MEMS microphone and method for manufacturing the same

Abstract

The present invention provides a MEMS microphone and a method for preparing the same. In the preparation method, the portion of the sacrificial material layer located at the end of the vibration membrane is removed so that the side edge of the back plate can abut against the end of the vibration membrane to support the formed back plate. In addition, in the process of etching the sacrificial material layer to expose the end of the vibration membrane, the etching process is adjusted to reduce the inclination of the side wall of the sacrificial material layer. In this way, the side edge of the back plate covered on the sacrificial material layer can have a smaller side wall inclination, which effectively reduces the stress on the top corner corresponding to the inclined side wall, reduces the risk of the top corner breaking when impacted, and improves the strength of the back plate.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a MEMS microphone and a preparation method thereof. Background Art

[0002] MEMS microphone devices, which are manufactured using the Micro Electro Mechanical System (MEMS) process, are widely used due to their miniaturization and thinness. MEMS microphone devices generally include a lower plate and an upper plate that are sequentially arranged on a substrate, a first support portion is further arranged below the edge of the lower plate to support the lower plate, and a back cavity is formed below the lower plate, and a second support portion is passed between the lower plate and the upper plate so that the lower plate and the upper plate are spaced apart from each other and a cavity is formed.

[0003] Among them, in some specific MEMS microphone devices, the side portion of the back plate is directly arranged above the end of the vibration membrane, so it is hoped that the mechanical strength of the side portion of the back plate can be improved to improve the supporting performance of the back plate. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a MEMS microphone, so that the back plate of the prepared MEMS microphone has higher strength.

[0005] To this end, the present invention provides a method for preparing a MEMS microphone, comprising: forming a vibration membrane on a substrate, the substrate having a first section, the end of the vibration membrane extending into the first section; forming a sacrificial material layer on the vibration membrane; forming a photoresist layer on the sacrificial material layer, the photoresist layer exposing a portion of the sacrificial material layer located in the first section; performing an etching process under a mask of the photoresist layer to etch the portion of the sacrificial material layer located in the first section to expose the end of the vibration membrane; forming a back plate, the back plate covering the end of the vibration membrane and the sacrificial material layer; and removing the sacrificial material layer to release the space between the vibration membrane and the back plate. The etching process for etching the second sacrificial layer comprises: a first etching process for at least partially removing the exposed portion of the sacrificial material layer; and a second etching process for reducing the sidewall inclination of the photoresist layer and the sidewall inclination of the sacrificial material layer.

[0006] Optionally, during the second etching process, the etching power is reduced to increase the consumption rate of the photoresist layer so as to reduce the sidewall inclination of the photoresist layer. In the second etching process, the etching power may decrease in a gradient.

[0007] Optionally, after performing the second etching process, the method further includes: a third etching process for trimming the top angle corresponding to the inclined side wall of the sacrificial material layer to make the top angle more gentle.

[0008] Optionally, the third etching process includes: reducing the flow rate of oxygen and performing etching in a first time period, and increasing the flow rate of oxygen and performing etching in a second time period.

[0009] Optionally, after performing the first etching process and before performing the second etching process, the inclination of the sidewall of the sacrificial material layer is 70°-90°.

[0010] Optionally, after performing the second etching process, the inclination of the sidewall of the sacrificial material layer is less than or equal to 45°.

[0011] Optionally, before forming the photoresist layer, it also includes: etching the portion of the sacrificial material layer within the first segment and the second segment, and etching to a predetermined depth position, wherein the predetermined depth position is higher than the top surface position of the vibration membrane, and the second segment is located on the side of the first area facing the central area of ​​the vibration membrane, and is connected to the first segment.

[0012] Based on the preparation method as described above, the present invention also provides a MEMS microphone, comprising: a vibration membrane and a back plate formed above a substrate, the back plate having a side portion and a flat plate portion, the bottom of the side portion abutting against the end of the vibration membrane, and the side portion also presents a step shape and gradually climbs to the flat plate portion, and the side wall inclination of at least the lowest step in the side portion is less than or equal to 45°.

[0013] Optionally, the top angle of at least the lowest step in the side portion is an arc-shaped top angle.

[0014] In the preparation method of the MEMS microphone provided by the present invention, before forming the back plate, the portion of the sacrificial material layer located at the end of the vibration membrane is removed, so that the side edge of the back plate can abut against the end of the vibration membrane to support the formed back plate. Among them, in the process of etching the sacrificial material layer to expose the end of the vibration membrane, it specifically includes a first etching process and a second etching process, and in the second etching process, the side wall inclination of the sacrificial material layer is reduced by reducing the side wall inclination of the photoresist layer. As the side wall inclination of the sacrificial material layer is reduced, the side edge of the back plate covered on the sacrificial material layer has a smaller side wall inclination, which effectively reduces the stress on the top corner corresponding to the inclined side wall, reduces the risk of the top corner breaking when impacted, and improves the strength of the back plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A schematic diagram of the structure of a MEMS microphone.

[0016] Figure 2 FIG. 4 is a flow chart of a method for manufacturing a MEMS microphone in an embodiment of the present invention.

[0017] Figure 3-Figure 10 FIG. 4 is a schematic structural diagram of a MEMS microphone during its preparation process in an embodiment of the present invention.

[0018] The reference numerals are as follows:

[0019] 100-substrate;

[0020] 100A- first section;

[0021] 100B-Second section;

[0022] 200 / 20-diaphragm;

[0023] 210- blocking part;

[0024] 310 - first sacrificial layer;

[0025] 320 - second sacrificial layer;

[0026] 320a / 320b-side wall;

[0027] 320c-top angle;

[0028] 400- photoresist layer;

[0029] 400a / 400b-side wall;

[0030] 500- back plate;

[0031] 500a-Vertex angle. DETAILED DESCRIPTION

[0032] As mentioned in the background art, the mechanical strength of the back plate of the MEMS microphone needs to be further optimized. Figure 1 In a MEMS microphone shown in FIG, the side edge of the back plate 50 is directly mounted on the end of the vibration membrane 20 to support the entire back plate 50. However, in the MEMS microphone, a step is formed on the side edge of the back plate 50, and the step is easily broken under external impact, thereby causing the back plate 50 to collapse.

[0033] In this regard, the inventors of the present invention discovered after extensive research that the side wall inclination angle θ of the step of the back plate 50 in the MEMS microphone is usually relatively large (for example, 70° to 80°), which causes stress concentration at the top angle of the step. Therefore, the device is very likely to break when it falls.

[0034] In view of this, the present invention provides a method for preparing a MEMS microphone, which can greatly improve the mechanical strength of the back plate, especially can improve the problem that the step of the side edge of the back plate is easy to break. Figure 2 As shown, a method for preparing a MEMS microphone in an embodiment of the present invention includes the following steps.

[0035] In step S100 , a vibration membrane is formed on a substrate, wherein the substrate has a first section, and an end of the vibration membrane extends into the first section.

[0036] Step S200: forming a sacrificial material layer on the vibration membrane.

[0037] Step S300 , forming a photoresist layer on the sacrificial material layer, wherein the photoresist layer exposes a portion of the sacrificial material layer located in the first section.

[0038] Step S400, performing an etching process under the mask of the photoresist layer to etch the portion of the sacrificial material layer located in the first section to expose the end of the vibration membrane. The etching process includes: a first etching process for at least partially removing the exposed portion of the sacrificial material layer; and a second etching process for reducing the sidewall inclination of the photoresist layer and the sidewall inclination of the sacrificial material layer.

[0039] Step S500 , forming a back plate, wherein the back plate covers the end of the vibration membrane and the sacrificial material layer.

[0040] Step S600, removing the sacrificial material layer to release the space between the vibration membrane and the back plate.

[0041] The following is combined with Figure 3-Figure 10 The MEMS microphone and its forming method proposed by the present invention are further described in detail in the following specific embodiments. Figure 3-Figure 10 Schematic diagram of the structure of a MEMS microphone in an embodiment of the present invention during its preparation process. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the drawings are all in a very simplified form and are not in precise proportions, which are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention. It should be recognized that relative terms such as "above", "below", "top", "bottom", "above" and "below" shown in the drawings can be used to describe the relationship between various elements. These relative terms are intended to cover different orientations of elements other than the orientation depicted in the drawings. For example, if the device is inverted relative to the view in the drawing, an element described as being "above" another element will now be below the element.

[0042] In step S100, refer to Figure 3 As shown, a substrate 100 is provided, and a vibration membrane 200 is formed on the substrate 100. The substrate 100 has a first section 100A, an end of the vibration membrane 200 extends into the first section 100A, and the material of the vibration membrane 200 may include polysilicon, etc.

[0043] In a specific example, before preparing the vibration film 200, a first sacrificial layer 310 is formed on the substrate 100, and the material of the first sacrificial layer 310 may include silicon oxide, for example. Also, the vibration film 200 is formed on the first sacrificial layer 310, wherein the portion of the first sacrificial layer 310 corresponding to the middle area of ​​the vibration film 200 will be removed in a subsequent step to release the space below the vibration film 200.

[0044] Continue to refer Figure 3 As shown, a blocking portion 210 is further formed below the end of the vibration membrane 200. In this embodiment, the blocking portion 210 is formed in the first section 100A, and the blocking portion 210 penetrates the first sacrificial layer 310 downward from the end of the vibration membrane 200. When the etching process is subsequently performed to remove the middle part of the first sacrificial layer 310, the blocking portion 210 can be used to block the lateral erosion of the etchant to prevent the sacrificial material directly below the end of the vibration membrane 200 from being removed, thereby protecting the sacrificial material at the end of the vibration membrane 200. In this way, the remaining sacrificial material can be used to form a support portion for supporting the vibration membrane 200.

[0045] Furthermore, at least one barrier 210 may be provided below the end of the vibrating membrane 210, or two or more barrier 210 may be provided, and the two or more barrier 210 may be arranged in sequence along the direction from the center to the end of the vibrating membrane 200. By providing multiple barrier 210, the blocking effect on the etchant may be effectively improved, and the barrier 210 may also be used to assist in supporting the vibrating membrane 200.

[0046] In this embodiment, the barrier 210 and the vibration membrane 200 may be made of the same material and prepared simultaneously in the same process. For example, the method for preparing the barrier 210 and the vibration membrane 200 may include: after forming the first sacrificial layer 310, forming at least one opening in the region of the first sacrificial layer 310 corresponding to the end of the vibration membrane; then, depositing a material layer for forming the vibration membrane, the material layer filling the opening to form the barrier 210, and the material layer also covering the top surface of the top sacrificial layer 310 to form the vibration membrane 200.

[0047] In step S200, refer to Figure 4The sacrificial material layer (ie, Figure 4 The second sacrificial layer 320 is shown in the figure, wherein the material of the second sacrificial layer 320 can be the same as that of the first sacrificial layer 310, for example, both include silicon oxide. In addition, the second sacrificial layer 320 can be used to provide a preparation platform for the back plate formed subsequently, and define the vibration space above the vibration membrane 200.

[0048] In the conventional process, after depositing the second sacrificial layer 320, a back plate is usually formed directly on the second sacrificial layer 320, and then the first sacrificial layer 310 and the second sacrificial layer 320 corresponding to the middle area of ​​the vibration membrane 200 are removed to release the vibration space on the upper and lower sides of the vibration membrane 200. However, in the etching process of partially removing the first sacrificial layer 310 and the second sacrificial layer 320, if it is difficult to strictly control the etching parameters, it is easy to cause the sacrificial material at the end position of the vibration membrane 200 to be laterally eroded and removed in large quantities, especially the second sacrificial layer located above the end of the vibration membrane has less excess, so it is difficult to ensure the stable support of the back plate.

[0049] To address the above problem, in this embodiment, after depositing the second sacrificial layer 320, the portion of the second sacrificial layer 320 covering the end of the vibration membrane 200 is further removed (including: at least removing the portion of the second sacrificial layer 320 located in the first section 100A), so that the subsequently formed back pole plate can be directly mounted on the end of the vibration membrane 200, avoiding the problem of poor supporting force caused by the easy erosion of the sacrificial material in the traditional process.

[0050] After removing the portion of the second sacrificial layer 320 located in the first section 100A, a step can be formed at the end of the second sacrificial layer 320. When the back plate is subsequently prepared, the side edge of the back plate can follow the step of the second sacrificial layer 320 and extend to the flat plate portion of the back plate in a step-by-step manner (for example, Fig. 9 In a specific example, the second sacrificial layer 320 may be etched multiple times to form two or more steps. For example, in this embodiment, the specific steps may be referred to Figure 5-Figure 8 As shown, the second sacrificial layer 320 forms two steps in the first section 100A and the second section 100B, wherein the bottom step is formed in the first section 100A, and the upper step is formed in the second section 100B, and the second section 100B is specifically located on one side of the first section 100A close to the center area of ​​the vibration membrane and is connected to the first section 100A.

[0051] After research, it is found that in the side portion of the back plate, the bottom step usually needs to bear greater stress, and when subjected to external impact, it is more likely to break and other problems. Therefore, it is necessary to improve the anti-destruction performance of the bottom step in the side portion. In this embodiment, the anti-destruction performance of the bottom step is improved by increasing the side wall inclination of the bottom step, which will be described in detail in the subsequent steps S300 and S400.

[0052] Before preparing the bottom step, the upper step is formed first. Figure 5 As shown, before executing step S300, it also includes: etching the portion of the second sacrificial layer 320 located in the first section 100A and the second section 100B, and etching to a predetermined depth position, wherein the predetermined depth position is higher than the top surface position of the vibration membrane 200, thereby defining the height position of the upper step.

[0053] Next, execute step S300, for details, refer to Figure 6 As shown, a photoresist layer 400 is formed on the second sacrificial layer 320, and the photoresist layer 400 exposes the portion of the second sacrificial layer 320 located in the first section 100A. At this time, the photoresist layer 400 correspondingly covers the second section 100B.

[0054] Specifically, the preparation method of the photoresist layer 400 includes: spin coating a photoresist material layer, and performing a photolithography process and a development process to form a photoresist layer 400 that exposes the end region of the vibration membrane. It should be noted that the photoresist layer directly formed by the photolithography process and the development process usually has a high sidewall inclination (for example, higher than 70°) of the sidewall 400a to ensure a high graphic resolution.

[0055] In this embodiment, the end boundary of the photoresist layer 400 stops within the first section 100A, and the end of the photoresist layer 400 also extends from the second section 100B to cover part of the first section 100A. The extension portion thus formed will be consumed in the subsequent push-back process, specifically refer to step S400.

[0056] In step S400, refer to Figure 6-Figure 8 As shown, the second sacrificial layer 320 is etched under the mask of the photoresist layer 400 to expose the end of the vibration membrane 200. The etching process for etching the second sacrificial layer 320 includes: a first etching process for at least partially removing the exposed portion of the second sacrificial layer 320; and a second etching process for reducing the sidewall inclination of the photoresist layer 400 and the sidewall inclination of the second sacrificial layer 320.

[0057] First reference Figure 6As shown, the exposed portion of the second sacrificial layer 320 is at least partially removed by the first etching process. In this embodiment, the etching can be stopped in the second sacrificial layer 320 without exposing the end of the vibrating membrane 200, and a small amount of sacrificial material is retained above the end of the vibrating membrane 200. It should be noted that in the first etching process, the second sacrificial layer 320 and the photoresist layer 400 have a high etching selectivity, so that the second sacrificial layer 320 can be quickly consumed, and the pattern of the photoresist layer 400 can be accurately copied to the second sacrificial layer 320, so that the sidewall 320a of the second sacrificial layer 320 has a high sidewall inclination θ1 (for example, 70°-90°).

[0058] Next reference Figure 7 As shown, the second etching process is used to reduce the sidewall inclination of the photoresist layer 400, and at the same time reduce the sidewall inclination of the second sacrificial layer 320. Specifically, as the sidewall inclination of the sidewall 400b of the photoresist layer 400 is reduced, when the second sacrificial layer 320 is continuously etched, the sidewall inclination θ2 of the sidewall 320b of the second sacrificial layer 320 can be correspondingly reduced (for example, it can be reduced to less than or equal to 45°, and in a specific example, the sidewall inclination θ2 can be reduced to 20°-45°).

[0059] Furthermore, the etching power in the second etching process can be reduced (in a specific example, the etching power in the second etching process can be reduced in a gradient) to increase the consumption rate of the photoresist layer 400, thereby reducing the thickness of the photoresist layer 400, so that the side wall 400b of the photoresist layer 400 is smoother. In this process, the end boundary of the photoresist layer 400 can be gradually pushed back (specifically, the end boundary of the photoresist layer 400 can be gradually pushed back from the first section 100A to the second section 100B). At this time, the second sacrificial layer 320 is etched at the same time, which is conducive to achieving a smoother side wall 320b of the second sacrificial layer 320 and reducing the side wall inclination θ2. That is, after the second etching process, the second sacrificial layer 320 can form a step with a smaller side wall inclination θ2 in the first section 100A. In addition, in the second etching process, the first sacrificial layer 310 can be further exposed.

[0060] In an optional solution, the etching process for etching the second sacrificial layer 320 may further include: a third etching process for trimming the top angle 320c corresponding to the inclined side wall of the second sacrificial layer 320 to make the top angle 320c more gentle.

[0061] Specifically, the third etching process includes, for example, first reducing the etching selectivity of the second sacrificial layer 320 and the photoresist layer 400 to further reduce the inclination of the top angle position; then, increasing the etching selectivity of the second sacrificial layer 320 and the photoresist layer 400, so that it is conducive to trimming the top angle 320C into a gentle and smooth top angle. In one example, the etching selectivity of the second sacrificial layer 320 and the photoresist layer 400 in the third etching process can be changed by adjusting the flow rate of oxygen, thereby achieving the purpose of rounding the top angle of the step. For example, in the third etching process, the flow rate of oxygen can be reduced and etching can be performed in the first time period, and the flow rate of oxygen can be gradually reduced in the first time period; then, the flow rate of oxygen can be increased and etching can be performed in the second time period, and the flow rate of oxygen can also be gradually increased in the second time period.

[0062] In step S500, refer to Fig. 9 As shown, a back plate 500 is formed, and the back plate 500 covers the end of the vibration membrane 200 and the second sacrificial layer 320. At this time, the back plate 500 conformally covers the surface of the second sacrificial layer 320, so that a step is correspondingly formed at the step position of the second sacrificial layer 320, and the step in the back plate 500 also has a smaller sidewall inclination.

[0063] Specifically, the bottom of the side portion of the back plate 500 contacts the end of the vibrating membrane 200, and the side portion also conforms to the surface coverage of the second sacrificial layer 320, so that the step formed on the side portion (at least including the bottom step) has a small sidewall inclination. In this embodiment, the top angle 500a of the step in the back plate 500 is also a gentle, smooth arc top angle, and even the entire side wall of the step can also be an arc side wall, further improving the anti-destruction performance of the back plate 500.

[0064] The method for preparing the back plate 500 may specifically include: sequentially forming an insulating material layer and a conductive material layer, wherein the insulating material layer may be made of, for example, silicon nitride. Figure 9-10 Although the insulating material layer and the conductive material layer are not explicitly illustrated, it can be understood that the insulating material layer and the conductive material layer are stacked from bottom to top.

[0065] In step S600, refer to Fig.10 As shown, the second sacrificial layer is removed to release the space between the vibration membrane 200 and the back plate 500 .

[0066] In this embodiment, the first sacrificial layer 310 and the second sacrificial layer 320 on the upper and lower sides of the vibration membrane 200 are removed at the same time. When removing the first sacrificial layer, since the blocking portion 210 is provided below the end of the vibration membrane 200, the sacrificial layer below the end of the vibration membrane 200 is prevented from being removed, and a support portion can be formed to support the vibration membrane 200. In addition, when removing the second sacrificial layer, the sacrificial material above the vibration membrane 200 can be completely removed. Therefore, in this embodiment, the etching difficulty of the first sacrificial layer and the second sacrificial layer is relatively low, and the problem of excessive erosion can be avoided without pursuing higher etching accuracy.

[0067] Based on the preparation method described above, the back plate of the formed MEMS microphone can have a higher strength, thereby improving the performance and service life of the MEMS microphone. The structure of the prepared MEMS microphone is described below.

[0068] For details, please refer to Fig.10 As shown, the MEMS microphone in this embodiment includes: a vibrating membrane 200 and a back plate 500 formed on a substrate 100. The back plate 500 has a side portion and a flat plate portion, and the bottom of the side portion abuts against the end of the vibrating membrane 200 so that the back plate 500 is supported above the vibrating membrane 200. In addition, the side portion is also stepped and gradually rises to the flat plate portion, and at least the lowest step in the side portion has a smaller side wall inclination, for example, the side wall inclination of the lowest step is less than or equal to 45°.

[0069] In this embodiment, the top angle 500a of at least the lowest step in the side portion is a gentle, rounded arc-shaped top angle, and even the entire side wall of the step can also be an arc-shaped side wall, further improving the anti-destruction performance of the back plate 500.

[0070] In summary, in the preparation method of the MEMS microphone provided in this embodiment, before forming the back plate, the portion of the sacrificial material layer located at the end of the vibration membrane is removed, so that the side edge of the back plate can abut against the end of the vibration membrane to support the formed back plate. In addition, by reducing the side wall inclination of the sacrificial material layer, the side edge of the back plate covered on the sacrificial material layer also has a lower side wall inclination, which effectively reduces the stress on the top corner corresponding to the inclined side wall, reduces the risk of the top corner breaking when impacted, and improves the strength of the back plate.

[0071] It should be noted that, although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.

[0072] It should also be understood that, unless otherwise specified or indicated, the terms "first", "second", "third", etc. in the specification are merely used to distinguish between the various components, elements, steps, etc. in the specification, and are not used to indicate the logical relationship or sequential relationship between the various components, elements, steps, etc.

[0073] It should also be recognized that the terms described herein are used only to describe specific embodiments and are not intended to limit the scope of the invention. It should be noted that the singular forms "a" and "an" used herein and in the appended claims include plural references unless the context clearly indicates otherwise. For example, a reference to "a step" or "a device" means a reference to one or more steps or devices, and may include secondary steps as well as secondary devices. All conjunctions used should be understood in the broadest sense. And, the word "or" should be understood to have the definition of a logical "or", not a logical "exclusive or", unless the context clearly indicates otherwise.

Claims

1. A method for preparing a MEMS microphone, characterized in that: include: forming a vibration membrane on a substrate, wherein the substrate has a first section, and an end of the vibration membrane extends into the first section; forming a sacrificial material layer on the vibration membrane; forming a photoresist layer on the sacrificial material layer, wherein the photoresist layer exposes a portion of the sacrificial material layer located in the first section; Performing an etching process under the mask of the photoresist layer to etch the portion of the sacrificial material layer located in the first section to expose the end of the vibration membrane; wherein the etching process includes: a first etching process for at least partially removing the exposed portion of the sacrificial material layer; and a second etching process for reducing the sidewall inclination of the photoresist layer and the sidewall inclination of the sacrificial material layer; forming a back plate that covers the end of the vibration membrane and the sacrificial material layer; and removing the sacrificial material layer to release the space between the vibration membrane and the back plate.

2. The method for preparing a MEMS microphone according to claim 1, characterized in that: In the second etching process, the etching power is reduced to increase the consumption rate of the photoresist layer so as to reduce the inclination of the side wall of the photoresist layer.

3. The method for preparing a MEMS microphone according to claim 2, characterized in that: In the second etching process, the etching power decreases gradually.

4. The method for preparing a MEMS microphone according to claim 1, characterized in that: After performing the second etching process, the method further includes: a third etching process for trimming the top angle corresponding to the inclined side wall of the sacrificial material layer to make the top angle more gentle.

5. The method for preparing a MEMS microphone according to claim 4, characterized in that: The third etching process includes: reducing the flow rate of oxygen and performing etching in a first time period, and increasing the flow rate of oxygen and performing etching in a second time period.

6. The method for preparing a MEMS microphone according to claim 1, characterized in that: After performing the first etching process and before performing the second etching process, the inclination of the sidewall of the sacrificial material layer is 70°-90°.

7. The method for preparing a MEMS microphone according to claim 1, characterized in that: After the second etching process is performed, the inclination of the sidewall of the sacrificial material layer is less than or equal to 45°.

8. The method for preparing a MEMS microphone according to claim 1, characterized in that: Before forming the photoresist layer, the method further comprises: The portions of the sacrificial material layer within the first section and the second section are etched to a predetermined depth position, wherein the predetermined depth position is higher than the top surface position of the vibration membrane, and the second section is located on the side of the first section facing the central area of ​​the vibration membrane and is connected to the first section.

9. A MEMS microphone formed by the method for preparing a MEMS microphone according to any one of claims 1 to 8, characterized in that: include: A vibration membrane and a back plate are formed above a substrate, wherein the back plate has a side portion and a flat plate portion, wherein the bottom of the side portion abuts against the end of the vibration membrane, and the side portion is also stepped and gradually rises to the flat plate portion, and the side wall inclination of at least the lowest step in the side portion is less than or equal to 45°.

10. The MEMS microphone according to claim 9, characterized in that: At least the top angle of the lowest step in the side portion is an arc-shaped top angle.

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