Acoustic structure and preparation method thereof

Abstract

The invention provides an acoustic structure and a preparation method thereof, and relates to the technical field of acoustic sensors, and the method comprises the steps: providing a substrate, the front surface of which is provided with a preset region; forming a boundary definition layer in a preset area on the front surface of the substrate, wherein the boundary definition layer is used for defining the boundary of the cavity of the acoustic structure in the preset area; forming a piezoelectric diaphragm stacked on the boundary definition layer in the preset area; etching from the back surface of the substrate to form a back cavity penetrating to the boundary definition layer, wherein the boundary definition layer covers an opening of the back cavity on the front surface of the substrate; and removing the boundary definition layer to form a cavity between the substrate and the piezoelectric diaphragm. The boundary definition layer which can be formed to be consistent with the expected height is utilized, so that the position, the shape and the size of the cavity in each preset area can be consistent with the expected height. Moreover, in batch manufacturing, the consistency of the cavities in the acoustic structures can be effectively improved by utilizing the high consistency of the boundary definition layers in the preset areas.

Description

Technical Field

[0001] This application relates to the field of acoustic sensor technology, and more specifically, to an acoustic structure and its fabrication method. Background Technology

[0002] Piezoelectric devices, manufactured using MEMS (Micro-Electro-Mechanical Systems) technology, are advanced acoustic sensors that have seen rapid development due to their advantages such as low power consumption, fast response, and high reliability. A piezoelectric device mainly consists of a support body and a diaphragm mounted on the support body. When the diaphragm is subjected to external excitation, it vibrates, causing the piezoelectric material to generate an electric charge and generate a signal output, thus achieving the sensing function. Alternatively, under voltage drive, the piezoelectric material deforms, causing the diaphragm to vibrate, thus achieving the driving function.

[0003] In existing piezoelectric devices, the boundary of the vibrating region of the diaphragm is typically defined by a back cavity located on the support, which is mainly formed by deep reactive ion etching (DRIE) of the support. However, the current DRIE process has certain non-idealities. Therefore, during the process of etching the back cavity using the DRIE process, there will be a significant deviation between the actual back cavity size and the ideal back cavity size, thus affecting the final response performance of the device. Especially when multiple piezoelectric devices are mass-produced on a wafer, these deviations will further deteriorate the response consistency of multiple piezoelectric devices. Summary of the Invention

[0004] The purpose of this application is to provide an acoustic structure and its preparation method in order to address the shortcomings of the prior art.

[0005] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows:

[0006] One aspect of this application provides a method for fabricating an acoustic structure, the method comprising:

[0007] Provide a substrate, the front of which has a preset area;

[0008] A boundary definition layer is formed within a predetermined area on the front of the substrate. The boundary definition layer is used to define the boundary of the cavity of the acoustic structure within the predetermined area.

[0009] A piezoelectric diaphragm is formed within a preset area, stacked on a boundary definition layer;

[0010] A back cavity is formed by etching from the back side of the substrate to the boundary definition layer, and the boundary definition layer covers the opening of the back cavity on the front side of the substrate.

[0011] Removing the boundary definition layer creates a cavity between the substrate and the piezoelectric diaphragm.

[0012] Optionally, forming a boundary definition layer within a predetermined area on the front side of the substrate includes:

[0013] A boundary definition layer protruding from the front of the substrate is formed within a predetermined area of ​​the substrate, so that the boundary definition layer forms a step relative to the front of the substrate at its sidewall.

[0014] Optionally, the edge of the piezoelectric diaphragm extends from the step to the front of the substrate.

[0015] Optionally, after forming a boundary definition layer within a predetermined area on the front side of the substrate, the method further includes:

[0016] A support layer is formed on the front side of the substrate, covering the boundary definition layer;

[0017] The front side of the support layer is planarized to obtain a planarized surface;

[0018] Forming a piezoelectric diaphragm stacked on a boundary definition layer within a preset area includes:

[0019] A piezoelectric diaphragm is formed within a preset area and stacked to a flattened surface.

[0020] Optionally, forming a boundary definition layer within a predetermined area on the front side of the substrate includes:

[0021] An oxide layer is grown on the front side of the substrate using a thermo-oxidative process;

[0022] The patterned oxide layer forms a boundary definition layer located within a preset area.

[0023] Optionally, etching from the back side of the substrate to form a back cavity extending to the boundary definition layer includes:

[0024] Using the boundary definition layer as an etching stop layer, a back cavity extending to the boundary definition layer is formed by etching from the back side of the substrate.

[0025] Optionally, after forming a piezoelectric diaphragm stacked on the boundary definition layer within a preset region, the method further includes:

[0026] The piezoelectric diaphragm is etched to form multiple cantilever beam diaphragms distributed in the same layer.

[0027] Optionally, forming a support layer on the front side of the substrate that covers the boundary definition layer includes:

[0028] A support layer covering the boundary definition layer is formed on the front side of the substrate by chemical vapor deposition.

[0029] Another aspect of this application provides an acoustic structure, including:

[0030] The base has a predetermined area on its front side, and a back cavity that runs through the base is formed within the predetermined area;

[0031] A piezoelectric diaphragm is located in a preset area and has a cavity protruding from the substrate between the piezoelectric diaphragm and the substrate.

[0032] Optionally, the acoustic structure further includes a support layer located between the substrate and the piezoelectric diaphragm, the front side of the support layer being a planarized surface, and a cavity located between the support layer and the substrate.

[0033] The beneficial effects of this application include:

[0034] This application provides an acoustic structure and its fabrication method. The method includes: providing a substrate with a predetermined region on its front side; forming a boundary definition layer within the predetermined region on the front side of the substrate, the boundary definition layer defining the boundaries of the cavities of the acoustic structure within the predetermined region; forming a piezoelectric diaphragm stacked on the boundary definition layer within the predetermined region; etching a back cavity extending to the boundary definition layer from the back side of the substrate, the boundary definition layer covering the opening of the back cavity on the front side of the substrate; and removing the boundary definition layer to form a cavity between the substrate and the piezoelectric diaphragm. By utilizing a boundary definition layer that can form a height consistent with the desired height, the position, shape, and size of the cavities within each predetermined region can also conform to the desired height. Furthermore, in mass production, the height consistency of the boundary definition layers within each predetermined region can effectively improve the consistency of the cavities within each acoustic structure. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the structure of a traditional piezoelectric device;

[0037] Figure 2 This is a schematic diagram of a back cavity in a traditional wafer;

[0038] Figure 3 This is one of the flowcharts illustrating an acoustic structure fabrication method provided in this application embodiment;

[0039] Figure 4 A second schematic flowchart illustrating an acoustic structure fabrication method provided in this application embodiment;

[0040] Figure 5 The third schematic flowchart of an acoustic structure fabrication method provided in this application embodiment;

[0041] Figure 6The fourth schematic flowchart of an acoustic structure fabrication method provided in this application embodiment;

[0042] Figure 7 Fifth schematic flowchart of an acoustic structure fabrication method provided in this application embodiment;

[0043] Figure 8 A schematic flowchart of an acoustic structure fabrication method provided in this application embodiment is shown in Figure 6.

[0044] Figure 9 The seventh schematic flowchart of an acoustic structure fabrication method provided in this application embodiment;

[0045] Figure 10 This is the eighth schematic flowchart of an acoustic structure fabrication method provided in this application embodiment;

[0046] Figure 11 This is a schematic diagram of an acoustic structure provided in an embodiment of this application;

[0047] Figure 12 This is one of the flowcharts illustrating another method for preparing an acoustic structure provided in this application.

[0048] Figure 13 A second schematic flowchart illustrating another method for preparing an acoustic structure provided in this application embodiment;

[0049] Figure 14 A third schematic flowchart illustrating another method for preparing an acoustic structure provided in this application embodiment;

[0050] Figure 15 Fourth schematic flowchart of another acoustic structure preparation method provided in the embodiments of this application;

[0051] Figure 16 This is a schematic diagram of another acoustic structure provided in an embodiment of this application;

[0052] Figure 17 This is a schematic diagram of the device under strong and weak fixation conditions;

[0053] Figure 18 This is a simulation diagram of the device under strong fixed conditions;

[0054] Figure 19 This is a simulation diagram of the device under weakly fixed conditions;

[0055] Figure 20 This is a graph showing the frequency response of the device under strong and weak fixed conditions.

[0056] Icons: 110-Substrate; 111-Back cavity; 120-Oxide layer; 121-Boundary definition layer; 130-Piezoelectric diaphragm; 131-Electrode layer; 132-Piezoelectric layer; 140-Interconnect hole; 150-Pad; 160-Etching groove; 170-Cavity; 180-Support layer; 190-Insulating layer. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0058] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. It should be noted that, unless otherwise specified, the various features in the embodiments of this application can be combined with each other, and the combined embodiments are still within the protection scope of this application.

[0059] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0060] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and 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 should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0061] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0062] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0063] The vibrating area of ​​a diaphragm usually refers to the suspended area of ​​the diaphragm, such as... Figure 1 As shown, a diaphragm 2 is provided on the support body 1. In order to facilitate the vibration of the diaphragm 2, a back cavity 11 needs to be formed on the back of the support body 1 by DRIE process, so that the diaphragm 2 is exposed in part 21 of the back cavity 11. Therefore, the area occupied by the exposed part 21 of the diaphragm 2 forms the vibrating area of ​​the diaphragm, that is, the boundary of the vibrating area of ​​the diaphragm 2 is usually defined by the back cavity 11.

[0064] As mentioned above, the formation of the back cavity 11 requires etching the support 1 using the DRIE process, which leads to the following problems:

[0065] (1) Dimensional deviation: The DRIE etching process requires complete penetration through the entire thickness of the support 1. In addition, the DRIE process cannot achieve a completely 90-degree perpendicular etching, and is usually skewed by a few degrees, resulting in a deviation between the actual size of the back cavity 11 and the expected size. Especially when the thickness of the support 1 is relatively thick, such as more than 400 micrometers, the deviation will be further amplified.

[0066] (2) The boundary of the back cavity 11 (the boundary of the vibrating area) is uncertain: Due to the non-ideal nature of the aforementioned DRIE process, the boundary position of the back cavity 11 cannot be precisely controlled, which affects the overall response of the device.

[0067] (3) The shape of the boundary of the back cavity 11 (the boundary of the vibrating area) is irregular: Also based on the non-ideal nature of the DRIE process, the boundary of the back cavity 11 is usually arc-shaped or irregularly curved, making it difficult to achieve the expected straight edge, which also affects the response of the device.

[0068] (4) In mass production, the consistency of the back cavity 11 of each device on the wafer is poor: such as Figure 2 As shown in the top-down view, the solid-lined boxes on wafer 3 represent the actual back cavity 11, and the dashed-lined boxes represent the expected back cavity 11. It can be seen that the actual back cavity 11 of each device deviates from its expected location. Furthermore, while the expected back cavity 11 dimensions are consistent across all devices, the actual back cavities formed after etching vary in size. Therefore, during mass production, the response consistency of each device on the wafer is poor.

[0069] To address the aforementioned technical problems, one aspect of this application provides a method for fabricating an acoustic structure. This method utilizes thin-layer etching to form a boundary definition layer that matches the desired height and dimensions. This boundary definition layer (rather than a back cavity) is then used to define the vibratory region of the final acoustic structure, thereby optimizing the response performance of the acoustic structure. Especially in mass production, this method effectively improves the response consistency of each acoustic structure.

[0070] Please refer to Figure 3 This paper illustrates a method for fabricating an acoustic structure, the method comprising:

[0071] S10: Provides a substrate with a preset area on the front side.

[0072] Please refer to Figure 5 This application provides a substrate 110 as a foundation for subsequent layer fabrication. The material of the substrate 110 is not specifically limited and can be a semiconductor material well known in the art, such as silicon wafer.

[0073] Substrate 110 typically has two opposing surfaces. For ease of distinction, one surface is defined as the front surface and the other as the back surface. Therefore, in this application, the front and back surfaces are used only to distinguish between the two and are not otherwise specifically designated, for example... Figure 5 In the diagram, the upper surface of the substrate 110 is designated as the front side (a), and the lower surface of the substrate 110 is designated as the back side (b).

[0074] The front side of the substrate 110 may have several preset areas. By defining the preset areas, it is convenient for subsequent process steps to fabricate the boundary definition layer 121 and the piezoelectric diaphragm 130 within the preset areas.

[0075] The preset area should be a virtual area, referring to a specific region on the front of the base 110, and is not represented by the actual structure (although it could be represented by the actual structure). For example... Figure 5 As shown, the front surface a of the substrate 110 is a predetermined region. Of course, in other embodiments not shown, the front surface a of the substrate 110 may include two or more predetermined regions, and the hierarchical structure within each predetermined region can be carried out with reference to the following process steps, which will not be specifically described in this application.

[0076] S20: A boundary definition layer is formed in a preset area on the front of the substrate. The boundary definition layer is used to define the boundary of the cavity of the acoustic structure within the preset area.

[0077] Please continue to refer to Figure 5A boundary definition layer 121 is formed in a predetermined area on the front side a of the substrate 110. The thickness of the boundary definition layer 121 is relatively thin, for example, hundreds of nanometers to several micrometers, which is much smaller than the thickness of the substrate 110 (typically hundreds of micrometers). Therefore, its size, shape and position can be defined very accurately by photolithography and etching processes, even if its size, shape and position match the expected height.

[0078] By utilizing the conformity between the boundary definition layer 121 and the expected height, when there are multiple preset regions in the front surface a of the substrate 110, the boundary definition layer 121 in each preset region has a high degree of consistency.

[0079] The material of the boundary definition layer 121 can be an oxide, such as silicon oxide.

[0080] The boundary definition layer 121 is used to define the vibratory region of the acoustic structure, that is, to define the cavity 170 of the subsequent acoustic structure, including the position, shape, and size of the cavity 170 within the preset region. Since the boundary definition layer 121 conforms to the expected height, the position, shape, and size of the cavity 170 formed by it will also conform to the expected height. Furthermore, the high consistency of the boundary definition layers 121 within each preset region effectively improves the consistency of the cavities 170 within each acoustic structure.

[0081] S30: Form a piezoelectric diaphragm stacked on the boundary definition layer within a preset area.

[0082] Please refer to Figure 6 A piezoelectric diaphragm 130 is formed within a preset area. The piezoelectric diaphragm 130 should be stacked above the boundary definition layer 121, and the orthographic projection of the piezoelectric diaphragm 130 within the preset area should cover the orthographic projection of the boundary definition layer 121 within the same preset area. That is, the orthographic projection area of ​​the piezoelectric diaphragm 130 within the preset area should be greater than the orthographic projection area of ​​the boundary definition layer 121 within the same preset area.

[0083] As a possible implementation, the piezoelectric diaphragm 130 may include various structural forms such as a single piezoelectric layer 132, a double piezoelectric layer 132, and a triple piezoelectric layer 132, wherein each piezoelectric layer 132 has an electrode layer 131 (also referred to as an upper electrode and a lower electrode) disposed on opposite sides of its surface. For example Figure 6As shown, the piezoelectric diaphragm 130 has a single piezoelectric layer 132 structure, meaning it includes a piezoelectric layer 132 and electrode layers 131 disposed on the upper and lower surfaces of the piezoelectric layer 132. Alternatively, the piezoelectric diaphragm 130 can have a double piezoelectric layer 132 structure, meaning it includes an electrode layer 131, a piezoelectric layer 132, an electrode layer 131, a piezoelectric layer 132, and an electrode layer 131 stacked sequentially. Therefore, when sound waves act on the piezoelectric diaphragm 130, the diaphragm 130 will begin to vibrate under the sound pressure and generate corresponding strain. At this time, the piezoelectric layer 132 within the diaphragm 130, due to the strain, generates charges on its upper and lower surfaces, which are then output as electrical signals via the electrode layer 131. When an electrical signal is applied to the piezoelectric layer 132 via the electrode layer 131, the piezoelectric diaphragm 130 will begin to vibrate under the action of the electrical signal and generate corresponding strain, thereby acting on the air around the piezoelectric diaphragm 130 to form sound waves that propagate outward.

[0084] S40: A back cavity is etched from the back side of the substrate to form a boundary definition layer, which covers the opening of the back cavity on the front side of the substrate.

[0085] Please refer to Figure 10 or Figure 15 A back cavity 111 is formed by etching (using a DRIE process) from the back side b of the substrate 110. The back cavity 111 extends from the back side b of the substrate 110 to the boundary definition layer 121, and the boundary definition layer 121 covers the opening of the back cavity 111 on the front side of the substrate 110. That is, the orthographic projection area of ​​the boundary definition layer 121 in the preset region is larger than the opening area of ​​the back cavity 111 on the front side of the substrate 110. In this way, the cavity 170 can be defined using the boundary definition layer 121 instead of using the back cavity 111.

[0086] S50: Remove the boundary definition layer to form a cavity between the substrate and the piezoelectric diaphragm.

[0087] Please refer to Figure 11 or Figure 16 After removing the boundary definition layer 121, the space it originally occupied becomes cavity 170.

[0088] Since the projected area of ​​the boundary definition layer 121 in the preset area is larger than the opening area of ​​the back cavity 111 on the front of the substrate 110, after removing the boundary definition layer 121, the area of ​​the piezoelectric diaphragm 130 exposed due to suspension is determined by the cavity 170, rather than the back cavity 111.

[0089] In summary, by utilizing the boundary definition layer 121 that can form a height consistent with the expected height, the position, shape, and size of the cavities 170 in each preset region can also conform to the expected height. Furthermore, during mass production, the height consistency of the boundary definition layer 121 in each preset region can effectively improve the consistency of the cavities 170 within each acoustic structure.

[0090] In possible implementations, the resonant frequency, sensitivity, and electromechanical coupling coefficient of the acoustic structure can be optimized. Specifically, when creating the boundary definition layer 121 using S20, this can be done using the following method:

[0091] S21: A boundary definition layer protruding from the front of the substrate is formed within a predetermined area of ​​the substrate, so that the boundary definition layer forms a step relative to the front of the substrate at its sidewall.

[0092] Please refer to Figure 5 As shown, when the boundary definition layer 121 is formed in the preset area of ​​the substrate 110, the boundary definition layer 121 needs to protrude relative to the front of the substrate 110. In this way, the upper surface c of the boundary definition layer 121 will have a height difference with the front a of the substrate 110, that is, the boundary definition layer 121 forms a step relative to the front of the substrate 110 at its sidewall d.

[0093] The optimization of the resonant frequency, sensitivity, and electromechanical coupling coefficient of an acoustic structure using steps can be illustrated with different examples:

[0094] Example 1

[0095] Based on S21, please refer to the following possible implementation methods: Figure 6 As shown, after the piezoelectric diaphragm 130 is formed by S30, the edge of the piezoelectric diaphragm 130 extends from the step to the front of the substrate 110. Due to the presence of the step, the piezoelectric diaphragm 130 itself also forms a stepped shape at the step. When the cavity 170 is formed after the boundary definition layer 121 is removed, the piezoelectric diaphragm 130 will still maintain a stepped shape at the boundary of the cavity 170 (vibrational area).

[0096] Please refer to Figure 17 , Figure 17 (a) in the middle shows Figure 1 The structure of the diaphragm at the boundary of the vibrating region of the device is specifically a clamping state. The completely fixed clamping state forms a strong fixed connection between the diaphragm and the support. This clamping state greatly restricts the movement of the diaphragm, which will have an adverse effect on the device's resonant frequency, sensitivity and electromechanical coupling coefficient.

[0097] In contrast. Figure 17(b) shows the structure of the piezoelectric diaphragm 130 of the acoustic structure in this application at the boundary of the cavity 170 (i.e., the vibrating region). Specifically, the structure at the boundary presents a stepped structure, which can transform the completely fixed clamping state into a weakly fixed spring boundary, thereby reducing the limiting effect of the boundary on the vibration of the piezoelectric diaphragm 130.

[0098] To more intuitively understand the impact of strong and weak fixation on device performance, such as Figures 18 to 20 As shown, Figure 18 The diagram shows a simulation of the device under strong fixed conditions. Figure 19 A simulation diagram of the device under weakly fixed conditions is shown. It should be understood that the two conditions have the same geometric parameters and excitation conditions. Figure 20 It can be seen that the device has a lower resonant frequency, higher sensitivity, and higher electromechanical coupling coefficient under weakly fixed conditions compared with strongly fixed conditions.

[0099] In some possible implementations, such as Figure 7 As shown, after S30, an insulating layer 190, such as a silicon oxide layer, can be formed on top of the piezoelectric diaphragm 130. Then, interconnect holes 140 are formed by photolithography and etching. The number of interconnect holes 140 should correspond to the number of electrode layers 131, with each interconnect responsible for leading out one electrode layer 131.

[0100] In some possible implementations, such as Figure 8 As shown, interconnect metal is formed by filling the interconnect holes 140 with metal. The material of the interconnect metal can be aluminum, aluminum / copper, gold, etc. The interconnect metal is patterned to form the desired electrical connections and pads 150.

[0101] In some possible implementations, if a cantilever beam structure is required, after S30, the method further includes: etching the piezoelectric diaphragm 130 to form multiple cantilever beam diaphragms distributed in the same layer. Specifically, such as... Figure 9 As shown, an etching groove 160 is formed by etching the insulating layer 190 (if present) and the piezoelectric diaphragm 130. The etching groove 160 divides the entire piezoelectric diaphragm 130 into multiple cantilever beam diaphragms distributed in the same layer, and slits exist between adjacent cantilever beam diaphragms.

[0102] In some possible implementations, such as Figure 11 As shown, a portion of the insulating layer 190 above the piezoelectric diaphragm 130 can be removed, especially the portion directly opposite the cavity 170. This reduces the vibration restriction of the piezoelectric diaphragm 130 by the insulating layer 190.

[0103] Example 2

[0104] Based on S21, after forming a boundary definition layer 121 within a predetermined area on the front side of the substrate 110, the method further includes:

[0105] S61: A support layer is formed on the front side of the substrate to cover the boundary definition layer.

[0106] like Figure 5 As shown, after forming the steps using boundary definition layer 121, please continue to refer to... Figure 12 As shown, a support layer 180 covering the boundary definition layer 121 is formed on the front side of the substrate 110, so that the support layer 180 will form a stepped shape at the step. When the boundary definition layer 121 is subsequently removed to form the cavity 170, the support layer 180 will still maintain a stepped shape at the boundary of the cavity 170 (vibrational area).

[0107] S62: Flatten the front side of the support layer to obtain a flattened surface.

[0108] To optimize the formation quality of the piezoelectric diaphragm 130, such as Figure 13 As shown, the front side (i.e., the upper surface) of the support layer 180 can be planarized, thereby making the upper surface of the support layer 180 a planarized surface.

[0109] This application does not impose any special restrictions on the planarization process, such as chemical mechanical polishing or etching back process.

[0110] Next, the piezoelectric diaphragm 130 is formed using S30, including:

[0111] S31: Form a piezoelectric diaphragm stacked to a planarized surface within a preset area.

[0112] A planarized surface provides a favorable growth environment for the piezoelectric diaphragm 130 formed on it, which helps to improve its quality.

[0113] In summary, by utilizing the support layer 180, a stepped shape can still be maintained at the boundary of the cavity 170 (vibrational region). Therefore, referring to Example 1, a weakly fixed state can also be formed, and a lower resonant frequency, higher sensitivity, and higher electromechanical coupling coefficient can also be achieved.

[0114] In some possible implementations, after S30, the method further includes: etching the piezoelectric diaphragm 130 to form multiple cantilever beam diaphragms distributed in the same layer. Specifically, as... Figure 14 As shown, if a cantilever beam structure is required, an etching groove 160 is formed by etching the insulating layer 190 (if present), the piezoelectric diaphragm 130 and the support layer 180. The etching groove 160 divides the entire piezoelectric diaphragm 130 and the support layer 180 into multiple cantilever beam diaphragms distributed in the same layer, and the slits exist between adjacent cantilever beam diaphragms.

[0115] In some possible implementations, the support layer 180 forming on the front side of the substrate 110 to cover the boundary definition layer 121 includes: Figure 12 As shown, a support layer 180 covering the boundary definition layer 121 is formed on the front side of the substrate 110 by chemical vapor deposition, so that the entire support layer 180 can be formed.

[0116] In some possible implementations, such as Figure 16 As shown, a portion of the insulating layer 190 above the piezoelectric diaphragm 130 can be removed, especially the portion directly opposite the cavity 170. This reduces the vibration restriction of the piezoelectric diaphragm 130 by the insulating layer 190.

[0117] In some examples, using S20 to form the boundary definition layer 121 includes:

[0118] S22: An oxide layer is grown on the front side of the substrate using a thermo-oxidative process.

[0119] S23: The patterned oxide layer forms a boundary definition layer located within a preset area.

[0120] Please refer to Figure 4 First, a whole oxide layer 120 is grown on the front side of the substrate 110 using a thermal oxidation process. For example, when the substrate 110 is a silicon wafer, silicon is used as a raw material to react chemically with oxygen to generate a silicon oxide layer on the front side of the substrate 110.

[0121] Then, the oxide layer 120 is patterned using photolithography and etching to form a shape such as... Figure 5 The boundary definition layer 121 shown is located within the preset area.

[0122] Based on this, the boundary definition layer 121 formed by the thermal oxidation process can also serve as an etching stop layer for the subsequent etching of the back cavity 111. Specifically, when forming the back cavity 111 using S40, it includes:

[0123] S41: Using the boundary definition layer as the etching stop layer, a back cavity extending to the boundary definition layer is formed by etching from the back side of the substrate.

[0124] like Figures 9 to 10 or Figures 14 to 15 As shown, when etching a cavity 111 extending to the boundary definition layer 121 from the back side of the substrate 110, the boundary definition layer 121 is used as an etching stop layer, which can effectively avoid over-etching and protect the piezoelectric diaphragm 130 or the support layer 180.

[0125] Another aspect of the embodiments of this application provides an acoustic structure, such as Figure 11 or Figure 16 As shown, it includes:

[0126] The base 110 has a predetermined area on its front side, and a back cavity 111 is formed in the predetermined area that penetrates the base 110.

[0127] The piezoelectric diaphragm 130 is located in a preset region and has a cavity 170 protruding from the substrate 110 between the piezoelectric diaphragm 130 and the substrate 110.

[0128] In summary, based on the aforementioned fabrication method, the cavity 170, rather than the back cavity 111, defines the vibratory region of the acoustic structure, thereby ensuring that the position, shape, and size of the cavities 170 within each preset region match the expected height. Furthermore, this method effectively improves the consistency of the cavities 170 within each acoustic structure during mass production. Additionally, the use of steps can optimize the resonant frequency, sensitivity, and electromechanical coupling coefficient of the acoustic structure.

[0129] Optionally, such as Figure 16 As shown, the acoustic structure also includes a support layer 180, which is located between the substrate 110 and the piezoelectric diaphragm 130. The front side of the support layer 180 is a planarized surface, and a cavity 170 is located between the support layer 180 and the substrate 110. The planarized surface provides a good growth environment for the piezoelectric diaphragm 130 formed thereon, which helps to improve its quality.

[0130] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing an acoustic structure, characterized in that: The method comprises: Providing a substrate, wherein the front surface of the substrate has a preset area; forming a boundary definition layer in a preset area on the front surface of the substrate, wherein the boundary definition layer is used to define a boundary of the cavity of the acoustic structure in the preset area; forming a piezoelectric diaphragm stacked on the boundary definition layer in the preset area; Etching from the back side of the substrate to form a back cavity penetrating to the boundary definition layer, wherein the boundary definition layer covers the opening of the back cavity at the front side of the substrate; Removing the boundary definition layer forms a cavity between the substrate and the piezoelectric diaphragm.

2. The preparation method according to claim 1, characterized in that The forming of a boundary definition layer in a preset area on the front side of the substrate comprises: A boundary definition layer protruding from the front surface of the substrate is formed in a preset area of ​​the substrate, so that the boundary definition layer forms a step relative to the front surface of the substrate at its side wall.

3. The preparation method according to claim 2, characterized in that: The edge of the piezoelectric diaphragm extends from the step to the front surface of the substrate.

4. The preparation method according to claim 2, characterized in that: After forming the boundary definition layer in the preset area on the front side of the substrate, the method further comprises: forming a support layer covering the boundary definition layer on the front side of the substrate; Performing a planarization process on the front surface of the support layer to obtain a planarized surface; The piezoelectric diaphragm formed in the preset area and stacked on the boundary definition layer includes: The piezoelectric diaphragm laminated to the planarized surface is formed in the predetermined area.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The forming of a boundary definition layer in a preset area on the front side of the substrate comprises: growing an oxide layer on the front side of the substrate by a thermal oxidation process; The oxide layer is patterned to form the boundary definition layer located in the predetermined area.

6. The preparation method according to claim 5, characterized in that: The etching from the back side of the substrate to form a back cavity penetrating to the boundary definition layer comprises: The boundary definition layer is used as an etching stop layer, and a back cavity penetrating to the boundary definition layer is formed by etching from the back side of the substrate.

7. The preparation method according to any one of claims 1 to 4, characterized in that: After forming a piezoelectric diaphragm stacked on the boundary definition layer in the preset area, the method further includes: The piezoelectric diaphragm is etched to form a plurality of cantilever beam diaphragms distributed in the same layer.

8. The preparation method according to claim 4, characterized in that: The support layer formed on the front side of the substrate and covering the boundary definition layer comprises: A support layer covering the boundary definition layer is formed on the front side of the substrate by chemical vapor deposition.

9. An acoustic structure, characterized in that: include: A substrate, wherein the front surface of the substrate has a preset area, and a back cavity penetrating the substrate is formed in the preset area; A piezoelectric diaphragm is located in the preset area, and a cavity is provided between the piezoelectric diaphragm and the substrate and protrudes from the substrate.

10. The acoustic structure according to claim 9, characterized in that Also includes: A supporting layer is located between the substrate and the piezoelectric diaphragm, the front side of the supporting layer is a flattened surface, and the cavity is located between the supporting layer and the substrate.

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