Bulk acoustic wave filter and method of manufacturing the same, radio frequency device

Abstract

The embodiment of the present disclosure provides a bulk acoustic wave filter, a preparation method thereof and a radio frequency device. The preparation method comprises the following steps: providing a substrate; wherein the substrate comprises a base layer, an insulating layer and a semiconductor layer which are sequentially stacked; etching the semiconductor layer to form a groove in the substrate; wherein the groove exposes the insulating layer; removing the insulating layer in a part of a bottom of the groove to expose the base layer, and the remaining insulating layer forms a first sacrificial layer; forming a stack structure covering the first sacrificial layer and part of the base layer in the groove; wherein the stack structure comprises a first electrode layer, a piezoelectric layer and a second electrode layer which are sequentially stacked along a thickness direction of the substrate, and a top of the stack structure is lower than a top of the semiconductor layer; and forming a packaging structure which encloses an opening of the groove.

Description

Technical Field

[0001] This disclosure relates to the semiconductor field, and in particular to a bulk acoustic wave filter, its fabrication method, and a radio frequency device. Background Technology

[0002] Advances in semiconductor manufacturing technology have led to the widespread application of bulk acoustic wave (BAW) filters and their components in fields such as biomedicine, automotive electronics, and mobile terminals. With the evolution of wireless communication and the arrival of the 5G era, the market demand for BAW filters will further increase, trending towards miniaturization and integration with RF terminal modules. Therefore, optimizing BAW filter manufacturing processes and shortening production cycles and costs will enhance their market competitiveness and lead to better application prospects. Summary of the Invention

[0003] According to a first aspect of this disclosure, a method for fabricating a bulk acoustic wave filter is provided, comprising:

[0004] A substrate is provided; wherein the substrate comprises a base layer, an insulating layer and a semiconductor layer stacked sequentially;

[0005] The semiconductor layer is etched to form a trench in the substrate; wherein the trench exposes the insulating layer;

[0006] The insulating layer in a portion of the bottom area of ​​the groove is removed to expose the base layer, and the remaining insulating layer forms a first sacrificial layer;

[0007] A stacked structure covering the first sacrificial layer and a portion of the substrate layer is formed within the groove; wherein the stacked structure includes a first electrode layer, a piezoelectric layer, and a second electrode layer sequentially stacked along the thickness direction of the substrate, and the top of the stacked structure is lower than the top of the semiconductor layer;

[0008] A packaging structure is formed to close the opening of the groove.

[0009] In some embodiments, the substrate comprises at least one of silicon-on-insulator or germanium-on-insulator.

[0010] In some embodiments, the thickness of the first sacrificial layer is equal to the thickness of the insulating layer.

[0011] In some embodiments, the encapsulation structure forming the closed recess opening includes:

[0012] A second sacrificial layer is formed covering the second electrode layer and a portion of the substrate layer;

[0013] Form an etch stop layer covering the second sacrificial layer;

[0014] An encapsulation layer is formed covering the etch stop layer, the encapsulation layer fills the remaining space in the groove, and the top of the encapsulation layer is substantially flush with the top of the semiconductor layer.

[0015] In some embodiments, the preparation method further includes:

[0016] A first through-hole is formed, penetrating the substrate layer and exposing the first electrode; a second through-hole is formed, penetrating the substrate layer and exposing the second electrode;

[0017] A conductive structure is filled into the first and second vias until the conductive structure covers the side of the substrate layer away from the semiconductor layer.

[0018] In some embodiments, the preparation method further includes:

[0019] A first release hole is formed that penetrates the substrate layer and exposes the first sacrificial layer, and a second release hole is formed that penetrates the substrate layer and exposes the second sacrificial layer;

[0020] The first sacrificial layer is removed through the first release hole to form a first cavity, and the second sacrificial layer is removed through the second release hole to form a second cavity.

[0021] In some embodiments, the preparation method further includes:

[0022] Etching agent is introduced into the first cavity through the first release hole to adjust the thickness of the first electrode layer; or...

[0023] Etching agent is introduced into the second cavity through the second release hole to adjust the thickness of the second electrode layer.

[0024] In some embodiments, the encapsulation structure forming the enclosure of the groove includes:

[0025] A thin film layer is covered on top of the semiconductor layer and at the groove opening to form the packaging structure.

[0026] In some embodiments, the preparation method further includes:

[0027] Multiple interfaces are formed on the side of the conductive structure away from the substrate layer;

[0028] Alternatively, the preparation method may further include:

[0029] An adapter board is provided; wherein the adapter board includes a first wiring layer and a second wiring layer, the first wiring layer and the second wiring layer being exposed on two opposing sides of the adapter board along its thickness direction;

[0030] The first wiring layer of the adapter board and the conductive structure are joined together;

[0031] Multiple interfaces are formed in the second wiring layer.

[0032] According to a second aspect of this disclosure, a bulk acoustic wave filter is provided, comprising:

[0033] A substrate includes a base layer, an insulating layer, and a semiconductor layer stacked sequentially. A groove is provided in the substrate, which penetrates the semiconductor layer and the insulating layer and exposes the base layer.

[0034] A stacked structure is located on the base layer within the groove. The stacked structure includes a first electrode layer, a piezoelectric layer, and a second electrode layer stacked sequentially. The first electrode layer partially protrudes away from the base layer to create a first cavity between the first electrode layer and the base layer. The top of the second electrode layer is lower than the top of the semiconductor layer.

[0035] The packaging structure is located on top of the stacked structure and in contact with the semiconductor layer. The packaging structure closes the opening of the groove, and a cavity structure is provided between the top of the second electrode layer and the bottom of the packaging structure.

[0036] In some embodiments, the substrate comprises at least one of silicon-on-insulator or germanium-on-insulator.

[0037] In some embodiments, at least a portion of the sidewalls of the stacked structure and the sidewalls of the groove are in contact.

[0038] In some embodiments, the packaging structure includes:

[0039] An etch stop layer is located on top of the second electrode layer, and a second cavity is provided between the etch stop layer and the second electrode layer, the cavity structure including the second cavity;

[0040] An encapsulation layer covers the etch stop layer and fills the remaining space within the groove, with the top of the encapsulation layer flush with the top of the semiconductor layer.

[0041] In some embodiments, the packaging structure includes: a thin film layer covering the top of the semiconductor layer and the opening of the recess;

[0042] A third cavity is provided between the top of the second electrode layer and the bottom of the thin film layer, and the cavity structure includes the third cavity.

[0043] In some embodiments, the bulk acoustic filter further includes:

[0044] A conductive structure is provided, covering the side of the substrate layer away from the stacked structure, the conductive structure extending through the substrate layer and connected to the first electrode layer and the second electrode layer.

[0045] In some embodiments, the bulk acoustic wave filter further includes: a plurality of interfaces located on the side of the conductive structure away from the substrate layer; or...

[0046] The bulk acoustic wave filter further includes an adapter plate, which includes a first wiring layer and a second wiring layer. The first wiring layer and the second wiring layer are respectively exposed on two opposite sides of the adapter plate along its thickness direction. The first wiring layer is bonded to the conductive structure, and the second wiring layer includes multiple interfaces.

[0047] According to a third aspect of this disclosure, a radio frequency device is provided, including one or more bulk acoustic wave filters as described in a second aspect of this disclosure.

[0048] The bulk acoustic wave (BAW) filter fabrication method provided in this disclosure utilizes a substrate structure comprising a base layer, an insulating layer, and a semiconductor layer. First, a groove is formed by etching the semiconductor layer. Then, a first sacrificial layer and a stacked structure are formed within the groove. The top of the stacked structure is lower than the top of the semiconductor layer. Subsequently, a packaging structure is formed to close the groove opening. A cavity can be formed between the top of the packaging structure and the top of the stacked structure. The first sacrificial layer can also form a cavity after being removed in a subsequent process. The stacked structure and the two cavities located at its top and bottom together constitute a resonant structure, thereby obtaining the BAW filter. In this disclosure, based on the substrate structure, the semiconductor process for fabricating the resonant structure and the packaging process are combined. The substrate can be used as a packaging mold, or the substrate and the packaging structure can be used together to seal the resonant structure, reducing the development of packaging molds and shortening the product manufacturing cycle and cost. Furthermore, the thickness of the base layer, insulating layer, and semiconductor layer in the substrate can be flexibly selected according to the different structural and dimensional requirements of each product, and the opening size of the groove can be flexibly adjusted. This results in high product design flexibility, enabling diverse packaging forms and improving the flexibility of the product in end-use. Attached Figure Description

[0049] Figure 1 A schematic flowchart illustrating a method for fabricating a bulk acoustic wave filter according to an embodiment of this disclosure;

[0050] Figures 2a to 2h A cross-sectional schematic diagram of a bulk acoustic wave filter during its fabrication process, provided in an embodiment of this disclosure;

[0051] Figure 3 This is a top view schematic diagram of a plurality of bulk acoustic wave filters formed on a wafer, provided as an embodiment of the present disclosure;

[0052] Figure 4 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic filter provided in this embodiment of the disclosure;

[0053] Figure 5 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic filter provided in this embodiment of the disclosure;

[0054] Figure 6 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic filter provided in this embodiment of the disclosure;

[0055] Figure 7 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic filter provided in this embodiment of the disclosure;

[0056] Figure 8 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic filter provided in this embodiment of the disclosure;

[0057] Figure 9 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic filter provided in this embodiment of the disclosure;

[0058] Figure 10 A cross-sectional schematic diagram of a bulk acoustic wave filter provided in an embodiment of this disclosure;

[0059] Figure 11 A cross-sectional schematic diagram of another bulk acoustic wave filter provided in an embodiment of this disclosure;

[0060] Figure 12 A cross-sectional schematic diagram of another bulk acoustic wave filter provided in an embodiment of this disclosure;

[0061] Figure 13 This is a cross-sectional schematic diagram of a radio frequency device provided in an embodiment of this disclosure. Detailed Implementation

[0062] Exemplary embodiments provided in this disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure may be implemented in various forms and should not be limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0063] The present disclosure is described in more detail below by way of example with reference to the accompanying drawings. The advantages and features of the present disclosure will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present disclosure. In the embodiments of the present disclosure, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be noted that the technical solutions described in the embodiments of the present disclosure can be arbitrarily combined without conflict.

[0064] Typically, the fabrication process of a bulk acoustic wave filter can begin by using semiconductor processes (such as bulk silicon processing or surface micromachining) to fabricate a bare die of the bulk acoustic wave filter. Then, the bare die is soldered to the substrate using a flip chip (FP) or a ball grid array (BGA). Finally, it is encapsulated using a mold, or packaged using a wafer level package (WLP) with the help of packaging thick film materials and auxiliary structures.

[0065] The former type of bulk acoustic wave filter has many steps in its fabrication process, resulting in a long product manufacturing cycle. It also requires customized molds, which have poor mold flexibility, a single packaging form, and insufficient flexibility in end-use. The latter type requires setting up a packaging support structure first and then selecting specific packaging auxiliary materials (such as packaging thick film). Furthermore, based on the strength of the film layer, it is impossible to guarantee the packaging of large-area wafers.

[0066] Therefore, this disclosure provides a method for fabricating a bulk acoustic wave filter. Figure 1 This is a schematic flowchart illustrating a method for fabricating a bulk acoustic wave filter according to an embodiment of the present disclosure, as shown below. Figure 1 As shown, the preparation method includes:

[0067] S100: Provides a substrate; wherein the substrate comprises a base layer, an insulating layer and a semiconductor layer stacked sequentially;

[0068] S200: Etching the semiconductor layer to form a trench in the substrate; wherein the trench exposes the insulating layer;

[0069] S300: Remove the insulating layer in a portion of the bottom area of ​​the groove to expose the base layer; the remaining insulating layer forms the first sacrificial layer.

[0070] S400: A stacked structure covering a first sacrificial layer and a portion of a substrate layer is formed in a groove; wherein the stacked structure includes a first electrode layer, a piezoelectric layer and a second electrode layer sequentially stacked along the substrate thickness direction, and the top of the stacked structure is lower than the top of the semiconductor layer;

[0071] S500: A packaging structure that forms a closed recess opening.

[0072] For example, the bulk acoustic wave filter is a film bulk acoustic wave filter (FBAR), and the reflection structure of the FBAR is a cavity. In this disclosure, the cavity-type reflection structure is formed after the first sacrificial layer and the subsequently formed second sacrificial layer are removed.

[0073] Figures 2a to 2h This is a cross-sectional schematic diagram illustrating the fabrication process of a bulk acoustic wave filter provided in this embodiment of the disclosure. It should be understood that... Figures 2a to 2h The operations shown are not necessarily performed in a precise order. Instead, the order of each step can be adjusted according to the actual situation, or other operations can be added to the preparation process, or one or more operations can be removed from the preparation process. Figure 3 This is a top view schematic diagram illustrating the formation of multiple bulk acoustic wave filters on a wafer, as provided in an embodiment of this disclosure. The following is in conjunction with... Figures 2a to 2h ,as well as Figure 3 The specific formation process of the bulk acoustic wave filter provided in the embodiments of this disclosure is described in detail.

[0074] See Figure 2a In step S100, a substrate 100 is provided, which includes a base layer 110, an insulating layer 120 and a semiconductor layer 130 stacked sequentially from bottom to top.

[0075] For example, the substrate 100 is made of semiconductor-on-insulator, such as silicon-on-insulator (SOI), germanium-on-insulator (GOI), or silicon-germanium-on-insulator (SGOI).

[0076] For example, the substrate 110 is made of silicon, the insulating layer 120 is made of silicon oxide, and the semiconductor layer 130 can be made of silicon (corresponding to SOI substrate), germanium (corresponding to GOI substrate) or silicon-germanium (corresponding to SGOI substrate).

[0077] See Figure 2b In step S200, the semiconductor layer 130 in a portion of the substrate 100 is removed, forming a trench 200 in the substrate 100. The bottom of the trench 200 is an insulating layer 120. For example, the semiconductor layer 130 can be etched using a dry etching process or a wet etching process to form the trench 200.

[0078] See Figure 2cIn step S300, the insulating layer 120 in the bottom portion of the groove 200 is removed, and the remaining insulating layer 120 forms the first sacrificial layer 310. For example, the insulating layer 120 can be etched using a dry etching process to obtain the desired first sacrificial layer 310.

[0079] In some embodiments, the thickness of the first sacrificial layer 310 is equal to the thickness of the insulating layer 120. In other words, the thickness of the insulating layer 120 in the substrate 100 can be customized according to the thickness of the first sacrificial layer 310. Thus, during the fabrication process, it is not necessary to thin or thicken the insulating layer 120, which can reduce the number of process steps and thus shorten the process cycle.

[0080] It should be understood that in some other embodiments, when the thickness of the insulating layer 120 in the substrate 100 does not meet the thickness requirement of the first sacrificial layer 310, the insulating layer 120 may be thinned or thickened first, and then the insulating layer 120 in the bottom part of the groove 200 may be removed to form the required first sacrificial layer 310.

[0081] See Figure 2d In step S400, a stacked structure 400 covering the first sacrificial layer 310 and a portion of the substrate layer 110 is formed within the groove 200. The top of the stacked structure 400 is lower than the top of the semiconductor layer 130. The tops of the stacked structure 400 and the semiconductor layer 130 refer to the sides of the stacked structure 400 and the semiconductor layer 130 that are away from the substrate layer 110, respectively.

[0082] The stacked structure 400 includes a first electrode layer 410, a piezoelectric layer 420, and a second electrode layer 430 stacked sequentially from bottom to top. The first electrode layer 410 is deposited on the surfaces of the first sacrificial layer 310 and the substrate layer 110. The piezoelectric layer 420 is deposited on the first electrode layer 410, the surface of the first sacrificial layer 310 not covered by the first electrode layer 410, and the surface of the substrate layer 110. The second electrode layer 430 is deposited on the surfaces of the piezoelectric layer 420 and the substrate layer 110. The overlapping region of the orthographic projections of the first sacrificial layer 310, the first electrode layer 410, the piezoelectric layer 420, and the second electrode layer 430 onto the substrate surface constitutes an active region. The portions of the first electrode layer 410 and the second electrode layer 430 located on the surface of the substrate layer 110 can form electrode leads for connection to pads and for connection to circuitry.

[0083] In some embodiments, a patterned photolithography process can be used to form the first electrode layer 410, the piezoelectric layer 420, and the second electrode layer 430. Taking the formation of the first electrode layer 410 as an example, a first electrode material layer covering the first sacrificial layer 310 and the substrate layer 110 is first formed, and a photoresist layer covering the first electrode material layer is formed. The photoresist layer is exposed and developed to form a patterned photoresist layer, and the first electrode material layer is etched through the patterned photoresist layer to form the first electrode layer 410.

[0084] In some embodiments, during the formation of the second electrode layer 430, a trimming process can be used to adjust the thickness of the second electrode layer 430 to obtain the desired resonant frequency. In some embodiments, such as Figure 3 As shown, multiple grooves 200 can be formed in the substrate 100, and a stacked structure 400 is formed in each groove 200. By adjusting the process, the second electrode layer 430 of the stacked structure 400 in some grooves 200 can be adjusted to different thicknesses, thereby forming a bulk acoustic wave filter with different resonant frequencies on a substrate 100.

[0085] For example, the piezoelectric layer 420 may be made of materials including, but not limited to, lithium tantalate, lithium niobate, aluminum nitride, and zinc oxide. The first electrode layer 410 may be made of materials including, but not limited to, metals (e.g., tungsten, copper, aluminum, molybdenum, ruthenium, iridium, platinum, etc.), and the second electrode layer 430 may be made of materials including, but not limited to, metals (e.g., tungsten, copper, aluminum, molybdenum, ruthenium, iridium, platinum, etc.).

[0086] In some embodiments, step S500 may specifically include:

[0087] A second sacrificial layer is formed, covering the resonant structure and part of the substrate layer;

[0088] An etch stop layer is formed covering the second sacrificial layer, wherein the top of the etch stop layer is lower than the top of the semiconductor layer;

[0089] An encapsulation layer is formed that covers the etch stop layer, and the encapsulation layer fills the remaining space in the groove.

[0090] like Figure 2d As shown, a second sacrificial layer 320 is deposited on the surfaces of the piezoelectric layer 420, the second electrode layer 430, and the substrate layer 110. Here, the second sacrificial layer 320 is partially located on the surface of the substrate layer 110 so that it can be removed later by forming a release hole in the substrate layer 110.

[0091] The etch stop layer 610 covers the second sacrificial layer 320, meaning that the etch stop layer 610 covers the sidewalls and top of the second sacrificial layer 320 to isolate the second sacrificial layer 320 from the subsequently formed encapsulation layer 620. The etch stop layer 610 can protect the encapsulation layer 620 when the second sacrificial layer 320 is removed, preventing the encapsulation layer 620 from being etched.

[0092] It should be understood that in some embodiments, the etch stop layer 610 may also cover the surface of the stacked structure 400 not covered by the second sacrificial layer 320. For example, the etch stop layer 610 may also cover... Figure 2d The sidewalls of the stacked structure 400 shown are not covered by the second sacrificial layer 320.

[0093] See also Figure 2d The remaining space within the recess 200 is filled with encapsulation material to form an encapsulation layer 620. The encapsulation layer 620 covers all surfaces of the etch stop layer 610 and the stacked structure 400 exposed within the recess 200. For example, the encapsulation layer 620 covers the top and sidewalls of the etch stop layer 610, as well as the sidewalls of the stacked structure 400 not covered by the etch stop layer 610. The encapsulation layer 620 protects the stacked structure 400 from damage that could cause the bulk acoustic wave filter to fail.

[0094] For example, encapsulation materials include, but are not limited to, thermosetting materials. Thermosetting materials are fluid in their initial state (e.g., at room temperature), such as being liquid or gel-like, and harden under certain conditions (e.g., heating, radiation, or catalysis) through a chemical reaction. Thermosetting materials can be made, for example, based on epoxy resins, silicone resins, or acrylic resins.

[0095] In this embodiment, a substrate is used as the packaging mold. Specifically, a groove is formed with the base layer as the bottom and the semiconductor layer as the sidewalls to accommodate the resonant structure. The groove is filled with a thermosetting material, and after hardening, the resonant structure is encapsulated. In this embodiment, using a substrate as the packaging mold reduces the development of packaging molds, shortens the product manufacturing cycle and cost. Furthermore, the thickness of the base layer, insulating layer and semiconductor layer in the substrate can be flexibly selected according to the different structural and size requirements of each product, and the opening size of the groove can be flexibly adjusted. In other words, the product design is highly flexible, enabling the diversification of packaging forms and improving the flexibility of the product in end-use.

[0096] Furthermore, using thermosetting materials to fill the grooves is not limited by the size of the grooves, has a good filling effect, and the filling thickness can be controlled. After hardening, it has a certain supporting strength, which makes the product more reliable and less prone to deformation.

[0097] For example, the top of the packaging layer 620 is flush with the top of the semiconductor layer 130, which allows for better packaging consistency of the product.

[0098] In some embodiments, step S500 may also specifically include:

[0099] A thin film layer is covered on top of the semiconductor layer and at the groove opening to form an encapsulation structure.

[0100] Figure 4 This is a schematic diagram of the fabrication process of another bulk acoustic wave filter provided in this embodiment of the present disclosure, as shown below. Figure 4 As shown, a thin film layer can be covered on the top of the semiconductor layer 130 and at the opening of the recess 200 to form a package structure 600. The thin film layer covers the opening of the recess 200 and its edges are fixed to the top of the semiconductor layer 130, thereby sealing the stacked structure 400.

[0101] Here, the space between the top of the second electrode layer 430 and the bottom of the thin film layer forms a third cavity. The first cavity can be obtained by removing the first sacrificial layer 310. The first cavity, the first electrode layer 410, the piezoelectric layer 420, the second electrode layer 430 and the third cavity together constitute the resonant structure of the bulk acoustic wave filter.

[0102] For example, the thin film layer includes dry film photoresist or other dry film layers.

[0103] In this embodiment, a substrate is used to form a sealed resonant cavity together with a thin film layer. This reduces the number of packaging steps and shortens the packaging cycle, thus reducing the product manufacturing cycle. It should be understood that when the size of the bulk acoustic wave filter is small, the groove opening size is also small, allowing the thin film layer to seal the groove opening, resulting in a short packaging cycle and ease of operation. When the groove opening size is large, the encapsulation layer 620 (e.g., a thermosetting material) can be used to fill the groove, resulting in a product with higher reliability and lower risk of deformation.

[0104] Here, when the opening of the groove 200 is sealed with a thin film layer, the second sacrificial layer and the etching stop layer are not required. Instead, a cavity-type reflective structure is formed by utilizing the gap between the stacked structure 400 and the thin film layer.

[0105] In summary, in the embodiments of this disclosure, utilizing a substrate structure comprising a base layer, an insulating layer, and a semiconductor layer, a groove is first formed by etching the semiconductor layer. Then, a first sacrificial layer and a stacked structure are formed within the groove. The top of the stacked structure is lower than the top of the semiconductor layer. Subsequently, a packaging structure is formed to close the groove opening. A cavity can be formed between the top of the packaging structure and the top of the stacked structure. A cavity can also be formed after the first sacrificial layer is removed in a subsequent process. The stacked structure and the two cavities located at its top and bottom together constitute a resonant structure, thereby obtaining a bulk acoustic wave filter. In this disclosure, based on the substrate structure, the semiconductor process for preparing the resonant structure and the packaging process are combined. The substrate is used as a packaging mold, or the substrate and the packaging structure are used together to seal the resonant structure, reducing the development of packaging molds and shortening the product manufacturing cycle and cost. Furthermore, the thickness of the base layer, insulating layer, and semiconductor layer in the substrate can be flexibly selected according to the different structural and dimensional requirements of each product, and the opening size of the groove can be flexibly adjusted. This means that the product design has high flexibility, enabling diverse packaging forms and improving the flexibility of the product in end-use.

[0106] In some embodiments, the preparation method further includes:

[0107] A first through-hole is formed, penetrating the substrate layer and exposing the first electrode; a second through-hole is formed, penetrating the substrate layer and exposing the second electrode;

[0108] A conductive structure is filled in the first and second vias until the conductive structure covers the side of the substrate layer away from the semiconductor layer stack structure.

[0109] See Figure 2e A first through-hole 701 is formed that penetrates the substrate layer 110 and exposes the first electrode layer 410, and a second through-hole 702 is formed that penetrates the substrate layer 110 and exposes the second electrode layer 430.

[0110] For example, the first through hole 701 and the second through hole 702 are formed simultaneously.

[0111] For example, the steps of forming the first via 701 and the second via 702 include: forming a photoresist layer covering the side of the substrate 110 away from the semiconductor layer 130 (i.e., the lower surface of the substrate 110); exposing and developing the photoresist layer to form a first via pattern and a second via pattern on the photoresist layer, the first via pattern and the second via pattern corresponding to the positions of the first via 701 and the second via 702, respectively; and etching the substrate 110 using a dry etching process to form the first via 701 and the second via 702. For example, the dry etching process includes deep reactive ion etching (DRIE).

[0112] See Figure 2f A conductive structure 703 is formed covering the lower surface of the substrate 110, the sidewalls and bottom of the first via 701, and the sidewalls and bottom of the second via 702. For example, the conductive structure 703 may be made of metals, such as copper, aluminum, tungsten, molybdenum, etc. In some embodiments, after forming the conductive structure 703, the remaining space within the first and second vias may be filled to form a first filling layer and a second filling layer (not shown in the figure). For example, the materials of the first and second filling layers may include conductive materials such as metals and polycrystalline silicon, and the materials of the first and second filling layers may also include insulating materials such as silicon oxide and silicon nitride.

[0113] It should be understood that in other embodiments, the conductive structures located within the first and second vias may not be formed simultaneously with the conductive structures covering the substrate layer. For example, after forming the first and second vias penetrating the substrate layer, the conductive structures located within the first and second vias may be formed first; subsequently, the conductive structures covering the substrate layer may be formed.

[0114] In this embodiment, the first electrode layer and the second electrode layer are connected to the circuit through a conductive structure that penetrates the substrate layer. The process is relatively simple and has almost no impact on the resonant structure. Therefore, the product has a high yield and reliability.

[0115] See Figure 2g The preparation method also includes:

[0116] A first release hole 801 is formed that penetrates the substrate 110 and exposes the first sacrificial layer 310;

[0117] A second release hole 802 is formed that penetrates the base layer 110 and exposes the second sacrificial layer 320.

[0118] Here, the diameters of the first release hole 801 and the second release hole 802 can be equal or unequal. The number of the first release hole 801 and the second release hole 802 can also be equal or unequal. The number and diameter of the first release hole 801 and the second release hole 802 can be adjusted according to the actual situation.

[0119] In some embodiments, the first release hole 801 and the second release hole 802 are formed simultaneously. The steps for forming the first release hole 801 and the second release hole 802 can be the same as the steps for forming the first through hole and the second through hole, so they will not be described in detail.

[0120] In some embodiments, the first release hole 801 and the second release hole 702 may be formed after the first through hole 701 and the second through hole 702 are formed and the conductive structure 703 is formed in the first through hole 701 and the second through hole 702. In this way, the first release hole 801 and the second release hole 802 can be prevented from being blocked by the material forming the conductive structure, which would affect the subsequent removal of the first sacrificial layer 310 and the second sacrificial layer 320.

[0121] See Figure 2h The preparation method also includes:

[0122] The first sacrificial layer 310 is removed through the first release hole 801 to form the first cavity 311;

[0123] The second sacrificial layer 320 is removed through the second release hole 802 to form the second cavity 321.

[0124] Here, the first cavity 311 and the second cavity 321 are cavity-type reflective structures. The first cavity 311, the first electrode layer 410, the piezoelectric layer 420, the second electrode layer 430, and the second cavity 321 together constitute the resonant structure of the bulk acoustic wave filter.

[0125] In some embodiments, an etchant can be introduced into the first release hole 801 and the second release hole 802 simultaneously to remove the first sacrificial layer 310 and the second sacrificial layer 320, thereby reducing the process flow; at the same time, a first cavity 311 and a second cavity 321 located at the top and bottom of the stacked structure 400 are formed.

[0126] For example, the first and second sacrificial layers are made of silicon oxide, and the etchant is composed of HF (hydrogen fluoride).

[0127] In this embodiment, the first and second sacrificial layers are released by forming a first release hole and a second release hole that penetrate the substrate layer, forming a cavity-type reflective structure. Compared to some embodiments where a release hole is formed from the top of the stacked structure to penetrate the first electrode layer, the release hole in this embodiment has virtually no impact on the resonant structure, thus resulting in higher product yield and reliability.

[0128] In some embodiments, the preparation method further includes:

[0129] Etching agent is introduced into the first cavity 311 through the first release hole 801 to adjust the thickness of the first electrode layer 410;

[0130] Etching agent is introduced into the second cavity 321 through the second release hole 802 to adjust the thickness of the second electrode layer 430.

[0131] For example, the etchant can be an etching liquid or an etching gas.

[0132] This step can be understood as a trimming process, where the etching targets are the first electrode layer and / or the second electrode layer, and the etching gas may include Ar (argon). In this embodiment, by adjusting the thickness of the first and second electrode layers through the release hole and cavity path, the frequency of the resonant structure can be accurately adjusted, improving product performance. It should be understood that the steps shown in this embodiment can also be used to... Figure 3 The first and / or second electrode layers of the stacked structures in the different grooves 200 shown are adjusted to different thicknesses, thereby forming bulk acoustic filters with different resonant frequencies on a substrate 100.

[0133] Figure 3 The diagram shows a top view of a wafer after multiple bulk acoustic wave (SAW) filters have been formed. The dashed box indicates a cross-sectional view of one of the SAW filters. This cross-sectional view of the SAW filter is similar to... Figure 2h Same. For example... Figure 3 As shown, there are multiple grooves 200 arranged in an array, and the region of the substrate 100 between adjacent grooves 200 includes a cut path 210. The fabrication method further includes:

[0134] After forming an encapsulation structure, a conductive structure, a first release hole, and a second release hole in each groove 200, the substrate 100 is cut along the dicing path 210 to form multiple independent bulk acoustic wave filters.

[0135] It should be understood that Figure 3 The bulk acoustic wave filter in the package can be any of the bulk acoustic wave filters provided in any embodiment of this disclosure. Furthermore, it should be noted that in some embodiments, the substrate may be diced between any steps after the package structure is formed.

[0136] like Figure 2h As shown, in the bulk acoustic wave filter obtained after cutting, the semiconductor layer 130 and the insulating layer 120 constituting the sidewall of the groove 200 can be retained.

[0137] Figure 5 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic wave filter provided in this disclosure embodiment, as shown below. Figure 5 As shown, in the bulk acoustic wave filter obtained after cutting, the semiconductor layer and insulating layer constituting the sidewall of the groove can be completely removed, and the encapsulation layer 620 covers the top of the etch stop layer 610 and surrounds the etch stop layer 610 and the sidewall of the stacked structure 400.

[0138] Figure 6 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic wave filter provided in this disclosure embodiment, as shown below. Figure 6 As shown, the sidewalls of the etch stop layer 610 and the sidewalls of the stacked structure 400 not covered by the etch stop layer 610 are in contact with the sidewalls of the groove 200. In other words, there are no gaps between the sidewalls of the etch stop layer 610 and the stacked structure 400 and the sidewalls of the groove 200, at which point the size of the groove 200 is minimized. Thus, more grooves 200 can be formed on the substrate 100 of the same area, thereby obtaining more bulk acoustic wave filters and reducing the unit cost of the bulk acoustic wave filter.

[0139] Figure 7 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic wave filter provided in this disclosure embodiment, as shown below. Figure 7 As shown, when the packaging structure 600 is a thin film layer and no etching stop layer is provided in the groove 200, the sidewall of the stacked structure 400 can contact the sidewall of the groove 200, which can increase the number of bulk acoustic wave filters fabricated per unit area of ​​substrate.

[0140] It should be understood that each sidewall of the groove may be in contact with the etch stop layer and / or the stacked structure, or only a portion of the sidewalls of the groove may be in contact with the etch stop layer and / or the stacked structure. This can also increase the number of bulk acoustic wave filters fabricated per unit area of ​​substrate.

[0141] In some embodiments, multiple interfaces may be provided on the side of the conductive structure away from the substrate layer (i.e., the lower surface of the conductive structure), through which the bulk acoustic wave filter and the circuit board in the radio frequency terminal module (i.e., radio frequency device) are electrically connected to integrate the bulk acoustic wave filter into the radio frequency terminal module.

[0142] For example, the interface is a pad, and the fabrication method may further include:

[0143] An isolation layer is covered on a portion of the conductive structure on the side away from the substrate, wherein the exposed area of ​​the conductive structure on the side relatively away from the substrate forms a pad.

[0144] Here, the pads of the bulk acoustic wave filter and the pads of the circuit board in the RF terminal module can be connected by soldering (e.g., SMT (surface mount technology)).

[0145] Figure 8 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic wave filter provided in this disclosure embodiment, as shown below. Figure 8 As shown, the interface structure is a solder ball, and the preparation method may further include:

[0146] Multiple solder balls 910 are provided on the side of the conductive structure 703 away from the substrate layer 110.

[0147] In this embodiment, solder balls 910 can improve the yield of circuit board soldering for bulk acoustic wave filters and RF terminal modules.

[0148] Figure 9 A cross-sectional schematic diagram of the fabrication process of another type of bulk acoustic wave filter provided in this disclosure embodiment, as shown below. Figure 9 As shown, the preparation method may further include:

[0149] An adapter board 920 is provided; wherein the adapter board 920 includes a first wiring layer 921 and a second wiring layer 922, the first wiring layer 921 and the second wiring layer 922 are respectively exposed on two sides of the adapter board 920 that are disposed opposite to each other along its thickness direction;

[0150] The first wiring layer 921 of the adapter board 920 is joined with the conductive structure 703.

[0151] Multiple pads or solder balls 910 are formed on the second wiring layer 922.

[0152] In this embodiment, when the interface position on the circuit board of the RF terminal module is inconsistent with the interface position on the bulk acoustic wave filter, an adapter board can be used to connect the interface in the first wiring layer of the adapter board with the interface of the bulk acoustic wave filter. Solder balls or pads corresponding to the pad positions on the terminal circuit board are provided on the second wiring layer of the adapter board. The first wiring layer and the second wiring layer can be electrically connected through conductive vias.

[0153] In summary, this disclosure provides pads, solder balls, or adapter plates and solder balls on the side of the substrate layer away from the semiconductor layer, increasing the diversity of packaging forms and enhancing the flexibility of the bulk acoustic wave filter in end-user applications. Furthermore, when implementing different packaging forms, only some processes after the interconnect layer formation need to be changed, while the processes before the interconnect layer formation can remain completely identical. Therefore, the time and cost required to achieve packaging diversification are lower, improving the product's market competitiveness.

[0154] This disclosure also provides a bulk acoustic wave filter. Figure 10 This is a cross-sectional schematic diagram of a bulk acoustic wave filter provided in an embodiment of this disclosure. Figure 11 A cross-sectional schematic diagram of another bulk acoustic wave filter provided in this disclosure embodiment is shown below. Figure 2h , Figure 10 and Figure 11 As shown, the bulk acoustic wave filter includes:

[0155] The substrate 100 includes a base layer 110, an insulating layer 120 and a semiconductor layer 130 stacked sequentially. A groove 200 is provided in the substrate 100, which penetrates the semiconductor layer 130 and the insulating layer 120 and exposes the base layer 110.

[0156] The stacked structure 400 is located on the base layer 110 within the groove 200. The stacked structure 400 includes a first electrode layer 410, a piezoelectric layer 420, and a second electrode layer 430 stacked sequentially. The first electrode layer 410 partially protrudes away from the base layer 110 to create a first cavity 311 between the first electrode layer 410 and the base layer 110. The top of the second electrode layer 430 is lower than the top of the semiconductor layer 130.

[0157] The package structure 600 is located on top of the stacked structure 400 and is in contact with the semiconductor layer 130. The package structure 600 closes the opening of the groove 200, and a cavity structure is provided between the top of the second electrode layer 430 and the bottom of the package structure 600.

[0158] In some embodiments, the substrate 100 includes a semiconductor on insulator, such as silicon on insulator, germanium on insulator, or silicon-germanium on insulator.

[0159] The bulk acoustic wave filter provided in this disclosure utilizes a substrate structure comprising a base layer, an insulating layer, and a semiconductor layer. A groove is formed by etching the semiconductor layer, and a resonant structure is formed within the groove. Finally, a packaging structure is used to seal the groove opening. In other words, this disclosure utilizes the substrate and packaging structure to jointly seal the resonant structure, reducing the need for packaging mold development and shortening the product manufacturing cycle and cost. Furthermore, the opening size of the groove can be flexibly adjusted by flexibly selecting the thickness of the base layer, insulating layer, and semiconductor layer in the substrate, meeting the structural and packaging requirements of different products. This results in high product design flexibility, enabling diverse packaging forms and improving the flexibility of the product in end-user applications.

[0160] In some embodiments, such as Figure 10 As shown, the package structure 600 includes:

[0161] An etch stop layer 610 is located on top of the second electrode layer 430, and a second cavity 321 is provided between the etch stop layer 610 and the second electrode layer 430. The cavity structure includes the second cavity 321.

[0162] The encapsulation layer 620 covers the etch stop layer 610 and fills the remaining space in the groove 200. The top of the encapsulation layer 620 is flush with the top of the semiconductor layer 130.

[0163] In this embodiment, the first cavity 311, the first electrode layer 410, the piezoelectric layer 420, the second electrode layer 430, and the second cavity 321 together constitute the resonant structure of the bulk acoustic wave filter.

[0164] For example, the material of the encapsulation layer 620 includes a thermosetting material, which can be made based on, for example, epoxy resin, silicone resin or acrylic resin.

[0165] In some embodiments, such as Figure 11 As shown, the packaging structure 600 may include a thin film layer covering the top of the semiconductor layer 130 and the opening of the recess 200. A third cavity 331 is provided between the top of the second electrode layer 430 and the bottom of the thin film layer. The cavity structure includes the third cavity 331. In this embodiment, the first cavity 311, the first electrode layer 410, the piezoelectric layer 420, the second electrode layer 430, and the third cavity 331 together constitute the resonant structure of the bulk acoustic wave filter.

[0166] For example, the thin film layer includes dry film photoresist or other dry film layers.

[0167] In some implementations, such as Figure 10 As shown, the sidewalls of the etch stop layer 610 and the sidewalls of the stacked structure 400 not covered by the etch stop layer 610 are in contact with the sidewalls of the groove 200, at which point the size of the groove 200 is at its minimum. Thus, more grooves 200 can be formed on the substrate 100 of the same area, resulting in more bulk acoustic wave filters and reducing the unit cost of the bulk acoustic wave filter.

[0168] In some embodiments, such as Figure 7 As shown, the sidewall of the stacked structure 400 is in contact with the sidewall of the groove 200. At this time, the size of the groove 200 is at its minimum, which can increase the number of bulk acoustic wave filters fabricated per unit area of ​​substrate.

[0169] In some embodiments, such as Figure 10 and Figure 11 As shown, the bulk acoustic wave filter also includes:

[0170] The conductive structure 703 covers the side of the substrate 110 away from the stacked structure 400 (i.e., covers the lower surface of the substrate 110), and the conductive structure 703 also penetrates the substrate 110 and is connected to the first electrode layer 410 and the second electrode layer 430.

[0171] In some embodiments, the bulk acoustic wave filter further includes a plurality of interfaces located on the side of the conductive structure away from the substrate layer (i.e., on the lower surface of the conductive structure).

[0172] For example, the interface is a pad (not shown in the figure). The bulk acoustic wave filter also includes an isolation layer (not shown in the figure) that covers a portion of the conductive structure on the side away from the substrate layer, and the exposed area of ​​the conductive structure on the side away from the substrate layer forms the pad.

[0173] For example, such as Figure 8 As shown, the interface is solder ball 910.

[0174] In some embodiments, such as Figure 9 As shown, the bulk acoustic wave filter further includes an adapter plate 920, which includes a first wiring layer 921 and a second wiring layer 922. The first wiring layer 921 and the second wiring layer 922 are respectively exposed on two opposing sides of the adapter plate 920 along its thickness direction. The first wiring layer 921 is bonded to the conductive structure 703, and the second wiring layer 922 includes a plurality of solder balls 910. In some embodiments, the second wiring layer 922 may also be covered with an isolation layer, and the exposed area of ​​the second wiring layer 922 constitutes a solder pad.

[0175] Figure 12 A schematic diagram of the structure of another bulk acoustic wave filter provided in this disclosure embodiment is shown below. Figure 12 As shown, the bulk acoustic wave filter includes:

[0176] Basal layer 110;

[0177] The stacked structure 400 is located on the substrate 110. The stacked structure 400 includes a first electrode layer 410, a piezoelectric layer 420 and a second electrode layer 430 stacked in sequence. The first electrode layer 410 protrudes locally in a direction away from the substrate 110 so that there is a first cavity 311 between the first electrode layer 410 and the substrate 110.

[0178] An etch stop layer 610 is located on top of the second electrode layer 430, and a second cavity 321 is formed between the etch stop layer 610 and the second electrode layer 430.

[0179] The encapsulation layer 620 surrounds the etch stop layer 610 and the stack structure 400, and covers the top of the etch stop layer 610.

[0180] The bulk acoustic wave filter also includes:

[0181] The conductive structure 703 covers the side of the substrate 110 away from the stacked structure 400. The conductive structure 703 penetrates the substrate 110 and is connected to the first electrode layer 410 and the second electrode layer 430.

[0182] In some embodiments, the conductive structure 703 of the bulk acoustic wave filter has multiple interfaces on the side away from the substrate layer 110. Alternatively, the bulk acoustic wave filter further includes an adapter plate, one side of which is coupled to the conductive structure 703, and the other side has multiple interfaces. For example, the interfaces are pads or solder balls.

[0183] This disclosure also provides a radio frequency device. Figure 13 This is a cross-sectional schematic diagram of a radio frequency device provided in an embodiment of this disclosure, as shown below. Figure 13 As shown, the radio frequency device 1000 includes:

[0184] Circuit board 1001;

[0185] One or more of the bulk acoustic wave filters described above are mounted on and electrically connected to the circuit board 1001.

[0186] For example, the radio frequency device 1000 includes at least Figure 2h , Figure 8 , Figure 9 , Figure 10 , Figure 11 and Figure 12 One or more of the bulk acoustic wave filters shown.

[0187] The conductive structure or second wiring layer of the bulk acoustic wave filter includes multiple interfaces, each including pads or solder balls. The bulk acoustic wave filter is soldered to pads on the circuit board 1001 of the RF device 1000 via the pads or solder balls, thereby integrating the bulk acoustic wave filter into the RF device 1000.

[0188] In the embodiments provided in this disclosure, it should be understood that the disclosed apparatus, systems, and methods can be implemented in other ways. The above descriptions are merely specific embodiments of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for fabricating a bulk acoustic wave filter, characterized in that, include: A substrate is provided; wherein the substrate comprises a base layer, an insulating layer and a semiconductor layer stacked sequentially; The semiconductor layer is etched to form a trench in the substrate; wherein the trench exposes the insulating layer; The insulating layer in a portion of the bottom area of ​​the groove is removed to expose the base layer, and the remaining insulating layer forms a first sacrificial layer; A stacked structure covering the first sacrificial layer and a portion of the substrate layer is formed within the groove; wherein the stacked structure includes a first electrode layer, a piezoelectric layer, and a second electrode layer sequentially stacked along the thickness direction of the substrate, and the top of the stacked structure is lower than the top of the semiconductor layer; A second sacrificial layer is formed covering the second electrode layer and a portion of the substrate layer; Form an etch stop layer covering the second sacrificial layer; An encapsulation layer is formed covering the etch stop layer, the encapsulation layer fills the remaining space in the groove, and the top of the encapsulation layer is substantially flush with the top of the semiconductor layer; The first sacrificial layer is removed to form the first cavity; The second sacrificial layer is removed to form a second cavity.

2. A method for fabricating a bulk acoustic wave filter, characterized in that, include: A substrate is provided; wherein the substrate comprises a base layer, an insulating layer and a semiconductor layer stacked sequentially; The semiconductor layer is etched to form a trench in the substrate; wherein the trench exposes the insulating layer; The insulating layer in a portion of the bottom area of ​​the groove is removed to expose the base layer, and the remaining insulating layer forms a first sacrificial layer; A stacked structure covering the first sacrificial layer and a portion of the substrate layer is formed within the groove; wherein the stacked structure includes a first electrode layer, a piezoelectric layer, and a second electrode layer sequentially stacked along the thickness direction of the substrate, and the top of the stacked structure is lower than the top of the semiconductor layer; A thin film layer is covered on the top of the semiconductor layer and at the groove opening to form an encapsulation structure that closes the groove opening. The space between the top of the second electrode layer and the bottom of the thin film layer constitutes a third cavity. The first sacrificial layer is removed to form the first cavity.

3. The method for fabricating a bulk acoustic wave filter according to any one of claims 1-2, characterized in that, The substrate includes at least one of silicon-on-insulator or germanium-on-insulator.

4. The method for fabricating a bulk acoustic wave filter according to any one of claims 1-2, characterized in that, The thickness of the first sacrificial layer is equal to the thickness of the insulating layer.

5. The method for fabricating a bulk acoustic wave filter according to any one of claims 1-2, characterized in that, The preparation method further includes: A first through-hole is formed, penetrating the substrate layer and exposing the first electrode; a second through-hole is formed, penetrating the substrate layer and exposing the second electrode; A conductive structure is filled into the first and second vias until the conductive structure covers the side of the substrate layer away from the semiconductor layer.

6. The method for fabricating a bulk acoustic wave filter according to claim 1, characterized in that, The removal of the first sacrificial layer forms the first cavity; Removing the second sacrificial layer to form the second cavity includes: A first release hole is formed that penetrates the substrate layer and exposes the first sacrificial layer, and a second release hole is formed that penetrates the substrate layer and exposes the second sacrificial layer; The first sacrificial layer is removed through the first release hole to form a first cavity, and the second sacrificial layer is removed through the second release hole to form a second cavity.

7. The method for fabricating a bulk acoustic wave filter according to claim 6, characterized in that, The preparation method further includes: Etching agent is introduced into the first cavity through the first release hole to adjust the thickness of the first electrode layer; or... Etching agent is introduced into the second cavity through the second release hole to adjust the thickness of the second electrode layer.

8. The method for fabricating a bulk acoustic wave filter according to claim 5, characterized in that, The preparation method further includes: Multiple interfaces are formed on the side of the conductive structure away from the substrate layer; Alternatively, the preparation method may further include: An adapter board is provided; wherein the adapter board includes a first wiring layer and a second wiring layer, the first wiring layer and the second wiring layer being exposed on two opposing sides of the adapter board along its thickness direction; The first wiring layer of the adapter board and the conductive structure are joined together; Multiple interfaces are formed in the second wiring layer.

9. A bulk acoustic wave filter, characterized in that, include: A substrate includes a base layer, an insulating layer, and a semiconductor layer stacked sequentially. A groove is provided in the substrate, which penetrates the semiconductor layer and the insulating layer and exposes the base layer. A stacked structure is located on the base layer within the groove. The stacked structure includes a first electrode layer, a piezoelectric layer, and a second electrode layer stacked sequentially. The first electrode layer partially protrudes away from the base layer to create a first cavity between the first electrode layer and the base layer. The top of the second electrode layer is lower than the top of the semiconductor layer. The packaging structure is located on top of the stacked structure and in contact with the semiconductor layer. The packaging structure closes the opening of the groove, and a cavity structure is provided between the top of the second electrode layer and the bottom of the packaging structure.

10. The bulk acoustic wave filter according to claim 9, characterized in that, The substrate includes at least one of silicon-on-insulator or germanium-on-insulator.

11. The bulk acoustic wave filter according to claim 9, characterized in that, At least part of the sidewalls of the stacked structure are in contact with the sidewalls of the groove.

12. The bulk acoustic wave filter according to claim 9, characterized in that, The packaging structure includes: An etch stop layer is located on top of the second electrode layer, and a second cavity is provided between the etch stop layer and the second electrode layer, the cavity structure including the second cavity; An encapsulation layer covers the etch stop layer and fills the remaining space within the groove, with the top of the encapsulation layer flush with the top of the semiconductor layer.

13. The bulk acoustic wave filter according to claim 9, characterized in that, The packaging structure includes: a thin film layer covering the top of the semiconductor layer and the opening of the groove; A third cavity is provided between the top of the second electrode layer and the bottom of the thin film layer, and the cavity structure includes the third cavity.

14. The bulk acoustic wave filter according to claim 9, characterized in that, The bulk acoustic wave filter also includes: A conductive structure is provided, covering the side of the substrate layer away from the stacked structure, the conductive structure extending through the substrate layer and connected to the first electrode layer and the second electrode layer.

15. The bulk acoustic wave filter according to claim 14, characterized in that, The bulk acoustic wave filter further includes: multiple interfaces located on the side of the conductive structure away from the substrate layer; or... The bulk acoustic wave filter further includes an adapter plate, which includes a first wiring layer and a second wiring layer. The first wiring layer and the second wiring layer are respectively exposed on two opposite sides of the adapter plate along its thickness direction. The first wiring layer is bonded to the conductive structure, and the second wiring layer includes multiple interfaces.

16. A radio frequency device, characterized in that, Includes one or more bulk acoustic filters as described in any one of claims 9 to 15.

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