CN105002476B - A kind of method of the chemical vapor deposition growth large scale single-layer molybdenum disulfide film of substrate modification - Google Patents

Abstract

The invention proposes a method for growing large-scale single-layer molybdenum disulfide by chemical vapor phase method of substrate modification. Using ammonium sulfide as the substrate surface modifier, the nucleation rate is controlled by controlling the concentration of the modifier, soaking time, cleaning method, etc., and the film thickness is controlled by controlling the growth temperature, growth time, and gas flow of chemical vapor deposition. The invention can efficiently grow large-size single-layer molybdenum disulfide film on the basis of the original growth chemical vapor deposition equipment under relatively low growth temperature conditions. The method for growing large-scale single-layer molybdenum disulfide provided by the invention is suitable for the growth of two-dimensional semiconductor materials similar in structure, such as large-scale single-layer tungsten disulfide, molybdenum diselenide and tungsten diselenide.

Description

Growth of large-scale monolayer molybdenum disulfide thin films by substrate-modified chemical vapor deposition Methods

technical field

The invention relates to a method for preparing a film by chemical vapor deposition, in particular to a method for growing a large-size single-layer molybdenum disulfide film by chemical vapor deposition of substrate modification.

Background of the invention

Monolayer molybdenum disulfide (MoS2) is a new type of two-dimensional semiconductor material with an ideal energy band gap (1.8eV). Field effect transistors (FETs) based on it can not only obtain a high switching ratio of 10 ⁸ , but also Has lower energy loss. On the other hand, the monolayer structure of molybdenum disulfide crystal is a direct bandgap semiconductor, and the change of energy band structure can effectively improve the fluorescence efficiency and light absorption cross section of monolayer molybdenum disulfide. In the honeycomb structure of single-layer molybdenum disulfide, molybdenum atoms and sulfur atoms alternately occupy adjacent lattice sites, and the central inversion symmetry of macroscopic crystals is broken; at the same time, the strong spin-orbit of d electrons of transition metal elements The coupling effect causes the monolayer molybdenum disulfide to have a new electronic state——energy valley quantum state. Therefore, it can be seen that monolayer molybdenum disulfide, as a new material complementary to graphene, will not only have very important application prospects in the fields of advanced semiconductors and micro-nano electronic devices in the future, but also the research on its energy band structure, energy valley and other physical properties It is of great value to the fields of condensed matter physics and optoelectronics.

At present, the methods for preparing single-layer molybdenum disulfide mainly include: mechanical exfoliation method, chemical exfoliation method and vapor phase deposition. The single-layer molybdenum disulfide films prepared by mechanical and chemical exfoliation methods are small in size and cannot meet the requirements of large-scale microelectronics fabrication processes. Chemical vapor deposition (CVD) is considered to be an effective method for growing single-layer molybdenum disulfide thin films. It utilizes the sulfidation reaction of gaseous sulfur and molybdenum oxide under high temperature conditions to achieve deposition and growth of single crystal/polycrystalline single crystal on different substrates. layer molybdenum disulfide. In traditional chemical vapor deposition methods, silicon-silicon dioxide is often used as the growth substrate. On the one hand, using silicon-silicon dioxide as the growth substrate is beneficial to the follow-up observation of the growth sample. On the other hand, the silicon-silicon dioxide substrate has Natural conductive layer and dielectric layer, the grown samples can be directly applied to later device processing, reducing the process flow and reducing the preparation cost. However, the current growth of molybdenum disulfide by chemical vapor deposition has disadvantages such as small film forming area and difficult control of sample thickness. How to grow large-size, single-layer molybdenum disulfide thin films has become one of the focus and hotspots in the field of two-dimensional semiconductor materials. There is no doubt that the breakthrough of this technology will not only lead to breakthroughs in the preparation process of similar two-dimensional semiconductor materials, such as large-scale single-layer tungsten disulfide, molybdenum diselenide, and tungsten diselenide, but will also be a new type of semiconductor material, integrated An important driving force for the development of the circuit field. Therefore, the growth technology of large-size, single-layer molybdenum disulfide thin films has huge market prospects.

Substrate surface modification technology is a method that can effectively increase the nucleation rate of epitaxial growth and achieve sample growth at low temperature and low saturation, and the selection of cost-effective substrate modification agent is the key factor for the promotion of this technology. The present invention proposes a method for modifying the surface of a silicon-silicon dioxide growth substrate and growing a large-sized single-layer molybdenum disulfide by chemical vapor phase method. The nucleation rate is controlled by controlling the concentration of the modifier, soaking time, and cleaning methods. Control the growth temperature, growth time, gas flow and other means to control the thickness of the film. The invention can efficiently grow large-size single-layer molybdenum disulfide film on the basis of the original growth chemical vapor deposition equipment under relatively low growth temperature conditions.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of the current chemical vapor deposition growth molybdenum disulfide film size is small, the film thickness is not easy to control, to propose a substrate surface modified chemical vapor deposition growth method for large-scale single-layer molybdenum disulfide.

The technical solution of the present invention is a method for growing a large-sized single-layer molybdenum disulfide film by chemical vapor deposition of substrate modification, which includes the following steps: 1) in the ammonia sulfide solution, the surface of the epitaxial growth substrate is modified so that the surface of the substrate is Forming a layer of chemically bonded vulcanization layer; 2) In a heating furnace continuously fed with protective gas, anneal the surface-modified substrate in step 1) placed therein, to eliminate excess sulfur element on the surface; 3) growing a molybdenum disulfide film on the surface of the annealed substrate described in step 2) by chemical vapor deposition to obtain the large-size single-layer molybdenum disulfide film; the annealing temperature of the annealing treatment is 100-500° C. , the annealing time is 10min-60min. In the above preparation method, in step 1), the epitaxial growth substrate also includes a step of cleaning it before the surface modification treatment, so as to modify the hydrophilicity of its surface. The specific steps are as follows: first, respectively pass through acetone, Ultrasonic cleaning with ethanol and deionized water for 10 minutes, then using a mixed solution of sulfuric acid and hydrogen peroxide with a volume ratio of (3-5): 1 to clean at 160°C for 30 minutes, and then ultrasonically cleaning with deionized water for 5 minutes to remove surface excess of concentrated sulfuric acid.

In the above preparation method, in step 1), the concentration of the ammonia sulfide is 40-44wt%, and the soaking time of the growth substrate is 24 hours.

In the above preparation method, in step 1), ultrasonic cleaning is performed on the surface-modified substrate, the cleaning agent is deionized water, the cleaning time is 2 minutes, and high-purity nitrogen is blown to dry.

In the above preparation method, step 1) further includes drying the treated substrate in a vacuum environment to remove residual organic matter on the surface. The epitaxial growth substrate can specifically be a silicon-silicon dioxide substrate, a quartz substrate, or an aluminum oxide substrate. The epitaxial growth substrate is a commercial product, and two of the silicon-silicon dioxide substrates are The thickness of the silicon oxide is about 10nm-500nm, and the growth planes of the quartz substrate and the aluminum oxide substrate can be various crystal planes such as [100] and [111].

In the above preparation method, in step 2), the protective gas may specifically be high-purity nitrogen.

The flow rate of the protective gas is 10 sccm-300 sccm.

In the above preparation method, in step 3), in the chemical vapor deposition method, a high and low temperature zone heating method is adopted, the solid raw material sulfur is placed in the low temperature zone, the purity of the sulfur powder is not less than 99.9%, and the heating temperature is 400 ℃, the high temperature zone places solid raw material molybdenum trioxide solid powder, the purity of the molybdenum trioxide is not less than 99.9%, the reaction temperature is 700-900 ℃, the reaction time is 5-30min, and the flow rate of the carrier gas is 20sccm-100sccm , The pressure of the reaction system is normal pressure growth.

When the reaction time of the reaction is longer than 10 minutes, a continuous molybdenum disulfide film spliced by single-crystal single-layer triangular molybdenum disulfide can be obtained.

In the above preparation method, step 3) includes removing the air in the quartz tube by using a mechanical vacuum pump, and then passing high-purity nitrogen gas when the vacuum degree reaches 1.0*10-3Torr. This process is repeated 3 times to reduce the oxygen in the quartz tube. and the influence of water vapor.

In the above preparation method, step 3) includes the process of temperature control in different growth temperature zones. First, heat the molybdenum trioxide temperature zone, and the heating rate is controlled at 20°C/min to 800°C; when the heating temperature of the molybdenum trioxide reaches 400°C, the solid sulfur starts to heat, and the heating rate is 40°C/min to 400°C ; When both the low temperature and high temperature regions reach the set maximum value, the carrier gas is turned on, and the flow rate of the carrier gas is 100 sccm; the growth lasts for 5 to 20 minutes.

In the above preparation method, in step 3), it also includes the step of rapidly cooling the grown large-size single-layer molybdenum disulfide thin film. Deposition of the second layer of molybdenum, or growth of the raw material molybdenum trioxide.

The monocrystalline single-layer triangular molybdenum disulfide film prepared by the above preparation method of the present invention and the continuous molybdenum disulfide film formed by splicing all belong to the protection scope of the present invention.

Surface modifiers similar to ammonia sulfide in the above preparation methods all belong to the protection scope of the present invention.

Beneficial effects of the present invention: the preparation method of the present invention adjusts the growth temperature, time and gas flow during the chemical vapor deposition growth of molybdenum disulfide on the surface of the substrate, and can efficiently prepare a long-sized single-layer disulfide Molybdenum thin film, this method can use different types and different sizes of growth substrates to obtain large-scale batches of molybdenum disulfide thin films, without high growth temperature, expensive surface modifiers, and long preparation time. Large-scale single-layer molybdenum disulfide films can be fabricated into electronic devices with special functions.

Description of drawings

Fig. 1 is the optical photograph of the monolayer molybdenum disulfide film that embodiment 1 grows on silicon-silicon dioxide substrate;

Fig. 2 is the Raman spectrogram of the monolayer molybdenum disulfide thin film grown on silicon-silicon dioxide substrate in embodiment 1;

Fig. 3 is the fluorescence spectrogram of the monolayer molybdenum disulfide film grown on the silicon-silicon dioxide substrate in embodiment 1.

detailed description

Example 1

A silicon-silicon dioxide substrate is used as the growth substrate, and the thickness of the silicon dioxide layer heat-treated on the silicon surface is 300nm. The substrate treatment process is as follows: first, the silicon-silicon dioxide substrate is cleaned, ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes, and then the mixed solution of sulfuric acid and hydrogen peroxide with a volume ratio of 3:1 is used at 160 Wash at ℃ for 30 minutes, then ultrasonically clean with deionized water for 5 minutes to remove excess concentrated sulfuric acid on the surface; put the cleaned silicon-silicon dioxide substrate into 40-44wt% ammonia sulfide solution for 24 hours, soak The final silicon-silicon dioxide substrate was ultrasonically cleaned in deionized water for 2 minutes, and the substrate was blown dry with high-purity nitrogen; the dried silicon-silicon dioxide substrate was stored in vacuum for 24 hours to remove residual organic matter. The above substrate was annealed at 300° C. for 30 min in a nitrogen atmosphere furnace. Molybdenum disulfide thin films were grown in a vacuum tube furnace using the aforementioned silicon-silica substrates. The growth process is as follows: the growth raw materials are high-purity molybdenum trioxide and sulfur; Placed together in a high-temperature reaction zone, the distance between the silicon wafer and the molybdenum trioxide is 2 cm, and the flow direction of the carrier gas is from sulfur to the molybdenum trioxide; first, use a mechanical vacuum pump to pump out the air in the quartz tube. *When 10 ^-3 Torr, high-purity nitrogen gas is passed again, and the process is repeated 3 times; the epitaxial growth of molybdenum disulfide thin film is normal pressure growth, and the reaction zone is first heated during the growth process, and heated to 800 °C at 20 °C/min; when molybdenum trioxide When the heating temperature reaches 400°C, the solid sulfur begins to heat, and the heating rate is 40°C/min to 400°C; when both the low temperature and high temperature areas reach the set maximum value, the carrier gas is turned on, and the flow rate of the carrier gas is 100 sccm; the growth lasts for 5 to 20 minutes; after the growth is completed, the electric furnace is automatically cooled to room temperature, and the carrier gas is always supplied during the process.

Figure 1 shows the optical photograph of a molybdenum disulfide monolayer film grown on a typical silicon-silicon dioxide substrate. The size of a single molybdenum disulfide single crystal triangle can reach 100um. When these single crystal triangles are spliced together, a polycrystalline film with a size of several millimeters can be formed. The surface of the polycrystalline film is flat and the grain boundaries are not obvious.

Figure 2 is the Raman spectrum of a molybdenum disulfide monolayer film grown on a typical silicon-silicon dioxide substrate. The Raman excitation wavelength is 514nm, the Raman vibration peak at 382cm ^-1 in the spectrum is the E ¹ _2g Raman vibration mode of molybdenum disulfide, and the Raman vibration peak at ^{402cm -1} is the Al _g Raman mode of molybdenum disulfide vibration pattern. ^The difference between the vibration frequencies of the E ¹ _2g and Al _g modes of molybdenum disulfide is related to the thickness of the film. It can be calculated from the figure that their frequency difference is 20cm ^-1 , which is the characteristic of a single layer of molybdenum disulfide.

Fig. 3 is the fluorescence emission spectrum of a molybdenum disulfide monolayer film grown on a typical silicon-silicon dioxide substrate. The fluorescence excitation wavelength is 514nm, and the large wave packet near 680nm in the spectrum is monolayer molybdenum disulfide exciton fluorescence. Compared with bulk MoS2, monolayer MoS2 exhibits a significantly higher photoluminescence intensity due to the band structure shift from indirect to direct bandgap.

Example 2

The aluminum oxide (Al ₂ O ₃ ) substrate is used as the growth substrate, and the film deposition surface is the (100) plane of the aluminum oxide. The substrate treatment process is as follows: firstly, the Al2O3 substrate is cleaned, ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes respectively, and then the mixed solution of sulfuric acid and hydrogen peroxide with a volume ratio of 3:1 is used at 160°C Clean it under water for 30 minutes, and then ultrasonically clean it with deionized water for 5 minutes to remove excess concentrated sulfuric acid on the surface; put the aluminum oxide substrate after cleaning into 40-44wt% ammonia sulfide solution and soak it for 24 hours. The aluminum oxide substrate was finally ultrasonically cleaned in deionized water for 2 minutes, and the substrate was blown dry with high-purity nitrogen; the dried aluminum oxide substrate was stored in vacuum for 24 hours to remove residual organic matter. . The above substrate was annealed at 300° C. for 30 min in a nitrogen atmosphere furnace. The molybdenum disulfide thin film was grown in a vacuum tube furnace using the above-mentioned aluminum oxide substrate. The growth process is as follows: the growth raw materials are high-purity molybdenum trioxide and sulfur, the carrier gas is high-purity nitrogen, the growth furnace is a double-temperature zone tubular growth furnace, and the solid sulfur is placed in the low temperature zone. The two aluminum substrates are placed together in the high-temperature reaction zone, the distance between the two aluminum oxide substrates and the molybdenum trioxide is 2 cm, and the flow direction of the carrier gas is from sulfur to the molybdenum trioxide; first, use a mechanical vacuum pump to remove the air in the quartz tube Pump it out, and then pass high-purity nitrogen gas when the vacuum degree reaches 1.0*10 ^-3 Torr. This process is repeated 3 times; the epitaxial growth of molybdenum disulfide thin film is normal pressure growth, and the reaction zone is heated first at 20°C/min during the growth process. to 800°C; when the heating temperature of molybdenum trioxide reaches 400°C, the solid sulfur starts to heat, and the heating rate is 40°C/min to 400°C; when both the low temperature and high temperature areas reach the set maximum value, the current carrying Gas, the flow rate of the carrier gas is 100 sccm; the growth lasts for 5 to 20 minutes; after the growth is completed, the electric furnace is automatically cooled to room temperature, and the carrier gas is always supplied during the process.

The implementation of the present invention does not limit the present invention, and any simple improvement based on the present invention does not go beyond the protection scope of the present invention.

Claims (10)

1. a method for chemical vapor deposition of substrate surface modification to grow large-scale single-layer molybdenum disulfide film, it is characterized in that comprising the steps: 1) in ammonia sulfide solution, epitaxial growth substrate is carried out surface modification, makes substrate A layer of chemically bonded vulcanized layer is formed on the bottom surface; 2) In a heating furnace continuously fed with protective gas, anneal the surface-modified substrate in step 1) to eliminate excess sulfur on the surface ; 3) grow a molybdenum disulfide film on the annealed substrate surface described in step 2) by chemical vapor deposition, to obtain the large-size single-layer molybdenum disulfide film; the annealing temperature of the annealing treatment is 100-500 ℃, the annealing time is 10min-60min. 2. The method according to claim 1, characterized in that, in step 1), the epitaxial growth substrate also includes a step of cleaning it before surface modification treatment, so as to modify its surface hydrophilicity , the specific steps are as follows: First, ultrasonically clean with acetone, ethanol and deionized water for 10 minutes, then use a mixed solution of sulfuric acid and hydrogen peroxide with a volume ratio of 3-5:1 to clean at 160°C for 30 minutes, and then deionize Ultrasonic cleaning with water for 5 minutes to remove excess concentrated sulfuric acid on the surface. 3. The method according to claim 2, characterized in that, in step 1), the concentration of the ammonia sulfide is 40-44wt%, and the immersion time of the growth substrate is 24 hours. 4. The method according to claim 3, wherein step 1) includes ultrasonic cleaning the surface-modified substrate, the cleaning agent is deionized water, the cleaning time is 2min, and the high-purity nitrogen is blown dry. 5. The method according to claim 4, characterized in that, in step 1), further comprising drying the processed substrate under a vacuum environment to remove residual organic matter on the surface. 6. The method according to any one of claims 1-5, wherein the epitaxial growth substrate is a silicon-silicon dioxide substrate, a quartz substrate, or an aluminum oxide substrate, and the epitaxial growth substrate The bottom is a commercial product, the thickness of silicon dioxide in the silicon-silicon dioxide substrate is 10nm-500nm, and the growth surface of the quartz substrate and aluminum oxide substrate is [100] or [111] noodle. 7. The method according to any one of claims 1-5, characterized in that, in step 2), the protective gas is high-purity nitrogen; the flow rate of the protective gas is 10 sccm-300 sccm. 8. The method according to any one of claims 1-5, characterized in that, in the above-mentioned method, in step 3), in the chemical vapor deposition method, a heating method with high and low dual temperature zones is adopted, and the solid raw material sulfur is placed in the low temperature zone , the purity of sulfur powder is not less than 99.9%, the heating temperature is 400°C, the solid raw material molybdenum trioxide solid powder is placed in the high temperature zone, the purity of the molybdenum trioxide is not less than 99.9%, the reaction temperature is 700-900°C, and the reaction time is 5-30min, the flow rate of the carrier gas is 20sccm-100sccm, and the pressure of the reaction system is normal pressure. 9. The method according to claim 8, characterized in that, when the reaction time of the reaction is greater than 10min, a continuous molybdenum disulfide film spliced by single-crystal single-layer triangular molybdenum disulfide is obtained. 10. The method according to claim 8, characterized in that, in step 3), comprising utilizing a mechanical vacuum pump to extract the air in the quartz tube, and then passing high-purity nitrogen gas when the vacuum degree reaches 1.0*10 ^-3 Torr, This process is repeated three times to reduce the influence of oxygen and water vapor in the quartz tube; the process of temperature control in different growth temperature zones: first, heat the molybdenum trioxide temperature zone, and the heating rate is controlled at 20°C/min to 800°C; When the heating temperature of molybdenum oxide reaches 400°C, the solid sulfur starts to heat, and the heating rate is 40°C/min to 400°C; The flow rate is 100 sccm; the growth lasts for 5 to 20 minutes; in step 3), the grown large-size single-layer molybdenum disulfide film is rapidly cooled, and the cooling is to move the sample from the high temperature area to the room temperature area, and quickly terminate the two Second layer deposition of molybdenum sulfide, or growth of raw molybdenum trioxide.