CN113013020B - Growth method of large-area ultrathin two-dimensional nitride based on thickness etching - Google Patents

Abstract

The invention discloses a method for preparing an ultra-thin two-dimensional nitride film, which includes: pretreating the substrate surface with an oxygen plasma cleaning machine, providing more active sites for the adsorption of oxygen atoms, and squeezing the liquid The bonding ability between the oxide film on the surface of the liquid metal and the substrate is significantly improved after metallization, but the quality of the inner oxide film is poor due to insufficient contact with the substrate and the degree of oxidation is not high enough. Therefore, in the subsequent nitrogen plasma chemical The process of vapor phase deposition will etch away this layer of oxide film to obtain ultra-thin two-dimensional film, and at the same time nitriding the oxide film to obtain ultra-thin two-dimensional nitride film.

Description

A Growth Method of Large Area Ultrathin Two-dimensional Nitride Based on Thickness Etching

technical field

The invention belongs to the field of materials, and in particular relates to a method for growing large-area ultra-thin two-dimensional nitrides based on thickness etching.

Background technique

As a new generation of semiconductor materials, nitride materials have been widely used in the field of optoelectronics. With the rise of two-dimensional material research, people have also generated strong interest in two-dimensional nitride materials. When the nitride reaches the thickness of a single atomic layer, its structure will become a graphene-like in-plane two-dimensional structure. Compared with the parent material, two-dimensional nitride materials have unique properties such as ultra-wide bandgap in the deep ultraviolet region, low thermal conductivity, and strong mechanical strain capacity, which broadens the application of nitrides in the fields of deep ultraviolet, thermoelectric and flexible devices. However, due to the wurtzite structure of the parent material, the bond between the nitride layer and the layer, the method of top-down mechanical exfoliation to obtain few-layer 2D materials is difficult to achieve. On the other hand, due to the lack of suitable epitaxial substrates and other factors, the thin film materials obtained by the bottom-up epitaxy method have a large number of defects and dislocations, and the obtained two-dimensional nitride materials often bond with the substrate and cannot be independent. out, which limits its further application. Therefore, there is a large gap in the preparation of large-area ultra-thin two-dimensional nitride materials, which needs to be solved urgently.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a large-area ultra-thin two-dimensional nitride material. The preparation method is simple and fast, and a nitride material with a thickness of a single atomic layer can be obtained.

The preparation method of the large-area ultra-thin two-dimensional nitride material provided by the present invention comprises the following steps:

1) Pretreat the substrate in an oxygen plasma environment to provide more active sites for the adsorption of oxygen atoms;

2) Place the two substrates pretreated in step 1) on the heating table, place metal on the surface of one of the substrates, and after the metal is melted, cover and squeeze the liquid metal with another substrate to make the two substrates The substrates are kept in a superimposed state, and then the two substrates are separated to remove the metal residue on the surface, and a metal oxide film is obtained on the surface of the substrate;

3) Put the substrate with metal oxide film on the surface obtained in step 2) into the plasma-enhanced chemical vapor deposition system, pass through the nitrogen plasma, and the oxide film is etched while the oxide film is nitriding, and the unstable area on the surface is etched, and finally a super Thin 2D Nitride Films.

The method specifically includes the following operations:

Use two oxygen plasma pretreated substrates to extrude metal droplets, leaving a metal oxide film on the substrate surface, and the obtained oxide film is placed in a nitrogen plasma enhanced chemical vapor deposition system (PECVD) for nitriding. At the same time as the nitride is obtained, the plasma produces a certain peeling and etching effect, and finally an ultra-thin large-area two-dimensional nitride film is obtained.

In step 1) of the above method, the substrate may be a silicon wafer, a silicon wafer with a silicon oxide layer, a quartz wafer, silicon nitride, a sapphire wafer, or the like. The thickness of the substrate may be 0.05 μm-2 mm.

The thickness of the silicon oxide layer on the surface of the silicon oxide wafer in the silicon wafer with the silicon oxide layer may be 10 nm-2000 nm.

According to an embodiment of the present invention, the thickness of the silicon wafer with a silicon oxide layer is 0.5 mm, and the thickness of the silicon oxide layer is 90 nm; the specification of the substrate may specifically be 1 cm*1 cm.

The substrate needs to be ultrasonically cleaned before use. Taking a silicon wafer with a silicon oxide layer as an example, the cleaning method is: use acetone, isopropanol, and deionized water to ultrasonically clean the silicon wafer with a silicon oxide layer in sequence. Wash for 5-10 minutes (specifically 5 minutes).

In step 1) of the above method, the pretreatment is performed in an oxygen plasma cleaning machine. The conditions are as follows: control the pressure of feeding oxygen to 100-240Pa and clean for 2-20 minutes, specifically: control the pressure of feeding oxygen to 110Pa and clean for 3 minutes.

In step 2) of the above method, the metal can be a low-melting metal (such as indium, tin, gallium) or an alloy (such as gallium-indium alloy, indium-tin alloy, aluminum-gallium alloy) with a melting point lower than 500 degrees Celsius. The low melting point metal or alloy may be in solid or liquid state.

The metal is a solid low melting point metal or alloy, and after the low melting point metal or alloy is melted, another substrate is used to cover and squeeze the liquid metal or alloy. The metal is a solid low-melting metal or alloy, and the temperature of the heating stage is 50-500° C. (specifically, 50° C., 75° C., 100° C.) according to the melting point of the metal or alloy.

The metal is a liquid metal with a low melting point or an alloy, and another substrate can be directly used to cover and squeeze the liquid metal. The metal is a liquid metal with a low melting point or an alloy, and the temperature of the heating stage is 50-200°C (specifically such as 50°C, 75°C, 100°C).

In step 2) of the above method, the standing time may be 0.1-60 minutes (specifically, such as 2 minutes).

In step 2) of the above method, there should be no lateral slip between the two substrates during the process of separating the two substrates.

In the above-mentioned method step 3), the specific method is as follows: place the oxide film of the substrate with the metal oxide film on the surface facing down on a quartz tile boat having a size equivalent to the substrate, and push the quartz tile to the In the center of the reaction zone of the plasma-enhanced tube furnace, use a mechanical pump until the pressure in the quartz tube is less than 1Pa. At this time, 5-30sccm argon gas is introduced into the quartz tube. Heating rate Raise the temperature of the reaction zone to 400-800°C, stop feeding argon gas after reaching the target temperature, and feed 1-30 sccm nitrogen gas at the same time, turn on the power of the plasma module, and set the plasma power to 10-80W (specifically, 10W ) and start, after reacting for 5-90 minutes (specifically as 20 minutes), turn off the plasma switch, and the temperature of the furnace body is rapidly cooled to room temperature within 20 minutes, during which the atmosphere in the reaction chamber remains constant as nitrogen.

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

The method of the present invention can significantly increase the bonding force between the oxide formed on the surface of the liquid metal and the substrate after using the oxygen plasma to treat the substrate in the early stage, and then use the nitrogen plasma enhanced chemical vapor deposition system to remove the unstable oxide on the upper layer. The oxide is nitrided while etching, and finally a large-area ultrathin two-dimensional nitride film is obtained. The prepared nitride film can be as low as 0.8nm, and it is a single layer or a double layer. The prepared nitride film can not only be deposited on different substrates, but also can be transferred to any other target substrate. This substrate-independent feature makes this two-dimensional nitride film have a broader application prospect.

Description of drawings

Fig. 1 is the growth flow diagram of the present invention; first, the substrate is treated with an oxygen plasma cleaning machine, and then two substrates are used to squeeze metal droplets, and a uniform oxide film is obtained after simple cleaning, and the obtained oxide film is put into a nitrogen plasma Nitriding is carried out in an enhanced chemical vapor deposition system, and finally a large-area ultra-thin nitride film is obtained.

2 is an optical microscope photo of the gallium oxide thin film before and after nitriding in Example 1 of the present invention; the metal oxide thin film before nitriding is shown in a, and the nitride thin film after nitriding is shown in b.

FIG. 3 is the atomic force microscope (AFM) data of the gallium oxide thin film prepared in Example 1 of the present invention.

FIG. 4 is the atomic force microscope (AFM) data of the two-dimensional gallium nitride thin film prepared in Example 1 of the present invention.

Fig. 5 is the X-ray photoelectron spectroscopy (XPS) data of the two-dimensional gallium nitride film prepared in Example 1 of the present invention; wherein, a is the fine-scan spectrum of the N1s orbital, and b is the fine-scan spectrum of the Ga2p orbital.

FIG. 6 is the X-ray photoelectron spectroscopy (XPS) data of the two-dimensional indium nitride thin film prepared in Example 2 of the present invention.

Fig. 7 is the atomic force microscope (AFM) data of the gallium nitride film obtained by reacting for 10 minutes at a power of 100W.

FIG. 8 is an optical microscope picture of a gallium oxide thin film deposited on the surface of a silicon oxide wafer without plasma pretreatment.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods are conventional methods unless otherwise specified. The raw materials can be obtained from open commercial channels unless otherwise specified.

Example 1. Preparation of Ultra-thin Gallium Nitride Using Silicon Wafer with Silicon Oxide Layer and Liquid Metal Gallium

According to the process flow in Figure 1, the method for preparing ultra-thin gallium nitride specifically includes the following steps:

(1) Cut a silicon wafer with a silicon oxide layer (thickness 0.5mm, wherein the thickness of the silicon oxide layer is 90nm) with a diamond knife to a size of 1cm*1cm, and wash it with acetone, isopropanol, and deionized water for 10 minutes in sequence, Put the silicon oxide wafer after cleaning into an oxygen plasma cleaning machine, control the air pressure of feeding oxygen to 110 Pa and clean it for 3 minutes.

(2) Put the silicon oxide layers of the two treated silicon oxide wafers upward on a heating platform at a temperature of 50°C, and take out a drop (about 5 mg) of gallium metal stored in isopropanol with a rubber dropper. Placed on one of the silicon oxide wafers, pick up another silicon oxide wafer with tweezers and squeeze the metal droplet to spread it on the silicon oxide wafer.

(3) Put the extruded two pieces of silicon oxide on the heating table, and after standing for two minutes, separate the two pieces of silicon oxide with tweezers. During the process, there should be no lateral slip between the two pieces. Put the silicon oxide wafer in isopropanol for simple cleaning with a cotton swab to remove the metal residue on the surface and obtain a clean and uniform oxide film.

(4) The prepared oxide film is placed on the heating table. After the organic solvent on the surface is volatilized, the silicon oxide wafer with the metal oxide film is placed face down on the quartz tile and sent to the plasma enhanced chemical vapor deposition system. The reaction zone was evacuated with a mechanical pump until the air pressure was less than 1 Pa, and 20 sccm of argon gas was introduced, and the temperature was raised to 800 °C at a rate of 30 °C/min.

(5) After the temperature rises to 800° C., stop feeding argon, feed 5-30 sccm nitrogen, turn on the switch of the plasma module, set the power to 10 W and start it.

(6) After 20 minutes of reaction, the plasma was turned off, and the temperature of the furnace body was rapidly lowered to room temperature, during which the atmosphere in the reaction chamber remained unchanged.

(7) Take out the sample after nitriding, observe its morphology with an optical microscope and a scanning electron microscope (SEM), determine the uniformity and size of the film, determine the elemental composition of the material by X-ray photoelectron spectroscopy (XPS), and use atomic force Microscopy (AFM) determines the thickness and surface uniformity of the samples.

The optical microscope photographs of the gallium oxide thin film prepared in this embodiment before and after nitriding are shown in Figure 2, as can be seen from Figure 2, the contrast of the thin film sample after plasma nitriding on the silicon oxide wafer is significantly reduced, which reflects the The ultra-thin nature of the film, the color of the film is uniform, and the thickness of the film prepared by the reaction is uniform.

The data of the atomic force microscope (AFM) of the gallium oxide thin film prepared in this embodiment is shown in FIG. 3 , and it can be seen from FIG. 3 that the thickness of the gallium oxide thin film is 3 nm.

The atomic force microscope (AFM) data of the two-dimensional gallium nitride thin film prepared in this embodiment is shown in FIG. 4 . It can be seen from FIG. 4 that the thickness of the two-dimensional gallium nitride film is as low as 0.8 nm, which is a monomolecular layer. Compared with Fig. 3, due to the etching effect of nitrogen plasma, the thickness of the gallium nitride film after nitride is significantly thinner than that of the gallium oxide film before nitride.

The X-ray photoelectron spectroscopy (XPS) data of the two-dimensional gallium nitride film prepared in this embodiment is shown in Figure 5. As can be seen from Figure 5, the fine scan spectra of N1s and Ga2p orbitals indicate that Ga atoms and N atoms are combined to form bonds, Gallium nitride material was obtained.

Example 2. Preparation of ultra-thin indium gallium nitride by silicon oxide wafer and gallium indium alloy

(1) Cut a silicon wafer with a silicon oxide layer (thickness 0.5mm, wherein the thickness of the silicon oxide layer is 90nm) with a diamond knife to a size of 1cm*1cm, and wash it with acetone, isopropanol, and deionized water for 10 minutes in sequence, Put the silicon oxide wafer after cleaning into an oxygen plasma cleaning machine, control the air pressure of feeding oxygen to 110 Pa and clean it for 3 minutes.

(2) In the glove box, metal indium and metal gallium were placed in a beaker with a mass ratio of 1:1 and heated and stirred. The temperature of the heating table was set at 75°C. After fully stirring, they were placed in isopropanol solution for later use.

(3) Place the two treated silicon oxide wafers on a heating platform with the silicon oxide layer facing up at 100°C, take the prepared gallium-indium alloy (about 10 mg) and place it on one of the silicon oxide wafers, and wait for the After melting, use tweezers to pick up another piece of silicon oxide and squeeze the molten metal to spread it on the silicon oxide.

(4) Put the extruded two pieces of silicon oxide on the heating table, and after standing for two minutes, separate the two pieces of silicon oxide with tweezers. During the process, there should be no lateral slip between the two pieces. Use PDMS (polydimethylsiloxane) to wipe off the metal residue on the surface to obtain a clean and uniform oxide film.

(5) The prepared oxide film is placed on the heating platform. After the organic solvent on the surface is volatilized, the silicon oxide wafer with the sample is placed face down on a quartz tile and sent to the plasma enhanced chemical vapor deposition system. The reaction zone was evacuated with a mechanical pump until the air pressure was less than 1 Pa, and 20 sccm of argon gas was introduced, and the temperature was raised to 500 °C at a rate of 20 °C/min.

(6) After the temperature rises to 500° C., stop feeding argon, feed 5-30 sccm nitrogen, turn on the switch of the plasma module, set the power to 10 W and start it.

(7) After 20 minutes of reaction, the plasma was turned off, and the temperature of the furnace body was rapidly lowered to room temperature, during which the atmosphere in the reaction chamber remained unchanged.

(8) Take out the sample after nitriding, observe its morphology with an optical microscope and a scanning electron microscope (SEM), determine the uniformity of the film, determine the elemental composition of the material with X-ray photoelectron spectroscopy (XPS), and use an atomic force microscope ( AFM) to determine the thickness and surface uniformity of the sample.

The X-ray photoelectron spectroscopy (XPS) data of the two-dimensional indium gallium nitride film prepared in this embodiment is shown in Figure 6. From Figure 6, it can be seen that the global scan 6a shows that the obtained alloy film contains Ga elements and In elements, N1s The fine-scan spectra of orbital 6b and In3d orbital 6c indicate that the two-dimensional InGaN alloy thin film was successfully prepared.

Embodiment 3, the impact of nitrogen plasma on the thickness uniformity of film

In Example 1, the power of the reactive plasma was increased, and it was found that the power was too high to destroy the surface morphology of the film. As shown in Figure 7, the nitrogen plasma power was increased to 100W during the reaction, and the surface roughness of the film measured by AFM Therefore, it is necessary to maintain the plasma power at a moderate level for the uniform synthesis of two-dimensional ultrathin nitrides.

Embodiment 4, the effect of oxygen plasma on substrate pretreatment

In Example 1, the oxygen plasma pretreatment step on the substrate was removed, and the adhesion ability of the metal oxide on the substrate was significantly weakened, and the process of simply peeling off the residual metal with a cotton swab would cause obvious damage to the metal oxide film, as shown in Figure 8 shows. However, the metal oxide film pretreated with oxygen plasma is more tightly bonded to the substrate, and the film will not be damaged during the process of peeling off the residual metal, and the finally prepared nitride film is more uniform.

Claims (9)

1. A method for preparing a large-area ultrathin two-dimensional nitride material, comprising the following steps: 1) Pretreat the substrate in an oxygen plasma environment to provide more active sites for the adsorption of oxygen atoms; 2) Put the two substrates pretreated in step 1) on the heating table, place metal on the surface of one of the substrates, and after the metal is melted, cover and squeeze the liquid metal with another substrate to make the two substrates The substrates are kept in a superimposed state, and then the two substrates are separated to remove the metal residue on the surface, and a metal oxide film is obtained on the surface of the substrate; 3) Put the substrate with the oxide film on the surface into the plasma-enhanced chemical vapor deposition system, pass through the nitrogen plasma, the oxide film is nitrided and the unstable area on the surface is etched, and finally the ultra-thin two-dimensional nitride is obtained film. 2 . The method according to claim 1 , wherein in the step 1), the substrate is a silicon wafer, a silicon wafer with a silicon oxide layer, a quartz wafer, sapphire or silicon nitride. 3. The method according to claim 1, characterized in that: in the step 1), the pretreatment is carried out in an oxygen plasma cleaning machine, and the air pressure of the oxygen is controlled to be 100-240Pa and cleaned for 2-30 minute. 4. The method according to claim 1, characterized in that: in the step 2), the metal is a low-melting metal or alloy with a melting point lower than 500 degrees Celsius; the low-melting metal or alloy is solid or liquid. 5. The method according to claim 4, characterized in that: The metal is a solid low-melting metal or alloy, and after the low-melting metal or alloy is melted, another substrate is used to cover and squeeze the liquid metal or alloy; the metal is a solid low-melting metal or alloy, so The temperature of the heating stage is 50-500°C. 6. The method according to claim 4, characterized in that: the metal is a liquid low-melting metal or an alloy, which can be directly covered and extruded with another substrate; the metal is a liquid low-melting metal or an alloy , the temperature of the heating stage is 50-200°C. 7. The method according to claim 1, characterized in that: in the step 2), the standing time is 2-120 minutes. 8. The method according to claim 1, characterized in that: in the step 3), the specific method is as follows: put the oxide film of the substrate with the oxide film on the surface facing down on the quartz tile and send it into the plasma enhanced In the reaction area of the chemical vapor deposition system, use a mechanical pump to pump the air pressure to less than 1Pa, pass in 5-30sccm argon, raise the temperature to 400-800°C at a speed of 5-30°C/min, stop the flow of argon, and pass in 5- 30sccm nitrogen, turn on the switch of the plasma module, set the power to 10-80W and start it, after 5-90 minutes of reaction, turn off the plasma, and quickly cool down the temperature of the furnace to room temperature, during which the atmosphere in the reaction chamber remains unchanged. 9. The large-area ultrathin two-dimensional nitride material prepared by the method according to any one of claims 1-8.

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