyl ketone and isopropyl alcohol for 40 to 70 seconds, and then immersed in isopropyl alcohol for 40 to 70 seconds to remove the PMMA coating on the graphene wafer.

7. The graphene film cutting method according to claim 1, characterized in that: Step S4 is specifically as follows: The graphene wafer was placed in a reactive ion etcher and treated with oxygen plasma for 15 seconds to etch the graphene on the cutting tracks of the graphene wafer, and then the etched graphene residues were blown away.

8. The graphene film cutting method according to claim 1, characterized in that: In step S5, the cutting is performed using a DISCO cutting machine with a blade model of NBC ZB1050.

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