A method for preparing hexagonal tantalum pentoxide single crystal thin film

Abstract

The present invention discloses a method for preparing a hexagonal tantalum pentoxide single crystal thin film, belonging to the technical field of optoelectronic information functional materials. Using tantalum ethoxide as an organometallic compound material and high-purity oxygen as the oxidizing gas, a twin-free hexagonal tantalum pentoxide single crystal thin film is prepared on a hexagonal lanthanum fluoride single crystal substrate using metal organic chemical vapor deposition equipment. The hexagonal tantalum pentoxide single crystal thin film prepared by the present invention has high single crystal quality and good stability, and therefore has good application prospects in the field of semiconductor devices.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-quality hexagonal tantalum pentoxide single crystal thin film based on a lanthanum fluoride substrate, and belongs to the technical field of wide-bandgap oxide semiconductor photoelectric materials. Background Art

[0002] In recent years, with the rapid development of semiconductor technology, conductor materials have been moving toward wide band gaps, higher breakdown voltages, and low losses. Correspondingly, semiconductor devices are developing toward high power, high integration, and low energy consumption, and wide-bandgap oxide materials have become a hot topic of research. Tantalum pentoxide (Ta2O5) primarily exists in tetragonal, orthorhombic, and hexagonal phases. Its wide band gap, high breakdown voltage, high dielectric constant, and stable physical and chemical properties make it a promising multifunctional material. With a band gap of approximately 3.9-4.5 eV and a dielectric constant of 20-22, Ta2O5 can be used as an insulating dielectric material in semiconductor devices such as thin-film transistors, high electron mobility transistors, and supercapacitors. In particular, hexagonal Ta2O5, with a lattice structure similar to gallium nitride, is a promising wide-bandgap oxide semiconductor material.

[0003] Ta2O5 powder materials (CN105197996B) and thin film materials (Optical Materials, 97 (2019) 109404) have been reported. Ta2O5 prepared by traditional methods such as sol-gel and radio frequency magnetron sputtering is often an amorphous or polycrystalline thin film. Thin film Ta2O5 materials grown by heteroepitaxial growth have been reported [orthorhombic Ta2O5 epitaxial film: Ceramics International, 48 (2022) 26800-26805; hexagonal Ta2O5 epitaxial film: Materials Science in Semiconductor Processing 135 (2021) 106065].

[0004] The currently prepared hexagonal tantalum pentoxide materials still have the following problems:

[0005] (1) The single crystal substrates currently used to grow hexagonal Ta2O5 thin films often have a twin structure due to differences in lattice structure or poor lattice matching with the substrate. This results in problems such as incomplete lattice structure, numerous lattice defects, and poor crystal quality. There are currently no reports on growing hexagonal Ta2O5 single crystal thin films using single crystal materials with the same lattice structure and good lattice matching as hexagonal Ta2O5 as substrates.

[0006] (2) Currently, amorphous or polycrystalline Ta2O5 thin films are mostly used as insulating dielectric layers in semiconductor devices. Using high-quality hexagonal Ta2O5 single crystal thin films as insulating dielectric layers will help reduce device leakage current, increase device integration, and thus enhance device performance.

[0007] (3) Currently, there is a lack of single crystal substrate materials that have a good lattice match with hexagonal Ta2O5. In this case, even with dedicated equipment for preparing single crystal thin films such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), it is difficult to obtain high-quality hexagonal Ta2O5 single crystal thin film materials. This is a major reason why twin-free, structurally complete hexagonal Ta2O5 single crystal thin films have not yet been obtained.

[0008] (4) Currently, there is a lack of research on improving the electrical properties of hexagonal Ta2O5 materials, which limits their application in semiconductor devices. Therefore, the acquisition of high-quality single-crystal thin films of twin-free hexagonal Ta2O5 will be beneficial for conducting doping research on Ta2O5 films and improving the electrical properties of the films.

[0009] In summary, finding single-crystal substrate materials that lattice-match hexagonal Ta2O5 and researching and preparing hexagonal Ta2O5 single-crystal thin films with complete lattice structures are of great value in expanding its application in semiconductor devices. To this end, this paper proposes a method for preparing high-quality hexagonal Ta2O5 single-crystal thin films based on a lanthanum fluoride substrate. The prepared hexagonal Ta2O5 single-crystal thin films have a complete lattice structure and are free of twins. Summary of the Invention

[0010] In view of the shortcomings of the existing technology, the present invention provides a method for preparing a high-quality hexagonal tantalum pentoxide single crystal thin film based on a lanthanum fluoride substrate.

[0011] MOCVD: Metal organic chemical vapor deposition, a common technique for preparing epitaxial single crystal thin films in this field.

[0012] The present invention uses a hexagonal lanthanum fluoride (LaF3) single crystal (lattice constant a = 0.719nm, c = 0.737nm) as an epitaxial substrate. Compared with hexagonal Ta2O5 (lattice constant a = 0.724nm, c = 1.161nm), the two not only have the same lattice structure, but also the lattice mismatch rate of their (0001) plane is only 0.7%. Therefore, LaF3 is an ideal heteroepitaxial substrate for hexagonal Ta2O5 single crystal thin films. Epitaxial growth of hexagonal Ta2O5 thin films on it not only has good lattice matching, but also does not produce twins, which is the key to obtaining high-quality hexagonal Ta2O5 single crystal thin films. The hexagonal Ta2O5 thin film is prepared using MOCVD technology, which is suitable for the growth of epitaxial single crystal thin films and is one of the important conditions for preparing single crystal thin films. Commercially available tantalum ethoxide (C 10 H 25 Using Ta2O5 (Ta2O5) as the metal organic compound raw material, ultra-high purity nitrogen as the metal organic source carrier gas, and high-purity oxygen as the oxidizing gas, Ta2O5 thin films were grown at high temperatures on LaF3 (0001) single crystal substrates. Under appropriate growth temperatures and deposition rates, twin-free hexagonal Ta2O5 single crystal films were successfully obtained. The growth temperature directly affects the film's crystallization quality. Too low a growth temperature prevents crystallization, while too high a temperature degrades the film's crystallization quality.

[0013] The technical solutions of the present invention are as follows:

[0014] A method for preparing a high-quality hexagonal tantalum pentoxide single crystal thin film based on a lanthanum fluoride substrate. The chemical composition of the hexagonal tantalum pentoxide single crystal thin film prepared by this preparation method is Ta2O5, and the single crystal film is a single-phase single crystal with a hexagonal structure. The specific preparation method adopts a conventional MOCVD process for preparing oxide thin films.

[0015] The specific preparation method is as follows:

[0016] According to the present invention, preferably, the growth substrate of the hexagonal Ta2O5 single crystal thin film is a hexagonal lanthanum fluoride (LaF3) single crystal sheet with a crystal plane of (0001).

[0017] According to the present invention, preferably, the MOCVD method is used to grow hexagonal Ta2O5 thin films at a temperature of 760-860°C;

[0018] According to the present invention, preferably, the crystal growth surface of the hexagonal Ta2O5 single crystal thin film is hexagonal Ta2O5 (0001).

[0019] According to the present invention, preferably, the out-of-plane and in-plane epitaxial relationships of the hexagonal Ta2O5 film and the LaF3 substrate are hexagonal Ta2O5(0001)|LaF3(0001) and hexagonal Ta2O5 ‖LaF3

[0020] According to the present invention, the preparation method of the above hexagonal Ta2O5 single crystal thin film adopts the MOCVD method, using TaC 10 H 25 O5 is used as the metal organic compound raw material, nitrogen is used as the carrier gas, and oxygen is used as the oxidizing gas to grow hexagonal Ta2O5 thin films on LaF3(0001) single crystal substrates. Hexagonal Ta2O5 single crystal thin films are obtained at a suitable growth temperature.

[0021] According to the present invention, preferably, the MOCVD method is used to prepare a hexagonal Ta2O5 single crystal thin film, and the process conditions are as follows:

[0022] Reaction chamber pressure 15~45Torr;

[0023] Growth temperature 760~860℃;

[0024] According to the present invention, further preferably, the process conditions are as follows:

[0025] The reaction chamber pressure is 25 Torr;

[0026] Growth temperature 810℃;

[0027] According to the present invention, preferably, the metal organic tantalum source is tantalum ethoxide (TaC 10 H 25 O5), the oxidizing gas is oxygen.

[0028] According to the present invention, preferably, the substrate is a hexagonal lanthanum fluoride single crystal sheet with a crystal plane of LaF3(0001).

[0029] According to the present invention, the Ta2O5 obtained by the above preparation method is a single crystal thin film with a hexagonal structure, and the growth plane of the hexagonal Ta2O5 is the (0001) plane of the hexagonal Ta2O5.

[0030] The hexagonal Ta2O5 single crystal thin film prepared by the present invention has many unique advantages, such as high crystal quality, complete lattice structure, no twins, few defects of the film, and broad application prospects.

[0031] Anything not described in detail in the present invention is prepared and implemented according to the existing technology in the field.

[0032] The hexagonal Ta2O5 film prepared by the present invention has the following advantages compared with the existing Ta2O5 film:

[0033] 1. The hexagonal Ta2O5 film of the present invention is a single crystal film with a hexagonal structure. The growth plane of the hexagonal Ta2O5 film is (0001), and the out-of-plane epitaxial relationship between the film and the substrate is Ta2O5(0001)|LaF3(0001). The in-plane epitaxial relationship is Ta2O5 ‖LaF3

[0034] 2. The hexagonal Ta2O5 single crystal thin film of the present invention has higher insulation properties and is suitable as an insulating dielectric material for manufacturing high-performance semiconductor devices, which is beneficial to reducing the leakage current of the device.

[0035] 3. The hexagonal Ta2O5 thin film of the present invention has a complete single crystal structure, free of twins, and minimal lattice defects, which facilitates improved doping efficiency. This provides high-quality single crystal films for future research into enhancing the electrical properties of hexagonal Ta2O5 through doping. This provides strong support for the application of hexagonal Ta2O5 single crystal thin films in semiconductor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the X-ray θ-2θ scanning diffraction pattern of the hexagonal Ta2O5 single crystal thin film prepared in the present invention, wherein the abscissa is 2θ (degrees) and the ordinate is intensity (arbitrary unit).

[0037] Figure 2 This is the rocking curve of the (0001) X-ray diffraction peak of the hexagonal Ta2O5 single crystal thin film prepared in the present invention, where the horizontal axis is ω (degrees) and the vertical axis is intensity (arbitrary unit).

[0038] Figure 3 Typical X-ray in-situ Φ scanning patterns of hexagonal Ta2O5 single crystal thin films and substrates prepared in this invention, where (a) is a LaF3 substrate Diffraction spectrum of the surface, (b) is the hexagonal Ta2O5 film The diffraction spectrum of the surface. Wherein, the horizontal axis is Φ (degrees) and the vertical axis is intensity (arbitrary unit).

[0039] Figure 4 This is a high-resolution transmission electron microscope (HRTEM) pattern of the hexagonal Ta2O5 single crystal thin film prepared by the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to examples and comparative examples, but is not limited thereto.

[0041] A method for preparing a hexagonal tantalum pentoxide single crystal thin film, the specific preparation method is as follows:

[0042] Step (1) turning on the high vacuum MOCVD equipment, evacuating the reaction chamber to a high vacuum state, placing the cleaned LaF3 single crystal substrate on the reaction chamber base and heating it to the growth temperature;

[0043] Step (2) Open the valve of the nitrogen bottle and introduce N2 into the reaction chamber with a pressure of 10 to 40 Torr;

[0044] Step (3) opening the oxygen cylinder valve and adjusting the oxygen flow;

[0045] Step (4) opening the valve of the tantalum ethoxide source bottle and adjusting the flow rate of the tantalum ethoxide source;

[0046] Step (5) The gases from steps (3) and (4) are introduced into the reaction chamber simultaneously to start growing the film, and the growth time is determined according to the required film thickness;

[0047] Step (6) Close the valves of the tantalum ethanol source bottle and the oxygen bottle to terminate the reaction; flush the pipeline with nitrogen and then cool naturally. In this way, a hexagonal Ta2O5 single crystal thin film is prepared.

[0048] Example 1:

[0049] Hexagonal Ta2O5 thin film material was prepared by MOCVD technology using hexagonal LaF3 (0001) single crystal as substrate, tantalum ethoxide as metal organic source, ultra-high purity nitrogen as carrier gas, and high purity oxygen as oxidizing gas.

[0050] Here are the steps:

[0051] (1) The MOCVD reaction chamber is evacuated to a high vacuum state with a vacuum degree of 2×10 -4 Pa, LaF3 single crystal substrate is placed in the reaction chamber and heated to 810℃;

[0052] (2) Open the nitrogen bottle valve and introduce background nitrogen into the reaction chamber. The reaction chamber pressure is 25 Torr.

[0053] (3) Open the oxygen cylinder valve and adjust the oxygen flow rate to 55 sccm;

[0054] (4) Open the valve of the metal organic source bottle and adjust the flow rate of tantalum ethoxide to 3.0×10 -6 mol / min;

[0055] (5) The oxygen gas from step (3) and the tantalum ethoxide from step (4) were introduced into the reaction chamber simultaneously for 180 minutes; a hexagonal Ta2O5 thin film was grown on a LaF3(0001) substrate;

[0056] (6) After the reaction is completed, close the valves of the metal organic source bottle and the oxygen bottle, flush the pipeline with nitrogen, and then cool it down naturally.

[0057] The film prepared in Example 1 is a hexagonal Ta2O5 single crystal film, and the growth plane of the film is Ta2O5(0001). The out-of-plane epitaxial relationship between the film and the substrate is Ta2O5(0001)|LaF3(0001), and the in-plane epitaxial relationship is Ta2O5 ‖LaF3 The prepared hexagonal Ta2O5 epitaxial single crystal film has a complete lattice structure and no twin structure exists.

[0058] The X-ray θ-2θ scanning diffraction pattern of the Ta2O5 single crystal film prepared by the present invention is as follows: Figure 1 The two diffraction peaks of the film are located at 22.92° and 46.95°, corresponding to the diffraction peaks of the hexagonal Ta2O5 (0001) and (0002) planes (JCPDS NO.19–1299), indicating that the prepared film has a hexagonal Ta2O5 structure and the growth plane is (0001).

[0059] The rocking curve of the (0001) X-ray diffraction peak of the hexagonal Ta2O5 single crystal film prepared by the present invention is as follows: Figure 2 The half-height width of the diffraction peak is only 0.7° and has good symmetry, indicating that it is a high-quality single crystal film.

[0060] The single crystal thin film Ta2O5 prepared by the present invention Surface and substrate LaF3 Typical patterns of X-ray in-situ Φ scanning of the surface are as follows Figure 3 As shown. Ta2O5 Surface and substrate LaF3 The diffraction peak positions are the same and correspond one to one. Therefore, it can be determined that the out-of-plane epitaxial relationship between the film and the substrate is hexagonal phase Ta2O5(0001)‖LaF3(0001), and the in-plane epitaxial relationship is Ta2O5 LaF3 And there is no twin structure in the film.

[0061] The high-resolution transmission electron microscopy (HRTEM) pattern of the hexagonal Ta2O5 single crystal thin film prepared by the present invention is as follows: Figure 4 The figure shows that the lattice of the Ta2O5 single crystal film is neatly arranged, and the relevant crystal planes and angles of the film are marked in the figure, further proving that the Ta2O5 single crystal film obtained by the present invention has a hexagonal structure.

[0062] Example 2:

[0063] A hexagonal Ta2O5 thin film was prepared using MOCVD technology. The substrate materials and film preparation process were the same as in Example 1, except that the preparation temperature was 860°C. The resulting hexagonal Ta2O5 thin film had the same growth surface and lattice structure as in Example 1. However, compared with Example 1, the film's crystalline quality was slightly reduced, and the film roughness was significantly increased.

[0064] Example 3:

[0065] Hexagonal Ta2O5 thin films were prepared using MOCVD technology. The substrate materials and film preparation process were the same as in Example 1, except that the growth temperature was 760°C. The resulting hexagonal Ta2O5 thin film had the same growth surface and lattice structure as in Example 1. However, compared with Example 1, the crystalline quality of the film was significantly reduced due to the lower substrate temperature.

[0066] Example 4:

[0067] Ta2O5 thin films were prepared using MOCVD technology. The substrate materials and film preparation process were the same as in Example 1, except that the growth temperature was 660°C. Because the temperature required for film crystallization was not reached, no distinct X-ray diffraction peaks were observed in the prepared film, indicating that the film did not form a distinct crystalline structure.

[0068] Comparative Example 1:

[0069] The substrate materials and film preparation process conditions used are the same as those described in Example 1, except that a yttrium-doped zirconium oxide (YSZ, cubic structure) single crystal wafer with a (111) crystal plane is used as the substrate, and the film growth temperature is 800°C. The prepared Ta2O5 film is a hexagonal Ta2O5 epitaxial film, and the epitaxial growth plane of the film is hexagonal Ta2O5 (0001) ‖ cubic YSZ (111), and the epitaxial relationship in the plane is Ta2O5 ‖YSZ Since the cubic YSZ substrate and the hexagonal Ta2O5 film have different lattice structures, the prepared hexagonal Ta2O5 film has a double twin structure.

[0070] Comparative Example 2:

[0071] The film preparation process conditions are the same as those described in Example 1, except that a C-plane sapphire (α-Al2O3) (0001) single crystal was used as the substrate material and the growth temperature was 750°C. The Ta2O5 film prepared was a hexagonal Ta2O5 epitaxial film, and the epitaxial growth surface of the film was Ta2O5. The epitaxial relationship of the surface is Ta2O5 ‖Al2O3 The film has a triple domain structure and twins exist in the film.

[0072] Comparative Example 3:

[0073] The film preparation process conditions used were the same as those described in Comparative Example 2, except that the substrate used was a gallium nitride epitaxial wafer (epi-GaN / α-Al2O3) with a GaN epitaxial plane (0001), and the Ta2O5 film was grown at a temperature of 850°C. The prepared Ta2O5 film was an orthorhombic Ta2O5 epitaxial film with an orthorhombic Ta2O5 (001) growth plane. Twins were present in the film, demonstrating a triple twin structure.

[0074] Comparative Example 4:

[0075] The film preparation process conditions were the same as those described in Example 1, except that a tetragonal yttrium vanadate (YVO4)(100) single crystal was used as the substrate and the growth temperature was 850°C. The prepared Ta2O5 film had a hexagonal structure and a Ta2O5 (0001) growth plane, but contained a triple twin structure.

Claims

1. A method for preparing a hexagonal tantalum pentoxide single crystal thin film, characterized by: Using organic metal chemical vapor deposition process, tantalum ethoxide TaC 10 H 25 Hexagonal tantalum pentoxide single crystal thin films were grown on lanthanum fluoride substrate wafers using MOCVD equipment, using O5 as a metal organic source, nitrogen as a carrier gas, and oxygen as an oxidizing gas. The specific preparation steps are as follows: Step (1) turning on a high vacuum MOCVD device and evacuating the reaction chamber to a high vacuum state; placing an ultrasonically cleaned lanthanum fluoride LaF3 (0001) surface single crystal substrate on a substrate base in the reaction chamber and heating it to a growth temperature; Step (2) setting the reaction chamber pressure, opening the nitrogen bottle valve, introducing background N2 into the reaction chamber and maintaining a stable flow rate; Step (3) opening the oxygen cylinder valve, adjusting the oxygen flow and keeping the flow stable; Step (4) opening the valve of the tantalum ethoxide source bottle, adjusting the flow rate of the tantalum ethoxide vapor and keeping the flow rate stable; Step (5) The oxygen gas of step (3) and the tantalum ethoxide vapor of step (4) are simultaneously introduced into the reaction chamber; the growth rate of the Ta2O5 thin film on the epitaxial substrate is 0.2 to 1.2 nm / min; After the reaction in step (6) is completed, the valves of the tantalum ethanol source bottle and the oxygen bottle are closed, the pipeline is flushed with nitrogen, the valve of the nitrogen bottle is closed, and the temperature is naturally lowered; a hexagonal Ta2O5 single crystal thin film is prepared; The hexagonal Ta2O5 single crystal film is a Ta2O5 single crystal film with a single phase of hexagonal structure; The growth substrate of the hexagonal Ta2O5 single crystal thin film is a lanthanum fluoride (LaF3) (0001) surface substrate single crystal; The out-of-plane and in-plane epitaxial relationships of the hexagonal Ta2O5 film and the LaF3 substrate are hexagonal Ta2O5(0001)||LaF3(0001) and hexagonal The process conditions are as follows: The reaction chamber pressure is 20 Torr; Growth temperature 850℃; Background N2 flow rate 120 sccm; Oxygen flow rate 50 sccm; Tantalum ethoxide flow rate 3.1×10 -6 mol / min; The metal organic tantalum source is tantalum ethoxide TaC 10 H 25 O5, the oxidizing gas is oxygen; the substrate is a lanthanum fluoride (LaF3) (0001) surface substrate single crystal; The Ta2O5 obtained by the above preparation method is a single crystal thin film with a hexagonal structure, and the growth plane of the hexagonal Ta2O5 is the (0001) plane of the hexagonal Ta2O5.

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