CN102373506B - Method for epitaxially growing graphene on SiC substrate, graphene and graphene device - Google Patents

Abstract

The invention provides a method for epitaxially growing graphene on a SiC substrate, the graphene prepared by the method and a method for preparing a graphene device, the method comprising the following steps: using a patterned preparation technology for the SiC substrate, Form a pattern array on the surface of the SiC substrate; thermally decompose the patterned SiC substrate to form graphene on the surface of the SiC substrate. Applying the method of the present invention can obtain continuous, uniform, and wrinkle-free high-quality graphene, and because the localization of each pattern on the pattern substrate is good, it is beneficial to carry out device process manufacturing to the obtained graphene, and is beneficial to realize wafer Large-scale graphene devices and wide applications of graphene devices.

Description

Method for epitaxially growing graphene on SiC substrate and graphene and graphene devices

technical field

The invention relates to a method for epitaxially growing graphene on a SiC substrate, graphene and graphene devices prepared by the method.

Background technique

Graphene is a monoatomic layer of graphite bonded by sp ² hybridized carbon atoms and has a hexagonal lattice honeycomb two-dimensional structure. This ideal two-dimensional crystal material that exists stably at room temperature overturns the previously generally accepted prediction that strict two-dimensional crystals cannot exist at a limited temperature, and will have a major impact on the development of condensed matter physics. At the same time, graphene, as the structural basis of zero-dimensional fullerenes, one-dimensional carbon nanotubes and three-dimensional graphite, has rapidly become a research frontier and hotspot in the field of new international materials due to its unique structure and properties.

Graphene has received such high attention mainly due to its unique energy band structure: the dispersion relationship between energy and wave vector is linear, the effective mass of electrons is zero, and it has the characteristics of relativistic particles, which provides the most suitable for studying quantum electrodynamic phenomena. A direct experimental platform; at the same time, it has a series of novel physical and chemical properties, so that graphene has huge application value.

For example, graphene has a very stable structure, which makes it have very excellent mechanical properties. Its tensile strength can reach 50-200GPa, which is 100 times that of steel, but its density is 1/6 of steel. In addition, its elasticity The modulus can reach 1TPa, which is equivalent to the elastic modulus of diamond and about 5 times that of steel. It is the material with the highest specific strength that can be prepared at present. At the same time, graphene can also be used as a mechanical reinforcement material to be combined with other materials to prepare composite materials with ultra-high mechanical strength, elasticity, fatigue resistance and many other excellent properties. At present, the use of graphene-enhanced polymer materials not only greatly improves the mechanical properties, but also has good electrical conductivity. It can be made into bendable conductive film materials and has a certain shielding ability against radio waves. It can be used in the preparation of national defense and military industries. Antistatic coatings, radar absorbing materials, and stealth materials for submarine aircraft.

At the same time, the mobility of carriers in graphene reaches 250,000 cm ² V ^-1 s ^-1 , or even higher, and the mobility is almost independent of temperature; the carrier density can reach 10 ¹³ cm ^-2 , etc., and the carrier Can be either electrons or holes. Transistors made of graphene have the characteristics of low power consumption, high frequency, and miniaturization. Therefore, graphene is a very promising nanoelectronic material, and it is expected to replace silicon as the next-generation integrated circuit material.

Graphene, due to its unique physical and chemical properties and wide application prospects, makes the preparation of high-quality graphene a focus. At present, there are three main methods for preparing graphene:

1. Mechanical exfoliation method, which peels graphite layer by layer to obtain graphene with only a few layers or even one layer. The advantage of this method is that it is simple and not easy to produce structural defects; but the yield is too low, the area is too small, it is difficult to precisely control, and it is difficult to prepare on a large scale.

2. Chemical vapor deposition method, using metal as catalyst and organic gas as carbon source to prepare graphene by chemical vapor deposition. The advantage of this method is that large-area continuous graphene can be prepared; however, graphene grows on metal, and if further device applications are required, it must be transferred to an insulating substrate, and in the transfer process, it is inevitable to introduce parasitic Contamination and destruction of graphene, thereby affecting its performance.

面上生长石墨烯的AFM图像，扫描面积为10μm×10μm，图中的白细线是由于生长后降温应力释放导致出现的褶皱)，严重影响了石墨烯中载流子的输运性能。同时，在石墨烯表面出现的褶皱，随机分布在表面上，给石墨烯器件制备带来极大的困难，限制了石墨烯材料的应用，更无法实现石墨烯的规模应用。3. Silicon carbide high-temperature pyrolysis method, using the high vapor pressure difference between C and Si at high temperature, makes Si atoms detach from the bulk material, while C atoms stay on the surface and restructure to form graphene. The advantage of this method is that graphene can be directly grown on semi-insulating substrates, and devices can be directly fabricated without transfer. This method is compatible with the existing microelectronics process technology and is considered to be the most promising preparation method for large-scale production of graphene. However, the graphene epitaxially grown on the SiC substrate is either small in size and discontinuous (Si surface epitaxy), or large in size and continuous but wrinkled (as shown in Figure 1, Figure 1 is on a 6H-SiC substrate

The AFM image of graphene grown on the surface, the scanning area is 10 μm × 10 μm, the thin white lines in the figure are the wrinkles caused by the release of cooling stress after growth), which seriously affects the carrier transport performance in graphene. At the same time, the wrinkles that appear on the surface of graphene are randomly distributed on the surface, which brings great difficulties to the preparation of graphene devices, limits the application of graphene materials, and cannot realize the large-scale application of graphene.

Contents of the invention

Therefore, the purpose of the present invention is to solve the problem that the epitaxial growth of large-area graphene on the SiC substrate is prone to wrinkles at present, and to provide a method for epitaxially growing continuous, uniform, and wrinkle-free high-quality graphene on the SiC substrate. .

After a lot of research, the inventors of the present invention have found that patterning the SiC substrate can effectively release the stress generated during the cooling process after the epitaxial growth of graphene through the boundaries of the graph, thereby obtaining continuous, uniform, and seamless substrates. Wrinkled high-quality graphene.

In order to achieve the above-mentioned purpose of the invention, the present invention provides a method for epitaxially growing graphene on a SiC substrate, the method comprising the following steps:

Using the preparation technology of patterning the SiC substrate, a pattern array is formed on the surface of the SiC substrate; the patterned SiC substrate is thermally decomposed to form graphene on the surface of the SiC substrate.

According to the method provided by the present invention, the graphics of the graphics array can be any simple geometric figures, for example, can be one or more of rectangles, squares, circles, triangles and rhombuses. In other words, the pattern array described in the present invention can be a single pattern composed of one pattern, or a combined array composed of two or more patterns. The area of each pattern in the pattern array can be 4-400 μm ² , preferably 8-50 μm ² ; the interval between two adjacent patterns can be 0.01-10 μm, preferably 0.05-1 μm.

According to the method provided by the present invention, wherein the preparation technique for patterning the SiC substrate may include any known patterning technique, for example, it may be a dry etching technique or a wet etching technique, preferably a dry etching technique. erosion technology. The dry etching technique and the wet etching technique are methods known in the art to pattern the surface of a semiconductor, and the reagents and specific operating methods used in this method are also well known to those skilled in the art, and will not be repeated here. . In terms of the present invention, the depth of etching or etching can be 10 nm-10 μm, preferably 50 nm-1 μm. The etching or etching depth mentioned in the present invention refers to the difference in height between the mesa formed by the above pattern and the groove around the mesa (ie the part between two adjacent patterns).

和它们的偏角方向中的任意一种。According to the method provided by the present invention, the SiC substrate may be conductive or insulating. The crystal form of the SiC substrate may be hexagonal or cubic, for example, any one of 4H, 6H and 3C crystal forms, preferably 4H or 6H crystal form. The orientation of the SiC substrate surface used for patterning can be any crystal orientation, for example, it can be 0001,

and any of their declination directions.

According to the method provided by the present invention, the thermal decomposition temperature may be 1000-1700°C, preferably 1450-1600°C, and the thermal decomposition time may be 10-120 minutes, preferably 15-30 minutes.

As known to those skilled in the art, the method provided by the present invention may also include the step of cleaning the surface of the SiC substrate before etching the SiC substrate, and performing a step of performing thermal decomposition on the SiC substrate after etching the SiC substrate. , performing a surface cleaning step on the SiC substrate. The reagents and operation methods used in the above two cleaning steps are well known to those skilled in the art and will not be repeated here. In addition, in a preferred situation, in order to prevent contamination during the preparation of graphene, all operations are performed in a clean room.

The method of the present invention is not only applicable to the epitaxial growth of graphene on SiC substrates, but also applicable to the improvement of the method of epitaxial growth of graphene on other substrates at a temperature of 1000-1700° C., so as to achieve the purpose of eliminating wrinkles.

The present invention also provides a kind of graphene prepared according to the method of the present invention. The graphene provided by the invention is continuous, uniform and wrinkle-free.

The present invention also provides a method for preparing a graphene device, which method includes the step of epitaxially growing graphene on a SiC substrate according to the above-mentioned method provided by the present invention, or the method includes using graphite prepared according to the method of the present invention alkene.

The method provided by the present invention solves the shortcomings of the current technology of epitaxially growing graphene on SiC substrates. By patterning the surface of SiC substrates, the stress generated during the cooling process after epitaxially growing graphene can be obtained through the boundary of the graph. Effective release to obtain continuous, uniform, wrinkle-free high-quality graphene. At the same time, due to the good localization of each graphic on the graphic substrate (each graphic has definite coordinates), the obtained continuous and uniform graphene position determination on each table top graphic is beneficial to the graphene obtained. The fabrication of devices is conducive to the realization of wafer-sized graphene devices and the wide application of graphene devices.

Description of drawings

Below, describe embodiment of the present invention in detail in conjunction with accompanying drawing, wherein:

面上生长的石墨烯的AFM图；Figure 1 Conventional method on 6H-SiC substrate

AFM image of graphene grown on the surface;

A schematic diagram of the mask used in Fig. 2 embodiment 1;

The Raman spectrogram of the graphene that Fig. 3 embodiment 1 makes;

The AFM figure of the graphene that Fig. 4 embodiment 1 makes;

Figure 5 is a schematic diagram of the mask used in Example 2;

FIG. 6 is a schematic diagram of the mask used in Embodiment 3. FIG.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, and the given examples are only for clarifying the present invention, not for limiting the scope of the present invention.

Example 1

This embodiment is used to illustrate the method for epitaxially growing graphene on a SiC substrate of the present invention.

1. Surface cleaning of 6H-SiC

Put the 6H-SiC substrate into the acetone solution, and ultrasonically oscillate for 10 minutes to remove organic matter such as oil on the surface; then put it into an ethanol solution, and ultrasonically oscillate for 10 minutes to remove the remaining acetone and organic matter on the surface; then put it into deionized water, and ultrasonically Shake for 10 minutes, then rinse three times with deionization; finally dry it with nitrogen.

面进行刻蚀2. For 6H-SiC

etching

6H-SiC processed in step 1 by means of a homogenizer Coat a layer of photoresist PPMA with a thickness of 1 μm on the surface, and then place the mask on the surface of the substrate for ultraviolet exposure. The pattern of the mask is a square array with a side length of 5 μm, and the pattern spacing is 1 μm, as shown in Figure 2 . Then develop the substrate after exposure, first dry the sample for 10 seconds, then put it in the developer solution for 30 seconds, take it out and then dry it for 10 seconds. Then put the developed sample into an ICP (Inductively Coupled Plasma Etching Machine), and use fluorine-based plasma (SF ₆ ) to etch to a depth of 0.1 μm. Finally, put the sample into an acetone solution to remove the light. Resist mask layer.

3. Epitaxial growth of graphene

Put the patterned 6H-SiC substrate on the 0001 side into a vacuum high-temperature heating furnace, use a mechanical pump and a molecular pump to evacuate the furnace chamber, so that the vacuum in the chamber reaches 1×10 ^-3 Pa, and then inject hydrogen and argon Mixed gas (wherein 5% hydrogen + 95% argon, unless otherwise specified, the hydrogen-argon mixed gas used in the present invention is the above ratio) to a standard atmospheric pressure, this process is called scrubbing. Then repeat the above gas washing process twice. At this time, the atmosphere in the chamber is a hydrogen-argon mixture, and the pressure in the chamber is a standard atmospheric pressure. The temperature is raised to 1550°C, kept at this temperature for 20 minutes, and then cooled down to room temperature naturally.

Adopt micro-area Raman spectrum technology, the graphene that makes is characterized, to confirm that graphene has grown on SiC substrate surface, this Raman spectrogram is as shown in Figure 3, wherein the typical characteristic peak of graphene, G peak ( At 1582cm ^-1 ) and 2D peak (at 2700cm ^-1 ) are symmetrical single peaks, and no D peak (at 1350cm ^-1 ) appears, indicating that the epitaxial graphene on the pattern substrate is of good quality. The morphology of the prepared graphene was observed with an atomic force microscope (AFM), and the results are shown in Figure 4 (3 μm×3 μm). Since graphene is very thin (only one or a few atomic layers thick), the step morphology of the substrate can be seen through the graphene from the figure, indicating that the grown graphene covers the surface of the SiC substrate uniformly and continuously, without There are wrinkles, which shows that the patterned substrate can effectively eliminate the wrinkles that are easy to appear in epitaxial graphene.

Example 2

This embodiment is used to illustrate the method for epitaxially growing graphene on a SiC substrate of the present invention.

Graphene is grown in the same manner as in Example 1, the difference is that graphene is grown on the 0001 face of the 4H-SiC substrate; the pattern of the mask plate is a regular triangle array with a side length of 5 μm as shown in Figure 5, and the The spacing is 2 μm, and the etching depth is 1 μm. Continuous, uniform, wrinkle-free epitaxial graphene was confirmed by Raman spectroscopy and AFM images.

Example 3

This embodiment is used to illustrate the method for epitaxially growing graphene on a SiC substrate of the present invention.

面生长石墨烯；掩模板的图形为如图6所示的3μm×50μm的长方形阵列，图形间距为3μm，刻蚀深度为0.5μm。采用Raman光谱和AFM图像证实得到了连续、均匀、无褶皱的外延石墨烯。Graphene is grown in the same manner as in Example 1, except that the 6H-SiC substrate

Surface-grown graphene; the pattern of the mask plate is a rectangular array of 3 μm×50 μm as shown in Figure 6, the pattern spacing is 3 μm, and the etching depth is 0.5 μm. Continuous, uniform, wrinkle-free epitaxial graphene was confirmed by Raman spectroscopy and AFM images.

By the description of Examples 1-3, in conjunction with the comparison of Fig. 1 and Fig. 4, it can be seen that applying the method of the present invention can obtain continuous, uniform, and wrinkle-free high-quality graphene, and because each pattern on the pattern substrate The localization is good, which is conducive to the device process of the obtained graphene, and is conducive to the realization of wafer-sized graphene devices and the wide application of graphene devices.

Claims (12)

1. A method for epitaxially growing graphene on a SiC substrate, the method comprising the steps of: adopting a preparation technique that makes the SiC substrate patterned, forming a pattern array on the SiC substrate surface, wherein each of the pattern arrays The area of each pattern is 4-400μm ² , and the preparation technique for patterning the SiC substrate makes the height difference between the mesa formed by the pattern in the pattern array and the groove around the mesa be 10nm-10μm; for the pattern The SiC substrate is thermally decomposed to form wrinkle-free graphene on the surface of the SiC substrate. 2. The method according to claim 1, wherein the graphics in the graphics array include one or more of rectangles, squares, circles, triangles and rhombuses. 3. The method according to claim 1, wherein the interval between two adjacent patterns in the pattern array is 0.01-10 μm. 4. The method according to claim 1, wherein the preparation technique for patterning the SiC substrate comprises dry etching or wet etching technique. 5. The method according to claim 4, wherein the preparation technique for patterning the SiC substrate is a dry etching technique. 6. The method according to claim 1, wherein the crystal form of the SiC substrate is hexagonal or cubic. 7. The method according to claim 1, wherein the crystal form of the SiC substrate is 4H, 6H or 3C crystal form. 8. The method according to claim 7, wherein the crystal form of the SiC substrate is 4H or 6H crystal form. 9. The method according to claim 1, wherein the crystal orientation of the SiC substrate comprises 0001, $\stackrel{\‾}{1},1\stackrel{\‾}{1}\mathrm{00,11}\stackrel{\‾}{2}0$ or their declination directions. 10. The method according to claim 1, wherein the thermal decomposition temperature is 1000-1700° C., and the thermal decomposition time is 10-120 minutes. 11. The method according to claim 4 or 5, wherein the method also includes the step of cleaning the surface of the SiC substrate before etching the SiC substrate, and thermally cleaning the SiC substrate after etching the SiC substrate. Before decomposition, the SiC substrate is subjected to a surface cleaning step. 12. A method for preparing a graphene device, the method comprising the step of epitaxially growing graphene on a SiC substrate according to the method according to any one of claims 1-11.

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