Composite piezoelectric thin film structure and method of manufacturing the same

Abstract

The application provides a composite piezoelectric film structure and a preparation method thereof. The preparation method comprises the following steps: providing an auxiliary support substrate, a piezoelectric wafer and a target support substrate; bonding the piezoelectric wafer and the auxiliary support substrate, performing thin film processing and planarization processing on the piezoelectric wafer, forming a piezoelectric film with a preset total thickness deviation on the surface of the auxiliary support substrate, and obtaining an intermediate composite structure; bonding the side surface of the intermediate composite layer with the piezoelectric film and the target support substrate, removing the auxiliary support substrate, and obtaining a composite structure; and repeating the above steps until a target number of piezoelectric films are formed on the side surface of the target support substrate, and obtaining a composite piezoelectric film structure with a composite piezoelectric layer. By using the preparation method provided by the application, each piezoelectric film can be independently thinned and planarized on the auxiliary support substrate with a uniform and flat surface, and the flatness of the composite piezoelectric layer can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor device manufacturing technology, specifically to a composite piezoelectric thin film structure and its preparation method. Background Technology

[0002] With the expansion of 5G / 6G wireless communication technology to higher frequency bands and the evolution of optical communication systems towards ultra-high speeds, the performance requirements for key functional materials in modern electronic and photonic devices are increasingly demanding. The 5G and 6G frequency bands require radio frequency filters to have higher operating frequencies and larger bandwidths, which places higher demands on the sound velocity and electromechanical coupling coefficient of acoustic resonators. Piezoelectric single-crystal thin films, represented by lithium niobate and lithium tantalate, have become ideal material platforms for constructing core devices such as radio frequency filters, resonators, and optical modulators due to their unique piezoelectric effect, electro-optic effect, and acoustic wave propagation characteristics. Traditional devices are usually based on heterostructures of single-layer piezoelectric thin films. However, single-layer structures have certain limitations: the thermal expansion coefficient of piezoelectric thin films differs significantly from that of commonly used substrates, making them prone to cracking or performance drift due to thermal mismatch stress during fabrication and use. Furthermore, in high-frequency applications, the thickness of the piezoelectric thin film needs to be reduced, increasing processing difficulty and losses. Therefore, multilayer stacked structures of piezoelectric single-crystal thin films, represented by lithium niobate and lithium tantalate, are an important way to overcome the performance limits of single-layer thin films.

[0003] Existing multilayer structure fabrication methods typically employ direct stacking of layers on a target substrate. Besides facing challenges such as thermal mismatch stress accumulation and severe interlayer coupling, this approach also suffers from process bottlenecks: firstly, as the number of composite film layers increases, the film thickness deviation becomes larger; secondly, increasing the number of film layers leads to multiple reflections of optical test signals at interfaces, causing distortion and making it impossible to accurately measure and control the film thickness. Therefore, there is an urgent need to develop a novel multilayer composite piezoelectric thin film structure and its fabrication method, suitable for large-scale manufacturing. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this application provides a composite piezoelectric thin film structure and its preparation method. The specific technical solution is as follows: On the one hand, this application provides a method for preparing a composite piezoelectric thin film structure, comprising: S1: Provides auxiliary support substrate, piezoelectric wafer and target support substrate; S2: The piezoelectric wafer is bonded to the auxiliary support substrate, and the piezoelectric wafer is subjected to thin film processing and planarization processing to form a piezoelectric thin film with a preset total thickness deviation on the surface of the auxiliary support substrate, thereby obtaining an intermediate composite structure; S3: Bond the side surface of the intermediate composite layer having the piezoelectric film to the target support substrate, remove the auxiliary support substrate, and obtain the composite structure; S4: Repeat S2 and S3 until the target number of piezoelectric films are formed on one side surface of the target support substrate, to obtain a composite piezoelectric film structure with a composite piezoelectric layer.

[0005] In a possible implementation, the preset total thickness deviation is 0-20 nm.

[0006] In a possible implementation, the thickness of the piezoelectric film is 100nm-2000nm.

[0007] In a possible implementation, the piezoelectric film has the same cutting type as the piezoelectric wafer.

[0008] In a possible implementation, the in-plane crystal axes of two adjacent piezoelectric thin films in the composite piezoelectric layer have a predetermined included angle.

[0009] In a possible implementation, the crystal axis of the piezoelectric thin film layer is aligned with or opposite to the direction of its thickness.

[0010] In a possible implementation, S2 satisfies at least one of the following characteristics: The thin-film treatment includes at least one of ion implantation, mechanical thinning, chemimechanical thinning, and chemical thinning. The planarization process includes at least one of chemical mechanical polishing and ion beam leveling.

[0011] In a possible implementation, the ion implantation satisfies at least one of the following characteristics: The ion implantation uses at least one of hydrogen ions, helium ions, or argon ions. The implantation energy of the ion implantation is 20keV-300keV; The implantation dose of the ion implantation is 10. 14 ions / cm 2 Up to 10 17 ions / cm 2 .

[0012] In a possible implementation, S3 includes: The intermediate composite layer with the piezoelectric film on one side surface is bonded to the target support substrate, and then heat-treated to obtain a bonded structure. Thinning and etching are performed on one side surface of the bonding structure having the auxiliary support substrate to form a piezoelectric thin film on one side surface of the target support substrate, thereby obtaining a composite structure.

[0013] In a possible implementation, the heat treatment satisfies at least one of the following characteristics: The heat treatment temperature is 200-400℃; The heat treatment time is 3-24 hours; The heating rate of the heat treatment is 0.1-5℃ / min.

[0014] In a possible implementation, the preparation method further includes: An isolation material is deposited on the surface of the piezoelectric thin film facing away from the target support substrate to form an isolation layer, resulting in a composite structure.

[0015] In a possible implementation, providing the target support substrate includes: Provide a supporting substrate layer; A thin film is deposited on at least one side surface of the supporting substrate layer to form a stress compensation layer, thereby obtaining the target supporting substrate.

[0016] In a possible implementation, the stress compensation layer includes a first stress compensation layer and a second stress compensation layer; The first stress compensation layer includes at least one of silicon oxide, silicon nitride, amorphous silicon, polycrystalline silicon, aluminum oxide, and aluminum nitride; the second stress compensation layer includes at least one of polycrystalline silicon and amorphous silicon.

[0017] In a possible implementation, after forming the stress compensation layer, the method further includes: A metal pattern layer is formed on one side of the support substrate layer having the stress compensation layer to obtain a target support substrate; the metal pattern layer has a partition structure, the partition structure including one of gas, vacuum and insulating dielectric material.

[0018] In a possible implementation, the auxiliary support substrate satisfies at least one of the following characteristics: The auxiliary support substrate has a first temporary protective layer on at least one side surface; The auxiliary substrate includes a silicon layer and a silicon oxide layer; The auxiliary substrate includes a quartz layer.

[0019] On the other hand, this application also provides a composite piezoelectric thin film structure, which is prepared by the preparation method described in any of the embodiments.

[0020] Based on the above technical solution, this application has the following beneficial effects: This application provides a composite piezoelectric thin film structure and its fabrication method, comprising: providing an auxiliary support substrate, a piezoelectric wafer, and a target support substrate; bonding the piezoelectric wafer to the auxiliary support substrate; performing thinning and planarization treatments on the piezoelectric wafer to form a piezoelectric thin film with a predetermined total thickness deviation on the surface of the auxiliary support substrate, thereby obtaining an intermediate composite structure; bonding one side surface of the intermediate composite layer with the piezoelectric thin film to the target support substrate; removing the auxiliary support substrate to obtain the composite structure; repeating the above steps until a target number of piezoelectric thin films are formed on one side surface of the target support substrate, thereby obtaining a composite piezoelectric thin film structure with a composite piezoelectric layer. In this way, each piezoelectric thin film is independently thinned and planarized on a uniformly flat auxiliary support substrate, improving the flatness of the composite piezoelectric layer and avoiding stress accumulation caused by direct stacking of multiple piezoelectric thin films. This results in an atomically flat interlayer interface in the composite piezoelectric thin film structure, which is beneficial for reducing scattering loss of sound waves or light waves during propagation. This fabrication method has high process flexibility, which is beneficial for improving the yield of the composite piezoelectric thin film structure and reducing manufacturing costs. Attached Figure Description

[0021] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This application provides a schematic diagram of a composite piezoelectric thin film structure. Figure 2 This application provides a schematic diagram of the structure of a target support substrate according to an embodiment; Figure 3 This application provides a schematic diagram of an intermediate composite structure. Figure 4 : A schematic diagram of another composite piezoelectric thin film structure provided in the embodiments of this application.

[0023] Reference numerals: 1-Supporting substrate layer, 2-Piezoelectric thin film, 3-Stress compensation layer, 31-First stress compensation layer, 32-Second stress compensation layer, 4-Metal pattern layer, 5-Isolation layer, 6-Auxiliary support substrate. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] It should be noted that, in the description of this application, the following definitions shall apply unless a different definition is given elsewhere in the claims or this specification. All numerical values, whether or not explicitly indicated, are defined herein as being modified by the term "about". The term "about" generally refers to a range of numerical values ​​that a person skilled in the art would consider equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A range of numerical values ​​indicated by a low value and a high value is defined as including all numerical values ​​within that range and all subranges included within that range.

[0026] It should be noted that in the description of this application, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0027] It should be noted that, in the description of this application, the terms "on," "above," "over," and "above" should be interpreted in the broadest sense, meaning that a description containing these terms is interpreted as "a component may be disposed on another component in direct contact, or there may be an intermediate component or layer between the components." Furthermore, for ease of description, this application may also use spatially relative terms such as "below," "under," "below," "on," "above," "lower," and "upper" to describe the relationship between one element or component and another element or component shown in the accompanying drawings.

[0028] As used in this application, the term "layer" refers to a portion of material comprising a region of a certain thickness. A layer may extend over the entire lower or upper structure, or it may extend within a localized area of ​​the lower or upper structure. Furthermore, a layer may be a region of a homogeneous or heterogeneous continuous structure with a thickness less than the thickness of the continuous structure. For example, a layer may be located between the top and bottom surfaces of a continuous structure, or between any pair of horizontal planes therebetween. A layer may extend horizontally, vertically, and / or along a conical surface. A single layer may comprise multiple layers.

[0029] It should be understood that the term "plane" as used in this application, such as "first plane" or "second plane", refers to the XY plane of the supporting substrate, etc., and "thickness direction" refers to the Z direction perpendicular to the XY plane. The terms "thickness" or "height" mentioned in this application refer to the Z-direction thickness or Z-direction height.

[0030] The following is for reference Figures 1-4 This application describes a method for preparing a composite piezoelectric thin film structure. The specification provides the method steps as described in the embodiments, but based on conventional or non-inventive methods, more or fewer steps may be included. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only possible order. In actual implementation, the preparation method can be performed in the order shown in the embodiments or accompanying drawings, or in parallel. The method for preparing the composite piezoelectric thin film structure may include S1-S4: S1: Provides auxiliary support substrate 6, piezoelectric wafer and target support substrate.

[0031] In a possible implementation, a target support substrate is provided, including: S11: Provides a supporting substrate layer 1; S12: A thin film is deposited on at least one side surface of the support substrate layer 1 to form a stress compensation layer 3, thereby obtaining the target support substrate.

[0032] In a possible implementation, the supporting substrate layer 1 includes at least one of silicon, silicon oxide, sapphire, silicon carbide, diamond, gallium nitride, and quartz, which can provide mechanical support for the composite piezoelectric thin film structure, ensuring structural flatness and stability; and can effectively conduct and dissipate heat, ensuring the reliability of subsequent preparation steps.

[0033] Specifically, the thickness of the support substrate layer 1 is 200-1000 μm; understandably, the thickness of the support substrate layer 1 can be any value within the range of 200-1000 μm; for example, the thickness of the support substrate layer 1 can be 200 μm, 400 μm, 500 μm, 800 μm, 1000 μm, etc. Controlling the thickness of the support substrate layer 1 within the above range can provide good mechanical strength and flatness for the target support substrate, avoiding breakage or warping during preparation and use; and the support substrate layer 1 can effectively dissipate heat, avoiding local overheating.

[0034] Specifically, the thin film deposition method for forming the stress compensation layer 3 can be at least one of thermal oxidation, physical vapor deposition, and chemical vapor deposition; the stress compensation layer 3 includes at least one of silicon oxide, silicon nitride, amorphous silicon, polycrystalline silicon, aluminum oxide, and aluminum nitride. The stress compensation layer 3 can compensate for the thermal mismatch stress caused by the subsequent fabrication of the composite piezoelectric layer, thereby preventing thin film cracking, and the stress compensation layer 3 can effectively isolate the composite piezoelectric layer and the supporting substrate layer 1.

[0035] In a possible implementation, thin films are deposited on both surfaces opposite to the support substrate layer 1 to form two stress compensation layers 3. The two stress compensation layers 3 are symmetrically distributed about the support substrate layer 1. In this way, thermal mismatch stress can be effectively offset, the warping deformation of the support substrate layer 1 during the preparation process can be suppressed, and mechanical stability can be improved.

[0036] In possible implementations, refer to Figure 1 The stress compensation layer 3 includes a first stress compensation layer 31 and a second stress compensation layer 32, with the second stress compensation layer 32 formed between the first stress compensation layer 31 and the supporting substrate layer 1. Specifically, the first stress compensation layer 31 includes at least one of silicon oxide, silicon nitride, amorphous silicon, polycrystalline silicon, aluminum oxide, and aluminum nitride, and the second stress compensation layer 32 includes at least one of polycrystalline silicon and amorphous silicon. Thus, the first stress compensation layer 31 can offset the stress of the composite piezoelectric layer, and the second stress compensation layer 32 can effectively reduce the RF loss of the device, acting as a stress buffer.

[0037] In a possible implementation, the thickness of the first stress compensation layer 31 is 100nm-15000nm; understandably, the thickness of the first stress compensation layer 31 can be any value within the range of 100-15000nm; for example, the thickness of the first stress compensation layer 31 can be 100nm, 500nm, 1000nm, 5000nm, 15000nm, etc. Thus, by controlling the thickness of the first stress compensation layer within the aforementioned range, the overall stress of the composite piezoelectric thin film structure can be effectively balanced, the warpage of the target support substrate can be significantly reduced, and the flatness of the target support substrate can be guaranteed.

[0038] Specifically, the thickness of the second stress compensation layer 32 is 50nm-1500nm; understandably, the thickness of the second stress compensation layer 32 can be any value within the range of 50nm-1500nm; for example, the thickness of the second stress compensation layer 32 can be 50nm, 100nm, 500nm, 1000nm, 1500nm, etc. Thus, the second stress compensation layer 32 can work together with the first stress compensation layer 31 to provide stress compensation, offsetting the thermal stress generated during the subsequent fabrication of the composite piezoelectric layer, effectively reducing the RF loss of the device.

[0039] In possible implementations, refer to Figure 2 After forming the stress compensation layer 3, the preparation method further includes: S13: A metal pattern layer 4 is formed on the side of the support substrate layer 1 with the stress compensation layer 3 to obtain the target support substrate.

[0040] In a possible implementation, forming the metal pattern layer 4 includes: depositing a metal layer on the surface of the support substrate layer 1 on the side having the stress compensation layer 3, and performing photolithography and etching on the metal layer to form a barrier structure.

[0041] Specifically, the metal pattern layer 4 has a partition structure, causing it to be discontinuously distributed in the horizontal direction. The metal pattern layer 4 isolates the stress compensation layer 3 and the composite piezoelectric layer, and the partition structure partially separates the stress compensation layer 3 and the composite piezoelectric layer, thus releasing localized stress. In electromagnetic shielding or absorbing bodies, the metal pattern layer 4 can interact with incident electromagnetic waves to generate resonance, thereby efficiently absorbing or reflecting electromagnetic energy in specific frequency bands.

[0042] Specifically, the partition structure includes one of gas, vacuum, and insulating media materials.

[0043] Specifically, the shape of the metal pattern layer 4 can be one of a circle, a polygon, or an interdigitated shape, and the metal pattern layer 4 includes at least one of gold, silver, copper, aluminum, nickel, platinum, titanium, tantalum, tungsten, chromium, and molybdenum. Thus, the metal pattern layer 4 can effectively optimize the occurrence of parasitic modes in the acoustic wave device and prevent energy leakage.

[0044] In some embodiments, the auxiliary support substrate 6 can be a single-layer structure made of a quartz substrate; in other embodiments, the auxiliary support substrate 6 can be a multi-layer composite structure, the auxiliary support substrate 6 including a silicon oxide thin film and a silicon substrate with a (100) crystal plane; it is understood that in the subsequent preparation process, the piezoelectric wafer can be bonded to the side surface of the auxiliary support substrate 6 with the silicon oxide thin film, the silicon oxide thin film can be used as an intermediate layer to prepare a high-quality piezoelectric thin film 2, and can effectively protect the piezoelectric thin film 2 layer in the subsequent transfer process of the piezoelectric thin film 2, avoiding damage to the piezoelectric thin film 2 during the transfer process.

[0045] Specifically, the thickness of the silicon oxide film is 50-1000 nm; understandably, the thickness of the silicon oxide film can be any value within the range of 50 nm to 1000 nm; for example, the thickness of the silicon oxide film is 50 nm, 100 nm, 500 nm, 800 nm, 1000 nm, etc. Controlling the thickness of the silicon oxide film within the above range can provide a flat and chemically stable surface for the piezoelectric wafer, which is beneficial for achieving high flatness of the piezoelectric film 2; and the silicon oxide film can alleviate the thermal mismatch stress caused by the difference in thermal expansion coefficients between the piezoelectric film 2 and the auxiliary support substrate 6.

[0046] S2: The piezoelectric wafer is bonded to the auxiliary support substrate 6. The piezoelectric wafer is then subjected to thin-film processing and planarization to form a piezoelectric thin film 2 with a preset total thickness deviation on the surface of the auxiliary support substrate 6, thus obtaining an intermediate composite structure. (See schematic diagram of the intermediate composite structure for reference.) Figure 3 .

[0047] In possible implementations, the thin-film treatment includes at least one of ion implantation, mechanical thinning, chemimechanical thinning, and chemical thinning. Using the above-described thin-film treatment methods, the film thickness can be precisely controlled, and the surface roughness of the piezoelectric wafer can be effectively reduced, resulting in a smooth surface and minimizing damage to the piezoelectric wafer.

[0048] In a possible implementation, the piezoelectric wafer is subjected to a thin-film processing method, including: ion implantation of the piezoelectric wafer to form an ion implantation layer, annealing, and wafer stripping of the ion implantation layer.

[0049] Specifically, the ion implantation uses at least one of hydrogen ions, helium ions, or argon ions; the implantation energy is 20keV-300keV; understandably, the implantation energy can be any value within the 20keV-300keV range; for example, the implantation energy can be 20keV, 50keV, 100keV, 200keV, 300keV, etc. Controlling the ion implantation energy within the above range can avoid wafer damage caused by excessively high implantation energy, while avoiding the inability to form a continuous damage layer due to excessively low implantation energy, thus preventing effective stripping.

[0050] Specifically, the implantation dose of ion implantation is 10. 14 ions / cm 2 -10 17 ions / cm 2 Understandably, the implantation dose of ion implantation is 10. 14 ions / cm 2 -10 17 ions / cm 2 Any point value in the range; for example, the implantation dose of ion implantation can be 10. 14 ions / cm 2 10 15 ions / cm 2 10 16 ions / cm 2 10 17 ions / cm 2By controlling the ion implantation energy within the aforementioned range, it is possible to avoid insufficient implantation dose, which would prevent the formation of enough charge carriers to alter material properties; and to avoid excessive implantation dose, which would introduce too many ions and cause excessive lattice damage.

[0051] In a possible implementation, the annealing temperature is between 100°C and 900°C; understandably, the annealing temperature can be any value within the range of 100°C to 900°C; exemplary examples include 100°C, 150°C, 500°C, 700°C, and 900°C. Annealing effectively restores crystal quality, and controlling the annealing temperature within the aforementioned range prevents repeated annealing from affecting the piezoelectric film 2. Preferably, the annealing temperature is between 300°C and 900°C.

[0052] Understandably, the annealing temperature can be adjusted according to the actual preparation requirements. In some embodiments, the piezoelectric wafer is lithium tantalate, and the annealing temperature for lithium tantalate is 250-600°C; in other embodiments, the piezoelectric wafer is lithium niobate, and the annealing temperature for lithium niobate is 350-900°C.

[0053] Specifically, the piezoelectric wafer includes at least one of lithium tantalate, lithium niobate, doped lithium niobate, and doped lithium tantalate; understandably, the piezoelectric wafer can be other single-crystal materials with piezoelectric effect.

[0054] Specifically, both doped lithium niobate and doped lithium tantalate include doping materials, which include, but are not limited to, at least one of magnesium, iron, zinc, hafnium, copper, and erbium. It can be understood that the lithium niobate single crystal material and lithium tantalate single crystal material described in the embodiments of this application can be either undoped intrinsic single crystal material or doped modified single crystal material.

[0055] Specifically, the annealing time is 3-15 hours; understandably, the annealing time can be any value within the range of 3-15 hours; for example, the annealing time is 3 hours, 5 hours, 10 hours, 12 hours, 15 hours, etc. Controlling the annealing time within the above range allows atoms sufficient time to diffuse and migrate to the damaged area, thereby effectively eliminating lattice defects.

[0056] Specifically, the gas atmosphere for the annealing treatment is at least one of nitrogen, vacuum, and inert gas atmosphere.

[0057] In a possible implementation, the planarization process includes at least one of chemical mechanical polishing and ion beam leveling. Planarization can obtain a smooth and undamaged surface of the piezoelectric film 2, which is beneficial for improving the quality and interface properties of the piezoelectric film 2, thereby enhancing the performance and reliability of products and devices incorporating this composite piezoelectric film structure.

[0058] In a possible implementation, the thickness of the piezoelectric film 2 is 100nm-2000nm; understandably, the thickness of the piezoelectric film 2 can be any value within the range of 100nm-2000nm; for example, the thickness of the piezoelectric film 2 is 100nm, 500nm, 1000nm, 1500nm, 2000nm, etc. Controlling the thickness of the piezoelectric film 2 within the above range is beneficial for achieving higher operating frequencies and meeting the requirements of high-frequency communication. It is understood that the thickness of the piezoelectric film 2 can be set according to the actual application requirements.

[0059] In a possible implementation, the piezoelectric film 2 has the same cutting type as the piezoelectric wafer.

[0060] S3: Bond the side surface of the intermediate composite layer with the piezoelectric thin film 2 to the target support substrate, and remove the auxiliary support substrate 6 to obtain the composite structure.

[0061] In a possible implementation, S3 includes: S31: Bond one side surface of the intermediate composite layer with the piezoelectric thin film 2 to the target support substrate, and perform heat treatment to obtain the bonded structure; S32: Thinning and etching are performed on one side surface of the bonding structure with auxiliary support substrate 6 to form a piezoelectric thin film 2 on one side surface of the target support substrate, thus obtaining a composite structure.

[0062] Heat treatment can eliminate microscopic defects at the bonding interface, resulting in a dense and complete bonding interface, improving the bonding strength between the piezoelectric film 2 and the target support substrate. It also redistributes the thermal and internal stresses generated during bonding, enhancing the long-term reliability of the composite piezoelectric film structure. Furthermore, thinning and etching processes can precisely remove the auxiliary support substrate 6 while avoiding affecting the flatness of the piezoelectric film 2.

[0063] In some embodiments, the auxiliary support substrate 6 is a single-layer structure made of quartz substrate; the thickness of the quartz substrate is reduced to less than 50 μm by thinning process, and the thinned quartz substrate is etched until the auxiliary support substrate 6 is completely removed.

[0064] In other embodiments, the auxiliary support substrate 6 is a multilayer composite structure, comprising a silicon oxide thin film and a silicon substrate with a (100) crystal plane; the silicon substrate with the (100) crystal plane is thinned to a thickness of less than 100 μm by a wafer thinning process, and then the remaining silicon substrate and silicon oxide are removed by an etching process until the auxiliary support substrate 6 is completely removed. Specifically, the etching process can be at least one of wet etching and dry etching.

[0065] In a possible implementation, the heat treatment temperature is 200-400°C; understandably, the heat treatment temperature can be any value within 200-400°C; exemplaryly, the heat treatment temperature is 200°C, 250°C, 300°C, 350°C, 400°C, etc. Specifically, the heat treatment time is 3-24 hours; understandably, the heat treatment time can be any value within 3-24 hours; exemplaryly, the heat treatment time is 3 hours, 10 hours, 15 hours, 20 hours, 24 hours, etc. Thus, by controlling the heat treatment temperature and time within the above range, the hydrogen bonds between the piezoelectric thin film 2 and the target support substrate during bonding can be converted into covalent bonds, avoiding excessively low annealing temperatures or times that would fail to strengthen the bonding interface, while also avoiding excessively high annealing temperatures and times that would damage material properties.

[0066] Specifically, the heating rate of the heat treatment is 0.1-5℃ / min; understandably, the heating rate of the heat treatment can be any value within the range of 0.1-5℃ / min; for example, the heating rate of the heat treatment is 0.1℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 5℃ / min, etc. Controlling the heating rate of the heat treatment within the above range can effectively alleviate the thermal stress caused by the difference in the thermal expansion coefficients of different materials, provide sufficient time for atomic diffusion and lattice repair, ensure that the material obtains a uniform and stable microstructure, and avoid the asynchronous expansion or contraction between different layers caused by rapid heating, which can generate large internal stress.

[0067] In a possible implementation, at least one surface of the auxiliary support substrate has a first temporary protective layer; the fabrication method further includes forming a first temporary protective layer on one surface of the intermediate composite layer before bonding the intermediate composite layer to the target support substrate. The first temporary protective layer can be used to prevent the target support substrate from being affected during the separation of the piezoelectric thin film 2 from its auxiliary support substrate 6. The material of the first temporary protective layer can be at least one of silicon dioxide, silicon nitride, aluminum oxide, polysilicon, and photoresist.

[0068] In a possible implementation, before bonding the intermediate composite layer to the target support substrate, the fabrication method further includes forming a second temporary protective layer on one side surface of the target support substrate. The material of the second temporary protective layer includes at least one of inorganic and organic protective materials. Specifically, the inorganic protective material includes at least one of silicon dioxide, silicon nitride, aluminum oxide, and polycrystalline silicon; the organic protective material includes at least one of photoresist, polyimide, thermoplastic protective wax, and alkali-resistant protective adhesive.

[0069] Understandably, the material selection for the second temporary protective layer can be related to the process used to remove the auxiliary support substrate. In one example, dry etching is used to remove the auxiliary support substrate, and the second temporary protective layer can be a conventional photoresist; in another example, wet etching is used to remove the silicon material in the auxiliary support substrate. Since conventional photoresist is easily corroded or stripped by strong alkaline solutions, the second temporary protective layer preferably includes one of alkali-resistant protective adhesive, thermoplastic protective wax, and polyimide. The above-mentioned organic protective materials have excellent chemical corrosion resistance, which can effectively block the erosion of the target support substrate by the etching solution. Moreover, after the process is completed, it can be removed by special solvents (such as acetone, alcohol, or special resist remover) or by heating, which can avoid damage to the surface of the piezoelectric film.

[0070] In a possible implementation, the fabrication method further includes: depositing an isolation material on the surface of the piezoelectric thin film 2 facing away from the target support substrate to form an isolation layer 5, as referenced. Figure 4 .

[0071] In some embodiments, after removing the auxiliary support substrate 6, an isolation material is deposited on the surface of the piezoelectric film 2 on the side opposite to the target support substrate to form an isolation layer 5.

[0072] In other embodiments, with a piezoelectric thin film on the target support substrate, the preparation method further includes forming an isolation layer 5 on the side surface of the piezoelectric thin film 2 facing away from the auxiliary support substrate 6 before repeating step S3.

[0073] Specifically, the insulating material may include at least one of silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, tantalum oxide, and niobium oxide. The insulating layer 5 can be formed on the surface of the piezoelectric thin film 2 by physical vapor deposition or chemical vapor deposition of the insulating material. The total thickness deviation of the insulating layer 5 is less than 20 nm. The insulating layer 5 can effectively reduce the interlayer coupling of acoustic waves or electromagnetic fields, which is beneficial to further improving the performance of the composite piezoelectric thin film structure.

[0074] S4: Repeat steps S2 and S3 until the target number of piezoelectric films 2 are formed on one side surface of the target support substrate, to obtain a composite piezoelectric film structure with a composite piezoelectric layer.

[0075] Specifically, the total thickness deviation of the composite piezoelectric layer is 0-20 nm; understandably, the total thickness deviation of the composite piezoelectric layer can be any value within the range of 0-20 nm; for example, the total thickness deviation of the composite piezoelectric layer can be 0, 5 nm, 10 nm, 15 nm, 20 nm, etc. By controlling the total thickness deviation of the composite piezoelectric layer within the above range, the composite piezoelectric film has high flatness, which is beneficial to improving the stability of the piezoelectric coefficient, ensuring the uniformity of the performance of the composite piezoelectric film structure, reducing interface defects and stress concentration, and reducing signal loss.

[0076] Understandably, the target quantity is the number of piezoelectric films 2 in the piezoelectric film structure required for the actual application. Specifically, the target quantity of piezoelectric films 2 can be n, and the number of insulating layers 5 is (n-1), where n is a positive integer greater than or equal to 2; when the target quantity is n, steps S2 and S3 are repeated n times.

[0077] In a possible implementation, adjacent piezoelectric thin films 2 in the composite piezoelectric layer have a preset angle between their corresponding crystal axes in the plane. Specifically, before bonding the side surface of the intermediate composite structure with the piezoelectric thin film 2 to the target support substrate, the main positioning edge of the intermediate composite structure is rotated by a preset angle θ relative to the main positioning edge of the target support substrate, so that adjacent piezoelectric thin films 2 have a preset angle between their corresponding crystal axes in the plane, where |θ| is 0~180°, and the preset angle can be 0-180 degrees.

[0078] In some embodiments, the crystal axes of the piezoelectric thin film layers are aligned in the thickness direction, which makes the polarization direction of each piezoelectric thin film layer consistent. The changes in electric dipole moments generated under external force can be superimposed in phase, which is beneficial to improving the effective piezoelectric coefficient. Furthermore, the alignment of the crystal axes in the thickness direction enables the electric field to effectively excite mechanical vibrations along the thickness direction, reducing energy loss in other directions.

[0079] In some embodiments, the thickness direction of the piezoelectric thin film layer is opposite to the direction of the crystal axis, which enables the optical signal to continuously accumulate and enhance during propagation, greatly improving the modulation efficiency and nonlinear effect of optical devices with this composite piezoelectric layer.

[0080] In a specific embodiment, the method for preparing the composite piezoelectric thin film structure includes: 1. providing a support substrate layer 1, depositing a thin film on at least one side surface of the support substrate layer 1 to form a first stress compensation layer 31 and a second stress compensation layer 32, and forming a metal pattern layer 4 on the side of the support substrate layer 1 having the first stress compensation layer 31 to obtain a target support substrate. 2. Provide n auxiliary support substrates 6 and n piezoelectric wafers; bond the n piezoelectric wafers to the n auxiliary support substrates 6 one-to-one to obtain n auxiliary bonding structures; 3. Perform thin-film processing and planarization processing on the piezoelectric wafers in each auxiliary bonding structure to form a piezoelectric thin film 2 with a preset total thickness deviation on the surface of the auxiliary support substrate 6 to obtain n intermediate composite structures; wherein, the preset total thickness deviation is 0-20nm; 4. Bond the surface of the first intermediate composite layer with the piezoelectric thin film 2 to the target support substrate, remove the auxiliary support substrate 6, and obtain the composite structure; 5. Rotate the main positioning edge of the nth intermediate composite layer relative to the main positioning edge of the target support substrate by a preset angle, so that the surface of the nth intermediate composite layer with the piezoelectric thin film 2 is bonded to the side of the target support substrate with the piezoelectric thin film layer 2, remove the auxiliary support substrate 6, and form a composite piezoelectric layer with n piezoelectric thin films on the target support substrate to obtain a composite piezoelectric thin film structure.

[0081] Based on the above preparation method, each piezoelectric film 2 is independently thinned and planarized on a uniformly flat auxiliary support substrate 6. High flatness is achieved before each piezoelectric film is bonded to the target support substrate, which helps improve the flatness of the composite piezoelectric layer. This avoids stress accumulation caused by direct stacking of multiple piezoelectric films 2, resulting in an atomically flat interlayer interface in the composite piezoelectric film structure. This helps reduce scattering loss of sound or light waves during propagation, significantly improving the Q value and efficiency of the composite piezoelectric film structure. Furthermore, each piezoelectric film can be precisely measured on the auxiliary support substrate, avoiding interference from complex multilayer structures. High-precision optical measurement equipment can accurately and quickly obtain key parameters such as the thickness and thickness uniformity of the single-layer piezoelectric film, providing feedback to guide the polishing process. This ensures that each piezoelectric film meets the preset standards before integration, guaranteeing the consistency of the final device performance. This preparation method offers high process flexibility, which helps improve the yield of the composite piezoelectric film structure and reduce manufacturing costs.

[0082] The existing multilayer piezoelectric film stacking method leads to an increase in the cumulative error of the total thickness deviation as the number of piezoelectric film layers increases, which also causes optical measurement failure. The preparation method of this application sets the total thickness deviation of each piezoelectric film layer 2 independently, which can effectively avoid error accumulation.

[0083] This application also provides a composite piezoelectric thin film structure, which is prepared using the preparation method described in any of the embodiments.

[0084] This application also provides an acoustic wave device, including a composite piezoelectric thin film structure and a surface electrode formed on the surface of the composite piezoelectric thin film structure, wherein the composite piezoelectric thin film structure is prepared by the preparation method of any embodiment.

[0085] This application also provides an optoelectronic device, including a composite piezoelectric thin film structure and a surface electrode formed on the surface of the composite piezoelectric thin film structure, wherein the composite piezoelectric thin film structure is prepared by the preparation method of any embodiment.

[0086] The foregoing description has fully disclosed the specific embodiments of this application. It should be noted that any modifications made by those skilled in the art to the specific embodiments of this application do not depart from the scope of the claims. Accordingly, the scope of the claims of this application is not limited to the foregoing specific embodiments.

Claims

1. A method for preparing a composite piezoelectric thin film structure, characterized in that, include: S1: Provides auxiliary support substrate, piezoelectric wafer and target support substrate; S2: The piezoelectric wafer is bonded to the auxiliary support substrate, and the piezoelectric wafer is subjected to thin film processing and planarization processing to form a piezoelectric thin film with a preset total thickness deviation on the surface of the auxiliary support substrate, thereby obtaining an intermediate composite structure; S3: Bond the side surface of the intermediate composite layer having the piezoelectric film to the target support substrate, remove the auxiliary support substrate, and obtain the composite structure; S4: Repeat S2 and S3 until the target number of piezoelectric films are formed on one side surface of the target support substrate, to obtain a composite piezoelectric film structure with a composite piezoelectric layer.

2. The preparation method according to claim 1, characterized in that, The piezoelectric thin film satisfies at least one of the following characteristics: The preset total thickness deviation is 0-20nm; The thickness of the piezoelectric film is 100nm-2000nm; The piezoelectric thin film and the piezoelectric wafer have the same cutting type; In the composite piezoelectric layer, there is a preset included angle between the same crystal axes of two adjacent piezoelectric thin films in the plane; The piezoelectric thin film layer has a thickness direction that is either aligned with or opposite to the direction of the crystal axis.

3. The preparation method according to claim 1, characterized in that, S2 satisfies at least one of the following characteristics: The thin-film treatment includes at least one of ion implantation, mechanical thinning, chemimechanical thinning, and chemical thinning. The planarization process includes at least one of chemical mechanical polishing and ion beam leveling.

4. The preparation method according to claim 3, characterized in that, The ion implantation satisfies at least one of the following characteristics: The ion implantation uses at least one of hydrogen ions, helium ions, or argon ions. The implantation energy of the ion implantation is 20keV-300keV; The implantation dose of the ion implantation is 10. 14 ions / cm 2 Up to 10 17 ions / cm 2 .

5. The preparation method according to any one of claims 1-4, characterized in that, S3 includes: The intermediate composite layer with the piezoelectric film on one side surface is bonded to the target support substrate, and then heat-treated to obtain a bonded structure. Thinning and etching are performed on one side surface of the bonding structure having the auxiliary support substrate to form a piezoelectric thin film on one side surface of the target support substrate, thereby obtaining a composite structure.

6. The preparation method according to claim 5, characterized in that, The heat treatment satisfies at least one of the following characteristics: The heat treatment temperature is 200-400℃; The heat treatment time is 3-24 hours; The heating rate of the heat treatment is 0.1-5℃ / min.

7. The preparation method according to any one of claims 1-4, characterized in that, The preparation method further includes: An isolation material is deposited on the surface of the piezoelectric thin film facing away from the target support substrate to form an isolation layer, resulting in a composite structure.

8. The preparation method according to any one of claims 1-4, characterized in that, The provision of the target support substrate includes: Provide a supporting substrate layer; A thin film is deposited on at least one side surface of the supporting substrate layer to form a stress compensation layer, thereby obtaining the target supporting substrate.

9. The preparation method according to claim 8, characterized in that, The stress compensation layer includes a first stress compensation layer and a second stress compensation layer; The first stress compensation layer includes at least one of silicon oxide, silicon nitride, amorphous silicon, polycrystalline silicon, aluminum oxide, and aluminum nitride. The second stress compensation layer includes at least one of polycrystalline silicon and amorphous silicon.

10. The preparation method according to claim 8, characterized in that, After forming the stress compensation layer, the method further includes: A metal pattern layer is formed on one side of the support substrate layer having the stress compensation layer to obtain a target support substrate; the metal pattern layer has a partition structure, the partition structure including one of gas, vacuum and insulating dielectric material.

11. The preparation method according to any one of claims 1-4, characterized in that, The auxiliary support substrate satisfies at least one of the following characteristics: The auxiliary support substrate has a first temporary protective layer on at least one side surface; The auxiliary substrate includes a silicon layer and a silicon oxide layer; The auxiliary substrate includes a quartz layer.

12. A composite piezoelectric thin film structure, characterized in that, It is prepared by the preparation method according to any one of claims 1-11.

13. The piezoelectric thin film structure according to claim 12, characterized in that, The composite piezoelectric thin film structure includes: a target support substrate, a stress compensation layer, and a composite piezoelectric layer.

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