CN108660430B

CN108660430B - Process method for quasi-direct growth of large-area graphene on oxide insulating substrate

Info

Publication number: CN108660430B
Application number: CN201810455783.0A
Authority: CN
Inventors: 徐晨; 孙捷; 董毅博; 解意洋; 潘冠中; 王秋华; 钱峰松
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2018-05-14
Filing date: 2018-05-14
Publication date: 2020-07-03
Anticipated expiration: 2038-05-14
Also published as: CN108660430A

Abstract

The invention discloses a process method for similar direct growth of large-area graphene on an oxide insulating substrate, belonging to the field of preparation of graphene materials. According to the invention, graphene is directly grown on the oxide insulating substrate without the graphene growth catalysis effect by adopting a CVD method, and the graphene can be directly used for preparing devices without transfer. A layer of metal is plated on an insulating substrate to serve as a catalyst, graphene grows on the surface of the metal by utilizing CVD, and the surface of the metal forms a hole shape during growth. And then, coating PMMA in a spinning mode, and corroding metal by using a wet method with PMMA as a graphene supporting layer. The corrosive liquid can penetrate through the PMMA and the graphene to corrode the metal below. And after the metal is corroded cleanly, the graphene and the PMMA fall on the substrate, and then the PMMA on the surface of the graphene is removed by using an organic solvent, so that the graphene film sample which is directly grown on the insulating substrate is finally obtained. The method has the advantages of simple process, high repeatability, high quality of the grown graphene, large area and almost no damage.

Description

Process method for quasi-direct growth of large-area graphene on oxide insulating substrate

Technical Field

The invention relates to a graphene preparation process, and belongs to the field of graphene material preparation.

Background

Graphene is a new material consisting of a single layer of carbon atoms, and has many excellent characteristics, such as: high carrier mobility, high young's modulus, high light transmittance, and the like. In the future, graphene may play an important role in the fields of electronics, energy, corrosion prevention and the like. At present, the preparation method of graphene mainly comprises the following four steps: mechanical lift-off, Chemical Vapor Deposition (CVD), redox, silicon carbide epitaxy. The CVD method for preparing the graphene has high quality and low cost, is suitable for large-scale production, and is the most main preparation way of the graphene at present. The CVD method requires the use of metal as a catalyst to prepare graphene on a metal substrate, wherein two metals, copper and nickel, are the most important metals for preparing graphene at present. The preparation of graphene electronic devices requires transferring graphene grown on the surface of a metal base onto a target substrate (such as a substrate of silicon dioxide, sapphire, etc.), and the general process is as shown in fig. 1: 1. coating the surface of the metal substrate graphene with a PMMA (polymethyl methacrylate) film in a spinning mode; 2. putting the sample coated with PMMA into a metal corrosion liquid to corrode metal; 3. fishing out the PMMA/graphene film by using a target substrate; 4. and (3) removing PMMA on the surface of the graphene by using an organic solvent (acetone and the like), and finally realizing the transfer of the graphene. As can be seen from the transfer step, the transfer of graphene is cumbersome, not suitable for large-scale application of graphene in the future, and due to the characteristics of the monoatomic layer of graphene, it is very vulnerable during the transfer process.

The direct growth of the graphene insulating substrate is a graphene preparation process which is emerging in recent years, and the purpose of the direct growth of the graphene insulating substrate is to prepare a high-quality graphene film by directly growing the graphene insulating substrate so as to avoid a transfer step of graphene. As can be seen from fig. 1, if the direct growth of graphene on the insulating substrate can be realized, the preparation of the graphene device can be realized only by one step, which greatly saves the preparation process of the device and improves the preparation efficiency of the device. At present, there are three main approaches for the direct growth of graphene: 1. direct growth without metal catalysis; 2. metal-assisted direct growth; 3. plasma-assisted enhanced direct growth (advanced materials,2016,28(25):4956), wherein the method is direct growth in a strict sense, the method can realize large-area growth regardless of the selected substrate, but the growth temperature is generally high (more than 1400 ℃) or the growth quality is generally poor, and the growth time is long; the second method is relatively complex in process, but due to metal catalysis, the quality of graphene is good; the third method can realize direct growth at lower temperature (less than 800 ℃), but the quality of graphene is poor and the growth controllability is poor; at present, no mature growth process which can be used for large-scale preparation exists for the direct growth of graphene.

Disclosure of Invention

The invention aims to provide a process method for directly growing large-area high-quality graphene on an oxide insulating substrate, which can simultaneously solve the problems of graphene transfer damage, poor adhesion with the substrate, doping of photoresist to graphene in the photoetching process and the like, and the grown graphene is high in quality. Meanwhile, the method is simple in process and suitable for large-scale production of graphene.

To achieve the above objects, the present invention converts the idea to realize the direct growth of graphene on an insulating substrate by a novel metal-assisted direct growth mechanism. As shown in fig. 2, the process method for quasi-direct growth of large-area graphene on an oxide insulating substrate includes the following steps: (1) firstly, plating a layer of metal film on a substrate; (2) growing a layer of graphene film on the surface of the metal by using metal catalysis through a CVD method; (3) continuously growing to enable the metal to be agglomerated to form holes, wherein the graphene film at the holes can fall on the substrate; (4) after the growth is finished, coating a layer of PMMA as a corrosion supporting layer in a spinning mode; (5) putting the sample into a metal corrosive liquid, wherein the metal corrosive liquid can penetrate through the PMMA and the graphene film to corrode the lower metal film; (6) after the metal film is corroded, the PMMA/graphene film falls on the insulated substrate, the PMMA is removed by using an organic solvent, and the graphene is left on the substrate. Finally, the quasi-direct growth of the insulating substrate is realized.

Since PMMA is a macromolecular organic matter, corrosive liquid can penetrate through PMMA, and meanwhile, the graphene film also has tiny holes or defects, so that the corrosive liquid penetrates through graphene. This is the most important theoretical basis on which the present invention can achieve quasi-direct growth of graphene.

The graphene grows on the metal surface instead of directly on the insulating substrate, but the transfer-free graphene is realized by the process of the invention, namely the finally obtained graphene film is on the insulating substrate, the graphene has high quality (see Raman spectrum of graphene in figure 3), is large in area and almost has no damage (see optical picture of graphene in figure 4), namely the purpose of directly growing the graphene is realized, and the process is called as the similar direct growth. The invention is different from the common oxide substrate nickel plating or copper plating growth graphene in that: in the common growth process, after the graphene grows, the graphene is coated with PMMA for transfer, and finally the graphene is transferred to other substrates. In the invention, the target substrate of the growth of the graphene and the final graphene is the same substrate, and the corrosion of the metal is performed by utilizing the mechanism that the corrosion liquid can penetrate through PMMA and the graphene, so that the transfer step does not exist, and the growth is similar to direct growth.

In the invention, nickel is used as a catalyst, and after graphene grows, the surface appearance of nickel is as shown in fig. 5, and the nickel surface needs to be agglomerated into holes at high temperature. Only in this way can PMMA/graphene be immobilized on a substrate after spinning on PMMA. If the nickel surface is not agglomerated to form pores, graphene will separate from the substrate and float in the etching solution after the nickel is etched, as shown in fig. 6, so that the direct growth of graphene cannot be realized.

In the invention, the holes can be formed by naturally agglomerating the nickel surface at high temperature to form irregular holes, and a regular hole array can be prepared by a photoetching-sputtering-stripping semiconductor process, as shown in fig. 7, the graphene can realize graphical growth.

In the invention, PMMA plays a supporting role on graphene in the process of corroding metal, so that the graphene is not damaged and is kept complete in the corrosion process.

In the present invention, the support layer of graphene is not limited to PMMA, but may be other organic substances that allow corrosive liquid to pass through.

The graphene catalytic metal used in the present invention is nickel or copper.

The insulating substrate used in the present invention is a silicon substrate having a silicon dioxide layer with a certain thickness, or a quartz substrate or a sapphire substrate.

The plating process in the invention is electron beam evaporation or magnetron sputtering.

The CVD growth equipment of the graphene in the invention can be Black Magic vertical cold wall type growth equipment of Aixtron company, and can also be tubular furnace equipment.

The graphical growth of the graphene is realized by controlling the metal graph, so that the grown graphene has a pattern consistent with that of the metal.

The invention has the advantages that:

1. the graphene direct growth process disclosed by the invention realizes transfer-free of graphene, the whole process flow from graphene growth to finally obtained direct growth-like graphene is less than 1 hour, and the preparation efficiency of a graphene device is greatly improved.

2. The graphene is almost free of damage and high in quality, and large-area graphene preparation can be achieved, which is difficult to achieve through a transfer process.

3. The patterned growth of the graphene can be realized by changing the metal pattern, the step of patterning the graphene after photoetching can be omitted, the graphene does not need to contact with the photoresist, the doping of the graphene by the photoresist is avoided, and the electrical property of the graphene is kept stable.

4. The process for directly growing the graphene in the graphical mode is simple, high in repeatability and suitable for large-scale production and application of the graphene.

Drawings

FIG. 1: a flow chart of preparing a graphene device by transferring metal substrate growth graphene;

FIG. 2: the invention adopts a flow chart of a process similar to direct growth of graphene;

FIG. 3: directly growing the Raman spectrum result of the graphene on different substrates;

FIG. 4: an optical microscope picture of similarly directly growing graphene on a silicon dioxide substrate, wherein the large area of the graphene is not damaged as can be seen from a picture a, and a picture b is an optical image seen by scratching a part of the graphene on the surface by using tweezers, so that the graphene can be more clearly displayed;

FIG. 5: an optical microscope picture of the morphology of the nickel surface after graphene growth;

FIG. 6: if the metal surface is not agglomerated to generate holes, the schematic diagram is shown after the metal is corroded. After the metal is corroded, the PMMA/graphene film is separated from the substrate, and the similar direct growth cannot be realized;

FIG. 7: a: a patterned metal film obtained by a semiconductor process of 'photolithography-sputtering-lift-off'; b, carrying out quasi-direct growth by using a patterned metal film to obtain a patterned graphene film; c: the intensity distribution graph of the 2D peak of the Raman spectrum of the patterned graphene film can be seen, and the patterned preparation of the graphene is actually realized through the confirmation of the Raman spectrum;

FIG. 8: a physical image of the graphical direct growth graphene film;

Detailed Description

The practice of the invention is illustrated by the following three examples.

Example 1: method for growing graphene film on silicon dioxide/silicon substrate by adopting nickel as catalytic metal

The whole process flow is shown in fig. 2, and the substrate is a silicon dioxide/silicon substrate.

The method comprises the following specific steps:

s1, after the substrate is cleaned, a 50 nm-thick nickel film is plated through a sputtering process, the carbon solid solubility of nickel is high, the number of layers of grown graphene can be controlled to a certain extent by controlling the thickness of nickel, and the number of grown graphene layers is small.

S2 graphene is prepared by Black Magic vertical cold wall type CVD equipment of Aixtron company, firstly, hydrogen annealing is carried out for 5min under the condition of 800 ℃, then, the temperature is raised to 1000 ℃, and growth is started: methane flow 10sccm, hydrogen flow 500sccm, argon flow: 500sccm, gas pressure 15mbar, growth time 5 min. Finally, a layer of graphene grows on the surface of the nickel, and the surface of the nickel forms a hole morphology as shown in fig. 5.

S3 the sample after growth is coated with a layer of PMMA at the rotation speed of 3000r/m of the spin coater for 40S. Coating with PMMA, and oven drying at 150 deg.C for 5 min.

S4, putting the PMMA-coated sample into a metal corrosive liquid, wherein the metal corrosive liquid is prepared according to the following steps: copper sulfate pentahydrate: hydrochloric acid: water 10 g: 50 ml: is prepared by mixing 50 ml. The corrosion time of nickel is about 10 min.

And S5, taking out the sample after the nickel is corroded cleanly, and drying the sample on a hot plate at 150 ℃ for 15min to enhance the adhesion between the graphene and the substrate.

S6, placing the sample into an acetone solution to be soaked for 30min to remove PMMA, then placing the sample into an isopropanol solution for 5min, and finally rinsing the sample with deionized water to obtain the large-area almost undamaged high-quality graphene film sample directly grown as shown in the figure 4.

Example 2: graphene film grown on quartz substrate by using copper as catalytic metal

The method comprises the following specific steps:

s1, after cleaning the substrate, plating a copper film with the thickness of 200nm through a sputtering process, because the melting point of copper is low (1083 ℃, the melting point of nickel is 1400 ℃), the thickness of the copper film needs to be increased in order to control the surface appearance of the grown copper, the carbon solid solubility of copper is low, the single layer rate of the grown graphene is high, and the number of layers of the grown graphene is not increased because of the increase of the thickness of copper.

S2 graphene is prepared by Black Magic vertical cold wall type CVD equipment of Aixtron company, firstly, hydrogen annealing is carried out for 5min under the condition of 800 ℃, then, the temperature is raised to 1000 ℃, and growth is started: methane flow 10sccm, hydrogen flow 40sccm, argon flow: 500sccm, gas pressure 15mbar, growth time 5 min. Finally, a layer of graphene grows on the copper surface, and the copper surface forms a hole morphology similar to that shown in fig. 5. Since copper has a weak catalytic ability, it is necessary to reduce the hydrogen flow rate at the time of growth.

The process is then described with reference to S3-S6 in example 1.

Finally, obtaining the large-area graphene film directly grown on the quartz substrate.

Example 3: and (3) carrying out patterning on the silicon dioxide/silicon substrate to directly grow the graphene film.

The specific process steps are as follows:

s1, cleaning the substrate, and patterning the nickel by a semiconductor process of photoetching-sputtering nickel metal-stripping.

The process is then described with reference to S1-S6 in example 1.

Since the insulating substrate does not have the catalytic action of graphene growth, graphene only grows on the surface of the metal, and finally a graphene film sample with a pattern consistent with that of the metal can be obtained, as shown in fig. 8.

The above description is only a preferred embodiment of the present invention and should not be taken as limiting the invention, and any modification, replacement, improvement, etc. made on the premise of the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. The process method for similar direct growth of large-area graphene on an oxide insulating substrate is characterized by comprising the following steps of: the method comprises the following steps: (1) firstly, plating a layer of metal film on a substrate; (2) growing a layer of graphene film on the surface of the metal by using metal catalysis through a CVD method; (3) continuously growing to enable the metal to be agglomerated to form holes, wherein the graphene film at the holes can fall on the substrate; (4) after the growth is finished, coating a layer of PMMA as a corrosion supporting layer in a spinning mode; (5) putting the sample into a metal corrosive liquid, wherein the metal corrosive liquid can penetrate through the PMMA and the graphene film to corrode the lower metal film; (6) after the metal film is corroded, the PMMA/graphene film falls on an insulated substrate, PMMA is removed by using an organic solvent, and graphene is left on the substrate; finally realizing the direct growth of the insulating substrate; since PMMA is a macromolecular organic matter, corrosive liquid can penetrate through PMMA, and meanwhile, the graphene film also has tiny holes or defects, so that the corrosive liquid penetrates through graphene.

2. The process of claim 1 for quasi-direct growth of large area graphene on oxide insulating substrates, wherein: nickel is used as a catalyst, and after graphene grows, the nickel surface needs to be agglomerated into holes at high temperature; only in this way, the PMMA/graphene can be fixed on the substrate after being coated with PMMA; if the nickel surface is not agglomerated to form holes, graphene is separated from the substrate and floats in the corrosive liquid after the nickel is corroded, so that the direct growth of graphene cannot be realized.

3. The process of claim 1 for quasi-direct growth of large area graphene on oxide insulating substrates, wherein: the holes can be formed by naturally agglomerating the nickel surface at high temperature to form irregular holes, a regular hole array can be prepared by a photoetching-sputtering-stripping semiconductor process, and the graphene can realize graphical growth.