N-type doped tantalum pentoxide film and preparation method thereof

Abstract

The invention discloses an n-type doped tantalum pentoxide film and a preparation method thereof, and belongs to the technical field of optoelectronic information functional materials. The tungsten-doped tantalum pentoxide film is prepared on a substrate by using tantalum ethoxide as an organic metal compound material, tungsten hexacarbonyl as a doping source and high-purity oxygen as an oxidizing gas and adopting metal organic chemical vapor deposition equipment. The prepared tungsten-doped tantalum pentoxide thin film material has good n-type semiconductor characteristics, so that the tungsten-doped tantalum pentoxide thin film material has good application prospects in the field of semiconductor devices.

Description

Technical Field

[0001] The present invention relates to a doped tantalum pentoxide thin film and a preparation method thereof, belonging to the technical field of semiconductor optoelectronic materials. Background Art

[0002] With the continuous development of semiconductor device technology, wide bandgap oxide semiconductor materials have attracted increasing attention and are developing towards wide bandgap, high breakdown voltage and high dielectric constant. In recent years, oxides with larger bandgaps such as gallium oxide, hafnium oxide and tantalum oxide have become popular materials after indium oxide, tin oxide and zinc oxide. Wide bandgap oxide materials can be used in the manufacture of flat panel displays, thin film solar cells, transparent thin film transistors, photodetectors and high-voltage power devices, etc.

[0003] Tantalum pentoxide (Ta2O5) commonly has hexagonal, tetragonal, orthorhombic and amorphous structures, and has advantages such as wide bandgap (3.9 - 4.5 eV), high dielectric constant (20 - 22) and good corrosion resistance, and is a very promising multifunctional material. It has been studied and applied in the fields of electrochemistry, biochemical sensors and photocatalysis, etc. Due to the high dielectric constant, Ta2O5 has very important application value as an insulating dielectric material in the fields of thin film transistors, field effect transistors and supercapacitors, etc.

[0004] The crystalline forms of Ta2O5 thin films can be amorphous, polycrystalline and single crystal structures. For example: amorphous and nanocrystalline Ta2O5 thin films [Optical Materials, 97(2019)109404; Journal of Applied Physics, 114, 8(2013)083515], Ta2O5 epitaxial thin films [Ceramics International, 47(2021)5510 - 5514, Materials Science in Semiconductor Processing, 135(2021)106065]. The bulk single crystal materials have also been reported. For example: tetragonal Ta2O5 [publication number CN201110257469.X]. Intrinsic Ta2O5 thin films are usually insulating materials and cannot be used as active layers in semiconductor devices.

[0005] Currently, there are the following problems in the preparation of doped Ta2O5 thin films:

[0006] (1) Most of the current doping studies on Ta2O5 are aimed at improving the photocatalytic and luminescence properties of this material [Visible Light Sensitive Photocatalysts, Nitrogen-Doped Ta2O5 Powders, J. Phys. Chem. B, 108, 40(2004)15803–15807; Fabrication and evaluation of green-light emitting Ta2O5:Er,Ce co-sputtered thin films, Results in Physics, 5(2015)78-79], while there are very few research reports on regulating the electrical properties of Ta2O5 materials through doping.

[0007] (2) Since tantalum atoms in Ta2O5 thin films exist in the form of a +5 high valence state, it is very difficult to obtain a good n-type doping effect when doping with elements below valence 5. Taking tin atoms as an example, if Sn +4 ions exist in the Ta2O5 thin film lattice in a substitutional form, it is an acceptor doping, but if Sn exists in the lattice in the form of interstitial atoms, it is a donor doping. Therefore, the self-compensation effect is serious when doping Ta2O5 thin films with tin.

[0008] (3) Although the structure of Ta2O5 material is similar to that of gallium nitride and silicon carbide, its bandgap width is higher and its breakdown voltage is also higher. Therefore, it is a very promising wide-bandgap semiconductor material. However, due to the lack of research on doping and electrical control of Ta2O5 thin films, its application in semiconductor devices is limited.

[0009] In summary, finding effective elements suitable for n-type doping of Ta2O5 thin film materials, improving the conductivity of the thin film, and developing and preparing n-type Ta2O5 semiconductor thin films are of great significance for the preparation of Ta2O5-based semiconductor devices. For this reason, the present invention is proposed. Summary of the Invention

[0010] Aiming at the deficiencies of the prior art, the present invention provides a method for preparing a tungsten-doped tantalum pentoxide n-type semiconductor thin film based on metalorganic chemical vapor deposition technology.

[0011] Term Explanation:

[0012] MOCVD: Metalorganic Chemical Vapor Deposition, which is a conventional technology for preparing epitaxial single crystal thin films in this field.

[0013] Doping concentration (%): The atomic ratio of X / (Ta+X), where X is the number of doping atoms and Ta is the number of tantalum atoms.

[0014] The present invention prepares a tungsten-doped tantalum pentoxide n-type semiconductor thin film by metalorganic chemical vapor deposition (MOCVD). The Ta2O5-doped thin film is prepared by MOCVD technology, which is suitable for the epitaxial growth and deposition of thin films. Using commercially available tantalum ethoxide (C 10 H 25 O5Ta) as the metalorganic compound raw material, ultra-high purity nitrogen as the carrier gas for the metalorganic source, high-purity oxygen as the oxidation gas, and tungsten hexacarbonyl (W(CO)6) and tungsten-containing compounds that can be used for chemical vapor deposition as the doping source, a tungsten-doped tantalum pentoxide n-type semiconductor thin film is prepared on a substrate by a metalorganic chemical vapor deposition device. Under optimized preparation process conditions, tantalum pentoxide thin films with different doping concentrations are obtained, among which the doping concentration range of tungsten is 0.1-10.0%. The present invention has successfully prepared a tungsten-doped tantalum pentoxide n-type semiconductor single crystal thin film with good electrical properties by selecting preferred raw materials and single crystal substrates and optimizing the preparation process conditions.

[0015] The technical solution of the present invention is as follows: A method for preparing an n-type doped tantalum pentoxide thin film, using tungsten as the doping element. The chemical composition of the tungsten-doped tantalum pentoxide thin film prepared by this preparation method is Ta2O5:W, wherein the tungsten doping concentration is 0.1-10.0%, and the specific preparation method adopts the MOCVD process for preparing oxide thin films.

[0016] The specific preparation method is as follows:

[0017] According to the present invention, a clean commercial wafer is selected as the substrate wafer.

[0018] According to the present invention, preferably, the temperature for growing the Ta2O5 thin film by the MOCVD method is 760-860 °C;

[0019] According to the present invention, for the above method for preparing the Ta2O5 thin film by the MOCVD method, using TaC 10 H 25 O5 as the metalorganic compound raw material, nitrogen as the carrier gas, oxygen as the oxidation gas, and tungsten hexacarbonyl as the doping source, a doped Ta2O5 thin film is grown on the substrate wafer, and a Ta2O5 thin film is obtained at a suitable growth temperature and on the substrate.

[0020] According to the present invention, for the MOCVD method for preparing the Ta2O5 thin film, the process conditions are as follows:

[0021] The reaction chamber pressure is 10-45 Torr;

[0022] The growth temperature is 700-900 °C;

[0023] The background N2 flow rate is 80-160 sccm;

[0024] The oxygen flow rate is 30 - 70 sccm;

[0025] Tantalum ethoxide TaC 10 H 25 The flow rate of H -6 O5 is 1.0×10 -6 - 6.0×10

[0026] The flow rate of tungsten hexacarbonyl is 1×10 -9 - 6×10 -7 mol / min;

[0027] The growth rate of the Ta2O5 film is 0.2 - 1.2 nm / min.

[0028] According to the present invention, the metal - organic tantalum source is tantalum ethoxide (TaC 10 H 25 O5), the oxidation gas is oxygen, and tungsten hexacarbonyl is the doping source.

[0029] According to the present invention, the Ta2O5 obtained by the above - mentioned preparation method is a tungsten - doped film.

[0030] For those not detailed in the present invention, the preparation and implementation are carried out according to the existing technologies in the art.

[0031] The Ta2O5 - doped film prepared by the present invention has the following excellent effects compared with the existing Ta2O5 film:

[0032] 1. The Ta2O5 - doped film of the present invention has n - type semiconductor properties, is suitable as a semiconductor active material for manufacturing high - performance semiconductor devices, and is beneficial to improving the anti - irradiation characteristics, breakdown voltage characteristics, and ultraviolet photoelectric response of the devices.

[0033] 2. Under the condition of selecting appropriate substrates and growth conditions, the Ta2O5 - doped film of the present invention can obtain a single - crystal film with a complete crystal structure and few lattice defects, which is beneficial to improving the doping efficiency, provides a high - quality single - crystal film for the research on improving the electrical properties of Ta2O5, and provides strong support for the application of Ta2O5 single - crystal film in semiconductor devices.

[0034] 3. The process scheme of the Ta2O5 - doped film of the present invention is suitable for large - area and low - cost industrial preparation. Description of the Drawings

[0035] Figure 1 It is the X - ray diffraction θ - 2θ scanning pattern of the 2.0% - doped δ - Ta2O5:W film prepared in Example 1 of the present invention. Among them, the abscissa: 2θ (degree), the ordinate: intensity (arbitrary unit).

[0036] Figure 2The rocking curve of the X-ray diffraction peak of the (0001) plane of the 2.0% doped δ-Ta2O5:W film prepared in Example 1 of the present invention. Among them, the abscissa: ω (degree), the ordinate: intensity (arbitrary unit).

[0037] Figure 3 The high-resolution transmission electron microscopy (HRTEM) pattern of the 2.0% doped δ-Ta2O5:W film prepared in Example 1 of the present invention. The out-of-plane epitaxial relationship between the film and the substrate is

[0038] Figure 4 The Ta 4f and W 4f core-level X-ray photoelectron spectra of the 2.0% doped δ-Ta2O5:W film prepared in Example 1 of the present invention. Among them, the abscissa: energy (eV), the ordinate: intensity (arbitrary unit). Detailed implementation manners

[0039] The present invention will be further described below in conjunction with examples and comparative examples, but not limited thereto.

[0040] A preparation method of a tungsten-doped tantalum pentoxide n-type semiconductor film is as follows:

[0041] Step (1): Turn on the high-vacuum MOCVD equipment, evacuate the reaction chamber to a high-vacuum state, place the cleaned substrate on the reaction chamber base and heat it to the growth temperature;

[0042] Step (2): Open the nitrogen cylinder valve, introduce N2 into the reaction chamber, and the pressure in the reaction chamber is 10-40 Torr;

[0043] Step (3): Open the oxygen cylinder valve and adjust the oxygen flow rate;

[0044] Step (4): Open the tantalum ethoxide source bottle valve and adjust the tantalum ethoxide source flow rate;

[0045] Step (5): Open the tungsten hexacarbonyl source bottle valve and adjust the tungsten hexacarbonyl source flow rate;

[0046] Step (6): Simultaneously introduce the gases in steps (3), (4) and (5) into the reaction chamber to start growing the film, and determine the growth time according to the required film thickness;

[0047] Step (7): Close the valves of the tantalum ethoxide, tungsten hexacarbonyl source bottle and oxygen cylinder, and the reaction ends; after flushing the pipeline with nitrogen, cool down naturally. Thus, the tungsten-doped Ta2O5 film is prepared.

[0048] According to the present invention, the Ta2O5:W film is obtained by the above preparation method and process conditions. By adjusting the flow rates of different organic sources, Ta2O5:W films with different tungsten doping concentrations can be prepared.

[0049] Example 1:

[0050] Using a LaAlO3(010) single crystal wafer as the substrate, tantalum ethoxide as the metal organic source, ultra-high purity nitrogen as the carrier gas, high purity oxygen as the oxidation gas, and tungsten hexacarbonyl as the doping source, a hexagonal single crystal Ta2O5 doped thin film material was prepared by MOCVD technology.

[0051] The steps are as follows:

[0052] (1) The MOCVD reaction chamber was evacuated to a high vacuum state with a vacuum degree of 2×10 -4 Pa, and the LaAlO3(010) single crystal substrate was placed in the reaction chamber and heated to 810 °C;

[0053] (2) Open the valve of the nitrogen gas cylinder, introduce background N2 into the reaction chamber, and the pressure in the reaction chamber is 25 Torr;

[0054] (3) Open the valve of the oxygen gas cylinder and adjust the oxygen flow rate to 55 sccm;

[0055] (4) Open the valve of the tantalum organic source bottle and adjust the flow rate of tantalum ethoxide to 3.0×10 -6 mol / min;

[0056] (5) Open the valve of the tungsten organic source bottle and adjust the flow rate of tungsten hexacarbonyl to 6.1×10 -8 mol / min;

[0057] (6) Simultaneously introduce the oxygen in step (3), tantalum ethoxide in step (4), and tungsten hexacarbonyl in step (5) into the reaction chamber and keep for 180 minutes; grow a hexagonal Ta2O5 thin film on the LaAlO3(010) substrate;

[0058] (8) After the reaction is completed, close the valves of the tantalum organic source bottle and the oxygen gas bottle, flush the pipeline with nitrogen and then cool down naturally.

[0059] The thin film prepared in this Example 1 is a hexagonal Ta2O5 single crystal tungsten doped thin film, and the out-of-plane epitaxial relationship between the thin film and the substrate is The lattice structure of the prepared hexagonal Ta2O5 epitaxial single crystal thin film is complete.

[0060] The X-ray θ~2θ scanning diffraction pattern of the Ta2O5 single crystal thin film prepared by the present invention is as Figure 1 shown. The two diffraction peaks of the thin film are respectively located at 28.36 ° and 58.53 ° °, corresponding to the diffraction peaks of the hexagonal and planes (JCPDS NO.19–1299), indicating that the prepared thin film is of hexagonal Ta2O5 structure and the growth plane is

[0061] The rocking curve of the X-ray diffraction peak of the tungsten-doped hexagonal Ta2O5 single-crystal doped film prepared by the present invention is as Figure 2 shown. The full width at half maximum of this diffraction peak is 0.72°, and it has good symmetry, indicating that it is a high-quality single-crystal film.

[0062] The high-resolution transmission electron microscopy (HRTEM) pattern of the hexagonal Ta2O5 single-crystal tungsten-doped film prepared by the present invention is as Figure 3 shown. The figure shows that the lattice of the Ta2O5 single-crystal film is neatly arranged, and the growth plane of the δ-Ta2O5 film is which further proves that the Ta2O5 single-crystal film obtained by the present invention is of a hexagonal structure.

[0063] The X-ray photoelectron spectroscopy (XPS) tantalum and tungsten characteristic peak patterns of the hexagonal Ta2O5 single-crystal doped film prepared by the present invention are as Figure 4 shown. The figure shows that a small amount of tungsten element is contained in the doped film, indicating that the doping preparation of tungsten element has been successfully achieved. After calculation, the doping concentration of tungsten is about 2.0%.

[0064] The hexagonal Ta2O5 single-crystal tungsten-doped film prepared by the present invention has n-type semiconductor characteristics. The carrier (electron) mobility measured by Hall test is 1.5 cm 2 / Vs, and the carrier concentration is 1.2×10 15 / cm 3 .

[0065] Example 2:

[0066] The tungsten-doped Ta2O5 single-crystal film is prepared by MOCVD technology. The substrate material and the film preparation process used are the same as those in Example 1, except that the YSZ(111) substrate is used. The prepared film is of the δ phase Ta2O5, and the epitaxial growth plane of the prepared film is hexagonal Ta2O5(0001)∥cubic YSZ(111). The X-ray θ~2θ scanning diffraction pattern shows the Ta2O5(0001) signal peak. The film shows n-type semiconductor characteristics rather than insulating characteristics, and the Hall mobility and carrier concentration can be measured.

[0067] Example 3:

[0068] The tungsten-doped Ta2O5 single-crystal thin film was prepared by MOCVD technology. The substrate material used and the thin film preparation process were the same as those in Example 1, except that the YVO4(100) substrate was used. The prepared thin film was the δ-phase Ta2O5, and the epitaxial growth plane of the prepared thin film was hexagonal Ta2O5(0001)∥cubic YVO4(100). The X-ray θ~2θ scanning diffraction pattern showed the Ta2O5(0001) signal peak. The thin film exhibited n-type semiconductor characteristics rather than insulating characteristics, and the Hall mobility and carrier concentration could be measured.

[0069] Example 4:

[0070] The tungsten-doped Ta2O5 single-crystal thin film was prepared by MOCVD technology. The substrate material used and the thin film preparation process were the same as those in Example 1, except that the sapphire α-Al2O3(0001) substrate was used. The prepared thin film was the δ-phase Ta2O5, and the epitaxial growth plane of the prepared thin film was hexagonal Ta2O5(0001)∥α-Al2O3(0001). The X-ray θ~2θ scanning diffraction pattern showed the Ta2O5(0001) signal peak. The thin film exhibited n-type semiconductor characteristics rather than insulating characteristics, and the Hall mobility and carrier concentration could be measured.

[0071] Example 5:

[0072] The tungsten-doped Ta2O5 single-crystal thin film was prepared by MOCVD technology. The substrate material used and the thin film preparation process were the same as those in Example 1, except that the lanthanum fluoride LaF3(0001) substrate was used. The prepared thin film was the δ-phase Ta2O5, and the epitaxial growth plane of the prepared thin film was hexagonal Ta2O5(0001)∥LaF3(0001). The X-ray θ~2θ scanning diffraction pattern showed the Ta2O5(0001) signal peak. The thin film exhibited n-type semiconductor characteristics rather than insulating characteristics, and the Hall mobility and carrier concentration could be measured.

[0073] Example 6:

[0074] The tungsten-doped Ta2O5 single-crystal thin film was prepared by MOCVD technology. The substrate material used and the thin film preparation process were the same as those in Example 1, except that the epitaxial gallium nitride epi-GaN(0001) substrate was used. The prepared thin film was the orthorhombic (β) phase Ta2O5, and the epitaxial growth plane of the prepared thin film was β-Ta2O5(001)∥GaN(0001). The X-ray θ~2θ scanning diffraction pattern showed the β-Ta2O5(001) signal peak. The thin film exhibited n-type semiconductor characteristics rather than insulating characteristics, and the Hall mobility and carrier concentration could be measured.

[0075] Example 7:

[0076] The tungsten-doped Ta2O5 amorphous thin film is prepared by MOCVD technology. The substrate materials used and the thin film preparation process are the same as those in Example 1, except that a lattice-mismatched substrate is used, including but not limited to silicon oxide, silicon, and glass. Multiple X-ray diffraction peaks of different crystal planes are measured for the prepared Ta2O5 thin film, indicating that the thin film is a polycrystalline structure. The thin film exhibits n-type semiconductor characteristics rather than insulating characteristics, and the Hall mobility and carrier concentration can be measured.

[0077] Example 8:

[0078] The tungsten-doped hexagonal Ta2O5 thin film is prepared by MOCVD technology. The substrate materials used and the thin film preparation process are the same as those in Example 1, except that the growth temperature is 760 °C. The prepared thin film is hexagonal Ta2O5, and the growth plane and lattice structure of the prepared thin film are the same as those in Example 1. However, compared with Example 1, due to the lower substrate temperature, the crystallization quality of the prepared thin film shows an obvious decline.

[0079] Example 9:

[0080] The Ta2O5 thin film is prepared by MOCVD technology. The substrate materials used and the thin film preparation process are the same as those in Example 1, except that the growth temperature is 660 °C. Since the temperature required for thin film crystallization is not reached, no obvious X-ray diffraction peaks are measured for the prepared thin film, indicating that no obvious crystalline structure is formed in the thin film.

Claims

1. A method for preparing an n-type doped tantalum pentoxide thin film, characterized in that: Using the metalorganic chemical vapor deposition process, tantalum ethoxide TaC 10 H 25 O5 is used as the metal organic source, tungsten hexacarbonyl is used as the doping source, nitrogen is used as the carrier gas, oxygen is used as the oxidation gas, and a tungsten-doped Ta2O5 thin film is grown on the substrate using a MOCVD device; The specific preparation steps are as follows: Step (1): Turn on the high-vacuum MOCVD equipment, evacuate the reaction chamber to a high-vacuum state; place the ultrasonically cleaned substrate wafer on the substrate stage in the reaction chamber and heat it to the growth temperature; Step (2): Set the pressure in the reaction chamber, open the valve of the nitrogen gas cylinder, introduce background N2 into the reaction chamber and keep the flow rate stable; Step (3): Open the valve of the oxygen gas cylinder, adjust the oxygen flow rate and keep the flow rate stable; Step (4): Open the valve of the tantalum ethoxide source bottle, adjust the tantalum ethoxide vapor flow rate and keep the flow rate stable; Step (5): Open the valve of tungsten hexacarbonyl, adjust the tantalum ethoxide vapor flow rate and keep the flow rate stable; Step (6): Introduce the oxygen in Step (3), the tantalum ethoxide vapor in Step (4), and the tungsten hexacarbonyl in Step (5) into the reaction chamber; the growth rate of the Ta2O5 thin film on the epitaxial substrate is 0.2 - 1.2 nm / min; Step (7): After the reaction ends, close the tantalum ethoxide source bottle, the doping source valve and the oxygen gas cylinder valve, flush the pipeline with nitrogen and then close the nitrogen gas cylinder valve and let it cool naturally; the doped Ta2O5 thin film is prepared.

2. The preparation method of the n-type doped tantalum pentoxide thin film according to claim 1, wherein: The concentration of the doping element in the Ta2O5 thin film is 0.1% - 10.0%.

3. The preparation method of the n-type doped tantalum pentoxide thin film according to claim 1, characterized in that: For the preparation of the doped Ta2O5 thin film by the MOCVD method, the process conditions are as follows: The pressure in the reaction chamber is 10 - 45 Torr; The growth temperature is 700 - 900 °C; The flow rate of the background N2 is 80 - 160 sccm; The oxygen flow rate is 30 - 70 sccm; Tantalum ethoxide TaC 10 H 25 O5 flow rate 1.0×10 -6 ~6.0×10 -6 mol / min; Tungsten hexacarbonyl flow rate: 1×10 -9 ~6×10 -7 mol / min; The growth rate of the Ta2O5 thin film is 0.2 - 1.2 nm / min.

4. The method for preparing an n-type doped tantalum pentoxide thin film according to claim 1, characterized in that: The process conditions are as follows: The pressure in the reaction chamber is 25 Torr; The growth temperature is 810 °C; The flow rate of the background N2 is 120 sccm; The oxygen flow rate is 55 sccm; The flow rate of tantalum ethoxide is 3.0×10 -6 mol / min; The flow rate of tungsten hexacarbonyl is 6.1×10 -8 mol / min.

5. The preparation method of the n-type doped tantalum pentoxide thin film according to claim 1, characterized in that: The metal-organic tantalum source is tantalum ethoxide TaC 10 H 25 O5, the oxidation gas is oxygen; the doping source is tungsten hexacarbonyl.

6. The preparation method of the n-type doped tantalum pentoxide thin film according to claim 1, wherein: When using single crystals of yttria-stabilized zirconia YSZ(111), lanthanum fluoride LaF3(0001), yttrium vanadate YVO4(100), sapphire α-Al2O3(0001), and lanthanum aluminate LaAlO3(010) as substrates, the grown doped tantalum pentoxide thin film presents a hexagonal crystal single crystal structure. When using sapphire epitaxial gallium nitride epi-GaN / α-Al2O3(0001) as the substrate, the grown doped tantalum pentoxide thin film presents a tetragonal crystal single crystal structure. When using silicon dioxide, silicon, and glass as substrates, the grown doped tantalum pentoxide thin film presents an amorphous structure.

7. The method for preparing an n-type doped tantalum pentoxide thin film according to claim 1, wherein: The thin film exhibits n-type semiconductor characteristics, and the carrier concentration of the thin film is higher than 0.5×10 14 cm -3 .

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