Method for improving quality of graphene catalytically grown at low temperature by vanadium oxide

Abstract

The application relates to a method for improving the quality of graphene catalytically grown by vanadium oxide at low temperature, belonging to the fields of material preparation technology and semiconductor photoelectric integration. The good surface morphology and lattice structure of a catalytic layer are crucial to the growth of high-quality graphene. V2O5 thin films prepared by sputtering-oxidation of a V target are uniform and continuous, have small surface roughness, and have obvious preferred orientation in the (001) crystal plane direction compared with V2O5 thin films prepared by direct sputtering, thereby improving the monocrystallization degree of the V2O5 thin films. The V2O5 thin film sample prepared by the oxidation method is placed in a PECVD for graphene growth, and a large amount of H2 is introduced after the growth is completed, so that H ions etch the growth defects and impurities of the graphene, and the quality of the graphene is further improved. Through the two methods, the quality of the graphene is effectively improved, and the growth temperature can be reduced to 300 DEG C.

Description

TECHNICAL FIELD

[0001] The application is a technology for improving the quality of graphene grown by low-temperature catalysis of vanadium oxide with phase change properties, and particularly relates to a method for preparing a vanadium oxide film by sputtering-oxidation and a process for low-temperature in-situ patterning growth of graphene, and belongs to the fields of material preparation technology and semiconductor optoelectronic integration. BACKGROUND

[0002] There are many methods for synthesizing graphene, and chemical vapor deposition is one of the most promising methods for growing graphene, which can produce large-area and relatively high-quality graphene films. In most direct growth methods, metal catalysts are used as the main method to improve the quality of graphene, which can easily cause pollution to mainstream semiconductor substrates, which will affect the reliability and performance of devices. Therefore, developing a process for low-temperature transfer-free growth of graphene by non-metal catalysts is of great significance to improve the preparation technology of graphene devices and promote the wide application of graphene devices. The metal-insulator transition (MIT) property of vanadium oxide can be used to catalyze the growth of graphene at low temperature. After the growth of graphene is completed, vanadium oxide can be removed as a sacrificial layer by etching, or can be retained as an insulating layer. At room temperature, vanadium oxide will not cause short circuit of graphene devices like metal catalysts, effectively solving the damage to graphene caused by subsequent transfer and photolithography steps, and is of great significance to promote the wide application of direct growth of graphene.

[0003] Currently, the vanadium oxide used for catalytic growth of graphene is a sputtered V2O5 film. V2O5 is used as a target material, and a thin film is deposited on a Si / SiO2 substrate by a magnetron sputtering device. This method is simple to operate and the thin film is dense, but the thin film obtained by sputtering is amorphous or polycrystalline, and has no obvious preferred orientation. The good surface morphology and lattice structure of the catalytic layer directly affect the growth of graphene, so it is very important to prepare a high-quality catalytic layer for growing graphene.

[0004] A vertical cold-wall PECVD furnace can grow graphene at low temperature (below 400℃), and the growth time can be greatly shortened compared with a tube furnace. In the growth process, Ar is used to provide plasma and dilute the gas concentration in the chamber, CH4 is used to provide a carbon source, and H2 has two main effects, one is to promote the cracking of the carbon source, and the other is to improve the uniformity and quality of graphene. SUMMARY

[0005] The purpose of the present application is to optimize the quality of vanadium oxide film substrate and the gas flow in the growth process, thereby improving the quality of graphene. It is proposed to use V2O5 film formed by oxidation of V as the graphene catalytic layer, and after the growth of graphene, ten times the flow of H2 is introduced, and the etching of graphene growth defects and impurities by H ions is used to further improve the quality of graphene, and finally a uniform large-area graphene film can be obtained. The improved technology for low-temperature in-situ patterning growth of graphene includes the following steps:

[0006] (1) Clean the Si / SiO2 substrate sheet to remove surface adsorbed dust and grease;

[0007] (2) Use a mask to perform photoetching and development on the substrate to expose the desired pattern;

[0008] (3) Use a magnetron sputtering device to deposit metal V, the thickness of the deposited metal V is adjusted according to the needs and the performance of the sputtering device, and the film is dense enough, usually 3-10 nm thick, preferably 5 nm thick;

[0009] (4) Peel off to obtain a patterned sputtered metal thin layer;

[0010] (5) Put it into a rapid annealing furnace, introduce O2, and heat it to 400℃ at a rate of 300℃ / min -1 , keep it for 10-20 min, preferably 15 min (the specific oxidation time is related to the V sputtering thickness, and for a 5 nm thick V, the corresponding holding time is 15 min), and then cool it to below 100℃ at a rate of 300℃ / min -1 , take it out, and at this time the surface is a V2O5 film;

[0011] (6) Put it in a vertical cold-wall PECVD to grow graphene; heat it to 300℃ at a rate of 200℃ / min -1 , the pressure is 10 mbar, and the gases Ar: H2 and CH4 are introduced, wherein the flow ratio of Ar: H2: CH4 is 960: 20: 5, the H2 flow is 20 sccm; at the same time, the plasma is ignited (80W, 15kHz), and the growth is performed for 5 min, then CH4 is turned off, H2 flow is increased to 200 sccm, and under this high H2 flow, it is kept for 12 min, then the plasma is turned off, and then it is cooled to 100℃ at a rate of 300℃ / min -1 , H2 is turned off, and Ar is turned off;

[0012] (7) After the growth is completed, the chamber is opened when the machine is cooled to below 100℃, and the sample is taken out to obtain graphene with a pattern.

[0013] Advantages of the present application

[0014] The key point of this invention is the use of V₂O₅ prepared by V oxidation as a catalyst layer, instead of directly sputtered V₂O₅, and the addition of a high H₂ flow rate annealing step after graphene growth. The advantages of this approach are:

[0015] 1) V2O5 is prepared by oxidation of V, resulting in uniform and continuous film formation with low surface roughness. The crystal plane has a distinct preferred orientation in the (001) direction, which improves the degree of single crystallization of V2O5 film. Good surface morphology and lattice structure are crucial for the growth of high-quality graphene.

[0016] 2) After growth, annealing was performed at a high H2 flow rate. H ions reacted with dangling bonds or defects in the graphene to repair or eliminate these defects, further optimizing the quality of the graphene and obtaining a uniform and large-area graphene film.

[0017] 3) Two improved methods were used to achieve the preparation of graphene at a lower temperature (300℃), which is 100℃ lower than the previous 400℃ growth process;

[0018] 4) Based on this invention, a new method is provided for optimizing the catalytic growth of graphene using vanadium oxides and phase change materials, and more possibilities are provided for other non-metallic materials as catalysts. Attached Figure Description

[0019] Figure 1 Clean the Si / SiO2 substrate; the SiO2 layer thickness is 300nm.

[0020] Figure 2 The first photolithography development of the substrate;

[0021] Figure 3 The photoresist used as a mask was removed after wet etching of the SiO2 in the patterned area.

[0022] Figure 4 Second photolithography development of the substrate;

[0023] Figure 5 The photoresist used as a mask was removed after sputtering the metal V film;

[0024] Figure 6 In a rapid annealing furnace, V is oxidized to V₂O₅, and the thickness is approximately four times the original thickness.

[0025] Figure 7 : Growth of graphene in PECVD;

[0026] Figure 8 : Third photolithography development of the substrate;

[0027] Figure 9 The photoresist used as a mask was removed after sputtering the metal electrodes;

[0028] in, Si substrate, SiO2 substrate, Photoresist It is metal V, It is V2O5, It is graphene. It is a Ti / Au electrode.

[0029] Figure 10 Comparison of Raman spectra of graphene before and after adopting the content of this invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the present invention is not limited to the following embodiments.

[0031] Example 1

[0032] The graphene-V2O5-Si (GVS) photodetector was fabricated by catalytic growth of V2O5 thin films prepared by oxidation. The process steps are as follows:

[0033] (I) Preparation of patterned V2O5 thin films

[0034] (1) Clean the Si / SiO2 substrate sequentially with acetone, anhydrous ethanol, and deionized water. See Appendix Figure 1 ;

[0035] (2) A 1.3 × 1.3 mm window was photolithographically etched onto the substrate using the first photolithography plate. (See attached image) Figure 2 ;

[0036] (3) Using photoresist as a mask, the 300nm thick SiO2 in the window area is removed by wet etching to expose the Si substrate;

[0037] (4) Remove the photoresist with a stripping solution and clean the substrate. See attached document. Figure 3 ;

[0038] (5) Using a second photolithography plate, a 1.5×1.5mm window is etched onto the substrate. This window is located above the window etched in the second step and is a square shape. See Appendix. Figure 4 ;

[0039] (6) Place the sample into a magnetron sputtering apparatus (Denton Vacuum Discovery) to deposit a 5 nm V layer on the surface. The sputtering power is 300W;

[0040] (7) Remove the sample, remove the photoresist with a stripping solution, and clean the substrate. See Appendix. Figure 5 ;

[0041] (8) Place in a rapid annealing furnace (RTP), introduce O2, and heat at 300℃ for min. -1 Heat to 400℃, hold for 15 minutes, then reduce to 300℃ for 1 minute. -1 After cooling to 100℃, the material was removed and a layer of V2O5 with a thickness of about 20nm was obtained.

[0042] See attached Figure 6 ;

[0043] (II) Growth of graphene on patterned V2O5 and sputtering of electrodes

[0044] (9) Graphene is grown on the substrate by plasma chemical vapor deposition in a PECVD furnace (Aixtron Black Magic);

[0045] (10) Evacuate the chamber to 0.2 mbar, then introduce Ar at a flow rate of 1000 sccm to clean the chamber, and circulate it twice, 1 min each time;

[0046] (11) After cleaning, shut off Ar, introduce H2 at a flow rate of 1000 sccm, and simultaneously control the chamber pressure to 10 mbar, then maintain the temperature at 200℃ for min. -1 The temperature was increased to 350℃ at a rate of [missing information] and stabilized for 10 seconds.

[0047] (12) Introduce 960 sccm Ar, 20 sccm H2 and 5 sccm CH4 into the chamber, and ignite the plasma (80 W, 15 kHz) at the same time. Maintain the plasma and mixed gas for 5 min to grow graphene.

[0048] (13) After growth, turn off CH4, increase the H2 flow rate to 200 sccm, maintain it for 12 min after stabilization, and use a large H2 flow rate to etch surface defects and impurities;

[0049] (14) Turn off the plasma, then set the temperature at 300℃ for min. -1 After the temperature drops to 275℃, H2 is turned off, and 1000 sccm of Ar is introduced to continue natural cooling.

[0050] (15) When the temperature drops below 100℃, end the program, open the furnace lid, and remove the sample. See appendix. Figure 7 ;

[0051] (16) Use a third photomask to overlay the electrode pattern. See appendix. Figure 8 ;

[0052] (17) Ti / Au (15 / 300nm) electrodes were fabricated on the positive electrode side and the negative electrode side of the back of the sample, respectively.

[0053] (18) The photoresist was removed using a stripping solution, and the sample was cleaned to obtain a graphene-V₂O₅-Si (GVS) photodetector. (See attached image) Figure 9 .

[0054] (III) Raman spectroscopy was performed on the graphene before and after the improvement to characterize the quality of the graphene.

[0055] Raman spectroscopy is a rapid method for assessing the quality of graphene. The D, G, and 2D peaks of the graphene Raman spectrum are located at 1337 cm⁻¹. -1 1597cm -1 and 2661cm -1 At this point, the peak intensity ratio of peak D to peak G (I D / I G The ratio of the peak intensity of the 2D peak to the G peak is typically used to determine the degree of defects in graphene; a lower value indicates fewer defects in the graphene. 2D / I G This allows us to roughly determine the number of graphene layers.

[0056] The black and red curves in the figure represent the Raman spectra of the graphene grown before and after the improvement, respectively (see appendix). Figure 10 To ensure the rigor of the experiment, all experimental conditions remained consistent except for the two points described in the invention. As can be seen from the image, after graphene is grown from the sputtered V₂O₅ film, its I₂... D / I G The Ig value was 0.90. Due to the excessively large half-widths (HW) of the D and G peaks, the two peaks exhibited adhesion, indicating poor graphene quality and numerous defects. After graphene was grown on V2O5 films prepared by the oxidation method and etched with a high flow rate of H2, its Ig... D / I G The value was 0.71, the D peak decreased, and the characteristic peaks became sharper, indicating that the quality of graphene has been significantly improved.

Claims

1. A method for improving the quality of graphene grown at low temperatures using vanadium oxide, characterized in that, By using V2O5 thin film oxidized from V as a graphene catalyst layer, and by introducing a large flow of H2 after the graphene is grown, the H ions are used to etch the graphene growth defects and impurities, thereby further improving the quality of graphene and finally obtaining a uniform large-area graphene film. The main process steps include the following: (1) Clean the Si / SiO2 substrate to remove dust and grease adsorbed on the surface; (2) Use a photomask to perform photolithography and development on the substrate to expose the desired pattern; (3) Deposit metal V using a magnetron sputtering device; (4) Peel off to obtain a patterned sputtered metal thin layer; (5) Place in a rapid annealing furnace, introduce O2, and heat at 300℃ for min. -1 Heat to 400℃, hold for 10-20 minutes, then reduce to 300℃ for 1 minute. -1 Cool it down to below 100℃ and take it out. At this time, the surface is a thin film of V2O5. (6) Then place it in a vertical cold-wall PECVD chamber to grow graphene; at 200℃ for min -1 The temperature was increased to 300℃ at a rate of 10 mbar, and Ar:H2 and CH4 gases were introduced, with an Ar:H2:CH4 flow rate ratio of 960:20:5 and an H2 flow rate of 20 sccm. Simultaneously, the plasma was ignited and grown for 5 min. Then, the CH4 flow was stopped, and the H2 flow rate was increased to 200 sccm. This high H2 flow rate was maintained for 12 min, after which the plasma was stopped, and the temperature was increased to 300℃ for 1 min. -1 Cool to 100℃ at a cooling rate, then shut off H2 and Ar; (7) After the growth is completed, wait for the machine to cool down to below 100°C, open the chamber, take out the sample, and obtain the patterned graphene.

2. The method according to claim 1, characterized in that, The V2O5 thin film catalyst layer is no longer prepared by sputtering with V2O5 as the target material. Instead, a two-step sputtering-oxidation method with V as the target material is used to prepare the V2O5 thin film. The film prepared by this method is uniform and continuous, with low surface roughness and obvious preferred orientation of the crystal plane in the (001) direction, which improves the degree of single crystallization of V2O5 film. Good surface morphology and lattice structure are crucial for the growth of high-quality graphene.

3. The method according to claim 1, characterized in that, After graphene growth, introducing a large flow rate of H2 can effectively etch impurities and defects on the graphene surface, further optimizing the graphene quality and obtaining a uniform and large-area graphene film.

4. The method according to claim 1, characterized in that, Graphene was grown at an even lower temperature of 300°C.

5. The method according to claim 1, characterized in that, The peak intensity ratio of peak D to peak G is I D / I G It is 0.

71.

6. The method according to claim 1, characterized in that, Step (5) Keep for 15 minutes.

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