Patent Publication Number: US-2023138991-A1

Title: Mems microphone including diaphragm

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Korean Patent Application No. 10-2021-0145653, filed on Oct. 28, 2021, and all the benefits accruing therefrom under 35 U.S.C. § 119, the contents of which are incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a MEMS (Micro Electro Mechanical System) microphone. More specifically, the present disclosure relates to a MEMS microphone capable of converting a sound into an acoustic signal using a diaphragm configured to be vibrated by a sound pressure. 
     BACKGROUND 
     A MEMS microphone may be used to convert a sound into an acoustic signal and may be manufactured by a MEMS technology. For example, the MEMS microphone may include a diaphragm disposed above a substrate and a back plate disposed above the diaphragm. The diaphragm and the back plate may be supported by a plurality of anchors on the substrate, and a predetermined air gap may be provided between the diaphragm and the back plate. 
     The diaphragm may include a lower conductive layer used as a lower electrode, and the back plate may include an upper conductive layer used as an upper electrode, and an insulating layer formed on the upper conductive layer to support the upper conductive layer. The diaphragm may be vibrated by an applied sound pressure, whereby the air gap between the diaphragm and the back plate may be changed. Further, a capacitance between the diaphragm and the back plate may be changed by the change in the air gap, and the acoustic signal may be detected from the change in the capacitance. 
     The diaphragm may have a plurality of ventilation holes, and the back plate may have a plurality of air holes. After the MEMS microphone is manufactured, an air blowing test may be performed. Air may be sprayed toward the diaphragm while performing the air blowing test, and the air may pass through the ventilation holes and the air holes. 
     Particularly, when increasing the size and number of the ventilation holes to pass the air blowing test, the sensitivity of the MEMS microphone may be deteriorated. Contrary to the above, when reducing the size and number of the ventilation holes, the diaphragm may be damaged while performing the air blowing test. 
     SUMMARY 
     The present disclosure provides a MEMS microphone including an improved diaphragm to solve the above problems. 
     In accordance with an aspect of the present disclosure, a MEMS microphone may include a substrate having a cavity, a diaphragm disposed above the substrate to correspond to the cavity, and a back plate disposed above the diaphragm. Particularly, the diaphragm may have a plurality of ventilation holes, each of the ventilation holes may include a plurality of slits, and the slits may extend in a radial direction from a center of the each of the ventilation holes. 
     In accordance with some embodiments of the present disclosure, when air pressure is applied to the diaphragm, portions of the diaphragm between the slits may be bent by the air pressure so that a size of the ventilation holes is increased. 
     In accordance with some embodiments of the present disclosure, each of the ventilation holes may further include a circular central hole, and the slits may extend in the radial direction from the circular central hole. 
     In accordance with some embodiments of the present disclosure, the slits may have a triangular pyramid shape that gradually decreases in a width in the radial direction. 
     In accordance with some embodiments of the present disclosure, the slits may have a linear shape extending in the radial direction. 
     In accordance with some embodiments of the present disclosure, each of the ventilation holes may further include end holes respectively connected to end portions of the slits. 
     In accordance with some embodiments of the present disclosure, each of the ventilation holes may further include second slits respectively connected to end portions of the slits. 
     In accordance with some embodiments of the present disclosure, the second slits may have an arc shape, and the end portions of the slits may be respectively connected to central portions of the second slits. 
     In accordance with another aspect of the present disclosure, a MEMS microphone may include a substrate comprising a vibration area, a support area surrounding the vibration area, and a periphery area surrounding the support area, and having a cavity formed through the vibration area, a diaphragm disposed above the substrate to correspond to the cavity and having a plurality of ventilation holes, and a back plate disposed above the diaphragm and having a plurality of air holes. Particularly, each of the ventilation holes may include a circular central hole and a plurality of slits extending in a radial direction from the circular central hole. 
     In accordance with some embodiments of the present disclosure, the slits may have a triangular pyramid shape that gradually decreases in a width in the radial direction. 
     In accordance with some embodiments of the present disclosure, the slits may have a linear shape extending in the radial direction. 
     In accordance with some embodiments of the present disclosure, each of the ventilation holes may further include end holes respectively connected to end portions of the slits. 
     In accordance with some embodiments of the present disclosure, each of the ventilation holes may further include second slits respectively connected to end portions of the slits. 
     In accordance with some embodiments of the present disclosure, the second slits may have an arc shape, and the end portions of the slits may be respectively connected to central portions of the second slits. 
     In accordance with some embodiments of the present disclosure, the diaphragm may include a first electrode layer having a disk shape, a ventilation region configured to surround the first electrode layer and through which the ventilation holes are formed, and a first anchor portion configured to surround the ventilation region and configured to fix the diaphragm on the substrate. 
     In accordance with some embodiments of the present disclosure, the first anchor portion may be formed on the support area of the substrate. 
     In accordance with some embodiments of the present disclosure, the back plate may include a second electrode layer disposed above the first electrode layer to correspond to the first electrode layer, and a support layer formed on the second electrode layer and configured to support the second electrode layer. In such case, the support layer may include a second anchor portion configured to fix the support layer on the substrate. 
     In accordance with some embodiments of the present disclosure, the second anchor portion may be configured to surround the first anchor portion and may be formed on the support area of the substrate. 
     In accordance with some embodiments of the present disclosure, the MEMS microphone may further include a first insulating layer formed on the periphery area of the substrate, a first electrode pad formed on the first insulating layer and electrically connected to the first electrode layer, a second insulating layer formed on the first insulating layer and the first electrode pad, and a second electrode pad formed on the second insulating layer and electrically connected to the second electrode layer. 
     In accordance with some embodiments of the present disclosure, the MEMS microphone may further include a first bonding pad formed on the first electrode pad, and a second bonding pad formed on the second electrode pad. In such case, an edge portion of the support layer may be formed on the second insulating layer, the first bonding pad may be connected to the first electrode pad through the edge portion of the support layer and the second insulating layer, and the second bonding pad may be connected to the second electrode pad through the edge portion of the support layer. 
     In accordance with the embodiments of the present disclosure as described above, the slits may be opened when the air pressure is applied to the diaphragm. Thus, damage to the diaphragm may be prevented while the air blowing test is performed. Further, it is not necessary to increase the size and number of the ventilation holes to pass the air blowing test. Particularly, the slits may be opened only when the air pressure is applied to the diaphragm, and accordingly, it is possible to prevent the sensitivity of the MEMS microphone from being deteriorated. 
     The above summary of the present disclosure is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The detailed description and claims that follow more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a schematic plan view illustrating a MEMS microphone in accordance with an embodiment of the present disclosure; 
         FIG.  2    is a schematic cross-sectional view taken along a line I — I′ as shown in  FIG.  1   ; 
         FIG.  3    is a schematic enlarged plan view illustrating a ventilation hole as shown in  FIG.  1   ; 
         FIGS.  4  to  9    are schematic enlarged plan views illustrating other examples of the ventilation hole as shown in  FIG.  3   ; and 
         FIGS.  10  to  22    are schematic cross-sectional views illustrating a method of manufacturing the MEMS microphone as shown in  FIGS.  1  and  2   . 
     
    
    
     While various embodiments are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the claimed inventions to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the claims. 
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention are described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below and is implemented in various other forms. Embodiments below are not provided to fully complete the present invention but rather are provided to fully convey the range of the present invention to those skilled in the art. 
     In the specification, when one component is referred to as being on or connected to another component or layer, it can be directly on or connected to the other component or layer, or an intervening component or layer may also be present. 
     Unlike this, it will be understood that when one component is referred to as directly being on or directly connected to another component or layer, it means that no intervening component is present. Also, though terms like a first, a second, and a third are used to describe various regions and layers in various embodiments of the present invention, the regions and the layers are not limited to these terms. 
     Terminologies used below are used to merely describe specific embodiments, but do not limit the present invention. Additionally, unless otherwise defined here, all the terms including technical or scientific terms, may have the same meaning that is generally understood by those skilled in the art. 
     Embodiments of the present invention are described with reference to schematic drawings of ideal embodiments. Accordingly, changes in manufacturing methods and/or allowable errors may be expected from the forms of the drawings. Accordingly, embodiments of the present invention are not described being limited to the specific forms or areas in the drawings, and include the deviations of the forms. The areas may be entirely schematic, and their forms may not describe or depict accurate forms or structures in any given area, and are not intended to limit the scope of the present invention. 
       FIG.  1    is a schematic plan view illustrating a MEMS microphone in accordance with an embodiment of the present disclosure, and  FIG.  2    is a schematic cross-sectional view taken along a line I-I′ as shown in  FIG.  1   .  FIG.  3    is a schematic enlarged plan view illustrating a ventilation hole as shown in  FIG.  1   , and  FIGS.  4  to  9    are schematic enlarged plan views illustrating another example of the ventilation hole as shown in  FIG.  3   . 
     Referring to  FIGS.  1  and  2   , a MEMS microphone  100 , in accordance with an embodiment of the present disclosure, may include a substrate  102  having a cavity  104 , a diaphragm  130  disposed above the substrate  102  to correspond to the cavity  104 , and a back plate  180  disposed above the diaphragm  130 . 
     For example, the substrate  102  may be a single-crystal silicon substrate, and may include a vibration area (VA), a support area (SA) surrounding the vibration area (VA), and a periphery area (PA) surrounding the support area (SA). In such case, the cavity  104  may be formed to pass through the vibration area (VA), and the diaphragm  130  may be exposed through the cavity  104 . 
     In accordance with an embodiment of the present disclosure, the diaphragm  130  may be spaced apart from the substrate  102  to be vibrated by an applied sound pressure. For example, the diaphragm  130  may include a first electrode layer  132  made of a conductive material and having a disk shape, and a first anchor portion  138  configured to surround the first electrode layer  132  and to fix the first electrode layer  132  on the substrate  102 . For example, the first electrode layer  132  may be made of polysilicon doped with impurities, and the first anchor portion  138  may be made of undoped polysilicon. Further, the first anchor portion  138  may have a ring shape surrounding the first electrode layer  132  and may be formed on the support area (SA) of the substrate  102 . In particular, the first electrode layer  132  may be disposed above the substrate  102  to face the cavity  104  as shown in  FIG.  2   . 
     Particularly, the diaphragm  130  may include a ventilation region  142  having a circular ring shape surrounding the first electrode layer  132 . In such case, the first anchor portion  138  may have a circular ring shape surrounding the ventilation region  142 . In accordance with an embodiment of the present disclosure, the diaphragm  130  may have a plurality of ventilation holes  140  formed to pass through the ventilation region  142 . 
     Further, the diaphragm  130  may include a first electrode pad  134  electrically connected to the first electrode layer  132 . For example, the first electrode pad  134  may be connected to the first electrode layer  132  by a first connection pattern  136  as shown in  FIG.  1   . In this case, the first electrode pad  134  and the first connection pattern  136  may be made of the same material as the first electrode layer  132 . 
     The back plate  180  may include a support layer  172  made of an insulating material, and a second electrode layer  162  attached to a lower surface of the support layer  172  and made of a conductive material. In particular, the second electrode layer  162  may be disposed above the first electrode layer  132  to correspond to the first electrode layer  132 , and may have a disk shape. For example, the back plate  180  may be disposed above the diaphragm  130  so that the second electrode layer  162  is spaced apart from the first electrode layer  132  by a predetermined distance. That is, a predetermined air gap (AG) may be provided between the first electrode layer  132  and the second electrode layer  162 . For example, the second electrode layer  162  may be made of polysilicon doped with impurities, and the support layer  172  may be made of silicon nitride. 
     In addition, the back plate  180  may include a second anchor portion  176  for fixing the support layer  172  and the second electrode layer  162  on the substrate  102 , and a second electrode pad  164  electrically connected to the second electrode layer  172 . For example, as shown in  FIG.  2   , the second anchor portion  176  may be disposed on the support area (SA) of the substrate  102  and may be made of silicon nitride. The second electrode layer  162  and the second electrode pad  164  may be electrically connected by a second connection pattern  166  as shown in  FIG.  1   . Further, the second electrode pad  164  and the second connection pattern  166  may be formed of the same material as the second electrode layer  162 . 
     The first anchor portion  138  may have a circular ring shape surrounding the cavity  104 , and the second anchor portion  176  may have a circular ring shape surrounding the first anchor portion  138 . For example, each of the first anchor part  138  and the second anchor part  176  may have a channel shape with an open top as shown in  FIG.  2   . 
     The ventilation region  142  may be disposed between the first electrode layer  132  and the first anchor portion  138 , and the ventilation holes  140  may be connected to the air gap AG through the ventilation region  142 . As shown in  FIG.  1   , four ventilation holes  140  are formed through the ventilation region  142 , but the number of the ventilation holes  140  may be variously changed. 
     A first insulating layer  110  may be disposed on the periphery area (PA) of the substrate  102 , and a second insulating layer  150  may be disposed on the first insulating layer  110 . In this case, the first electrode pad  134  may be disposed on the first insulating layer  110 , and the second electrode pad  164  may be disposed on the second insulating layer  150 . For example, the first insulating layer  110  and the second insulating layer  150  may be made of silicon oxide, and may be formed to surround the second anchor portion  176 . 
     A first bonding pad  192  may be disposed on the first electrode pad  134 , and a second bonding pad  194  may be disposed on the second electrode pad  164 . For example, an edge portion of the support layer  172  may be formed on the second insulating layer  150 , the first bonding pad  192  may be connected to the first electrode pad  134  through the edge portion of the support layer  172  and the second insulating layer  150 , and the second bonding pad  194  may be connected to the second electrode pad  164  through the edge portion of the support layer  172 . 
     Specifically, a first contact hole (CH 1 ; refer to  FIG.  18   ) exposing the first electrode pad  134  may be formed through the edge portion of the support layer  172  and the second insulating layer  150 , and the first bonding pad  192  may be formed in the first contact hole (CH 1 ). Further, a second contact hole (CH 2 ; refer to  FIG.  18   ) exposing the second electrode pad  164  may be formed through the edge portion of the support layer  172 , and the second bonding pad  194  may be formed in the second contact hole (CH 2 ). 
     In addition, the support layer  172  may include protrusions  174  penetrating through the second electrode layer  162  and protruding toward the first electrode layer  132 . The protrusions  174  may be made of the same material as the support layer  172 , and may be used to prevent the first electrode layer  132  and the second electrode layer  162  from contacting each other. 
     Further, the back plate  180  may have a plurality of air holes  196  connected to the air gap (AG). The air holes  196  may be formed through the support layer  172  and the second electrode layer  162 . For example, the air holes  196  may be disposed among the protrusions  174 . 
     Referring to  FIG.  3   , each of the ventilation holes  140  may include a plurality of slits  140 A. The slits  140 A may extend in a radial direction from a center (C) of the each of the ventilation holes  140 . Particularly, when air pressure is applied to the diaphragm  130 , portions of the diaphragm  130  between the slits  140 A may be bent by the air pressure so that a size of the ventilation holes  140  is increased. For example, when an air blowing test is performed, an air may be sprayed to the diaphragm  130 , whereby an air pressure may be applied to the diaphragm  130 . In particular, portions of the ventilation region  142  between the slits  140 A may be bent by the air pressure, thereby opening the slits  140 A. That is, the ventilation holes  140  may be expanded by the air pressure, and accordingly, the air may easily pass through the expanded ventilation holes  140 . 
     As a result, damage to the diaphragm  130  may be prevented by the expanded ventilation holes  140  while the air blowing test is performed. In particular, the slits  140 A may be opened only when the air pressure is applied to the diaphragm  130 , and accordingly, the sensitivity of the MEMS microphone  100  may be prevented from being deteriorated. In addition, it is not necessary to increase the size and number of the ventilation holes  140 , and accordingly, the noise of the MEMS microphone  100  may be reduced. 
     As an example, as shown in  FIG.  3   , each of the slits  140 A may have a triangular pyramid shape that gradually decreases in a width in the radial direction, that is, in the extension direction of the slits  140 A. 
     As another example, as shown in  FIG.  4   , each of the ventilation holes  140  may include a circular central hole  140 B. In this case, the slits  140 A may extend in the radial direction from the circular central hole  140 B. 
     As still another example, as shown in  FIG.  5   , each of the ventilation holes  140  may include end holes  140 C respectively connected to end portions of the slits  140 A. In such case, the end holes  140 C may be used to prevent stress from being concentrated at the end portions of the slits  140 A. 
     As still another example, as shown in  FIG.  6   , each of the ventilation holes  140  may include second slits  140 D respectively connected to end portions of the slits  140 A. In such case, the second slits  140 D may be used to prevent stress from being concentrated at the end portions of the slits  140 A. For example, the second slits  140 D may have an arc shape, and the end portions of the slits  140 A may be respectively connected to central portions of the second slits  140 D. 
     As still another example, as shown in  FIG.  7   , each of the ventilation holes  140  may include a circular central hole  140 B and a plurality of slits  140 E extending in a radial direction from the circular central hole  140 B. In such case, the slits  140 E may have a linear shape extending in the radial direction. 
     As still another example, as shown in  FIG.  8   , each of the ventilation holes  140  may include end holes  140 C respectively connected to end portions of the slits  140 E. In such case, the end holes  140 C may be used to prevent stress from being concentrated at the end portions of the slits  140 E. 
     As still another example, as shown in  FIG.  9   , each of the ventilation holes  140  may include second slits  140 D respectively connected to end portions of the slits  140 E. In such case, the second slits  140 D may be used to prevent stress from being concentrated at the end portions of the slits  140 E. For example, the second slits  140 D may have an arc shape, and the end portions of the slits  140 E may be respectively connected to central portions of the second slits  140 D. 
       FIGS.  10  to  22    are schematic cross-sectional views illustrating a method of manufacturing the MEMS microphone as shown in  FIGS.  1  and  2   . 
     Referring to  FIG.  10   , a first insulating layer  110  may be formed on a substrate  102 . For example, the substrate  102  may be a silicon wafer, and the first insulating layer  110  may be made of an insulating material such as silicon oxide. The first insulating layer  110  may be formed conformally, that is, to have an approximately uniform thickness through a chemical vapor deposition process. 
     Referring to  FIG.  11   , the first insulating layer  110  may be patterned to form a first anchor channel  112  exposing a surface portion of the substrate  102 . The substrate  102  may include a vibration area (VA), a support area (SA) surrounding the vibration area (VA), and a periphery area (PA) surrounding the support area (SA), and the first anchor channel  112  may be formed on the support area (SA). In particular, the first anchor channel  112  may have a circular ring shape surrounding the vibration region (VA). For example, after forming a photoresist pattern exposing a portion where the first anchor channel  112  is to be formed on the first insulating layer  110 , an etching process using the photoresist pattern as an etching mask may be performed, whereby the first anchor channel  112  may be formed to expose a portion of the upper surface of the substrate  102 . 
     After forming the first anchor channel  112 , a first silicon layer  120  may be conformally formed on the first insulating layer  110  to have an approximately uniform thickness. For example, the first silicon layer  120  may be a polysilicon layer formed by a chemical vapor deposition process. In such case, a portion of the first silicon layer  120  formed in the first anchor channel  112  may be used as a first anchor portion  138  for fixing a diaphragm  130  to be formed subsequently on the substrate  102 . 
     Referring to  FIG.  12   , an ion implantation process may be performed to form a portion of the first silicon layer  120  into a first electrode layer  132  having conductivity. Further, a first electrode pad  134  and a first connection pattern  136  (refer to  FIG.  1   ) for connecting the first electrode layer  132  and the first electrode pad  134  may be formed in the first silicon layer  120  by the ion implantation process. For example, the first electrode layer  132  may have a disk shape and may be formed above the vibration area (VA). The first electrode pad  134  may be formed above the periphery area (PA). 
     Referring to  FIG.  13   , the first silicon layer  120  may be patterned to form a diaphragm  130  including the first electrode layer  132 , the first electrode pad  134 , and the first connection pattern  136 . In addition, a first anchor portion  138  for fixing the diaphragm  130  on the substrate  102  may be formed on a portion of the substrate  102  exposed by the first anchor channel  112 . 
     Particularly, a plurality of ventilation holes  140  may be formed between the first electrode layer  132  and the first anchor portion  138 . Specifically, a portion of the first silicon layer  120  between the first electrode layer  132  and the first anchor portion  138  may be used as a ventilation region  142 , and the ventilation holes  140  may be formed to pass through the ventilation region  142 . For example, the first electrode layer  132  may have a disk shape, and the ventilation region  142  may have a circular ring shape surrounding the first electrode layer  132 . 
     For example, a photoresist pattern covering portions where the first electrode layer  132 , the first electrode pad  134 , the first connection pattern  136 , and the first anchor portion  138  are to be formed may be formed on the first silicon layer  120 , and then, an etching process using the photoresist pattern as an etching mask may be performed until the first insulating layer  110  is exposed. Further, the photoresist pattern may expose portions of the first silicon layer  120  where the ventilation holes  140  are to be formed, and the ventilation holes  140  may be formed by the etching process. 
     Referring to  FIG.  14   , a second insulating layer  150  may be formed on the first insulating layer  110  and the diaphragm  130 . For example, the second insulating layer  150  may include silicon oxide, and may be formed conformally, that is, to have an approximately uniform thickness by a chemical vapor deposition process. 
     Referring to  FIG.  15   , a second silicon layer  160  may be conformally formed on the second insulating layer  150  to have an approximately uniform thickness. For example, the second silicon layer  160  may be a polysilicon layer formed by a chemical vapor deposition process. Subsequently, an ion implantation process may be performed to form the second silicon layer  160  into a conductive layer (not shown), that is, into a polysilicon layer doped with impurities. 
     Referring to  FIG.  16   , the conductive layer may be patterned to form a second electrode layer  162  corresponding to the first electrode layer  132 , a second electrode pad  164 , and a second connection pattern  166  (refer to  FIG.  1   ) for connecting the second electrode layer  162  and the second electrode pad  164 . That is, as shown in  FIG.  16   , remaining portions of the conductive layer excluding the second electrode layer  162 , the second electrode pad  164 , and the second connection pattern  166  may be removed. For example, a photoresist pattern may be formed on the conductive layer to cover regions where the second electrode layer  162 , the second electrode pad  164 , and the second connection pattern  166  are to be formed, and then, an etching process using the photoresist pattern as an etching mask may be performed until the second insulating layer  150  is exposed. 
     Then, a plurality of holes  168  for forming protrusions  174  (refer to  FIG.  2   ) extending toward the first electrode layer  132  may be formed by removing portions of the second electrode layer  162  and the second insulating layer  150 . The holes  168  may have a predetermined depth so as to extend through the second electrode layer  162  to a portion of the second insulating layer  150 . For example, after forming a photoresist pattern exposing portions where the holes  168  are to be formed on the second electrode layer  162 , an anisotropic etching process using the photoresist pattern as an etching mask may be performed for a predetermined time. 
     Referring to  FIG.  17   , a support layer  172  may be formed on the second insulating layer  150  and the second electrode layer  162 . For example, the second insulating layer  150  and the first insulating layer  110  may be patterned to form a second anchor channel  170  having a circular ring shape surrounding the first anchor portion  138 . For example, a photoresist pattern exposing portions where the second anchor channel  170  is to be formed may be formed on the second insulating layer  150 , and then, an anisotropic etching process using the photoresist pattern as an etching mask may be performed until the upper surface of the substrate  102  is exposed. 
     After the second anchor channel  170  is formed, a support layer  172  may be conformally formed on the second electrode layer  162  and the second insulating layer  150  to have an approximately uniform thickness. As a result, a back plate  180  including the second electrode layer  162  and the support layer  172  may be formed above the substrate  102 . For example, the support layer  172  may be a silicon nitride layer formed by a chemical vapor deposition process. In particular, the support layer  172  may be formed to fill the holes  168 , whereby protrusions  174  extending downward from the support layer  172  through the second electrode layer  162  may be formed. In addition, a portion of the support layer  172  formed in the second anchor channel  170  may be used as a second anchor portion  176  for fixing the support layer  172  on the substrate  102 . 
     Referring to  FIG.  18   , a first contact hole (CH 1 ) exposing the first electrode pad  134  may be formed by patterning the support layer  172  and the second insulating layer  150 . In addition, a second contact hole (CH 2 ) exposing the second electrode pad  164  may be formed by patterning the support layer  172 . For example, after forming a photoresist pattern exposing portions of the support layer  172  corresponding to the first electrode pad  134  and the second electrode pad  164  on the support layer  172 , the first contact hole (CH 1 ) and the second contact hole (CH 2 ) may be formed by an anisotropic etching process using the photoresist pattern as an etching mask. 
     Referring to  FIG.  19   , a first bonding pad  192  and a second bonding pad  194  may be respectively formed on the first electrode pad  134  and the second electrode pad  164 . For example, the first bonding pad  192  and the second bonding pad  194  may be made of a metal such as aluminum, and may be formed by forming an aluminum layer (not shown) on the support layer  172  and then patterning the aluminum layer. 
     Referring to  FIG.  20   , the support layer  172  and the second electrode layer  162  may be patterned to form a plurality of air holes  196 . For example, after forming a photoresist pattern exposing portions where the air holes  196  are to be formed on the support layer  172 , the air holes  196  may be formed by an anisotropic etching process using the photoresist pattern as an etching mask. 
     Referring to  FIG.  21   , a cavity  104  penetrating through the substrate  102  may be formed. For example, a back grinding process may be performed to reduce the thickness of the substrate  102 , and then a cavity  104  penetrating the substrate  102  may be formed. In this case, the cavity  104  may be formed to correspond to the diaphragm  130  and to expose the first insulating layer  110  by an anisotropic etching process. 
     Referring to  FIG.  22   , an air gap (AG) may be formed by partially removing the first and second insulating layers  110  and  150 . For example, a portion of the first insulating layer  110  and a portion of the second insulating layer  150  formed inside the second anchor portion  176  may be removed by an etching process. In such case, an etching solution or an etching gas may be supplied between the diaphragm  130  and the back plate  180  through the air holes  196  and the ventilation holes  140 . As a result, the diaphragm  130  may be exposed downwardly through the cavity  104 , and the air gap (AG) may be formed between the diaphragm  130  and the back plate  180 . 
     Although the example embodiments of the present disclosure have been described with reference to the specific embodiments, they are not limited thereto. Therefore, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the present disclosure defined by the appended claims.