MEMS microphone and method of manufacturing the same

Abstract

Disclosed are a MEMS microphone and a manufacturing method thereof. The MEMS microphone comprises a substrate, a diaphragm and a backplate electrode located on a first surface of the substrate, the diaphragm and the backplate electrode being spaced apart from each other, a first surface of the diaphragm and a first surface of the backplate electrode being opposite to each other, and an acoustic cavity penetrating through the substrate to a second surface of the diaphragm, the second surface of the diaphragm and the first surface of the substrate being in point contact through a connecting part. The present application releases the stress of the diaphragm greatly by point contact between the diaphragm and the substrate, and improves the sensitivity of mechanical response of the diaphragm.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of micro microphone, and more particularly, to a MEMS microphone and a manufacturing method thereof. BACKGROUND

[0002] A MEMS microphone is a MEMS (Micro-Electro-Mechanical System) device manufactured by microfabrication process. Due to its small size, high sensitivity, and good compatibility with existing semiconductor technology, the MEMS microphone is increasingly widely used in mobile terminals such as mobile phones. The structure of the MEMS microphone includes a diaphragm and a backplate electrode opposite to each other, which are respectively connected to corresponding electrodes via lead wires. A cavity is formed between the diaphragm and the backplate electrode to provide the required vibration space for the diaphragm.

[0003] With the development of microfabrication process, the distance between the diaphragm and the backplate electrode in the MEMS microphone is getting smaller and smaller, but at the same time, the process requirements in the manufacturing and application of the MEMS microphone are getting higher and higher. The structural defects introduced by process deviation not only affect the yield of the microphone, but also cause the performance of the MEMS microphone to deteriorate sharply in the application environment. It is expected to further improve the structure of the MEMS microphone to suppress the adverse effects of process deviation on the performance of the device, and thus to improve the yield and reliability of the device. SUMMARY

[0004] The purpose of the present application is to provide a MEMS microphone and a manufacturing method thereof, wherein the diaphragm is in point contact with the substrate, thereby releasing the stress of the diaphragm to improve the working sensitivity of the device.

[0005] According to an aspect of the present application, a MEMS microphone is provided, comprising: a substrate; a diaphragm and a backplate electrode on a first surface of the substrate, the diaphragm and the backplate electrode being spaced apart from each other, a first surface of the diaphragm and a first surface of the backplate electrode being opposite to each other; and an acoustic cavity penetrating through the substrate to a second surface of the diaphragm, wherein the second surface of the diaphragm is in point contact with the first surface of the substrate through a connecting portion.

[0006] Preferably, the diaphragm comprises: a middle portion; and a peripheral portion surrounding the middle portion.

[0007] Preferably, it further comprises: a first connecting portion on the first surface of the substrate, in point contact with the peripheral portion of the diaphragm.

[0008] Preferably, it further comprises: a second connecting portion on the first surface of the substrate, nested between the diaphragm and extending upward to the first surface of the diaphragm.

[0009] Preferably, further comprising a third connecting portion located at a peripheral portion of the diaphragm and extending toward the first surface of the substrate, and further comprising a dielectric layer between the third connecting portion and the substrate.

[0010] Preferably, the diaphragm further comprises a spring structure for connecting the intermediate portion and the peripheral portion, the spring structure being a concentric ring-shaped corrugated portion or a spiral-shaped corrugated portion.

[0011] Preferably, the peripheral portion of the diaphragm comprises a discontinuous region.

[0012] Preferably, the intermediate portion of the diaphragm comprises at least one through hole.

[0013] Preferably, the backplate electrode is located above the movable region of the diaphragm, and an area of the backplate electrode is less than or equal to an area of the movable region of the diaphragm.

[0014] Preferably, an area of the backplate electrode is less than or equal to a minimum cross-sectional area of the acoustic cavity.

[0015] Preferably, a spacing between the backplate electrode and the diaphragm is 1-3 microns.

[0016] Preferably, further comprising a first isolation layer on the first surface of the substrate, and a second isolation layer on a surface of the first isolation layer away from the substrate, wherein the acoustic cavity penetrates the first isolation layer.

[0017] Preferably, further comprising a first protective layer and a second protective layer, the backplate electrode being located between the first protective layer and the second protective layer, the first protective layer being located between the second isolation layer and the backplate electrode.

[0018] Preferably, the first protective layer forms a plurality of protrusions on a surface facing the first surface of the diaphragm to prevent adhesion between the backplate electrode and the diaphragm.

[0019] Preferably, the second protective layer serves as a mechanical support layer of the backplate electrode to provide rigidity, so that the backplate electrode maintains a non-deformed state in an operating state.

[0020] Preferably, further comprising a plurality of release holes penetrating the first protective layer, the backplate electrode and the second protective layer, and a cavity located in the second isolation layer, the cavity exposing the first surface of the diaphragm and a side surface for connecting the first surface and the second surface of the diaphragm, the cavity further comprising a spacing between the second isolation layer and the side surface of the diaphragm.

[0021] Preferably, the release holes and the acoustic cavity are in communication via the cavity.

[0022] Preferably, the plurality of release holes are in any one of a circular shape, a polygonal shape, a cross shape.

[0023] Preferably, the plurality of release holes are arranged in a rectangular array, a staggered rectangular array, or a circular array.

[0024] Preferably, further comprising a first lead wire passing through the second protective layer, the first protective layer, and the second isolation layer to the first surface of the diaphragm, and a second lead wire passing through the second protective layer to the second surface of the backplate electrode.

[0025] Preferably, the first connecting portion is a SiO2 layer or a SiBN layer.

[0026] Preferably, the second connecting portion is a SiO2 layer or a SiBN layer.

[0027] Preferably, the dielectric layer is a SiO2 layer or a SiBN layer.

[0028] Preferably, the ratio of the maximum width of the portion of the diaphragm beyond the maximum opening of the acoustic cavity to the spacing between the substrate and the diaphragm is 30:1 to 200:1.

[0029] Preferably, the connecting portions are discrete and uniformly distributed.

[0030] According to another aspect of the present application, there is provided a method of manufacturing a MEMS microphone, comprising: sequentially forming a diaphragm and a backplate electrode on a substrate, the diaphragm and the backplate electrode being spaced apart from each other, a first surface of the diaphragm and a first surface of the backplate electrode facing each other; and forming an acoustic cavity passing through the substrate to a second surface of the diaphragm, wherein the second surface of the diaphragm and the first surface of the substrate are in point contact through a connecting portion.

[0031] Preferably, the diaphragm comprises a central portion and a peripheral portion surrounding the central portion.

[0032] Preferably, the step of the second surface of the diaphragm and the first surface of the substrate being in point contact through a connecting portion comprises: forming a second connecting portion on the first surface of the substrate, nested with the diaphragm and extending upward to the first surface of the diaphragm.

[0033] Preferably, the step of the second surface of the diaphragm and the first surface of the substrate being in point contact through a connecting portion comprises: forming a first connecting portion on the first surface of the substrate, in point contact with the peripheral portion of the diaphragm.

[0034] Preferably, the step of point contacting the second surface of the diaphragm to the first surface of the substrate with a connecting portion includes having a third connecting portion extending from the peripheral portion of the diaphragm to the first surface of the substrate, and further including a dielectric layer between the substrate.

[0035] Preferably, further comprising forming a spring structure on the diaphragm connecting the intermediate portion and the peripheral portion, the spring structure being a concentric ring-shaped corrugated portion or a spiral-shaped corrugated portion.

[0036] Preferably, further comprising forming a discontinuous region on the peripheral portion of the diaphragm.

[0037] Preferably, further comprising forming at least one through hole on the intermediate portion of the diaphragm.

[0038] Preferably, the back plate electrode is formed above the movable region of the diaphragm, and an area of the back plate electrode is less than or equal to an area of the movable region of the diaphragm.

[0039] Preferably, an area of the back plate electrode is less than or equal to a minimum cross-sectional area of the acoustic cavity.

[0040] Preferably, a spacing between the back plate electrode and the diaphragm is 1 to 3 micrometers.

[0041] Preferably, further comprising forming a first isolation layer on the first surface of the substrate; and forming a second isolation layer between the back plate electrode and the diaphragm, wherein the acoustic cavity penetrates the first isolation layer.

[0042] Preferably, further comprising forming a first protective layer on the second isolation layer; and forming a second protective layer on the back plate electrode, the back plate electrode being between the first protective layer and the second protective layer.

[0043] Preferably, further comprising forming a plurality of release holes through the first protective layer, the back plate electrode, and the second protective layer; and forming a cavity in the second isolation layer, the cavity exposing the first surface of the diaphragm and a side surface for connecting the first surface and the second surface of the diaphragm, the cavity further including a spacing between the second isolation layer and the side surface of the diaphragm.

[0044] Preferably, the release holes and the acoustic cavity are in communication via the cavity.

[0045] Preferably, further comprising forming a first lead through the second protective layer, the first protective layer, and the second isolation layer to the first surface of the diaphragm; and forming a second lead through the second protective layer to a second surface of the back plate electrode.

[0046] Preferably, the ratio of the maximum width of the portion of the diaphragm beyond the maximum opening of the acoustic cavity to the spacing between the substrate and the diaphragm is 30:1 to 200:1.

[0047] Preferably, the connecting portions are discrete and uniformly distributed.

[0048] The MEMS microphone according to the embodiments of the present application supports the diaphragm on the substrate by point contact between the second surface of the diaphragm and the first surface of the substrate. The diaphragm of the MEMS microphone is free from the traditional microphone structure of diaphragm and substrate surface support, greatly releasing the stress of the diaphragm and improving the sensitivity of the mechanical response of the diaphragm. Specifically, a plurality of first connecting portions are provided on the first surface of the substrate to point contact with part of the peripheral portion of the second surface of the diaphragm. As an alternative embodiment, a plurality of second connecting portions are formed on the first surface of the substrate to point contact with the first surface of the substrate, and the second connecting portions are nested with the diaphragm and extend upward to the first surface of the diaphragm. As an alternative embodiment, part of the peripheral portion of the second surface of the diaphragm has a third connecting portion extending outward to point contact with the first surface of the substrate.

[0049] In a preferred embodiment, the backplate electrode is located above the movable area of the diaphragm, and the area of the backplate electrode is less than or equal to the area of the movable area of the diaphragm, so that the influence of the parasitic capacitance which does not contribute to the sensitivity of the MEMS microphone can be reduced. Even if there is process fluctuation, since the backplate electrode only needs to be aligned with the movable area of the diaphragm, the two can be easily aligned.

[0050] In a preferred embodiment, the area of the backplate electrode is less than or equal to the minimum cross-sectional area of the acoustic cavity, avoiding the problem of reduced reliability of the MEMS microphone due to process fluctuation in mass production, and improving the overall performance of the product.

[0051] In a preferred embodiment, the first protective layer forms a plurality of protrusions on the surface facing the first surface of the diaphragm to prevent adhesion between the backplate electrode and the diaphragm. The second protective layer serves as a mechanical support layer for the backplate electrode to provide rigidity, so that the backplate electrode maintains an undeformed state in the working state. Since the second protective layer serves as a mechanical support layer, the design freedom of the device can be improved. The pattern design of the backplate electrode of the MEMS microphone only needs to be based on the electrical performance design, without considering the requirement of mechanical rigidity, so that the pattern of the backplate electrode can be used to define the effective capacitance area, thereby reducing the influence of the parasitic capacitance which does not contribute to the sensitivity of the MEMS microphone.

[0052] In a preferred embodiment, the diaphragm of the MEMS microphone comprises a spring structure of concentric annular corrugated portions or spiral corrugated portions. The spring structure of the diaphragm effectively releases the stress of the diaphragm and improves the sensitivity of the MEMS microphone.

[0053] In a preferred embodiment, the partial area of the peripheral portion of the diaphragm is a discontinuous area. The discontinuous area is a discontinuous edge of the peripheral portion or a hollow structure of the peripheral portion. The discontinuous area of the diaphragm cannot form a capacitance structure with the upper and lower dielectric layers, thereby reducing the parasitic capacitance that is detrimental to the sensitivity of the microphone. At the same time, the discontinuous area can release a part of the stress of the diaphragm, effectively improving the sensitivity of the diaphragm.

[0054] In a preferred embodiment, the MEMS microphone further comprises a plurality of release holes penetrating the first protective layer, the back plate electrode and the second protective layer. The release holes not only serve as a supply channel for etching agents during the process, but also reduce the acoustic resistance in the working state of the MEMS microphone.

[0055] In a preferred embodiment, the cavity comprises a gap between the second isolation layer and the diaphragm, and the release hole and the acoustic cavity are connected via the cavity. That is, the diaphragm and the isolation layer are not in contact so that the acoustic cavity and the release hole are connected through the cavity, releasing the stress of the diaphragm and improving the sensitivity of the mechanical response of the diaphragm. BRIEF DESCRIPTION OF DRAWINGS

[0056] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0057] Figure 1 A flowchart showing a manufacturing method of a MEMS microphone according to an embodiment of the present application is shown;

[0058] Figures 2 to 13 Cross-sectional views showing different stages of a manufacturing method of a MEMS microphone according to an embodiment of the present application are shown;

[0059] Figure 14a A structural diagram of a diaphragm of a MEMS microphone according to an embodiment of the present application is shown; Figure 14b A structural diagram of another diaphragm of a MEMS microphone according to an embodiment of the present application is shown;

[0060] Figure 15a A structural diagram of a diaphragm of a MEMS microphone according to another embodiment of the present application is shown; Figure 15b A structural diagram of another diaphragm of a MEMS microphone according to another embodiment of the present application is shown;

[0061] Figure 16a A structural diagram of a diaphragm of a MEMS microphone according to another embodiment of the present application is shown;Figure 13 a partial enlarged view at C in another embodiment; Figure 16b shows Figure 13 a partial enlarged view at C in another embodiment; Figure 16c shows Figure 13 a partial enlarged view at C in another embodiment. DETAILED DESCRIPTION

[0062] Various embodiments of the present application will be described in more detail below with reference to the accompanying drawings. In the various drawings, like elements are denoted by the same or similar reference numerals. Each part in the drawings is not drawn to scale for the sake of clarity.

[0063] The present application can be presented in various forms and some examples will be described below.

[0064] Figure 1 shows a flowchart of a manufacturing method of a MEMS microphone according to an embodiment of the present application, Figures 2 to 1 4 shows cross-sectional views of different stages of a manufacturing method of a MEMS microphone according to an embodiment of the present application.

[0065] In step S01, a first isolation layer 102 is formed on a substrate 101, as shown in Figure 2 .

[0066] In this embodiment, the substrate 101 is a <100> oriented substrate silicon wafer, for example. Optionally, the substrate is doped as N-type. The first isolation layer 102 is a silicon oxide layer, for example. The silicon oxide layer is formed on the substrate 101 as the first isolation layer 102 by a method of thermal oxidation or Chemical Vapor Deposition (CVD), for example.

[0067] A portion of the first isolation layer 102 will serve as a sacrificial layer for forming a portion of the acoustic cavity under the diaphragm. The thickness of the first isolation layer 102 is 0.5 micrometers to 2 micrometers, for example.

[0068] In step S02, a recess 131 is formed on the surface of the first isolation layer 102, as shown in Figure 3 .

[0069] In this embodiment, a photoresist layer is formed on the surface of the first isolation layer 102, and a pattern including an opening is formed in the photoresist layer by a photolithography process. The exposed portion of the first isolation layer 102 is removed by a selective etchant with the photoresist layer as a mask, thereby forming the recess 131. The etching can be stopped at a predetermined depth of the first isolation layer 102 by controlling the etching time. After the etching, the photoresist layer can be removed by ashing or dissolving in a solvent.

[0070] The recess 131 is open at the surface of the first isolation layer 102 and extends downward. The shape of the recess 131 is a concentric ring shape, for example, including 1 to 6 nested circular ring shapes, as viewed from the surface of the first isolation layer 102. The shape of the recess 131 is a substantially trapezoidal or V-shaped shape with a bottom surface size smaller than an opening surface size, as viewed from the cross section of the first isolation layer 102, and in a preferred embodiment, the shape of the recess 131 is a square shape, as viewed from the cross section of the first isolation layer 102. The depth of the recess 131 is, for example, 0.5 microns to 0.8 microns. The recess 131 is used to define a connection portion to be formed in a subsequent step for point contact with the diaphragm.

[0071] Preferably, the opening surface of the recess 131 forms a smooth transition curve with the surface of the first isolation layer 102. To this end, an additional deposition step can be employed to form a conformal cover layer, for example, a thin oxide layer, to improve the topography of the recess 131 to obtain a smooth transition curve. The thickness of the cover layer is, for example, 0.1 microns to 2 microns.

[0072] In step S03, a diaphragm 103 is formed on the first isolation layer 102 for point contact with the substrate surface, as shown in FIG. 3. Figure 4

[0073] In this embodiment, the diaphragm 103 is composed of, for example, doped polysilicon. For example, the polysilicon is deposited on the first isolation layer 102 by low pressure chemical vapor deposition (LPCVD) at a deposition temperature of, for example, 570 degrees Celsius to 630 degrees Celsius. Further, the polysilicon layer is patterned by a photolithography and etching step to form patterns of the diaphragm 103 and the contact 121 in different regions of the polysilicon layer, respectively. The thickness of the diaphragm 103 is, for example, 0.3 microns to 1.5 microns.

[0074] The diaphragm 103 includes a middle portion and a peripheral portion surrounding the middle portion. The middle portion includes at least one through hole 1031 to serve both stress release and frequency response curve adjustment functions of the microphone.

[0075] In this example, before the diaphragm 103 is formed, a layer of, for example, SiO2 or SiBN is deposited in the recess 131 of the first isolation layer 102 by low pressure chemical vapor deposition (LPCVD) and chemical mechanical polishing (CMP) to form a plurality of first connection portions 171 (as shown in FIG. 4) on the first surface of the substrate 101 for point contact with a portion of the peripheral portion of the second surface of the diaphragm 103 to be formed subsequently. Figure 16a ​​

[0076] In an alternative embodiment, a layer of SiO2or SiBN is deposited in the recess 131 of the first isolation layer 102 before the formation of the membrane 103, and then the membrane 103 is formed, a layer of SiO2or SiBN is formed above the membrane 103, and is patterned to form a plurality of second connection portions 172 (as shown in Figure 16b ) in point contact with the first surface of the substrate 101, and the second connection portions 172 are nested with the membrane 103 formed subsequently and extend upward to the first surface of the membrane 103.

[0077] In an alternative embodiment, a layer of dielectric 180 is formed on the first isolation layer 102 to fill the recess 131 and cover at least part of the surface of the first isolation layer 102. The dielectric 180 is, for example, a layer of SiO2or SiBN. When the membrane is formed, a layer of polysilicon is deposited conformally on the first isolation layer 102 by low pressure chemical vapor deposition (LPCVD), and then the polysilicon layer is patterned by photolithography and etching to form a third connection portion 173 (as shown in Figure 16c ) on the peripheral part of the second surface of the membrane 103 to extend to the first surface of the substrate 101 in point contact. The dielectric 180 is provided between the substrate 101 and the third connection portion 173.

[0078] In a preferred embodiment, before the formation of the membrane 103, a recess is formed on the surface of the first isolation layer 102 to define a spring structure in the membrane 103 for connecting the intermediate part and the peripheral part, the intermediate part and the peripheral part of the membrane 103 cover the surface of the first isolation layer 102, and the spring structure continuously and conformally covers the bottom and sidewall of the recess. The spring structure is a concentric annular corrugated part 1042 (as shown in Figure 14b ) consistent with the shape of the recess. The intermediate part of the membrane 103 and the spring structure are movable regions of the membrane 103. In an alternative embodiment, the spring structure of the membrane 103 is a spiral corrugated part 1041 (as shown in Figure 14a ). Figure 14aThe radius of curvature of the threads in the spring structure can vary with position, either remaining constant or changing accordingly. These two implementations can be selected based on the specific application requirements. Compared to a diaphragm with a flat surface, a diaphragm 103 with a spring structure formed on its surface can improve the diaphragm's elastic properties, control the vibration region, improve the elastic coefficient of the diaphragm structure, and meet the performance design requirements of the MEMS microphone. In a preferred embodiment, the radius of curvature of each spiral thread is the same. In an alternative embodiment, the spring structure extends to the periphery of the diaphragm 103, effectively releasing stress on the diaphragm and improving the sensitivity of the MEMS microphone.

[0079] In an alternative embodiment, a portion of the peripheral region of the diaphragm 103 is a discontinuous region (e.g., Figure 15a , 15b As shown). Figure 15a As shown, the edges of the peripheral portion of the diaphragm 103 are discontinuous. Specifically, the edges of the peripheral portion are serrated, and the plurality of serrated notches 1043 form a discontinuous region. In an alternative embodiment, as... Figure 15b As shown, the discontinuous area of ​​the peripheral portion of the diaphragm 103 includes a hollow structure. Specifically, the hollow structure includes multiple through holes 1044, which are circular, trapezoidal, or polygonal. In this embodiment, the through holes 1044 are fan-shaped. Multiple through holes 1044 are arranged in a crisscross pattern in the peripheral portion of the diaphragm 103. Further, the diaphragm 103 is sunflower-shaped. More specifically, the edges of the diaphragm 103 are connected by multiple rounded edges.

[0080] In step S04, a second isolation layer 104 is formed on the diaphragm 103, and a plurality of openings are formed on the surface of the second isolation layer 104, such as... Figure 5 As shown.

[0081] In this embodiment, the second isolation layer 104 is, for example, a silicon oxide layer. For instance, a silicon oxide layer is formed on the film 103 as the second isolation layer 104 using methods such as low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). After forming the second isolation layer 104, its surface is planarized, for example, using chemical mechanical planarization.

[0082] A portion of the second isolation layer 104 will serve as a sacrificial layer for forming a cavity above the diaphragm 103, and also defines the spacing between the diaphragm and the backplate electrode using the thickness of the second isolation layer 104. The thickness of the second isolation layer 104 is selected according to the electrical and acoustic performance of the MEMS microphone, for example, 2 to 4 micrometers.

[0083] Next, a resist layer is formed on the surface of the second isolation layer 104, and a pattern including openings is formed in the resist layer using a photolithography process. Using the resist layer as a mask, the exposed portion of the second isolation layer 104 is removed using a selective etchant, thereby forming a plurality of openings 132. The etching can be stopped at a predetermined depth reaching the second isolation layer 104 by controlling the etching time. After etching, the resist layer can be removed by ashing or dissolution in a solvent.

[0084] The openings 132 are open at the surface of the second isolation layer 104 and extend downward. From the surface of the second isolation layer 104, the shape of the openings 132 is a circular hole, a square hole, or a triangular hole. From the cross section of the second isolation layer 104, the shape of the openings 132 is a substantially trapezoidal or V-shaped shape with a bottom surface size smaller than an opening surface size, for defining a protrusion to be formed in a subsequent step for preventing adhesion of the backplate electrode.

[0085] In step S05, a first protective layer 105 is formed on the second isolation layer 104, as shown in Figure 6 .

[0086] The first protective layer 105 is composed of, for example, any one selected from a silicon nitride layer, a boron nitride layer, and a silicon carbide layer. In this embodiment, the first protective layer 105 is, for example, a boron nitride layer. The boron nitride layer is formed on the second isolation layer 104, for example, by a method of hot wire assisted plasma enhanced chemical vapor deposition (PECVD), in which N2, H2, and B2H6 diluted with H2 are used as reaction gases, the substrate temperature is 400 to 500 degrees Celsius, and the reaction pressure is about 100 Pa. The thickness of the first protective layer 105 is, for example, 800 to 1500 angstroms.

[0087] The first protective layer 105 fills the openings 132 on the surface of the second isolation layer 104, thereby forming protrusions 105a. The shape of the protrusions 105a coincides with the shape of the openings 132, for example, any one of a multi-prism, a multi-prism, and a cylinder. The diameter of the protrusions 105a is, for example, 0.5 to 1.5 micrometers, and the depth is, for example, 0.5 to 1.5 micrometers.

[0088] In step S06, a backplate electrode 106 is formed on the first protective layer 105, and a contact 122 connected to the backplate electrode 106 is formed, as shown in Figure 7 .

[0089] The backplate electrode 106, the contact 122 are conductive layers, for example, composed of any one selected from Al, Cu, Au, Ti, Ni, Wu and alloys thereof doped polycrystalline silicon. For example, a doped polycrystalline silicon layer is formed on part of the surface of the first protective layer 105 by low pressure chemical vapor deposition (LPCVD). Then, the polycrystalline silicon layer is patterned by photolithography and etching steps to form the pattern of the backplate electrode 106 and the contact 122 connecting the backplate electrode 106. The thickness of the backplate electrode 106 is, for example, 0.3 microns to 1 micron.

[0090] In this embodiment, the backplate electrode 106 and the diaphragm 103 constitute two plates of a capacitor. In a preferred embodiment, the area of the backplate electrode 106 is less than or equal to the area of the movable region of the diaphragm 103. More preferably, the area of the backplate electrode 106 is 70% to 100% of the area of the movable region of the diaphragm 103. By using the area of the backplate electrode 106 less than or equal to the area of the movable region of the diaphragm 103, thus removing the invalid capacitance component from the detection signal, the sensitivity of the detection signal is only related to the effective capacitance component, thereby improving the sensitivity of the MEMS microphone. The movable region of the diaphragm includes the middle portion and the connecting portion. Wherein, when there is a spring structure in the diaphragm 103, the spring structure and the middle portion constitute the movable region of the diaphragm 103.

[0091] In some preferred embodiments, after this step, a recess 133 is etched through the first protective layer 105 and the second isolation layer 102 to reach the surface of the contact 122 by a conventional semiconductor process etching method.

[0092] In step S07, a second protective layer 107 is formed on the backplate electrode 106, as shown in Figure 8 .

[0093] The second protective layer 107 is, for example, composed of any one selected from a silicon nitride layer, a boron nitride layer, a silicon carbide layer. In this embodiment, the second protective layer 107 is, for example, a boron nitride layer. For example, a conformal boron nitride layer is formed on the backplate electrode 106 by a hot-wire assisted plasma enhanced chemical vapor deposition (PECVD) method, wherein N2, H2, and B2H6 diluted by H2 are used as reaction gases, the substrate temperature is 400 degrees Celsius to 500 degrees Celsius, and the reaction pressure is about 100 Pa. The thickness of the second protective layer 108 is, for example, 0.1 microns to 1.5 microns. Wherein, the first protective layer 105, the backplate electrode 106, and the second protective layer 107 constitute a backplate structure.

[0094] Since the backplate electrode 106 is patterned, the first part of the second protective layer 107 is formed on the surface of the backplate electrode 106 and the contact 122, and the second part is formed on the surface of the first protective layer 105.

[0095] It is noted that if the recess 133 is etched through the first protective layer 105 and the second isolation layer 102 to reach the surface of the contact 122 before the second protective layer 107 is formed, the third portion of the second protective layer 107 is also filled in the recess 133 in this step.

[0096] In step S08, the via holes 111 and 112 are formed to respectively reach the contacts 121 of the membrane 103 and the contacts 122 of the backplate electrodes 106, as shown in Figure 9 .

[0097] In this embodiment, a resist layer is formed on the surface of the second protective layer 107, and a pattern including openings is formed in the resist layer by a photolithography process. The via holes 111 and 112 are formed by using the resist layer as a mask and using a selective etchant. In the third portion of the second protective layer 107, the portion of the second protective layer 107 exposed through the mask openings is removed by etching to form the via holes 111 reaching the contacts 121 of the membrane 103. In the first portion of the second protective layer 107, the portion of the second protective layer 107 exposed through the mask openings above the contacts 122 is removed by etching to form the via holes 112 reaching the contacts 122 of the backplate electrodes 106. After etching, the resist layer can be removed by ashing or dissolving in a solvent.

[0098] Due to the patterning of the backplate electrodes 106 as described above, the second portion of the second protective layer 107 is in direct contact with the corresponding portion of the first protective layer 105. The at least one via hole 111 extends from the surface of the second portion of the second protective layer 107, through the second protective layer 107, the first protective layer 105, the second isolation layer 104, to the contacts 121 of the membrane 103. The at least one via hole 112 extends from the surface of the first portion of the second protective layer 107, through the second protective layer 107, to the contacts 122 of the backplate electrodes 106.

[0099] In step S09, the first lead 123 is formed as a conductive channel to respectively reach the contacts 121 of the membrane 103 and the second lead 124 is formed as a conductive channel to respectively reach the contacts 122 of the backplate electrodes 106, as shown in Figure 10 .

[0100] In this embodiment, the second lead 124 and the first lead 123 are composed of a conductive material, for example, selected from any one of aluminum, gold, silver, copper, nickel, titanium, chromium, or an alloy thereof. An aluminum alloy for the lead includes, for example, an aluminum-silicon alloy (1% by weight of silicon), and a titanium alloy includes titanium nitride. A metal layer is formed on the surface of the second protective layer 107, for example, by a sputtering or evaporation method. The thickness of the metal layer is, for example, 1 to 2 micrometers, and fills the through-hole 111 and 112. The first lead 123 and the second lead 124 serve as a lead layer of the two electrodes of the capacitive micro-silicon microphone.

[0101] A resist layer is formed on the surface of the metal layer, and a pattern including an opening is formed in the resist layer by a photolithography process. The exposed portions of the metal layer are removed with a selective etchant using the resist layer as a mask. Due to the selectivity of the etchant, the etching is stopped at the second protective layer 107. After the etching, the resist layer can be removed by ashing or dissolution in a solvent.

[0102] In the first partial region of the second protective layer 107, at least one second lead 124 passes through the second protective layer 107 to the back plate electrode 106. In the second partial region of the second protective layer 107, at least one first lead 123 passes through the second protective layer 107, the first protective layer 105, and the second isolation layer 104 in order to reach the diaphragm 103.

[0103] In step S10, a release hole 151 is formed through the second protective layer 107, the back plate electrode 106, and the first protective layer 105, as shown in Figure 11 .

[0104] In this embodiment, a resist layer is formed on the surface of the second protective layer 107, and a pattern including an opening is formed in the resist layer by a photolithography process. The exposed portions of the second protective layer 107, the back plate electrode 106, and the first protective layer 105 are removed with a selective etchant using the resist layer as a mask, thereby forming the release hole 151. Due to the selectivity of the etchant, the second isolation layer 104 serves as a stop layer. After the etching, the resist layer can be removed by ashing or dissolution in a solvent.

[0105] The releasing hole 151 is formed by, for example, a dedicated deep trench etching machine. The releasing hole 151 serves not only as a supply channel of etchant in the manufacturing process, but also as an acoustic hole in the finally formed MEMS microphone to reduce acoustic resistance. The shape of the releasing hole 151 is, for example, any one of a circle, a cross hole, and a polygon, as viewed from the surface of the second protective layer 107. When the shape of the releasing hole 151 is a circle, the diameter of the releasing hole 151 is 1 to 15 μm. When the shape of the releasing hole 151 is any one of a polygon or a cross hole, the maximum value of the distance between two vertices of the releasing hole 151 is 1 to 15 μm. In this embodiment, the shape of the releasing hole 151 is a hexagon, and a plurality of releasing holes 151 are arranged in a honeycomb structure array (a staggered rectangular array). In alternative embodiments, a plurality of releasing holes 151 can be arranged in a rectangular array, a circular array, or the like.

[0106] In step Sll, an acoustic cavity 161 is formed through the substrate 101 below the diaphragm 103, as shown in FIG. 2. Figure 12

[0107] In this embodiment, the thickness of the substrate 101 is reduced to a design value, for example, 350 to 450 μm, preferably 400 μm, by a chemical mechanical planarization or thinning process. For example, the first surface and the second surface of the substrate 101 opposite to each other, the first surface of the substrate 101 on which the first isolation layer 102 is formed, and the second surface of the substrate 101 as a free surface are ground to reduce the thickness of the substrate 101. Then, a resist layer is formed on the second surface of the substrate 101, and a pattern including an opening is formed in the resist layer by a photolithography process. The exposed portion of the substrate 101 is removed by a selective etchant with the resist layer as a mask, thereby forming the acoustic cavity 161. In this embodiment, the acoustic cavity is a square opening, and alternatively, can be an inverted trapezoidal opening. Due to the selectivity of the etchant, the first isolation layer 102 serves as a stop layer. After etching, the resist layer can be removed by ashing or dissolution in a solvent. Preferably, the area of the back plate electrode 106 is less than or equal to the minimum cross-sectional area of the acoustic cavity 161. It should be noted that when the opening of the acoustic cavity 161 is square, the cross-sectional area of the acoustic cavity 161 obtained at different levels is the same, and this unique cross-sectional area is the minimum cross-sectional area of the acoustic cavity 161. When the opening of the acoustic cavity 161 is an inverted trapezoidal or trapezoidal shape, the cross-sectional area of the acoustic cavity 161 at the first surface or the second surface of the substrate 101 is the minimum. In some embodiments, the radius of the minimum cross-section is 385 to 415 μm.

[0108] The acoustic cavity 161 is formed by, for example, a conventional Bosch process in MEMS technology and a dedicated deep trench etching machine.

[0109] ​In step S12, a portion of the first isolation layer 102 is removed via the acoustic cavity 161, and a portion of the second isolation layer 104 is removed via the release hole 151 to release the diaphragm 103, as shown in Figure 13

[0110] In this embodiment, for example, HF acid is used as the etchant, and the acoustic cavity 161 and the release hole 151 formed in the above steps are used as the access channels for the etchant. The first protective layer 105 and the second protective layer 107 respectively serve as protective films for the backplate electrode 106, so that the backplate electrode 106 is not etched in this etching step.

[0111] A portion of the first isolation layer 102 and a portion of the second isolation layer 104 are respectively removed by means of HF acid gas-phase fumigation or HF acid wet etching, so that a portion of the first surface and a portion of the second surface of the diaphragm 103 opposite to each other are re-exposed, thus releasing the diaphragm 103. After removing the portion of the first isolation layer 102, the acoustic cavity 161 extends from the second surface of the substrate 101 to the second surface of the diaphragm 103. After removing the portion of the second isolation layer 104, the cavity 162 is formed between the first protective layer 105 and the first surface of the diaphragm 103 and the side surface of the diaphragm for connecting the first surface and the second surface of the diaphragm 103. The cavity 162 includes the gap between the second isolation layer 104 and the side surface of the diaphragm 103, and the release hole 151 is in communication with the cavity 162 and the acoustic cavity 161, and provides an airflow channel during the vibration of the diaphragm 103. In addition, the through hole 1031 on the diaphragm 103 directly connects the cavity 162 and the acoustic cavity 161.

[0112] It should be noted that when the discontinuous region is provided on the diaphragm 103, the through hole or the opening in the discontinuous region is in communication with the cavity 162, and further in communication with the release hole 152 and the acoustic cavity 161.

[0113] After releasing the diaphragm 103, the substrate 101 and the diaphragm 103 have a gap h, and the maximum width d of the portion of the diaphragm 103 beyond the maximum opening of the acoustic cavity 161 on one side. The ratio of the width d to the gap h is 30:1 to 200:1. Further, when the portion of the diaphragm 103 beyond the maximum opening of the acoustic cavity 161 is a ring in this embodiment, the maximum width of the ring is d. It should be noted that the shape of the portion of the diaphragm 103 beyond the maximum opening of the acoustic cavity 161 is related to the shape of the diaphragm 103 and the maximum opening of the acoustic cavity.

[0114] In this step, the spring structure of the connecting portion of the diaphragm 103 is also exposed to the acoustic cavity 161 and the cavity 162.

[0115] The structure of the MEMS microphone manufactured by the above method is shown in Figure 13 ​​

[0116] The MEMS microphone 100 comprises: a first isolation layer 102, a diaphragm 103 and a second isolation layer 104 formed in sequence on a substrate 101; a first protection layer 105, a backplate electrode 106 and a second protection layer 107 formed in sequence on the second isolation layer 104; a release hole 151 penetrating through the first protection layer 105, the backplate electrode 106 and the second protection layer 107; a cavity 162 penetrating through the second isolation layer 104, the cavity 162 being in communication with the release hole 151; an acoustic cavity 161 penetrating through the substrate 101 and the first isolation layer 102; a first surface and a second surface of the diaphragm 103 opposite to each other and a side surface connecting the first surface and the second surface being exposed through the cavity 162 and the acoustic cavity 161. The second surface of the diaphragm 103 is in point contact with a first surface of the substrate 101 through a connecting portion. The connecting portion is discretely distributed, and further, for example, at least includes two connecting portions opposite to each other, or includes a plurality of connecting portions uniformly distributed in a circumference.

[0117] The diaphragm 103 and the backplate electrode 106 are respectively composed of doped polysilicon. Each of the first protection layer 105 and the second protection layer 107 is composed of any one of a silicon nitride layer, a boron nitride layer and a silicon carbide layer. Among them, the first protection layer 105, the backplate electrode 106 and the second protection layer 107 constitute a backplate structure. The spacing between the backplate electrode 106 and the diaphragm 103 is 1-3 microns.

[0118] The diaphragm 103 comprises a middle portion and a peripheral portion surrounding the middle portion.

[0119] In a preferred embodiment, the middle portion comprises at least one through hole 1031 for releasing stress and adjusting the frequency response curve of the microphone.

[0120] The MEMS microphone 100 further comprises a plurality of conductive channels. At least one second lead 124 penetrates through the second protection layer 107 to reach a contact 122 of the backplate electrode 106. At least one first lead 123 penetrates through the second protection layer 107, the first protection layer 105 and the second isolation layer 104 in sequence to reach a contact 121 of the diaphragm 103.

[0121] Further, a plurality of first connecting portions 171 (as shown in the enlarged view at middle C) are arranged on the first surface of the substrate 101, and further, are in point contact with a part of the peripheral portion of the second surface of the diaphragm 103. Figure 16a Figure 13 Further, a plurality of first connecting portions 171 (as shown in the enlarged view at middle C) are arranged on the first surface of the substrate 101, and further, are in point contact with a part of the peripheral portion of the second surface of the diaphragm 103. Figure 16b Figure 13 ​​(Enlarged view at point C), the second connecting portion 172 is nested and connected to the subsequently formed diaphragm 103 and extends upward to the first surface of the diaphragm 103. As an alternative embodiment, a portion of the peripheral region of the second surface of the diaphragm 103 has a third connecting portion 173 extending toward the first surface of the substrate 101 (e.g., ...). Figure 16c shown Figure 13 (Enlarged view at point C) to make point contact with the first surface of substrate 101.

[0122] In a preferred embodiment, the diaphragm 103 further includes a spring structure for connecting the intermediate portion and the peripheral portion, the spring structure being a concentric annular pleated portion. Alternatively, the spring structure may be a helical pleated portion.

[0123] In a preferred embodiment, a portion of the peripheral region of the diaphragm 103 is a discontinuous region (e.g., Figure 15a , 15b As shown). Figure 15a As shown, the edges of the peripheral portion of the diaphragm 103 are discontinuous. Specifically, the edges of the peripheral portion are serrated, and the plurality of serrated notches 1043 form a discontinuous region. In an alternative embodiment, as... Figure 15b As shown, the discontinuous area of ​​the peripheral portion of the diaphragm 103 includes a hollow structure. Specifically, the hollow structure includes multiple through holes 1044, which are circular, trapezoidal, or polygonal. In this embodiment, the through holes 1044 are fan-shaped. Multiple through holes 1044 are arranged in a crisscross pattern in the peripheral portion of the diaphragm 103. Further, the diaphragm 103 is sunflower-shaped. More specifically, the edges of the diaphragm 103 are connected by multiple rounded edges.

[0124] In a preferred embodiment, the area of ​​the back electrode 106 is less than or equal to the minimum cross-sectional area of ​​the acoustic cavity 161. More preferably, the area of ​​the back electrode is less than the minimum cross-sectional area of ​​the acoustic cavity 161, avoiding the problem of decreased reliability of the MEMS microphone caused by process fluctuations in mass production and improving the overall performance of the product. It should be noted that when the opening of the acoustic cavity 161 is square, the cross-sectional area of ​​the acoustic cavity 161 is the same on different horizontal planes, and this unique cross-sectional area is the minimum cross-sectional area of ​​the acoustic cavity 161. When the opening of the acoustic cavity 161 is an inverted trapezoid or trapezoidal shape, the cross-sectional area of ​​the acoustic cavity 161 located at the first or second surface of the substrate 101 is the smallest. In some embodiments, the radius of its minimum cross-section is 385 micrometers to 415 micrometers.

[0125] In the preferred embodiment, the first protective layer 105 forms a plurality of protrusions 105a on the surface facing the first surface of the diaphragm 103 to prevent adhesion between the backplate electrode 106 and the diaphragm 103. The second protective layer 107 serves as a mechanical support layer for the backplate electrode 106 to provide rigidity so that the backplate electrode 106 maintains a non-deformed state in the working condition.

[0126] In the preferred embodiment, the backplate electrode 106 is formed above the movable area of the diaphragm 103, and the area of the backplate electrode 106 is less than or equal to the area of the movable area of the diaphragm 103. In the preferred embodiment, the area of the backplate electrode 106 is less than the area of the movable area of the diaphragm 103, and more preferably, the area of the backplate electrode 106 is 70% to 100% of the area of the movable area of the diaphragm 103. By adopting the backplate electrode 106 with an area less than or equal to the area of the movable area of the diaphragm 103, the invalid capacitance component is removed from the detection signal, so that the sensitivity of the detection signal is only related to the valid capacitance component, thereby improving the sensitivity of the MEMS microphone.

[0127] The embodiments of the present application as described above are not exhaustive of all details of the embodiments, nor limit the present application to only the specific embodiments described. It is obvious that many modifications and variations can be made according to the above description. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well utilize the present application and make modifications and uses based on the present application. The scope of protection of the present application should be subject to the scope defined by the claims of the present application.

Claims

1. A MEMS microphone, comprising: Substrate; A first isolation layer located on the first surface of the substrate; A second isolation layer located on the surface of the first isolation layer away from the substrate; A diaphragm and a back electrode are located on the first surface of the substrate, the diaphragm and the back electrode are spaced apart from each other, and the first surface of the diaphragm and the first surface of the back electrode are opposite to each other; A first protective layer and a second protective layer, wherein the back electrode is located between the first protective layer and the second protective layer, and the first protective layer is located between the second isolation layer and the back electrode; and The acoustic cavity extends through the substrate to the second surface of the diaphragm. The second surface of the diaphragm is in point contact with the first surface of the substrate through a connecting portion; It also includes a cavity that exposes a first surface of the diaphragm and a side surface for connecting the first and second surfaces of the diaphragm; The back electrode is located above the movable area of ​​the diaphragm, and the area of ​​the back electrode is less than or equal to the area of ​​the movable area of ​​the diaphragm.

2. The MEMS microphone according to claim 1, wherein, The membrane includes: The middle part; and The surrounding portion surrounding the central portion.

3. The MEMS microphone according to claim 2, wherein, Also includes: The first connection portion located on the first surface of the substrate makes point contact with the peripheral portion of the diaphragm.

4. The MEMS microphone according to claim 2, wherein, Also includes: A second connecting portion located on the first surface of the substrate is nested and connected to the diaphragm and extends upward to the first surface of the diaphragm.

5. The MEMS microphone according to claim 2, wherein, Also includes: The third connecting portion, located at the peripheral portion of the diaphragm and extending toward the first surface of the substrate, further includes a dielectric layer between itself and the substrate.

6. The MEMS microphone according to claim 2, wherein, The diaphragm further includes: A spring structure is used to connect the middle part and the peripheral part, wherein the spring structure is a concentric ring-shaped pleated part or a spiral pleated part.

7. The MEMS microphone according to claim 2, wherein, The peripheral portion of the diaphragm includes discontinuous areas.

8. The MEMS microphone according to claim 2, wherein, The middle portion of the diaphragm includes at least one through-hole.

9. The MEMS microphone according to claim 1, wherein, The area of ​​the back electrode is less than or equal to the minimum cross-sectional area of ​​the acoustic cavity.

10. The MEMS microphone according to claim 1, wherein, The distance between the back electrode and the diaphragm is 1 micrometer to 3 micrometers.

11. The MEMS microphone according to claim 1, wherein, The acoustic cavity extends through the first isolation layer.

12. The MEMS microphone according to claim 1, wherein, The first protective layer forms a plurality of protrusions on the surface of the first surface facing the diaphragm to prevent adhesion between the back electrode and the diaphragm.

13. The MEMS microphone according to claim 1, wherein, The second protective layer serves as a mechanical support layer for the back electrode to provide rigidity, so that the back electrode remains in a non-deformable state during operation.

14. The MEMS microphone according to claim 1, wherein, Also includes: Multiple release holes, the multiple release holes penetrating the first protective layer, the back electrode plate, and the second protective layer; The cavity also includes a gap between the second isolation layer and the side of the diaphragm.

15. The MEMS microphone according to claim 14, wherein, The release hole and the acoustic cavity are connected via the cavity.

16. The MEMS microphone according to claim 14, wherein, The multiple release holes can be any one of the following shapes: circular, polygonal, or cross-shaped.

17. The MEMS microphone according to claim 14, wherein, The plurality of release holes are arranged in a rectangular array, or a staggered rectangular array, or a circular array.

18. The MEMS microphone according to claim 1, wherein, Also includes: A first lead passes through the second protective layer, the first protective layer, and the second insulating layer to reach the first surface of the diaphragm; as well as The second lead passes through the second protective layer to reach the second surface of the back electrode.

19. The MEMS microphone according to claim 3, wherein, The first connecting part is a SiO2 layer or a SiBN layer.

20. The MEMS microphone according to claim 4, wherein, The second connecting part is a SiO2 layer or a SiBN layer.

21. The MEMS microphone according to claim 5, wherein, The dielectric layer is a SiO2 layer or a SiBN layer.

22. The MEMS microphone according to claim 1, wherein, The ratio of the maximum width of one side of the portion of the diaphragm that extends beyond the maximum opening of the acoustic cavity to the spacing between the substrate and the diaphragm is 30:1 to 200:

1.

23. The MEMS microphone according to claim 1, wherein, The connecting parts are discrete and uniformly distributed.

24. A method for manufacturing a MEMS microphone, wherein, include: A first isolation layer is formed on the first surface of the substrate; A membrane is placed on the first isolation layer; A second isolation layer is formed on the diaphragm; A first protective layer is formed on the second isolation layer; A back electrode is formed on the first protective layer of the site, the diaphragm and the back electrode are spaced apart from each other, and the first surface of the diaphragm and the first surface of the back electrode are opposite to each other; A second protective layer is formed on the back electrode, the back electrode being located between the first and second protective layers, the back electrode being formed above the movable region of the diaphragm, and the area of ​​the back electrode being less than or equal to the area of ​​the movable region of the diaphragm. as well as A second acoustic cavity is formed, penetrating the substrate and reaching the second surface of the diaphragm. The second surface of the diaphragm is in point contact with the first surface of the substrate through a connecting portion; It also includes the step of forming a cavity that exposes a first surface of the diaphragm and a side surface for connecting the first and second surfaces of the diaphragm.

25. The method according to claim 24, wherein, The diaphragm includes a central portion and a peripheral portion surrounding the central portion.

26. The method of claim 25, wherein, The step of making point contact between the second surface of the diaphragm and the first surface of the substrate through the connection portion includes: A second connection portion is formed on the first surface of the substrate, nested and connected to the diaphragm and extending upward to the first surface of the diaphragm.

27. The method according to claim 25, wherein, The step of making point contact between the second surface of the diaphragm and the first surface of the substrate through the connection portion includes: A first connection portion is formed on the first surface of the substrate, which makes point contact with the peripheral portion of the diaphragm.

28. The method according to claim 25, wherein, The step of making point contact between the second surface of the diaphragm and the first surface of the substrate through the connection portion includes: The peripheral portion of the diaphragm has a third connection portion extending toward the first surface of the substrate, and a dielectric layer is also included between the diaphragm and the substrate.

29. The method according to claim 25, wherein, Also includes: A spring structure is formed on the diaphragm to connect the middle part and the peripheral part. The spring structure is a concentric annular pleated part or a spiral pleated part.

30. The method according to claim 25, wherein, Also includes: A discontinuous region is formed in the peripheral portion of the diaphragm.

31. The method according to claim 25, wherein, Also includes: At least one through hole is formed in the middle portion of the diaphragm.

32. The method according to claim 24, wherein, The area of ​​the back electrode is less than or equal to the minimum cross-sectional area of ​​the acoustic cavity.

33. The method according to claim 24, wherein, The distance between the back electrode and the diaphragm is 1 micrometer to 3 micrometers.

34. The method according to claim 24, wherein, The acoustic cavity extends through the first isolation layer.

35. The method according to claim 26, wherein, Also includes: Multiple release holes are formed through the first protective layer, the back electrode, and the second protective layer; as well as A cavity is formed in the second isolation layer, the cavity also including a space between the second isolation layer and the side of the diaphragm.

36. The method according to claim 35, wherein, The release hole and the acoustic cavity are connected via the cavity.

37. The method according to claim 24, wherein, Also includes: A first lead is formed through the second protective layer, the first protective layer, and the second insulating layer to reach the first surface of the diaphragm; as well as A second lead is formed through the second protective layer to reach the second surface of the back electrode.

38. The method according to claim 24, wherein, The ratio of the maximum width of one side of the portion of the diaphragm that extends beyond the maximum opening of the acoustic cavity to the spacing between the substrate and the diaphragm is 30:1 to 200:

1.

39. The method according to claim 24, wherein, The connecting parts are discrete and uniformly distributed.

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