Fluorine-doped metal oxide thin film, and preparation method and application thereof

Abstract

The present application relates to a kind of fluorine-doped metal oxide thin film and its preparation method and application, belong to material technical field.The substrate and metal wire after cleaning are fixed in the chamber of hot wire chemical vapor deposition (CVD) device respectively, metal wire is located below the substrate in the chamber, after the chamber is evacuated, the metal wire is preheated by electrification;The preheated metal wire is continuously electrified and heated, while continuously mixed gas is input into the chamber, a layer of fluorine-doped metal oxide thin film is deposited on the surface of the substrate, and the mixed gas includes fluorine-containing gas and oxygen.The method of the present application can greatly improve the safety feasibility of fluorine doping while not affecting the original low-temperature performance of the material.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a fluorine-doped metal oxide thin film, its preparation method, and its application. Background Technology

[0002] Metal oxides, as functional materials, have been widely used in solar cells, electrolytic materials, catalysts, and other fields. Fluorine doping of metal oxides is currently a hot research topic. Existing technologies typically employ high-temperature solid-state methods and spray pyrolysis to prepare fluorine-doped metal oxides. However, these methods require high temperatures and are not suitable for fluorine doping of metal oxides that are not heat-resistant or prone to high-temperature degradation. For example, at high temperatures, the work function of molybdenum oxide decreases, and the oxygen vacancy content increases. Furthermore, directly using fluorine gas for doping at low temperatures poses significant safety risks.

[0003] Therefore, it is essential to improve the preparation methods of fluorine-doped metal oxide thin films. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fluorine-doped metal oxide thin film, its preparation method and application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a fluorine-doped metal oxide thin film, comprising the following steps:

[0007] S1. Clean the substrate;

[0008] S2. Fix the cleaned substrate and metal wire in the chamber of the hot filament CVD device, with the metal wire located below the substrate in the chamber. After evacuating the chamber, preheat the metal wire by energizing it.

[0009] S3. Continue to heat the preheated metal wire by applying electricity, while continuously introducing a mixed gas into the chamber to deposit a fluorine-doped metal oxide film on the substrate surface. The mixed gas includes fluorine-containing gas and oxygen.

[0010] This invention involves introducing a mixed gas during the heating of a metal wire. Oxygen in the mixed gas reacts with the metal wire in a redox reaction to generate a metal oxide. Carbon tetrafluoride in the mixed gas undergoes a cracking reaction at high temperature, releasing fluorine. The released fluorine is incorporated into the generated metal oxide and sublimates onto a substrate along with the metal oxide, forming a fluorine-doped metal oxide film. This method significantly improves the safety and feasibility of fluorine doping without affecting the original low-temperature performance of the material.

[0011] Preferably, in step S1, the substrate is a silicon wafer.

[0012] Preferably, in step S2, the metal wire includes any one of tungsten wire, molybdenum wire, and tantalum wire, and the diameter of the metal wire is 1 to 5 mm.

[0013] Preferably, in step S2, the air pressure in the chamber after evacuation is no greater than 0.1 Pa, and the temperature of the metal wire after preheating is 900-1000℃.

[0014] Preferably, in step S3, the electric heating includes: heating the preheated metal wire to 1000-1500°C within 5-20 minutes and then holding it at that temperature.

[0015] The present invention controls the temperature of the metal wire in step S3 within the range of 1000 to 1500°C, which can prevent the metal wire from melting and ensure that the generated metal oxide can sublimate rapidly.

[0016] Preferably, in step S3, the partial pressure of the oxygen is P1, the partial pressure of the fluorine-containing gas is P2, and the total pressure of the mixed gas is P. P1, P2, and P satisfy the following conditions:

[0017] (1)0.4≤P1 / P≤0.7; (2)0.1≤P2 / P≤0.4; (3)0.5≤(P1+P2) / P≤1.

[0018] Further preferred, P1, P2, and P satisfy the following conditions:

[0019] (1) 0.6 ≤ P1 / P ≤ 0.7; (2) 0.2 ≤ P2 / P ≤ 0.3.

[0020] This invention controls parameters such as the flow rate of fluorine-containing gas and the partial pressure ratio of each gas in the mixed gas to regulate the deposition rate and fluorine content of fluorine-doped metal oxide films. This, in turn, allows for the control of the contact resistance between the fluorine-doped metal oxide film and the substrate, as well as the resistivity of the fluorine-doped metal oxide film. This expands the application range of fluorine-doped metal oxide films, enabling them to be used as hole transport layers, sacrificial layers, or insulating layers in solar cells, as electrode materials in ion batteries, and as catalyst materials in catalytic reactions.

[0021] The inventors discovered that controlling P1 / P within the range of 0.4–0.7, P2 / P within the range of 0.1–0.4, and (P1+P2) / P within the range of 0.5–1, can improve the passivation level of fluorine-doped metal oxide films while ensuring the film deposition rate. If P1 / P > 0.7, further increasing the oxygen content in the mixed gas significantly increases the risk of chemical reactions within the chamber, while the passivation level of the fluorine-doped metal oxide film does not change significantly.

[0022] Preferably, the flow rate of the mixed gas is 20-300 sccm, more preferably 80-150 sccm.

[0023] The inventors discovered that, with a fixed content (i.e., partial pressure ratio) of each gas in the mixed gas, controlling the flow rate of the mixed gas to 80–150 sccm can improve the passivation level of the fluorine-doped metal oxide film while ensuring the deposition rate of the film.

[0024] Preferably, in step S3, the fluorine-containing gas includes at least one of carbon tetrafluoride, trifluoromethane, and tetrafluoroethane.

[0025] Preferably, in step S3, the mixed gas further includes an inert gas, which includes at least one of argon and nitrogen.

[0026] Preferably, in step S3, the air pressure in the chamber is 10-20 Pa.

[0027] Preferably, in step S3, the substrate is rotated at a speed of 5–20 rad / min while the mixed gas is introduced. Rotating the substrate during sublimation deposition can improve the thickness uniformity of the fluorine-doped metal oxide film.

[0028] Secondly, the present invention provides a fluorine-doped metal oxide thin film, which is prepared by the preparation method described in the first aspect.

[0029] Thirdly, the present invention provides the application of a fluorine-doped metal oxide thin film as described in the second aspect as a hole transport layer in the fabrication of solar cells.

[0030] Fourthly, the present invention provides the application of a fluorine-doped metal oxide thin film as described in the second aspect as an electrode material in the preparation of ion batteries.

[0031] Fifthly, the present invention provides the application of a fluorine-doped metal oxide thin film as described in the second aspect in the preparation of a catalyst.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] This invention introduces a mixed gas during the heating of a metal wire. The oxygen in the mixed gas reacts with the metal wire in a redox reaction to generate a metal oxide. The carbon tetrafluoride in the mixed gas undergoes a cracking reaction at high temperature, releasing fluorine. The released fluorine is incorporated into the generated metal oxide and sublimates and deposits onto a substrate along with the oxide, forming a fluorine-doped metal oxide film. This invention can achieve fluorine doping without affecting the original low-temperature performance of the material, greatly improving the safety and feasibility of fluorine doping. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the preparation principle of fluorine-doped metal oxides provided by the present invention.

[0035] Figure 2 The images show the SEM morphology, EDS energy dispersive spectroscopy analysis results, and elemental content analysis results of the fluorine-doped metal oxide thin film provided in Example 2 of this invention. Detailed Implementation

[0036] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0037] In the following examples, the temperature of the molybdenum wire was obtained by testing the edge of the molybdenum wire in contact with a thermocouple.

[0038] A fluorine-doped metal oxide thin film with a thickness of 50 nm was formed on a silicon wafer using the methods described in the following examples and comparative examples, and then tested:

[0039] (1) SEM morphology test, EDS energy dispersive spectroscopy analysis and element content analysis were performed on each fluorine-doped metal oxide film;

[0040] (2) Passivation level: The passivation level of the film is represented by the implied open circuit voltage level, which is tested using a Sinton minority carrier lifetime tester.

[0041] (3) Contact resistance between fluorine-doped metal oxide thin film and silicon wafer: TLM method to test contact resistance, four-wire method to eliminate line resistance, and KEITHLEY 2400 source meter to collect current and voltage information;

[0042] (4) The intrinsic resistivity of fluorine-doped metal oxide thin films is tested by using a KEITHLEY 2400 source meter to collect current and voltage information and then testing the film resistance using the two-wire method.

[0043] (5) Deposition rate: The film thickness is measured by the change in vibration frequency caused by the deposition of the film on the crystal oscillator. The deposition rate is calculated according to the following formula: Deposition rate = film thickness / deposition time.

[0044] Examples 1-11

[0045] Examples of the fluorine-doped metal oxide thin films and their preparation methods according to the present invention are provided below. The preparation principle of the fluorine-doped metal oxide is as follows: Figure 1 As shown, Figure 1 In the diagram, 1 represents the substrate, and 2 represents the molybdenum wire; the method for preparing the fluorine-doped metal oxide thin film includes the following steps:

[0046] S1. Clean the silicon wafer (i.e., substrate) using the RCA process;

[0047] S2. Fix the cleaned substrate and molybdenum wire in the chamber of the hot filament CVD device. The diameter of the molybdenum wire is 2 mm. The molybdenum wire is located below the substrate in the chamber. Evacuate the chamber. Under the condition of vacuum degree of 0.1 Pa, preheat the molybdenum wire by energizing it until the temperature of the molybdenum wire reaches 900°C.

[0048] S3. Continue to heat the preheated molybdenum wire with electricity, raise the temperature of the preheated metal wire to 1500°C within 5 minutes and keep it at that temperature. At the same time, continuously introduce mixed gas into the chamber from the bottom of the chamber to maintain the gas pressure in the chamber at 15Pa, and deposit a fluorine-doped metal oxide film on the surface of the substrate.

[0049] The mixed gas is a mixture of carbon tetrafluoride, oxygen and argon, with the partial pressure of oxygen being P1, the partial pressure of carbon tetrafluoride being P2, and the partial pressure of argon being P3.

[0050] In step S3, the substrate is rotated at a speed of 10 rad / min while the mixed gas is introduced.

[0051] The partial pressure ratios P1:P2:P3 and the flow rates of the mixed gas in Examples 1 to 11 are shown in Table 1.

[0052] Energy dispersive spectroscopy (EDS) analysis results of the fluorine-doped metal oxide films obtained in Examples 1-11 show that the prepared films are fluorine-doped molybdenum oxide films, and no carbon impurities are introduced during the preparation process.

[0053] The test results for implicit open-circuit voltage, contact resistance, and intrinsic resistivity are shown in Table 1.

[0054] Table 1

[0055]

[0056] As can be seen from Table 1, the contact resistance between the fluorine-doped metal oxide film and the silicon wafer in each embodiment is extremely small (less than 100 mΩ·cm). 2The intrinsic resistivity of the fluorine-doped metal oxide thin films in each embodiment is extremely high, and the changes in contact resistance and intrinsic resistivity in each embodiment have almost negligible impact on the performance of the solar cells.

[0057] As can be seen from Examples 1 to 4, when the ratio between the partial pressure of oxygen and the total pressure of the mixed gas is 0.6 to 0.8, a larger deposition rate can be ensured, a larger implicit open-circuit voltage can be obtained, and the passivation level of the fluorine-doped metal oxide film is higher.

[0058] As can be seen from Examples 3 and 5-8, when the ratio between the partial pressure of the fluorine-containing gas and the total pressure of the mixed gas is 0.2-0.3, the measured implicit open-circuit voltage is larger and the passivation level of the fluorine-doped metal oxide film is higher.

[0059] As can be seen from Examples 3 and 9-11, controlling the flow rate of the mixed gas to 80-150 sccm can ensure a large deposition rate and obtain a large implicit open-circuit voltage, resulting in a higher passivation level of the fluorine-doped metal oxide film.

[0060] Example 12

[0061] An embodiment of the fluorine-doped metal oxide thin film and its preparation method according to the present invention includes the following steps:

[0062] S1. Clean the silicon wafer (i.e., substrate) using the RCA process;

[0063] S2. Fix the cleaned substrate and tungsten wire in the chamber of the hot filament CVD device. The diameter of the tungsten wire is 2 mm. The tungsten wire is located below the substrate in the chamber. Evacuate the chamber. Under the condition of vacuum degree of 0.1 Pa, preheat the tungsten wire by energizing it until the temperature of the tungsten wire reaches 1000℃.

[0064] S3. Continue to heat the preheated tungsten wire with electricity, raise the temperature of the preheated metal wire to 1300°C within 5 minutes and keep it at that temperature. At the same time, continuously introduce mixed gas into the chamber from the bottom of the chamber to maintain the gas pressure in the chamber at 10Pa, and deposit a fluorine-doped metal oxide film on the surface of the substrate.

[0065] The mixed gas is a mixture of carbon tetrafluoride, oxygen and argon, with the partial pressure of oxygen being P1, the partial pressure of carbon tetrafluoride being P2, and the partial pressure of argon being P3. The partial pressure ratio P1:P2:P3 and the flow rate of the mixed gas are the same as in Example 3.

[0066] In step S3, the substrate is rotated at a speed of 5 rad / min while the mixed gas is introduced.

[0067] SEM images and energy dispersive spectroscopy analysis of fluorine-doped metal oxide thin films are as follows: Figure 2 As shown, from Figure 2 It can be seen that this embodiment can prepare a fluorine-doped tungsten oxide film with a fluorine content of 9.41% and a carbon content of 0, which indicates that the method of the present invention does not introduce carbon impurity elements during the preparation process.

[0068] The implied open-circuit voltage test result was 650.2mV;

[0069] The contact resistance between the fluorine-doped metal oxide film and the silicon wafer obtained in this embodiment is 59.7 mΩ·cm. 2 ;

[0070] The intrinsic resistivity of the fluorine-doped metal oxide thin film obtained in this embodiment is 1.68*10⁻⁶. 7 Ω·cm.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for producing a fluorine-doped metal oxide thin film, characterized by comprising the steps of: The method comprises the following steps: ​ S1, cleaning the substrate; S2, fixing the cleaned substrate and the metal wire in a chamber of a hot wire CVD device, with the metal wire below the substrate, preheating the metal wire by electrifying after vacuumizing the chamber; S3, continuously electrifying and heating the preheated metal wire, and introducing mixed gas during the electrifying and heating process, the mixed gas comprising fluorine-containing gas and oxygen, the flow rate of the mixed gas being 20-300sccm, the oxygen in the mixed gas reacting with the metal wire to generate metal oxide, the fluorine-containing gas in the mixed gas cracking at high temperature to release fluorine, the released fluorine being doped into the generated metal oxide and sublimating and depositing on the substrate with the metal oxide to form a fluorine-doped metal oxide film; In step S2, the metal wire comprises any one of tungsten wire, molybdenum wire and tantalum wire; In step S2, the pressure in the chamber after vacuumizing is not more than 0.1Pa, and the temperature of the metal wire after preheating is 900-1000℃; In step S3, the fluorine-containing gas comprises at least one of carbon tetrafluoride, trifluoromethane and tetrafluoroethane; In step S3, the electrifying and heating comprises: heating the preheated metal wire to 1000-1500℃ within 5-20min and then keeping the temperature; In step S3, the pressure in the chamber is 10-20Pa, the partial pressure of the oxygen is P1, the partial pressure of the fluorine-containing gas is P2, and the total pressure of the mixed gas is P, P1, P2 and P satisfying the following conditions: (1) 0.4≤P1 / P≤0.7; (2) 0.1≤P2 / P≤0.4; (3) 0.5≤(P1+P2) / P≤1.

2. The method for preparing fluorine-doped metal oxide thin films as described in claim 1, characterized in that, In step S3, the substrate is rotated at a speed of 5-20rad / min while the mixed gas is introduced.

3. A fluorine-doped metal oxide thin film, characterized by, The fluorine-doped metal oxide film is prepared by the method of any one of claims 1-2.

4. The fluorine-doped metal oxide film of claim 3 as a hole transport layer, a sacrificial layer or an insulating layer in the preparation of a solar cell.

5. The fluorine-doped metal oxide film of claim 3 as electrode material in the preparation of an ion battery.

6. The fluorine-doped metal oxide film of claim 3 in the preparation of a catalyst.

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