Preparation method of high-quality gallium oxide epitaxial film and gallium oxide film

Abstract

The application relates to the technical field of gallium oxide film preparation, in particular to a preparation method and device of high-quality gallium oxide epitaxial film, the gallium oxide epitaxial film and application thereof, and the preparation method of the high-quality gallium oxide epitaxial film comprises the following steps: preparing a substrate and a plurality of target materials, performing two-stage distributed deposition, forming a high-quality buffer layer by off-axis target material / low-power target material deposition in a first stage, promoting grain growth by coaxial target material / high-power target material in a second stage, and introducing dynamic gas distribution, dynamic substrate rotation, independent magnetic control system and other precise regulation and control deposition process parameters; finally, annealing under an oxygen atmosphere to improve the crystallization quality. The prepared film has high crystallinity, the thickness can reach 10 microns at most, and the film surface uniformity error can be controlled within 2%. The application significantly improves the crystallization quality, uniformity and electrical properties of the film, and provides technical support for semiconductor device application.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material preparation technology, and in particular to a method for preparing high-quality gallium oxide epitaxial thin films through a specific process, as well as gallium oxide thin films obtained therefrom suitable for high-voltage power devices, deep ultraviolet optoelectronic devices and other fields. Background Technology

[0002] Gallium oxide (Ga2O3) is an emerging ultra-wide bandgap semiconductor material with enormous market potential. With its exceptional 4.9 eV bandgap and high breakdown electric field strength of up to 8 MV / cm, gallium oxide significantly surpasses traditional semiconductor materials such as silicon (Si), silicon carbide (SiC), and gallium nitride (GaN).

[0003] The main preparation methods for Ga2O3 nanomaterials or thin films are divided into gas-phase synthesis and liquid-phase synthesis. Gas-phase synthesis includes physical vapor deposition (PVD) techniques (including radio frequency magnetron sputtering (MS); pulsed laser deposition (PLD) and molecular beam epitaxy (MBE)) and chemical vapor deposition (CVD) techniques (including metal-organic chemical vapor deposition (MOCVD); plasma-enhanced chemical vapor deposition (PECVD); mist chemical vapor deposition (Mist-CVD); atomic layer deposition (ALD), etc.).

[0004] Among them, magnetron sputtering (MS) technology is a novel thin-film epitaxial technology developed from conventional physical deposition (PMD) techniques. MS methods offer advantages such as high safety, no need for ultra-high vacuum in the film growth environment, ease of operation, and rapid target fabrication, making them highly promising for material epitaxy. However, existing methods have certain limitations. In traditional one-step magnetron sputtering for gallium oxide thin films, the problem of poor film crystal quality often arises, leading to numerous crystal defects that severely affect the electrical and optical properties of the film. Simultaneously, film uniformity is difficult to guarantee, with significant differences in thickness and performance across different regions, hindering subsequent device integration and applications. Furthermore, existing magnetron sputtering methods have relatively slow growth rates, low production efficiency, and stringent requirements for process parameter control, making operation challenging.

[0005] Therefore, how to effectively decouple the contradictory requirements of the initial nucleation and stable epitaxy stages in the thin film growth process by systematically optimizing the magnetron sputtering process, and fundamentally suppress the generation of crystal defects while ensuring high growth efficiency, so as to obtain high-quality gallium oxide epitaxial films with high crystal quality, smooth surface morphology and uniform performance, has become a key technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The first aspect of this invention addresses a technical problem by overcoming the bottleneck in existing magnetron sputtering technology for preparing gallium oxide epitaxial thin films. This bottleneck stems from the conflicting demands on sputtering energy and particle flux between the initial nucleation stage and the subsequent stable growth stage, making it difficult to simultaneously achieve optimal film crystal quality and growth efficiency. Existing one-step sputtering processes either sacrifice efficiency with low power or sacrifice initial crystal quality with high power, neither of which can fundamentally suppress defect generation.

[0007] To address the aforementioned technical problems, this invention first provides a method for preparing high-quality gallium oxide thin films, the method comprising:

[0008] Step S1: Prepare a pretreated substrate and a plurality of targets opposite the substrate, the plurality of targets including coaxial targets and off-axis targets;

[0009] Step S2: Place the substrate on the substrate stage, close the vacuum chamber, and start the vacuum pump to evacuate the vacuum.

[0010] Step S3: Introduce working gas and deposit a buffer layer on the substrate using an off-axis target;

[0011] Step S4: Deposit the main layer on the buffer layer using a coaxial target;

[0012] Step S5: Cool to room temperature to obtain a high-quality gallium oxide thin film.

[0013] In one embodiment of the present invention, in order to further eliminate defects, optimize the crystal structure of gallium oxide, and eliminate residual inhomogeneities, the obtained high-quality gallium oxide film is subjected to high-temperature annealing in an oxygen or air atmosphere.

[0014] In another embodiment of the present invention, in step S1, the plurality of targets include a first target and a second target, and all targets are coaxial targets. In this case, by precisely controlling the process parameters at each stage in steps S3 and S4, high-quality buffer layer and main layer deposition are achieved. Specifically, in step S3: a working gas is introduced, maintaining the oxygen volume at a first oxygen volume, the substrate rotation speed is set to a first rotation speed, and the sputtering power is set to a first sputtering power; a buffer layer is then deposited on the substrate using the first target.

[0015] Step S4: Keep the oxygen volume at the second oxygen volume, set the substrate rotation speed to the second rotation speed, set the sputtering power to the second sputtering power, and deposit the main layer on the buffer layer using the second target material, wherein the oxygen volume ratio decreases under the second gas distribution, the second rotation speed is greater than the first rotation speed, and the second sputtering power is not less than the first sputtering power.

[0016] In another embodiment of the present invention, in step S1, all of the multiple targets are configured as off-axis targets.

[0017] Furthermore, in step S1, the substrate is selected from sapphire, magnesium oxide, gallium oxide, gallium nitride, silicon, silicon carbide, quartz glass, etc., and the substrate is pretreated by ultrasonic cleaning and drying with water, acetone, and anhydrous ethanol.

[0018] In one embodiment of the invention, after each cleaning with acetone and anhydrous ethanol, the substrate is cleaned again with water. After cleaning, the substrate is dried with nitrogen or placed in a vacuum drying oven for later use.

[0019] Furthermore, in step S1, all of the plurality of targets are gallium oxide ceramic targets with a purity of not less than 99.99%.

[0020] In one embodiment of the present invention, the target material used for depositing the buffer layer in step S3 is different from the target material used for depositing the main layer in step 4. The target material used for depositing the buffer layer includes metallic gallium, aluminum nitride, gallium nitride, and gallium oxide doped with elements such as aluminum, magnesium, silicon, and strontium.

[0021] In another embodiment of the present invention, the plurality of targets are pre-sputtered to clean impurities such as oxides from the target surface, ensuring the purity of the sputtered particle stream.

[0022] Furthermore, in step S2, the vacuum pump is started to evacuate to a vacuum level of 5×10⁻⁶. -4 Below Pa, the preferred 10 -5 Below Pa, it provides a highly clean deposition environment.

[0023] In one embodiment of the present invention, step S3 further includes: depositing a nucleation layer on the substrate before depositing the buffer layer using a coaxial target or a second target. The high-flow-rate particle stream of the coaxial target or a second target with high sputtering power shortens the nucleation time, enabling rapid deposition of an ultrathin, uniform seed layer.

[0024] In one embodiment of the present invention, step S3 further includes: before depositing the main body layer, performing post-treatment on the buffer layer to further repair defects and optimize the structure. The post-treatment includes high-temperature annealing of the buffer layer in oxygen or an inert atmosphere, or chemical mechanical polishing or surface cleaning pretreatment on the surface of the buffer layer.

[0025] Furthermore, when an off-axis target is used in an embodiment of the present invention, an off-axis angle β (°) and an off-axis distance L (cm) are set. The off-axis angle β is the offset distance or tilt angle between the axis of the off-axis target and the normal of the substrate. The value range of β is 5-90°. The off-axis distance L is the distance between the off-axis target and the substrate. The value range of L is usually 1-50. The product of β and L is not less than 30, or not less than 50, or not less than 80.

[0026] A second aspect of the present invention includes providing an apparatus for manufacturing high-quality gallium oxide epitaxial thin films, the apparatus being used to implement the method of the first aspect of the present invention, the apparatus comprising:

[0027] A vacuum chamber, wherein a vacuum pump assembly and a gas supply system are connected to the vacuum chamber, and the gas supply system includes at least one first mass flow controller and a second mass flow controller;

[0028] A substrate stage is disposed in the vacuum chamber. The substrate stage integrates a heating module and a temperature sensing module, and has a rotation function.

[0029] A magnetron sputtering unit, disposed within the vacuum chamber, includes multiple independently controlled targets opposite to the substrate, an RF power supply unit, and a magnetic field control system. The multiple targets include a first target and a second target, and the multiple targets are either off-axis targets or coaxial targets, and a baffle is disposed vertically above the surface of each target. The RF power supply module has a programmable power output function and includes at least one first RF power supply module and one second RF power supply module. The magnetic field control system includes at least one first magnetic field control system and one second magnetic field control system.

[0030] In one embodiment of the present invention, the baffle can be rotated by a rotating mechanism to rotate and shield the unused target material, or the baffle can be temporarily closed to block stray particles when switching targets.

[0031] In one embodiment of the present invention, the multiple targets or the first target of the device are off-axis targets. The offset distance or tilt angle between the axis of the off-axis target and the normal of the substrate constitutes the off-axis angle β, the value of which ranges from 5 to 90°. The distance between the off-axis target and the substrate constitutes the off-axis distance L, the value of which typically ranges from 1 to 50 cm. The product of β and L is such that it is not less than 30, not less than 50, or not less than 80. The present invention, through the layout design of the off-axis targets, utilizes a unique off-axis angle and a specific off-axis distance to form a synergistic effect. This is key to achieving the sputtering of particles at a suitable angle and energy onto the substrate surface, creating conditions for high-quality growth of the buffer layer. This is an important structural feature that distinguishes it from traditional magnetron sputtering equipment.

[0032] According to another aspect of the present invention, a high-quality gallium oxide epitaxial film is also provided, wherein the high-quality gallium oxide epitaxial film is prepared by the method described in the present invention or using the equipment described in the present invention. The thickness of the gallium oxide epitaxial film is approximately 1-10 μm, the thickness uniformity error is within 2%, and the crystal orientation exhibits [specific characteristics]. With preferential crystal plane growth, the full width at half maximum (FWHM) in X-ray diffraction is approximately 1.5°.

[0033] According to another aspect of the present invention, the present invention also provides the application of high-quality gallium oxide epitaxial thin films in the fabrication of high-voltage power devices and deep ultraviolet optoelectronic devices.

[0034] Technical effect

[0035] 1. This invention solves the problems of numerous crystal defects and poor uniformity mentioned in the background art through a multi-target layout structure design. By utilizing a unique off-axis angle and a specific off-axis distance to form a synergistic effect, it can ensure that sputtered particles are incident on the substrate surface at an appropriate angle and energy, reducing damage to the substrate by high-energy particles, creating conditions for high-quality growth of the buffer layer, and also providing a good epitaxial foundation for the main layer.

[0036] 2. The process of first growing a buffer layer off-axis and then growing the main body layer coaxially effectively solves the problems of difficulty in achieving both thin film crystal quality and thickness, numerous interface defects, and an imbalance between efficiency and quality in traditional magnetron sputtering. The buffer layer grown off-axis uses low-energy, multi-angle particles to construct a high-quality crystal template, providing a good epitaxial foundation for the main body layer; coaxial growth achieves rapid thicknessing with high power, and the buffer layer guides the continuous crystallization of the main body layer. Thus, the overall crystal quality of the thin film is improved, interface stress and defects are reduced, and growth efficiency is increased while ensuring quality, achieving efficient preparation of high-quality thick films, and fulfilling the invention's objective of improving the quality and preparation efficiency of gallium oxide thin films.

[0037] 3. The step-by-step control process of the present invention relies on a gradient power output mode, a dynamic gas regulation mechanism, and a dynamic rotating substrate. By precisely controlling process parameters such as sputtering power, oxygen volume ratio in the working gas, and substrate rotation speed during the deposition of the buffer layer and the main layer, the deposition efficiency, stoichiometry, and crystal quality of the thin film are effectively adjusted and optimized, thereby increasing the film thickness and improving large-area uniformity.

[0038] 4. Each of the multiple targets in this invention has an independently controlled magnetron sputtering control system, equipped with an independent power supply and magnetic field control device. These independent control modules can precisely regulate the plasma distribution during the sputtering process. By independently adjusting the power output and magnetic field strength and direction, key parameters such as the energy, trajectory, and deposition rate of sputtered particles can be flexibly adjusted according to different process requirements, ensuring precise control of the buffer layer growth process. Attached Figure Description

[0039] Figure 1 This is a process flow diagram of the gallium oxide epitaxial thin film preparation method in Embodiment 1 of the present invention, which shows the overall steps of the two-stage deposition process.

[0040] Figure 2 shows the gallium oxide epitaxial film in Example 1 of the present invention. Figure 2a A schematic diagram of the gallium oxide epitaxial film structure is shown. Figure 2b A photograph of a gallium oxide epitaxial thin film is shown.

[0041] Figure 3 The X-ray diffraction (XRD) patterns of gallium oxide thin films prepared in Example 1 and the comparative example of the present invention show the epitaxial thin films obtained by the staged deposition process of the present invention and the one-step deposition process in the prior art. Differences in the intensity of characteristic peaks.

[0042] Figure 4 The comparison of surface morphology atomic force microscopy (AFM) images of the thin films in Example 1 of the present invention with those of the comparative example shows a significant improvement in surface roughness of the epitaxial thin films obtained by the staged deposition process of the present invention compared with the one-step deposition process in the prior art.

[0043] Figure 5 This is a process flow diagram of the gallium oxide thin film preparation method in Embodiment 2 of the present invention, showing the overall steps of the three-stage deposition process.

[0044] Figure 6 This is a schematic diagram of the off-axis target layout structure in an embodiment of the present invention.

[0045] Figure 7 This is a schematic diagram of the structure of a power device using a high-quality gallium oxide thin film according to an embodiment of the present invention.

[0046] Embodiments of the present invention

[0047] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0048] In the description of embodiments disclosed herein, it should be understood that terms such as “comprising” or “having” are intended to indicate the presence of the disclosed features, figures, steps, components, portions or combinations thereof in this specification, and do not exclude the possibility of the presence of one or more other features, figures, steps, components, portions or combinations thereof.

[0049] Unless otherwise stated, " / " means "or". For example, A / B can mean A or B. In this article, "and / or" is merely a way of describing the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A alone, A and B at the same time, and B alone.

[0050] The terms "first," "second," etc., are used only for ease of description to distinguish identical or similar technical features and should not be construed as indicating or implying the relative importance or number of these technical features. Therefore, a feature defined by "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, the term "multiple" means two or more. Detailed Implementation

[0051] Figure 1 This is a process flow diagram of a gallium oxide epitaxial thin film preparation method according to the present invention, illustrating the overall steps of a two-stage deposition process. It includes:

[0052] Step S1: Prepare a sapphire substrate. Referring to Figure 2, this substrate will be used to deposit a buffer layer and a host layer. The substrate is then ultrasonically cleaned sequentially with water, acetone, water, anhydrous ethanol, and water for 15-20 minutes, followed by drying in a vacuum drying oven at 80-100°C for 30-40 minutes. After removal, it is placed in a magnetron sputtering growth chamber.

[0053] In this invention, the substrate is selected from sapphire, magnesium oxide, gallium oxide, gallium nitride, silicon, silicon carbide, quartz glass, etc. Different substrate materials have different effects on the adjustment and control of subsequent deposition process parameters.

[0054] Next, prepare two high-purity gallium oxide targets (99.99% purity), one of which will be set as an off-axis target, combined with... Figure 6The off-axis target axis has an offset distance or tilt angle β between it and the substrate normal, defined in this invention as the off-axis angle, with a value ranging from 5 to 90°. The distance between the off-axis target and the substrate is defined as the off-axis distance L, typically ranging from 1 to 50 cm, depending on the actual size of the magnetron sputtering equipment; only a typical example is given here. The product of β and L must be not less than 30, not less than 50, or not less than 80.

[0055] In the sputtering process of gallium oxide epitaxial thin films, the off-axis angle and off-axis distance directly affect the crystal nucleation, growth mode and defect evolution of the thin film by changing the incident direction, energy distribution and flux density of sputtered particles. Ultimately, they have a significant impact on the crystal structure, resulting in thin films with high crystallinity, single preferred orientation, low defect density (dislocations, vacancies, etc.) and stable stoichiometry.

[0056] The off-axis angle mainly controls the incident direction of sputtered particles (the angle between them and the substrate surface), thereby affecting the diffusion behavior of atoms on the substrate surface, the epitaxial matching degree, and defect formation. The control of the off-axis angle is related to the substrate material. Different substrates have different lattice matching degrees with Ga2O3, and the preferred off-axis angles are also different. For example, when using a homogeneous substrate (such as β-Ga2O3(100)), the lattice mismatch is minimal, and a small angle (5°~10°) is preferred. At this time, the tilt of the particle incident direction is small, and atoms are easy to stack in an orderly manner along the substrate lattice, reducing dislocations and point defects and promoting epitaxial growth. When using a heterogeneous substrate (such as sapphire(0001) or SiC(0001)), there is a large lattice mismatch (such as the mismatch degree between sapphire and α-Ga2O3 ≈ 10%), and the angle needs to be appropriately increased to 30°~45°. The tilted incident particles can alleviate the lattice mismatch stress and reduce the dislocation multiplication caused by forced matching through tilted incident. When a non-polar substrate (such as Si(100)) is used, the lattice mismatch is extremely large (>20%), and the angle needs to be further increased to 60°~90°. Local ordered growth is promoted by the lateral diffusion of particles, or by preferential orientation shift, to avoid complete amorphization.

[0057] Off-axis distance primarily controls the sputtering particle flux density (number of particles per unit area) and kinetic energy loss (probability of collision with gas molecules), thereby affecting atomic migration ability and growth rate, ultimately altering crystal grain size, crystallinity, and defect distribution. From the perspective of deposition rate, a deposition rate that is too slow leads to discontinuous growth, while a rate that is too fast results in insufficient atomic diffusion, leading to disordered stacking. In other words, with a small off-axis distance (e.g., L = 1–8 cm), the sputtering particle flux is high, and the deposition rate is fast, but insufficient atomic diffusion time can easily lead to decreased crystallinity. Furthermore, high flux can cause localized overheating, inducing thermal stress defects and dislocations. With a large off-axis distance (e.g., L > 15 cm), the sputtering particle flux is low, the deposition rate is slow, atomic migration ability decreases, and amorphous or nanocrystalline structures are easily formed. In some cases, the low flux can even cause growth interruption, resulting in discontinuous films in an island-like growth mode.

[0058] Furthermore, the off-axis angle and off-axis distance do not act independently; their synergistic regulation has a significant impact on the crystal structure. The off-axis angle, by controlling the particle incident direction, dominates the orientation order and strain state of the crystal. The off-axis distance, by controlling the particle flux and kinetic energy, dominates the crystallinity and grain size of the crystal. In addition, in actual fabrication, the off-axis parameters need to be optimized in conjunction with the substrate type to ultimately obtain gallium oxide epitaxial films with low defects and high orientation.

[0059] Therefore, although β and L can take any value within the relevant numerical range, from the perspective of the core objective of the preparation process, the technical solution proposed in this invention requires that the product of β and L be no less than 30, or no less than 50, or no less than 80. At the same time, the product of β and L is preferably no greater than 900, or no greater than 750, or no greater than 300.

[0060] Secondly, it is set as a coaxial target, that is, there is no or only a very small tilt angle between the axis of the target and the normal of the substrate, such as less than 5° or even less than 2°.

[0061] Two targets are placed opposite the substrate. Simultaneously, physical shielding devices (such as rotating blinds or partitioned baffles) are used to isolate unused target positions when switching targets, preventing cross-contamination and reducing the impact of stray particle flow on film uniformity. In embodiments of the invention, the multiple targets undergo pre-sputtering treatment to clean impurities such as oxides from the target surface, ensuring a pure sputtered atomic flow. Furthermore, the surfaces of the multiple targets undergo special polishing treatment, with a roughness controlled below Ra 0.1 μm to ensure uniform particle release during sputtering.

[0062] In step S2, the substrate is placed on the substrate stage, the vacuum chamber is closed, and the mechanical pump and molecular pump are turned on to evacuate the gas pressure in the growth chamber to below 5 × 10⁻⁶. -4 Pa, or below 10 -5Pa maintains a highly clean sputtering deposition environment.

[0063] The following steps S3 and S4 are the core processes of this invention. In existing magnetron sputtering techniques for preparing gallium oxide thin films, problems often arise regarding poor film crystal quality, uniformity, and the difficulty in balancing growth rate. Simply pursuing a high deposition rate easily leads to numerous crystal defects and compromises film uniformity, severely impacting the electrical and optical properties of the film and hindering subsequent device integration and applications. Conversely, focusing on the quality of the film's crystal structure often results in slow growth rates and low production efficiency. Furthermore, the control of process parameters is demanding, making operation difficult. Through dedicated research and numerous experiments, the inventors of this invention have creatively proposed a two-stage preparation process: off-axis sputtering followed by coaxial sputtering. This process deposits a buffer layer and a main body layer in stages. First, a high-quality buffer layer is formed at a low rate using off-axis sputtering in step S3. Then, a uniform main body layer is rapidly grown at a high rate using coaxial sputtering in step S4, ultimately achieving a balance between deposition rate and crystal quality.

[0064] In step S3, as mentioned above, different substrates have different lattice matching degrees with Ga2O3, requiring the off-axis angle to be set with reference to the substrate material. Off-axis sputtering alters surface migration dynamics through tilted particle incidence, promoting the transition from island growth to step flow mode, optimizing crystal orientation, or suppressing defect formation. This enhances the controllability of thin film structures, making it particularly suitable for the uniform deposition of buffer layers on large-size substrates (such as wafers larger than 4 inches) and meeting stringent requirements for wafer-level uniformity. Furthermore, the off-axis layout effectively avoids the plasma focusing deviation or localized substrate overheating problems of traditional coaxial targets, and can well adapt to complex vacuum cavity constraints or non-standard substrates, such as curved substrates.

[0065] Furthermore, the off-axis angle can be dynamically adjusted based on the growth stage. During the buffer layer deposition stage, the goal is to ensure particles reach the substrate with appropriate direction and energy, allowing atoms sufficient time to accumulate in an orderly manner along the target crystal orientation. Therefore, random nucleation must be suppressed, and a larger angle is preferred. Tilted incident particles can increase surface diffusion time, reduce isolated nucleation, and decrease grain boundary defects.

[0066] Next, the off-axis distance needs to be set. Besides the synergistic effect of off-axis distance and off-axis angle discussed above, and considering the initial distance setting based on the deposition rate, the off-axis distance should also be adjusted based on the gas atmosphere during the actual sputtering process. The pressure of the mixed argon and oxygen sputtering gas and the off-axis distance will further synergistically affect the particle kinetic energy. At lower pressures (0.5–1 Pa), gas molecules are sparse, particle collisions are few, and kinetic energy loss is small. The distance can be appropriately increased to 10–20 cm (to avoid excessively high deposition rates). Otherwise, if the distance is too close, oxygen may be excessively "entrained" into the film due to target sputtering, leading to oxygen enrichment, forming oxygen gaps or gallium vacancies, and inducing lattice distortion. At higher pressures (1–3 Pa), gas molecules are dense, particle collisions are numerous, and kinetic energy loss is large. The distance needs to be shortened to 1–15 cm to reduce excessive kinetic energy loss and ensure atomic diffusion capability. Otherwise, oxygen atoms may be lost due to severe scattering, resulting in Ga-rich films (Ga:O>2:3), inducing Ga interstitial defects and disrupting lattice integrity.

[0067] After setting the off-axis angle and off-axis distance, a mixed working gas of argon and oxygen is introduced, wherein the argon is high-purity argon with a purity of 99.999%. The gas flow rate is adjusted to 10-100 sccm, the volume ratio of argon and oxygen is 1-10, the oxygen volume is maintained at the first oxygen volume, and the gas pressure is adjusted to maintain it at 0.1-10 Pa. The substrate heating power supply and rotation device are turned on, the substrate temperature is set to the first substrate temperature, and the rotation speed is set to the first rotation speed. The power supply and magnetic field control devices of the off-axis sputtering target system are turned on, and the sputtering power is set to the first sputtering power. A buffer layer is deposited on the substrate through the first target material.

[0068] In this embodiment of the invention, the oxygen volume percentage is 20%-30%, and the vacuum chamber pressure is adjusted to 0.5-1.2 Pa. The off-axis sputtering power is set to 80-150 W, the substrate sputtering temperature is maintained at 200-400 °C, the rotation speed is set to 15-40 rpm, and a buffer layer is grown for 10-20 minutes to form a buffer layer with a thickness of 50-200 nm, at a deposition rate of approximately 3-8 nm / min.

[0069] In this invention, the inventors also propose that off-axis parameters and substrate parameters, including substrate temperature and substrate rotation speed, have a synergistic effect. For example, in some embodiments, step S3 involves depositing a buffer layer using an off-axis target. Since the time for particles to reach the substrate is longer, a slightly higher substrate temperature can enhance diffusion, and a slower substrate rotation speed ensures sufficient atomic diffusion. In other embodiments, step S3 can also involve depositing a buffer layer using a coaxial target. In this case, the time for particles to reach the substrate is shorter, allowing for a slightly lower substrate temperature and a slightly higher substrate rotation speed to ensure rapid and uniform growth of the buffer layer.

[0070] After the buffer layer deposition is complete, the off-axis sputtering target system is shut down, and step S4 is executed to turn on the power and magnetic field control devices of the coaxial sputtering target system, setting the sputtering power to the second sputtering power. The substrate temperature is adjusted to the second substrate temperature, and the substrate rotation speed is set to the second rotation speed. The oxygen flow rate in the mixed gas is adjusted to maintain the oxygen volume at the second oxygen volume, and the host layer is deposited on the buffer layer using the coaxial target. The structural schematic and appearance of the obtained gallium oxide epitaxial film are shown in the figure. Figure 2a and Figure 2b As shown. According to the inventors' research, precise dynamic control of the deposition process parameters of the buffer layer and the host layer is crucial for forming high-quality gallium oxide epitaxial films. All parameters, such as target angle, distance from the target, substrate movement, gas ratio, and magnetic field configuration, are deeply interconnected and work synergistically. During sputtering deposition, in-situ monitoring (QCM / RHEED) can be introduced to fine-tune various parameters in real time to correct thickness or composition deviations in a closed-loop manner.

[0071] The goal of step S4 is to achieve rapid deposition of the host layer. Therefore, the second sputtering power should not be less than the first sputtering power, the second substrate temperature should be maintained at least at the level of the first substrate temperature, preferably appropriately increased, and can be adjusted according to actual needs. The second rotation speed should also be greater than the first rotation speed. At the same time, the oxygen volume ratio in the second gas distribution decreases, while the vacuum chamber pressure is adjusted to a higher level.

[0072] In an embodiment of the present invention, when performing step S4, coaxial sputtering growth of the host layer, the coaxial sputtering power is set to 250-400W, and the substrate temperature is maintained at 300-500℃. The gas control system is adjusted to introduce a mixture of argon and oxygen into the coaxial sputtering target area, with oxygen accounting for 10%-20% of the volume, and the vacuum chamber pressure is adjusted to 1.5-2.0 Pa. The substrate stage is kept rotating, with the rotation speed adjustable to 30-60 rpm, for host layer growth. The growth time is set according to the required thickness, generally 60-180 minutes, to form a host layer of the predetermined thickness.

[0073] In some embodiments of the present invention, step S4 can also involve depositing a buffer layer using an off-axis target. In this case, since the deposition of the main layer requires rapid completion and enhanced orientation consistency is necessary, sputtering with an off-axis target involves adjusting the off-axis angle to a smaller angle, further reducing the off-axis distance. This shortens the time it takes for particles to reach the substrate, ensuring that particles can continuously and orderly accumulate along the established crystal orientation, consolidating the dominance of the main crystal orientation, and preventing polymorphism. Furthermore, appropriately increasing the substrate temperature can enhance diffusion, and a faster substrate rotation speed can maintain a faster growth rate.

[0074] The combined design of the staged growth process, off-axis target layout, and substrate motion mechanism of this invention ensures a buffer layer for high-quality crystal structure, providing a foundation for the growth of the epitaxial host layer. Simultaneously, by optimizing the atomic diffusion path and balancing the atomic flux distribution, it compensates for plasma divergence distribution and target etching raceway effects, eliminating the inherent gradient of thicker center and thinner edge, significantly improving film thickness uniformity, and minimizing wafer-level thickness deviation. Figure 3 As can be seen, the method of this invention can grow high-quality gallium oxide epitaxial films on 4-inch substrates, with higher gallium oxide characteristic peak intensities and narrower half-widths, indicating superior crystal quality and better crystal integrity compared to films prepared by traditional magnetron sputtering methods. Figure 2b and Figure 4 The gallium oxide epitaxial film has a diameter of up to 4 inches and a thickness of up to 10 μm, which can meet the requirements of thick film devices and the requirements of wafer-level thickness uniformity. The surface roughness of the film is 2.19 nm and the thickness uniformity deviation is <2%.

[0075] In some embodiments of the present invention, the target material used for depositing the buffer layer in step S3 is different from the target material used for depositing the main layer in step S4. The target material used for depositing the buffer layer may include metallic gallium, aluminum nitride, gallium nitride, or gallium oxide doped with elements such as aluminum, magnesium, silicon, and strontium. The selection of the buffer layer material is mainly based on two requirements: first, the substrate material. If the substrate has a large lattice mismatch with the target gallium oxide phase (such as β-Ga2O3), such as silicon or quartz substrates, a gallium metal buffer layer can be annealed to convert it into gallium oxide. Alternatively, a transition layer with a closer lattice constant can be introduced, such as depositing an AlN buffer layer on a sapphire or silicon substrate. Such buffer layers can effectively reduce interfacial stress, promote the growth of the subsequent epitaxial main layer, reduce island nucleation, and indirectly improve deposition uniformity and rate. Second, electrical performance optimization. Doped gallium oxide thin films can effectively regulate crystal properties and improve deposition kinetics. Introducing trace dopants (such as Si, Sn, or Mg) into the buffer layer can optimize atomic adsorption and migration behavior by changing the surface energy or defect state density, thereby promoting rapid and uniform growth of the buffer layer.

[0076] In some embodiments of the present invention, the growth of the buffer layer is also performed in stages, which facilitates more precise control over the crystal quality and film uniformity of the buffer layer. Specifically, before depositing the buffer layer in step 3, a nucleation layer is pre-deposited on the substrate using a coaxial target or a target with higher power. A high-flow-rate particle stream is generated with higher sputtering power, allowing for rapid pre-deposition of an ultrathin nucleation layer under lower gas pressure and substrate stability, shortening the nucleation time and promoting preferred orientation growth (e.g., the (-201) crystal plane of β-Ga2O3). The thickness of the nucleation layer is controlled within the range of 10-50 nm, its function being to reduce the generation of crystal defects during subsequent deposition and to provide a structural basis for the growth of high-quality thin films.

[0077] In one embodiment of the present invention, step S3 further includes: post-treatment of the buffer layer before depositing the host layer. For example, immediately after deposition, high-temperature annealing is performed in an oxygen or inert atmosphere at 500-900°C to promote atomic redistribution, grain coarsening, and stress release, further repairing the microstructure inhomogeneity of the buffer layer and improving its flatness. Alternatively, the surface of the buffer layer can be pre-treated with chemical mechanical polishing or surface cleaning to eliminate nanoscale roughness and particle residue, providing an ultra-flat interface for the host layer and improving uniformity and deposition rate.

[0078] After the main layer is deposited and grown, step S5 is executed to close the coaxial sputtering target system and gas valves, allow the vacuum chamber to cool naturally to room temperature, remove the substrate, and obtain a high-quality gallium oxide thin film.

[0079] In an embodiment of the present invention, in order to further eliminate defects, optimize the crystal structure of gallium oxide, and eliminate residual inhomogeneities, a post-film processing step S6 can be performed, in which the obtained high-quality gallium oxide film is annealed at high temperature in an oxygen or air atmosphere, for example, annealed at 600-800°C for 1-2 hours in an oxygen atmosphere.

[0080] The high-quality gallium oxide epitaxial thin film prepared by the staged deposition process according to the present invention has an optical transmittance of over 80%. It can be used to fabricate high-voltage power devices and deep-ultraviolet optoelectronic devices. See also... Figure 7 , Figure 7 An ultraviolet photodetector fabricated using the high-quality gallium oxide epitaxial thin film of the present invention is demonstrated.

[0081] This invention provides a magnetron sputtering apparatus for fabricating high-quality gallium oxide epitaxial thin films, enabling the growth of a buffer layer via off-axis sputtering followed by the growth of the main layer via coaxial sputtering. The apparatus includes:

[0082] A vacuum chamber is provided, to which a vacuum pump assembly and a gas supply system are connected. The gas supply system includes at least one first mass flow controller and one second mass flow controller. The flow rate of argon is set by the first mass flow controller, and the flow rate of oxygen is set by the second mass flow controller. Thus, the gas supply system can precisely control the flow rate and ratio of sputtering gases such as argon and oxygen, and can provide independent gas paths for off-axis and coaxial sputtering targets respectively, ensuring that the gas environment during the growth of the buffer layer and the main layer does not interfere with each other.

[0083] A substrate stage is disposed within the vacuum chamber. The substrate stage integrates a heating module and a temperature sensing module, and has a rotation function. Its rotation speed can be adjusted within the range of 0-100 rpm to ensure that the substrate can uniformly receive sputtered particles during the growth process. The heating module can achieve precise temperature control from 200-900℃, meeting the substrate temperature requirements of different process stages.

[0084] A magnetron sputtering unit is disposed in the vacuum chamber and includes multiple independently controllable targets opposite to the substrate, an RF power supply unit, and a magnetic field control system.

[0085] In this invention, the plurality of targets includes a first target and a second target. The target used for sputtering and depositing the buffer layer is referred to as the first target, and the target used for sputtering and depositing the main layer is referred to as the second target. In some embodiments, the first target is an off-axis target, and the second target is a coaxial target. Figure 6 The off-axis angle β is defined as the angle or offset between the axis of the first target and the normal to the substrate stage, and β can range from 5° to 90°. The axis of the second target coincides with the normal to the substrate stage. In actual sputtering deposition, this off-axis angle can be adjusted according to the substrate material, substrate movement, substrate temperature, and growth stage. This unique angle design is key to achieving appropriate angle and energy for sputtered particles to be incident on the substrate surface, creating conditions for high-quality growth of the buffer layer. It is an important structural feature that distinguishes it from traditional magnetron sputtering equipment.

[0086] In some embodiments of the present invention, the distance between the off-axis target and the substrate constitutes the off-axis distance L, the value of which is typically in the range of 1-50 cm, wherein the product of β and L is not less than 30, or not less than 50, or not less than 80. The present invention, through the layout design of the off-axis target, utilizes a unique off-axis angle and a specific off-axis distance to form a synergistic effect, enabling the efficient fabrication of high-quality gallium oxide epitaxial films at the wafer level, providing technical support for the industrialization of ultra-wide bandgap semiconductor devices.

[0087] In some embodiments of the present invention, the second target can also be configured as an off-axis arrangement. The advantage of this design is that it can effectively avoid the plasma focusing deviation or local overheating of the substrate caused by traditional coaxial targets, eliminate the inherent gradient of thick center and thin edge, and minimize wafer-level thickness deviation. It is particularly suitable for the uniform deposition requirements of large-area substrates such as curved substrates, constrained by complex vacuum cavities or non-standard substrates, such as curved substrates, for wafers larger than 4 inches.

[0088] In some embodiments of the present invention, the first target can also be configured in a coaxial arrangement. In this case, the time for particles to reach the substrate is shorter, allowing for a suitable reduction in substrate temperature and a suitable increase in substrate rotation speed to ensure rapid and uniform growth of the buffer layer. This method is applicable to standard deposition processes for small-sized substrates.

[0089] According to the inventive concept of the present invention, the multiple targets support in-situ switching mode, with each target position equipped with an electrically operated shielding cylinder and a flip-top baffle perpendicular to the target surface. After buffer layer growth or during segmented buffer layer deposition, without disrupting the vacuum environment, switching to the next target position can be achieved quickly by rotating the shielding component or closing the baffle, reducing the impact of stray atomic flow on film uniformity while maintaining continuous atomic flow to avoid growth interruption and prevent cross-contamination. Furthermore, during target pre-sputtering, rotating the shielding component or closing the baffle can clean impurities from the new target surface, ensuring a pure atomic flow after switching.

[0090] The radio frequency (RF) power module has a programmable power output function and includes at least one first RF power module and one second RF power module. The magnetic field control system includes at least one first magnetic field control system and one second magnetic field control system. The first RF power module and the first magnetic field control system constitute an independent control system for off-axis targets, and the second RF power module and the second magnetic field control system constitute an independent control system for coaxial targets. That is, each target is equipped with a separate RF power supply and a separate magnetic field control system. Equipping each target with these independent control modules enables precise control of the plasma distribution during sputtering. By independently adjusting the power output and magnetic field strength and direction, key parameters such as the energy, trajectory, and deposition rate of sputtered particles can be flexibly adjusted according to different process requirements, ensuring precise control of the growth process of the buffer layer and the main layer.

[0091] According to the inventive concept of this invention, the equipment may further include an automated control unit, which controls the process timing, parameter feedback, and safety interlocks through a PLC or computer system. Through the deep integration of modular mechanical engineering, automated timing control, and innovative target structure layout, it becomes a core piece of equipment for preparing high-speed, uniform gallium oxide buffer layers, facilitating wafer-level mass production of ultra-wide bandgap semiconductor devices.

[0092] The present invention will be further illustrated below through specific embodiments.

[0093] Comparative Example

[0094] A comparative example demonstrates the preparation of gallium oxide epitaxial thin films using a traditional one-step method. This method includes the following steps:

[0095] Step S1: Prepare the target and substrate. The target is a high-purity gallium oxide ceramic bulk target, and the substrate is a sapphire substrate with a (0001) plane.

[0096] Step S2: The substrate is ultrasonically cleaned sequentially with acetone, ethanol and deionized water to remove surface impurities and then dried with high-purity nitrogen.

[0097] Step S3: Sputter the target material onto the substrate using an RF magnetron sputtering device. First, evacuate the reaction chamber, then introduce 99.9% pure argon gas, maintain an Ar flow rate of 10 sccm, keep the substrate temperature at 300℃, adjust the sputtering power to 420W, and the sputtering time to 60min to deposit and grow a gallium oxide layer;

[0098] Step S4: Anneal the sample obtained in step S3 in a tube furnace. The annealing environment is O2 atmosphere, the annealing temperature is 850℃, and the annealing time is 1h to obtain gallium oxide epitaxial film.

[0099] Figure 3 XRD patterns were analyzed to compare the gallium oxide thin films prepared in the example. The results showed that the product obtained by the one-step growth method did not show the (-201) characteristic peak at all, indicating poor crystal quality. Figure 4 b is an atomic force microscopy image of the gallium oxide thin film prepared in comparison. The test results show that the surface roughness of the film obtained by the one-step growth method is about 4.18 nm, and the overall thickness uniformity is poor.

[0100] Example 1

[0101] See Figure 1 The process flow diagram shown is for a gallium oxide epitaxial thin film preparation method, which includes:

[0102] Step S1: Prepare a sapphire substrate. Clean the substrate sequentially with water, acetone, water, anhydrous ethanol, and water using ultrasonic cleaning for 15-20 minutes. Then, dry it in a vacuum drying oven at 80-100℃ for 30-40 minutes. After drying, place it into a magnetron sputtering growth chamber.

[0103] Two high-purity gallium oxide targets (99.99% purity) were prepared. The surfaces of the targets underwent special polishing treatment, with the roughness controlled below Ra 0.1 μm to ensure uniform particle release during sputtering. One target was set as an off-axis target, combined with... Figure 6 From the schematic diagram of the off-axis target layout, the off-axis angle β between the axis of the off-axis target and the normal to the substrate is set to 30°. The off-axis distance L between the off-axis target and the substrate is 10cm. The product of β and L is 300. Alternatively, a coaxial target can be used, i.e., the off-axis angle is 0°. The two targets are placed opposite each other on the substrate stage. The baffle is closed to perform pre-sputtering treatment on the targets to clean impurities such as oxides on the target surface, ensuring the purity of the sputtered atomic stream.

[0104] Step S2: Place the substrate on the substrate stage, close the vacuum chamber, and turn on the mechanical pump and molecular pump to evacuate the gas pressure in the growth chamber to below 5 × 10⁻⁶. -4 Pa maintains a highly clean sputtering deposition environment.

[0105] Step S3: Introduce a mixed working gas of argon and oxygen, wherein the argon is high-purity argon with a purity of 99.999%. Adjust the gas flow rate to 30 sccm, the oxygen volume percentage to 30%, and adjust the vacuum chamber pressure to 0.5-1.0 Pa. Turn on the substrate heating power supply and rotation device to maintain the substrate sputtering temperature at 300-400℃, and set the rotation speed to 15-25 rpm. Turn on the power supply and magnetic field control device of the off-axis sputtering target system, set the sputtering power to 80-120W, and perform buffer layer growth for 10 minutes to form a buffer layer with a thickness of 50 nm, at a deposition rate of approximately 5 nm / min.

[0106] Step S4: Close the baffle above the off-axis target and switch to the coaxial target for host layer sputtering. Set the coaxial sputtering power to 250-300W and maintain the substrate temperature at 400-500℃. Adjust the gas control system to introduce a mixture of argon and oxygen into the coaxial sputtering target area, with oxygen accounting for 20% of the volume. Adjust the vacuum chamber pressure to 1.5-1.8Pa. Keep the substrate stage rotating, with the rotation speed adjustable to 30-45 rpm, to grow the host layer. Set the growth time to 60 minutes to obtain a host layer of the predetermined thickness.

[0107] Figure 2 shows the gallium oxide epitaxial film in Example 1 of the present invention. Figure 2a A schematic diagram of the structure of a gallium oxide epitaxial thin film is shown. It can be seen that the gallium oxide epitaxial thin film of Example 1 includes a buffer layer and an epitaxial host layer formed sequentially on a substrate. Figure 2b A photograph of a gallium oxide epitaxial thin film is shown. Figure 4 This is a comparison of atomic force microscopy (AFM) images of the surface morphology of the thin film in Example 1 of the present invention with that of the comparative example. Figure 4 Image a shows an atomic force microscopy (AFM) image of the thin film from Example 1, indicating a smooth surface with a roughness as low as 2.19 nm. The surface roughness of the thin film in Example 1 is significantly improved. (Combined with...) Figure 2b and Figure 4 The gallium oxide epitaxial film has a diameter of 4 inches and a thickness of approximately 1.2 μm, and meets the requirements for wafer-level thickness uniformity, with a film thickness uniformity deviation of <2%.

[0108] Figure 3 The images show a comparison of X-ray diffraction (XRD) spectra of gallium oxide thin films prepared in Example 1 and the comparative example of this invention. Figure 3 It is evident that the method of this invention can grow high-quality gallium oxide epitaxial films on 4-inch substrates, with higher gallium oxide characteristic peak intensities and narrower half-widths, indicating that the crystal quality is superior to that of films prepared by traditional magnetron sputtering methods, and the crystal integrity is better.

[0109] The high-quality gallium oxide epitaxial thin film prepared by the staged deposition process according to the present invention has an optical transmittance of over 80%. It can be used to fabricate high-voltage power devices and deep-ultraviolet optoelectronic devices. See also... Figure 7 , Figure 7 An ultraviolet photodetector fabricated using the high-quality gallium oxide epitaxial thin film of this invention is demonstrated. The detector comprises a sapphire single crystal substrate with an epitaxial gallium oxide thin film on top, utilizing gallium oxide's natural solar-blind ultraviolet absorption characteristics and ultra-high breakdown field strength (8 MV / cm). Periodically arranged metal ohmic electrodes are formed on the substrate surface through photolithography and etching processes to modulate the light field distribution and enhance light absorption efficiency.

[0110] Example 2

[0111] Figure 5 This is a process flow diagram of the gallium oxide thin film preparation method in Embodiment 2 of the present invention, illustrating the overall steps of the three-stage deposition process, which includes:

[0112] Step S1: Prepare a sapphire substrate. Clean the substrate sequentially with water, acetone, water, anhydrous ethanol, and water using ultrasonic cleaning for 15-20 minutes, then dry it with high-purity nitrogen. Remove the substrate and place it into the magnetron sputtering growth chamber.

[0113] Two high-purity gallium oxide targets (99.99% purity) were prepared. The targets underwent special polishing treatment, with a roughness controlled below Ra 0.1 μm to ensure uniform particle release during sputtering. One target was set as an off-axis target, with an off-axis angle β of 45° between its axis and the substrate normal. The off-axis distance L between the off-axis target and the substrate was 8 cm. The product of β and L was 360°. The second target was set as a coaxial target, with an off-axis angle of 0°. The two targets were placed opposite each other on the substrate stage. The baffle was closed to perform a pre-sputtering treatment on the targets to clean impurities such as oxides from the target surface, ensuring a pure sputtered atomic stream.

[0114] Step S2: Place the substrate on the substrate stage, close the vacuum chamber, and turn on the mechanical pump and molecular pump to evacuate the gas pressure in the growth chamber to below 9 × 10⁻⁶. -4 Pa maintains a highly clean sputtering deposition environment.

[0115] Step S3: Introduce a mixed working gas of argon and oxygen, wherein the argon is high-purity argon with a purity of 99.999%. Adjust the gas flow rate to 50 sccm, the oxygen volume percentage to 20%, and adjust the vacuum chamber pressure to 0.5-1.0 Pa. Turn on the substrate heating power supply and rotation device to maintain the substrate sputtering temperature at 300-400℃, and set the rotation speed to 15 rpm. Turn on the power supply and magnetic field control device of the off-axis sputtering target system, set the sputtering power to 100-150W, and perform buffer layer growth for 20 minutes to form a buffer layer with a thickness of 120 nm, at a deposition rate of approximately 6 nm / min.

[0116] Step S4: Close the baffle above the off-axis target and switch to the coaxial target for host layer sputtering. Set the coaxial sputtering power to 300-400W and maintain the substrate temperature at 400-500℃. Adjust the gas control system to introduce a mixture of argon and oxygen into the coaxial sputtering target area, with oxygen accounting for 10% of the volume. Adjust the vacuum chamber pressure to 1.8-2.0Pa. Keep the substrate stage rotating; the rotation speed can be adjusted to 60rpm. Perform host layer growth, setting the growth time to 180 minutes to obtain a host layer of the predetermined thickness.

[0117] Step S5: Close the coaxial sputtering target system and gas valves, allow the vacuum chamber to cool naturally to room temperature, remove the substrate, and obtain a high-quality gallium oxide thin film.

[0118] Step S6: Anneal the obtained high-quality gallium oxide film at 600-800℃ for 2 hours in an oxygen atmosphere.

[0119] The gallium oxide epitaxial film in Example 2 is similar to that in the previous example, with a diameter of 4 inches and a thickness of approximately 4.8 μm, meeting the requirements for thick-film devices and wafer-level thickness uniformity, with a thickness uniformity deviation of <5%. Due to the annealing treatment, the crystal structure of the film was further optimized. In the X-ray diffraction (XRD) of the gallium oxide film in Example 2, the characteristic peak intensity of gallium oxide was higher and the full width at half maximum (FWHM) was narrower, indicating that the crystal quality was superior to that of films prepared by traditional magnetron sputtering methods, and the crystal integrity was better.

[0120] Example 3

[0121] The gallium oxide thin film preparation method in Example 3 includes the following steps:

[0122] Step S1: Prepare a sapphire substrate. Clean the substrate sequentially with water, acetone, water, anhydrous ethanol, and water using ultrasonic cleaning for 15-20 minutes, then dry it with high-purity nitrogen. Remove the substrate and place it into the magnetron sputtering growth chamber.

[0123] Two high-purity gallium oxide targets (99.99% purity) were prepared. The targets underwent special polishing treatment, with a roughness controlled below Ra 0.1 μm to ensure uniform particle release during sputtering. One target was set as an off-axis target for sputtering the buffer layer, with an off-axis angle β of 45° between its axis and the substrate normal. The off-axis distance L between the target and the substrate was 10 cm. The product of β and L was 360°. The second target was also set as an off-axis target with an off-axis angle of 5° and an off-axis distance of 6 cm. The two targets were placed opposite each other on the substrate stage. The baffle was closed to perform a pre-sputtering treatment on the targets to clean impurities such as oxides from the target surface, ensuring the purity of the sputtered atomic stream.

[0124] Step S2: Place the substrate on the substrate stage, close the vacuum chamber, and turn on the mechanical pump and molecular pump to evacuate the gas pressure in the growth chamber to below 10. -5 Pa maintains a highly clean sputtering deposition environment.

[0125] Step S3: Introduce a mixed working gas of argon and oxygen, wherein the argon is high-purity argon with a purity of 99.999%. Adjust the gas flow rate to 30 sccm, with oxygen comprising 30% by volume, and maintain the total gas pressure between 0.5 and 0.8 Pa. Turn on the substrate heating power supply and the rotation device to maintain the substrate sputtering temperature at 150-200℃ and the rotation speed at 15 rpm. Turn on the power supply and magnetic field control device of the off-axis sputtering target system, and set the sputtering power to 250W. Under these conditions, a dense nucleus layer will rapidly form on the substrate surface, with a thickness in the range of 10-30 nm.

[0126] Subsequently, the gas flow rate was adjusted to 100 sccm, the oxygen volume percentage was 25%, and the vacuum chamber pressure was adjusted to 0.8-1.0 Pa. The substrate heating power supply and rotation device were turned on to maintain the substrate sputtering temperature at 300-400℃, and the rotation speed was set to 20 rpm. The power supply and magnetic field control devices of the off-axis sputtering target system were turned on, and the sputtering power was set to 100-150W to grow the buffer layer for 20 minutes, forming a buffer layer with a thickness of 100 nm at a deposition rate of approximately 5 nm / min.

[0127] Immediately after deposition, the material is subjected to high-temperature annealing at 500-700℃ in an oxygen or inert atmosphere for 1 hour.

[0128] Step S4: Close the baffle above the off-axis target and switch to the second off-axis target for host layer sputtering. Set the coaxial sputtering power to 300-400W and maintain the substrate temperature at 400-500℃. Adjust the gas control system to introduce a mixture of argon and oxygen into the coaxial sputtering target area, with oxygen accounting for 15% of the volume. Adjust the vacuum chamber pressure to 1.8-2.0Pa. Keep the substrate stage rotating; the rotation speed can be adjusted to 60rpm. Perform host layer growth, setting the growth time to 180 minutes to obtain a host layer of the predetermined thickness.

[0129] Step S5: Close the coaxial sputtering target system and gas valves, allow the vacuum chamber to cool naturally to room temperature, remove the substrate, and obtain a high-quality gallium oxide thin film.

[0130] Step S6: Anneal the obtained high-quality gallium oxide film at 600-800℃ for 2 hours in an oxygen atmosphere.

[0131] The gallium oxide epitaxial film in Example 3 is similar to that in Example 1, with a diameter of 4 inches and a thickness of approximately 5.8 μm, meeting the requirements for thick-film devices and wafer-level thickness uniformity, with a thickness uniformity deviation of <2%. Due to the stepwise deposition of the buffer layer and multiple annealing processes, the crystal structure of the film was further optimized. In the X-ray diffraction (XRD) of the gallium oxide film in Example 3, the characteristic peak intensity of gallium oxide was higher and the full width at half maximum (FWHM) was narrower, indicating that the crystal quality was superior to that of films prepared by traditional magnetron sputtering methods, and the crystal integrity was better.

[0132] The present invention has been described in detail above. For those skilled in the art, the invention can be implemented in a wide range of ways with equivalent parameters, scenarios, and conditions without departing from its spirit and scope, and without requiring unnecessary experimentation. Although specific embodiments have been given, it should be understood that this disclosure is not limited to the specific implementations disclosed, and further improvements can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some basic features can be applied within the scope of the following appended claims.

Claims

1. A method for preparing high-quality gallium oxide thin films, characterized in that, The method includes: Step S1: Prepare a pretreated substrate and a plurality of targets opposite the substrate, the plurality of targets including coaxial targets and off-axis targets; Step S2: Place the substrate on the substrate stage, close the vacuum chamber, and start the vacuum pump to evacuate the vacuum. Step S3: Introduce working gas and deposit a buffer layer on the substrate using an off-axis target, wherein the off-axis angle β is 5-90°, the off-axis distance L is 1-50 cm, and the product of β and L is not less than 300; the off-axis sputtering power is the first sputtering power, the substrate rotation speed is the first rotation speed, and the oxygen volume in the working gas is the first oxygen volume; Step S4: Deposit the main layer on the buffer layer using a coaxial target, with the coaxial sputtering power being the second sputtering power, the substrate rotation speed being the second rotation speed, and the oxygen volume in the working gas being the second oxygen volume, wherein the second oxygen volume is smaller than the first oxygen volume, the second rotation speed is greater than the first rotation speed, and the second sputtering power is not less than the first sputtering power; Step S5: Cool to room temperature to obtain a high-quality gallium oxide thin film.

2. A method for preparing high-quality potassium oxide thin films, characterized in that, The method includes: Step S1: Prepare a pretreated substrate and a plurality of targets opposite the substrate. The plurality of targets include a first target and a second target. The plurality of targets are all off-axis targets, wherein the off-axis angle β is 5-90° and the off-axis distance L is 1-50 cm. The product of β and L of the first target is not less than 300, and the product of β and L of the second target is not less than 30. Step S2: Place the substrate on the substrate stage, close the vacuum chamber, and start the vacuum pump to evacuate the vacuum. Step S3: Introduce working gas, maintain oxygen volume at the first oxygen volume, set substrate rotation speed to the first rotation speed, set sputtering power to the first sputtering power, and deposit a buffer layer on the substrate using the first target. Step S4: Maintain the oxygen volume as the second oxygen volume, set the bottom rotation speed as the second rotation speed, set the sputtering power as the second sputtering power, and deposit the main layer on the buffer layer through the second target material, wherein the oxygen volume becomes smaller under the second gas distribution, the second rotation speed is greater than the first rotation speed, and the second sputtering power is not less than the first sputtering power; Step S5: Cool to room temperature to obtain a high-quality gallium oxide thin film.

3. The method according to claims 1 to 2, characterized in that, The method further includes step S6: annealing the obtained high-quality gallium oxide film in an oxygen or air atmosphere.

4. The method according to claims 1 to 2, characterized in that, In step S1, the substrate is selected from sapphire, magnesium oxide, gallium oxide, gallium nitride, silicon, silicon carbide or quartz glass, and the substrate is pretreated by ultrasonic cleaning and drying with water, acetone and anhydrous ethanol.

5. The method according to claim 4, characterized in that, In step S1, after each cleaning with acetone and anhydrous ethanol, water is used for cleaning again; the target material is a gallium oxide ceramic target material with a purity of not less than 99.99%, and the multiple targets are pre-sputtered.

6. The method according to claims 1 to 2, characterized in that, In step S2, the vacuum pump is started to evacuate to a vacuum level of 5×10⁻⁶. - 4 Below Pa, it provides a highly clean deposition environment.

7. The method according to claim 6, characterized in that, In step S2, the vacuum pump is started to evacuate to 10. -5 Below Pa, it provides a highly clean deposition environment.

8. The method according to claims 1 to 2, characterized in that, Step S3 further includes: Before depositing the buffer layer, a nucleation layer is pre-deposited on the substrate using a coaxial target.

9. The method according to claims 1 to 2, characterized in that, Step S3 further includes: Before depositing the main layer, the buffer layer is post-treated to further repair defects and optimize the structure. The post-treatment includes high-temperature annealing of the buffer layer in oxygen or an inert atmosphere, or chemical mechanical polishing or surface cleaning pretreatment of the buffer layer surface.

10. The method according to claim 2, characterized in that, The product of β and L of the second target material is not less than 50.

11. The method according to claim 2, characterized in that, The product of β and L of the second target material is not less than 80.

12. The method according to claims 1 to 2, characterized in that, The target material used for depositing the buffer layer in step S3 is different from the target material used for depositing the main layer in step S4. The target material used for depositing the buffer layer includes metallic gallium, aluminum nitride, gallium nitride, gallium oxide doped with aluminum, magnesium, silicon and / or strontium.

13. A manufacturing apparatus for high-quality gallium oxide epitaxial thin films, said apparatus being used to prepare high-quality gallium oxide epitaxial thin films according to the methods of claims 1 to 12, characterized in that, The manufacturing equipment includes: A vacuum chamber, wherein a vacuum pump assembly and a gas supply system are connected to the vacuum chamber, and the gas supply system includes at least one first mass flow controller and a second mass flow controller; A substrate stage is disposed in the vacuum chamber. The substrate stage integrates a heating module and a temperature sensing module, and has a rotation function. A magnetron sputtering unit, disposed within the vacuum chamber, includes multiple independently controlled targets opposite the substrate, an RF power supply unit, and a magnetic field control system. The multiple targets include a first target for sputtering a buffer layer and a second target for sputtering a host layer. The multiple targets are either off-axis or coaxial targets, and a baffle is disposed vertically above the surface of each target. The RF power supply module has a programmable power output function and includes at least one first RF power supply module and one second RF power supply module. The magnetic field control system includes at least one first magnetic field control system and one second magnetic field control system.

14. A high-quality gallium oxide epitaxial thin film, wherein the high-quality gallium oxide epitaxial thin film is prepared by the method according to claims 1 to 12, characterized in that, The thickness of the gallium oxide epitaxial film is 1-10 μm, the thickness uniformity error is within 2%, the crystal orientation is preferential growth of the (-201) crystal plane, and the full width at half maximum (FWHM) in X-ray diffraction is about 1.5°.

15. The application of the high-quality gallium oxide epitaxial thin film according to claim 14 in the fabrication of high-voltage power devices and deep ultraviolet optoelectronic devices.

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