Abstract:
The invention relates to a capacitive MEMS microphone and a method for manufacturing the same. The microphone includes: a substrate; a first dielectric supporting layer on the substrate; a movable sensitive layer formed on the first dielectric supporting layer and having a movable diaphragm extending within the air; a backplate disposed over the movable sensitive layer and spaced from the movable diaphragm; a chamber recessed from and extending through the substrate and the first dielectric supporting layer; and an impact resisting device connecting to the movable diaphragm. The impact resisting device is exposed downwardly and disposed above the chamber. The movable sensitive layer has a number of anchors formed around the movable diaphragm, a number of flexible beams each of which is employed to connect one of the anchors to the movable diaphragm, and a bonding portion connecting to the anchor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the priority to Chinese Patent Application No. 201410391494.0, filed on Aug. 11, 2014 in the Chinese Intellectual Property Office, the disclosure of which is incorporated in its entirety herein by reference. 
     TECHNICAL FIELD 
     The present invention relates a microphone, particularly to a capacitive micro-electro-mechanical system (MEMS) microphone and a method for manufacturing the same. 
     BACKGROUND 
     The MEMS technology is an advanced technology with fast development speed in recent years. Compared with the electronic components manufactured by the traditional technology, the components manufactured by the MEMS technology have notable advantages in volume, power consumption, weight, and cost. Besides, the MEMS components can be of mass production through advanced semiconductor manufacturing process. Nowadays, the MEMS components are actually applied in pressure sensors, accelerometers, gyroscopes, and silicon microphones, and the like. 
     Generally, SMT technology for assembling a microphone to a circuit board needs to subject to high temperature. As for a conventional Electret Capacitor Microphone (ECM), it will become invalid because of leakage of electricity in high temperature working environment. Assembly of ECM can be achieved only via handwork. While, the capacitive MEMS microphone can subject to high temperature and can be assembled by SMT technology so that automatic assembly procedure can be used. Recently, more requirements, such as smaller-dimension, lower-cost, better-performance, of microphones are needed to be satisfied, simultaneously. 
     Therefore, it is required to provide an improved capacitive MEMS microphone. 
     SUMMARY 
     One objective of the present invention is to provide an improved capacitive micro-electro-mechanical system (MEMS) microphone, which is capable of improving resistance of impact. 
     To achieve the above objective, the present invention employs the following technical solution: A capacitive micro-electro-mechanical system (MEMS) microphone, includes: a substrate having a top surface and a bottom surface; a first dielectric supporting layer on the top surface of the substrate and defining an opening therewith; a movable sensitive layer formed on the first dielectric supporting layer and having a movable diaphragm extending within the air; a backplate disposed over the movable sensitive layer and spaced from the movable diaphragm; a chamber recessed from the bottom surface of the substrate and extending through the substrate and the first dielectric supporting layer to thereby expose the movable diaphragm, the chamber communicating with the opening of the first dielectric supporting layer; and an impact resisting device connecting to the movable diaphragm, the impact resisting device exposed downwardly within the opening of the first dielectric supporting layer and disposed above the chamber; wherein the movable sensitive layer comprises a plurality of anchors formed around the movable diaphragm which are fastened between the substrate and the backplate, a plurality of flexible beams each of which is employed to connect one of the anchors to the movable diaphragm, and a bonding portion connecting to the anchor. 
     As a further improvement of the present invention, the movable diaphragm is in shape of circle and the impact resisting device extends outwards from periphery of the movable diaphragm. 
     As a further improvement of the present invention, the impact resisting device is composed by a plurality of impact resisting members which are evenly positioned around the movable diaphragm. 
     As a further improvement of the present invention, the plurality of anchors are evenly positioned around the movable diaphragm, each of which connects to the movable diaphragm by the flexible beam. 
     As a further improvement of the present invention, the impact resisting members and the anchors are alternatively arranged. 
     As a further improvement of the present invention, the flexible beam is Z-shaped. 
     As a further improvement of the present invention, the anchor extends farther than a neighboring impact resisting member from the periphery of the movable diaphragm. 
     As a further improvement of the present invention, each impact resisting member is disposed over the substrate in a vertical direction. 
     As a further improvement of the present invention, it further comprises a second dielectric supporting layer assembled between the movable sensitive layer and the backplate. 
     As a further improvement of the present invention, the second dielectric supporting layer defines a room between the movable diaphragm and the backplate. 
     As a further improvement of the present invention, each of said impact resisting member comprises a distal portion extending from periphery of the movable diaphragm, a bearing portion formed on the backplate, and a buffer extending within the room and connecting the bearing portion and the distal portion. 
     As a further improvement of the present invention, the impact resisting member is disposed over the chamber and that the bearing portion, the buffer and the distal portion are arranged along a height direction of the microphone. 
     As a further improvement of the present invention, the backplate comprises a conductive layer and a frame layer. 
     As a further improvement of the present invention, an anti-adhering structure is provided on the conductive layer. 
     As a further improvement of the present invention, the anti-adhering structure is formed by a plurality of embossments which protrude from the backplate towards the movable diaphragm. 
     To achieve the above objective, the present invention also employs the following technical solution: a method for fabricating a capacitive micro-electro-mechanical system (MEMS) microphone, comprises the steps of: 
     S 1 : providing a substrate having a top surface and a bottom surface; 
     S 2 : depositing insulating material on the substrate to thereby form a first dielectric supporting layer; 
     S 3 : depositing conductive material on the first dielectric supporting layer to form a movable sensitive layer, then, defining a plurality of slits on the movable sensitive layer to form a movable diaphragm therebewteen, and forming a flexible beam on a periphery of the movable diaphragm, an anchor connecting to the flexible beam, a bonding portion connecting with the anchor, and an impact resisting device connecting with the movable diaphragm; 
     S 4 : depositing insulating material on the movable sensitive layer to form a second dielectric supporting layer; 
     S 5 : forming a conductive layer on the second dielectric supporting layer and defining a plurality of round-holes on the conductive layer; 
     S 6 : depositing insulating material on the conductive layer to form a frame layer and defining a plurality of through-holes on the frame layer, the through-holes positioned correspondingly to the plurality of round-holes, the conductive layer and the frame layer together forming a backplate, the round-holes and the through-holes constituting sound apertures; 
     S 7 : forming metallic conductive member on the bonding portion; 
     S 8 : silicon deep etching the substrate from the bottom surface to define a chamber, the chamber extending through out the substrate from the bottom surface to the top surface; and 
     S 9 : removing part material of the first dielectric supporting layer, via wet etching technology, to thereby expose the movable diaphragm from the bottom surface of the substrate and make the movable diaphragm and the flexible beam suspended; and removing part material of the second dielectric supporting layer between the movable diaphragm, the flexible beam and the backplate, to thereby define a room adjacent to the chamber, the impact resisting device suspending within the room. 
     As a further improvement of the present invention, the step S 4  comprises a step of defining recesses on the second dielectric supporting layer. 
     As a further improvement of the present invention, the conductive layer is formed at the recesses to thereby providing projections on the conductive layer correspondingly to the recesses, the projections projecting towards the movable diaphragm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a capacitive MEMS microphone according to one embodiment of the present invention; 
         FIGS. 2  is another cross-sectional view of the capacitive MEMS microphone shown in  FIG. 1  while from another aspect; 
         FIG. 3  is a perspective view of a movable sensitive layer of the capacitive MEMS microphone of  FIG. 1 ; 
         FIGS. 4-15  are schematic views showing a processing procedure of fabricating the capacitive MEMS microphone illustrated in  FIG. 1 , respectively; and 
         FIG. 16  is a cross-sectional view of the capacitive MEMS microphone according to the other embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIGS. 1 to 3 , as provided in one embodiment of the present invention, a capacitive micro-electro-mechanical system (MEMS) comprises a substrate  1  having a top surface  11  and a bottom surface  12 , a first dielectric supporting layer  2  assembled on the top surface  11  of the substrate  1 , a movable sensitive layer  3  disposed on the first dielectric supporting layer  2 , a second dielectric supporting layer  4  provided on the movable sensitive layer  3 , a conductive layer  5  provided on the second dielectric supporting layer  4 , a frame layer  6  provided on the conductive layer  5 , a metallic conductive member  71  and an impact resisting device  36  employed to prevent an undesired floating of the movable sensitive layer  3  which is subject to a large shock. The conductive layer  5  and the frame layer  6  together defines a backplate  8  which is above the movable sensitive layer  3 . 
     The substrate  1  can be formed by silicon or glasses which have metal material covered thereon. The first dielectic supporting layer  2  is positioned between the movable sensitive layer  3  and the substrate  1 , which is used to support the movable sensitive layer  3  on the substrate  1  and electrically isolate the movable sensitive layer  3  from the substrate  1 . A chamber  13  is defined between the substrate  1  and the first dielectric supporting layer  2 , which is recessed from the bottom surface  12  of the substrate  1  and extends towards the top surface  11  of the substrate  1 . The movable sensitive layer  3  is thereby exposed to the chamber  13 . The chamber  13  can be of either a circular shape or a rectangular shape. The shape of the chamber  13  can be designed according to actual requirement. The first dielectric supporting layer  2  comprises an opening  21  communicating with the chamber  13 . 
     Referring together to  FIGS. 1 to 3 , the movable sensitive layer  3  is positioned between the first dielectric supporting layer  2  and the second dielectric supporting layer  3 . The movable sensitive layer  3  includes a movable diaphragm  34  exposed and suspended in the chamber  13 , a plurality of anchors  31  formed around the movable diaphragm  34 , which are fastened between the backplate  8  and the substrate  1 , a plurality of flexible beams  33  each of which is employed to connect one of the anchors  31  to the movable diaphragm  34 , and a bonding portion  35  connecting to one of the anchors  31  for electrical signals transmission. The flexible beams  33  are also exposed downwardly to the chamber  13 . 
     In the preferred embodiment, the shape of the movable diaphragm  34  is provided correspondingly to the shape of the chamber  13 , which is in circle shape. Understandably, the movable diaphragm  34  can has other shapes. The flexible beams  33  and the anchors  31  are evenly disposed around the periphery of the movable diaphragm  34 . The flexible beams  33  are Z-shaped and comprises a first connecting portion  331  connecting to the peripheral edge of the movable diaphragm  34 , a second connecting portion  333  connecting the first connecting portion  331  and the corresponding anchor  31 , and a beam body  332  interconnecting the first connecting portion  331  and the second connecting portion  333 . In the preferred embodiment, the first connecting portion  331  and the second connecting portion  333  extend substantially along a radial direction of the movable diaphragm  34 . A slit  32  is defined between the movable diaphragm  34  and the beam body  332  and a groove is defined between the anchor  31  and the beam body  332 . By such slits  32  and grooves  37 , the flexible beams  33  provide enough space for buffer of undesired force. 
     The movable diaphragm  34  and the flexible beams  33  are suspended positioned, which together constitute a movable structure of the movable sensitive layer  3 . Under the sound pressure, the movable structure can be vibrated to thereby generate vary electric capacity. The anchors  31  are distributed around the movable diaphragm  34 , and are fastened to the substrate  1  through the first dielectric supporting layer  2 . 
     Together referring to  FIGS. 1 to 3 , in the preferred embodiment, the impact resisting device is composed by a plurality of impact resisting members  36  which is formed in a shape of projection  36 . The projection  36  extends into the opening  21  and suspends overhead the substrate  1  in a vertical direction. When the movable diaphragm  34  subjects to outside undesired shocks and then moves to the chamber  13 , the movement of the projection  36  is limited by the substrate  1  so as to limit the distance of the movable diaphragm  34  in an acceptable, designed range. Further, the flexible beams  33  are also protected to move in a limited range. 
     In the preferred embodiment, the impact resisting device  36  is formed on the periphery of the movable diaphragm  34  and extends along a radial direction. The impact resisting members  36  and the plurality of anchors  31  together with the corresponding flexible beams  33  are alternatively arranged. The anchor  31  extends farther than a neighboring impact resisting member  36  from the periphery of the movable diaphragm  34 . 
     Referring to  FIGS. 1 and 2 , the second dielectric supporting layer  4  is positioned between the movable sensitive layer  3  and the backplate  8 . A thickness of the seond dielectric supporting layer  4  effects the distance between of the movable sensitive layer  3  and the backplate  8 . The second dielectric supporting layer  4  defines a room  43  between the movable diaphragm  34  and the backplate  8 . Consequently, the movable diaphragm  34  and the conductive layer  5  of the backplate  8  achieve a capacity. The movable diaphragm  34  and the conductive layer  5  are regards as two electrode plates. 
     In the backplate  8 , round holes  52  and soldering points  54  are formed on the conductive layer  5 . The soldering point  54  electrically connects with the bonding portion  35 . The round hole  52  transmits sounds to the movable diaphragm  34  and provides path for corrosive liquid during releasing procedure. when fabricating the microphone The frame layer  6  is positioned above the conductive layer  5  and defines through holes  62  transmitting sounds to the movable diaphragm  34 . Also the through holes  62  provide paths for corrosive liquid during releasing procedure. The locations and the dimensions of the round holes  52  and the through holes  62  are the same to thereby together define sound holes. The sound holes can be circle or other shapes. An anti-adhering structure  53  is provided on the conductive layer  5 . In the preferred embodiment, the anti-adhering structure  53  is formed by a plurality of embossments which protrude from the backplate  8  towards the movable diaphragm  34 . The embossments  53  and the round holes  52  of the conductive layer  5  are alternatively arranged to thereby prevent the movable diaphragm  34  from adhering to the conductive layer  5 . The shapes of the embossment  53  can be either circle or rectangle. The frame layer  6  provides cutouts  61  locating above and exposing the bonding portion  35  and the soldering point  53 . The metallic conductive member  71  is positioned in the cutout  61  for signal transmission. Understandably, the frame layer  6  and the conductive layer can switch positions. 
     Turning to  FIG. 16 , according to the other embodiment of the present invention, the impact resisting device can be achieved by different structure compared to the first embodiment. In this embodiment, the impact resisting device includes a distal portion  91  connecting to a periphery edge of the movable diaphragm  34 , a bearing portion  93  positioned on the backplate  8 , and a buffer  92 . The buffer  92  is located in the room  43  of the second dielectric supporting layer  4  and connecting the distal portion  91  and the bearing portion  93 . The buffer  92  is overhead the chamber  13 . A bearing hole  95  is defined between the bearing portion  93  and other part of the backplate. In this embodiment, when the movable diaphragm  34  subjects to shock and moves to the chamber  13 , the buffer  93  can be stopped by the substrate  1  so as to protect the flexible beams  33  from destroy due to undesired large movement. 
     Referring together to  FIGS. 4 to 15 , a method of fabricating the capacitive MEMS microphone includes following steps. 
     Referring to  FIG. 4 , in step S 1 , a substrate  1  having a top surface  11  and a bottom surface  12  is provided. The substrate  1  can be formed by either silicon or glasses with metallic layer covered thereon. The substrate  1  is employed to provide supporting to others components. 
     Referring to  FIG. 5 , in step S 2 , a first dielectric supporting layer  2  is formed by depositing dielectric material on the top surface  11  of the substrate  1 . The dielectric material can be oxidized silicon. 
     Together referring to  FIGS. 3, 6 and 7 , in step S 3 , a movable sensitive layer  3  is formed by depositing conductive material on the first dielectric supporting layer  2 . The conductive material can be polysilicon, which makes the movable sensitive layer  2  conductive. Simultaneously, a plurality of slits  32  are defined on the movable sensitive layer  2  to form a movable diaphragm  34  therebewteen by lithography/photoetching, anisotropic etching. A flexible beams  33  on a periphery of the movable diaphragm  34 , an anchor  31  connecting to the flexible beam  33 , a bonding portion  35  connecting with the anchor  31 , and an impact resisting device  36  connecting with the movable diaphragm  34  are also formed. During forming procedure, the dimension of the movable diaphragm  34  is defined by the slit  32 . 
     Turning to  FIGS. 8 to 10 , in step S 4 , a second dielectric supporting layer  4  is formed on the movable sensitive layer  3  by depositing oxidized silicon thereon. S 4  comprises steps S 41  to S 43 . 
     Referring to  FIG. 8 , in step S 41 , the second dielectric supporting layer  4  is formed on the movable sensitive layer  3  by depositing oxidized silicon thereon. 
     Referring to  FIG. 9 , in step S 42 , by photoetching, etching mask, anisotropyic etching etc. technologies, a plurality of recesses  41  are defined on the second dielectric supporting layer  4 . The recesses  41  are overhead the movable diaphragm  34 . 
     Referring to  FIG. 10 , in step S 43 , by photoetching, the bonding portion  35  is exposed from the second dielectric supporting layer  4 . 
     Together referring to  FIGS. 1 and 11 , in step S 5 , by chemical vapor deposition (CVD) technology, polysilicon is deposited on the second dielectric supporting layer  4  to thereby form the conductive layer  5 . Then, by photoetching or etching, the round holes  52  and the soldering points  54  are defined. During forming the conductive layer  5 , the conductive material fills in the recesses  41  and the projections  54  are formed. The projections  54  are provided to prevent the backplate  8  from the movable diaphragm  34 . Understandably, the projections  53  are also formed overhead the movable diaphragm  34 . 
     Together referring to  FIGS. 12 and 13 , in step S 6 , by CVD technology, the dielectric material is deposited on the conductive layer  5  to thereby form the frame layer  6 . The dielectric material can be silicon nitride. Then, by photoetching or etching, the through holes  62  are formed on the frame layer  6 . The locations and the dimensions of the round holes  52  and the through holes  62  are same to thereby together define the sound holes. The embossments  53  and the sound holes are alternatively arranged to thereby prevent the movable diaphragm  34  from adhering to the conductive layer  5 . The sound holes are positioned overhead the movable diaphragm  34 . Simultaneously, in step S 6 , the cutouts  61  are formed and the bonding portion  35  and the soldering points  54  are exposed from the cutouts  61 . 
     Referring to  FIG. 14 , in step S 7 , by sputtering, photoetching, etching etc. technologies, the metallic conducive member  71  is formed and connects to the bonding portion  35 . 
     Referring to  FIGS. 15 , in step S 8 , by dual surface lithography and silicon deep etching, a part of the chamber  13  is formed on the bottom surface  12  of the substrate  1  and extends to the top surface  11 . In this step, the silicon deep etching is halted at the first dielectric supporting layer  2  which is deemed as a stopping layer. The shape and the dimension of the chamber  13  are designed according to the requirements, which can be either round or rectangle. 
     Referring to  FIGS. 1 and 2 , in step S 9 , wet etching is operated from the chamber  13  and the sound holes on the opposed side. Part of the first dielectric supporting layer  1  is removed and the movable diaphragm  34  is exposed from the chamber  13 . At this time, the movable diaphragm  34  and the flexible beams  33  are suspending. The impact resisting device or members  36  are suspended and located between the substrate  1  and the backplate  8 . The room  43  is formed by removing part of material from the dielectric supporting layer  4 , which is between the movable diaphragm  34 , the flexible beams  33  and the backplate  8 . The suspending, movable diaphragm  34  is worked as movable structure of the movable sensitive layer  3 . The movable diaphragm  34  and the backplate  8  are worked as two electrode plates correspondingly and define a capacitor therebetween. 
     In summary, the present invention of the capacitive MEMS microphone can fully release residual stresses deriving from the processing. In other words, the fabricating process does not affect the sensitivity of the capacitive MEMS microphone. Moreover, by employing flexible beams  33 , it is easily to obtain high sensitivity and high signal-noise ration (SNR) of the microphone while the dimensions of the chip should not be changed to be large. Further, the impact resisting device and the projections protect the movable diaphragm  34  and the flexible beams  33  from damages of any undesired shocks. 
     Additionally, by employing the present fabricating method, the dimensions of the capacitive MEMS microphone is reduced and the qualities of the microphones from different batches remains the same. Further, the stress from packaging procedure is reduced which may effect the sensitivity of the microphone. 
     Although some preferred embodiments of the present invention have been disclosed for illustration purpose, persons of ordinary skill in the art will appreciate that various improvements, additions, and replacements may be made without departing from the scope and spirit of the present invention as disclosed in the appended claims.