MEMS microphone and forming method thereof

Abstract

The invention discloses an MEMS microphone and a forming method thereof, and the MEMS microphone comprises a first substrate which is internally provided with a first cavity with an opening along the substrate surface of the first substrate, and the depth of the first cavity is smaller than the thickness of the first substrate; the back polar plate is located on the substrate surface of the first substrate and covers the opening of the first cavity, and a first acoustic air hole is formed in the position, corresponding to the opening covering the first cavity, in the back polar plate; the second substrate is internally provided with a second cavity, the part, at the bottom of the second cavity, of the second substrate serves as a vibrating diaphragm, the second substrate is in bonding connection with the first substrate, an opening of the first cavity is opposite to an opening of the second cavity, and the second cavity is communicated with the first cavity through a first acoustic air hole; the first cavity and the second cavity jointly form a reference pressure cavity which is sealed in an airtight mode. According to the MEMS microphone, the defects that a traditional MEMS microphone is poor in low-frequency response and prone to being interfered and has reliability risks are overcome.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a MEMS microphone and a method for forming the same. Background Technology

[0002] Traditional MEMS microphones typically consist of a movable diaphragm and a fixed backplate, forming a variable capacitor between them. The diaphragm's mobility is achieved through a cavity between it and the backplate. Traditional MEMS microphones also incorporate a vent hole in the backplate or substrate, allowing the cavity to slowly connect to the outside atmosphere. During operation, sound waves enter through the acoustic vent hole, causing the diaphragm to vibrate and thus changing the capacitance, achieving sound-to-electricity conversion.

[0003] However, because the back cavity is slowly connected to the outside atmosphere through the confining hole, it results in inherent defects such as poor low-frequency response, susceptibility to interference, and reliability risks. Specifically: (1) The limiting aperture and the back cavity form a high-pass acoustic filter, causing the MEMS microphone to experience a sharp attenuation in its response to low-frequency signals below 100Hz. This severely restricts its application in low-frequency spectrum analysis, infrasound monitoring, and other fields, resulting in poor low-frequency response. (2) The limiting hole makes the inside of the MEMS microphone susceptible to airflow impact, generating "Pop" noise and wind noise, affecting audio quality and making it susceptible to interference.

[0004] (3) Under extremely rapid pressure changes, the limiting hole cannot balance the pressure in time, which poses a risk of diaphragm rupture and thus a reliability risk. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a MEMS microphone and a method for forming the same, so as to improve the defects of MEMS microphones such as poor low-frequency response, susceptibility to interference and reliability risks.

[0006] To address the aforementioned technical problems, the present invention provides a MEMS microphone, comprising: a first substrate having a first cavity opening along the substrate surface of the first substrate, the depth of the first cavity being less than the thickness of the first substrate; a back electrode plate located on the substrate surface of the first substrate and covering the opening of the first cavity, the back electrode plate having a first acoustic vent hole corresponding to the opening of the first cavity; a second substrate having a second cavity, the second substrate at the bottom of the second cavity serving as a diaphragm, the second substrate being bonded to the first substrate, the opening of the first cavity being opposite to the opening of the second cavity, and the second cavity and the first cavity being connected through the first acoustic vent hole, the first cavity and the second cavity together constituting an airtight reference pressure chamber.

[0007] Optionally, the internal air pressure of the reference pressure chamber is less than 10. -1 Pa.

[0008] Optionally, the reference pressure chamber is filled with inert gas, and the internal pressure range of the reference pressure chamber is 10 kPa to 80 kPa.

[0009] Optionally, the second substrate further includes a third opening communicating with the second cavity. The third opening is located on both sides of the second cavity along a direction parallel to the surface of the second substrate. The second substrate at the bottom of the third opening serves as a connecting membrane connected to the vibrating diaphragm. The MEMS microphone further includes: a first support structure located within the third opening, the thickness of the first support structure being less than the depth of the third opening; and a second support layer located on the surface of the first support structure and covering the opening of the second cavity. The second support layer at the opening of the second cavity has a second acoustic vent communicating with the first acoustic vent, so as to connect the first cavity and the second cavity.

[0010] Optionally, it further includes: a release hole penetrating through the first substrate under the first cavity to communicate with the first cavity; an insulating layer located on the back side of the first substrate and filling the release hole to seal the release hole, wherein the back side of the first substrate faces away from the opening of the first cavity; a first deep through-hole conductive structure penetrating the insulating layer, the first substrate, the first support structure, and the second support layer to contact the connection film; and a second conductive through-hole structure penetrating the insulating layer and the first substrate to contact the back electrode plate between the first substrate and the first support structure.

[0011] Accordingly, the technical solution of the present invention also provides a method for forming a MEMS microphone, comprising: forming a first cavity with an opening along the substrate surface of the first substrate in a first substrate, wherein the depth of the first cavity is less than the thickness of the first substrate; forming a back electrode plate on the substrate surface of the first substrate, wherein the back electrode plate covers the opening of the first cavity; forming a through first acoustic vent hole in the back electrode plate corresponding to the opening of the first cavity; forming a second cavity in a second substrate; after forming the first acoustic vent hole and the second cavity, bonding the second substrate to the first substrate in a direction opposite to the opening of the first cavity and the opening of the second cavity to form an hermetically sealed package, wherein the first cavity and the second cavity together constitute a hermetically sealed reference pressure chamber, and the second cavity and the first cavity are connected through the first acoustic vent hole; thinning the second substrate from the back side of the second substrate, and using the second substrate located at the bottom of the second cavity in the thinned second substrate as a diaphragm, wherein the back side of the second substrate and the opening of the second cavity face opposite directions.

[0012] Optionally, the second substrate is bonded to the first substrate under a first vacuum environment or a first preset atmosphere.

[0013] Optionally, the method for forming the back electrode plate and the first acoustic vent further includes: forming a first sacrificial layer in the first cavity; forming the back electrode plate on the surface of the first substrate and the first sacrificial layer; etching the back electrode plate on the first cavity until the first sacrificial layer is exposed to form the first acoustic vent; the method for forming the MEMS microphone further includes: forming a second sacrificial layer in at least the second cavity before bonding the second substrate to the first substrate; after thinning the second substrate, removing the first sacrificial layer and the second sacrificial layer in the second cavity to release the diaphragm and the back electrode plate.

[0014] Optionally, the method for removing the first sacrificial layer and the second sacrificial layer within the second cavity includes: etching the first substrate from the back side of the first substrate to form a release hole within the first substrate, the release hole penetrating the first substrate under the first cavity to expose the first sacrificial layer, the back side of the first substrate facing away from the opening of the first cavity; etching the first sacrificial layer and the second sacrificial layer within the second cavity through the release hole; after etching the first sacrificial layer and the second sacrificial layer within the second cavity, the method for forming the MEMS microphone further includes: forming an insulating layer filling the release hole on the back side of the first substrate in a second vacuum environment or a second preset atmosphere environment, the insulating layer sealing the release hole.

[0015] Optionally, it further includes: simultaneously forming the second cavity, forming a third opening communicating with the second cavity within the second substrate, the third opening being located on both sides of the second cavity in a direction parallel to the surface of the second substrate, and the second sacrificial layer also being formed within the third opening; thinning the second substrate from the back side of the second substrate, and using the second substrate located at the bottom of the second cavity in the thinned second substrate as a vibrating membrane, and also using the second substrate located at the bottom of the third opening in the thinned second substrate as a connecting membrane connected to the vibrating membrane; while removing the second sacrificial layer within the second cavity, retaining the second sacrificial layer within the third opening, so as to... A first support structure is formed inside the opening; a first deep conductive hole is formed in the insulating layer, the first substrate, the first support structure, and a second support layer located on the surface of the first support structure, the first deep conductive hole exposing the connection film; a second conductive hole is formed in the insulating layer and the first substrate, the second conductive hole exposing the back electrode plate between the first substrate and the first support structure; conductive material is filled in the first deep conductive hole and the second conductive hole to form a first deep through-hole conductive structure and a second conductive through-hole structure, the first deep through-hole conductive structure contacting the connection film, and the second conductive through-hole structure contacting the back electrode plate between the first substrate and the first support structure.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The MEMS microphone and its forming method provided by the present invention include a first substrate with a depth less than the thickness of the first substrate, a back electrode plate located on the surface of the first substrate and covering the opening of the first cavity, and a first acoustic vent hole in the back electrode plate corresponding to the opening of the first cavity. A second substrate with a second cavity at its bottom serves as a diaphragm. The second substrate and the first substrate are bonded together with the openings of the first and second cavities facing each other and connected through the first acoustic vent hole. This allows the first and second cavities to jointly form an airtight, sealed reference pressure chamber, thus constituting a fully sealed single-diaphragm MEMS microphone. This completely isolates the microphone from external environmental pressure shocks, enabling it to operate stably in harsher environments. Furthermore, the acoustic performance of the MEMS microphone is unaffected by changes in environmental air pressure and altitude. Furthermore, by eliminating the limiting aperture, the high-pass filter formed by the limiting aperture is also eliminated, allowing the low-frequency response of the MEMS microphone to extend to near 0Hz (DC). This greatly expands its application in low-frequency spectrum analysis, geological monitoring, infrastructure health monitoring, and other fields. At the same time, it also fundamentally eliminates the generation mechanism of "Pop" sound and wind noise, resulting in extremely high audio capture purity. Attached Figure Description

[0017] Figures 1 to 11 This is a cross-sectional structural schematic diagram of each step in the method for forming a MEMS microphone according to an embodiment of the present invention; Explanation of reference numerals in the attached figures: 100 - First substrate; 110 - First cavity; 120 - First sacrificial layer; 130 - Back electrode plate; 131 - First acoustic vent; 200, 209 - Second substrate; 210 - Second cavity; 220 - Third opening; 230 - Second sacrificial layer; 231 - First support structure; 240 - Second support layer; 241 - Second acoustic vent; 251 - Vibrating diaphragm; 252 - Connecting diaphragm; 260 - Release hole; 270 - Insulating layer; 310 - First deep through-hole conductive structure; 320 - Second conductive through-hole structure; 101, 201 - Front; 102, 202 - Back. Detailed Implementation

[0018] As described in the background section, the slow connection between the back cavity and the outside atmosphere through the limiting hole results in inherent defects such as poor low-frequency response, susceptibility to interference, and reliability risks.

[0019] To address the aforementioned technical problems, the present invention provides a MEMS microphone and its forming method. By constructing a hermetically sealed reference pressure chamber within a second substrate and a first substrate that are bonded together, a fully sealed single-diaphragm MEMS microphone is provided to improve the defects of MEMS microphones, such as poor low-frequency response, susceptibility to interference, and reliability risks.

[0020] To make the above-mentioned objectives, features, and beneficial effects of the present invention more apparent and understandable, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus. Additionally, directional terms such as above, below, up, down, upward, downward, left, right, etc., are used relative to exemplary embodiments as they are shown in the figures, with upward or upper directions pointing towards the top of the corresponding figure and downward or lower directions pointing towards the bottom of the corresponding figure.

[0022] Figures 1 to 11 This is a cross-sectional structural schematic diagram of each step in the method for forming a MEMS microphone according to an embodiment of the present invention.

[0023] Please refer to Figure 1 Provide a first substrate 100.

[0024] In this embodiment, the first substrate 100 is a silicon substrate.

[0025] In other embodiments, the first substrate may include at least one of the following materials: Ge, SiGe, SiC, SiGeC, InAs, GaAs, InP, InGaAs, or other III / V compound semiconductors. Alternatively, the first substrate may also include silicon-on-insulator (SOI), silicon-on-insulator stacked (SSOI), silicon-on-insulator stacked (S-SiGeOI), silicon-on-insulator (SiGeOI), or germanium-on-insulator (GeOI), etc.

[0026] In this embodiment, the first substrate 100 includes a front side 101 and a back side 102.

[0027] Please continue to refer to this. Figure 1 A first cavity 110 is formed inside the first substrate 100, opening along the substrate surface of the first substrate 100, and the depth D1 of the first cavity 110 is less than the thickness H1 of the first substrate 100.

[0028] In this embodiment, the front side 101 exposes the first cavity 110, and the back side 102 faces away from the opening of the first cavity 110.

[0029] Specifically, the method for forming the first cavity 110 may include: forming a patterned first cavity mask layer (not shown) on the front side 101 of the first substrate 100; using the first cavity mask layer as a mask, etching the first substrate 100 from the exposed front side 101 until the first cavity 110 is formed.

[0030] The material of the first cavity mask layer may include at least one of silicon oxide thermally grown on the front side 101 and a patterned photoresist layer formed on the front side 101.

[0031] In this embodiment, after the first cavity 110 is formed, the first cavity mask layer is removed.

[0032] Furthermore, a back electrode plate 130 is formed on the substrate surface of the first substrate 100, and a through first acoustic vent hole 131 is formed in the back electrode plate 130 corresponding to the opening of the first cavity 110.

[0033] The following combination Figure 2 and Figure 3 The specific steps for forming the back electrode plate 130 and the first acoustic vent 131 are explained.

[0034] Please refer to Figure 2 A first sacrificial layer 120 is formed within the first cavity 110.

[0035] The material of the first sacrificial layer 120 can be phosphosilicate glass (PSG) or silicon oxide.

[0036] In this embodiment, the method of forming the first sacrificial layer 120 may include: depositing a first sacrificial material layer (not shown) in the first cavity 110 and the front side 101, wherein the surface of the first sacrificial material layer is higher than the front side 101 to ensure that the first cavity 110 is filled with the first sacrificial material layer; planarizing the first sacrificial material layer until the front side 101 is exposed to form the first sacrificial layer 120.

[0037] Preferably, the surface of the first sacrificial layer 120 is flush with the front side 101.

[0038] Specifically, the process for planarizing the first sacrificial material layer can be chemical mechanical polishing (CMP), etc.

[0039] Please continue to refer to this. Figure 2 A back electrode 130 is formed on the surfaces of the first substrate 100 and the first sacrificial layer 120. Specifically, the back electrode 130 is formed on the surfaces of the front side 101 and the first sacrificial layer 120.

[0040] In this embodiment, the back electrode plate 130 covers the opening of the first cavity 110.

[0041] In this embodiment, the material of the back electrode 130 can be phosphorus-doped polycrystalline silicon.

[0042] Specifically, the material of the back electrode 130 can be formed by low-pressure chemical vapor deposition (LPCVD).

[0043] Please refer to Figure 3 The back electrode plate 130 on the first cavity 110 is etched until the first sacrificial layer 120 is exposed. A through first acoustic vent 131 is formed in the back electrode plate 130 corresponding to the opening of the first cavity 110.

[0044] The first acoustic vent 131 exposes the first sacrificial layer 120. Therefore, after the first sacrificial layer 120 is removed, the first cavity 110 and the second cavity 210 can be connected through the first acoustic vent 131.

[0045] Please refer to Figure 4 Provide a second substrate 200.

[0046] In this embodiment, the second substrate 200 is a silicon substrate.

[0047] In other embodiments, the second substrate may include at least one of the following materials: Ge, SiGe, SiC, SiGeC, InAs, GaAs, InP, InGaAs, or other III / V compound semiconductors. Alternatively, the second substrate may also include silicon-on-insulator (SOI), silicon-on-insulator stacked (SSOI), silicon-on-insulator stacked (S-SiGeOI), silicon-on-insulator (SiGeOI), or germanium-on-insulator (GeOI), etc.

[0048] In this embodiment, the second substrate 200 includes a front side 201 and a back side 202 facing each other.

[0049] Please continue to refer to this. Figure 4 A second cavity 210 is formed within the second substrate 200.

[0050] The depth D2 of the second cavity 210 is less than the thickness H2 of the second substrate 200.

[0051] In this embodiment, the front side 201 exposes the second cavity 210, and the back side 202 faces away from the opening of the second cavity 210.

[0052] In this embodiment, while forming the second cavity 210, a third opening 220 communicating with the second cavity 210 is formed in the second substrate 200. The third opening 220 is located on both sides of the second cavity 210 in a direction parallel to the surface of the second substrate 200. That is to say, the second cavity 210 and the third opening 220 together constitute a larger cavity.

[0053] Furthermore, the second cavity 210 and the third opening 220 have the same depth.

[0054] Specifically, the method for forming the second cavity 210 and the third opening 220 may include: forming a patterned second cavity mask layer (not shown) on the front side 201 of the second substrate 200; using the second cavity mask layer as a mask, etching the second substrate 200 from the exposed front side 201 until the second cavity 210 and the third opening 220 are formed.

[0055] In this embodiment, the material of the second cavity mask layer may include at least one of silicon oxide thermally grown on the front side 101 and a patterned photoresist layer formed on the front side 101.

[0056] In this embodiment, after the second cavity 210 and the third opening 220 are formed, the mask layer of the second cavity is removed.

[0057] Please refer to Figure 5 At least a second sacrificial layer 230 is formed within the second cavity 210.

[0058] In this embodiment, a second sacrificial layer 230 is formed within the second cavity 210 and the third opening 220.

[0059] The thickness H3 of the second sacrificial layer 230 is less than the depth of the second cavity 210 (that is, the depth of the third opening 220), thus reserving space for the subsequent formation of the second support layer 240.

[0060] In this embodiment, the material of the second sacrificial layer 230 may be phosphosilicate glass or silicon oxide.

[0061] Specifically, the method for forming the second sacrificial layer 230 may include: depositing a second sacrificial material layer in the second cavity 210, the third opening 220, and the front surface 201; and etching the second sacrificial material layer back until the front surface 201 is exposed and the surface of the second sacrificial material layer is at a preset height to form the second sacrificial layer 230.

[0062] Please refer to Figure 6 A second support layer 240 is formed on the surface of the second sacrificial layer 230.

[0063] In this embodiment, the projection of the second cavity 210 onto the surface of the second substrate 200 is located within the range of the projection of the second support layer 240 onto the surface of the second substrate 200, thereby ensuring that the second support layer 240 covers the second cavity 210.

[0064] Specifically, the second support layer 240 is located not only on the second cavity 210, but also on the third opening 220.

[0065] In this embodiment, the material of the second support layer 240 may be silicon nitride.

[0066] Please continue to refer to this. Figure 6 The second support layer 240 at the second cavity 210 is etched until the second sacrificial layer 230 is exposed, forming a through second acoustic vent 241.

[0067] The second acoustic vent 241 exposes the second sacrificial layer 230. Therefore, after the second sacrificial layer 230 is subsequently removed, the first cavity 110 and the second cavity 210 can be connected through the first acoustic vent 131 and the second acoustic vent 241.

[0068] Furthermore, the number of the first acoustic vent 131 and the number of the second acoustic vent 241 can both be one or more, and the first acoustic vent 131 and the second acoustic vent 241 correspond one-to-one.

[0069] Next, please refer to Figure 7 With the opening of the first cavity 110 and the opening of the second cavity 210 facing each other, the second substrate 200 and the first substrate 100 are bonded together, so that the first cavity 110 and the second cavity 210 together constitute an airtight reference pressure chamber.

[0070] The second cavity 210 is connected to the first cavity 110 through the first acoustic vent 131.

[0071] Furthermore, when the second substrate 200 is bonded to the first substrate 100, the second acoustic vent 241 is positioned to correspond to the first acoustic vent 131, forming a first acoustic vent 131 and a second acoustic vent 241 that are interconnected. This allows the first cavity 110 and the second cavity 210 to be connected after the first sacrificial layer 120 and the second sacrificial layer 230 in the second cavity 210 are subsequently removed.

[0072] Specifically, the second substrate 200 is bonded to the first substrate 100 through a wafer bonding process to achieve an airtight seal for the reference pressure chamber.

[0073] In this embodiment, the second substrate 200 is bonded to the first substrate 100 under a first vacuum environment.

[0074] Specifically, the method for bonding the second substrate 200 to the first substrate 100 may further include: aligning the first substrate 100 and the second substrate 200 and placing them into a bonding machine; evacuating the chamber of the bonding machine after placement; and performing direct silicon-silicon bonding at a preset temperature and pressure after evacuating the chamber of the bonding machine. Specifically, the internal pressure within the chamber of the bonding machine after evacuation may be 10... -3 Pa.

[0075] In other embodiments, glass powder sintering bonding may be used instead of silicon-silicon direct bonding.

[0076] In other embodiments, the second substrate 200 is bonded to the first substrate 100 in a first preset atmosphere. Specifically, after aligning the first substrate 100 and the second substrate 200 and placing them in a bonding machine, the chamber of the bonding machine is maintained in the first preset atmosphere, and silicon-silicon direct bonding or glass powder sintering bonding is performed at a preset temperature and preset pressure.

[0077] Furthermore, when the number of first acoustic vent holes 131 and second acoustic vent holes 241 are both more than two, when bonding the second substrate 200 to the first substrate 100, the corresponding first acoustic vent holes 131 and second acoustic vent holes 241 need to be aligned one by one.

[0078] Please refer to Figure 8 The second substrate 200 is thinned from the back side to form the thinned second substrate 209.

[0079] In this embodiment, the second substrate 209 located at the bottom of the second cavity 210 in the thinned second substrate 209 is used as the vibrating diaphragm 251.

[0080] In this embodiment, the second substrate 209 located at the bottom of the third opening 220 in the thinned second substrate 209 is also used as the connecting film 252 connected to the vibrating film 251. Therefore, after the second sacrificial layer 230 in the second cavity 210 is subsequently removed, the connecting film 252 can be supported by the second sacrificial layer 230 (i.e., the first support structure) left in the third opening 220, thereby realizing the structure in which the vibrating film 251 is suspended relative to the second cavity 210.

[0081] Specifically, chemical mechanical polishing and etching processes can be used to thin the second substrate 200.

[0082] In this embodiment, after the diaphragm 251 is formed, the diaphragm 251 is pre-stretched so that the design tension of the diaphragm 251 is sufficient to resist the deformation caused by the pressure change of the gas inside the reference pressure chamber due to the change in working temperature.

[0083] Specifically, the pre-stretching process can be high-temperature annealing.

[0084] Please refer to Figure 9 After thinning the second substrate 200, the first sacrificial layer 120 and the second sacrificial layer 230 in the second cavity 210 are removed, and the diaphragm 251 and the back electrode plate 130 are released.

[0085] In this embodiment, while removing the second sacrificial layer 230 in the second cavity 210, a first support structure 231 is formed in the third opening 220 by retaining the second sacrificial layer 230 in the third opening 220.

[0086] Since the thickness H3 of the second sacrificial layer 230 is less than the depth of the third opening 220, the thickness of the first support structure 231 is correspondingly less than the depth of the third opening 220.

[0087] In this embodiment, the method for removing the first sacrificial layer 120 and the second sacrificial layer 230 in the second cavity 210 includes: etching the first substrate 100 from the back side of the first substrate 100 to form a release hole 260 in the first substrate 100, the release hole 260 exposing the first sacrificial layer 120; and etching the first sacrificial layer 120 and the second sacrificial layer 230 in the second cavity 210 through the release hole 260.

[0088] In this process, the first substrate 100 can be etched from the back side of the first substrate 100 through deep etching to form a release hole 260 within the first substrate 100.

[0089] The release hole 260 penetrates the first substrate 100 under the first cavity 110 to form a channel for etchant to enter and etch the first sacrificial layer 120 and the second sacrificial layer 230 in the reference pressure chamber.

[0090] Specifically, the first substrate 100 can be etched from the back side of the first substrate 100 by anisotropic etching. Anisotropic etching is, for example, deep reactive ion etching (DRIE).

[0091] Specifically, gaseous hydrogen fluoride (HF) can be used as an etchant to etch the first sacrificial layer 120 and the second sacrificial layer 230.

[0092] Please refer to Figure 10 After etching the first sacrificial layer 120 and the second sacrificial layer 230 in the second cavity 210, an insulating layer 270 is formed on the back side 102 of the first substrate 100 to fill the release hole 260 under a second vacuum environment, and the insulating layer 270 closes the release hole 260.

[0093] Since the first sacrificial layer 120 and the second sacrificial layer 230 in the second cavity 210 are etched through the release hole 260 to release the diaphragm 251 and the back electrode plate 130, an insulating layer 270 is formed on the back side of the first substrate 100 to fill the release hole 260 in the second vacuum environment to seal the release hole 260. Therefore, the release hole 260 communicating with the reference pressure chamber can be sealed in the second vacuum environment. This not only ensures the airtightness of the reference pressure chamber, but also reduces the pressure change caused by the change in operating temperature, thereby reducing the deformation caused accordingly.

[0094] Correspondingly, the internal pressure of the reference pressure chamber is a high vacuum.

[0095] Specifically, in this embodiment, the internal air pressure of the reference pressure chamber is less than 10. -1 Pa.

[0096] In other embodiments, an insulating layer 270 filling the release hole 260 may be formed on the back side of the first substrate 100 in a second preset atmosphere to seal the release hole 260.

[0097] Since the first sacrificial layer 120 and the second sacrificial layer 230 in the second cavity 210 are etched through the release hole 260 to release the diaphragm 251 and the back electrode plate 130, an insulating layer 270 filling the release hole 260 is formed on the back side of the first substrate 100 in the second preset atmosphere to seal the release hole 260. Therefore, the release hole 260 communicating with the reference pressure chamber can be sealed in the preset gas environment and pressure environment. Thus, not only is the airtightness of the reference pressure chamber ensured, but the internal gas pressure and gas of the reference pressure chamber are also controllable, thereby making the pressure change caused by the change of operating temperature controllable.

[0098] Correspondingly, in other embodiments, the reference pressure chamber is filled with a preset type of inert gas and maintained at a preset pressure. Specifically, the preset type of inert gas can be nitrogen, argon, or helium, and the preset pressure can range from 10 kPa to 80 kPa.

[0099] Furthermore, the process for forming the insulating layer 270 can be a deposition process.

[0100] Please refer to Figure 11 This forms a first deep through-hole conductive structure 310 and a second conductive through-hole structure 320.

[0101] The first deep through-hole conductive structure 310 penetrates the insulating layer 270, the first substrate 100, the first support structure 231 and the second support layer 240, and the first deep through-hole conductive structure 310 is in contact with the connecting film 252.

[0102] The second conductive via structure 320 penetrates the insulating layer 270 and the first substrate 100, and the second conductive via structure 320 contacts the back electrode plate 130 between the first substrate 100 and the first support structure 231.

[0103] In this embodiment, the method for forming the first deep through-hole conductive structure 310 and the second conductive through-hole structure 320 includes: forming a first deep conductive hole (not shown) in the insulating layer 270, the first substrate 100, the first support structure 231 and the second support layer 240, the first deep conductive hole exposing the connecting film 252; forming a second conductive hole (not shown) in the insulating layer 270 and the first substrate 100, the second conductive hole exposing the back electrode plate 130 between the first substrate 100 and the first support structure 231; filling the first deep conductive hole and the second conductive hole with conductive material to form the first deep through-hole conductive structure 310 and the second conductive through-hole structure 320.

[0104] Specifically, conductive materials can be filled through electroplating or deposition.

[0105] Accordingly, this embodiment of the invention also provides a MEMS microphone formed by the above-described MEMS microphone forming method. Please continue to refer to... Figure 11 The MEMS microphone includes: a first substrate 100, a back electrode plate 130, and a second substrate 200.

[0106] In this embodiment, the first substrate 100 is a silicon substrate.

[0107] In other embodiments, the first substrate 100 may include at least one of the following materials: Ge, SiGe, SiC, SiGeC, InAs, GaAs, InP, InGaAs, or other III / V compound semiconductors. Alternatively, the first substrate 100 may also include silicon-on-insulator (SOI), silicon-on-insulator stacked (SSOI), silicon-on-insulator stacked (S-SiGeOI), silicon-on-insulator (SiGeOI), or germanium-on-insulator (GeOI), etc.

[0108] In this embodiment, the first substrate 100 includes a front side 101 and a back side 102.

[0109] The first substrate 100 has a first cavity 110 with an opening along the substrate surface of the first substrate 100, and the depth D1 of the first cavity 110 is less than the thickness H1 of the first substrate 100.

[0110] In this embodiment, the front side 101 exposes the first cavity 110, and the back side 102 faces away from the opening of the first cavity 110.

[0111] The back electrode plate 130 is located on the substrate surface of the first substrate 100, and the back electrode plate 130 covers the opening of the first cavity 110, wherein the back electrode plate 130 corresponding to the opening of the first cavity 110 has a first acoustic vent hole 131.

[0112] The material of the back electrode 130 can be phosphorus-doped polycrystalline silicon.

[0113] The second substrate 209 is bonded to the first substrate 100.

[0114] In this embodiment, the second substrate 209 is a silicon substrate.

[0115] In other embodiments, the second substrate 209 may include at least one of the following materials: Ge, SiGe, SiC, SiGeC, InAs, GaAs, InP, InGaAs, or other III / V compound semiconductors. Alternatively, the second substrate 209 may also include silicon-on-insulator (SOI), silicon-on-insulator stacked (SSOI), silicon-on-insulator stacked (S-SiGeOI), silicon-on-insulator (SiGeOI), or germanium-on-insulator (GeOI), etc.

[0116] The second substrate 209 has a second cavity 210, the depth D2 of which is less than the thickness H2 of the second substrate 209.

[0117] The opening of the first cavity 110 is opposite to the opening of the second cavity 210, and the second cavity 210 and the first cavity 110 are connected through the first acoustic vent 131. The first cavity 110 and the second cavity 210 together constitute an airtight reference pressure chamber.

[0118] Furthermore, the second substrate 209 at the bottom of the second cavity 210 serves as a vibrating diaphragm 251.

[0119] In this embodiment, the internal pressure of the reference pressure chamber is a high vacuum.

[0120] Specifically, the internal air pressure of the reference pressure chamber is less than 10. -1 Pa.

[0121] In other embodiments, the reference pressure chamber is filled with a predetermined type of inert gas and maintained at a predetermined pressure.

[0122] Specifically, the preset type of inert gas can be nitrogen, argon, or helium, and the preset pressure range can be 10 kPa to 80 kPa. This preset pressure range is equivalent to removing a portion of the standard atmospheric pressure (approximately 101 kPa) to create a vacuum of approximately 20% to 90%.

[0123] In this embodiment, the second substrate 209 also has a third opening 220 that communicates with the second cavity 210.

[0124] The third opening 220 is located on both sides of the second cavity 210 in a direction parallel to the surface of the second substrate 209, and the second substrate 209 at the bottom of the third opening 220 serves as a connecting membrane 252 connected to the vibrating membrane 251.

[0125] In this embodiment, the MEMS microphone further includes a first support structure 231.

[0126] The material of the first support structure 231 can be phosphosilicate glass or silicon oxide.

[0127] The first support structure 231 is located inside the third opening 220, and the thickness of the first support structure 231 is less than the depth of the third opening 220.

[0128] By connecting the connecting membrane 252 at the bottom of the third opening 220 to the vibrating membrane 251, the connecting membrane 252 can be supported by the first support structure 231 located in the third opening 220, thereby achieving a structure in which the vibrating membrane 251 is suspended relative to the second cavity 210.

[0129] In this embodiment, the MEMS microphone further includes a second support layer 240.

[0130] The material of the second support layer 240 can be silicon nitride.

[0131] The second support layer 240 is located on the surface of the first support structure 231 and covers the opening of the second cavity 210. The second support layer 240 corresponding to the opening of the second cavity 210 has a through second acoustic vent 241, which is connected to the first acoustic vent 131 and the second cavity 210 to connect the first cavity 110 and the second cavity 210.

[0132] Specifically, the projection of the second cavity 210 onto the surface of the second substrate 209 is located within the range of the projection of the second support layer 240 onto the surface of the second substrate 209, thereby ensuring that the second support layer 240 covers the second cavity 210.

[0133] In this embodiment, the second support layer 240 is located not only on the second cavity 210, but also on the third opening 220.

[0134] Furthermore, the number of the first acoustic vent 131 and the number of the second acoustic vent 241 can both be one or more, and the first acoustic vent 131 and the second acoustic vent 241 correspond one-to-one.

[0135] In this embodiment, the MEMS microphone further includes a release hole 260.

[0136] A first substrate 100 extends through the first cavity 110 to connect the first cavity 110.

[0137] In this embodiment, the MEMS microphone further includes an insulating layer 270.

[0138] The insulating layer 270 is located on the back side of the first substrate 100, and a portion of the insulating layer 270 extends into the release hole 260 to fill the release hole 260 and seal the release hole 260.

[0139] In this embodiment, the MEMS microphone further includes a first deep through-hole conductive structure 310 that penetrates the insulating layer 270, the first substrate 100, the first support structure 231, and the second support layer 240 to contact the connection film 252.

[0140] In this embodiment, the MEMS microphone further includes a second conductive via structure 320 that penetrates the insulating layer 270 and the first substrate 100 to contact the back electrode plate 130 between the first substrate 100 and the first support structure 231.

[0141] In the MEMS microphone and its forming method of this invention, the first substrate 100 has a first cavity 110 with a depth D1 less than the thickness H1 of the first substrate 100. The back electrode plate 130 is located on the surface of the first substrate 100 and covers the opening of the first cavity 110. The back electrode plate 130 corresponding to the opening of the first cavity 110 has a first acoustic vent 131. The second substrate 209 has a second cavity 210. The bottom of the second cavity 210 serves as a diaphragm 251. The second substrate 209 and the first substrate 100 are bonded together such that the opening of the first cavity 110 and the opening of the second cavity 210 are opposite to each other and are connected through the first acoustic vent 131. Thus, the first cavity 110 and the second cavity 210 together constitute an airtight reference pressure chamber. Therefore, a fully sealed single-diaphragm MEMS microphone is formed. This completely isolates the MEMS microphone from external environmental pressure shocks, enabling it to operate stably in harsher environments. Furthermore, the acoustic performance of the MEMS microphone is unaffected by changes in ambient air pressure and altitude. Moreover, by eliminating the limiting aperture, the high-pass filter formed by it is also eliminated, allowing the low-frequency response of the MEMS microphone to extend to near 0Hz (DC). This significantly expands its applications in low-frequency spectrum analysis, geological monitoring, and infrastructure health monitoring. On the other hand, it fundamentally eliminates the generation mechanisms of "pop" sounds and wind noise, resulting in extremely high audio capture purity.

[0142] The materials, forming process, working principle, specific implementation method and beneficial effects of the MEMS microphone in the embodiments of the present invention can be found in the forming method of the MEMS microphone in the embodiments of the present invention, and will not be repeated here.

[0143] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A MEMS microphone, characterized in that, include: A first substrate, wherein the first substrate has a first cavity that opens along the substrate surface of the first substrate, and the depth of the first cavity is less than the thickness of the first substrate; A back electrode plate is located on the substrate surface of the first substrate and covers the opening of the first cavity. The back electrode plate corresponding to the opening of the first cavity has a first acoustic vent hole. The second substrate has a second cavity inside. The second substrate at the bottom of the second cavity serves as a vibrating diaphragm. The second substrate is bonded to the first substrate. The opening of the first cavity is opposite to the opening of the second cavity. Furthermore, the second cavity and the first cavity are connected through the first acoustic vent hole. The first cavity and the second cavity together constitute an airtight reference pressure chamber.

2. The MEMS microphone as described in claim 1, characterized in that, The internal air pressure of the reference pressure chamber is less than 10. - 1 Pa.

3. The MEMS microphone as described in claim 1, characterized in that, The reference pressure chamber is filled with inert gas, and the internal pressure range of the reference pressure chamber is 10 kPa to 80 kPa.

4. The MEMS microphone as described in claim 1, characterized in that, The second substrate also has a third opening communicating with the second cavity. The third opening is located on both sides of the second cavity in a direction parallel to the surface of the second substrate. The second substrate at the bottom of the third opening serves as a connecting membrane connected to the vibrating membrane. The MEMS microphone also includes: A first support structure is located within the third opening, and the thickness of the first support structure is less than the depth of the third opening; A second support layer is located on the surface of the first support structure and covers the opening of the second cavity. The second support layer at the opening of the second cavity has a second acoustic vent that communicates with the first acoustic vent, so as to connect the first cavity and the second cavity.

5. The MEMS microphone as described in claim 4, characterized in that, Also includes: A release hole extends through the first substrate beneath the first cavity to connect the first cavity; An insulating layer is located on the back side of the first substrate and fills the release hole to seal the release hole, wherein the back side of the first substrate faces away from the opening of the first cavity; A first deep through-hole conductive structure penetrates the insulating layer, the first substrate, the first support structure, and the second support layer to contact the connecting film; A second conductive via structure penetrates the insulating layer and the first substrate to contact the back electrode plate between the first substrate and the first support structure.

6. A method for forming a MEMS microphone, characterized in that, include: A first cavity is formed within a first substrate, opening along the substrate surface of the first substrate, wherein the depth of the first cavity is less than the thickness of the first substrate; A back electrode plate is formed on the substrate surface of the first substrate, the back electrode plate covering the opening of the first cavity; A through-hole acoustic vent is formed in the back electrode plate corresponding to the opening of the first cavity. A second cavity is formed within the second substrate; After forming the first acoustic vent and the second cavity, the second substrate is bonded to the first substrate in a direction where the opening of the first cavity is opposite to the opening of the second cavity, so as to form an airtight package, so that the first cavity and the second cavity together constitute an airtight reference pressure chamber, and the second cavity and the first cavity are connected through the first acoustic vent. The second substrate is thinned from the back side, and the second substrate located at the bottom of the second cavity in the thinned second substrate is used as a vibrating diaphragm, with the back side of the second substrate facing away from the opening of the second cavity.

7. The method for forming a MEMS microphone as described in claim 6, characterized in that, The second substrate is bonded to the first substrate under a first vacuum environment or a first preset atmosphere.

8. The method for forming a MEMS microphone as described in claim 6, characterized in that, The method for forming the back electrode plate and the first acoustic vent further includes: forming a first sacrificial layer in the first cavity; forming the back electrode plate on the surface of the first substrate and the first sacrificial layer; etching the back electrode plate on the first cavity until the first sacrificial layer is exposed to form the first acoustic vent. The method for forming the MEMS microphone further includes: forming a second sacrificial layer in at least the second cavity before bonding the second substrate to the first substrate; and removing the first sacrificial layer and the second sacrificial layer in the second cavity after thinning the second substrate, thereby releasing the diaphragm and the back electrode plate.

9. The method for forming a MEMS microphone as described in claim 8, characterized in that, The methods for removing the first sacrificial layer and the second sacrificial layer within the second cavity include: The first substrate is etched from the back side to form a release hole in the first substrate. The release hole penetrates the first substrate under the first cavity to expose the first sacrificial layer. The back side of the first substrate faces away from the opening of the first cavity. The first sacrificial layer and the second sacrificial layer within the second cavity are etched through the release hole. After etching the first sacrificial layer and the second sacrificial layer within the second cavity, the method for forming the MEMS microphone further includes: forming an insulating layer that fills the release hole on the back side of the first substrate in a second vacuum environment or a second preset atmosphere environment, wherein the insulating layer seals the release hole.

10. The method for forming a MEMS microphone as described in claim 9, characterized in that, Also includes: While forming the second cavity, a third opening communicating with the second cavity is formed in the second substrate. The third opening is located on both sides of the second cavity in a direction parallel to the surface of the second substrate, and the second sacrificial layer is also formed in the third opening. The second substrate is thinned from the back side, and the second substrate located at the bottom of the second cavity in the thinned second substrate is used as a vibrating membrane, while the second substrate located at the bottom of the third opening in the thinned second substrate is used as a connecting membrane connected to the vibrating membrane. While removing the second sacrificial layer in the second cavity, the second sacrificial layer is retained in the third opening to form a first support structure in the third opening; A first deep conductive hole is formed in the insulating layer, the first substrate, the first support structure, and the second support layer located on the surface of the first support structure, and the first deep conductive hole exposes the connecting film. A second conductive hole is formed within the insulating layer and the first substrate, the second conductive hole exposing the back electrode plate between the first substrate and the first support structure; Conductive material is filled into the first deep conductive hole and the second conductive hole to form a first deep through-hole conductive structure and a second conductive through-hole structure. The first deep through-hole conductive structure is in contact with the connecting film, and the second conductive through-hole structure is in contact with the back electrode plate between the first substrate and the first support structure.

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