Bulk acoustic wave filter, preparation method thereof and radio frequency module

Abstract

The invention discloses a bulk acoustic wave filter, a preparation method thereof and a radio frequency module. The bulk acoustic wave filter includes at least: a substrate; the first film layer is located on one side of the substrate, the first film layer comprises a first area and a second area surrounding the first area, and a photosensitive dry film surrounding the first area is arranged in the second area; the piezoelectric film is positioned on one side, far away from the substrate, of the first film layer; wherein the piezoelectric film comprises a lithium niobate film and / or a lithium tantalate film; and the substrate, the photosensitive dry film and the piezoelectric film jointly form a cavity. According to the bulk acoustic wave filter, the photosensitive dry film is introduced and serves as the supporting layer and the sacrificial layer, the effect of supporting the lithium niobate thin film and / or the lithium tantalate thin film is achieved, and the effect of sacrificing part of the photosensitive dry film to form the cavity is achieved; and meanwhile, by utilizing the flexibility of the photosensitive dry film, the limitation on the lithium niobate and / or lithium tantalate crystal phase can be reduced, so that the application range of the lithium niobate film and / or lithium tantalate film in the radio frequency communication field is widened.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular, to a bulk acoustic wave filter and a preparation method thereof, and a radio frequency module. Background Art

[0002] In the field of radio frequency communications, bulk acoustic wave filters often use thin film materials such as aluminum nitride prepared by magnetron sputtering technology as piezoelectric layers. However, polycrystalline piezoelectric materials prepared by magnetron sputtering have a large number of lattice defects, which leads to energy loss of acoustic waves, thus affecting the quality factor of the device and making it difficult to achieve low insertion loss. In addition, the electromechanical coupling coefficient of aluminum nitride is low, which limits the bandwidth of the filter. Therefore, it is urgent to develop a new type of bulk acoustic wave filter to overcome the above defects.

[0003] It should be noted that the above statements are only used to provide background technical information related to the present application and do not necessarily constitute prior art. Summary of the invention

[0004] In the first aspect of the present application, the present application provides a bulk acoustic wave filter, comprising at least: a substrate; a first film layer, the first film layer is located on one side of the substrate, the first film layer includes a first region and a second region surrounding the first region, the second region has a photosensitive dry film arranged around the first region; a piezoelectric film, the piezoelectric film is located on the side of the first film layer away from the substrate; wherein the piezoelectric film includes at least one of a lithium niobate film and a lithium tantalate film; the substrate, the photosensitive dry film, and the piezoelectric film together form a cavity. Thus, the bulk acoustic wave filter of the present application introduces a flexible photosensitive dry film, which serves as a supporting layer and a sacrificial layer, and has the function of supporting the lithium niobate film and / or the lithium tantalate film, and has the function of sacrificing part of the photosensitive dry film to form a cavity; at the same time, by utilizing the flexibility of the photosensitive dry film, the restriction on the lithium niobate crystal phase and / or the lithium tantalate crystal phase can be reduced, so as to broaden the application scope of the lithium niobate film and / or the lithium tantalate film in the field of radio frequency communication.

[0005] In some embodiments, the piezoelectric film has a thickness of 100 nm to 2000 nm. Thus, by selecting a piezoelectric film of appropriate thickness, the electromechanical coupling performance and frequency response of the BAW filter can be improved.

[0006] In some embodiments, the thickness of the photosensitive dry film is 50 nm-2000 nm. Thus, a suitable thickness of the photosensitive dry film is selected to balance the mechanical properties and manufacturing flexibility of the BAW filter.

[0007] In some embodiments, the thickness of the substrate is 100 μm-2000 μm. Therefore, by selecting a substrate with a suitable thickness, sufficient mechanical support can be provided while satisfying the performance of the BAW filter.

[0008] In some embodiments, the substrate includes at least one of silicon, silicon carbide, sapphire, and glass. Thus, the overall performance of the BAW filter can be optimized.

[0009] In some embodiments, it also includes a patterned electrode layer, which is located on the side of the piezoelectric film away from the first film layer, and the patterned electrode layer satisfies at least one of the following conditions: the thickness of the patterned electrode layer is 50nm-500nm; the material of the patterned electrode layer includes at least one of aluminum, molybdenum, gold, platinum, copper, silver, titanium, tungsten, and nickel; the patterned electrode layer includes an interdigitated electrode layer and / or a connecting line electrode layer. Thus, the interdigitated electrode layer and / or the connecting line electrode layer facilitate the electrical connection and signal transmission of the bulk acoustic wave filter. At the same time, selecting the appropriate electrode layer material and thickness can improve the signal transmission efficiency.

[0010] In some embodiments, along the length direction of the BAW filter, the length of the cavity is greater than the length of the interdigital electrode layer, thereby providing a larger space to reduce the reflection of the sound wave, thereby improving the frequency selectivity and insertion loss of the BAW filter.

[0011] In some embodiments, an adhesion layer is further included, and the adhesion layer is located between the piezoelectric film and the patterned electrode layer, and the adhesion layer satisfies at least one of the following conditions: the thickness of the adhesion layer is 5nm-20nm; the adhesion layer includes at least one of titanium, chromium, and aluminum oxide. Thus, the adhesion stability of the electrode layer on the surface of the piezoelectric film can be improved to reduce the risk of the electrode layer peeling off; at the same time, selecting a suitable thickness and material of the adhesion layer can further improve the adhesion stability of the electrode layer on the surface of the piezoelectric film.

[0012] In a second aspect of the present application, the present application provides a method for preparing the aforementioned bulk acoustic wave filter, comprising: performing ion implantation treatment on a substrate to form a damaged surface inside the substrate to obtain a substrate having a damaged surface; wherein the substrate comprises at least one of a lithium niobate wafer and a lithium tantalate wafer; forming a photosensitive dry film layer on one side of the substrate, laminating the substrate having the damaged surface with a side of the photosensitive dry film layer away from the substrate, and performing a bonding treatment to obtain a substrate after the bonding treatment; performing an annealing treatment on the substrate after the bonding treatment to disconnect the substrate at the damaged surface to obtain a photosensitive dry film layer having a piezoelectric film; the piezoelectric film comprises at least one of a lithium niobate film and a lithium tantalate film; performing a mask exposure treatment on a side of the piezoelectric film away from the photosensitive dry film layer to make the photosensitive dry film layer have an exposed area; forming a release hole in the piezoelectric film to allow the photosensitive dry film in the exposed area to dissolve from the release hole to obtain the bulk acoustic wave filter having a cavity.

[0013] Therefore, by utilizing the flexibility of the photosensitive dry film, the bonding process requirements for the surface flatness of lithium niobate wafers and / or lithium tantalate wafers can be reduced, thereby improving the bonding yield; and the residual stress after bonding is small, which can significantly reduce the risk of breakage of the lithium niobate film and / or lithium tantalate film when it is peeled off from the lithium niobate wafer and / or lithium tantalate wafer, making the crystal phase selection of lithium niobate and / or lithium tantalate more flexible, improving the design flexibility of the filter, and broadening the application scenarios of lithium niobate film and / or lithium tantalate film in the field of radio frequency communications.

[0014] In some embodiments, the bonding process temperature is 0-50° C., and the bonding process pressure is 10 KPa-500 KPa. Thus, the bonding of the photosensitive dry film and the lithium niobate film and / or lithium tantalate film can be completed at room temperature and under relatively low pressure, which reduces the difficulty of the bonding process.

[0015] In some embodiments, the annealing temperature is 100° C.-200° C., and the annealing time is 10 min-60 min. Thus, by selecting appropriate annealing parameters, the piezoelectric film can be effectively peeled off from the substrate smoothly while reducing the damage to the structure caused by the annealing.

[0016] In some embodiments, the step of obtaining the photosensitive dry film having the piezoelectric film further includes polishing the surface of the piezoelectric film, thereby further reducing the difficulty of the bonding process.

[0017] In some embodiments, the edge of the exposed area does not exceed the edge of the photosensitive dry film layer, thereby reducing excessive dissolution of the photosensitive dry film layer.

[0018] In some embodiments, the method of forming the release hole in the piezoelectric film includes at least one of ion beam etching and wet etching.

[0019] In some embodiments, the edge of the release hole in the photosensitive dry film layer does not exceed the edge of the exposed area. Thus, the solution used to dissolve the photosensitive dry film in the exposed area can directly contact the photosensitive dry film in the exposed area, thereby increasing the dissolution rate of the photosensitive dry film.

[0020] In some embodiments, the method further includes: forming a patterned photoresist layer on a side of the piezoelectric film away from the photosensitive dry film layer; forming an electrode layer on a side of the piezoelectric film not covered by the patterned photoresist layer; and then removing the patterned photoresist layer.

[0021] In some embodiments, the method of forming the patterned photoresist layer includes at least one of a dry etching method, a wet etching method, and a stripping method.

[0022] In some embodiments, the method of removing the patterned photoresist layer comprises a metal lift-off process.

[0023] In some embodiments, the ion implantation process satisfies at least one of the following conditions: the ion species of the ion implantation process includes at least one of helium, hydrogen, nitrogen, oxygen, and argon; the implantation dose of the ion implantation process is 1×10 15 ions / cm 2 -5×10 17 ions / cm 2 The implantation energy of the ion implantation process is 10KeV-1000KeV. Therefore, selecting appropriate ion implantation process parameters is helpful to control the thickness of the lithium niobate film and / or the lithium tantalate film.

[0024] In a third aspect of the present application, the present application provides a radio frequency module, including the bulk acoustic wave filter of the first aspect of the present application, or including the bulk acoustic wave filter prepared by the preparation method of the second aspect of the present application. Thus, the radio frequency module includes all the advantages of the bulk acoustic wave filter of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0026] Figure 1-Figure 11 It is a process flow chart of the preparation process of the bulk acoustic wave filter in Example 1.

[0027] Description of reference numerals:

[0028] 101, lithium niobate wafer; 101-1, lithium niobate film; 102, damaged surface; 201, single crystal silicon wafer; 202, photosensitive dry film layer; 202-1, exposed area; 203, photoresist layer; 204, adhesion layer; 205, electrode layer; 206, photolithography layer; 207, etching window; 208, release hole; 209, cavity. DETAILED DESCRIPTION

[0029] Hereinafter, the BAW filter and its preparation method, and the implementation method of the RF module of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0030] " Scope " disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be to include end values ​​or not include end values, and can be combined arbitrarily, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0033] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0034] In the description of the present application, "A and / or B" may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for examples and may be any technical feature connected by "and / or" in the present application.

[0035] Lithium niobate (LiNbO3, LN) and lithium tantalate (LiTaO3, LT) are widely used in surface acoustic wave devices and bulk acoustic wave devices because of their excellent acoustic properties. Take the single crystal lithium niobate bulk acoustic wave filter (SLBAR) as an example. SLBAR is based on a composite piezoelectric substrate of single crystal lithium niobate thin film on insulator (LNOI). It uses the smaller lattice defects and larger electromechanical coupling coefficient of single crystal lithium niobate to prepare a high-frequency, low insertion loss, and large bandwidth RF filter.

[0036] At present, the LNOI wafers used by SLBAR are mostly prepared by ion implantation and stripping (Smart-cut) technology based on silicon dioxide bonding. However, this technology has the following defects: First, the bonding of rigid substrates is difficult, and the surface flatness of lithium niobate films is extremely high, which leads to a low wafer yield; second, there is a significant lattice mismatch between silicon dioxide and lithium niobate, and the residual stress after the two are bonded is large, which makes the lithium niobate film easy to break during the stripping process. Only a few crystal directions can be successfully prepared. The limited crystal direction selection reduces the design flexibility of subsequent filters and limits its application scenarios; finally, because the Smart-cut technology does not support pre-buried sacrificial layers, the cavity structure required by the filter needs to be prepared by a back etching process, which reduces the reliability of the device and increases the difficulty of packaging; the above defects seriously limit the large-scale application of lithium niobate films in the field of radio frequency communications.

[0037] In the first aspect of the present application, the present application provides a bulk acoustic wave filter, comprising at least: a substrate; a first film layer, the first film layer is located on one side of the substrate, the first film layer includes a first area and a second area surrounding the first area, the second area has a photosensitive dry film arranged around the first area; a piezoelectric film, the piezoelectric film is located on a side of the first film layer away from the substrate; wherein the piezoelectric film includes at least one of a lithium niobate film and a lithium tantalate film; the substrate, the photosensitive dry film, and the piezoelectric film together form a cavity.

[0038] Lithium niobate film and / or lithium tantalate film serve as the key functional layer of the bulk acoustic wave filter, which has the functions of converting and filtering sound waves. The bulk acoustic wave filter of the present application introduces a flexible photosensitive dry film, which serves as a supporting layer and a sacrificial layer, and has the function of supporting the lithium niobate film and / or lithium tantalate film, and also has the function of sacrificing part of the photosensitive dry film to form a cavity; at the same time, by utilizing the flexibility of the photosensitive dry film, the restrictions on the lithium niobate crystal phase and / or lithium tantalate crystal phase can be reduced, so as to broaden the application scope of the lithium niobate film and / or lithium tantalate film in the field of radio frequency communication.

[0039] In some embodiments, the thickness of the piezoelectric film is 100 nm-2000 nm. Therefore, by selecting a piezoelectric film with a suitable thickness, the electromechanical coupling performance and frequency response of the BAW filter can be improved.

[0040] As an example, the thickness of the piezoelectric film may be 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, or 2000 nm.

[0041] In some embodiments, the thickness of the photosensitive dry film is 50 nm-2000 nm. Thus, a suitable thickness of the photosensitive dry film is selected to balance the mechanical properties and manufacturing flexibility of the BAW filter.

[0042] As an example, the thickness of the photosensitive dry film may be 50 nm, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, or 2000 nm.

[0043] In some embodiments, the thickness of the substrate is 100 μm-2000 μm. Therefore, by selecting a substrate with a suitable thickness, sufficient mechanical support can be provided while satisfying the performance of the BAW filter.

[0044] As an example, the thickness of the substrate may be 100 μm, 200 μm, 400 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1400 μm, 1600 μm, 1800 μm or 2000 μm.

[0045] In some embodiments, the substrate includes at least one of silicon, silicon carbide, sapphire, and glass. Thus, the overall performance of the BAW filter can be optimized.

[0046] In some embodiments, it also includes a patterned electrode layer, which is located on the side of the piezoelectric film away from the first film layer, and the patterned electrode layer satisfies at least one of the following conditions: the thickness of the patterned electrode layer is 50nm-500nm; the material of the patterned electrode layer includes at least one of aluminum, molybdenum, gold, platinum, copper, silver, titanium, tungsten, and nickel; the patterned electrode layer includes an interdigitated electrode layer and / or a connecting line electrode layer. Therefore, the interdigitated electrode layer and / or the connecting line electrode layer contribute to the completion of the electrical connection and signal transmission of the bulk acoustic wave filter. At the same time, selecting the appropriate electrode layer material and thickness can improve the signal transmission efficiency.

[0047] As an example, the thickness of the patterned electrode layer may be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm.

[0048] In some embodiments, the patterned electrode layer satisfies the following conditions at the same time: the thickness of the patterned electrode layer is 50nm-500nm; the material of the patterned electrode layer includes at least one of aluminum, molybdenum, gold, platinum, copper, silver, titanium, tungsten, and nickel; the patterned electrode layer includes an interdigitated electrode layer and / or a connecting line electrode layer.

[0049] In some embodiments, along the length direction of the BAW filter, the length of the cavity is greater than the length of the interdigital electrode layer, thereby providing a larger space to reduce the reflection of the sound wave, thereby improving the frequency selectivity and insertion loss of the BAW filter.

[0050] In some embodiments, an adhesive layer is further included, and the adhesive layer is located between the piezoelectric film and the patterned electrode layer, and the adhesive layer satisfies at least one of the following conditions: the thickness of the adhesive layer is 5nm-20nm; the adhesive layer includes at least one of titanium, chromium, and aluminum oxide. Thus, the adhesion stability of the electrode layer on the surface of the piezoelectric film can be improved to reduce the risk of the electrode layer peeling off; at the same time, selecting a suitable thickness and material of the adhesive layer can further improve the adhesion stability of the electrode layer on the surface of the piezoelectric film.

[0051] As an example, the thickness of the adhesion layer may be 5 nm, 10 nm, 15 nm or 20 nm.

[0052] In some embodiments, the adhesion layer satisfies the following conditions simultaneously: the thickness of the adhesion layer is 5 nm-20 nm; and the adhesion layer includes at least one of titanium, chromium, and aluminum oxide.

[0053] In a second aspect of the present application, the present application provides a method for preparing the aforementioned bulk acoustic wave filter, comprising:

[0054] S100, performing ion implantation on the substrate to form a damaged surface inside the substrate, so as to obtain a substrate having a damaged surface; wherein the substrate comprises at least one of a lithium niobate wafer and a lithium tantalate wafer. The sizes of the lithium niobate wafer and the lithium tantalate wafer are not specifically limited, and are specifically set according to the required bulk acoustic wave filter.

[0055] In some embodiments, the surface of the lithium niobate wafer and / or the lithium tantalate wafer is cleaned.

[0056] In some embodiments, the cleaning process includes an RCA standard cleaning method. As an example, the cleaning solution used in the RCA standard cleaning method includes at least one of a sulfuric acid / hydrogen peroxide mixture, hydrofluoric acid, and an ammonia / hydrogen peroxide / water mixture.

[0057] The ion implantation process is to accelerate charged ions in a vacuum and then shoot them at the material to be damaged. These ions will penetrate the surface of the material and embed into the material. The ions will collide with the atoms in the material and change the chemical composition and physical properties of the material in the area where the ions are implanted. The depth of ion implantation is determined by the implantation energy, so the thickness of the damaged layer can be adjusted by adjusting the ion implantation depth.

[0058] In some embodiments, the ion implantation process satisfies at least one of the following conditions: the ion species of the ion implantation process includes at least one of helium, hydrogen, nitrogen, oxygen, and argon; the implantation dose of the ion implantation process is 1×10 15 ions / cm 2 -5×10 17 ions / cm 2 The implantation energy of the ion implantation process is 10KeV-1000KeV. Therefore, selecting appropriate ion implantation process parameters is helpful to control the thickness of the lithium niobate film and / or the lithium tantalate film.

[0059] As an example, the implantation dose of the ion implantation process may be 1×10 15 ions / cm 2 , 5×10 15 ions / cm 2 , 1×10 16 ions / cm 2 , 2×10 16 ions / cm 2 , 3×10 16 ions / cm 2 , 4×10 16 ions / cm 2 , 5×10 16 ions / cm 2 , 6×10 16 ions / cm 2,7×10 16 ions / cm 2 , 8×10 16 ions / cm 2 ,9×10 16 ions / cm 2 , 1×10 17 ions / cm 2 , 2×10 17 ions / cm 2 , 3×10 17 ions / cm 2 , 4×10 17 ions / cm 2 or 5×10 17 ions / cm 2 .

[0060] As an example, the implantation energy of the ion implantation process may be 10 KeV, 100 KeV, 200 KeV, 300 KeV, 400 KeV, 500 KeV, 600 KeV, 700 KeV, 800 KeV, 900 KeV, or 1000 KeV.

[0061] In some embodiments, the ion implantation process needs to meet the following conditions at the same time: the ion species of the ion implantation process includes at least one of helium, hydrogen, nitrogen, oxygen, and argon; the implantation dose of the ion implantation process is 1×10 15 ions / cm 2 -5×10 17 ions / cm 2 ; The implantation energy of the ion implantation process is 10KeV-1000KeV.

[0062] S200, forming a photosensitive dry film layer on one side of the substrate, attaching the substrate with the damaged surface to the side of the photosensitive dry film layer away from the substrate, and performing a bonding process to obtain a substrate after the bonding process. Thus, by utilizing the flexibility of the photosensitive dry film, the bonding process can reduce the requirements for the surface flatness of the lithium niobate wafer and / or lithium tantalate wafer, thereby improving the bonding yield.

[0063] In some embodiments, a cleaning process is performed on the surface of the substrate. As an example, the cleaning process includes an RCA standard cleaning method.

[0064] In some embodiments, the method of forming the photosensitive dry film layer includes spin coating a photosensitive dry film slurry on a surface of a substrate, and drying the photosensitive dry film to form the photosensitive dry film layer.

[0065] In some embodiments, the temperature of the bonding process is 0-50°C, and the pressure of the bonding process is 10KPa-500KPa. Thus, the bonding of the photosensitive dry film and the lithium niobate film and / or lithium tantalate film can be completed at room temperature and under relatively low pressure, and the residual stress after bonding is relatively small, which can significantly reduce the risk of breakage of the lithium niobate film and / or lithium tantalate film when peeled off from the lithium niobate wafer and / or lithium tantalate wafer, making the crystal phase selection of lithium niobate and / or lithium tantalate more flexible, improving the design flexibility of the filter, and expanding the application scenarios in the field of radio frequency communication.

[0066] As an example, the temperature of the bonding process may be 0, 10°C, 20°C, 30°C, 40°C or 50°C.

[0067] As an example, the pressure of the bonding process may be 10 KPa, 50 KPa, 100 KPa, 200 KPa, 300 KPa, 400 KPa, or 500 KPa.

[0068] In some embodiments, the substrate after bonding is heated at a temperature of 90° C. to 110° C., thereby making the bonding stronger and curing part of the photosensitive dry film.

[0069] As an example, the temperature of the heat treatment may be 90°C, 95°C, 100°C, 105°C, or 110°C.

[0070] S300, annealing the substrate after bonding, so that the substrate is broken at the damaged surface to obtain a photosensitive dry film layer with a piezoelectric film; the piezoelectric film includes at least one of a lithium niobate film and a lithium tantalate film. Thus, the piezoelectric film is peeled off from the surface of the substrate.

[0071] In some embodiments, the annealing temperature is 100° C.-200° C., and the annealing time is 10 min-60 min. Thus, by selecting appropriate annealing parameters, the piezoelectric film can be effectively peeled off from the substrate smoothly while reducing the damage to the structure caused by the annealing.

[0072] As an example, the temperature of the annealing process may be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C.

[0073] As an example, the annealing treatment time may be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min.

[0074] In some embodiments, obtaining a photosensitive dry film having a piezoelectric film further includes polishing the surface of the piezoelectric film, thereby further reducing the difficulty of the bonding process. As an example, the polishing process includes mechanical chemical polishing (CMP).

[0075] In some embodiments, the surface roughness of the piezoelectric film after polishing is less than 2 nm.

[0076] S400, performing mask exposure processing on a side of the piezoelectric film away from the photosensitive dry film layer, so that the photosensitive dry film layer has an exposed area.

[0077] In some embodiments, the edge of the exposed area does not exceed the edge of the photosensitive dry film layer, thereby reducing excessive dissolution of the photosensitive dry film layer.

[0078] In some embodiments, a patterned photoresist layer is formed on the side of the piezoelectric film that has been subjected to mask exposure processing and is away from the photosensitive dry film layer. The pattern of the photoresist layer includes a complementary pattern of the interdigital electrodes and / or the connecting line electrodes. As an example, the method of forming the patterned photoresist layer includes at least one of a dry etching method, a wet etching method, and a stripping method.

[0079] In some embodiments, an adhesion layer and an electrode layer are sequentially formed on one side of the piezoelectric film not covered by the patterned photoresist layer. As an example, the method of forming the adhesion layer and / or the electrode layer includes at least one of magnetron sputtering and vacuum evaporation.

[0080] In some embodiments, the patterned photoresist layer is removed. As an example, the method of removing the patterned photoresist layer includes a metal lift-off process.

[0081] S500, forming a release hole in the piezoelectric film to allow the photosensitive dry film in the exposed area to be dissolved from the release hole to obtain a bulk acoustic wave filter with a cavity.

[0082] In some embodiments, the method of forming the release hole includes forming a photolithography layer having an etching window on the surface of the piezoelectric film, and etching the piezoelectric film through the etching window until the piezoelectric film is penetrated to form the release hole.

[0083] In some embodiments, the edge of the release hole in the photosensitive dry film layer does not exceed the edge of the exposed area. Therefore, the solution used to dissolve the photosensitive dry film in the exposed area can directly contact the photosensitive dry film in the exposed area, thereby increasing the dissolution rate of the photosensitive dry film.

[0084] In some embodiments, the etching process includes at least one of an ion beam etching method and a wet etching method.

[0085] In some embodiments, the release holes on the piezoelectric film are within the corresponding range of the exposed area.

[0086] In the third aspect of the present application, the present application provides a radio frequency module, including the bulk acoustic wave filter of the first aspect of the present application, or including the bulk acoustic wave filter prepared by the preparation method of the second aspect of the present application. Thus, the radio frequency module has all the advantages of the bulk acoustic wave filter of the present application.

[0087] The scheme of the present application is described below by specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained commercially.

[0088] Example 1

[0089] A method for preparing a bulk acoustic wave filter, combining Figure 1-Figure 11 , including the following steps:

[0090] S100, Reference Figure 1 , the surface of the lithium niobate wafer 101 is cleaned by using the RCA standard cleaning method to obtain a clean lithium niobate wafer 101; then, a helium ion beam is implanted into the clean lithium niobate wafer 101 by using an ion implantation process, Figure 1 The middle arrow indicates the implantation direction of the helium ion beam, so as to form a damaged surface 102 inside the lithium niobate wafer 101; wherein the implantation dose of the ion implantation process is 4×10 16 ions / cm 2 The implantation energy of the ion implantation process is 500KeV.

[0091] S200, Reference Figure 2 , using RCA standard cleaning method for 500μm thick <100> The crystal-oriented single crystal silicon wafer 201 is cleaned to obtain a clean single crystal silicon wafer 201; then, a photosensitive dry film slurry is spin-coated on the surface of the single crystal silicon wafer 201, and a photosensitive dry film layer 202 with a thickness of 500 nm is obtained after the photosensitive dry film slurry is cured.

[0092] refer to Figure 3 , the surface of the lithium niobate wafer 101 that has been treated with ion implantation is attached to the photosensitive dry film layer 202 for bonding treatment; then baked at 100° C. to make the lithium niobate wafer 101 and the photosensitive dry film layer 202 bonded more firmly; wherein, the bonding treatment temperature is 25° C., and the bonding treatment pressure is 30 KPa.

[0093] S300, Reference Figure 3 and Figure 4The single crystal silicon wafer 201 and the lithium niobate wafer 101 after bonding are annealed to disconnect the lithium niobate wafer 101 from the damaged surface 102, so that the lithium niobate film 101-1 is peeled off from the surface of the lithium niobate wafer 101 to obtain a lithium niobate film wafer based on a silicon substrate; wherein the annealing temperature is 200°C and the annealing time is 20 minutes; then, the thickness of the lithium niobate film 101-1 on the surface of the photosensitive dry film layer 202 is thinned to 500nm by using a mechanical chemical polishing (CMP) method, at which time the surface roughness of the lithium niobate film 101-1 is about 1nm.

[0094] S400, Reference Figure 5 , a mask exposure process is performed on the surface of the lithium niobate film 101-1, so that the photosensitive dry film layer 202 has an exposed area 202-1; in this embodiment, the edge of the exposed area 202-1 does not exceed the edge of the photosensitive dry film layer 202; Figure 6 , and then a patterned photoresist layer 203 is formed on the surface of the lithium niobate film 101-1, wherein the pattern of the photoresist layer 203 includes complementary patterns of the interdigital electrodes and the connecting line electrodes; Figure 7 , and then an adhesion layer 204 with a thickness of 10 nm and an electrode layer 205 with a thickness of 100 nm are formed in sequence toward the photoresist layer 203 by magnetron sputtering; wherein the material of the adhesion layer 204 is metal titanium, and the material of the electrode layer 205 is metal aluminum. At this time, the surface of the photoresist layer 203 has the adhesion layer 204 and the electrode layer 205, and the surface of the lithium niobate film 101-1 not covered by the photoresist layer 203 also has the adhesion layer 204 and the electrode layer 205.

[0095] refer to Figure 7 and Figure 8 After the photoresist layer 203 and the adhesion layer 204 and the electrode layer 205 on the surface of the photoresist layer 203 are removed by using a metal lift-off process, at this time, the surface of the lithium niobate film 101 - 1 has interdigital electrodes and connecting line electrodes.

[0096] S500, Reference Fig. 9 , a photolithography layer 206 having an etching window 207 is formed on the surface of the lithium niobate film 101-1; Fig.10 , the lithium niobate film 101-1 is ion-beam etched through the etching window 207 until the lithium niobate film 101-1 is penetrated to expose the photosensitive dry film layer 202. At this time, a release hole 208 is formed on the lithium niobate film 101-1, and the edge of the release hole 208 at the edge of the photosensitive dry film layer 202 does not exceed the edge of the exposed area 202-1.

[0097] refer to Fig.10 and Fig.11, immerse the wafer in an acetone solution at room temperature for 10 minutes to remove the photoresist layer 206; immerse the wafer in a photosensitive dry film developer (1% sodium carbonate) solution, the solution enters from the release hole 208 until it contacts the exposed area 202-1, the photosensitive dry film in the exposed area 202-1 gradually dissolves, and then is discharged from the release hole 208, so that a cavity 209 is gradually formed inside the wafer; the unexposed photosensitive dry film is difficult to dissolve and is thus retained; after the photosensitive dry film in the exposed area 202-1 is completely dissolved, the wafer is taken out of the solution, and after drying, a bulk acoustic wave filter with a cavity 209 structure is formed.

[0098] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A bulk acoustic wave filter, characterized in that: At least: substrate; A first film layer, the first film layer is located on one side of the substrate, the first film layer includes a first area and a second area surrounding the first area, and the second area has a photosensitive dry film arranged around the first area; A piezoelectric film, the piezoelectric film being located on a side of the first film layer away from the substrate; wherein the piezoelectric film comprises at least one of a lithium niobate film and a lithium tantalate film; The substrate, the photosensitive dry film, and the piezoelectric film together form a cavity.

2. The bulk acoustic wave filter according to claim 1, characterized in that The thickness of the piezoelectric film is 100nm-2000nm; and / or, The thickness of the photosensitive dry film is 50nm-2000nm; and / or, The thickness of the substrate is 100 μm-2000 μm; and / or, The substrate includes at least one of silicon, silicon carbide, sapphire and glass.

3. The bulk acoustic wave filter according to claim 1, wherein: The device further includes a patterned electrode layer, wherein the patterned electrode layer is located on a side of the piezoelectric film away from the first film layer, and the patterned electrode layer satisfies at least one of the following conditions: The thickness of the patterned electrode layer is 50nm-500nm; The material of the patterned electrode layer includes at least one of aluminum, molybdenum, gold, platinum, copper, silver, titanium, tungsten, and nickel; The patterned electrode layer includes an interdigitated electrode layer and / or a connecting line electrode layer.

4. The bulk acoustic wave filter according to claim 3, characterized in that Along the length direction of the BAW filter, the length of the cavity is greater than the length of the interdigital electrode layer.

5. The bulk acoustic wave filter according to claim 3, characterized in that The device further comprises an adhesive layer, wherein the adhesive layer is located between the piezoelectric film and the patterned electrode layer, and the adhesive layer satisfies at least one of the following conditions: The thickness of the adhesion layer is 5nm-20nm; The adhesion layer includes at least one of titanium, chromium, and aluminum oxide.

6. A method for preparing a bulk acoustic wave filter as claimed in any one of claims 1 to 5, characterized in that: include: Performing ion implantation on the substrate to form a damaged surface inside the substrate, so as to obtain a substrate having a damaged surface; wherein the substrate comprises at least one of a lithium niobate wafer and a lithium tantalate wafer; Forming a photosensitive dry film layer on one side of the substrate, attaching the substrate having the damaged surface to the side of the photosensitive dry film layer away from the substrate, and performing a bonding process to obtain a substrate after the bonding process; Annealing the substrate after bonding to break the substrate at the damaged surface to obtain a photosensitive dry film layer having a piezoelectric film; the piezoelectric film includes at least one of a lithium niobate film and a lithium tantalate film; Performing mask exposure processing on a side of the piezoelectric film away from the photosensitive dry film layer, so that the photosensitive dry film layer has an exposed area; A release hole is formed in the piezoelectric film to allow the photosensitive dry film in the exposed area to be dissolved from the release hole, so as to obtain the bulk acoustic wave filter with a cavity.

7. The method according to claim 6, characterized in that The temperature of the bonding process is 0-50° C., and the pressure of the bonding process is 10 KPa-500 KPa; and / or, The annealing temperature is 100° C.-200° C., and the annealing time is 10 min-60 min; and / or, The step of obtaining the photosensitive dry film having the piezoelectric film further comprises polishing the surface of the piezoelectric film; and / or, The edge of the exposed area does not exceed the edge of the photosensitive dry film layer; and / or The method of forming the release hole in the piezoelectric film comprises at least one of an ion beam etching method and a wet etching method; and / or, The edge of the release hole at the photosensitive dry film layer does not exceed the edge of the exposed area.

8. The method according to claim 6, characterized in that Also includes: Forming a patterned photoresist layer on a side of the piezoelectric film away from the photosensitive dry film layer; forming an electrode layer on a side of the piezoelectric film not covered by the patterned photoresist layer; then removing the patterned photoresist layer; Wherein, the method for forming the patterned photoresist layer includes at least one of a dry etching method, a wet etching method, and a stripping method; and / or, The method for removing the patterned photoresist layer includes a metal stripping process.

9. The method according to claim 6, characterized in that The ion implantation process satisfies at least one of the following conditions: The ion species of the ion implantation process include at least one of helium, hydrogen, nitrogen, oxygen and argon; The implantation dose of the ion implantation process is 1×10 15 ions / cm 2 -5×10 17 ions / cm 2 ; The implantation energy of the ion implantation process is 10KeV-1000KeV.

10. A radio frequency module, characterized in that: A bulk acoustic wave filter comprising the bulk acoustic wave filter according to any one of claims 1 to 5, or a bulk acoustic wave filter prepared by the method according to any one of claims 6 to 9.

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