MEMS microphone, preparation method and electro-acoustic conversion device

Abstract

The invention discloses an MEMS microphone, a preparation method and an electro-acoustic conversion device, the MEMS microphone comprises a substrate and a capacitor assembly supported on the substrate, the substrate is provided with a through cavity in a penetrating manner in a preset axis direction, the through cavity comprises a first cavity and a second cavity which are coaxially arranged, the inner diameter of the second cavity is greater than that of the first cavity, and the first cavity and the second cavity are coaxially arranged. The second cavity is closer to the capacitor assembly than the first cavity. Compared with the prior art, according to the MEMS microphone and the preparation method of the MEMS microphone provided by the invention, the MEMS microphone realizes enhancement or suppression of specific frequency sound waves and optimizes frequency response characteristics by adjusting the size proportion of the first cavity and the second cavity. According to the preparation method of the MEMS microphone, oxidation layer deposition and polishing are carried out by dividing the CMP technological process into two or more steps. In this way, the thickness of the oxide layer deposited each time can be reduced, the thin oxide layer can be more easily and evenly removed in the CMP process, and interlayer stripping cannot be caused.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, and in particular to a MEMS microphone, its fabrication method, and an electroacoustic conversion device. Background Technology

[0002] Existing MEMS microphones include a substrate and a capacitor assembly disposed on the substrate and insulated from and connected to the substrate. A front chamber is first established within the substrate, and then the capacitor assembly is stacked on the substrate.

[0003] During fabrication, an oxide film of appropriate thickness is required to provide sufficient polishing volume for chemical mechanical polishing (CMP) planarization. The CMP process needs to remove a large amount of oxide film from the substrate and planarize the large area of ​​oxide film filling the pre-cavity. As the film thickness increases, the risk of film peeling, wafer bending, and warping increases. Controlling pitting and erosion during the CMP process is crucial for success. Summary of the Invention The purpose of this invention is to provide a MEMS microphone, a fabrication method, and an electroacoustic conversion device to solve the technical problems in the prior art.

[0004] In a first aspect, the present invention provides a MEMS microphone, comprising: A substrate, wherein a through cavity is provided through the substrate; A diaphragm, which is supported on the substrate and located above the cavity; A back plate is provided at a distance from the diaphragm along the vibration direction of the diaphragm. in: The cavity includes a first cavity and a second cavity arranged coaxially. The second cavity is located between the diaphragm and the first cavity. The width of the second cavity in any direction perpendicular to the vibration direction of the diaphragm is greater than the width of the first cavity.

[0005] In the MEMS microphone described above, preferably, the depth of the second cavity along the vibration direction of the diaphragm is greater than 3 μm.

[0006] In the MEMS microphone described above, preferably, the second cavity is annular and the diameter of the second cavity is greater than 1000 μm.

[0007] In the MEMS microphone described above, preferably, the first cavity is annular, and the inner diameter of the first cavity is smaller than the inner diameter of the second cavity.

[0008] In the MEMS microphone described above, preferably, the first cavity is rectangular or rhomboid.

[0009] Secondly, the present invention provides a method for fabricating a MEMS microphone, comprising the following steps: Provide a base; The substrate is etched on its upper surface to form a first groove on the substrate; An oxide is deposited on the substrate to form an oxide layer covering the upper surface of the substrate and the first groove, wherein the thickness of the oxide layer is less than the thickness of the first groove; Polishing is performed to remove the oxide layer from the upper surface of the substrate and retain the oxide layer in the first groove; If the total thickness of the oxide previously deposited in the first groove is less than the depth of the first groove, then a predetermined number of oxide layers are deposited and the oxide layers on the upper surface of the substrate are removed. When the total thickness of the previously deposited oxide in the first groove is greater than the depth of the first groove, polishing is performed to remove the oxide layer from the upper surface of the substrate and remove the oxide outside the first groove; A diaphragm and a backplate are sequentially formed on the upper surface of the substrate; The substrate is etched from the bottom surface opposite the upper surface of the substrate to form a through cavity in the substrate; Release the oxides retained in the first groove.

[0010] In the method for fabricating a MEMS microphone as described above, preferably, the first groove is annular, the first groove surrounds and forms a first protrusion, and the axis of the first protrusion coincides with the axis of the substrate.

[0011] In the method for fabricating a MEMS microphone as described above, preferably, Etching the substrate from a bottom surface opposite to the upper surface of the substrate to form a through cavity on the substrate includes: Etching is performed on the bottom surface opposite the upper surface of the substrate until the oxide layer within the first groove is reached, thereby forming the first cavity and exposing the first protrusion; The first protrusion is etched away at the bottom of the first cavity; Release the oxide layer in the first groove.

[0012] In the method for fabricating a MEMS microphone as described above, preferably, the first groove is a closed annular structure.

[0013] Thirdly, the present invention provides an electroacoustic conversion device, including the aforementioned MEMS microphone and a circuit device electrically connected to the MEMS microphone.

[0014] Compared with existing technologies, the MEMS microphone and its fabrication method provided by this invention enable the MEMS microphone to enhance or suppress sound waves of specific frequencies and optimize frequency response characteristics by adjusting the size ratio of the first and second cavities. The fabrication method of the MEMS microphone divides the CMP process into two or more steps for oxide layer deposition and polishing. This reduces the thickness of the oxide layer deposited each time, and the thinner oxide layer is more easily and uniformly removed during the CMP process without causing interlayer delamination, thus avoiding film peeling problems and reducing the risk of film peeling due to internal stress of the oxide layer. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the MEMS microphone provided in an embodiment of the present invention; Figures 2a to 2i This is a flowchart of the MEMS microphone polishing process provided in an embodiment of the present invention.

[0016] Explanation of reference numerals in the attached figures: 10-Base, 11-Cavity, 111-First cavity, 112-Second cavity, 13-First groove, 14-First protrusion; 20-Capacitor assembly, 21-Diaphragm, 211-Vibrating part, 212-Fixing part, 213-Slit, 22-Back plate, 221-Through hole; 30-Oxide layer; 40 - Sacrifice layer. Detailed Implementation

[0017] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0018] Reference Figure 1 As shown, this embodiment of the invention provides a MEMS microphone, including a substrate 10 and a capacitor assembly 20 supported on the substrate 10. The substrate 10 serves as the supporting structure for the entire MEMS microphone, supporting other components. The capacitor assembly 20 responds to changes in sound waves by changing its capacitance value, converting the sound wave signal into an electrical signal. The capacitor assembly 20 includes a diaphragm 21 and a back plate 22. Along the vibration direction of the diaphragm 21, the back plate 22 is spaced apart from the diaphragm 21. A cavity 11 is provided through the substrate 10 along a predetermined axis, which is the centerline of the substrate 10. The cavity 11 is located in the middle of the substrate 10 and is symmetrically distributed along the centerline (predetermined axis) of the substrate 10 to ensure mechanical symmetry and acoustic sensitivity. Preferably, the inner contour surface of the cavity 11 is a circular groove structure. The cavity 11 includes a first cavity 111 and a second cavity 112 coaxially arranged. The second cavity 112 is located between the diaphragm 21 and the first cavity 111. The width of the second cavity 112 in any direction perpendicular to the vibration direction of the diaphragm 21 is greater than the width of the first cavity 111. The larger inner diameter of the second cavity 112 can reduce the contact area between the capacitor assembly 20 and the substrate 10, thereby reducing the damping effect and damping noise.

[0019] The first cavity 111 and the second cavity 112 form a stepped structure. Cavities with different inner diameters can reflect, refract, or focus sound waves to varying degrees. In the embodiment provided by this invention, after the sound wave enters the through cavity 11, it first passes through the first cavity 111 and then enters the second cavity 112. Because the inner diameter of the second cavity 112 is larger than that of the first cavity 111, the sound wave undergoes a certain focusing and diffusion effect during its propagation from the first cavity 111 to the second cavity 112. The smaller inner diameter of the first cavity 111 can constrain the sound wave to a certain extent, keeping it relatively concentrated before entering the second cavity 112. When the sound wave enters the second cavity 112, due to its larger inner diameter, the sound wave gradually diffuses. This results in a more uniform distribution of the sound wave within the second cavity 112, thereby improving the interaction efficiency between the sound wave and the capacitor component 20.

[0020] Furthermore, by adjusting the size ratio of the first cavity 111 and the second cavity 112, it is possible to enhance or suppress sound waves of a specific frequency and optimize frequency response characteristics.

[0021] In one feasible embodiment, the diaphragm 21 includes a vibrating part 211 and a fixing part 212. The fixing part 212 is supported on the base 10 and is located around the vibrating part 211. A slit 213 is formed between the fixing part 212 and the vibrating part 211, allowing the vibrating part 211 to vibrate freely when subjected to external stimuli (such as sound waves or pressure changes).

[0022] Along the preset axis, the back plate 22 and the diaphragm 21 are spaced apart, and there is a certain distance between the back plate 22 and the diaphragm 21. The back plate 22 is provided with through holes 221. There can be multiple through holes 221 on the back plate 22 for communicating with the external environment.

[0023] When the MEMS microphone is powered on, the backplate 22 and the diaphragm 21 acquire opposite charges, thus forming a capacitor. The diaphragm 21 acts as a sound wave receiver; when a sound wave strikes the diaphragm 21, the vibrating part 211 vibrates. This vibration changes the distance between the diaphragm 21 and the backplate 22, thereby altering the capacitance between them. By measuring the change in capacitance, the presence and intensity of the sound wave can be detected, converting the sound wave signal into an electrical signal.

[0024] The depth of the second cavity 112 is shallower than that of the first cavity 111. In one feasible embodiment, the depth of the second cavity 112 is greater than 3 μm, which allows the sound wave to act on the diaphragm 21 quickly after entering the second cavity 112, reducing the propagation distance of the sound wave in the cavity, thereby reducing the reflection and standing wave effect of the sound wave.

[0025] If the depth of the second cavity 112 does not reach the minimum value of the preset range, that is, if the depth of the second cavity 112 is too shallow, the propagation path of the sound wave within the cavity will become shorter. This leads to more significant reflection and standing wave effects of the sound wave within the cavity. The standing wave will form a fixed interference pattern within the second cavity 112, excessively enhancing the high-frequency response, resulting in excessively high sensitivity of high-frequency sound waves and insufficient low-frequency response, affecting the uniformity and stability of acoustic performance. At the same time, the ability of an excessively shallow second cavity 112 to absorb sound waves will be significantly reduced, causing more sound waves to be reflected back to the first cavity 111, increasing sound wave echo and interference, thereby reducing the signal-to-noise ratio and sound quality of the microphone. Furthermore, an excessively shallow second cavity 112 will restrict the vibration space of the diaphragm 21. The diaphragm 21 needs a certain amount of space to vibrate freely under the action of sound waves. If the second cavity 112 is too shallow, the vibration of the diaphragm 21 may be restricted, thus affecting its sensitivity and response speed.

[0026] If the second cavity 112 is too deep, the propagation path of sound waves within the cavity will increase significantly, leading to increased propagation delay of high-frequency sound waves. High-frequency sound waves have shorter wavelengths, and an excessively deep cavity will require a longer time for sound waves to reach the diaphragm 21 after entering the second cavity 112, thus reducing the sensitivity of the high-frequency response. An excessively deep second cavity 112 will also result in more sound wave reflections and echoes, especially in the low-frequency range. These reflected sound waves may interfere with the incident sound waves, reducing the microphone's signal-to-noise ratio and thus affecting sound quality.

[0027] The diameter of the second cavity 112 is greater than 1000 μm. The second cavity 112 provides a larger acoustic receiving area, thereby improving the microphone's sensitivity to sound waves and helping to capture more sound wave energy, especially in the low-frequency range, significantly improving the low-frequency response. The larger diameter of the second cavity 112 also contributes to achieving a wider frequency response range. Low-frequency sound waves have longer wavelengths, and a larger second cavity 112 can better accommodate these sound waves, reducing reflection and loss of low-frequency sound waves. Simultaneously, the larger cavity diameter can be combined with a shallow cavity design to optimize the high-frequency response, thereby achieving a balanced response between high and low frequencies.

[0028] Secondly, referring to Figures 2a to 2i As shown, the present invention also provides a method for fabricating a MEMS microphone, which includes the following steps: S101: A substrate 10 is provided, which serves as the basic structure of the entire MEMS microphone and supports the subsequent capacitor assembly 20 and other structures. In this embodiment of the invention, silicon wafer is used as the material of the substrate 10, which has good mechanical strength, electrical insulation and thermal stability, and is easy to micro-process.

[0029] S102: The substrate 10 is etched on its upper surface to form a first groove 13. The first groove 13 provides space for the subsequent formation of the second cavity 112. The etching depth and width of the first groove 13 are adaptively controlled according to the depth and diameter of the second cavity 112. The first groove 13 is a closed annular structure used to define the position and shape of the subsequently formed first cavity 111 and second cavity 112.

[0030] S103: An oxide layer 30 is deposited on the substrate 10 to form an oxide layer 30 covering the upper surface of the substrate 10 and the first groove 13. The thickness of the oxide layer 30 is less than the thickness of the first groove 13. The oxide layer 30 is typically made of silicon dioxide, which has good insulation and chemical stability. The oxide layer 30 is not only used to form the cavity structure, but also serves as a protective layer for subsequent processes, preventing the substrate 10 from being contaminated or damaged in subsequent steps.

[0031] S104: Polishing removes the oxide layer 30 from the upper surface of the substrate 10 and retains the oxide layer 30 in the first groove 13. In the embodiment provided by the present invention, chemical mechanical polishing (CMP) is used to precisely control the thickness and surface smoothness of the oxide layer 30. After CMP polishing, the oxide layer 30 on the surface of the substrate 10 is removed, while the oxide film in the first groove 13 is retained. This ensures that the oxide film in the first groove 13 remains intact before the next deposition and CMP polishing.

[0032] S105: If the total thickness of the oxide previously deposited in the first groove 13 is less than the depth of the first groove 13, then a predetermined number of oxide layers 30 are deposited and the oxide layers 30 on the upper surface of the substrate 10 are removed.

[0033] S106: When the total thickness of the previously deposited oxide in the first groove 13 is greater than the depth of the first groove 13, polishing is performed to remove the oxide layer 30 from the upper surface of the substrate 10 and remove the oxide outside the first groove 13. The embodiments provided by this invention divide the process flow into two or more steps for oxide layer 30 deposition and polishing, depending on the depth of the second cavity 112 and the desired oxide layer 30 thickness. This reduces the thickness of the oxide layer 30 deposited each time, and the thinner oxide layer 30 is more easily and uniformly removed during the CMP process without causing interlayer delamination, avoiding film peeling problems, and reducing the risk of film peeling due to internal stress of the oxide layer 30. After the CMP process and oxide layer 30 removal, a flat surface area with minimal CMP pitting and erosion is obtained.

[0034] S107: A capacitor assembly 20 is formed on the substrate 10. The capacitor assembly 20 is the core part of the MEMS microphone and is used to convert the mechanical vibration caused by sound waves into capacitance changes. The capacitor assembly 20 includes a diaphragm 21 and a back plate 22. The vibrating part 211 and the fixing part 212 of the diaphragm 21 are connected through a slit 213. A sacrificial layer 40 is provided in the capacitor assembly 20. The sacrificial layer 40 is an oxide.

[0035] S108: Etch the substrate 10 from the bottom surface opposite the upper surface of the substrate 10 to form a through cavity 11 on the substrate 10.

[0036] S109: Release the oxide and sacrificial layer 40 retained in the first groove 13 by using BOE (hydrofluoric acid and acetic acid) to release the oxide layer 30 and sacrificial layer 40 in the first groove 13.

[0037] In one feasible implementation, the first groove 13 surrounds to form a first protrusion 14, the axis of which coincides with the axis of the substrate 10. The substrate 10 is made of silicon material, and the first protrusion 14 can serve as a silicon island. Since silicon has higher selectivity than oxide layer 30 in the CMP process, the first protrusion 14 can be used as a CMP stop layer. The CMP stop layer is a reference layer used in the CMP process to indicate when polishing should stop. The presence of the silicon island makes material removal during the CMP process easier to control. Polishing continues until the silicon island is exposed, at which point the polishing depth can be precisely controlled to ensure the desired surface smoothness and thickness are achieved, effectively avoiding large-area depressions in the central region of the first cavity 111 during the CMP process.

[0038] Step S108 includes the following sub-steps: S1081: Etching is performed on the bottom surface opposite the upper surface of the substrate 10 until the oxide layer 30 within the first groove 13 is reached, forming the first cavity 111 and exposing the first protrusion 14. In this step, a portion of the substrate 10 is removed using DRIE (Deep Reactive Ion Etching). DRIE is an anisotropic etching technique that allows precise control of the etching shape and depth, suitable for forming microstructures with high aspect ratios. Etching stops when the first protrusion 14 is exposed; the portion etched at this point serves as the first cavity 111. The oxide layer 30 within the first groove 13 plays a protective and positioning role during the etching process. It not only prevents the substrate 10 from being over-etched but also provides a clear boundary for the subsequent etching of the second cavity 112.

[0039] S1082: The first protrusion 14 is etched away at the bottom of the first cavity 111 until the substrate 10 is penetrated.

[0040] In step S109, by decomposing the etching process into multiple steps (first forming the first cavity 111, then forming the second cavity 112), the etching depth and shape of each step can be independently controlled, which can avoid the errors caused by one-time etching, accurately control the size and shape of the through cavity 11, ensure that the inner diameter and position of the first cavity 111 and the second cavity 112 meet the design requirements, and ensure that the size and shape of the final structure meet the design requirements.

[0041] Based on the above embodiments, the present invention also provides an electroacoustic conversion device, including the aforementioned MEMS microphone and an ASIC electrically connected to the MEMS microphone. The electroacoustic conversion device may be a microphone or a speaker, etc.

[0042] The above description, based on the embodiments shown in the figures, details the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the figures. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, that do not exceed the spirit covered by the specification and figures, should be within the protection scope of the present invention.

Claims

1. A MEMS microphone, characterized by, The application relates to an electro-acoustic transducer, comprising: a substrate provided with a through cavity; a diaphragm supported on the substrate and located above the through cavity; a back plate spaced apart from the diaphragm along the vibration direction of the diaphragm; wherein: the through cavity comprises a first cavity and a second cavity coaxially arranged, the second cavity being located between the diaphragm and the first cavity, and the width of the second cavity along any direction perpendicular to the vibration direction of the diaphragm is greater than the width of the first cavity.

2. The MEMS microphone of claim 1, wherein, The depth of the second cavity along the vibration direction of the diaphragm is greater than 3 um.

3. The MEMS microphone of claim 2, wherein, The second cavity is annular, and the diameter of the second cavity is greater than 1000 um.

4. The MEMS microphone of claim 1, wherein, The first cavity is annular, and the inner diameter of the first cavity is smaller than the inner diameter of the second cavity.

5. The MEMS microphone of claim 1, wherein, The first cavity is rectangular or rhombic.

6. A method for manufacturing a MEMS microphone according to any one of claims 1 to 5, characterized in that, The application further relates to a method for manufacturing the electro-acoustic transducer, comprising the following steps: providing a substrate; etching the substrate on the upper surface of the substrate to form a first groove on the substrate; depositing an oxide on the substrate to form an oxide layer covering the upper surface of the substrate and the first groove, the thickness of the oxide layer being smaller than the depth of the first groove; polishing to remove the oxide layer from the upper surface of the substrate and retain the oxide layer in the first groove; if the total thickness of the previously deposited oxide in the first groove is smaller than the depth of the first groove, repeating the deposition of a preset number of oxide layers and the removal of the oxide layer on the upper surface of the substrate; when the total thickness of the previously deposited oxide in the first groove is greater than the depth of the first groove, polishing to remove the oxide layer from the upper surface of the substrate and remove the oxide outside the first groove; sequentially forming a diaphragm and a back plate on the upper surface of the substrate; etching the substrate from the bottom surface opposite to the upper surface of the substrate to form a through cavity on the substrate; releasing the oxide retained in the first groove.

7. The method of claim 6, wherein the MEMS microphone is prepared by: The first groove is annular, and the first groove encloses a first protrusion, the axis of the first protrusion coinciding with the axis of the substrate.

8. The method of claim 7, wherein the MEMS microphone is prepared by: The etching of the substrate from the bottom surface opposite to the upper surface of the substrate to form a through cavity on the substrate comprises: etching the bottom surface opposite to the upper surface of the substrate until the oxide layer in the first groove is reached to form the first cavity and expose the first protrusion; etching away the first protrusion from the bottom of the first cavity; releasing the oxide in the first groove.

9. The method of claim 6, wherein: The first groove is a closed annular structure.

10. An electro-acoustic transducer comprising the MEMS microphone according to any one of claims 1-5 and a circuit device electrically connected to the MEMS microphone.

Images