MEMS Microphones

Abstract

The present invention provides a MEMS microphone, wherein a support wall on a substrate encloses a cavity, a vibration membrane is suspended in the cavity and the edge extends into the support wall to be fixed. A release hole array on a back plate structure includes a plurality of release holes that penetrate the back plate structure and are connected to the cavity. In the process of releasing a sacrificial layer through the release hole array to form a support wall, the contour of the inner wall of the support wall follows the contour of the outermost release hole on one side close to the support wall. The outermost release hole in the release hole array is configured so that the second side facing away from the center of the release hole array is flatter than the first side facing the center of the release hole array, thereby smoothing the contour of the inner wall of the support wall, inhibiting the formation of sharp corners, preventing the sharp corners from piercing the vibration membrane and causing the vibration membrane to fall off, and improving the life and reliability of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-microphones, and in particular to a MEMS microphone. Background Art

[0002] MEMS microphones are MEMS (Micro-Electro-Mechanical System) devices manufactured using micromachining technology. Due to their small size, high sensitivity, and good compatibility with existing semiconductor technologies, MEMS microphones are increasingly used in mobile terminals such as mobile phones.

[0003] The structure of the MEMS microphone includes a vibration membrane, a back plate structure and a supporting wall. The supporting wall encloses a cavity B'. The back plate structure is located on the supporting wall and covers the cavity B'. The vibration membrane is suspended in the cavity B' and the edge extends to the supporting wall 200' for fixation. Figure 1 is a schematic diagram of the structure of an existing supporting wall 200', such as Figure 1 As shown, during the preparation of the MEMS microphone, the support wall 200' is formed by releasing the sacrificial layer using the release hole array on the back plate structure (the etchant uses the release hole array as a channel to corrode part of the sacrificial layer, and the remaining sacrificial layer forms the support wall 200', and the corroded part forms the cavity B'), resulting in the contour of the inner wall of the support wall 200' not being smooth enough, but wavy, and the wavy shape has a sharp corner Q. Since the vibration membrane needs to vibrate up and down in the cavity B', and the edge of the vibration membrane is fixed by the support wall 200', during the vibration of the vibration membrane, the sharp corner Q can easily pierce the vibration membrane, thereby causing the vibration membrane to rupture or even fall off from the support wall 200', thereby causing damage to the device. Summary of the invention

[0004] The object of the present invention is to provide a MEMS microphone, which can smooth the contour of the inner wall of the supporting wall and suppress sharp corners, thereby improving the reliability and life of the device.

[0005] In order to achieve the above object, the present invention provides a MEMS microphone, comprising:

[0006] substrate;

[0007] A supporting wall is arranged on the substrate and encloses a cavity;

[0008] A vibration membrane is suspended in the cavity and its edge extends to be fixed in the supporting wall;

[0009] a back plate structure, located on the supporting wall and covering the cavity; and,

[0010] A release hole array comprises a plurality of release holes penetrating the back plate structure and connected to the cavity, wherein the outermost release holes in the release hole array have at least a first side and a second side, wherein the first side faces the center of the release hole array, and the second side faces away from the center of the release hole array, and the second side is flatter than the first side.

[0011] Optionally, the center of the cavity coincides with the center of the release hole array.

[0012] Optionally, the shapes and sizes of the outermost circle release holes are the same.

[0013] Optionally, the first side and the second side are both arc-shaped or straight-line-shaped.

[0014] Optionally, the outermost circle of release holes is located on a virtual circle with the center of the release hole array as the center.

[0015] Optionally, the distances between adjacent release holes in the outermost circle are equal.

[0016] Optionally, the release holes within the outermost circle of release holes are inner circle release holes, and the inner circle release holes are arranged in a rectangular array, a honeycomb structure array or a concentric rotating array.

[0017] Optionally, the back plate structure has a release area corresponding to the cavity, and the release hole array is located in the release area.

[0018] Optionally, the release holes have a pore size of 1 micron to 20 microns.

[0019] Optionally, the outermost circle release holes are one or more of circular cut holes, polygonal cut holes and elliptical cut holes, and the side corresponding to the cut edge is the second side.

[0020] Optionally, the supporting wall includes two stacked supporting layers, and the edge of the vibration membrane is clamped between the two supporting layers.

[0021] Optionally, an acoustic cavity is formed in the substrate, and the acoustic cavity passes through the substrate and is connected with the cavity.

[0022] Optionally, the back plate structure includes a first protective layer, a second protective layer, and a back plate electrode located between the first protective layer and the second protective layer, and the first protective layer is closer to the vibration membrane than the second protective layer.

[0023] Optionally, the first protective layer has a plurality of protrusions facing the cavity.

[0024] Optionally, also include:

[0025] A first contact point is located in the same layer as the vibration membrane and is electrically connected to the vibration membrane;

[0026] A second contact point is located in the same layer as the back plate electrode and is electrically connected to the back plate electrode;

[0027] a first pad electrically connected to the first contact point via a conductive path penetrating the second protective layer, the first protective layer and at least a portion of the supporting wall;

[0028] The second pad is electrically connected to the second contact point through a conductive path penetrating the second protective layer.

[0029] In the MEMS microphone provided by the present invention, the support wall on the substrate encloses a cavity, and the vibration membrane is suspended in the cavity and the edge extends into the support wall to be fixed. The release hole array on the back plate structure includes a plurality of release holes that penetrate the back plate structure and are connected to the cavity. In the process of releasing the sacrificial layer through the release hole array to form the support wall, the contour of the inner wall of the support wall will follow the contour of the outermost release hole on the side close to the support wall. The outermost release hole in the release hole array is configured so that the second side facing away from the center of the release hole array is flatter than the first side facing the center of the release hole array, thereby smoothing the contour of the inner wall of the support wall, inhibiting the formation of sharp corners, preventing the sharp corners from piercing the vibration membrane and causing the vibration membrane to fall off, and improving the life and reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic structural diagram of an existing supporting wall provided by an embodiment of the present invention;

[0031] Figures 2 to 14c A schematic diagram of the structure corresponding to the corresponding steps of the method for preparing a MEMS microphone provided by an embodiment of the present invention, wherein: Fig.14a This is a schematic diagram of the structure of a MEMS microphone. Fig.14b for Fig.14a Distribution diagram of the release hole array in Fig.14c for Fig.14b A schematic diagram of the structure of the outermost circle release hole in FIG.

[0032] Figures 15a to 15c A schematic diagram of the structure of three outermost circle release holes provided in an embodiment of the present invention;

[0033] Wherein, the accompanying drawings are marked as follows:

[0034] 200'-supporting wall; Q-sharp corner; B'-cavity;

[0035] 100-substrate; 200-support wall; 210-first support layer; 220-second support layer; 310-first groove; 320-second groove; 330-third groove; 340-fourth groove; 350-fifth groove; 410-vibration membrane; 420-first contact point; 510-first protective layer; 521-back plate electrode; 522-second contact point; 530-second protective layer; 610-first pad; 620-second pad; 700-release hole array; 710-outermost ring release hole; 710a-first side; 710b-second side; 720-inner ring release hole; 800-acoustic cavity;

[0036] B-cavity; R-fold structure; S-bulge. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention will be described in more detail below in conjunction with the schematic diagram. The advantages and features of the present invention will become clearer based on the following description. It should be noted that the drawings are all in a very simplified form and are not in exact proportions, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0038] Fig.14a and Fig.14b FIG. 1 is a schematic diagram of the structure of the MEMS microphone of this embodiment. Fig.14a and Fig.14b As shown, the MEMS microphone includes a substrate 100, a supporting wall 200, a vibration membrane 410 and a back plate structure. The substrate 100 is used to support the device, and the supporting wall 200 is located between the substrate 100 and the back plate structure to form a sandwich structure. The supporting wall 200 encloses a cavity B, and the vibration membrane 410 is suspended in the cavity B and the edge extends into the supporting wall 200 for fixation. The upper and lower surfaces of the vibration membrane 410 are respectively at a certain distance from the back plate structure and the substrate 100, so that the vibration membrane 410 can vibrate up and down in the cavity B.

[0039] Please continue reading Fig.14a In this embodiment, the substrate 100 has an acoustic cavity 800, which runs through the substrate 100 and is connected to the cavity B. The cross-sectional shape of the acoustic cavity 800 along the thickness direction can be an inverted trapezoid, a square or a hexagon.

[0040] Furthermore, the support wall 200 is annular to enclose the cavity B. In this embodiment, the support wall 200 includes two stacked support layers, and the edge of the vibration membrane 410 is clamped between the two support layers and fixed. In this way, the height of the cavity B can be controlled by controlling the thickness of the support wall 200, and the distance between the vibration membrane 410 and the substrate 100 and the back plate structure can be adjusted by adjusting the thickness ratio of the two layers of support membranes constituting the support wall 200. Generally, the distance between the vibration membrane 410 and the back plate structure is 1 micron to 5 microns.

[0041] In this embodiment, the widths of the two support layers in the direction perpendicular to the thickness are unequal, so that the sizes of the upper and lower parts of the cavity B are unequal. At this time, the cross-sectional shape of the cavity B along the thickness direction is roughly T-shaped; of course, the lateral widths of the two support layers can also be equal, so that the cavity B is roughly cylindrical.

[0042] As an optional embodiment, the vibration membrane 410 includes a middle part and a peripheral part surrounding the middle part, the edge of the peripheral part extends into the supporting wall 200, and the middle part includes at least one through hole (not shown in the figure) for releasing stress and adjusting the frequency response curve of the microphone. The vibration membrane 410 also includes a pleated structure R for connecting the middle part and the peripheral part, and the pleated structure R is a concentric annular pleated part on the vibration membrane 410, and the middle part of the vibration membrane 410 and the pleated structure R are movable areas. Optionally, the pleated structure R can also be a spiral pleat, and the curvature radius of the thread of the pleated structure R does not change with the position or changes with the position, for example, the curvature radius of each spiral line is the same. The pleated structure R can be selected according to the needs of the actual application.

[0043] Compared with a flat surface of the vibration membrane 410, the vibration membrane 410 with the pleated structure R can improve the elastic properties of the diaphragm, control the movable area, improve the elastic coefficient of the membrane structure, and meet the performance design requirements of the MEMS microphone. Furthermore, the pleated structure R can extend to the peripheral part of the vibration membrane 410, effectively releasing the stress of the vibration membrane 410 and improving the sensitivity of the MEMS microphone.

[0044] Furthermore, because the outer contour of the pleated structure R is located within the range of the acoustic cavity 800, the problem of reduced reliability of the MEMS microphone due to process fluctuations in mass production can be avoided, thereby improving the overall performance of the product.

[0045] In this embodiment, the thickness of the vibration membrane 410 is, for example, 0.3 micrometers to 1 micrometer.

[0046] Further, the back plate structure includes a first protective layer 510, a back plate electrode 521 and a second protective layer 530, wherein the first protective layer 510 faces the cavity B, and the back plate electrode 521 is located between the first protective layer 510 and the second protective layer 530 to form a sandwich structure. The first protective layer 510 and the second protective layer 530 are both composed of any one of a boron nitride (BN) layer, a silicon nitride (SIN) layer, a silicon boron nitride (SIBN) layer, a borophosphosilicate glass (BPSG) layer, and a phosphosilicate glass (PSG) layer. In this embodiment, the first protective layer 510 and the second protective layer 530 are both boron nitride layers.

[0047] In this embodiment, the thickness of the first protective layer 510 is, for example, 0.08 micrometers to 0.25 micrometers; the thickness of the second protective layer 530 is, for example, 0.1 micrometers to 1.5 micrometers; the thickness of the back plate electrode 521 is, for example, 0.3 micrometers to 1 micrometer.

[0048] In this embodiment, in the direction perpendicular to the thickness, the cross-sectional area of ​​the vibration membrane 410 is greater than the maximum cross-sectional area of ​​the acoustic cavity 800, and the cross-sectional area of ​​the back plate electrode 521 is less than or equal to the minimum cross-sectional area of ​​the acoustic cavity 800. More preferably, the cross-sectional area of ​​the back plate electrode 521 is less than the minimum cross-sectional area of ​​the acoustic cavity 800. It should be noted that when the cross-sectional shape of the acoustic cavity 800 along the thickness direction is a square, the cross-sectional areas of the acoustic cavity 800 are all the same, and the only cross-sectional area is the minimum cross-sectional area; when the cross-sectional shape of the acoustic cavity 800 along the thickness direction is an inverted trapezoid, a trapezoid or a hexagon, the cross-sectional area of ​​the acoustic cavity 800 located at the upper surface or the lower surface of the substrate 100 is the smallest. In some embodiments, the radius of the minimum cross-sectional area of ​​the acoustic cavity 800 is 250 microns to 600 microns.

[0049] In this embodiment, the first protective layer 510 has a protrusion S facing the vibration membrane 410, which is used to prevent the back plate electrode 521 from sticking to the vibration membrane 410 when the vibration membrane 410 is deformed by more than 33% under a large impact or excitation during the use of the MEMS microphone (this phenomenon will greatly prolong the duration of the MEMS microphone in the current state, causing the MEMS microphone to fail intermittently or even permanently). Optionally, the protrusion S can be a polygonal pyramid, a polygonal prism, a cone or a cylinder; the diameter of the protrusion S is, for example, 0.5 microns to 1.5 microns, and the height is, for example, 0.5 microns to 1.5 microns.

[0050] It should be understood that the second protective layer 530 can serve as a mechanical support layer of the back plate electrode 521 to provide rigidity, so that the back plate electrode 521 maintains a non-deformed state in a working state.

[0051] Optionally, the back plate electrode 521 is formed above the movable area of ​​the vibrating membrane 410, and the back plate electrode 521 and the vibrating membrane 410 constitute two plates of a capacitor. The area of ​​the back plate electrode 521 is less than or equal to the area of ​​the movable area of ​​the vibrating membrane 410. In this embodiment, the area of ​​the back plate electrode 521 is less than the area of ​​the movable area of ​​the vibrating membrane 410. For example, the area of ​​the back plate electrode 521 is 70% to 100% of the movable area of ​​the vibrating membrane 410. Since the area of ​​the back plate electrode 521 is less than or equal to the area of ​​the movable area of ​​the vibrating membrane 410, the invalid capacitance component is removed from the detection signal, so that the sensitivity of the detection signal is only related to the effective capacitance component, thereby improving the sensitivity of the MEMS microphone. The movable area of ​​the vibrating membrane 410 includes a middle part and a connecting part.

[0052] Optionally, the back plate electrode 521 may be in a circular, concentric annular, circular with radial strips on the edge, triangular, square or other geometric shapes, which are not limited in the present invention. Further, the back plate electrode 521 may also have a plurality of perforations, which may also be circular or polygonal.

[0053] In this embodiment, the vibration membrane 410 and the back plate electrode 521 are both composed of doped polysilicon, so that the vibration membrane 410 and the back plate electrode 521 have electrical conductivity. In this embodiment, the MEMS microphone further has a first contact point 420 disposed in the same layer as the vibration membrane 410 and electrically connected, and a second contact point 522 disposed in the same layer as the back plate electrode 521 and electrically connected, and a first pad 610 and a second pad 620 are further formed on the second protective layer 530, and the first pad 610 and the second pad 620 are electrically connected to the first contact point 420 and the second contact point 522 respectively through a conductive channel.

[0054] It should be understood that the vibration membrane 410 and the back plate electrode 521 may also be made of metal materials such as aluminum, copper, gold, titanium, nickel, tungsten and alloys thereof, and the present invention is not limited thereto.

[0055] In this embodiment, the first pad 610 and the second pad 620 are made of a conductive material, such as any one of aluminum, gold, copper, nickel, titanium, chromium or alloys thereof, and the thickness is, for example, 1 micrometer to 2 micrometers.

[0056] It should be understood that the number of the first pad 610 and the second pad 620 may be one, two, or more, which is not limited in the present invention.

[0057] Please continue reading Fig.14a and Fig.14bThe back plate structure has a release area corresponding to the cavity B, and the area outside the release area is arranged on the supporting wall 200. A release hole array 700 is arranged in the release area. The release hole array 700 includes a plurality of release holes penetrating the back plate structure and communicating with the cavity B. The release hole array 700 includes an outermost circle of release holes 710. Fig.14b As can be seen in FIG. 7 , the outermost release holes 710 are the release holes farthest from the center of the release hole array 700. The release holes in the release hole array 700 not only serve as supply channels for the etchant in the manufacturing process, but also serve as acoustic holes in the final MEMS microphone to reduce acoustic resistance.

[0058] Fig.14c for Fig.14b The schematic diagram of the structure of the outermost release hole 710 in FIG. Fig.14b and Fig.14c In this embodiment, the outermost circle release holes 710 include a first side 710a and a second side 710b, wherein the first side 710a faces the center of the release hole array 700, the second side 710b faces away from the center of the release hole array 700, and the second side 710b is flatter than the first side 710a. The release holes in the outermost circle release holes 700 are all inner circle release holes 720, and the inner circle release holes 720 are arranged in a honeycomb structure array, a rectangular array, or a concentric rotation array.

[0059] In the process of releasing the sacrificial layer through the release hole array 700 to form the support wall 200, the inner circle release holes 720 are mainly used to remove the sacrificial layer on a large area to form the cavity B, while the outermost circle release holes will affect the side contour of the cavity B, that is, affect the contour of the inner wall of the support wall 200 formed by the remaining sacrificial layer, and the contour of the inner wall of the support wall 200 will follow the contour of the outermost circle release holes 710 close to the side of the support wall 200. In this embodiment, the outermost circle release holes 710 in the release hole array 700 are configured as follows: the second side 710b facing away from the center of the release hole array 700 is flatter than the first side 710a facing the center of the release hole array 700. Since the contour segment of the outermost circle release holes 710 corresponding to the support wall 200 is flatter, it is equivalent to smoothing the contour of the inner wall of the support wall 200, inhibiting the formation of sharp corners, preventing sharp corners from piercing the vibration membrane 410 and causing the vibration membrane 410 to fall off, thereby improving the life and reliability of the device.

[0060] Furthermore, since the cavity B is formed by releasing the sacrificial layer through the release hole array 700, and the inner circle release holes 720 are usually regularly arranged, the center of the cavity B coincides with the center of the release hole array 700, thereby making the structure of the device symmetrical and stable.

[0061] Please continue reading Fig.14a and Fig.14b In this embodiment, the shapes and sizes of the outermost circle release holes 710 are the same, so that the contour of the inner wall of the support wall 200 is relatively symmetrical. Of course, as an optional embodiment, the shapes and sizes of the outermost circle release holes 710 can also be different.

[0062] Please continue reading Fig.14b In this embodiment, the outermost circle release holes 710 are located on a virtual circle with the center of the release hole array 700 as the center, that is, each of the outermost circle release holes 710 is equidistant from the center of the release hole array 700.

[0063] Please continue reading Fig.14b In this embodiment, the outermost circle release holes 710 are evenly distributed on the virtual circumference so that the distances between adjacent outermost circle release holes 710 are equal. In this way, the arrangement of the outermost circle release holes 710 in the outermost circle of the release hole array 700 is also regular, which can make the contour of the inner wall of the support wall 200 more uniform.

[0064] Please continue reading Fig.14b and Fig.14c In this embodiment, the first side 710a of the outermost circle release hole 710 is arc-shaped, the second side 710b is straight-line-shaped, and the second side 710b is composed of a line segment, so that the flatness of the second side 710b is optimal, and the contour of the inner wall of the supporting wall 200 can be flattened to the maximum extent and sharp corners can be eliminated.

[0065] like Fig.14c As shown, in this embodiment, the outermost release hole 710 is a circular cut hole (a portion of the circular hole is cut off); Fig.15b and Fig.15c As shown, the outermost circle release hole 710 can also be an elliptical cut hole (a part of the elliptical hole is cut off) or a polygonal cut hole (a part of the polygonal hole is cut off), wherein the side corresponding to the tangent line is usually a relatively flat side, so it is used as the second side 710b. When the outermost circle release hole 710 is a cut hole, the shape is relatively simple, and the mask for forming the outermost circle release hole 710 is relatively easy to manufacture.

[0066] Please continue reading Fig.15a , Fig.15b and Fig.15c When the outermost circle release hole 710 is a cut hole, the tangent line is not limited to a straight line, but can also be a curve, so that the second side 710b can also be an arc, which is not limited in the present invention.

[0067] It is understandable that the outermost circle release holes 710 are not limited to cut holes, but can also be other types of holes, as long as the relatively flat side is facing away from the center of the release hole array 700.

[0068] Please continue reading Fig.14a and 14b , observed from the surface of the second protective layer 530, the inner ring release holes 720 are, for example, one or more of circular holes, cross holes and polygonal holes, and the shapes of the inner ring release holes 720 can be the same or different. In this embodiment, the inner ring release holes 720 are all circular holes.

[0069] In this embodiment, the diameters of the release holes are all in a range from 1 micron to 20 microns, such as 5 microns, 10 microns or 15 microns.

[0070] Please continue reading Fig.14a and Fig.14b It should be understood that since the support wall 200 is formed by two supporting layers, the sacrificial layer forming the support wall 200 is also a double-layer structure. In the process of releasing the sacrificial layer, in order to improve efficiency, the layer of the sacrificial layer facing the back plate structure is released through the release hole array 700, while the layer facing the substrate 100 can be released through the acoustic cavity 800. Therefore, the release hole array 700 actually improves the contour of part of the inner wall of the support wall 200.

[0071] Figures 2 to 14b The following is a schematic diagram of the structure corresponding to the corresponding steps of the method for preparing a MEMS microphone provided in this embodiment. Figures 2 to 14b The preparation method of the MEMS microphone is described in detail.

[0072] See also Figure 2 First, a substrate 100 is provided. For example, the substrate 100 is <100> The substrate 100 is a silicon wafer with a crystal orientation, and the doping type of the substrate 100 is N-type. However, it should be understood that the present invention has no limitation on the crystal orientation and doping type of the substrate 100.

[0073] Next, a first supporting layer 210 is formed on the substrate 100, and the first supporting layer 210 is, for example, a silicon oxide layer. The method for forming the first supporting layer 210 is, for example, to form a silicon oxide layer on the substrate 100 by thermal oxidation or chemical vapor deposition (CVD) as the first supporting layer 210. In this embodiment, a portion of the first supporting layer 210 will be used as a sacrificial layer to form a portion of the cavity, and the thickness of the first supporting layer 210 is, for example, 0.5 micrometers to 2 micrometers.

[0074] See also Figure 3 , a first groove 310 is formed on the surface of the first supporting layer 210, and the first groove 310 is composed of a plurality of sub-grooves arranged at intervals. In this embodiment, a resist layer is formed on the surface of the first supporting layer 210, and a pattern including an opening is formed in the resist layer by a photolithography process. The resist layer is used as a mask, and a selective etchant is used to remove the exposed portion of the first supporting layer 210, thereby forming the first groove 310. By controlling the etching time, the etching can be stopped after reaching a predetermined depth of the first supporting layer 210. After etching, the resist layer can be removed by ashing or dissolving in a solvent.

[0075] The first groove 310 is open on the surface of the first supporting layer 210 and extends downward. Observed from the surface of the first supporting layer 210, the shape of the first groove 310 is a concentric ring, for example, including 1 to 6 nested circular rings. In this embodiment, observed from the cross section of the first supporting layer 210, the shape of the first groove 310 is a square; as an optional embodiment, observed from the cross section of the first supporting layer 210, the shape of the first groove 310 is a trapezoid or a V-shape with a bottom size smaller than the opening size. The depth of the first groove 310 is, for example, 0.5 microns to 0.8 microns.

[0076] Preferably, the opening surface of the first groove 310 forms a smooth transition surface with the surface of the first support layer 210. To this end, an additional deposition step may be used to form a conformal cover layer, such as a thin oxide layer, to improve the morphology of the first groove 310 and obtain a smooth transition surface. The thickness of the cover layer is, for example, 0.1 micrometer to 2 micrometers.

[0077] See also Figure 4 , a vibration membrane 410 and a first contact point 420 are formed on the first supporting layer 210, and the vibration membrane 410 and the first contact point 420 are located in the same layer and are both composed of doped polysilicon. The method for forming the vibration membrane 410 and the first contact point 420 is, for example: using low pressure chemical vapor deposition (LPCVD) to deposit polysilicon on the first supporting layer 210, the deposition temperature is, for example, 570 degrees Celsius to 630 degrees Celsius; using photolithography and etching steps to pattern the polysilicon layer, so as to form the patterns of the vibration membrane 410 and the first contact point 420 in different regions of the polysilicon layer.

[0078] The vibration membrane 410 is conformally formed on the first supporting layer 210, so the vibration membrane 410 has a second groove 320 corresponding to the first groove 310, and the second groove 320 is used to define the middle part and the peripheral part of the vibration membrane 410. The part of the vibration membrane 410 corresponding to the first groove 310 and the second groove 320 is equivalent to a fold structure R, and the fold structure R continuously and conformally covers the first supporting layer 210 with the middle part and the peripheral part. Consistent with the shape of the first groove 310 and the second groove 320, the fold structure R is also a concentric annular fold.

[0079] See also Figure 5 and Figure 6 , forming a second support layer 220 on the vibration membrane 410, and forming a plurality of third grooves 330 on the upper surface of the second support layer 220. In this embodiment, the second support layer 220 is a silicon oxide layer. The method for forming the second support layer 220 is, for example, forming a silicon oxide layer on the vibration membrane 410 by a low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD) method as the second support layer 220. After the second support layer 220 is formed, for example, a chemical mechanical planarization process is used to flatten the upper surface of the second support layer 220.

[0080] A portion of the second supporting layer 220 will be used as a sacrificial layer to form a portion of the cavity, and the thickness of the second supporting layer 220 is also used to define the distance between the vibration membrane 410 and the back plate structure. The thickness of the second supporting layer 220 is selected according to the electrical and acoustic performance of the MEMS microphone, for example, 2 to 4 microns.

[0081] Next, a resist layer is formed on the surface of the second supporting layer 220, and a pattern including openings is formed in the resist layer by using a photolithography process. The resist layer is used as a mask, and a selective etchant is used to remove the exposed portion of the second supporting layer 220, thereby forming a plurality of third grooves 330. By controlling the etching time, the etching can be stopped when reaching a predetermined depth of the second supporting layer 220. After etching, the resist layer can be removed by ashing or dissolving in a solvent.

[0082] The third groove 330 is open on the surface of the second supporting layer 220 and extends downward. When viewed from the surface of the second supporting layer 220, the shape of the third groove 330 can be a polygonal hole such as a circular hole, a square hole or a triangular hole. When viewed from the cross section of the second supporting layer 220, the shape of the third groove 330 is a rectangle or a trapezoid or V-shape with a bottom surface size smaller than the opening surface size, which is used to define a protrusion formed in a subsequent step to prevent the back plate structure from adhering.

[0083] See also Figure 6 and Figure 7 , forming a first protective layer 510 on the second supporting layer 220. The method of forming the first protective layer 510 is, for example, forming a boron nitride layer on the second supporting layer 220 by a plasma enhanced chemical vapor deposition method.

[0084] The first protection layer 510 fills the third groove 330 to form a protrusion S. The shape of the protrusion S is consistent with the shape of the third groove 330 .

[0085] See also Figure 8 , a back plate electrode 521 and a second contact point 522 connected to the back plate electrode 521 are formed on the first protective layer 510. In this embodiment, the back plate electrode 521 and the second contact point 522 are located in the same layer and are both composed of doped polysilicon. The method of forming the back plate electrode 521 and the second contact point 522 is, for example, to form a doped polysilicon layer on a portion of the surface of the first protective layer 510 by low pressure chemical vapor deposition (LPCVD). Then, the polysilicon layer is patterned by photolithography and etching steps to form a pattern of the back plate electrode 521 and the second contact point 522 connected to the back plate electrode 521.

[0086] Please continue reading Figure 8 After forming the back plate electrode 521 , the first protective layer 510 and the second supporting layer 220 above the first contact point 420 are etched by a conventional semiconductor process etching method to form a fourth groove 340 , and the fourth groove 340 does not expose the surface of the first contact point 420 .

[0087] See also Fig. 9 , forming a second protective layer 530 on the back plate electrode 521. The method of forming the second protective layer 530 is, for example, forming a conformal boron nitride layer on the back plate electrode 521 by a plasma enhanced chemical vapor deposition (PECVD) method.

[0088] The first protective layer 510 , the back plate electrode 521 , and the second protective layer 530 constitute a back plate structure.

[0089] Furthermore, since the back plate electrode 521 is patterned, a portion of the second protective layer 530 is formed on the surface of the back plate electrode 521 and the second contact point 522 , and another portion is formed on the surface of the first protective layer 510 , and a portion of the fourth groove 340 is also filled.

[0090] See also Fig.10 , remove the second protection layer 530 in the fourth groove 340, and etch the second support layer 220 at the bottom of the fourth groove 340 to expose the first contact point 420, and then form a fifth groove 350 to expose the second contact point 522. It can be understood that the second support layer 220 at the bottom of the fourth groove 340 can protect the first contact point 420 in this step to prevent the first contact point 420 from being damaged by excessive etching.

[0091] See also Fig.10 and Fig.11 , a conductive material is filled in the fourth groove 340 and the fifth groove 350 as a conductive channel, and then a first pad 610 and a second pad 620 are respectively formed on the conductive channel formed by the fourth groove 340 and the fifth groove 350 as the lead layers of the two electrodes of the MEMS microphone. The method of forming the first pad 610, the second pad 620 and the conductive channel is, for example: a metal layer is formed on the surface of the second protective layer 530 by sputtering or evaporation, and the metal layer fills the fourth groove 340 and the fifth groove 350 and covers the surface of the second protective layer 530; a resist layer is formed on the surface of the metal layer, and a pattern including an opening is formed in the resist layer by a photolithography process. The resist layer is used as a mask, and a selective etchant is used to remove the exposed part of the metal layer. Due to the selectivity of the etchant, the etching uses the second protective layer 530 as a stop layer; after etching, the resist layer can be removed by ashing or dissolving in a solvent.

[0092] See also Fig.12 , forming a plurality of release holes penetrating the second protective layer 530, the back plate electrode 521 and the first protective layer 510, and the plurality of release holes constitute a release hole array 700. The method for forming the release holes is, for example: forming a resist layer on the surface of the second protective layer 530, and forming a pattern including openings in the resist layer by using a photolithography process; using the resist layer as a mask, and using a selective etchant to remove the exposed portions of the second protective layer 530, the back plate electrode 521 and the first protective layer 510, thereby forming the release holes. Due to the selectivity of the etchant, the second supporting layer 220 serves as a stop layer; after etching, the resist layer can be removed by ashing or dissolving in a solvent.

[0093] As an optional embodiment, a special deep groove etching machine may be used to form the release hole.

[0094] In this embodiment, the release hole array 700 includes an outermost circle release holes 710 and inner circle release holes 720 located inside the outermost circle release holes 710. The outermost circle release holes 710 are located at the outermost circle of the release hole array 700, and the second side of the outermost circle release holes 710 facing away from the center of the release hole array 700 is flatter than the first side facing the center of the release hole array 700; the inner circle release holes 720 are located inside the outermost circle release holes 710 and are distributed in an array. For ease of preparation, the outermost circle release holes 710 are circular cut holes.

[0095] See also Fig.13 , forming an acoustic cavity 800 in the substrate 100. In this embodiment, the substrate 100 is thinned to a design value, such as 350 microns to 450 microns, preferably 400 microns, by a chemical mechanical planarization process. Then, a resist layer is formed on the lower surface of the substrate 100, and a pattern containing an opening is formed in the resist layer by a photolithography process. Using the resist layer as a mask, a selective etchant is used to remove the exposed portion of the substrate 100, thereby forming the acoustic cavity 800. In this embodiment, the acoustic cavity 800 is an opening with an inverted trapezoidal cross-sectional shape along the thickness direction. Optionally, the acoustic cavity 800 can also be an opening with a square or hexagonal cross-sectional shape along the thickness direction. Due to the selectivity of the etchant, the first supporting layer 210 serves as a stop layer. After etching, the resist layer can be removed by ashing or dissolving in a solvent.

[0096] Optionally, the acoustic cavity 800 is formed by using a conventional Bosch process in MEMS technology and a special deep trench etcher.

[0097] See also Fig.13 and Fig.14a , a portion of the first supporting layer 210 is removed through the acoustic cavity 800, and a portion of the second supporting layer 220 is removed through the release hole array 700 to release the vibration membrane 410. In this embodiment, hydrofluoric acid is used as an etchant, and the acoustic cavity 800 and the release hole array 700 are used as an entry channel for the etchant. The first protective layer 510 and the second protective layer 530 are respectively used as protective films for the back plate electrode 521, so that the back plate electrode 521 will not be etched in this etching step.

[0098] By means of hydrofluoric acid vapor fumigation or hydrofluoric acid wet etching, the hydrofluoric acid contacts the first supporting layer 210 and the second supporting layer 220 with the release hole array 700 and the acoustic cavity 800 as channels, thereby removing a portion of the first supporting layer 210 and the second supporting layer 220, respectively, so that a portion of the upper and lower surfaces of the vibration membrane 410 are exposed again, thereby releasing the vibration membrane 410.

[0099] After removing a portion of the first supporting layer 210 and the second supporting layer 220, the remaining first supporting layer 210 and the second supporting layer 220 constitute a supporting wall 200. The supporting wall 200 encloses a cavity B, and the vibrating membrane 410 is suspended in the cavity B after being released, and the cavity B is divided into two parts, the upper and lower parts, and the cavity B, the release holes in the release hole array 700, and the sound cavity 800 are connected to each other, so as to provide an air flow channel during the vibration of the vibrating membrane 410.

[0100] In summary, in the MEMS microphone provided by the present invention, the supporting wall encloses a cavity, the vibrating membrane is suspended in the cavity and the edge extends into the supporting wall to be fixed. The release hole array on the back plate structure includes a plurality of release holes that penetrate the back plate structure and are connected to the cavity. In the process of releasing the sacrificial layer through the release hole array to form the supporting wall, the contour of the inner wall of the supporting wall will follow the contour of the outermost circle of release holes close to the supporting wall. The outermost circle of release holes in the release hole array is configured so that the second side facing away from the center of the release hole array is flatter than the first side facing the center of the release hole array, thereby smoothing the contour of the inner wall of the supporting wall, inhibiting the formation of sharp corners, preventing the sharp corners from piercing the vibrating membrane and causing the vibrating membrane to fall off, and improving the life and reliability of the device.

[0101] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the content of the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. A MEMS microphone, characterized in that: include: substrate; A supporting wall is disposed on the substrate and encloses a cavity; A vibration membrane is suspended in the cavity and its edge extends to be fixed in the supporting wall; A back plate structure, located on the supporting wall and covering the cavity; as well as, A release hole array, comprising a plurality of release holes penetrating the back plate structure and communicating with the cavity, wherein the outermost release holes in the release hole array have at least a first side and a second side, wherein the first side faces the center of the release hole array, and the second side faces away from the center of the release hole array, and the second side is flatter than the first side; The supporting wall includes two stacked supporting layers, the edge of the vibration membrane is clamped between the two supporting layers, and the back plate structure is located above the vibration membrane.

2. The MEMS microphone according to claim 1, wherein: The center of the cavity coincides with the center of the release hole array.

3. The MEMS microphone according to claim 1, wherein: The shapes and sizes of the release holes in the outermost circle are the same.

4. The MEMS microphone according to claim 1, wherein: The first side and the second side are both arc-shaped or straight-line-shaped.

5. The MEMS microphone according to claim 1, wherein: The outermost circle release holes are located on a virtual circle with the center of the release hole array as the center.

6. The MEMS microphone according to claim 5, characterized in that: The distances between adjacent release holes in the outermost circle are equal.

7. The MEMS microphone according to claim 1, wherein: The release holes inside the outermost circle release holes are inner circle release holes, and the inner circle release holes are arranged in a rectangular array, a honeycomb structure array or a concentric rotation array.

8. The MEMS microphone according to claim 1, wherein: The back plate structure has a release area corresponding to the cavity, and the release hole array is located in the release area.

9. The MEMS microphone according to any one of claims 1 to 8, characterized in that: The pore diameters of the release holes are all in a range of 1 micron to 20 microns.

10. The MEMS microphone according to any one of claims 1 to 8, characterized in that: The outermost circle release holes are one or more of circular cut holes, polygonal cut holes and elliptical cut holes, and the side corresponding to the cut edge is the second side.

11. The MEMS microphone according to claim 1, wherein: An acoustic cavity is formed in the substrate, and the acoustic cavity penetrates the substrate and communicates with the cavity.

12. The MEMS microphone according to claim 1, wherein: The back plate structure includes a first protective layer, a second protective layer and a back plate electrode located between the first protective layer and the second protective layer. The first protective layer is closer to the vibration membrane than the second protective layer.

13. The MEMS microphone according to claim 12, wherein: The first protection layer has a plurality of protrusions facing the cavity.

14. The MEMS microphone according to claim 12, wherein: Also includes: A first contact point is located in the same layer as the vibration membrane and is electrically connected to the vibration membrane; A second contact point is located in the same layer as the back plate electrode and is electrically connected to the back plate electrode; a first pad electrically connected to the first contact point via a conductive path penetrating the second protective layer, the first protective layer and at least a portion of the supporting wall; The second pad is electrically connected to the second contact point through a conductive path penetrating the second protective layer.

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