Method for preparing large-grain-size monolayer molybdenum disulfide thin film on amorphous silicon dioxide substrate

Abstract

This invention discloses a method for preparing a large-domain-size monolayer MoS2 thin film on an amorphous SiO2 substrate. The method involves placing sulfur powder, MoO3 powder, and a clean SiO2 / Si substrate in a first, second, and third temperature zones, respectively. The spacing between the two powders and the distance between the MoO3 powder and the substrate are adjusted. Each temperature zone is heated to a set temperature. An Ar / O2 mixed carrier gas flow sequentially from the first temperature zone to the second and third temperature zones, transporting the sulfur powder and MoO3 powder onto the substrate where a chemical reaction occurs, resulting in the growth of a large-domain-size monolayer MoS2 thin film on the SiO2 / Si substrate. This invention employs chemical vapor deposition to prepare a monolayer MoS2 thin film with good uniformity, large domain size, and high-quality crystallinity on a SiO2 / Si substrate, with an average domain size reaching 20. m m~78 m This method is simple to operate, low in cost, and highly reproducible.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of two-dimensional atomic crystal materials, and relates to a method for preparing a large-crystalline-domain-size monolayer MoS2 film on an amorphous SiO2 substrate. BACKGROUND

[0002] Two-dimensional atomic crystal materials refer to materials in which electrons can only move freely in two dimensions of non-nanometer scale (1-100 nm) in length and width, such as nanosheets, superlattices, quantum wells, etc. Because of its atomic-level thickness, no dangling bonds on the surface, and excellent electrical transmission characteristics, it can effectively solve the current bottleneck problems of field effect transistors, such as short channel effect and high power consumption of devices, and is one of the most promising candidates for continuing the traditional Si-based chips in the advanced nodes of sub-10 nm in the post-Moore era. In 2004, Geim's group at Manchester University first obtained single-layer two-dimensional graphene from bulk graphite through mechanical exfoliation, and proved its unique and excellent electrical properties, and won the Nobel Prize in Physics in 2010. In the nearly 20 years since then, two-dimensional atomic crystal materials represented by graphene have entered a period of rapid development and have attracted widespread interest and research enthusiasm from the scientific and industrial communities. In addition to graphene, a series of new two-dimensional atomic crystal materials have also been discovered, including single-element silicene, antimonene and black phosphorus, and transition metal dichalcogenides (TMDCs) such as MoS2, WS2, WSe2 and ReS2. Among them, MoS2, as an important member of the TMDCs family, has been widely studied and researched due to its adjustable band gap value (Eg), atomic-level thickness and excellent mechanical properties, and has shown great potential in the fields of logic circuits (CMOS) and flexible electronics. In addition, MoS2 has been included in the international semiconductor technology development roadmap (ITRS) as a promising ideal channel material for continuing Moore's Law in the future.

[0003] The existing preparation methods of monolayer MoS2 thin film mainly include solution synthesis, atomic layer deposition and chemical vapor deposition. At present, monolayer MoS2 thin film with large size crystal domain is mainly synthesized on sapphire substrate, which can be attributed to the fact that sapphire substrate is a single crystal substrate, and sapphire has good lattice parameter matching with MoS2, which is beneficial to the two-dimensional epitaxial growth of MoS2 thin film. However, sapphire is not an ideal substrate for traditional Si-based substrate and the construction of electrical transistor devices. The main reason is that MoS2 thin film grown on sapphire needs to be transferred to the target substrate (such as Si substrate) for electrical device construction and testing by using wet transfer technology. In the transfer process, the residual of chemical reagents and the release of stress will inevitably damage the film quality and cause its quality to decline. The amorphous SiO2 substrate with a certain thickness of oxide layer can not only epitaxially grow MoS2 thin film, but also directly construct electrical transistor devices on it, which avoids the pollution and stress accumulation in the transfer process. However, the crystal domain size of monolayer MoS2 thin film grown on amorphous SiO2 substrate is small, which seriously hinders the release of the potential of MoS2 thin film to integrated transistor array in electrical performance. For example, document 1 prepared 4-inch MoS2 thin film on SiO2 / Si substrate by atomic layer deposition method. Although this method can quickly obtain large-area MoS2 thin film, the uniformity of the thin film is poor and the grain size is very small (Pyeon J J, Kim S H, Jeong D S, et al. Wafer-scale growth of MoS2 thin films by atomic layer deposition. Nanoscale, 2016, 8: 10792-10798). Document 2 prepared monolayer MoS2 thin film on SiO2 / Si substrate by chemical vapor deposition method, which improved the uniformity of the thin film, but the crystal domain size was still small (<1 μm) (Zhang J, Yu H, Chen W, et al. Scalable Growth of High-Quality Polycrystalline MoS2 Monolayers on SiO2 with Tunable Grain Sizes [J]. Acs Nano, 2014, 8(6): 6024-6030).Document 3 uses metal chemical vapor deposition to prepare a 4-inch MoS2 film on a SiO2 / Si substrate. This method can better control the volatilized source and the uniformity of the grown film is good. However, the average domain size of the grown MoS2 film is only about 1 μm (Kang K, Xie S E, Huang L J, et al. High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity [J]. Nature, 2015, 520(7549): 656-660). SUMMARY

[0004] The purpose of the present application is to provide a method for preparing a large-domain-size monolayer MoS2 film on an amorphous SiO2 substrate. The method can quickly and at low cost prepare a large-domain-size monolayer MoS2 film on an amorphous silicon substrate, with an average domain size of 20 μm to 78 μm.

[0005] The technical solution for achieving the purpose of the present application is as follows:

[0006] The method for preparing a large-domain-size monolayer MoS2 film on an amorphous SiO2 substrate comprises the following steps:

[0007] (1) Place a clean SiO2 / Si substrate on a quartz support bracket at an angle of 30° and in the third temperature zone. Place S powder and MoO3 powder in two ceramic boats, and place the two ceramic boats in a quartz glass tube. Place the S powder in the first temperature zone and the MoO3 powder in the second temperature zone. The distance between the two powders is 18-21 cm, and the distance between the MoO3 powder and the substrate is 15-18.5 cm.

[0008] (2) Set the temperature of the first temperature zone to 135-150°C, the temperature of the second temperature zone to 640-700°C, and the temperature of the third temperature zone to 700-810°C. Raise the temperature of each temperature zone to the set temperature, and let the first temperature zone reach the set temperature 10-15 min earlier than the second and third temperature zones. Use the Ar / O2 mixed carrier gas flow from the first temperature zone to the second and third temperature zones in turn to transport the S powder and MoO3 powder to the substrate and cause a chemical reaction, thereby growing a large-domain-size monolayer MoS2 film on the SiO2 / Si substrate.

[0009] Further, in step (1), the thickness of the SiO2 layer in the SiO2 / Si substrate is 285 nm, and the thickness of the Si substrate is 500 μm.

[0010] Further, in step (1), the distance between the two powders is 21 cm, and the distance between the MoO3 powder and the substrate is 18.5 cm.

[0011] Further, in step (2), the flow ratio of the carrier gas in the heating stage is Ar:O2=70:1-5, preferably 70:5, and the flow ratio of the carrier gas in the growth stage is Ar:O2=70:1-5, preferably 70:2-3.

[0012] Further, in step (2), the temperature of the first temperature zone is 145℃, the temperature of the second temperature zone is 675℃, and the temperature of the third temperature zone is 725℃.

[0013] Further, in step (2), the holding time of the first temperature zone is 30 min, and the holding time of the second and third temperature zones is 15 min.

[0014] Further, in step (2), the growth time is 15 min, and the total pressure in the quartz glass tube is 1.45 torr.

[0015] Further, in step (2), the average domain size of the single-layer MoS2 thin film is 20-78 μm, and the thickness is 0.65 nm.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] (1) The present application uses a chemical vapor deposition (CVD) method to prepare a single-layer MoS2 thin film with good uniformity, large domain size, and high-quality crystallinity on an amorphous (285 nm) / Si (500 μm) substrate. The average domain size of the thin film can reach 20-78 μm. The method is simple to operate, low in cost, and good in repeatability. Moreover, the prepared single-layer MoS2 thin film does not need to be transferred, which simplifies the construction process of the transistor device and avoids the influence of chemical reagents and residual stress in the transfer process on the quality of the material.

[0018] (2)The application can effectively avoid poisoning of the precursor MoO3 powder source by controlling the flow of oxygen (O2) in the heating stage and the growth stage, and can also etch and remove unstable crystal grains in the growth process, thereby reducing the nucleation density of MoS2, so that a single-layer MoS2 film with large-size crystal domains is obtained, and the maximum size of a single crystal domain in the film can reach 78 mu m; the influence of the phased oxygen supply on the nucleation density and the size of a single crystal domain can be seen through an optical microscope (OM); through scanning electron microscope (SEM) testing, the regulation process of the MoS2 film crystal domain size by selecting different O2 flow rates in the growth stage can be seen; the thickness of the obtained MoS2 film can be analyzed through atomic force microscope (AFM) data; it can be proved that the prepared MoS2 film is single-layer through Raman spectrometer (Raman) and photoluminescence (PL) analysis testing; through the diffraction pattern of a transmission electron microscope (TEM) and the atomic structure arrangement mode test result analysis of a high-resolution transmission electron microscope (HRTEM), it is proved that the obtained film is a single-layer MoS2 film and has good crystallinity, and the energy dispersive spectrometer (EDS) element analysis also proves that the prepared film is a MoS2 composition of Mo and S elements, and has good uniformity and high quality. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A growth device structure schematic diagram for preparing a single-layer MoS2 film of the application;

[0020] Figure 2 An OM diagram of a single-layer MoS2 film prepared in Example 1;

[0021] Figure 3 An SEM diagram of a single-layer MoS2 film prepared in Example 1;

[0022] Figure 4 An AFM height diagram of a single-layer MoS2 film prepared in Example 1;

[0023] Figure 5 A Raman spectrum diagram of a single-layer MoS2 film prepared in Example 1;

[0024] Figure 6 A PL spectrum diagram of a single-layer MoS2 film prepared in Example 1;

[0025] Figure 7 A SAED diffraction pattern diagram of a single-layer MoS2 film prepared in Example 1;

[0026] Figure 8 An HRTEM atomic structure arrangement diagram of a single-layer MoS2 film prepared in Example 1;

[0027] Figure 9EDS pattern and Mo, S element distribution pattern of the monolayer MoS2 thin film prepared for Example 1;

[0028] Figure 10 AFM pattern of the monolayer MoS2 thin film prepared for Comparative Example 1;

[0029] Figure 11 OM pattern of the monolayer MoS2 thin film prepared for Example 2;

[0030] Figure 12 OM pattern of the monolayer MoS2 thin film prepared for Example 3;

[0031] Figure 13 OM pattern of the monolayer MoS2 thin film prepared for Example 4;

[0032] Figure 14 OM pattern of the monolayer MoS2 thin film prepared for Comparative Example 2;

[0033] Figure 15 AFM pattern of the monolayer MoS2 thin film prepared for Comparative Example 3. DETAILED DESCRIPTION

[0034] The present application will be further clarified by the following examples, which should not be construed as limiting the scope of the application. After reading this description, it will become apparent to one skilled in the art how to make and use various modifications of the present application without departing from the scope of the application. It will also become apparent that various "preferred" embodiments have been set forth in this example, and that certain applications have specific, preferred embodiments.

[0035] Example 1

[0036] Step (1): SiO2 / Si substrate (285 nm SiO2, 500 μm Si) was cut into a square of 3 cm x 3 cm;

[0037] Step (2): The cut 3 cm x 3 cm silicon wafer was placed into acetone, isopropyl alcohol, and ethanol with purity ≥ 99.95% respectively for ultrasonic cleaning for 10 min, and dried with N2;

[0038] Step (3): The dried SiO2 / Si substrate was placed into a UV cleaning machine for ultraviolet light irradiation for 30 min;

[0039] Step (4): 790 mg of S powder and 35 mg of MoO3 powder were weighed and placed in two ceramic boats respectively, and the two ceramic boats were placed in a quartz glass tube, the S powder was placed in the first temperature zone and the MoO3 powder was placed in the second temperature zone, the distance between the two was 21 cm, and the clean SiO2 / Si substrate was placed on a quartz support bracket with an angle of 30°, placed in the third temperature zone, the distance between the substrate and the MoO3 powder was 18.5 cm;

[0040] Step (5): Ar gas was introduced into the three-zone CVD tube furnace system, and then the quartz tube was repeatedly evacuated twice by a mechanical pump to remove residual air and impurity gases in the quartz tube;

[0041] Step (6): A temperature rising curve was set, the first temperature zone was kept for 15 min, then heated to 145℃ within 30 min, and kept for 30 min; the second temperature zone was raised to 675℃ within 60 min, and the third temperature zone was raised to 725℃ within 60 min and kept for 15 min;

[0042] Step (7): The flow rate of carrier gas was set, Ar:O2=70:5 (unit: sccm) in the temperature rising stage, and Ar:O2=70:2 in the growth stage; the pressure was 1.45 torr;

[0043] Step (8): After the reaction was completed, the sample was naturally cooled to room temperature, and then taken out for characterization and observation, and a single-layer MoS2 film was obtained.

[0044] The OM image of the single-layer MoS2 film prepared in this example 1 is shown in Figure 2 ; the SEM image of the single-layer MoS2 film prepared in this example is shown in Figure 3 , the maximum grain size of the single-layer MoS2 film is 78 μm; the AFM height map of the single-layer MoS2 film prepared in this example is shown in Figure 4 , the thickness is about 0.65 nm; the Raman spectrum of the single-layer MoS2 film prepared in this example is shown in Figure 5 , the difference between the in-plane and out-of-plane characteristic peaks is 19.46 cm -1 , which is consistent with the characteristics of the single-layer MoS2 film; the PL spectrum of the single-layer MoS2 film prepared in this example is shown in Figure 6 , the band gap is 1.87 eV; the SAED diffraction pattern of the single-layer MoS2 film prepared in this example is shown in Figure 7 ; the HRTEM atomic structure arrangement map of the single-layer MoS2 film prepared in this example is shown in Figure 8 ; the EDS map and element distribution map of the single-layer MoS2 film prepared in this example are shown in Figure 9 .

[0045] Comparative Example 1

[0046] Similar to Example 1, the difference is that the Ar:O2 in the growth stage of step (7) is adjusted to 70:1.

[0047] The AFM of the single-layer MoS2 film prepared in this example is shown in Figure 10 , it can be seen from the figure that the grain size of the MoS2 film is small, and the average grain size is 300 nm.

[0048] Example 2

[0049] Similar to Example 1, except that the Ar:O2 ratio during the growth stage in step (7) of Example 1 was adjusted to 70:3.

[0050] The OM of the monolayer MoS2 film prepared in this example is shown in Fig. 1. It can be seen from the figure that the average grain size of the monolayer MoS2 film is 45 μm. Figure 11

[0051] Example 3

[0052] Similar to Example 1, except that the Ar:O2 ratio during the growth stage in step (7) of Example 1 was adjusted to 70:4.

[0053] The OM of the monolayer MoS2 film prepared in this example is shown in Fig. 1. It can be seen from the figure that the average grain size of the monolayer MoS2 film is 45 μm. Figure 12 Example 4

[0054] Similar to Example 1, except that the Ar:O2 ratio during the growth stage in step (7) of Example 1 was adjusted to 70:5.

[0055] The OM of the monolayer MoS2 film prepared in this example is shown in Fig. 1. It can be seen from the figure that the average grain size of the monolayer MoS2 film is 45 μm.

[0056] Figure 13 Example 4

[0057] Similar to Example 1, except that the Ar:O2 ratio during the growth stage in step (6) of Example 1 was adjusted to 545°C.

[0058] The OM of the monolayer MoS2 film prepared in this example is shown in Fig. 1. It can be seen from the figure that the average grain size of the monolayer MoS2 film is 45 μm.

[0059] The OM of the monolayer MoS2 film prepared in this example is shown in Fig. 1. It can be seen from the figure that the average grain size of the monolayer MoS2 film is 45 μm. Figure 14 Example 4

[0060] Similar to Example 1, except that the pressure during the growth stage in step (7) of Example 1 was adjusted to 1 torr.

[0061] The AFM image of the monolayer MoS2 film prepared in this example is shown in Fig. 1. It can be seen from the figure that as the pressure decreases, the amount of source deposited on the substrate decreases, and the prepared monolayer MoS2 film has small crystal domains with an average crystal domain size of 10 μm.

[0062] Figure 15 Example 4

[0063] ​​​As can be seen from the above examples and comparative examples, the preparation method provided by the application is simple in operation and low in preparation cost, the nucleation density can be effectively reduced by adjusting the oxygen flow rate in the heating stage and the growth stage, the crystal domain size of the monolayer MoS2 film on the amorphous SiO2 substrate can be regulated, the crystallinity of the film can be improved, and finally the high-quality large-crystal-domain monolayer MoS2 film on the SiO2 substrate is obtained.

Claims

1. A method for preparing a large-grain-size monolayer MoS2 thin film on an amorphous SiO2 substrate, characterized in that, Comprising the following steps: (1) Place the clean SiO2 / Si substrate on a quartz support bracket with an elevation angle of 30° in the third temperature zone; place S powder and MoO3 powder in two ceramic boats respectively, and place the two ceramic boats in a quartz glass tube, with the S powder placed in the first temperature zone and the MoO3 powder placed in the second temperature zone, the distance between the two powders being 18-21 cm, and the distance between the MoO3 powder and the substrate being 15-18.5 cm; (2) Set the temperature of the first temperature zone to 135-150°C, the temperature of the second temperature zone to 640-700°C, and the temperature of the third temperature zone to 700-810°C, raise the temperature of each temperature zone to the set temperature, and make the first temperature zone reach the set temperature 10-15 min earlier than the second and third temperature zones, transport the S powder and MoO3 powder to the substrate and cause a chemical reaction through the Ar / O2 mixed carrier gas flow from the first temperature zone to the second and third temperature zones in turn, grow a large crystal domain size monolayer MoS2 film on the SiO2 / Si substrate, the flow ratio of the carrier gas in the warming-up stage being Ar:O2=70:1-5, the flow ratio of the carrier gas in the growth stage being Ar:O2=70:2-5, and the total pressure in the quartz glass tube being 1.45 torr.

2. The method of claim 1, wherein, In step (1), the thickness of the SiO2layer in the SiO2 / Si substrate was 285 nm, and the Si substrate thickness was 500 In step (1), the distance between the two powders is 21 cm, and the distance between the MoO3 powder and the substrate is 18.5 cm. m.

3. The method of claim 1, wherein, In step (2), the flow ratio of the carrier gas in the growth stage is Ar:O2=70:2-3.

4. The method of claim 1, wherein, In step (2), the temperature of the first temperature zone is 145°C, the temperature of the second temperature zone is 675°C, and the temperature of the third temperature zone is 725°C.

5. The method of claim 1, wherein, In step (2), the holding time of the first temperature zone is 30 min, and the holding time of the second and third temperature zones is 15 min.

6. The method of claim 1, wherein, In step (2), the growth time is 15 min.

7. The method of claim 1, wherein, In step (2), the flow ratio of the carrier gas in the growth stage is Ar:O2=70:2-3.

8. The method of claim 1, wherein, In step (2), the average domain size of the single-layer MoS2 film was 20 In step (2), the temperature of the first temperature zone is 145°C, the temperature of the second temperature zone is 675°C, and the temperature of the third temperature zone is 725°C. m~78 In step (2), the holding time of the first temperature zone is 30 min, and the holding time of the second and third temperature zones is 15 min. In step (2), the growth time is 15 min. m, with a thickness of 0.65 nm.

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