A method for manufacturing a bulk acoustic wave filter and a bulk acoustic wave filter

Abstract

The present application discloses a method for manufacturing a bulk acoustic wave filter and a bulk acoustic wave filter, comprising: depositing a piezoelectric layer on a preset structure to be removed, wherein the piezoelectric layer comprises a first single crystal piezoelectric layer and a second single crystal piezoelectric layer of the same thickness, and the first single crystal piezoelectric layer and the second single crystal piezoelectric layer have opposite crystal phases; manufacturing a resonant structure on a side of the piezoelectric layer away from the structure to be removed; manufacturing a filter support body on the other side of the resonant structure; removing the structure to be removed, and forming an upper electrode structure on the piezoelectric layer, wherein the upper electrode structure and the resonant structure are arranged relative to the piezoelectric layer; and forming a resonant cavity in the resonant structure.

Description

Technical Field

[0001] The present application relates to the technical field of filters, and in particular to a method for manufacturing a bulk acoustic wave filter and a bulk acoustic wave filter. Background Art

[0002] Since the single crystal piezoelectric layer is a key component to realize the core function of the BAW filter, a single crystal piezoelectric layer is usually deposited in a traditional BAW filter. Although the single crystal piezoelectric layer has many advantages, including converting electrical signals into BAW, determining the resonant frequency, and improving the filter performance, the single crystal piezoelectric layer is prone to stress under certain conditions, which may affect the stability of the BAW filter's operating frequency, reduce the BAW filter's filtering efficiency, and shorten the life of the BAW filter. For example, when BAW propagates in the single crystal piezoelectric layer and forms a standing wave, the periodic compression and stretching inside the material will cause local stress concentration.

[0003] In order to solve the above problems, technicians eliminate the stress generated by the single crystal piezoelectric layer by depositing a metal layer and a filling layer in the BAW filter. However, the above method of eliminating the stress generated by the single crystal piezoelectric layer by depositing a metal layer and a filling layer has certain disadvantages. For example, although depositing a metal layer and a filling layer in the BAW filter can not only provide mechanical support but also alleviate the effects of stress concentration, it increases the process steps for making the BAW filter and increases the complexity of making the BAW filter.

[0004] With regard to the technical problem existing in the above-mentioned prior art that in order to offset the stress of the single crystal piezoelectric layer, it is necessary to deposit a metal layer and a filling layer in the BAW filter, thereby increasing the process steps for manufacturing the BAW filter and increasing the complexity of manufacturing the BAW filter, no effective solution has been proposed so far. Summary of the invention

[0005] The embodiments of the present disclosure provide a method for manufacturing a bulk acoustic wave filter and a bulk acoustic wave filter, so as to at least solve the technical problem in the prior art that in order to offset the stress of a single crystal piezoelectric layer, a metal layer and a filling layer need to be deposited in the bulk acoustic wave filter, thereby increasing the process steps for manufacturing the bulk acoustic wave filter and increasing the complexity of manufacturing the bulk acoustic wave filter.

[0006] According to one aspect of an embodiment of the present disclosure, a method for manufacturing a bulk acoustic wave filter is provided, comprising: depositing a piezoelectric layer on a preset structure to be removed, wherein the piezoelectric layer comprises a first single crystal piezoelectric layer and a second single crystal piezoelectric layer of the same thickness, and the first single crystal piezoelectric layer and the second single crystal piezoelectric layer have opposite crystal phases; making a resonant structure on a side of the piezoelectric layer away from the structure to be removed; making a filter support body on the other side of the resonant structure; removing the structure to be removed and forming an upper electrode structure on the piezoelectric layer, wherein the upper electrode structure and the resonant structure are arranged relative to the piezoelectric layer; and forming a resonant cavity in the resonant structure.

[0007] Optionally, the structure to be removed includes a single crystal epitaxial layer, and the operation of depositing a piezoelectric layer on the preset structure to be removed includes: depositing a first single crystal piezoelectric layer on the single crystal epitaxial layer; and depositing a second single crystal piezoelectric layer on the other side of the first single crystal piezoelectric layer.

[0008] Optionally, the method further includes: setting the thickness of the first single crystal piezoelectric layer and the second single crystal piezoelectric layer to 0.01 um to 3 um.

[0009] Optionally, the operation of making a filter support body on the other side of the resonant structure includes: depositing a first sacrificial layer on the side of the resonant structure away from the piezoelectric layer; and depositing a filter carrier substrate on the other side of the first sacrificial layer, wherein the first sacrificial layer is directly bonded to the filter carrier substrate.

[0010] Optionally, the operation after forming the upper electrode structure on the piezoelectric layer further includes: forming a first conductor for electrical connection on the upper electrode structure, and forming a second conductor for electrical connection on the piezoelectric layer.

[0011] Optionally, the upper electrode structure includes an upper electrode layer deposited on one side of the first single crystal piezoelectric layer and a first passivation layer deposited on the other side of the upper electrode layer, and the lower electrode structure includes a lower electrode layer deposited on one side of the second single crystal piezoelectric layer. The operations of forming a first conductor for electrical connection in the upper electrode structure and forming a second conductor for electrical connection in the piezoelectric layer include: etching a first through hole in the first passivation layer, and forming a first conductor in the first through hole, wherein the first conductor is electrically connected to the upper electrode layer and exposed outside the first passivation layer; etching a second through hole in the first single crystal piezoelectric layer and etching a third through hole in the second single crystal piezoelectric layer; and forming a second conductor in the second through hole and the third through hole, wherein the second conductor is electrically connected to the lower electrode layer and exposed outside the first single crystal piezoelectric layer.

[0012] Optionally, the BAW filter includes a working area and an edge area surrounding the working area, wherein the working area includes a first conductor, a second conductor and a resonant structure, and the method further includes: etching a plurality of fourth through holes in the edge area, wherein the plurality of fourth through holes penetrate the piezoelectric layer.

[0013] Optionally, the operation of etching a plurality of fourth through holes in the edge region includes: etching fourth through holes in the edge region of the piezoelectric layer away from the first conductor, wherein the depth of the fourth through holes is greater than or equal to the thickness of the piezoelectric layer; and / or etching fourth through holes in the edge region of the upper electrode structure away from the second conductor, and the depth of the fourth through holes is greater than or equal to the sum of the thicknesses of the upper electrode structure and the piezoelectric layer.

[0014] According to another aspect of the embodiment of the present disclosure, a bulk acoustic wave filter is also provided, comprising: a structure to be removed, a piezoelectric layer, a resonant structure, a filter support body and an upper electrode structure, wherein the piezoelectric layer is deposited on one side of the structure to be removed, and the piezoelectric layer comprises a first single crystal piezoelectric layer and a second single crystal piezoelectric layer of the same thickness, and the first single crystal piezoelectric layer and the second single crystal piezoelectric layer have opposite crystal phases; the resonant structure is formed on a side of the piezoelectric layer away from the structure to be removed; the filter support body is formed on a side of the resonant structure away from the piezoelectric layer; when the structure to be removed is removed, the upper electrode structure is formed on a side of the piezoelectric layer away from the resonant structure; and a resonant cavity is formed inside the resonant structure.

[0015] Optionally, the structure to be removed includes a single crystal epitaxial layer, a first single crystal piezoelectric layer is deposited on the single crystal epitaxial layer; and a second single crystal piezoelectric layer is deposited on the first single crystal piezoelectric layer.

[0016] Optionally, the thickness of the first single crystal piezoelectric layer and the second single crystal piezoelectric layer is 0.01 um to 3 um.

[0017] Optionally, the filter support body includes: a first sacrificial layer and a filter carrier substrate, wherein the first sacrificial layer is deposited on a side of the resonant structure away from the piezoelectric layer; and the filter carrier substrate is deposited on the other side of the first sacrificial layer, wherein the first sacrificial layer is directly bonded to the filter carrier substrate.

[0018] Optionally, the device further comprises: a first conductor formed on the upper electrode structure and a second conductor formed on the piezoelectric layer, wherein the first conductor and the second conductor are used for electrical connection.

[0019] Optionally, the upper electrode structure includes an upper electrode layer deposited on one side of the first single crystal piezoelectric layer and a first passivation layer deposited on the other side of the upper electrode layer, the lower electrode structure includes a lower electrode layer deposited on one side of the second single crystal piezoelectric layer, the first passivation layer is etched with a first through hole, and a first conductor is formed inside the first through hole, wherein the first conductor is electrically connected to the upper electrode layer and exposed outside the first passivation layer; the first single crystal piezoelectric layer is etched with a second through hole and the second single crystal piezoelectric layer is etched with a third through hole; and a second conductor is formed inside the second through hole and the third through hole, wherein the second conductor is electrically connected to the lower electrode layer and exposed outside the first single crystal piezoelectric layer.

[0020] Optionally, the BAW filter includes a working area and an edge area surrounding the working area, wherein the working area includes a first conductor, a second conductor and a resonant structure, and the device further includes: a plurality of fourth through holes etched in the edge area, wherein the plurality of fourth through holes penetrate the piezoelectric layer.

[0021] Optionally, a fourth through hole is etched in an edge region of the piezoelectric layer away from the first conductor, wherein a depth of the fourth through hole is greater than or equal to the thickness of the piezoelectric layer; and / or a fourth through hole is etched in an edge region of the upper electrode structure away from the second conductor, wherein a depth of the fourth through hole is greater than or equal to the sum of the thicknesses of the upper electrode structure and the piezoelectric layer.

[0022] Unlike the prior art, the present application does not eliminate the stress generated by the first single crystal piezoelectric layer by adding a metal layer and a filling layer, but further deposits a second single crystal piezoelectric layer with an opposite crystal phase and the same thickness on the basis of the first single crystal piezoelectric layer when the first single crystal piezoelectric layer is deposited, thereby offsetting the stress existing in the first single crystal piezoelectric layer. Therefore, compared with the traditional method of eliminating the stress existing in the single crystal piezoelectric layer by adding a metal layer and a filling layer, the present application only needs to deposit a second single crystal piezoelectric layer on the first single crystal piezoelectric layer to offset the stress of the first single crystal piezoelectric layer, thereby reducing the process steps of making the bulk acoustic wave filter compared to the traditional method, and greatly reducing the complexity of making the bulk acoustic wave filter. This solves the technical problem that in order to offset the stress of the single crystal piezoelectric layer in the prior art, it is necessary to deposit a metal layer and a filling layer in the bulk acoustic wave filter, thereby increasing the process steps of making the bulk acoustic wave filter and increasing the complexity of making the bulk acoustic wave filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Hereinafter, some specific embodiments of the present application will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0024] Figure 1 is a flow chart of a method for manufacturing a bulk acoustic wave filter according to an embodiment of the present application;

[0025] Figures 2 to 15 is a schematic diagram of various structures in the process of manufacturing a bulk acoustic wave filter according to an embodiment of the present application;

[0026] Fig.16 It is a schematic diagram of the working area and edge area of ​​multiple BAW filters according to the embodiments of the present application. DETAILED DESCRIPTION

[0027] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] In order to enable those skilled in the art to better understand the scheme of the present disclosure, the technical scheme in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present disclosure.

[0029] It should be noted that the terms "first", "second", etc. in the specification and claims of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so as to describe the embodiments of the present disclosure described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0030] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0031] Secondly, the present application is described in detail with reference to the schematic diagram. When describing the embodiments of the present application in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present application. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0032] According to a first aspect of the present embodiment, a method for manufacturing a bulk acoustic wave filter is provided. Figure 1 A schematic diagram showing the process of the method is shown in FIG. Figure 1 As shown, the method includes:

[0033] S101: depositing a piezoelectric layer on a preset structure to be removed, wherein the piezoelectric layer includes a first single crystal piezoelectric layer and a second single crystal piezoelectric layer having the same thickness, and the first single crystal piezoelectric layer and the second single crystal piezoelectric layer have opposite crystal phases;

[0034] S102: making a resonant structure on a side of the piezoelectric layer away from the structure to be removed;

[0035] S103: making a filter support body on the other side of the resonant structure;

[0036] S104: removing the structure to be removed, and forming an upper electrode structure on the piezoelectric layer, wherein the upper electrode structure and the resonant structure are arranged relative to the piezoelectric layer; and

[0037] S105: forming a resonant cavity in the resonant structure.

[0038] A method for manufacturing a bulk acoustic wave filter provided by an embodiment of the present disclosure is adopted, wherein a piezoelectric layer is deposited on a preset structure to be removed, wherein the piezoelectric layer includes a first single crystal piezoelectric layer and a second single crystal piezoelectric layer that are subsequently identical, and the crystal phases of the first single crystal piezoelectric layer and the second single crystal piezoelectric layer are opposite; a resonant structure is fabricated on a side of the piezoelectric layer away from the structure to be removed; a filter support body is fabricated on the other side of the resonant structure; the structure to be removed is removed, and an upper electrode structure is formed on the piezoelectric layer, wherein the upper electrode structure and the resonant structure are arranged relative to the piezoelectric layer; and a resonant cavity is formed in the resonant structure.

[0039] Therefore, unlike the prior art, the present application does not eliminate the stress generated by the first single crystal piezoelectric layer by adding a metal layer and a filling layer, but further deposits a second single crystal piezoelectric layer with opposite crystal phase and the same thickness on the basis of the first single crystal piezoelectric layer when the first single crystal piezoelectric layer is deposited, thereby offsetting the stress existing in the first single crystal piezoelectric layer. Therefore, compared with the traditional method of eliminating the stress existing in the single crystal piezoelectric layer by adding a metal layer and a filling layer, the present application only needs to deposit a second single crystal piezoelectric layer on the first single crystal piezoelectric layer to offset the stress of the first single crystal piezoelectric layer, thereby reducing the process steps of making the bulk acoustic wave filter compared to the traditional method, and greatly reducing the complexity of making the bulk acoustic wave filter. Furthermore, the technical problem existing in the prior art that in order to offset the stress of the single crystal piezoelectric layer, it is necessary to deposit a metal layer and a filling layer in the bulk acoustic wave filter, thereby increasing the process steps of making the bulk acoustic wave filter and increasing the complexity of making the bulk acoustic wave filter is solved.

[0040] The following are specific steps for manufacturing a bulk acoustic wave filter provided in the embodiment of the present application:

[0041] refer to Figure 2As shown, before depositing the piezoelectric layer on the structure to be removed, the structure to be removed needs to be fabricated in advance. Specifically, first, a single crystal buffer layer 110 is deposited on one side of the substrate 100 to be removed. Then, a single crystal epitaxial layer 120 is deposited on the other side of the single crystal buffer layer 110 .

[0042] Optionally, the substrate 100 to be removed is made of silicon, silicon carbide or sapphire.

[0043] Further optionally, the material of the single crystal buffer layer 110 matches the lattice structure and lattice constant of the material of the single crystal epitaxial layer 120. For example, the material of the single crystal epitaxial layer 120 is aluminum nitride, and aluminum nitride or gallium nitride matching the lattice structure and lattice constant of the material of the single crystal epitaxial layer 120 is selected to make the single crystal buffer layer 110.

[0044] Therefore, by selecting a material that matches the lattice structure and lattice constant of the single crystal epitaxial layer 120 to make the single crystal buffer layer 110 and then making the single crystal epitaxial layer 120 on the single crystal buffer layer 110, a high-quality single crystal epitaxial layer 120 can be grown.

[0045] refer to Figure 3 As shown, when the structure to be removed is completed, a piezoelectric layer is deposited on the structure to be removed. Specifically, the piezoelectric layer is deposited on one side of the single crystal epitaxial layer 120 of the structure to be removed. The piezoelectric layer and the single crystal buffer layer 110 are relatively arranged on both sides of the single crystal epitaxial layer 120. And the piezoelectric layer includes a first single crystal piezoelectric layer 130a and a second single crystal piezoelectric layer 130b. The first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b have the same thickness and opposite crystal phases. Therefore, since a layer of the second single crystal piezoelectric layer 130b is deposited on the first single crystal piezoelectric layer 130a, the stress of the first single crystal piezoelectric layer 130a can be offset, thereby reducing the process steps of manufacturing the bulk acoustic wave filter compared to the traditional method, and greatly reducing the complexity of manufacturing the bulk acoustic wave filter.

[0046] Further references Figure 3 As shown, the operation of depositing a piezoelectric layer on the preset structure to be removed includes: depositing a first single crystal piezoelectric layer 130a on the single crystal epitaxial layer 120; and depositing a second single crystal piezoelectric layer 130b on the other side of the first single crystal piezoelectric layer 130a.

[0047] Optionally, it also includes: setting the thickness of the first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b to 0.01um~3um. Therefore, when the thickness of the first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b are the same, and the thickness of the first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b are set in the range of 0.01um~3um, the stress of the first single crystal piezoelectric layer 130a changes from -3000MPa to 0Pa, and the stress of the second single crystal piezoelectric layer 130b changes from +3000MPa to 0Pa. It can be seen from the above data that the technical solution provided in the present application can completely offset the stress of the first single crystal piezoelectric layer 130a, thereby effectively ensuring the performance of the bulk acoustic wave filter.

[0048] Further optionally, the sum of the thicknesses of the first single crystal piezoelectric layer 130 a and the second single crystal piezoelectric layer 130 b may be in the range of plus or minus 20% of the sum of the above thickness values ​​(ie, 0.02 um to 6 um).

[0049] refer to Figure 4~Figure 8 As shown, after the piezoelectric layer is deposited on the structure to be removed, a resonant structure is further fabricated on the side of the piezoelectric layer away from the structure to be removed. The specific operation includes: forming a lower electrode structure on the side of the second single crystal piezoelectric layer 130b away from the structure to be removed; and forming a cavity structure to be etched on the other side of the lower electrode structure, and the lower electrode structure and the cavity structure to be etched constitute a resonant structure.

[0050] refer to Figure 4 and Figure 5 As shown, the operation of forming the lower electrode structure on the side of the second single crystal piezoelectric layer 130b away from the structure to be removed includes: first, depositing the lower electrode layer 140 on the side of the second single crystal piezoelectric layer 130b away from the structure to be removed. Then, depositing the first passivation layer 150 on the other side of the lower electrode layer 140. Further, etching the lower electrode layer 140 and the first passivation layer 150, and exposing the piezoelectric layer (specifically, the second single crystal piezoelectric layer 130b). Thus, the first passivation layer 150 can protect the lower electrode layer 140 and prevent the lower electrode layer 140 from being oxidized and affecting the performance of the bulk acoustic wave filter.

[0051] Optionally, the lower electrode layer 140 and the first passivation layer 150 are etched by a wet chemical etching process and / or a plasma excitation etching process.

[0052] Further optionally, the lower electrode layer 140 is made of one or more metal materials having conductive properties such as molybdenum Mo, aluminum Al, copper Cu, platinum Pt, tantalum Ta, tungsten W, palladium Pd and ruthenium Ru.

[0053] Further optionally, the first passivation layer 150 is made of a non-conductive material, such as silicon nitride, aluminum nitride, etc.

[0054] refer to Figure 6~Figure 8 As shown, the operation of forming a cavity structure to be etched on the side of the lower electrode structure away from the piezoelectric layer, and the lower electrode structure and the cavity structure to be etched to form a resonant structure includes: first, depositing a second sacrificial layer 160 on the side of the first passivation layer 150 away from the lower electrode layer 140, wherein the second sacrificial layer 160 covers the first passivation layer 150 and the second single crystal piezoelectric layer 130b exposed outside the first passivation layer 150. Then, etching the second sacrificial layer 160 to form an island structure to be etched. Further, depositing a cutoff boundary layer 170 on one side of the second single crystal piezoelectric layer 130b, the island structure to be etched and the lower electrode structure, and forming a cavity structure to be etched surrounded by the cutoff boundary layer 170, the lower electrode layer 140 and the second single crystal piezoelectric layer 130b.

[0055] Optionally, the operation after depositing the second sacrificial layer 160 further includes: planarizing and polishing the second sacrificial layer 160. Further optionally, the second sacrificial layer 160 may be deposited by a CVD (Chemical Vapor Deposition) process and / or a PVD (Physical Vapor Deposition) process. The second sacrificial layer 160 may also be planarized and polished by CMP (chemical mechanical polish).

[0056] Further, refer to Figure 7 As shown, the second sacrificial layer 160 is etched to form an island structure to be etched, wherein a portion of the island structure to be etched covers the first passivation layer 150 and another portion covers the second single crystal piezoelectric layer 130b.

[0057] Further, refer to Figure 8 As shown, a cut-off boundary layer 170 is deposited on one side of the second single crystal piezoelectric layer 130b, the island structure to be etched, and the lower electrode structure, and the cut-off boundary layer 170 covers the island structure to be etched, the first passivation layer 150 exposed outside the island structure to be etched, and the second single crystal piezoelectric layer 130b exposed outside the island structure to be etched and the first passivation layer 150. Thus, when the cut-off boundary layer 170, the first passivation layer 150, and the second single crystal piezoelectric layer 130b are surrounded, a cavity structure to be etched can be formed. The cavity structure to be etched corresponds to the island structure to be etched.

[0058] refer to Fig. 9 and Fig.10As shown, when the resonant structure is completed, a filter support body is manufactured on the other side of the resonant structure away from the piezoelectric layer. The specific operations include: first, depositing a first sacrificial layer 180 on the side of the cutoff boundary layer 170 away from the piezoelectric layer. Then, a filter carrier substrate 190 is deposited on the other side of the first sacrificial layer 180, and the first sacrificial layer 180 is directly bonded to the filter carrier substrate 190. Therefore, since a second single crystal piezoelectric layer 130b having the same thickness and opposite crystal phase as the first single crystal piezoelectric layer 130a is provided in the present application to offset the stress generated by the first single crystal piezoelectric layer 130a, and the metal layer and the filling layer are omitted, the first sacrificial layer 180 can be directly bonded to the filter carrier substrate 190.

[0059] Optionally, the resonator carrier substrate 190 is made of silicon, silicon carbide or sapphire.

[0060] refer to Fig.11 As shown, after the filter support body is deposited, the bulk acoustic wave filter is turned over as a whole.

[0061] refer to Fig.12 As shown, when the BAW filter is flipped, the structure to be removed is removed. Optionally, the structure substrate 100 to be removed is removed by a grinding process. The single crystal buffer layer 110 and the single crystal epitaxial layer 120 are removed by a plasma dry etching process and / or a wet chemical etching process.

[0062] refer to Fig.13 As shown, in the case where the structure to be removed is removed, an upper electrode structure is formed on the piezoelectric layer. The specific operation includes: first, depositing an upper electrode layer 200 on the side of the first single crystal piezoelectric layer 130a away from the resonant structure. Then, depositing a first passivation layer 210 on the other side of the upper electrode layer 200. Further, etching the upper electrode layer 200 and the first passivation layer 210, and exposing the first single crystal piezoelectric layer 130a. Thereby, the first passivation layer 210 can protect the upper electrode layer 200 and prevent the upper electrode layer 200 from being oxidized and affecting the performance of the bulk acoustic wave filter.

[0063] refer to Fig.13 As shown, when the upper electrode structure is formed, the cavity structure to be etched is etched to form a resonant cavity.

[0064] Optionally, the cavity structure to be etched is etched by one or more of hydrofluoric acid solution wet etching, BOE (Buffered Oxide Etchant) solution wet etching and hydrofluoric acid vapor etching.

[0065] Further, refer to Fig.14As shown, after forming the upper electrode structure on the piezoelectric layer, the method further includes: forming a first conductor 220 for electrical connection on the upper electrode structure, and forming a second conductor 230 for electrical connection on the piezoelectric layer.

[0066] Optionally, the operation of forming the first conductor 220 for electrical connection on the upper electrode structure includes: first, etching a first through hole in the first passivation layer 210, so that the first through hole can expose the upper electrode layer 200. Then, forming the first conductor 220 in the first through hole, so that the first conductor 220 is connected to the upper electrode layer 200 through the first through hole and exposed outside the first passivation layer 210.

[0067] Optionally, the operation of forming the second conductor 230 for electrical connection in the piezoelectric layer includes: first, etching a second through hole in the first single crystal piezoelectric layer 130a, so that the second through hole can expose the second single crystal piezoelectric layer 130b. Then, etching a third through hole in the second single crystal piezoelectric layer 130b, so that the third through hole can expose the lower electrode layer 140. Further, forming the second conductor 230 in the second through hole and the third through hole, so that the second conductor 230 is connected to the lower electrode layer 140 through the second through hole and the third through hole, and is exposed outside the first single crystal piezoelectric layer 130a.

[0068] In some embodiments, during the use of the BAW filter, one end of the first conductor 220 is electrically connected to the upper electrode layer 200, and the other end is electrically connected to the external circuit. One end of the second conductor 230 is electrically connected to the lower electrode layer 140, and the other end is electrically connected to the external circuit. Thus, the first conductor 220, the second conductor 230 and the external circuit can form a loop together, thereby ensuring the normal use of the BAW filter.

[0069] In addition, since the present application offsets the stress of the first single crystal piezoelectric layer 130a by setting a second single crystal piezoelectric layer 130b with the same thickness and opposite crystal phase as the first single crystal piezoelectric layer 130a, rather than eliminating the stress of the first single crystal piezoelectric layer 130a by setting a metal layer and a filling layer, there is no problem of parasitic capacitance caused by the metal layer. Furthermore, since there is no problem of parasitic capacitance caused by the metal layer, the present application does not need to set up an additional third conductor for grounding, thereby greatly reducing the manufacturing process of the bulk acoustic wave filter and reducing the manufacturing complexity of the bulk acoustic wave filter.

[0070] Further, refer to Fig.15 As shown, the BAW filter includes a working area and an edge area surrounding the working area. The working area includes a first conductor 220, a second conductor 230 and a resonant structure. After the BAW filter is manufactured, a fourth through hole 240 can be added to the edge area of ​​the BAW filter to further reduce stress. A plurality of fourth through holes 240 penetrate the piezoelectric layer.

[0071] In one embodiment, the specific operation of etching a plurality of fourth through holes in the edge region includes: first, etching the fourth through holes 240 in the edge region of the piezoelectric layer away from the first conductor 220. The fourth through holes 240 penetrate the first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b.

[0072] Optionally, the depth of the fourth through hole 240 is greater than or equal to the sum of the thicknesses of the first single-crystal piezoelectric layer 130 a and the second single-crystal piezoelectric layer 130 b .

[0073] In another embodiment, the specific operation of etching a plurality of fourth through holes in the edge region includes: first, etching a fourth through hole 240 in the edge region of the upper electrode structure away from the second conductor 230. The fourth through hole 240 penetrates the first passivation layer 210, the upper electrode layer 200, the first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b.

[0074] Optionally, the depth of the fourth through hole 240 is greater than or equal to the sum of the thicknesses of the first passivation layer 210 , the upper electrode layer 200 , the first single crystal piezoelectric layer 130 a , and the second single crystal piezoelectric layer 130 b .

[0075] Further, Fig.16 The working areas 250 of multiple BAW filters and multiple fourth through holes 240 opened in the edge area are shown. The frames of the working areas 250 of the multiple BAW filters and the multiple fourth through holes 240 in the edge area are the piezoelectric layer etching areas. In addition, when multiple fourth through holes 240 are etched in the edge area of ​​the working area 250 of each BAW filter and the frames of the working areas 250 of the multiple BAW filters are etched, the stress can be further reduced.

[0076] Optionally, the shape of the fourth through hole 240 is not limited to a circle, and may also be other shapes such as a square or a rectangle, which is not limited here.

[0077] According to another aspect of the present application, a bulk acoustic wave filter is also provided, comprising: a structure to be removed, a piezoelectric layer, a resonant structure, a filter support body and an upper electrode structure, wherein the piezoelectric layer is deposited on one side of the structure to be removed, and the piezoelectric layer comprises a first single crystal piezoelectric layer 130a and a second single crystal piezoelectric layer 130b of the same thickness, and the first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b have opposite crystal phases; the resonant structure is arranged on the other side of the piezoelectric layer; a filter support body is formed on one side of the resonant structure relative to the piezoelectric layer; when the structure to be removed is removed, the upper electrode structure is formed on the side of the piezoelectric layer away from the resonant structure; and a resonant cavity is formed inside the resonant structure.

[0078] Optionally, the first single crystal piezoelectric layer 130a is deposited on the single crystal extension layer 120; and the second single crystal piezoelectric layer 130b is deposited on the first single crystal piezoelectric layer 130a.

[0079] Optionally, the thickness of the first single crystal piezoelectric layer 130a and the second single crystal piezoelectric layer 130b is 0.01 um to 3 um.

[0080] Optionally, the filter support body includes: a first sacrificial layer 180 deposited on a side of the resonant structure away from the piezoelectric layer; and a filter carrier substrate 190 deposited on the other side of the first sacrificial layer 180 , wherein the first sacrificial layer 180 is directly bonded to the filter carrier substrate 190 .

[0081] Optionally, the device further includes: a first conductor 220 formed on the upper electrode structure and a second conductor 230 formed on the piezoelectric layer, wherein the first conductor 220 and the second conductor 230 are used for electrical connection.

[0082] Optionally, the first passivation layer 210 is etched with a first through hole, and a first conductor 220 is formed inside the first through hole, wherein the first conductor 220 is electrically connected to the upper electrode layer 200 and exposed outside the first passivation layer 210; the first single crystal piezoelectric layer 130a is etched with a second through hole and the second single crystal piezoelectric layer 130b is etched with a third through hole; and a second conductor 230 is formed inside the second through hole and the third through hole, wherein the second conductor 230 is electrically connected to the lower electrode layer 140 and exposed outside the first single crystal piezoelectric layer 130a.

[0083] Optionally, the BAW filter includes a working area and an edge area surrounding the working area, wherein the working area includes a first conductor 220, a second conductor 230 and a resonant structure, and the device also includes: a plurality of fourth through holes 240 etched in the edge area, wherein the plurality of fourth through holes 240 penetrate the piezoelectric layer.

[0084] Optionally, a fourth through hole 240 is etched in an edge region of the piezoelectric layer away from the first conductor 220, wherein the depth of the fourth through hole 240 is greater than or equal to the thickness of the piezoelectric layer; and / or a fourth through hole 240 is etched in an edge region of the upper electrode structure away from the second conductor 230, wherein the depth of the fourth through hole 240 is greater than or equal to the sum of the thicknesses of the upper electrode structure and the piezoelectric layer.

[0085] Unlike the prior art, the present application does not eliminate the stress generated by the first single crystal piezoelectric layer by adding a metal layer and a filling layer, but further deposits a second single crystal piezoelectric layer with an opposite crystal phase and the same thickness on the basis of the first single crystal piezoelectric layer when depositing the first single crystal piezoelectric layer, thereby offsetting the stress existing in the first single crystal piezoelectric layer. Therefore, compared with the traditional method of eliminating the stress existing in the single crystal piezoelectric layer by adding a metal layer and a filling layer, the present application only needs to deposit a second single crystal piezoelectric layer on the first single crystal piezoelectric layer to offset the stress of the first single crystal piezoelectric layer, thereby reducing the process steps of making the bulk acoustic wave filter compared to the traditional method, and greatly reducing the complexity of making the bulk acoustic wave filter. This solves the technical problem that in order to offset the stress of the single crystal piezoelectric layer in the prior art, a metal layer and a filling layer need to be set in the bulk acoustic wave filter, thereby increasing the process steps of making the bulk acoustic wave filter and increasing the complexity of making the bulk acoustic wave filter.

[0086] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present disclosure. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0087] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0088] In the description of the present disclosure, it is necessary to understand that the orientation or positional relationship indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present disclosure and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present disclosure; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0089] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for manufacturing a bulk acoustic wave filter, characterized in that: include: Depositing a piezoelectric layer on a preset structure to be removed, wherein the piezoelectric layer includes a first single crystal piezoelectric layer and a second single crystal piezoelectric layer having the same thickness, and the first single crystal piezoelectric layer and the second single crystal piezoelectric layer have opposite crystal phases, and wherein the structure to be removed includes a single crystal epitaxial layer, and the operation of depositing the piezoelectric layer on the preset structure to be removed includes: depositing the first single crystal piezoelectric layer on the single crystal epitaxial layer; and Depositing the second single crystal piezoelectric layer on the other side of the first single crystal piezoelectric layer; Making a resonant structure on a side of the piezoelectric layer away from the structure to be removed; Making a filter support body on the other side of the resonant structure; The structure to be removed is removed, and an upper electrode structure is formed on the piezoelectric layer, wherein the upper electrode structure and the resonant structure are arranged relative to the piezoelectric layer, and the upper electrode structure includes an upper electrode layer deposited on one side of the first single crystal piezoelectric layer and a first passivation layer deposited on the other side of the upper electrode layer, and the lower electrode structure includes a lower electrode layer deposited on one side of the second single crystal piezoelectric layer, wherein the operation after forming the upper electrode structure on the piezoelectric layer further includes: forming a first conductor for electrical connection on the upper electrode structure, and forming a second conductor for electrical connection on the piezoelectric layer; and A resonant cavity is formed in the resonant structure.

2. The method according to claim 1, characterized in that Also includes: The thickness of the first single crystal piezoelectric layer and the second single crystal piezoelectric layer is set to 0.01 um~3 um.

3. The method according to claim 1, characterized in that The operation of making a filter support body on the other side of the resonant structure comprises: Depositing a first sacrificial layer on a side of the resonant structure away from the piezoelectric layer; and A filter carrier substrate is deposited on the other side of the first sacrificial layer, wherein the first sacrificial layer is directly bonded to the filter carrier substrate.

4. The method according to claim 3, characterized in that The operation of forming a first conductor for electrical connection on the upper electrode structure and forming a second conductor for electrical connection on the piezoelectric layer comprises: Etching a first through hole in the first passivation layer, and forming a first conductor in the first through hole, wherein the first conductor is electrically connected to the upper electrode layer and exposed outside the first passivation layer; Etching a second through hole in the first single crystal piezoelectric layer and etching a third through hole in the second single crystal piezoelectric layer; and A second conductor is formed in the second through hole and the third through hole, wherein the second conductor is electrically connected to the lower electrode layer and is exposed outside the first single crystal piezoelectric layer.

5. The method according to claim 4, characterized in that The BAW filter includes a working area and an edge area surrounding the working area, wherein the working area includes the first conductor, the second conductor and the resonant structure, and the method further includes: etching a plurality of fourth through holes in the edge area, wherein the plurality of fourth through holes penetrate the piezoelectric layer.

6. The method according to claim 5, characterized in that The operation of etching a plurality of fourth through holes in the edge region includes: Etching the fourth through hole in an edge region of the piezoelectric layer away from the first conductor, wherein a depth of the fourth through hole is greater than or equal to a thickness of the piezoelectric layer; and / or The fourth through hole is etched in an edge region of the upper electrode structure away from the second conductor, and a depth of the fourth through hole is greater than or equal to the sum of the thickness of the upper electrode structure and the piezoelectric layer.

7. A bulk acoustic wave filter, characterized in that: include: The structure to be removed, the piezoelectric layer, the resonant structure, the filter support body and the upper electrode structure, wherein The piezoelectric layer is deposited on one side of the structure to be removed, and the piezoelectric layer includes a first single crystal piezoelectric layer and a second single crystal piezoelectric layer with the same thickness, and the first single crystal piezoelectric layer and the second single crystal piezoelectric layer have opposite crystal phases, wherein the structure to be removed includes a single crystal epitaxial layer, and the first single crystal piezoelectric layer is deposited on the single crystal epitaxial layer; and The second single crystal piezoelectric layer is deposited on the first single crystal piezoelectric layer; The resonant structure is formed on a side of the piezoelectric layer away from the structure to be removed; The filter support body is formed on a side of the resonant structure away from the piezoelectric layer; In the case where the structure to be removed is removed, the upper electrode structure is formed on a side of the piezoelectric layer away from the resonant structure, wherein the upper electrode structure includes an upper electrode layer deposited on one side of the first single crystal piezoelectric layer and a first passivation layer deposited on the other side of the upper electrode layer, and the lower electrode structure includes a lower electrode layer deposited on one side of the second single crystal piezoelectric layer, and the device further includes: a first conductor formed on the upper electrode structure and a second conductor formed on the piezoelectric layer, wherein the first conductor and the second conductor are used for electrical connection; as well as A resonant cavity is formed inside the resonant structure.

8. The bulk acoustic wave filter according to claim 7, characterized in that The thickness of the first single crystal piezoelectric layer and the second single crystal piezoelectric layer is 0.01 um to 3 um.

9. The bulk acoustic wave filter according to claim 7, characterized in that The filter support body comprises: a first sacrificial layer and a filter carrier substrate, wherein The first sacrificial layer is deposited on a side of the resonant structure away from the piezoelectric layer; and The filter carrier substrate is deposited on the other side of the first sacrificial layer, wherein the first sacrificial layer is directly bonded to the filter carrier substrate.

10. The bulk acoustic wave filter according to claim 9, wherein the lower electrode structure comprises a lower electrode layer deposited on one side of the second single crystal piezoelectric layer, characterized in that: A first through hole is etched in the first passivation layer, and the first conductor is formed inside the first through hole, wherein the first conductor is electrically connected to the upper electrode layer and exposed outside the first passivation layer; The first single crystal piezoelectric layer is etched with a second through hole and the second single crystal piezoelectric layer is etched with a third through hole; and The second conductor is formed inside the second through hole and the third through hole, wherein the second conductor is electrically connected to the lower electrode layer and is exposed outside the first single crystal piezoelectric layer.

11. The bulk acoustic wave filter according to claim 10, characterized in that The bulk acoustic wave filter includes a working area and an edge area surrounding the working area, wherein the working area includes the first conductor, the second conductor and the resonant structure, and the device also includes: a plurality of fourth through holes etched in the edge area, wherein the plurality of fourth through holes penetrate the piezoelectric layer.

12. The bulk acoustic wave filter according to claim 11, characterized in that The fourth through hole is etched in an edge region of the piezoelectric layer away from the first conductor, wherein the depth of the fourth through hole is greater than or equal to the thickness of the piezoelectric layer; and / or The fourth through hole is etched in an edge region of the upper electrode structure away from the second conductor, wherein a depth of the fourth through hole is greater than or equal to the sum of the thickness of the upper electrode structure and the piezoelectric layer.

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