MEMS microphone and microphone processing technology

Abstract

The embodiment of the present application discloses a kind of MEMS microphone and microphone processing technology, MEMS microphone includes substrate and is installed on the first diaphragm, second diaphragm and back plate of the substrate, support column is arranged between the first diaphragm and second diaphragm, the back plate is equipped with through-hole, the support column passes through the through-hole, the support column includes the first support column connected to the first diaphragm connection, the second support column connected to the second diaphragm, the first support column and / or the second support column are made of plastic material.The technical effect of one embodiment of the present application is that by making the first support column and / or the second support column from plastic material, the stress concentration effect is significantly reduced while providing sufficient support to the diaphragm, thereby improving the structural reliability of the MEMS microphone.

Description

Technical Field

[0001] This application belongs to the field of microphone technology, specifically, it relates to a MEMS microphone and microphone processing technology. Background Technology

[0002] With the rapid development of electronic technology, MEMS (Micro-Electro-Mechanical Systems) microphones have been increasingly widely used due to their advantages such as low signal-to-noise ratio (SNR) and maximum sound pressure level (AOP), and are continuously expanding their market share.

[0003] The MEMS microphone includes two diaphragms, with a back electrode plate having through holes positioned between them. The back electrode plate is located between the two diaphragms and forms a differential capacitor structure with the two diaphragms. To achieve synchronous vibration of the two diaphragms and to support them, several support columns connected to the two diaphragms are provided between them.

[0004] However, due to mechanical performance issues such as stress concentration, the connection between the support column and the diaphragm is prone to breakage, resulting in low mechanical reliability of the dual-diaphragm microphone, which greatly limits its application in mobile phones, smart wearables and other fields. Summary of the Invention

[0005] The purpose of this application is to provide a new technology solution for MEMS microphones and microphone processing technology.

[0006] According to a first aspect of the present application, a MEMS microphone is provided, including a substrate and a first diaphragm, a second diaphragm and a back electrode plate mounted on the substrate, wherein the first diaphragm and the second diaphragm are spaced apart on both sides of the back electrode plate;

[0007] A support post is provided between the first diaphragm and the second diaphragm, and a through hole is provided on the back electrode plate, through which the support post passes;

[0008] The support column includes a first support column connected to the first diaphragm and a second support column connected to the second diaphragm, wherein the first support column and / or the second support column are made of plastic material.

[0009] Optionally, the support column further includes a connecting layer disposed between the first support column and the second support column.

[0010] Optionally, the connecting layer and the back electrode plate are located on the same plane.

[0011] Optionally, the plastic material includes polymers, permanent photoresists, soft metals, alloys, etc.

[0012] Optionally, the Young's modulus of the plastic material is less than 10 GPa.

[0013] Optionally, the first support column is made of a plastic material, and the cross-sectional area of ​​the first support column is larger than that of the second support column.

[0014] Optionally, the second support column is made of a high-density rigid material.

[0015] Optionally, the first support column is made of a plastic material and has a diameter of 4μm-8μm.

[0016] Optionally, the spacing between adjacent first support columns is 40μm-80μm.

[0017] Optionally, a sealed cavity is formed between the first diaphragm and the second diaphragm.

[0018] Optionally, the sealed cavity is filled with a gas with a viscosity coefficient less than that of air.

[0019] Optionally, the air pressure inside the sealed cavity is less than atmospheric pressure.

[0020] Optionally, it also includes a pressure relief hole penetrating through the first diaphragm and the second diaphragm, the wall of the pressure relief hole and the first diaphragm and the second diaphragm forming the sealed cavity.

[0021] Optionally, the wall of the pressure relief hole is made of a plastic material, and a sealing layer is provided on the surface of the wall of the pressure relief hole.

[0022] According to a second aspect of the embodiments of this application, a fabrication process for the MEMS microphone provided in the first aspect is also provided, comprising the following steps:

[0023] Pre-processing the top wafer: A first diaphragm is disposed on a first substrate, a first sacrificial layer is disposed on the surface of the first diaphragm, the first sacrificial layer is etched, and a plurality of first support pillars are formed on the first diaphragm;

[0024] Pre-processing the bottom wafer: A second diaphragm is disposed on the second substrate, a second sacrificial layer is disposed on the surface of the second diaphragm, a back electrode plate with through holes is formed on the second sacrificial layer, the second sacrificial layer is etched, and a plurality of second support pillars are formed on the second diaphragm;

[0025] The top wafer and the bottom wafer are bonded together by a hybrid wafer bonding method, wherein the first support post and the second support post form a connection relationship;

[0026] Remove the first substrate.

[0027] Optionally, pressure relief holes are provided on the first diaphragm and the second diaphragm, and the first support column and the second support column form the sidewall of the pressure relief hole, thereby repairing the pressure relief hole for airtightness and forming a sealing layer.

[0028] Optionally, the back electrode plate is etched to form a through-hole and a bonding layer is retained in the through-hole;

[0029] The second sacrificial layer is etched to form a second support pillar, the two ends of which are connected to the connecting layer and the second diaphragm, respectively.

[0030] One technical advantage of this application embodiment is that the support column includes a first support column, a second support column, and a connecting layer, wherein the first support column and / or the second support column are made of plastic material, and the connecting layer is located between the first support column and the second support column and is bonded together. This achieves a significant reduction in stress concentration at the connection between the first diaphragm and the second diaphragm and the support column while providing sufficient support for the first diaphragm and the second diaphragm, thereby improving the structural reliability of the MEMS microphone.

[0031] Other features and advantages of this application will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the present application and, together with their description, serve to explain the principles of the present application.

[0033] Figure 1 This is a schematic diagram of the overall structure of a MEMS microphone embodiment 1 provided in this application.

[0034] Figure 2 This is a schematic diagram of the overall structure of the MEMS microphone embodiment two provided in this application.

[0035] Figure 3 This is a schematic diagram of the overall structure of the MEMS microphone embodiment three provided in this application.

[0036] Figure 4 This is a schematic diagram of the overall structure of the MEMS microphone embodiment four provided in this application.

[0037] Figure 5 This is a schematic diagram of stress concentration in the diaphragm.

[0038] Figure 6 This is a schematic diagram illustrating the improvement of stress concentration in the diaphragm.

[0039] Figure 7 This is a schematic diagram showing the relationship between the spacing of the support columns and the diaphragm deflection;

[0040] Figure 8 This is one of the schematic diagrams of microphone manufacturing process provided in the embodiments of this application;

[0041] Figure 9This is the second schematic diagram of the microphone manufacturing process provided in the embodiments of this application.

[0042] Explanation of reference numerals in the attached drawings: 1. Substrate; 2. First diaphragm; 3. Second diaphragm; 4. Back electrode plate; 41. Through hole; 5. Support post; 51. First support post; 52. Second support post; 6. Connecting layer; 7. Sealing cavity; 8. Pressure relief hole; 9. Sealing layer; 10. Support layer; 11. Top wafer; 12. First substrate; 13. First sacrificial layer; 14. Bottom wafer; 15. Second substrate; 16. Second sacrificial layer. Detailed Implementation

[0043] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0044] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the scope of this application and its application or use.

[0045] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0046] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0047] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0048] Reference Figures 1-4 This application discloses a MEMS microphone, including a substrate 1 and a first diaphragm 2, a second diaphragm 3, and a back electrode plate 4 mounted on the substrate 1. The first diaphragm 2 and the second diaphragm 3 are spaced apart on both sides of the back electrode plate 4. (Refer to...) Figure 1 The back electrode plate 4 has a first surface and a second surface arranged opposite to each other, wherein the first surface is... Figure 1 The upper surface of the middle back plate 4, the second surface is Figure 1 The lower surface of the back electrode plate 4. A support layer 10 is provided at the edge of the first surface of the back electrode plate 4, and the first diaphragm 2 is connected to the back electrode plate 4 through the support layer 10. A support layer 10 is provided at the edge of the second surface of the back electrode plate 4, and the second diaphragm 3 is connected to the back electrode plate 4 through the support layer 10.

[0049] The first diaphragm 2, the second diaphragm 3, and the back electrode plate 4 of the present invention can be formed on the substrate 1 by deposition and etching. The substrate 1 can be made of monocrystalline silicon, and the first diaphragm 2, the second diaphragm 3, and the back electrode plate 4 can be made of monocrystalline silicon or polycrystalline silicon. The selection of such materials and the deposition process are common knowledge to those skilled in the art and will not be specifically described here. The back electrode plate 4 is provided with through holes 41 that penetrate the back electrode plate 4, so as to allow air to flow freely on both sides of the first surface and the second surface of the back electrode plate 4. Multiple through holes 41 are provided. This application does not limit the number and position of the through holes 41. Preferably, the through holes 41 are evenly distributed on the surface of the back electrode plate 4.

[0050] A support column 5 is provided between the first diaphragm 2 and the second diaphragm 3. The support column 5 passes through the through hole 41 to support the first diaphragm 2 and the second diaphragm 3. The support column 5 includes a first support column 51 connected to the first diaphragm 2 and a second support column 52 connected to the second diaphragm 3. The first support column 51 and / or the second support column 52 are made of plastic material.

[0051] In one embodiment, the support column 5 includes a first support column 51 and a second support column 52. The upper end of the first support column 51 is insulated from the first diaphragm 2, the lower end of the first support column 51 passes through the through hole 41 and is connected to the upper end of the second support column 52, and the lower end of the second support column 52 is insulated from the second diaphragm 3.

[0052] In one embodiment, the support column 5 includes a first support column 51, a connecting layer 6, and a second support column 52. (Refer to...) Figure 1 The upper end of the first support column 51 is insulated from the first diaphragm 2, and the lower end of the first support column 51 is connected to the upper surface of the connecting layer 6. The upper end of the second support column 52 is connected to the lower surface of the connecting layer 6, and the lower end of the second support column 52 is insulated from the second diaphragm 3. Any part of the support column 5 can pass through the through hole 41 of the back electrode plate 4.

[0053] For example, the connecting layer 6 can be located on the side of the back electrode plate 4 close to the first diaphragm 2, in which case the second support column 52 passes through the through hole 41 of the back electrode plate 4.

[0054] For example, the connecting layer 6 can be located inside the through hole 41 of the back electrode plate 4. In this case, the connecting layer 6 and the back electrode plate 4 are located on the same plane, and the first support column 51 and the second support column 52 are distributed on both sides of the back electrode plate 4.

[0055] In addition, the connecting layer 6 can also be located on the side of the back electrode plate 4 near the second diaphragm 3, in which case the first support column 51 passes through the through hole 41 of the back electrode plate 4.

[0056] Preferably, the connecting layer 6 is located within the through hole 41 of the back electrode plate 4, and the connecting layer 6 and the back electrode plate 4 are on the same plane. In this structure, the connecting layer 6 can be cut from the back electrode plate 4, and the heights of the first support column 51 and the second support column 52 are the same as the thickness of the support layer 10. During processing, the connecting layer 6 and the back electrode plate 4 are on the same horizontal plane, which facilitates the control of the heights of the first support column 51 and the second support column 52 according to the support layer 10, thereby improving the processing accuracy. At the same time, it is beneficial to the accuracy and convenience of connecting the first support column 51 and the second support column 52 to the connecting layer 6.

[0057] The first support column 51 is located above the second support column 52. The first support column 51 and the second support column 52 are distributed on both sides of the back electrode plate 4, and at least one of them is formed of a plastic material, while the other is made of a conventional high-density hard material such as silicon nitride. The Young's modulus of the plastic material is lower than that of silicon nitride. Young's modulus is used to characterize the stiffness of a material; stiffness refers to the material's resistance to elastic deformation. The greater the stiffness of the material, the greater its Young's modulus.

[0058] Specifically, in Example 1, as Figure 1 As shown, the first support column 51 of the support column 5 is made of materials such as silicon nitride, and the second support column 52 is made of a plastic material; in embodiment two, as... Figure 2 As shown, both the first support column 51 and the second support column 52 are made of plastic material; in Embodiment 3, as... Figure 3 As shown, the first support column 51 is made of plastic material, and the second support column 52 is made of materials such as silicon nitride.

[0059] Reference Figure 5 In existing technologies, the support column 5 is typically made of high-density hard materials such as silicon nitride. However, the support column 5, formed of high-density hard materials, generates high stress at the interface with the diaphragm. During diaphragm deformation, the stress at the interface between the diaphragm and the support column 5 increases, and the local stress concentration effect of the support column 5 is very obvious. If subjected to additional mechanical impact, the stress at the connection between the diaphragm and the support column 5 can easily exceed the diaphragm's fracture strength, leading to diaphragm rupture and resulting in low reliability of the dual-diaphragm microphone structure.

[0060] Reference Figure 6 In the scheme disclosed in this application, the upper first support column 51 is made of a plastic material, while the lower second support column 52 is still made of a high-density hard material. That is, the support column 52 is made of... Figure 5 The entire structure shown, which uses high-density hard materials, is replaced with Figure 6 The structure is made of at least a portion of a plastic material. Because the Young's modulus of plastic materials is significantly smaller than that of high-density hard materials such as silicon nitride, it can buffer stress.

[0061] Reference Figures 7-8 During the vibration of the first diaphragm 2 and the second diaphragm 3, surface bending occurs at the contact points between the first diaphragm 2 and the support column 5. Because the first support column 51, made of a plastic material, has a low Young's modulus, the stress between the first support column 51 and the first diaphragm 2 is significantly reduced. Simultaneously, since the first support column 51 and the second support column 52 are integrally connected through the connecting layer 6, stress buffering and transfer occur between them. This also reduces the stress between the second support column 52, which is not made of a plastic material, and the second diaphragm 3, thereby significantly reducing the overall stress concentration effect and improving the mechanical reliability of the MEMS microphone.

[0062] Optionally, the plastic material includes polymers, elastomers, adhesives, permanent photoresists, soft metals, alloys, etc. The Young's modulus of the plastic material is less than 10 GPa.

[0063] The Young's modulus of high-density hard materials such as silicon nitride used in existing technologies is typically greater than 50 GPa, resulting in significant stress at the contact points between these materials and the diaphragm. In contrast, this application selects a plastic material with a Young's modulus less than 10 GPa to process the first support column 51 and / or the second support column 52. This ensures effective support for the first diaphragm 2 and the second diaphragm 3 while significantly reducing stress at their contact points, thereby improving the overall mechanical reliability of the MEMS microphone.

[0064] Optionally, the first support column 51 is made of a plastic material, and the cross-sectional area of ​​the first support column 51 is larger than the cross-sectional area of ​​the second support column 52. (Refer to...) Figure 3 The first support column 51 located at the top is made of plastic materials such as polymer and permanent photoresist, while the second support column 52 located at the bottom is made of conventional high-density hard materials such as silicon nitride. On a plane parallel to the back electrode plate 4, the cross-sectional area of ​​the first support column 51 is larger than that of the second support column 52.

[0065] In this embodiment, the support pillar 5 is formed by joining the ends of the first support pillar 51 and the connecting layer 6, and the second support pillar 52 and the connecting layer 6. During the joining process, a hybrid wafer bonding method is typically used. However, bonding misalignment is prone to occur during the bonding process. In most industry applications, the misalignment value after bonding is typically between 2μm and 5μm or greater than 5μm, making it difficult to achieve high-precision bonding. This results in the first support pillar 51 and the second support pillar 52 failing to accurately connect to the connecting layer 6, thereby affecting the overall structural strength of the support pillar 5.

[0066] Preferably, this application employs fusion bonding for bonding, which can produce a smaller misalignment value. Since the Young's modulus of ductile materials is lower than that of high-density hard materials, the cross-sectional area of ​​the first support post 51 is larger than that of the second support post 52. This serves two purposes: firstly, it absorbs misalignments and deviations generated during bonding, improving the bonding accuracy between the first and second support posts 51 and 52. Secondly, the larger cross-sectional area of ​​the first support post 51, made of ductile material, compared to the larger cross-sectional area of ​​the second support post 52 made of high-density hard material, helps reduce the stress between the first support post 51 and the first diaphragm 2, thereby mitigating stress concentration effects and improving the overall mechanical reliability of the MEMS microphone.

[0067] Optionally, the second support column 52 is made of a high-density rigid material. Commonly used high-density rigid materials include SiNx, SiO2, polycrystalline silicon, amorphous silicon, glass, and hard metals. In this embodiment, the first support column 51 is made of a plastic material, and the second support column 52 is made of a high-density rigid material. This helps to ensure the overall structural strength of the support column 5, thereby ensuring the support force of the support column 5 on the first diaphragm 2 and the second diaphragm 3; on the other hand, it helps to reduce the stress at the connection between the support column 5 and the first diaphragm 2 and the second diaphragm 3, thereby reducing the stress concentration effect.

[0068] Optionally, the first support column 51 is made of a plastic material, and the diameter of the first support column 51 is 4μm-8μm. Preferably, the diameter of the first support column 51 is 6μm.

[0069] The larger the diameter of the first support column 51, the larger the contact area between the first support column 51 and the first diaphragm 2, and the smaller the stress generated between them. However, if the diameter of the first support column 51 is too large, it will reduce the effective vibration area of ​​the first diaphragm 2, resulting in significant capacitance loss and a decrease in effective capacitance.

[0070] The smaller the diameter of the first support column 51, the smaller the contact area between the first support column 51 and the first diaphragm 2, and the greater the stress generated between them. However, due to the low Young's modulus of the plastic material, it will deform under the action of external atmospheric pressure. When the diameter of the first support column 51 is very small, it is difficult to effectively support the first diaphragm 2.

[0071] Therefore, within the 4μm-8μm range provided in this application, the first support column 51 made of plastic material can achieve a balance between the support force and effective capacitance of the first diaphragm 2.

[0072] Optionally, the spacing between adjacent first support columns 51 is 40μm-80μm. Preferably, the spacing between adjacent first support columns 51 is 60μm. The spacing is the distance between the axis of one first support column 51 and the axis of the adjacent first support column 51.

[0073] Optionally, a sealed cavity 7 is formed between the first diaphragm 2 and the second diaphragm 3. (Refer to...) Figure 1 The support layer 10 is insulated and sealed to the first diaphragm 2 and the second diaphragm 3 respectively. Since the back electrode plate 4 has a through hole 41, a sealed cavity 7 is formed between the first diaphragm 2 and the second diaphragm 3. The air in the sealed cavity 7 can flow freely on the upper and lower sides of the back electrode plate 4.

[0074] Figure 7 This diagram illustrates the relationship between the spacing of the support columns 5 and the diaphragm deflection. The horizontal axis represents the spacing of the support columns 5, i.e., the distance between the axes of adjacent support columns 5. Specifically, when the diaphragm thickness is 0.5 μm and the pressure difference is 1 atmosphere (1 atm), the sealed cavity 7 between the first diaphragm 2 and the second diaphragm 3 is a vacuum environment due to the external environment being at 1 atmosphere (1 atm). (Refer to...) Figure 7 Curve 2 in the figure shows that the maximum spacing of the support columns 5 is 18 μm. When the diaphragm thickness is 1 μm and the pressure difference is 0.1 atmospheres (0.1 atm), the pressure inside the sealed cavity 7 between the first diaphragm 2 and the second diaphragm 3 is 0.9 atm, meaning the pressure inside the sealed cavity 7 is close to atmospheric pressure. (Refer to...) Figure 7 In curve 6, the maximum spacing of the first support column 51 is 55μm.

[0075] When the pressure difference between the sealed cavity 7 and the environment is fixed, the larger the spacing of the support columns 5, the smaller the distribution density of the support columns 5 on the diaphragm surface, that is, the fewer the number of support columns 5 per unit area of ​​the diaphragm, the larger the effective vibration area of ​​the diaphragm, and the better the acoustic performance of the microphone. In other words, the larger the spacing of the support columns 5, the better the acoustic performance of the microphone.

[0076] The vertical axis represents the diaphragm deflection, which is the distance the diaphragm moves towards the back electrode plate 4. In the prior art, the distance between the diaphragm and the back electrode plate 4 is usually less than 2μm. At the same time, in order to ensure the normal movement of the diaphragm, the diaphragm deflection needs to be less than 10% of the distance between the diaphragm and the back electrode plate 4. Therefore, the smaller the diaphragm deflection, the better the acoustic performance of the microphone.

[0077] Referring to curves 1-6, it can be seen that the diaphragm deflection gradually increases with the increase of the spacing of the support columns 5. Specifically, when the pressure difference between the inside and outside of the sealed cavity 7 is fixed, the larger the spacing of the support columns 5, the greater the compressive stress borne by a single support column 5. The greater the deformation of the support column 5 along its own axial direction, the greater the amount of movement of the diaphragm connected to the support column 5 towards the back electrode plate 4. The distance the diaphragm moves towards the back electrode plate 4 is the diaphragm deflection; that is, the diaphragm deflection increases with the increase of the spacing of the support columns 5.

[0078] For example, existing technologies require the maximum deflection of the diaphragm to be less than 0.16 μm, that is... Figure 7 The corresponding location on the vertical axis is around 1E-7m. Taking the support columns 5 arranged in a square pattern on the diaphragm surface as an example:

[0079] Referring to curves 1-3, when the pressure difference between the inside and outside of the sealed cavity 7 is 1 atm, that is, when the sealed cavity 7 is in a vacuum or near-vacuum state, the spacing of the support columns 5 in curve 3 (diaphragm thickness 0.3 μm) is smaller than that in curve 2 (diaphragm thickness 0.5 μm), and the spacing of the support columns 5 in curve 2 (diaphragm thickness 0.5 μm) is smaller than that in curve 1 (diaphragm thickness 1 μm). In other words, as the diaphragm thickness increases, a larger spacing can be set for the support columns 5.

[0080] Referring to curves 1 and 4, when the diaphragm thickness is 1 μm, the spacing of the support columns 5 in curve 1 (pressure difference of 1 atm) is smaller than that in curve 4 (pressure difference of 0.1 atm). That is, the smaller the pressure difference, the closer the air pressure inside the sealed cavity 7 is to atmospheric pressure, and the larger the spacing of the support columns 5 can be.

[0081] To minimize static diaphragm deflection, i.e., reduce diaphragm deflection, and improve the microphone's acoustic performance, the sealed cavity 7 may optionally be filled with a gas with a viscosity coefficient lower than that of air.

[0082] Viscosity coefficient characterizes the internal friction force generated by the interaction between gas molecules when subjected to force, and it is usually related to temperature and pressure. Therefore, a gas with a viscosity coefficient less than that of air refers to a gas with a viscosity coefficient less than that of air under the same conditions. These "same conditions" could be, for example, the operating range of a microphone, such as -20°C to 100°C. Of course, some microphones need to operate in extreme environments, depending on the application.

[0083] In the existing technology, there are many gases with a viscosity coefficient lower than that of air. Gases with a viscosity coefficient lower than that of air under microphone operating conditions can be selected. These gases can be at least one of isobutane, propane, propylene, hydrogen, ethane, ammonia, acetylene, ethyl chloride, ethylene, CH3Cl, methane, SO2, H2S, chlorine, CO2, N2O, and N2.

[0084] Filling the sealed cavity 7 with a low-viscosity gas ensures that the pressure inside the cavity remains consistent with the external environmental pressure, meaning the pressure difference between the sealed cavity 7 and the environment is less than 0.1 atm. For example, when filling and sealing with hydrogen, the sealing can be performed in a hydrogen atmosphere at room temperature and normal pressure (or close to one atmosphere) to compensate for the external environmental pressure. In other words, the pressure difference between the sealed cavity 7 and the external environment is zero, thus allowing the first diaphragm 2 and the second diaphragm 3 to remain flat in a static state, preventing bulging or collapsing. This eliminates the need for the support column 5, thereby improving the microphone's sensitivity and ensuring its acoustic performance.

[0085] Optionally, the sealed cavity 7 is filled with a gas at a pressure lower than atmospheric pressure, and the gas pressure inside the sealed cavity 7 is lower than atmospheric pressure. When the sealed cavity 7 is a vacuum, the pressure difference between the sealed cavity 7 and the environment is 1 atm.

[0086] The relationship between gas pressure P and dynamic viscosity μ of the gas is as follows:

[0087] If the gap is greater than the mean free path L: the dynamic viscosity μ of the gas is independent of the gas pressure P;

[0088] If the gap is less than or equal to the mean free path L: the dynamic viscosity μ of the gas is proportional to the gas pressure P.

[0089] For air at room temperature: mean free path L = 6.6 / P (L is in mm, P is in Pa)

[0090] Taking a microphone as an example: the air gap is 1-5μm, the mean free path L is 6.6μm at 1kPa, and 6.6m at 1mPa. At this time, the air gap is smaller than the mean free path L, and the dynamic viscosity μ of the gas is proportional to the gas pressure P. The lower the gas pressure in the sealed cavity 7, the lower the dynamic viscosity μ of the gas.

[0091] Therefore, in order to greatly reduce noise, the air pressure in the sealed cavity 7 is much less than 1 atm, specifically, the air pressure in the sealed cavity 7 is much less than 1 kPa.

[0092] In summary, to improve the acoustic performance of the microphone, a microphone structure with a large spacing between the support columns 5 and a small diaphragm deflection is required. The first support column 51 is made of a plastic material. When the spacing between the first support columns 51 is 60 μm and the diameter of the first support column 51 is 6 μm, a compressive stress of 10 MPa along the axial direction of the support column 5 will be generated when the pressure difference between the inside and outside of the sealed cavity 7 is 1 atmosphere. The Young's modulus of the first support column 51 is 3 GPa. This compressive stress reduces the height of the support column 5 along the axial direction by about 0.3%. At this time, the deformation of the support column 5 is negligible.

[0093] Optionally, refer to Figures 1-4 It also includes a pressure relief hole 8 penetrating the first diaphragm 2 and the second diaphragm 3, used to reduce the acoustic impedance between the first diaphragm 2 and the second diaphragm 3 and the external environment during vibration. To prevent the pressure relief hole 8 from communicating with the sealing cavity 7, the wall of the pressure relief hole 8 and the first diaphragm 2 and the second diaphragm 3 form the sealing cavity 7. In one specific embodiment, there may be one pressure relief hole 8, located at the center of the first diaphragm 2 and the second diaphragm 3. Alternatively, there may be multiple pressure relief holes 8, distributed in the horizontal direction of the first diaphragm 2 and the second diaphragm 3. This application does not limit the specific number or location of the pressure relief holes 8.

[0094] A support column 5 is provided at the wall of the pressure relief hole 8. In this application, the support column 5 forming the wall of the pressure relief hole 8 is not limited. The first support column 51 and the second support column 52 can both be formed of high-density rigid material; or the first support column 51 can be made of plastic material and the second support column 52 can be formed of high-density rigid material; or both the first support column 51 and the second support column 52 can be formed of plastic material.

[0095] Optionally, the wall of the pressure relief hole 8 is formed of a plastic material, and a sealing layer 9 is provided on the surface of the wall of the pressure relief hole 8. (Refer to...) Figure 4 In one embodiment of this application, the support pillars 5 at the wall of the pressure relief hole 8 are arranged such that the first support pillar 51 above the connecting layer 6 is made of a plastic material, and the second support pillar 52 below the connecting layer 6 is made of a high-density hard material. The first support pillar 51, made of plastic material, is bonded to the connecting layer 6. To improve the sealing performance at this location, a sealing layer 9 is formed on the surface of the wall of the pressure relief hole 8, for example, by ICP-CVD, PECVD, Sputtered SiNx, or SiO2 deposition. The sealing layer 9 can be made of a high-density hard material such as silicon nitride. This application does not limit the material or thickness of the sealing layer 9.

[0096] Of course, the wall of the pressure relief hole 8 can be made of high-density rigid material, and a sealing layer 9 can also be set on the surface of the wall of the pressure relief hole 8 to improve the sealing performance of the wall of the pressure relief hole 8.

[0097] Reference Figures 8-9 This application also discloses a microphone manufacturing process, including the following steps:

[0098] Pre-processing the top wafer 11: depositing a silicon dioxide layer on the surface of the first substrate 12, depositing a first diaphragm 2 on the surface of the silicon dioxide layer, depositing a first sacrificial layer 13 on the surface of the first diaphragm 2, etching the first sacrificial layer 13, forming a support layer 10 and a plurality of first support pillars 51 on the surface of the first diaphragm 2, the support layer 10 being located at the edge of the first diaphragm 2, and the first support pillars 51 being located within the area enclosed by the support layer 10.

[0099] Pre-processing the bottom wafer 14: A silicon dioxide layer is deposited on the surface of the second substrate 15, a second diaphragm 3 is deposited on the surface of the silicon dioxide layer, and a second sacrificial layer 16 is deposited on the surface of the second diaphragm 3. A back electrode 4 is formed on the upper surface of the second sacrificial layer 16, and several through holes 41 are formed on the back electrode 4. The second sacrificial layer 16 is etched to form a support layer 10 and a plurality of second support pillars 52 on the surface of the second diaphragm 3. The support layer 10 is located at the edge of the second diaphragm 3, and the second support pillars 52 are located below the connecting layer 6 and connected to the connecting layer 6.

[0100] The top wafer 11 and the bottom wafer 14 are bonded together using a hybrid wafer bonding method, specifically fusion bonding. The first support post 51 and the second support post 52 are connected. The first support post 51 and the second support post 52 can be directly connected, with their ends mated. Alternatively, the first support post 51 and the second support post 52 can be indirectly connected, for example, by providing a connecting layer 6 between them.

[0101] The first substrate 12 is removed by means of etching, grinding, or other methods.

[0102] Conductive holes are formed on the silicon dioxide layer connected to the first diaphragm 2, respectively, to the second diaphragm 3, the back electrode plate 4, and the first diaphragm 2.

[0103] A pad is formed inside the conductive hole.

[0104] An acoustic hole is formed on the second substrate 15, and the remaining second substrate 15 forms the substrate.

[0105] The silicon dioxide layer connecting the first diaphragm 2 and the second diaphragm 3 is removed by etching with liquids such as hydrogen fluoride to obtain a dual-diaphragm microphone.

[0106] Optionally, pressure relief holes 8 are provided on the first diaphragm 2 and the second diaphragm 3. The first support column 51 and the second support column 52 form the sidewalls of the pressure relief holes 8, and the pressure relief holes 8 are repaired for airtightness to form a sealing layer 9. For example, the sealing layer 9 can be processed by ICP-CVD, PECVD, spraying SiNx, SiO2 deposition, etc. In addition, the through holes 41 formed on the second sacrificial layer 16 to the back electrode on the second diaphragm 3, the back electrode plate 4, and the first diaphragm 2 can also be repaired for airtightness to form a sealing layer 9.

[0107] Optionally, the back electrode plate 4 is etched to form a through hole 41 and a connection layer 6 is retained in the through hole 41. The connection layer 6 and the back electrode plate 4 are located on the same plane and have the same structure.

[0108] The second sacrificial layer 16 is etched to form the second support pillar 52, which is located between and connected to the connecting layer 6 and the second diaphragm 3. The connecting layer 6 is located between the first support pillar 51 and the second support pillar 52.

[0109] A connecting layer 6 is formed by etching the back electrode plate 4, so that the connecting layer 6 and the back electrode plate 4 are on the same plane. Subsequently, a second sacrificial layer 16 is etched to form a second support pillar 52. The second support pillar 52 is located below the connecting layer 6 and the two are connected. The portion formed by the second support pillar 52 and the connecting layer 6 is on the same plane as the back electrode plate 4.

[0110] Furthermore, during the preprocessing of the top wafer 11, the first support post 51 is etched from the first sacrificial layer 13. The thickness of the first sacrificial layer 13 determines the distance between the first diaphragm 2 and the back electrode plate 4. Therefore, when the top wafer 11 and the bottom wafer 14 are bonded, that is, when the first support post 51 is bonded to the second support post 52 and the connecting layer 6, the thickness of the first sacrificial layer 13 at the edge of the first diaphragm 2 determines the distance between the first diaphragm 2 and the back electrode plate 4. At this time, the length of the first support post 51 is the same as the thickness of the first sacrificial layer 13, and the connecting layer 6 and the back electrode plate 4 are located on the same plane, so that the first support post 51 can accurately contact and bond with the back electrode plate 4.

[0111] If a separate connecting layer 6 is not formed by etching the back electrode plate 4, then in order to connect the first support post 51 and the second support post 52, the length of the first support post 51 or the second support post 52 needs to be greater than the thickness of the first sacrificial layer 13 or the second sacrificial layer 16. If this method is used for processing, firstly, the processing accuracy of the first support post 51 and the second support post 52 is difficult to control; secondly, the alignment accuracy requirements during the bonding process of the first support post 51 and the second support post 52 are high, increasing the processing difficulty and making it difficult to guarantee processing accuracy.

[0112] This application employs etching of the back electrode plate 4 to form a separate connecting layer 6, etching of the first sacrificial layer 13 to form a first support pillar 51, etching of the second sacrificial layer 16 to form a second support pillar 52, the second support pillar 52 being connected to the connecting layer 6, and then bonding the first support pillar 51 to the connecting layer 6. By using this processing technology, it is easier to precisely ensure that the overall length of the bonded support pillar 5 is the same as the distance between the first diaphragm 2 and the second diaphragm 3, reducing the possibility of diaphragm damage due to excessively long support pillars 5 and improving the accuracy of the support pillar 5 processing.

[0113] While specific embodiments of this application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of this application. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this application. The scope of this application is defined by the appended claims.

Claims

1. A MEMS microphone, characterized by, The loudspeaker comprises a substrate (1), a first diaphragm (2), a second diaphragm (3) and a back plate (4) mounted on the substrate (1), the first diaphragm (2) and the second diaphragm (3) are arranged on both sides of the back plate (4) in a spaced manner; A support column (5) is arranged between the first diaphragm (2) and the second diaphragm (3), and a through hole (41) is formed in the back plate (4), and the support column (5) passes through the through hole (41); The support column (5) comprises a first support column (51) connected to the first diaphragm (2) and a second support column (52) connected to the second diaphragm (3), the first support column (51) is made of plastic material, the second support column (52) is made of high-density hard material, and the cross-sectional area of the first support column (51) is larger than that of the second support column (52).

2. The MEMS microphone of claim 1, wherein, The support column (5) further comprises a connecting layer (6) arranged between the first support column (51) and the second support column (52).

3. The MEMS microphone of claim 2, wherein, The connecting layer (6) and the back plate (4) are located in the same plane.

4. The MEMS microphone of claim 1, wherein, The plastic material comprises a polymer, a permanent photoresist, a soft metal or an alloy.

5. The MEMS microphone of claim 4, wherein, The Young's modulus of the plastic material is less than 10 GPa.

6. The MEMS microphone of claim 1, wherein, The first support column (51) is made of plastic material, and the diameter of the first support column (51) is 4-8 μm.

7. The MEMS microphone of claim 6, wherein, The distance between adjacent first support columns (51) is 40-80 μm.

8. The MEMS microphone of claim 1, wherein, A sealed cavity (7) is formed between the first diaphragm (2) and the second diaphragm (3).

9. The MEMS microphone of claim 8, wherein, The sealed cavity (7) is filled with a gas having a viscosity coefficient less than that of air.

10. The MEMS microphone of claim 8, wherein, The pressure in the sealed cavity (7) is less than atmospheric pressure.

11. The MEMS microphone of claim 8, wherein, A pressure relief hole (8) penetrating the first diaphragm (2) and the second diaphragm (3) is further provided, and the hole wall of the pressure relief hole (8) and the first diaphragm (2) and the second diaphragm (3) form the sealed cavity (7).

12. The MEMS microphone of claim 11, wherein, The hole wall of the pressure relief hole (8) is made of plastic material, and a sealing layer (9) is arranged on the surface of the hole wall of the pressure relief hole (8).

13. A process for manufacturing a MEMS microphone according to any one of claims 1 to 12, characterized in that, The method comprises the following steps: Preprocessing the top wafer (11): arranging a first diaphragm (2) on a first substrate (12), arranging a first sacrificial layer (13) on the surface of the first diaphragm (2), etching the first sacrificial layer (13), and forming a plurality of first support columns (51) on the first diaphragm (2); Preprocessing the bottom wafer (14): arranging a second diaphragm (3) on a second substrate (15), arranging a second sacrificial layer (16) on the surface of the second diaphragm (3), forming a back plate (4) with a through hole (41) on the second sacrificial layer (16), etching the second sacrificial layer (16), and forming a plurality of second support columns (52) on the second diaphragm (3); The top wafer (11) and the bottom wafer (14) are connected by hybrid wafer bonding, wherein the first support column (51) and the second support column (52) form a connection relationship, the first support column (51) is made of plastic material, the cross-sectional area of the first support column (51) is larger than that of the second support column (52), and the second support column (52) is made of high-density hard material. The first substrate (12) is removed.

14. The process of claim 13, wherein, The first diaphragm (2) and the second diaphragm (3) are provided with pressure relief holes (8), the first support column (51) and the second support column (52) form the side wall of the pressure relief hole (8), and the pressure relief hole (8) is air-tightly repaired and forms a sealing layer (9).

15. The process of claim 13, wherein, The back plate (4) is etched to form a through hole (41) and the connection layer (6) is reserved in the through hole (41); The second support column (52) is etched from the second sacrificial layer (16), and the two ends of the second support column (52) are connected with the connection layer (6) and the second diaphragm (3) respectively.

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