Method for growing large-area high-performance hole-conducting tungsten diselenide single crystals on silicon-based insulating layers

Abstract

The application discloses a method for growing large-area high-performance hole-conducting tungsten diselenide monocrystals on a silicon-based insulating layer. The method is to use a molten salt to react with a tungsten source to generate an intermediate product with a lower melting point and a higher vapor pressure, so that it is easier to grow tungsten diselenide monocrystals on the silicon oxide or high-dielectric-constant insulating layer on the silicon substrate based on the principle of chemical vapor deposition. At the same time, the large-area growth of tungsten diselenide is realized by changing the placing mode of the substrate. The method can effectively control the growth of large-area multilayer tungsten diselenide monocrystals, obtain a silicon-compatible high-mobility hole-conducting two-dimensional material, and is simple to operate, does not need to be transferred, and has higher material quality.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material growth technology, specifically relating to a silicon-compatible method for directly growing large-area, high-performance hole-conducting tungsten diselenide single crystals on silicon oxide and a high-dielectric-constant insulating layer by chemical vapor deposition. Background Technology

[0002] Transition metal chalcogenides (TMCs) have attracted widespread attention as two-dimensional materials that are not readily reacted with water and oxygen, exhibit good stability, are easy to grow using various methods, have a wide bandgap, and offer tunable conductivity. Among them, tungsten diselenide, as a bipolar TMC, shows great promise for applications in the field of CMOS nanosheets for integrated circuits.

[0003] Currently, high-performance tungsten diselenide materials are mainly obtained through mechanical exfoliation. However, mechanical exfoliation suffers from drawbacks such as uncontrollable layer count and size limitations, hindering large-scale application. Chemical vapor deposition (CVD) can theoretically achieve large-area, high-quality thin film growth; however, current traditional CVD methods still suffer from poor quality, small size, low hole mobility, and difficulty in achieving controllable multilayer growth, limiting the development of CMOS circuits based on two-dimensional materials. Achieving high-performance hole-conducting tungsten diselenide growth is one of the key challenges to be addressed in the current development of two-dimensional material growth. Summary of the Invention

[0004] The purpose of this invention is to provide a method for directly growing large-area, high-performance hole-conducting tungsten diselenide single crystals on a silicon-compatible silicon substrate insulating layer. This method improves the key reaction participants and substrate placement in the preparation process by using a mixture of halides and tungsten source materials. The reactants have a lower melting point and higher vapor pressure than the tungsten source, enabling the growth of single-layer or multi-layer tungsten diselenide on the silicon-based insulating layer. By changing the placement of the substrate and tungsten source, large-area single-layer tungsten diselenide films and multi-layer tungsten diselenide single crystals can be grown, and the hole mobility of tungsten diselenide is relatively high, reaching over 140 square centimeters per volt-second.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for growing large-area tungsten diselenide single crystals on a silicon-based insulating layer, using chemical vapor deposition (CVD) to grow tungsten diselenide on a silicon-based insulating layer substrate, is characterized by placing a tungsten source and a halide in a first carrier boat, with the substrate inserted obliquely downwards into the first carrier boat, such that the tungsten source and halide are located within a triangular space formed by the bottom and sidewalls of the substrate and the first carrier boat, with the tungsten source and halide close to the sidewalls of the first carrier boat but not in contact with the substrate; placing a selenium source in a second carrier boat, with a carrier gas flowing from the second carrier boat to the first carrier boat; heating to a set growth temperature, whereby the halide melts and reacts with the tungsten source to generate an intermediate product, which then reacts with the selenium source brought by the carrier gas to chemically vapor deposit tungsten diselenide single crystals on the substrate surface.

[0007] The present invention provides a method for growing large-area tungsten diselenide single crystals using a molten salt-assisted chemical vapor deposition (CVD) method. Unlike the traditional method where the substrate is placed horizontally with its growth surface facing down above the tungsten source, in this invention, the substrate is inserted upside down into a first carrier boat. The tungsten source is placed within the triangular space formed by the substrate and the first carrier boat, while ensuring the tungsten source remains close to the wall of the first carrier boat without contacting the substrate. A second carrier boat upstream of the tungsten source contains selenium source material, and a carrier gas flows from the second carrier boat to the first carrier boat. In addition to the tungsten source material, the first carrier boat also contains halides, which are located above the tungsten source or are uniformly mixed with it. When the furnace reaches the preset growth temperature, before the selenium source material melts, the halides melt and react with the tungsten source material to generate an intermediate product. This intermediate product then reacts with the selenium source brought by the carrier gas to chemically vapor deposit tungsten diselenide single crystals on the substrate surface.

[0008] Preferably, the halide is an alkali metal halide (e.g., sodium or potassium), and most preferably potassium chloride. The mass ratio of the halide to the tungsten source is 1:120 to 1:8.

[0009] As a further preferred embodiment of the present invention, the substrate may be a low-resistivity silicon substrate having a silicon oxide layer or a high-dielectric-constant silicon nitride layer or other high-dielectric-constant insulating layer. The silicon oxide or silicon nitride on the silicon substrate may be obtained by thermal oxidation / nitridation, atomic layer deposition or plasma-enhanced chemical vapor deposition.

[0010] As a further preferred embodiment of the present invention, the first and second cargo boats are placed in the pipes of the tubular heating furnace. The heating method involves heating to a set temperature at a position downstream of the cargo boats, and then moving the heating furnace to the position of the cargo boats. After a heating time that is shorter than the heating time, the chemical vapor deposition reaction begins. The purpose is to avoid premature melting of halides due to a relatively long heating time.

[0011] As a further preferred embodiment of the present invention, the preset growth temperature is 800-900°C, the heating center of the tubular heating furnace is located at the position of the first loading boat; the second loading boat is located at the edge of the tubular heating furnace, and the temperature is lower, at 300-500°C.

[0012] As a further preferred embodiment of the present invention, the tungsten diselenide single crystal obtained by growth can be a single-layer or multi-layer tungsten diselenide. The number of layers of the tungsten diselenide single crystal can be controlled by adjusting the amount of halide and the growth time, such as single-layer, double-layer and triple-layer tungsten diselenide. The side length of the prepared tungsten diselenide single crystal is not less than 40 micrometers, preferably not less than 200 micrometers.

[0013] The beneficial effects of this invention are:

[0014] (1) Simple operation and controllable results: Traditional mechanical peeling methods are complex and the number and size of layers are uncontrollable. Chemical vapor deposition equipment is simple and can achieve high-quality, large-scale and controllable single crystal growth of two-dimensional materials.

[0015] (2) Large material size: The method of the present invention realizes large-area single-layer material thin film and large-size multilayer tungsten diselenide single crystal through oblique insertion method, with a maximum side length of 221 micrometers.

[0016] (3) Silicon-based compatible direct growth: The two-dimensional material deposited on the insulating layer / silicon substrate in this invention does not need to be transferred and can be directly used to prepare hole-conducting devices, avoiding material damage and process residue caused by transfer and ensuring high material quality.

[0017] (4) High quality of materials: The double-layer tungsten diselenide thin film single crystal prepared by this invention is an equilateral triangle with a clean surface and sharp edges without serrations, which has a very high quality and the hole mobility can reach 140 square centimeters per volt-second. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the apparatus used in the chemical vapor deposition method for preparing large-area tungsten diselenide single crystals in this invention.

[0019] Figure 2 An optical microscope image of a double-layered tungsten diselenide single crystal prepared for an embodiment of the present invention.

[0020] Figure 3 The photoluminescence spectrum of a double-layer tungsten diselenide single crystal prepared in an embodiment of the present invention.

[0021] Figure 4 The Raman spectrum of the double-layer tungsten diselenide single crystal prepared in an embodiment of the present invention. Detailed Implementation

[0022] To make the content of this invention easier to understand, the technical solutions of this invention will be further described below with reference to specific embodiments. However, the following examples are merely examples of this invention and do not represent the scope of protection of this invention. The scope of protection of this invention is determined by the claims.

[0023] In summary, this invention achieves multilayer growth of tungsten diselenide single crystals on a silicon-based insulating layer by using halide molten salt-assisted growth, and expands the multilayer growth region and increases the multilayer size by changing the placement of the substrate and tungsten source.

[0024] The following are specific examples:

[0025] This embodiment presents a silicon-compatible chemical vapor deposition method for growing bilayer tungsten diselenide, which achieves chemical vapor deposition within a tubular furnace. A schematic diagram of the equipment is shown below. Figure 1 As shown, the tungsten source (tungsten oxide) and halide (potassium chloride) are mixed and placed in the first carrier boat. The substrate is inserted obliquely into the first carrier boat with its front side facing down, so that the tungsten source and halide are located in the triangular space enclosed by the substrate, the bottom surface of the carrier boat, and the sidewalls. The tungsten source and halide are required to be close to the sidewalls of the carrier boat but not in contact with the substrate. The second carrier boat contains the selenium source (selenium powder), and the carrier gas flows from the second carrier boat to the first carrier boat. The specific operating steps are as follows:

[0026] 1. Cleaning the substrate: Clean the low-resistivity silicon substrate with the silicon oxide layer using the standard RCA method, and dry it with high-purity nitrogen gas for later use.

[0027] 2. Weighing the Sample: The required sample mass varies depending on the size of the tubular furnace. In this embodiment, a quartz tube with an outer diameter of one inch is used. The selenium powder, tungsten dioxide powder, and potassium chloride used in the reaction are 200 mg, 40 mg, and 3 mg, respectively. The selenium powder is placed in a ceramic boat (the second carrier boat). The tungsten dioxide and potassium chloride powders are mixed evenly and then placed in a corundum boat (the first carrier boat). The cleaned substrate is placed upside down and obliquely on top of the powder in the corundum boat, with one edge of the substrate contacting the bottom of the corundum boat and the other edge resting on the side wall edge of the corundum boat, forming a triangular space with the corundum boat.

[0028] 3. Sample Placement and Heating: Use argon gas to restore the low-pressure quartz tube to normal pressure so that the baffle can be opened for sample placement. Use a metal rod to push the corundum boat and ceramic boat to the designated positions one after the other. When the furnace reaches the designated temperature and is pushed to the reaction position, the corundum boat should be in the center of the furnace, and the ceramic boat should be at the edge of the furnace, with a distance of 19 cm between the two boats. After sample placement, cover the baffle and turn on the vacuum pump, opening the angle valve to evacuate the air until the pressure inside the tube is less than 5 Pa. Set the growth temperature to 850 degrees Celsius, the heating rate to 30 degrees Celsius per minute, and the argon gas flow rate to 50 standard milliliters per minute during the heating process.

[0029] 4. Reaction: After heating is complete, slide the furnace to the upstream position of the quartz tube. After a 5-minute heating process, the temperature reaches 850 degrees Celsius. At this point, the temperature at the center (corundum boat) is 850 degrees Celsius, and at the edge (ceramic boat) is 300 degrees Celsius. The reaction begins, with a reaction time of 15 minutes. The flow rates of argon and hydrogen are 105 and 7 standard milliliters per minute, respectively. During the reaction, the angle valve needs to be adjusted as needed to maintain the pressure between 1000 and 2000 Pa. After the reaction is complete, slide the furnace downstream to allow it to cool naturally, with the argon flow rate at 50 standard milliliters per minute.

[0030] 5. Sampling and observation: After the substrate temperature drops to room temperature, close the angle valve, use a large flow of argon gas to break the vacuum, remove the sample, and observe the size, morphology, and number of layers of the sample under a microscope.

[0031] Figure 2 It is a double-layered tungsten diselenide single crystal under an optical microscope. The single crystal is triangular and the side length can reach 200 micrometers. Figure 3 and Figure 4 The images show the photoluminescence and Raman spectra of bilayer tungsten diselenide, respectively, and the positions of the characteristic peaks are consistent with those reported in the literature for bilayer tungsten diselenide. Testing of the single-crystal bilayer tungsten diselenide material revealed that the material is hole-conductive with a mobility of 140 cm² / V / s.

Claims

1. A method for growing large-area tungsten diselenide single crystals on a silicon-based insulating layer, comprising growing tungsten diselenide on a silicon-based insulating layer substrate by chemical vapor deposition, characterized in that, A tungsten source and a halide are placed in a first carrier boat. The substrate is inserted obliquely into the first carrier boat with its growth surface facing down, so that the tungsten source and the halide are located in the triangular space formed by the bottom surface and sidewalls of the substrate and the first carrier boat, and the tungsten source and the halide are close to the sidewalls of the first carrier boat but not in contact with the substrate. A selenium source is placed in a second carrier boat, and a carrier gas flows from the second carrier boat to the first carrier boat. The temperature is heated to a set growth temperature, wherein the temperature at the first carrier boat is 800-900°C and the temperature at the second carrier boat is 300-500°C. The halide melts and reacts with the tungsten source to generate an intermediate product. The intermediate product then reacts with the selenium source brought by the carrier gas to chemically vapor-deposit tungsten diselenide single crystals on the substrate surface.

2. The method as described in claim 1, characterized in that, The halide is located above the tungsten source or is mixed uniformly with the tungsten source.

3. The method as described in claim 1, characterized in that, The halide is an alkali metal halide.

4. The method as described in claim 3, characterized in that, The halide is potassium chloride.

5. The method as described in claim 1, characterized in that, The mass ratio of the halide to the tungsten source is 1:120 to 1:

8.

6. The method as described in claim 1, characterized in that, The silicon-based insulating substrate has a silicon oxide layer or a high dielectric constant insulating layer on a low-resistivity silicon substrate.

7. The method as described in claim 1, characterized in that, The first and second cargo boats are placed into the pipes of the tubular furnace for chemical vapor deposition. The furnace is first heated to the set temperature at a position downstream of the cargo boats, and then the furnace is moved to the position of the cargo boats to quickly start the chemical vapor deposition reaction.

8. The method as described in claim 1, characterized in that, The first cargo boat is a corundum boat, and the second cargo boat is a ceramic boat.

9. The method as described in claim 1, characterized in that, The number of layers in a tungsten diselenide single crystal can be controlled by adjusting the amount of halide and the growth time.

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