Layer-by-layer van der waals epitaxial growth of wafer-scale mo s2 continuous thin films

Abstract

A continuous MoS2 thin film on a substrate is characterized in that the domain sizes of the continuous MoS2 thin film are respectively greater than 100 μm (number of layers = 1) and 10 μm (number of layers ≥ 2). The high-quality continuous MoS2 thin films of the present invention have different numbers of layers (≥ 2) on the substrate. These films can be continuous on a large area (e.g., a 4-inch wafer). The film can be prepared based on a chemical vapor deposition method. These films can be used in electrical and electronic devices (e.g., high-performance thin-film transistors, logic devices, sensors).

Description

Technical Field

[0001] This invention discloses the growth of large-area continuous MoS2 films with different numbers of layers. More specifically, this invention discloses the growth of 4-inch high-quality MoS2 multilayer continuous films by layer-by-layer van der Waals epitaxy. Background Technology

[0002] MoS2, as a representative two-dimensional material, has shown great potential in large-scale integrated circuits. Researchers have devoted considerable effort to producing high-quality MoS2 thin films. To date, controllable fabrication of high-quality wafer-level monolayer MoS2 thin films has been achieved. In fact, multilayer MoS2, due to its higher electronic state density, is more suitable for high-performance electronic devices. However, producing wafer-level layered MoS2 thin films with high spatial uniformity and high quality remains a significant challenge.

[0003] To date, existing methods for producing large-area bilayer or multilayer (≥3 layers) films (e.g., atomic layer deposition and sulfidation of metals or metal compounds) typically suffer from low crystallinity and small domain sizes (typically less than 0.1 μm), resulting in materials that generally exhibit poor electronic properties. For example, sulfidation of metals or metal compounds can only control the average thickness of the resulting film, leading to poor film continuity and inhomogeneity. Chemical vapor deposition (CVD) is an effective method for growing large-area, high-quality monolayer two-dimensional material films on various substrates; however, the growth of bilayer continuous films remains very challenging due to the self-limiting growth process of monolayer continuous films. For the growth of MoS2, highly crystalline multilayer MoS2 flakes have been obtained via CVD. However, MoS2 flakes with different numbers of layers (from monolayer to multilayer) are often grown simultaneously during batch production. The controlled production of highly crystalline bilayer and multilayer continuous MoS2 films remains a significant challenge. To date, it remains impossible to achieve large-area, uniform multilayer MoS2 films with large domain sizes (≥10μm per layer).

[0004] Therefore, a new method is needed to produce high-quality MoS2 continuous films with controllable layer number. Summary of the Invention

[0005] This invention includes the epitaxial growth of controllable-layer-number continuous MoS2 thin films on various substrates (e.g., sapphire, Si / SiO2 substrates, mica, SiC, etc.). The resulting films exhibit high crystallinity, with domain sizes greater than 100 μm (layer number = 1) and 10 μm (layer number ≥ 2), respectively. In one example, a method can realize a 4-inch wafer-level multilayer continuous MoS2 thin film. The growth of this multilayer film exhibits good layer number control characteristics. The method includes using a relatively low growth temperature to grow the first layer and using a relatively high temperature to grow the second layer.

[0006] A first aspect of the present invention provides a continuous MoS2 thin film on a substrate, characterized in that the domain size of the continuous MoS2 thin film is greater than 10 μm; wherein the continuous MoS2 thin film is a single layer or multiple layers.

[0007] According to the MoS2 continuous thin film of the first aspect, the substrate is selected from one or more of the following: sapphire, Si / SiO2 substrate, mica, SiC, BN, SrTiO3; preferably, the substrate is sapphire.

[0008] According to the first aspect, the MoS2 continuous thin film is a monolayer, the domain size of the MoS2 thin film is greater than 100 μm, and / or the average field-effect mobility is 70–80 cm⁻¹. 2 / Vs.

[0009] According to the first aspect, the MoS2 continuous thin film is a bilayer, and the average field-effect mobility is 110–120 cm⁻¹. 2 / Vs; and / or

[0010] The MoS2 thin film is a three-layer film, and the average field-effect mobility is 120–140 cm⁻¹. 2 / Vs.

[0011] A second aspect of the present invention provides a method for preparing a continuous MoS2 thin film according to the first aspect, the method comprising the following steps:

[0012] (1) Sublimation of S and MoO3;

[0013] (2) Transfer of S and MoO3 via different carrier gases;

[0014] (3) S reacts with MoO3 to generate MoS2;

[0015] (4) Forming a monolayer of MoS2 on the substrate; and

[0016] (5) Increase the growth temperature and form a multilayer MoS2 on the substrate.

[0017] According to the method of the second aspect, in step (2), the carrier gas of S is selected from one or more of the following: Ar or N2; and / or

[0018] The carrier gas for the MoO3 is selected from one or more of the following: Ar, N2, and O2.

[0019] According to the method of the second aspect, in step (3), the reaction temperature of the S source is 120-140°C, and the reaction temperature of the MoO3 is 540-570°C; and / or

[0020] In step (4), the growth temperature is 760–930°C.

[0021] According to the method of the second aspect, in step (5), the growth temperature is 820-970℃.

[0022] According to the method of the second aspect, in step (5), the chamber pressure is 0.8 to 1.3 torr; preferably, the chamber pressure is 1 torr.

[0023] According to the method of the second aspect, when the MoS2 film has two or more layers, the second MoS2 film is formed after the first MoS2 film has formed 95% or more coverage on the substrate.

[0024] A third aspect of the present invention provides an electrical and / or electronic device, the electronic device comprising: a MoS2 continuous thin film according to the first aspect; and / or a MoS2 continuous thin film prepared according to the method of the second aspect;

[0025] Preferably, the electrical and / or electronic equipment is selected from one or more of the following: thin-film transistors, logic devices, sensors, storage devices, wearable electronic devices, neuromorphic computing devices, neuromorphic electronic devices, complex electronic circuits or systems.

[0026] In one aspect, the present invention provides a method for epitaxially producing high-quality continuous MoS2 films ranging from single-layer to multi-layer. The method is based on a 4-inch multi-source chemical vapor deposition (CVD) system. The method is based on a layer-controlled growth mode.

[0027] In one example, the obtained 4-inch bilayer MoS2 continuous film exhibited good spatial uniformity. Single-layer and triple-layer regions were very few, indicating that the growth process of this invention has excellent layer number control. Furthermore, only two stacking orders were observed in the bilayer MoS2 continuous film of this invention; no other rotational angles or twisted stacking arrangements were observed, indicating that the obtained film has high quality.

[0028] In another example, the obtained 4-inch three-layer MoS2 continuous film exhibited ideal spatial uniformity and electronic properties.

[0029] In one respect, the obtained continuous thin film can be used in, but is not limited to, logic circuits, storage devices, and thin-film transistors.

[0030] Typically, the difficulty in synthesizing multilayer continuous MoS2 films lies in achieving planar growth of each layer in a controlled manner. For example, sulfidation methods of metals or metal compounds often produce a mixture of monolayers, multilayers, and no-growth regions.

[0031] In this invention, the inventors employ a two-stage CVD method to grow multilayer continuous MoS2 thin films via layer-by-layer van der Waals epitaxy. The invention first uses a relatively low growth temperature to grow a single layer of MoS2, and then uses a relatively high temperature to grow a second layer of MoS2. The high temperatures of the substrate and source promote the formation of the second layer on top of the first MoS2 layer. Furthermore, this invention uses a multi-source CVD system to ensure a uniform source supply throughout the growth process, thereby achieving a high degree of spatial uniformity in the multilayer continuous thin film.

[0032] Brief description of the attached figures

[0033] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

[0034] Figure 1 A schematic diagram of a 4-inch multi-source CVD device is shown.

[0035] Figure 2 A 4-inch wafer-level MoS2 with a sapphire substrate is shown.

[0036] Figure 3 Optical images of MoS2 growth states with different number of layers are shown; where Figure 3 a shows an optical image of the obtained monolayer film (with intentional scratches in the upper left corner); Figure 3 b shows a monolayer of MoS2 with a second layer of grains (~1.6L MoS2) covering 60% of the surface area. The epitaxial second layer grains are approximately 10 μm in size and are hexagonal. Figure 3 c shows a continuous bilayer MoS2 thin film; Figure 3 d shows a continuous bilayer MoS2 film with a small number of multilayer grains. Figure 3 e shows a continuous three-layer MoS2 film with a small number of multilayer grains.

[0037] Figure 4 Raman spectra of MoS2 films with different layers (layer number = 1, 2, 3) are shown.

[0038] Figure 5 Photoluminescence (PL) spectra of MoS2 thin films with different layers (layer number = 1, 2, 3) are shown.

[0039] Figure 6 Raman spectra of MoS2 collected at different locations on wafers with different numbers of MOS2 layers (layer number = 1, 2, 3) are shown. Figure 6 A corresponds to a single-layer MoS2 wafer. Figure 6 B corresponds to a double-layer MoS2 wafer. Figure 6 C corresponds to a three-layer MoS2 wafer.

[0040] Figure 7 Cross-sectional images of MoS2 thin films with different layers (layer number = 1, 2, 3) are shown by transmission electron microscopy (TEM), in which Figure 7 A corresponds to a single layer of MoS2. Figure 7 B corresponds to a double-layered MoS2. Figure 7 C corresponds to three layers of MoS2.

[0041] Figure 8 Typical selected area electron diffraction (SAED) patterns of MoS2 thin films with different layers (layer number = 1, 2, 3) are shown. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0043] This application provides a method for forming continuous MoS2 thin films with different layers at the wafer level.

[0044] Specifically, in a multi-source system, wafer-level continuous MoS2 films of varying numbers are epitaxially grown using chemical vapor deposition (CVD) with oxygen assistance. The wafer-level continuous multilayer MoS2 films obtained on substrates (such as sapphire, Si / SiO2 substrates, mica, SiC, etc.) exhibit high spatial uniformity and electrical consistency. The obtained multilayer MoS2 continuous films demonstrate excellent electrical properties, including an average field-effect mobility of approximately 70 cm⁻¹ for a single layer at room temperature. 2 / Vs, average field-effect mobility of bilayer thin film >100cm 2 The average field-effect mobility of the three-layer thin film is approximately 130 cm⁻¹. 2 / Vs.

[0045] The following embodiments further illustrate the present invention, but do not limit the scope of the invention.

[0046] Example 1

[0047] This embodiment describes the process of epitaxially growing multilayer continuous MoS2 thin films with different numbers of layers on a substrate. Sulfur powder (S), molybdenum trioxide (MoO3), and a 4-inch sapphire substrate were placed in zones I, II, and III. These three temperature zones (Zone I, Zone II, and Zone III) are sequentially distributed along the gas flow direction. A vacuum was evacuated to below 0.01 torr, and then 280 sccm of Ar and 10 sccm of O2 were introduced into the chamber. The first stage involved growing a continuous monolayer MoS2 thin film on the sapphire substrate, which took approximately 30 minutes. This first stage was carried out at a relatively low growth temperature of ~900°C, with S and MoO3 heated to 120°C and 540°C, respectively. After the monolayer continuous film completely covered the substrate, because a higher growth temperature is beneficial for vertical growth, the inventors increased the substrate temperature to ~940°C and the MoO3 temperature to 560°C to grow a second MoS2 thin film.

[0048] S, MoO3, and a 4-inch Si / SiO2 substrate were placed in regions I, II, and III, respectively. The vacuum was evacuated to below 0.01 torr, and then 280 sccm of Ar and 5 sccm of O2 were introduced into the chamber. The first stage of growth was carried out at a relatively low growth temperature of ~760°C for approximately 30 minutes, with the S and MoO3 temperatures raised to 120°C and 540°C, respectively. After the monolayer continuous film completely covered the substrate, the inventors increased the substrate temperature to ~820°C and the MoO3 temperature to 560°C to grow the second film.

[0049] Figure 1 The diagram shows a multi-source CVD system. In this specially designed system, there are more than one microtube to load the MoO3 source; up to six microtubes are used to load the MoO3 source and are evenly distributed around the microtubes used to load the S source. This is crucial for achieving uniformity in the multilayer MoS2. Microtube 101 loads the S source, and microtubes 102, 103, and 104 load the MoO3 source. Sulfur powder (S), molybdenum trioxide (MoO3), and a 4-inch sapphire substrate are placed in regions I, II, and III, respectively. The system is evacuated to below 0.01 torr, and then 280 sccm of Ar and 10 sccm of O2 are introduced into the chamber. The first stage of growth is carried out at a relatively low growth temperature of ~910°C for approximately 30 minutes, with the S and MoO3 temperatures raised to 120°C and 540°C, respectively. After the monolayer continuous film completely covers the substrate, the inventors raise the substrate temperature to ~950°C and the MoO3 temperature to 560°C to grow the second film. After 20 minutes, the inventors further increased the temperature of the MoO3 to 570°C to grow a third thin film. The substrate temperature was maintained at ~950°C. After approximately 20 minutes, the present invention yielded a wafer-level three-layer continuous MoS2 thin film. Subsequent growth under these conditions yielded multilayer continuous thin films (≥4 layers).

[0050] Figure 2 Photographs of 4-inch single-layer (1L), double-layer (2L), and triple-layer (3L) MoS2 wafers are shown. The inventors grew the first MoS2 film at ~900°C. After ~30 minutes, the first MoS2 film completely covered the substrate. The inventors then heated the temperature to ~940°C to grow the second MoS2 layer. Figure 3 Image a shows an optical microscope image of a monolayer MoS2 grown on sapphire for 20 minutes, showing that the average domain size of the monolayer film is greater than 100 μm. Figure 3 b shows an optical image of the obtained monolayer film (with intentional scratches in the upper left corner), where the second layer is barely visible. Figure 3 As shown in Figure c, a second layer of crystalline domains (~1.6 L MoS2) has grown over 60% of the monolayer MoS2. The grain size of the epitaxially grown second layer is approximately 10 μm and is hexagonal, which is much larger than the grain size in previously reported bilayer continuous films (the crystalline domain size of the second layer of MoS2 is typically less than 0.1 μm). Figure 3 Figure d shows a continuous bilayer MoS2 film with very few monolayer and trilayer regions, indicating that the epitaxial growth of the present invention has good layer number control. Figure 3 e shows a continuous three-layer MoS2 thin film with a small number of multilayer grains.

[0051] The obtained MoS2 thin film was characterized using Raman spectroscopy and photoluminescence (PL) spectroscopy. Figure 4 Raman spectra of continuous MoS2 films with different numbers of layers prepared on a 4-inch sapphire substrate are shown. For a 1L MoS2 film, E1 2g and A 1g The peak frequency difference (Δ) between vibration modes is approximately ~20 cm. -1 Compared to 1L MoS2 films, 2L MoS2 exhibits a larger peak frequency difference (Δ) and higher peak intensity. Furthermore, 3L exhibits an even larger peak frequency difference (Δ) and higher peak intensity than 2L. Figure 5 The photoluminescence (PL) spectra of continuous MoS2 films with different numbers of layers prepared on a 4-inch sapphire substrate are shown. A strong PL peak can be observed at ~1.9 eV for 1L MoS2, while the PL peak intensity is suppressed for 2L and 3L films due to interlayer coupling causing the direct bandgap to become an indirect bandgap. The peak positions of the indirect bandgap peaks are also observed to be 1.50 eV and 1.42 eV for 2L and 3L MoS2, respectively.

[0052] Figure 6AC shows Raman spectra collected from five different regions of 1L, 2L, and 3L MoS2 continuous films. It can be seen that, in different regions of any number of layers in the MoS2 continuous film, these measured spectra have almost the same peak positions, indicating that the MoS2 continuous films prepared in this invention have high uniformity. Figure 7 Transmission electron microscopy (TEM) cross-sectional images of the grown 1L, 2L, and 3L MoS2 continuous films are shown. These images demonstrate excellent layer number control of the obtained multilayer MoS2, with each layer exhibiting uniformity.

[0053] The grown 1L, 2L and 3L MoS2 continuous films exhibited excellent crystallinity. Figure 8 The selected area electron diffraction (SAED) patterns of the obtained thin films are shown, all of which show only one set of hexagonal diffraction spots, indicating that there are only two stacking orders in the thin films of the present invention, without other rotation angles and twisted stacking arrangements.

[0054] The technical solutions of the present invention have been described above with reference to the preferred embodiments shown in the accompanying drawings. However, those skilled in the art should understand that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and these changes or substitutions also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a continuous MoS2 thin film, characterized in that, The MoS2 continuous thin film is a multilayer continuous thin film with a crystal domain size greater than 10 μm on a substrate, and the substrate is sapphire. ； Furthermore, the number of layers in the multilayer continuous thin film is ≥ 3; wherein, the preparation method includes the following steps: (1) Sublimation of S and MoO3; (2) S and MoO3 are transferred by different carrier gases, wherein the carrier gas for S is Ar2 and the carrier gas for MoO3 is O2; (3) S reacts with MoO3 to generate MoS2, wherein the reaction temperature of S is 120-140℃ and the reaction temperature of MoO3 is 540℃-570℃; (4) A monolayer of MoS2 is formed on the substrate at a growth temperature of 760–930 °C; and (5) Increase the growth temperature and form a multilayer MoS2 on the substrate, wherein the growth temperature is 820-970°C.

2. The method according to claim 1, characterized in that, The MoS2 continuous thin film is a three-layer film with an average field-effect mobility of 120–140 cm⁻¹. 2 / Vs.

3. The method according to claim 1 or 2, characterized in that, In step (5), the chamber pressure is 0.8 to 1.3 torr.

4. The method according to claim 3, characterized in that, In step (5), the chamber pressure is 1 torr.

5. The method according to claim 1 or 2, characterized in that, The second MoS2 film is formed after the first MoS2 film has formed 95% or more coverage on the substrate.

6. An electrical and / or electronic device, characterized in that, The electrical and / or electronic equipment includes: a continuous MoS2 thin film prepared by the method according to any one of claims 1 to 5.

7. The electrical and / or electronic equipment according to claim 6, characterized in that, The electrical and / or electronic equipment is selected from one or more of the following: thin-film transistors, logic devices, sensors, storage devices, wearable electronic devices, neuromorphic computing devices, neuromorphic electronic devices, complex electronic circuits or systems.

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