CN113691916B - MEMS microphone and method for manufacturing the same - Google Patents

Abstract

The present invention provides a MEMS microphone and a preparation method thereof. The microphone includes a substrate, a back electrode and a back plate material layer, wherein a cavity is formed in the substrate; a diaphragm is mounted on the substrate, wherein a pleated structure and an air leakage hole are formed in the diaphragm; the back electrode is located above the diaphragm and has a spacing with the diaphragm, and a plurality of sound holes are formed in the back electrode; the back plate material layer is located on the back electrode and extends outward to the surface of the substrate, wherein a plurality of openings, a plurality of back electrode blocking blocks and a support column are formed in the back plate material layer, wherein the openings correspond to each other to reveal the sound holes, the support column and the back electrode blocking block pass through the back electrode and extend downward, and the support column is connected to the diaphragm. The present invention provides a pleated structure on the diaphragm and a support column located between the back electrode and the diaphragm, thereby ensuring that the MEMS microphone has a high detection sensitivity while avoiding excessive local amplitude of the diaphragm, avoiding damage to the diaphragm and adhesion to the back electrode, and thus helping to improve the mechanical strength and performance of the MEMS microphone.

Description

MEMS microphone and method for manufacturing the same

Technical Field

The present invention relates to the field of micro-electromechanical technology, and in particular to a MEMS microphone and a preparation method thereof.

Background Art

With the rapid development of consumer electronics, the microphone industry has also flourished. Microphones are widely used in consumer electronics, smart homes and other fields. It can be said that all devices with voice control functions need them. In recent years, traditional electret condenser microphones have been replaced by MEMS microphones due to the relatively cumbersome matching work.

A MEMS microphone contains a diaphragm that can vibrate up and down and a fixed back plate. The back plate has excellent rigidity and is etched with sound holes, allowing air to flow without causing deviation. The diaphragm can bend with sound waves, causing the diaphragm to move relative to the back plate, producing a certain capacitance change. This weak capacitance change is then amplified and converted into an electrical signal output through an ASIC chip connected to the MEMS microphone.

The existing MEMS microphone structure is usually provided with a pleated structure on the diaphragm 21, which is conducive to increasing the diaphragm amplitude under the same area, but the grooves of the pleated structure will cause the back electrode 17 to grow with the shape during the preparation process, resulting in stress concentration in the area A indicated by the dotted box shown in Figure 1, which may cause crack damage, etc. In addition, when the amplitude of the diaphragm is too large or there are conductive particles between the diaphragm and the back electrode, the diaphragm and the back electrode are easily attracted.

Summary of the invention

In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a MEMS microphone and a preparation method thereof, so as to solve the problems in the prior art that, when a MEMS microphone is provided with a pleated structure, stress concentration corresponding to the pleated structure of the diaphragm may occur in the preparation process due to the conformal growth of the back electrode, resulting in cracks in the back electrode, and the diaphragm and the back electrode may be easily attracted when the amplitude of the diaphragm is too large or conductive particles are present between the diaphragm and the back electrode.

To achieve the above object and other related objects, the present invention provides a method for preparing a MEMS microphone, comprising the steps of:

Providing a substrate, and forming a first sacrificial layer on the substrate;

Performing a patterning process on the first sacrificial layer to form a first groove corresponding to the diaphragm;

forming a diaphragm material layer on the first sacrificial layer, wherein the diaphragm material layer fills the first groove to form a diaphragm, wherein the diaphragm comprises a pleated structure and a bracket located outside the pleated structure;

forming an air leakage hole in the diaphragm, wherein the air leakage hole exposes the first sacrificial layer;

A second sacrificial layer is formed by a conformal deposition method, wherein the second sacrificial layer covers the diaphragm and the air leakage holes, and the upper surface of the second sacrificial layer has a concave-convex structure corresponding to the fold structure of the diaphragm;

Grinding the second sacrificial layer to make the upper surface of the second sacrificial layer flush;

Etching in the second sacrificial layer to form a second groove corresponding to the back electrode blocking block, wherein the depth of the second groove corresponding to the back electrode blocking block is less than the height of the second sacrificial layer;

forming a back electrode material layer on the surface of the second sacrificial layer, wherein the back electrode material layer covers the second sacrificial layer and fills the second groove;

Etching the back electrode material layer to form a back electrode, wherein a plurality of acoustic holes are formed in the back electrode, the second groove corresponding to the back electrode blocking block is exposed in the back electrode, and the plurality of acoustic holes expose the second sacrificial layer;

Forming a back plate material layer, wherein the back plate material layer covers the back pole material layer and fills the acoustic hole and the second groove;

Removing the back plate material layer corresponding to the acoustic hole until the second sacrificial layer is exposed in the acoustic hole, wherein the back plate material filled in the second groove corresponding to the back pole blocking block constitutes the back pole blocking block, and the back pole blocking block passes through the back pole and extends downward;

forming a cavity in the substrate that penetrates the substrate;

The first sacrificial layer and the second sacrificial layer are etched to release the diaphragm and the back pole.

Optionally, before forming the cavity penetrating the substrate in the substrate, the method further includes a step of thinning the substrate, and then forming the cavity in the thinned substrate.

Optionally, the first sacrificial layer and the second sacrificial layer are both made of silicon oxide.

Optionally, the thickness of the second sacrificial layer is greater than the thickness of the first sacrificial layer.

Optionally, the material of the diaphragm and the back electrode includes polysilicon.

Optionally, there are multiple air leakage holes and multiple brackets, and the multiple air leakage holes are located between the pleated structure and the bracket.

Optionally, while forming the air vent holes in the diaphragm, a step of forming a cutting line on the periphery of the diaphragm is also included, and the cutting line exposes the first sacrificial layer. Subsequently, in the process of processing the second sacrificial layer, the back electrode material layer and the back plate material layer, the step of etching the corresponding material layers to expose the cutting line is included.

Optionally, the back plate material layer is made of silicon nitride, and the back plate material layer extends outward to the surface of the substrate and has a distance from the diaphragm.

Optionally, in the process of etching the second groove corresponding to the back pole blocking block in the second sacrificial layer, the second groove corresponding to the support column is also synchronously formed, wherein the second groove corresponding to the support column passes through the second sacrificial layer, and the back plate material subsequently filled in the second groove corresponding to the support column constitutes the support column, the support column passes through the back pole and extends downward to connect with the diaphragm, and the support column is located above the cavity.

The present invention also provides a MEMS microphone, comprising:

a substrate, wherein a cavity is formed in the substrate and passes through the substrate;

A diaphragm, wherein the diaphragm is mounted on the substrate through a bracket, and a pleated structure and an air leakage hole penetrating the diaphragm are formed in the diaphragm;

A back pole, located above the diaphragm and spaced apart from the diaphragm, wherein a plurality of sound holes are formed in the back pole;

A back plate material layer is located on the back pole and extends outward to the surface of the substrate. A plurality of openings, a plurality of back pole blocking blocks and support columns are formed in the back plate material layer. The openings correspond one by one to reveal the sound holes. The support columns and back pole blocking blocks pass through the back pole and extend downward. The support columns are connected to the diaphragm.

Optionally, the support column includes any one of a circular column and a polygonal column.

Optionally, the height of the back pole blocking block is 1/4-3/4 of the distance between the back pole and the diaphragm.

Optionally, the back pole blocking block is not arranged above the pleated structure.

Optionally, the pleated structure is an annular structure, which is arranged around the periphery of the support column.

As described above, the MEMS microphone and the preparation method thereof of the present invention have the following beneficial effects: the present invention forms the second sacrificial layer by conformal deposition, and then grinds the second sacrificial layer. The stress of the second sacrificial layer can be effectively released by grinding, and the upper surface thereof is made horizontal, so as to avoid excessive local stress causing cracks in the second sacrificial layer and adversely affecting subsequent processes, such as causing excessive local stress in the subsequent back electrode material layer causing cracks in the back electrode. By providing a pleated structure on the diaphragm and a support column between the back electrode and the diaphragm, it can be ensured that the MEMS microphone has a high detection sensitivity while avoiding excessive local amplitude of the diaphragm, avoiding damage to the diaphragm and adhesion to the back electrode, which helps to improve the mechanical strength and performance of the MEMS microphone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an exemplary structure of a MEMS microphone in the prior art.

2-16 are schematic diagrams showing the cross-sectional structures of the MEMS microphone provided by the present invention at various steps during the preparation process.

Component number description

11 Base

111 Cavity

12. First Sacrificial Layer

121, 121a, 121b, 121c first groove

13 Diaphragm

131 Folded structure

132 Bracket

133 Vent Hole

13a Diaphragm material layer

14 Second Sacrificial Layer

141, 141a, 141b second groove

142 Concave and convex structure

15 Support column

16 Back pole block

17 Dorsal Pole

171 sound hole

17a Back electrode material layer

18 Backplane material layer

181 Opening

19 Cutting Road

21 Diaphragm

22 Back Panel

DETAILED DESCRIPTION

The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general proportion, and the schematic diagram is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

For ease of description, spatially relative terms such as "under," "below," "below," "below," "above," "on," etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

It should be noted that the diagrams provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the diagrams only show the components related to the present invention rather than the number, shape and size of the components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the layout of the components may also be more complicated. In order to make the diagrams as concise as possible, not all structures are marked in the drawings.

In order to improve the detection accuracy of MEMS microphones, through holes or pleated structures are usually set on the diaphragm to improve the diaphragm's response to external excitation, but this may cause the diaphragm to be damaged or attracted to the back pole due to excessive local amplitude. At the same time, during the preparation process, the local stress of the MEMS microphone may be too concentrated, affecting the performance of the device. To this end, the inventor has proposed an improvement plan after long-term research, which helps to improve the mechanical strength of the microphone while retaining the diaphragm pleated structure.

Specifically, the present invention provides a method for preparing a MEMS microphone, comprising the steps of:

A substrate 11 is provided, and a first sacrificial layer 12 is formed on the substrate 11; the substrate 11 is preferably a substrate 11 of a semiconductor material, including but not limited to silicon, silicon germanium, silicon carbide, SOI or sapphire, and the first sacrificial layer 12 is preferably but not limited to a silicon oxide layer, and the formation method is but not limited to an oxidation method and a vapor deposition method. The structure obtained after this step is shown in FIG2 ;

The first sacrificial layer 12 is patterned to form a first groove 121 corresponding to the diaphragm 13; this step may specifically include firstly using a photolithography process to form a first groove 121a corresponding to the fold structure of the diaphragm 13, and in this step, a first groove 121b corresponding to the diaphragm stopper may be formed simultaneously, that is, the first grooves 121a and 121b corresponding to the stopper and the fold structure may have the same depth, and the obtained structure is shown in FIG. 3, and then the first sacrificial layer 12 is further etched using photolithography to obtain a first groove 121c corresponding to the bracket 132 and penetrating the first sacrificial layer 12, and the obtained structure is shown in FIG. 4;

A diaphragm material layer 13a is formed on the first sacrificial layer 12, and the diaphragm material layer 13a fills the first groove 121 to form a diaphragm 13, and the diaphragm 13 includes a pleated structure 131 and a bracket 132 located outside the pleated structure 131 (the side away from the center is defined as the outside); the diaphragm material layer 13a is preferably a polycrystalline silicon layer, and the formation method is preferably a conformal deposition process such as atomic layer deposition, that is, the first groove 121 is completely filled on the deposited polycrystalline silicon layer to form a diaphragm 13 including the pleated structure 131, the blocking block and the bracket 132; the structure obtained after this step is shown in FIG5;

An air leakage hole 133 is formed in the diaphragm 13 by using a process including but not limited to an etching process, and the air leakage hole 133 exposes the first sacrificial layer 12; in this step, a cutting path 19 can be etched on the periphery of the diaphragm 13 simultaneously or after this step, and the cutting path 19 exposes the surface of the substrate 11; the structure obtained after this step is shown in FIG6;

A second sacrificial layer 14 is formed by a conformal deposition process, and the second sacrificial layer 14 covers the diaphragm 13 and the air leakage hole 133; specifically, the second sacrificial layer 14 is preferably a silicon dioxide layer, and is preferably formed by a conformal deposition process such as atomic layer deposition, so that the upper surface of the second sacrificial layer 14 is formed with a concave-convex structure 142 corresponding to the fold structure 131 of the diaphragm 13, and the obtained structure is shown in FIG. 7. The second sacrificial layer 14 is preferably thicker than the first sacrificial layer 12 to ensure that a cavity with a certain volume is formed between the back pole 17 and the diaphragm 13 formed subsequently; a concave-convex structure 142 is formed on the second sacrificial layer 14 corresponding to the fold structure 131 of the diaphragm 13. In the case of the convex structure 142, a grinding process is then performed, for example, a chemical mechanical grinding process can be used to flatten the second sacrificial layer 14 to remove the concave-convex structure 142 so that the upper surface of the second sacrificial layer 14 is a horizontal plane. The stress of the second sacrificial layer 14 can be effectively released by chemical mechanical grinding, and at the same time, its upper surface is made a horizontal plane, so as to avoid excessive local stress causing cracks in the second sacrificial layer 14 and adverse effects on subsequent processes, such as excessive local stress in the subsequent back electrode material layer 17a causing cracks in the back electrode; the structure obtained after grinding is shown in FIG8 ;

A second groove 141 corresponding to the back pole blocking block 16 is etched in the second sacrificial layer 14 by adopting, including but not limited to, an etching process, and in this step, a second groove corresponding to the support column 15 can be formed simultaneously, wherein the second groove 141b corresponding to the support column 15 penetrates the second sacrificial layer 14 until the diaphragm 13 is exposed, and the depth of the second groove 141a corresponding to the back pole blocking block 16 is less than the height of the second sacrificial layer 14, for example, it can be 1/4-3/4 of the thickness of the second sacrificial layer 14, preferably within 1/2; the structure obtained after this step is shown in FIG9; after this step, etching can be continued to expose the cutting road 19, and the obtained structure is shown in FIG10;

A back electrode material layer 17a is formed on the surface of the second sacrificial layer 14, and the back electrode material layer 17a covers the second sacrificial layer 14 and fills the second groove 141; the back electrode material layer 17a is preferably but not limited to a polysilicon layer, and the formation method is but not limited to a vapor deposition method. The structure obtained after this step is shown in FIG. 11;

The back electrode material layer 17a is etched to form a back electrode 17, a plurality of acoustic holes 171 are formed in the back electrode 17, the second groove 141 corresponding to the back electrode blocking block 16 and the support column 15 is exposed in the back electrode 17 (that is, the back electrode material layer 17a in the second groove is removed), the plurality of acoustic holes 171 expose the second sacrificial layer 14, and the back electrode material located on the cutting path 19 can be removed at the same time; the structure obtained after this step is shown in FIG. 12;

A back plate material layer 18 is formed, the back plate material layer 18 covers the back electrode material layer 17a and fills the acoustic hole 171 and the second groove 141; the back plate material layer 18 is preferably a silicon nitride layer, and the formation method is preferably a vapor deposition method, which can extend to the surface of the substrate 11 but has a spacing with the diaphragm 13; the structure obtained after this step is shown in FIG13;

The backplane material layer 18 corresponding to the acoustic hole 171 is removed until the second sacrificial layer 14 is exposed in the acoustic hole 171 (it can also be described as forming a plurality of openings in the backplane material layer 18, and the plurality of openings correspond to each other to expose the acoustic hole 171, or the two are connected up and down, and the openings in the backplane material layer 18 can also be considered as part of the acoustic hole 171). If a second groove corresponding to the support column is formed before, then in this step, the backplane material filled in the second groove corresponding to the support column 15 constitutes the support column 15 (that is, the support column 15 and the backplane material layer 18 are integrally connected, or the support column 15 extends from the backplane material layer 18 downward to below the back pole 17, and the support column 15 can contact the back pole 17). The backplane filled in the second groove corresponding to the back pole blocking block 16 The material constitutes the back pole blocking block 16, the back pole blocking block 16 and the support column 15 pass through the back pole 17 and extend downward, and the support column 15 is connected to the diaphragm 13; the back pole blocking block 16 is preferably multiple (but the back pole blocking block 16 is preferably not arranged above the pleated structure to avoid the part corresponding to the pleated structure from colliding with the back pole blocking block 16 due to excessive amplitude), evenly distributed on the opposite sides of the support column 15, the pleated structure is an annular structure, which is arranged around the periphery of the support column 15, the support column 15 can be a circular column or a polygonal column (such as a quadrilateral, pentagon, hexagon, etc., preferably a circular column from the perspective of process and other aspects), and the back plate material layer 18 located at the cutting path 19 can be etched away synchronously during the etching process; the structure obtained after this step is shown in Figure 14;

A cavity penetrating the substrate 11 is formed in the substrate 11, and the previously formed support column 15 is located above the cavity; specifically, the substrate 11 may be firstly back-ground and thinned, and then the cavity may be formed in the thinned substrate 11 by a dry etching process, and the obtained structure is shown in FIG15;

Preferably, wet etching is used to etch the first sacrificial layer 12 and the second sacrificial layer 14 to release the diaphragm 13 and the back pole 17. The resulting structure is shown in Figure 16. It can be seen that the diaphragm 13 is mounted on the substrate 11 through a bracket 132, the pleated structure 131 is located above the cavity, the diaphragm 13 is spaced from the back plate material layer 18, and the lower surface of the diaphragm 13 has a number of blocking blocks (not marked) to prevent the diaphragm 13 and the substrate 11 from sticking together.

As an example, there are multiple air leakage holes 133 and multiple brackets 132 , and the multiple air leakage holes 133 are located between the pleated structure 131 and the bracket 132 .

The present invention also provides a MEMS microphone, which can be prepared based on any of the above methods, so the above content can be quoted here in its entirety. Specifically, as shown in FIG16 , the MEMS microphone includes:

A substrate 11, wherein a cavity is formed in the substrate 11 and passes through the substrate 11;

A diaphragm 13, wherein the diaphragm 13 is mounted on the substrate 11 via a bracket 132, wherein a pleated structure 131 and an air leakage hole 133 penetrating the diaphragm 13 are formed in the diaphragm 13, and the pleated structure 131 is preferably located above the cavity;

A back pole 17, located above the diaphragm 13 and spaced apart from the diaphragm 13, wherein a plurality of sound holes 171 are formed in the back pole 17;

The back plate material layer 18 is located on the back pole 17 and extends outward to the surface of the substrate 11. A plurality of openings, a plurality of back pole blocking blocks 16 and support columns 15 are formed in the back plate material layer 18. The openings correspond to each other to reveal the sound holes 171. The support columns 15 and the back pole blocking blocks 16 pass through the back pole 17 and extend downward. The support columns 15 are connected to the diaphragm 13. A plurality of auxiliary support columns (not shown) can also be formed on the back plate material layer and are spaced apart from the support columns. The auxiliary support columns also pass through the back pole and extend downward, but the height of the auxiliary support columns is less than the height of the support columns and are not connected to the diaphragm. The provision of auxiliary support columns helps to further improve the mechanical strength of the MEMS microphone.

As an example, the support column 15 includes any one of a circular column and a polygonal column.

As an example, the height of the back pole blocking block 16 is 1/4-3/4 of the distance between the back pole 17 and the diaphragm 13 , preferably within 1/2, and preferably, the back pole blocking block 16 is not arranged above the pleated structure 131 .

As an example, the pleated structure 131 is an annular structure, which is arranged around the periphery of the support column 15 .

As an example, the diaphragm 13 and the back electrode 17 are preferably polysilicon layers, and the back plate material layer 18 is preferably a polysilicon layer.

As an example, the MEMS microphone further includes a cutting path 19 located on the periphery of the diaphragm 13 .

The substrate may be any one of semiconductor substrates such as a silicon substrate, a germanium substrate, an SOI substrate, a germanium silicon substrate, and a silicon carbide substrate.

For more information about the MEMS microphone, please refer to the above content, which will not be repeated for the sake of brevity.

In summary, the present invention provides a MEMS microphone and a method for manufacturing the same. The MEMS microphone comprises a substrate, a back electrode and a back plate material layer, wherein a cavity penetrating the substrate is formed in the substrate; the diaphragm is mounted on the substrate through a bracket, and a pleated structure and an air leakage hole penetrating the diaphragm are formed in the diaphragm; the back electrode is located above the diaphragm and has a spacing with the diaphragm, and a plurality of sound holes are formed in the back electrode; the back plate material layer is located on the back electrode and extends outward to the surface of the substrate, and a plurality of openings, a plurality of back electrode blocking blocks and support columns are formed in the back plate material layer, and the openings correspond to each other to reveal the sound holes, and the support columns and back electrode blocking blocks pass through the back electrode and extend downward, and the support columns are connected to the diaphragm. The present invention forms a second sacrificial layer by conformal deposition and then grinds the second sacrificial layer, which can effectively release the stress of the second sacrificial layer and make its upper surface horizontal, thereby avoiding excessive local stress that causes cracks in the second sacrificial layer and adversely affects subsequent processes, such as causing excessive local stress in the subsequent back electrode material layer, resulting in cracks in the back electrode. By providing a pleated structure on the diaphragm and a support column between the back electrode and the diaphragm, it can be ensured that the MEMS microphone has a high detection sensitivity while avoiding excessive local amplitude of the diaphragm, avoiding damage to the diaphragm and adhesion to the back electrode, which helps to improve the mechanical strength and performance of the MEMS microphone. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims (10)

1. A method for preparing a MEMS microphone, characterized in that it comprises the steps of: Providing a substrate, and forming a first sacrificial layer on the substrate; Performing a patterning process on the first sacrificial layer to form a first groove corresponding to the diaphragm; forming a diaphragm material layer on the first sacrificial layer, wherein the diaphragm material layer fills the first groove to form a diaphragm, wherein the diaphragm comprises a pleated structure and a bracket located outside the pleated structure; forming an air leakage hole in the diaphragm, wherein the air leakage hole exposes the first sacrificial layer; A second sacrificial layer is formed by a conformal deposition method, wherein the second sacrificial layer covers the diaphragm and the air leakage holes, and the upper surface of the second sacrificial layer has a concave-convex structure corresponding to the fold structure of the diaphragm; Grinding the second sacrificial layer to make the upper surface of the second sacrificial layer flush; Etching in the second sacrificial layer to form a second groove corresponding to the back electrode blocking block, wherein the depth of the second groove corresponding to the back electrode blocking block is less than the height of the second sacrificial layer; forming a back electrode material layer on the surface of the second sacrificial layer, wherein the back electrode material layer covers the second sacrificial layer and fills the second groove; Etching the back electrode material layer to form a back electrode, wherein a plurality of acoustic holes are formed in the back electrode, the second groove corresponding to the back electrode blocking block is exposed in the back electrode, and the plurality of acoustic holes expose the second sacrificial layer; Forming a back plate material layer, wherein the back plate material layer covers the back pole material layer and fills the acoustic hole and the second groove; Removing the back plate material layer corresponding to the acoustic hole until the second sacrificial layer is exposed in the acoustic hole, wherein the back plate material filled in the second groove corresponding to the back pole blocking block constitutes the back pole blocking block, and the back pole blocking block passes through the back pole and extends downward; forming a cavity in the substrate that passes through the substrate; Etching the first sacrificial layer and the second sacrificial layer to release the diaphragm and the back electrode; Wherein, the back pole blocking block is not arranged above the pleated structure. 2. The method for preparing a MEMS microphone according to claim 1, characterized in that before forming the cavity penetrating the substrate in the substrate, the method further comprises a step of thinning the substrate, and then forming the cavity in the thinned substrate. 3 . The method for preparing a MEMS microphone according to claim 1 , wherein the first sacrificial layer and the second sacrificial layer are both made of silicon oxide, and the thickness of the second sacrificial layer is greater than that of the first sacrificial layer. 4. The method for preparing a MEMS microphone according to claim 1, wherein the material of the diaphragm and the back electrode comprises polysilicon, the number of the air leakage holes and the number of the brackets are multiple, and the multiple air leakage holes are located between the pleated structure and the bracket. 5. The method for preparing a MEMS microphone according to claim 1 is characterized in that, while forming the vent hole in the diaphragm, it also includes the step of forming a cutting path on the periphery of the diaphragm, wherein the cutting path exposes the first sacrificial layer, and then the process of processing the second sacrificial layer, the back electrode material layer and the back plate material layer includes the step of etching the corresponding material layers to expose the cutting path. 6 . The method for preparing a MEMS microphone according to claim 1 , wherein the back plate material layer is made of silicon nitride, and the back plate material layer extends outward to the surface of the substrate and has a distance from the diaphragm. 7. The method for preparing a MEMS microphone according to any one of claims 1 to 6 is characterized in that, in the process of etching the second groove corresponding to the back electrode blocking block in the second sacrificial layer, a second groove corresponding to the support column is also synchronously formed, wherein the second groove corresponding to the support column passes through the second sacrificial layer, and the back plate material subsequently filled in the second groove corresponding to the support column constitutes the support column, the support column passes through the back electrode and extends downward to be connected to the diaphragm, and the support column is located above the cavity. 8. A MEMS microphone, characterized in that it is prepared by the method for preparing a MEMS microphone according to any one of claims 1 to 7, comprising: a substrate, wherein a cavity is formed in the substrate and passes through the substrate; A diaphragm, wherein the diaphragm is mounted on the substrate through a bracket, and a pleated structure and an air leakage hole penetrating the diaphragm are formed in the diaphragm; A back pole, the lower surface of which is a horizontal plane, is located above the diaphragm and has a distance from the diaphragm, and a plurality of sound holes are formed in the back pole; A back plate material layer, located on the back pole and extending outward to the surface of the substrate, wherein a plurality of openings, a plurality of back pole blocking blocks and support columns are formed in the back plate material layer, wherein the openings correspond to each other to reveal the acoustic holes, the support columns and the back pole blocking blocks pass through the back pole and extend downward, and the support columns are connected to the diaphragm; Wherein, the back pole blocking block is not arranged above the pleated structure. 9 . The MEMS microphone according to claim 8 , wherein the supporting column comprises any one of a circular column and a polygonal column. 10 . The MEMS microphone according to claim 8 , wherein the height of the back pole blocking block is 1/4-3/4 of the distance between the back pole and the diaphragm; and the pleated structure is an annular structure, which is wound around the periphery of the support column.