CN110318021B - Preparation method of wafer-level vanadium dioxide film - Google Patents

Preparation method of wafer-level vanadium dioxide film Download PDF

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CN110318021B
CN110318021B CN201910682193.6A CN201910682193A CN110318021B CN 110318021 B CN110318021 B CN 110318021B CN 201910682193 A CN201910682193 A CN 201910682193A CN 110318021 B CN110318021 B CN 110318021B
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film
vanadium
vanadium dioxide
dioxide film
metal
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CN110318021A (en
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邹崇文
任慧
李博文
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University of Science and Technology of China USTC
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/08—Oxides
    • C23C14/083—Oxides of refractory metals or yttrium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/14—Metallic material, boron or silicon
    • C23C14/16—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/14—Metallic material, boron or silicon
    • C23C14/18—Metallic material, boron or silicon on other inorganic substrates
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C23C14/28—Vacuum evaporation by wave energy or particle radiation
    • C23C14/30—Vacuum evaporation by wave energy or particle radiation by electron bombardment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/34—Sputtering
    • C23C14/35—Sputtering by application of a magnetic field, e.g. magnetron sputtering
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/58—After-treatment
    • C23C14/5846—Reactive treatment
    • C23C14/5853—Oxidation

Abstract

The invention provides a preparation method of a wafer-level vanadium dioxide film, which comprises the following steps: s1, providing a uniformly-grown metal vanadium film; and S2, oxidizing the metal vanadium film by using water vapor at the temperature of 450-650 ℃ under the oxygen-free condition to obtain the monoclinic phase vanadium dioxide film. The invention can prepare the vanadium dioxide film with excellent performance and wafer-level size, and the vanadium dioxide film is uniform and compact, and the resistance change of three to four orders of magnitude can be achieved in the phase change process. The method takes water vapor as a mild oxidant, and can realize a self-adjusting oxidation mechanism in the growth process when preparing the vanadium dioxide film, namely the stable positive quadrivalent monoclinic phase vanadium dioxide film can be prepared. The method greatly expands the growth temperature area for preparing the vanadium dioxide film, and the vanadium dioxide film can be efficiently prepared within the range of 450-650 ℃; the method is simple and easy to implement, high in repeatability, non-toxic and environment-friendly in the whole film growth process and low in cost.

Description

Preparation method of wafer-level vanadium dioxide film
Technical Field
The invention belongs to the technical field of functional film preparation, and particularly relates to a preparation method of a wafer-level vanadium dioxide film, in particular to a wet thermal oxidation preparation method of the vanadium dioxide film.
Background
Vanadium dioxide has reversible giant-metal-insulator transition (MIT) behavior, and the crystal structure of vanadium dioxide can be changed from an insulating monoclinic phase to a metal tetragonal phase reversible phase structure at the temperature of about 68 ℃, and is accompanied by 3-5 orders of magnitude of resistance jump and excellent infrared switching performance. The vanadium dioxide thin film material has small volume change problem, and has wide application prospect in the fields of energy-saving intelligent windows, photoelectric switches, infrared imaging, photoresistors, optical storage, infrared laser protection and the like. Because of these unique phase change properties, vanadium dioxide has attracted much attention in the relevant fields of physics, chemistry, materials, etc. since its first discovery in the united states bell laboratory in the last 50 s. However, the vanadium atom has abundant chemical valence states (common valence states are +5, +4, +3, +2), which makes it difficult to prepare vanadium oxide in a single chemical valence state. Meanwhile, tetravalent vanadium dioxide also has a multi-phase structure (M phase, R phase, A phase, B phase and T phase are equal), so that the preparation of pure M-phase vanadium dioxide with remarkable metal insulation phase change has great challenges.
At present, common methods for preparing vanadium dioxide films include molecular beam epitaxy, magnetron sputtering, pulsed laser deposition, chemical vapor deposition, thermal oxidation of metal vanadium films and the like. The vanadium dioxide film prepared by the molecular beam epitaxy method is excellent in quality, and the growth thickness of the film can be accurately controlled to be in a nanometer level. However, the method has extremely high requirements on vacuum conditions, and molecular beam epitaxy equipment is expensive and low in volume production. The magnetron sputtering method generally uses a high-purity vanadium target or a vanadium oxide target for sputtering, generally the quality of the obtained film is easily influenced by the substrate temperature, the gas partial pressure, the heat treatment process and the like, the repeatability is poor, and generally the subsequent treatment such as annealing and the like is required, and the flow is complex. The pulsed laser deposition is to focus the high-power pulsed beam generated by the pulsed laser on the surface of the target material, so that the target material generates high temperature and ablation to generate high-temperature and high-pressure plasma, the plasma is directionally locally expanded and emitted, and a film is deposited on the substrate. The thin film prepared by the method has good crystallinity, but the film forming surface of the thin film is easy to have particle problems and the large-area uniformity is not good enough.
The chemical vapor deposition method is to utilize gaseous precursors to carry out chemical reaction on a gas phase or a gas-solid interface so as to generate solid deposits on a solid substrate, namely the vanadium dioxide film is prepared. The method has high preparation efficiency, but the preparation process is easily influenced by factors such as temperature, gas flow rate, gas distribution uniformity and the like, so that the stability and uniformity of the film are poor.
The thermal oxidation method of the vanadium metal film is generally a thermal treatment in the presence of oxygen, thereby oxidizing to obtain a vanadium dioxide film. Compared with the preparation method, the thermal oxidation method of the metal vanadium film has simpler requirements on equipment, but has rigorous requirements on process parameters, and has very narrow parameter windows of oxidation temperature, annealing time, oxygen partial pressure and the like. Meanwhile, the prepared vanadium dioxide film often contains multiple valence states and mixed phases, a high-quality large-size film cannot be obtained, the repeatability is poor, and the large-scale production is not facilitated.
Therefore, a simple method for preparing a large-size vanadium dioxide thin film with excellent performance is developed, and the method has great significance for practical application.
Disclosure of Invention
In view of the above, the present application provides a method for preparing a wafer-level vanadium dioxide thin film, which is simple and has high repeatability, and the prepared vanadium dioxide thin film is uniform and compact, has excellent metal-insulator transition performance, and can reach the wafer size.
The invention provides a preparation method of a wafer-level vanadium dioxide film, which comprises the following steps:
s1, providing a uniformly-grown metal vanadium film;
and S2, oxidizing the metal vanadium film by using water vapor at the temperature of 450-650 ℃ under the oxygen-free condition to obtain the monoclinic phase vanadium dioxide film.
Preferably, the thickness of the metal vanadium film is 10-400 nm.
Preferably, the metal vanadium film is obtained according to the following steps:
selecting aluminum oxide, silicon oxide or silicon wafers as substrates; and (3) coating in a vacuum chamber by using an electron beam thermal evaporation or magnetron sputtering mode, wherein the substrate keeps moving at a constant speed in the coating process, so that the uniformly grown metal vanadium film is obtained.
Preferably, the background vacuum degree of the vacuum chamber is better than 5 × 10-3Pa。
Preferably, the substrate keeps rotating at a constant speed in the coating process, and the rotating speed does not exceed 10 r/min.
Preferably, the step S2 is specifically:
and placing the metal vanadium film in a tube furnace, heating the tube furnace to 450-650 ℃, introducing a carrier gas to the vicinity of the metal vanadium film, wherein the carrier gas contains water vapor and inert gas, and oxidizing the metal vanadium film by using the water vapor to obtain the monoclinic phase vanadium dioxide film.
Preferably, the inert gas is argon, and the flow rate is 0.3-1.0L/min.
Preferably, the tube furnace comprises a high-temperature-resistant quartz glass tubular reactor which is connected with a water vapor generation device through a carrier gas pipeline; the water vapor generation device includes: the gas outlet is communicated with a water container of the reactor and heating equipment for heating the water container, and the water container is provided with an inert gas channel.
Preferably, the heating equipment is water bath heating equipment, and the adjustable range of the water bath temperature is 25-90 ℃.
Preferably, the time of the oxidation is 0.5 to 2 hours.
The method disclosed by the invention is based on the uniform growth of the metal vanadium film, and the high-quality vanadium dioxide film is obtained by utilizing the mild oxidability of water vapor at high temperature. The method can prepare the vanadium dioxide film with excellent performance and wafer-level size, and the vanadium dioxide film is uniform and compact and can achieve three to four orders of magnitude of resistance change in the phase change process. Compared with the traditional method for adjusting complex parameters in the growth process in high vacuum equipment, the method takes water vapor as a mild oxidant, can realize a self-adjusting oxidation mechanism in the growth process when preparing the vanadium dioxide film, and can prepare the stable positive quadrivalent monoclinic phase vanadium dioxide film. The method greatly expands the growth temperature area for preparing the vanadium dioxide film, and the vanadium dioxide film can be efficiently prepared within the range of 450-650 ℃; the method is simple and easy to implement, high in repeatability, non-toxic and environment-friendly in the whole film growth process, low in cost, uniform in quality of the prepared vanadium dioxide film, excellent in performance, capable of growing large-size high-quality films and beneficial to realization of large-scale production and application.
Drawings
FIG. 1 is a schematic view of an apparatus for growing a vanadium dioxide thin film by steam oxidation according to an embodiment of the present invention;
FIG. 2 is a schematic representation of a vanadium metal thin film prepared in example 1;
FIG. 3 is a schematic representation of a vanadium dioxide film obtained by steam oxidation in example 1;
FIG. 4 is an XRD pattern of a vanadium dioxide thin film obtained by steam oxidation in example 1;
FIG. 5 is a Raman spectrum of a vanadium dioxide thin film obtained by steam oxidation in example 1;
FIG. 6 is a temperature-resistance plot of a 20nm thick vanadium dioxide film obtained by steam oxidation of example 1;
FIG. 7 is a graph of the resistance distribution of a 2 inch diameter vanadium dioxide film prepared by steam oxidation of example 1 before phase transformation;
FIG. 8 is a graph of the resistance distribution after phase transition of a 2 inch diameter vanadium dioxide film prepared by steam oxidation in example 1;
FIG. 9 is a temperature-resistance graph of a 210nm thick vanadium dioxide film obtained by steam oxidation in example 2;
FIG. 10 is a schematic diagram of a vanadium dioxide film obtained by heating and oxidizing a vanadium metal film in air in comparative example 1;
FIG. 11 is a comparison of the effect of oxidation with steam and heating in air in accordance with an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a preparation method of a wafer-level vanadium dioxide film, which comprises the following steps:
s1, providing a uniformly-grown metal vanadium film;
and S2, oxidizing the metal vanadium film by using water vapor at the temperature of 450-650 ℃ under the oxygen-free condition to obtain the monoclinic phase vanadium dioxide film.
The method for preparing the vanadium dioxide film is simple, high in repeatability and low in cost; the prepared vanadium dioxide film is uniform and compact, has excellent metal-insulator conversion performance, can reach the wafer level in size, and is beneficial to application.
Referring to fig. 1, fig. 1 is a schematic view of an apparatus for growing a vanadium dioxide thin film by steam oxidation according to an embodiment of the present invention. In order to solve the problems of harsh experimental conditions, expensive experimental equipment and the like existing in the existing preparation method of the vanadium dioxide film, the invention discloses a method for oxidizing a metal vanadium film by introducing water vapor under the heating atmosphere of a tubular furnace by taking the water vapor as a mild oxidant to obtain the high-quality vanadium dioxide film.
In an embodiment of the present invention, the tube furnace includes a tubular reactor in which a sample is placed for reaction. The reactor is connected with a water vapor generating device through a carrier gas pipeline; the water vapor generation device includes: the gas outlet is communicated with a water container of the reactor and heating equipment for heating the water container, and the water container is provided with an inert gas channel.
Conventional tube furnaces typically include only one quartz glass tube with openings at both ends; the tubular reactor in the embodiment of the present invention is also a quartz glass tube, which is closed at one end and open at the other end, and has a cap at the open end. Meanwhile, in the embodiment of the invention, a thin glass guide pipe is arranged to extend into the vicinity of the closed end of the quartz tube, and the thin glass guide pipe is welded with the quartz tube. Preferably, the tube furnace comprises a high temperature resistant quartz glass tubular reactor (referred to as a high temperature resistant quartz glass tube for short). In the embodiment of the invention, when the metal vanadium film is conveyed to the tubular furnace, the metal vanadium film can be pushed to the position near the carrier gas outlet of the quartz glass tubular reactor after being put into the alumina ark. The water vapor generation device specifically comprises: water bath heating equipment such as erlenmeyer flasks, water containers for flasks, and water baths.
According to the embodiment of the invention, argon gas can be introduced into a conical flask filled with deionized water according to a certain flow rate (controlled by a flow meter), and the equipment is placed into a water bath kettle for water bath heating; wherein, argon enters from the long glass tube and exits from the short glass tube in the conical flask, so that the argon with water vapor is introduced into the tube furnace. Moreover, the water vapor content introduced into the quartz glass tubular reactor can be controlled by adjusting the temperature of the water bath; the adjustable range of the water bath temperature is 25-90 ℃, and preferably 50-85 ℃. The temperature of the water bath can be from room temperature to 90 ℃, but the water vapor content is lower at room temperature, and the effect is not as stable as the higher temperature. In addition, one end of the quartz glass tubular reactor, which is far away from the sample, is provided with a water discharge outlet which can be communicated to deionized water.
The embodiment of the invention is based on the growth of a uniform metal vanadium film, the thickness of the film is generally 10 nm-400 nm, and a round sample can be adopted. The embodiment of the invention firstly prepares the metal vanadium film, and preferably comprises the following steps: selecting aluminum oxide, silicon oxide or silicon wafers as substrates; and (3) coating in a vacuum chamber by using an electron beam thermal evaporation or magnetron sputtering mode, wherein the substrate keeps moving at a constant speed in the coating process, and a uniform vanadium metal film is obtained by growing.
The selected substrate material is preferably a crystalline material such as alumina or silica. The invention preferably adopts a thermal evaporation coating method to prepare the metal vanadium film; background vacuum degree of vacuum chamber is better than 5
10-3Pa. In order to ensure the uniformity of the vanadium metal film, the substrate keeps rotating at a constant speed in the film coating process; the substrate is rotated at a speed not exceeding 10 rpm, for example, at a constant speed of 2 to 6 rpm.
Some embodiments of the invention prepare a vanadium metal film: selecting Al2O3(0001) Substrate, clean alumina (Al)2O3) Transferring the substrate to a high vacuum growth chamber with vacuum degree of 5 × 10 or more-3Pa. Rotating the substrate, spraying the vanadium atom beam on the substrate by a thermal evaporation method, controlling the flow velocity of the vanadium atom beam to be 5.5-7.5 angstroms/minute, controlling the growth time, thereby controlling the thickness of the prepared film, and finally taking out the prepared metal vanadium film from the vacuum chamber. The vanadium atom is obtained according to the following method: the electron beam heating is used for evaporating the vanadium metal, the speed is preferably 5.5-6 angstroms/minute, and the growth time is generally 40-260 minutes. After the growth process is finished, closing the metal vanadium atom beam, and taking out the metal vanadium film; the thickness of the film is 10nm to 400nm, and further 20nm to 200 nm.
After the metal vanadium film is obtained, the embodiment of the invention utilizes steam to assist oxidation to grow the vanadium dioxide film; the specific process is as follows:
the metal produced by thermal evaporation may be treatedAfter the vanadium film is put into an alumina ark, the vanadium film is pushed to the position near the carrier gas outlet in a quartz glass tube of the tube furnace. The conical flask filled with deionized water is placed in a water bath kettle, and water bath heating is carried out to a proper temperature, so that water vapor is generated in the conical flask. Inert gas such as argon is led into the conical flask filled with water vapor from the glass tube, and the glass tube is in length and short out. Finally, a carrier gas (argon Ar + water vapor H) containing water vapor is added2O) is introduced into a quartz tube, the temperature of the tube furnace is raised to a growth temperature range of 450-650 ℃ according to a certain speed, then the metal vanadium film is oxidized mildly by a steam mild auxiliary oxidation method under a heating atmosphere, after oxidation growth is carried out for a period of time, the temperature of the tube furnace is reduced to below 200 ℃, and the ark is taken out, so that the high-quality vanadium dioxide film is obtained.
Wherein, the content ratio of the water vapor to the argon gas is mainly controlled by controlling the temperature of the water bath and the flow of the argon gas. The water bath heating temperature range is generally 25-90 ℃; the flow rate of the argon gas can be 0.3-1.0L/min. The temperature rise rate of the tubular furnace is preferably 10 ℃/min, and the temperature rise time is preferably 45-65 min. The growth temperature range of the vanadium dioxide film is generally 450-650 ℃, such as 500-600 ℃ and 500-550 ℃; the growth time is preferably 0.5 to 2 hours. If the temperature is too high, the catalyst will be over oxidized and other heterogeneous structures appear.
In the invention, water vapor is used as a mild oxidant, a self-adjusting oxidation mechanism can be realized in the process of oxidizing and growing the vanadium dioxide film, and the whole film growth process is nontoxic and environment-friendly. The method greatly expands the growth temperature zone for preparing the vanadium dioxide film, can efficiently prepare the vanadium dioxide film within the range of 450-650 ℃, and has the advantages of simple experimental operation, high repeatability and low cost. The vanadium dioxide film prepared by the embodiment of the invention is very uniform and compact, has excellent metal-insulator transition performance, and all parts of the wafer-sized film with resistance jump before and after phase change can reach 3-4 orders of magnitude.
The method can grow the high-quality vanadium dioxide film with the wafer size by utilizing the simple and easy-to-operate method, and can be widely applied to the preparation of other oxides.
In order to further understand the present application, the following specifically describes the preparation method of the wafer-level vanadium dioxide thin film provided by the present application with reference to the examples. It should be understood, however, that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention, which is defined by the following examples. Meanwhile, various raw material reagents and equipment referred to in the specification of the present application are commercially available and can be used as they are without further description.
Example 1
Selecting round Al with the diameter of 2 inches2O3(0001) Substrate, using thermal evaporation method at vacuum degree better than 4 × 10-3Pa and then the substrate is rotated at a constant speed of 4 revolutions per minute.
And opening an electron gun for heating, evaporating metal vanadium with the purity of 99.99% to generate vanadium atom beams, measuring the speed of the vanadium atom beams by using a quartz crystal film thickness gauge, and adjusting the power of an electron beam evaporation source to generate stable vanadium atom beams at the speed of 5.5 angstroms/minute. And opening the baffle, spraying the metal vanadium atomic beam to the surface of the substrate for reaction and deposition, and growing to form a metal vanadium film, wherein the growth time is 40 minutes.
And after the growth process is finished, closing the metal vanadium atom beam, and taking out the prepared metal vanadium film from the vacuum chamber. The thickness of the metal vanadium film is 20nm, and a physical photograph thereof is shown in FIG. 2.
With the apparatus shown in FIG. 1, a vanadium metal thin film produced by thermal evaporation was placed in an alumina ark and pushed to the vicinity of the outlet of the carrier gas in the quartz glass tube of the tube furnace. The flask containing 1000mL of deionized water was placed in a water bath and heated to 50 ℃ in a water bath to produce water vapor in the flask. And introducing high-purity argon with the purity of 99.999 percent into the conical flask filled with the water vapor from a glass tube, wherein the glass tube is long and short, and the flow rate of the argon is 1.0L/min. And finally, introducing a carrier gas (argon and water vapor) containing water vapor into the quartz glass tube, raising the temperature of the tube furnace to 550 ℃ at the speed of 10 ℃/minute, raising the temperature for 55 minutes, then mildly oxidizing the metal vanadium film by using a water vapor oxidation method under a heating atmosphere, naturally cooling the tube furnace after the metal vanadium film grows for 2 hours, reducing the temperature to below 200 ℃, and taking out the square boat to obtain the vanadium dioxide film shown in the figure 3, wherein the thickness of the vanadium dioxide film is 20 nm.
FIG. 4 is an X-ray diffraction (XRD) test result of the prepared vanadium dioxide thin film, and FIG. 5 is a Raman test result thereof, thereby showing VO2The crystal phase structure of (1).
The vanadium dioxide film was subjected to performance tests, the results of which are shown in FIGS. 6-8. FIG. 6 is a temperature-resistance plot of a 20nm thick vanadium dioxide film obtained by steam oxidation of example 1; the obtained film resistance has three to four orders of change, which is typical VO2Phase change characteristics.
Fig. 7 is a distribution diagram of the resistance of the vanadium dioxide film with the diameter of 2 inches prepared by steam oxidation in example 1 before phase change, and fig. 8 is a diagram after phase change, thereby showing that the vanadium dioxide film with large size obtained by the invention has good uniformity.
Example 2
Selecting round Al with the diameter of 2 inches2O3(0001) Substrate, using thermal evaporation method at vacuum degree better than 5 × 10-3Pa and then the substrate is rotated at a constant speed of 4 revolutions per minute.
And opening an electron gun for heating, evaporating metal vanadium with the purity of 99.99% to generate vanadium atom beams, measuring the speed of the vanadium atom beams by using a quartz crystal film thickness gauge, and adjusting the power of an electron beam evaporation source to generate stable vanadium atom beams at the speed of 7.5 angstroms/minute. And opening the baffle, spraying the metal vanadium atomic beam to the surface of the substrate for reaction and deposition, and growing to form a metal vanadium film, wherein the growth time is 260 minutes.
And after the growth process is finished, closing the metal vanadium atomic beam, and taking out the prepared metal vanadium film from the vacuum chamber, wherein the thickness of the film is 200 nm.
With the apparatus shown in FIG. 1, a vanadium metal thin film produced by thermal evaporation was placed in an alumina ark and pushed just below the outlet of the carrier gas in the quartz glass tube of the tube furnace. The flask containing 1000mL of deionized water was placed in a water bath and heated to 80 ℃ in a water bath to generate enough water vapor in the flask. And introducing high-purity argon with the purity of 99.999 percent into the conical flask filled with the water vapor from a glass tube, wherein the glass tube is long and short, and the flow rate of the argon is 0.6L/min. And finally, introducing a carrier gas (argon and water vapor) containing water vapor into the quartz glass tube, heating the tube furnace to 500 ℃ at the temperature of 10 ℃/min for 50 min, then mildly oxidizing the metal vanadium film by using a water vapor mild auxiliary oxidation method under a heating atmosphere, reducing the temperature of the tube furnace to below 200 ℃ after 2 h of growth, taking out the square boat, and obtaining the high-quality vanadium dioxide film with the film thickness of 210 nm.
Performance testing was performed as described in example 1, and FIG. 9 is a temperature-resistance plot of a 210nm thick vanadium dioxide film obtained by steam oxidation in example 2, illustrating the three to four orders of magnitude change in the resulting film resistance.
Comparative example 1
On the basis of the vanadium metal film prepared in example 1, argon gas was directly introduced under the same conditions without passing through a pipe in a conical flask, and the vanadium dioxide film shown in FIG. 10 was obtained by heating and oxidizing in air; FIG. 10 is a schematic diagram of a vanadium dioxide thin film obtained by heating and oxidizing the metal vanadium thin film in air in comparative example 1.
As can be seen from the comparison between FIG. 3 and FIG. 10, the vanadium dioxide film prepared by the present invention has uniform quality and is a large-size high-quality film.
The performance of the vanadium dioxide film obtained in the comparative example 1 is compared with that of the vanadium dioxide film obtained in the example 1, and VO prepared under the conditions of introducing water vapor and not introducing water vapor at different temperatures is tested2The magnitude of the resistance-temperature change of the thin film was compared to the VO obtained2The larger the magnitude of the change in the quality of the film, the better the quality is. Results referring to fig. 11, fig. 11 compares the effects of heating oxidation in air and oxidation using water vapor. As can be seen from FIG. 11, if the ratio of the resistances before and after the phase transition is more than three orders of magnitude, the window of the temperature region for the steam oxidation is about 90 degrees (500-590 ℃), while the window of the annealing temperature region for the conventional air oxidation is only about 30 degrees(530 ℃ to 560 ℃). Further, the wider the temperature window under water passing conditions, the easier the production conditions.
From the above embodiments, the invention provides a simple preparation method of a wafer-level vanadium dioxide monoclinic phase film based on water vapor oxidation, which is a brand new method, and not only can overcome the defects of the prior art, but also can remarkably improve the quality of the wafer-size vanadium dioxide film. The method mainly utilizes water vapor as a mild oxidant, and oxidizes the metal vanadium film through the water vapor under the heating atmosphere of the tubular furnace, thereby obtaining the high-quality vanadium dioxide film with the wafer size. Compared with the traditional oxidation process under the oxygen atmosphere, the method has the advantages that the temperature window for preparing the vanadium dioxide film is greatly widened, and the vanadium dioxide film with a single-phase structure can be obtained in a large temperature area range by using water vapor as an oxidant. Meanwhile, the film prepared by the method has excellent metal insulation transition property, and the prepared vanadium dioxide film with the wafer size has uniform and controllable phase transition characteristics and is beneficial to application.
The above description is only a preferred embodiment of the present invention, and it should be noted that various modifications to these embodiments can be implemented by those skilled in the art without departing from the technical principle of the present invention, and these modifications should be construed as the scope of the present invention.

Claims (7)

1. A preparation method of a wafer-level vanadium dioxide film comprises the following steps:
s1, providing a uniformly-grown metal vanadium film;
s2, placing the metal vanadium film in a tube furnace, heating the tube furnace to 450-650 ℃, introducing a carrier gas to the vicinity of the metal vanadium film, wherein the carrier gas contains water vapor and an inert gas, the inert gas is argon, the flow rate is 0.3-1.0L/min, oxidizing the metal vanadium film by using the water vapor, and the oxidation time is 0.5-2 hours, so as to obtain the monoclinic phase vanadium dioxide film.
2. The method according to claim 1, wherein the thickness of the vanadium metal thin film is 10 to 400 nm.
3. The method according to claim 1, wherein the metal vanadium thin film is obtained by the following steps:
selecting aluminum oxide, silicon oxide or silicon wafers as substrates; and (3) coating in a vacuum chamber by using an electron beam thermal evaporation or magnetron sputtering mode, wherein the substrate keeps moving at a constant speed in the coating process, so that the uniformly grown metal vanadium film is obtained.
4. The method of claim 3, wherein the vacuum chamber has a background vacuum of greater than 5 × 10- 3Pa。
5. The method according to claim 4, wherein the substrate is rotated at a constant speed during the coating process, and the rotation speed is not more than 10 rpm.
6. The preparation method according to any one of claims 1 to 5, wherein the tube furnace comprises a high-temperature-resistant quartz glass tubular reactor, and the reactor is connected with a water vapor generation device through a carrier gas pipeline; the water vapor generation device includes: the gas outlet is communicated with a water container of the reactor and heating equipment for heating the water container, and the water container is provided with an inert gas channel.
7. The preparation method according to claim 6, wherein the heating device is a water bath heating device, and the temperature of the water bath is adjustable within a range of 25-90 ℃.
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