Method for preparing large-domain-size single-layer MoS2 film on amorphous SiO2 substrate

Abstract

The invention discloses a method for preparing a single-layer MoS2 film with a large crystal domain size on an amorphous SiO2 substrate. The method comprises the steps that S powder, MoO3 powder and a clean SiO2 / Si substrate are placed in a first temperature zone, a second temperature zone and a third temperature zone respectively, the distance between the two kinds of powder and the distance between the MoO3 powder and the substrate are regulated and controlled, and the temperature of each temperature zone is increased to the set temperature; the Ar / O2 mixed carrier gas flow which sequentially flows to the second temperature zone and the third temperature zone through the first temperature zone conveys S powder and MoO3 powder to the substrate for chemical reaction, and the large-domain-size single-layer MoS2 film grows on the SiO2 / Si substrate. A chemical vapor deposition method is adopted, the single-layer MoS2 film with good uniformity, large domain size and high-quality crystallinity is prepared on the SiO2 / Si substrate, the average domain size of the single-layer MoS2 film can reach 20-78 microns, and the method is easy to operate, low in cost and good in repeatability.

Description

Technical Field

[0001] The invention belongs to the field of two-dimensional atomic crystal materials and relates to a method for preparing a single-layer MoS2 film with a large crystal domain size on an amorphous SiO2 substrate. Background Art

[0002] Two-dimensional atomic crystal materials refer to materials in which electrons can move freely only on non-nanoscale (1-100nm) in length and width, such as nanosheets, superlattices, quantum wells, etc. Because of their atomic-level thickness, no dangling bonds on the surface, and excellent electrical transmission properties, they can effectively solve the bottleneck problems currently faced by field-effect transistors, such as short channel effects and high device power consumption. They are one of the most promising candidates for continuing the traditional Si-based chips at sub-10nm advanced nodes in the post-Moore era. In 2004, the Geim group at the University of Manchester took the lead in obtaining a single layer of two-dimensional graphene from bulk graphite by mechanical exfoliation, and proved its unique and excellent electrical properties, and won the 2010 Nobel Prize in Physics. In the nearly 20 years since then, two-dimensional atomic crystal materials represented by graphene have entered a rapid development, and have aroused widespread interest and research enthusiasm in the scientific and industrial communities. In addition to graphene, a series of new two-dimensional atomic crystal materials have also been explored, including single-element silicene, antimonene, and black phosphorus, as well as 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 concerned and studied by researchers due to its adjustable energy 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 listed in the International Technology Roadmap for Semiconductors (ITRS) as an ideal channel material that is expected to continue Moore's Law in the future.

[0003] The existing preparation methods of single-layer MoS2 films mainly include solution synthesis, atomic layer deposition and chemical vapor deposition. At present, single-layer MoS2 films with large-size crystal domains are mainly synthesized on sapphire substrates. The reason can be attributed to the fact that sapphire substrates are single crystal substrates, and sapphire and MoS2 have good lattice parameter matching, which is conducive to the two-dimensional epitaxial growth of MoS2 films. However, sapphire is not an ideal substrate for compatible with traditional Si-based substrates and for constructing electrical transistor devices. The main reason is that the MoS2 film grown on sapphire needs to be transferred to the target substrate (for example: Si substrate) by wet transfer technology for electrical device construction and testing, and the residual chemical reagents and stress release involved in the transfer process will inevitably damage the film quality and cause its quality to deteriorate. However, amorphous SiO2 substrates with a certain oxide layer thickness can not only epitaxially grow MoS2 films, but also directly construct electrical transistor devices thereon, eliminating the pollution and stress accumulation during the transfer process. However, the crystal domain size of the single-layer MoS2 film currently grown on the amorphous SiO2 substrate is small, which seriously hinders the release of the electrical performance potential of the MoS2 film to the integrated transistor array. For example, Reference 1 uses atomic layer deposition to prepare a 4-inch MoS2 film on a SiO2 / Si substrate. Although this method can quickly obtain a large-area MoS2 film, the uniformity of the film is poor and the grain size is very small (Pyeon JJ, Kim SH, Jeong DS, et al. Wafer-scale growth of MoS2 thin films by atomic layer deposition. Nanoscale, 2016, 8: 10792-10798). Reference 2 uses chemical vapor deposition to prepare a single-layer MoS2 film on a SiO2 / Si substrate. Although the uniformity of the film is improved, the crystal domain size is still small (<1μm) (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).Reference 3 uses metal chemical vapor deposition to prepare a 4-inch MoS2 film on a SiO2 / Si substrate. This method can better control the source of volatilization and the grown film has good uniformity. However, the average crystal domain size of the grown MoS2 film is only about 1μm (Kang K, Xie SE, Huang LJ, et al. High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity[J]. Nature, 2015, 520(7549): 656-660). Summary of the invention

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

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

[0006] A method for preparing a large crystal domain size single-layer MoS2 film on an amorphous SiO2 substrate comprises the following steps:

[0007] (1) Place a clean SiO2 / Si substrate on a quartz support bracket with an elevation angle of 30° and place it 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 is 18 to 21 cm, and the distance between the MoO3 powder and the substrate is 15 to 18.5 cm;

[0008] (2) The temperature of the first temperature zone is set to 135°C ~ 150°C, the temperature of the second temperature zone is set to 640°C ~ 700°C, and the temperature of the third temperature zone is set to 700°C ~ 810°C. Each temperature zone is heated to the set temperature, and the first temperature zone reaches the set temperature 10 to 15 minutes earlier than the second and third temperature zones. The Ar / O2 mixed carrier gas flows from the first temperature zone to the second and third temperature zones in turn to transport S powder and MoO3 powder to the substrate and react chemically, thereby growing a single-layer MoS2 film with a large crystal domain size on the SiO2 / Si substrate.

[0009] Furthermore, 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] Furthermore, 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] Furthermore, 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] Furthermore, 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.

[0013] Furthermore, in step (2), the insulation time of the first temperature zone is 30 minutes, and the insulation time of the second and third temperature zones is 15 minutes.

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

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

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

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

[0018] (2) The present invention can effectively avoid poisoning of the precursor MoO3 powder source by controlling the flow rate of oxygen (O2) during the heating stage and the growth stage. At the same time, it can also etch away unstable grains during the growth process and reduce the density of MoS2 nucleation crystals, thereby obtaining a single-layer MoS2 film with large-sized crystal domains. The maximum size of a single crystal domain inside the film can reach 78 μm. The effect of staged oxygen supply on the nucleation density and the size of a single crystal domain can be seen through optical microscopy (OM). The scanning electron microscopy (SEM) test shows that in the growth stage, the selection of different O2 flow rates has a significant effect on the regulation of the crystal domain size of the MoS2 film. process; the thickness of the MoS2 film can be analyzed by atomic force microscopy (AFM) data; Raman spectroscopy (Raman) and photoluminescence (PL) analysis tests can both prove that the prepared MoS2 film is a single layer; the test results of the diffraction pattern of transmission electron microscopy (TEM) and the atomic structure arrangement of high-resolution transmission electron microscopy (HRTEM) prove that the obtained film is a single-layer MoS2 film with good crystallinity, and energy dispersive spectrometer (EDS) element analysis also proves that the prepared film contains Mo and S elements of MoS2 components, and has good uniformity and high quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the structure of a growth device for preparing a single-layer MoS2 thin film according to the present invention;

[0020] Figure 2 OM image of the single-layer MoS2 film prepared in Example 1;

[0021] Figure 3 The SEM image of the single-layer MoS2 film prepared in Example 1;

[0022] Figure 4 AFM height image of the single-layer MoS2 film prepared in Example 1;

[0023] Figure 5 The Raman spectrum of the single-layer MoS2 film prepared in Example 1;

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

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

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

[0027] Fig. 9The EDS image and Mo and S element distribution map of the single-layer MoS2 film prepared in Example 1;

[0028] Fig.10 AFM image of the single-layer MoS2 film prepared in Comparative Example 1;

[0029] Fig.11 OM image of the single-layer MoS2 film prepared in Example 2;

[0030] Fig.12 OM image of the single-layer MoS2 film prepared in Example 3;

[0031] Fig.13 OM image of the single-layer MoS2 film prepared in Example 4;

[0032] Fig.14 OM image of a single-layer MoS2 film prepared in Comparative Example 2;

[0033] Fig.15 This is the AFM image of the single-layer MoS2 film prepared in comparative example 3. DETAILED DESCRIPTION

[0034] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0035] Example 1

[0036] Step (1): Cut the SiO2 / Si substrate (285nm SiO2, 500μm Si) into 3cm×3cm squares;

[0037] Step (2): Place the cut 3 cm × 3 cm silicon wafers into acetone, isopropanol, and ethanol with a purity of ≥ 99.95% and ultrasonically clean them for 10 min each, and then blow dry them with N2;

[0038] Step (3): placing the dried SiO2 / Si substrate in a UV cleaning machine and irradiating it with ultraviolet light for 30 minutes;

[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, and the distance between the two was 21 cm. A clean SiO2 / Si substrate was placed on a quartz support bracket with an elevation angle of 30° and placed in the third temperature zone, and the distance between the substrate and the MoO3 powder was 18.5 cm;

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

[0041] Step (6): Set a heating curve: after the first temperature zone is kept warm for 15 minutes, it is heated to 145°C within 30 minutes and kept warm for 30 minutes; the second temperature zone is heated to 675°C within 60 minutes, and the third temperature zone is heated to 725°C within 60 minutes and kept warm for 15 minutes;

[0042] Step (7): Set the carrier gas flow rate to Ar:O2=70:5 (in sccm) during the heating stage and Ar:O2=70:2 during the growth stage; the pressure is 1.45 torr;

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

[0044] The OM image of the single-layer MoS2 film prepared in Example 1 is as follows: Figure 2 The SEM image of the single-layer MoS2 film prepared in this embodiment is shown in Figure 3 As shown, 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 embodiment is as shown in Figure 4 As shown, the thickness is 0.65 nm; the Raman spectrum of the single-layer MoS2 film prepared in this embodiment is as shown Figure 5 As shown, the difference between the in-plane and out-plane characteristic peaks is 19.46 cm -1 , which is consistent with the characteristics of a single-layer MoS2 film; the PL spectrum of the single-layer MoS2 film prepared in this embodiment is as follows Figure 6 As shown, the band gap is 1.87 eV; the SAED diffraction pattern of the single-layer MoS2 film prepared in this embodiment is as follows Figure 7 The HRTEM atomic structure arrangement diagram of the single-layer MoS2 film prepared in this embodiment is shown in Figure 8 The EDS map and element distribution map of the single-layer MoS2 film prepared in this embodiment are shown in Fig. 9 shown.

[0045] Comparative Example 1

[0046] Similar to Example 1, except that the Ar:O2 in the growth stage in step (7) is regulated to be 70:1.

[0047] The AFM images of the single-layer MoS2 film prepared in this example are as follows: Fig.10 As shown in the figure, it can be seen that the grain size of the MoS2 film is small, and the average grain size is 300nm.

[0048] Example 2

[0049] Similar to Example 1, the difference is that the Ar:O2=70:3 in the growth stage in step (7) of Example 1 is regulated.

[0050] The OM of the single-layer MoS2 film prepared in this example is as follows Fig.11 As shown in the figure, it can be seen that the average grain size of the single-layer MoS2 film is 45μm.

[0051] Example 3

[0052] Similar to Example 1, except that the Ar:O2 in the growth stage in step (7) of Example 1 is regulated to be 70:4.

[0053] The OM of the single-layer MoS2 film prepared in this example is as follows Fig.12 As shown in the figure, it can be seen that the average grain size of the single-layer MoS2 film is 30μm.

[0054] Example 4

[0055] Similar to Example 1, except that the Ar:O2 in the growth stage in step (7) of Example 1 is regulated to be 70:5.

[0056] The OM of the single-layer MoS2 film prepared in this example is as follows Fig.13 As shown in the figure, it can be seen that the average grain size of the single-layer MoS2 film is 20μm.

[0057] Comparative Example 2

[0058] Similar to Example 1, except that the second temperature zone in step (6) of Example 1 is regulated to rise to 545°C.

[0059] The single-layer MoS2 thin film OM prepared in this comparative example is Fig.14 As shown in the figure, it can be seen that the single-layer MoS film coverage is incomplete.

[0060] Comparative Example 3

[0061] Similar to Example 1, except that the pressure in step (7) of Example 1 is adjusted to 1 torr.

[0062] The AFM image of the single-layer MoS2 film prepared in this comparative example is as follows Fig.15 As shown in the figure, it can be seen that as the pressure decreases, the source deposited on the substrate becomes less, and the crystal domain of the prepared single-layer MoS2 film is small, with an average crystal domain size of 10μm.

[0063] It can be seen from the above embodiments and comparative examples that the preparation method provided by the present invention is simple to operate and has low preparation cost. By adjusting the flow rate of oxygen in the heating stage and the growth stage, the nucleation density can be effectively reduced, the crystal domain size of the single-layer MoS2 film on the amorphous SiO2 substrate can be regulated, and the crystallinity of the film can be improved, ultimately obtaining a high-quality large-domain single-layer MoS2 film on the SiO2 substrate.

Claims

1. A method for preparing a large crystal domain size single-layer MoS2 film on an amorphous SiO2 substrate, characterized in that: The following steps are involved: (1) Place a clean SiO2 / Si substrate on a quartz support with an elevation angle of 30° and place it 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 S powder placed in the first temperature zone and MoO3 powder placed in the second temperature zone. The distance between the two powders is 18-21 cm, and the distance between MoO3 powder and the substrate is 15-18.5 cm; (2) The temperature of the first temperature zone is set to 135 ℃~150 ℃, the temperature of the second temperature zone is set to 640 ℃~700 ℃, and the temperature of the third temperature zone is set to 700 ℃~810 ℃. Each temperature zone is heated to the set temperature, and the first temperature zone reaches the set temperature 10~15 minutes earlier than the second and third temperature zones. The Ar / O2 mixed carrier gas flow flows from the first temperature zone to the second and third temperature zones in turn, transports S powder and MoO3 powder to the substrate and reacts chemically, thereby growing a single-layer MoS2 film with a large crystal domain size on the SiO2 / Si substrate.

2. The method according to claim 1, characterized in that 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 nm. μ m.

3. The method according to claim 1, characterized in that 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.

4. The method according to claim 1, characterized in that In step (2), the flow ratio of the carrier gas in the heating stage is Ar:O2=70:1~5, and the flow ratio of the carrier gas in the growth stage is Ar:O2=70:2~5.

5. The method according to claim 1, characterized in that In step (2), the flow ratio of the carrier gas during the growth phase is Ar:O2=70:2~3.

6. The method according to claim 1, characterized in that 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.

7. The method according to claim 1, characterized in that In step (2), the insulation time of the first temperature zone is 30 minutes, and the insulation time of the second and third temperature zones is 15 minutes.

8. The method according to claim 1, characterized in that In step (2), the growth time is 15 min and the total pressure in the quartz glass tube is 1.45 torr.

9. The method according to claim 1, characterized in that In step (2), the average crystal domain size of the single-layer MoS2 film is 20 μ m~78 μ m, and the thickness is 0.65 nm.

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