MEMS MICROPHONE AND METHOD OF MANUFACTURING THE SAME

A MEMS microphone includes a substrate having a cavity, a diaphragm disposed above the cavity and having a ventilation path, and a back plate disposed above the diaphragm and having a plurality of air holes. The ventilation path includes a plurality of slits extending in a circumferential direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Korean Patent Application No. 10-2022-0064291, filed on May 25, 2022, 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 and a method of manufacturing the same. More specifically, the present disclosure relates to a MEMS microphone including a diaphragm and a back plate formed using semiconductor processing technology and a method of manufacturing the same.

BACKGROUND

A MEMS microphone may be manufactured by a semiconductor processing technology and may output a change in capacitance caused by a change in a distance between a diaphragm and a back plate as an electrical signal.

Specifically, the diaphragm may be vibrated by a sound pressure, and as a result, a change in the distance between the diaphragm and the back plate may occur. The diaphragm may include a lower electrode layer, and the back plate may include an upper electrode layer. Accordingly, the capacitance between the lower electrode layer and the upper electrode layer may be changed by the vibration of the diaphragm.

The capacitance may be proportional to areas of the lower electrode layer and the upper electrode layer and inversely proportional to a distance between the lower electrode layer and the upper electrode layer. Therefore, the sensitivity of the MEMS microphone may be improved by increasing the areas of the lower electrode layer and the upper electrode layer. However, there is a limit to increasing the areas of the lower electrode layer and the upper electrode layer when the size of the MEMS microphone is reduced.

In addition, when the size of the MEMS microphone is reduced, the elastic strength of the diaphragm may be increased. In such case, the vibration of the diaphragm due to the sound pressure may be reduced, and thus the sensitivity of the MEMS microphone may be lowered.

SUMMARY

The present disclosure provides a MEMS microphone with improved sensitivity and a method of manufacturing the same.

In accordance with an aspect of the present disclosure, a MEMS microphone may include a substrate having a cavity, a diaphragm disposed above the cavity and having a ventilation path, and a back plate disposed above the diaphragm and having a plurality of air holes. Particularly, the ventilation path may include a plurality of slits extending in a circumferential direction.

In accordance with some embodiments of the present disclosure, the MEMS microphone may further include a first anchor portion configured to surround the diaphragm and fixing the diaphragm on the substrate. In such case, the diaphragm may include a lower electrode layer made of a conductive material, and a ventilation region disposed between the lower electrode layer and the first anchor portion and through which the slits are formed.

In accordance with some embodiments of the present disclosure, the ventilation path may include inner slits adjacent to the lower electrode layer and extending in the circumferential direction, and outer slits adjacent to the first anchor portion and extending in the circumferential direction.

In accordance with some embodiments of the present disclosure, the ventilation path may further include first intermediate slits disposed between the inner slits and the outer slits and extending in the circumferential direction.

In accordance with some embodiments of the present disclosure, the ventilation path may further include second intermediate slits radially extending and connecting between the inner slits and the outer slits.

In accordance with some embodiments of the present disclosure, the ventilation path may further include third intermediate slits radially extending between the inner slits and the outer slits.

In accordance with some embodiments of the present disclosure, the ventilation path may further include first extending slits radially extending from ends of the inner slits toward the outer slits, and second extending slits radially extending from ends of the outer slits toward the inner slits.

In accordance with some embodiments of the present disclosure, the ventilation path may further include first branch slits radially extending from the inner slits toward the first anchor portion, and second branch slits radially extending from the outer slits toward the lower electrode layer.

In accordance with some embodiments of the present disclosure, the diaphragm may include a plurality of convex portions respectively corresponding to the air holes and protruding toward the back plate.

In accordance with some embodiments of the present disclosure, each of the convex portions may have a hollow truncated cone or hollow truncated pyramid shape.

In accordance with some embodiments of the present disclosure, the back plate may include a plurality of second convex portions configured to surround the air holes, respectively, and protruding in a same direction as the convex portions.

In accordance with some embodiments of the present disclosure, each of the convex portions may have an upper inclined surface, and each of the second convex portions may have a lower inclined surface corresponding to the upper inclined surface.

In accordance with another aspect of the present disclosure, a method of manufacturing a MEMS microphone may include forming a diaphragm having a ventilation path on a substrate, forming a back plate having a plurality of air holes above the diaphragm, and forming a cavity exposing the diaphragm through the substrate. Particularly, the ventilation path may include a plurality of slits extending in a circumferential direction.

In accordance with some embodiments of the present disclosure, forming the diaphragm may include forming a lower insulating layer on the substrate, partially removing the lower insulating layer to form a first anchor channel partially exposing the substrate, forming a lower silicon layer on the lower insulating layer and the first anchor channel, performing an ion implantation process to form a portion of the lower silicon layer into a lower electrode layer, and patterning the lower silicon layer to form the diaphragm and the ventilation path. In such case, the lower silicon layer may be patterned so that the diaphragm includes the lower electrode layer.

In accordance with some embodiments of the present disclosure, a portion of the lower silicon layer formed in the first anchor channel may function as a first anchor portion for fixing the diaphragm on the substrate, and the lower silicon layer may be patterned so that the first anchor portion remains in the first anchor channel.

In accordance with some embodiments of the present disclosure, the ventilation path may be formed through a ventilation region disposed between the lower electrode layer and the first anchor portion.

In accordance with some embodiments of the present disclosure, the diaphragm may be formed to include a plurality of convex portions respectively corresponding to the air holes and protruding toward the back plate.

In accordance with some embodiments of the present disclosure, forming the diaphragm may further include forming a mask layer on the substrate to cover portions where the convex portions are to be formed, performing an etching process using the mask layer as an etching mask to partially remove a surface portion of the substrate, and removing the mask layer. In such case, the lower insulating layer may be formed on the substrate after the mask layer is removed.

In accordance with some embodiments of the present disclosure, forming the back plate may include forming an upper insulating layer on the diaphragm, forming an upper silicon layer on the upper insulating layer, performing an ion implantation process to form a portion of the upper silicon layer into an upper electrode layer, removing another portion of the upper silicon layer to expose a portion of the upper insulating layer, and forming a support layer for supporting the upper electrode layer on the upper electrode layer and the exposed portion of the upper insulating layer.

In accordance with some embodiments of the present disclosure, forming the back plate may further include partially removing the upper insulating layer and the lower insulating layer to form a second anchor channel partially exposing the substrate. In such case, a portion of the support layer formed in the second anchor channel may function as a second anchor portion for fixing the back plate on the substrate.

In accordance with the embodiments of the present disclosure as described above, the ventilation path including the plurality of slits may be formed in the ventilation region. Accordingly, the elastic strength of the diaphragm may be reduced, thereby improving the sensitivity of the MEMS microphone. Further, the diaphragm may include the convex portions corresponding to the air holes formed through the back plate, thereby increasing an area of the lower electrode layer. In addition, the back plate may include the second convex portions corresponding to the convex portions, thereby increasing an area of the upper electrode layer. As a result, the capacitance of the MEMS microphone may be increased, and thus the sensitivity of the MEMS microphone may be significantly improved.

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.

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.1is a schematic plan view illustrating a MEMS microphone in accordance with an embodiment of the present disclosure, andFIG.2is a schematic cross-sectional view taken along a line II′-II″ as shown inFIG.1.

Referring toFIGS.1and2, a MEMS microphone100, in accordance with an embodiment of the present disclosure, may include a substrate102having a cavity104, a diaphragm132disposed above the substrate102to correspond to the cavity104, and a back plate162disposed above the diaphragm132and having a plurality of air holes194. The diaphragm132may be disposed above the substrate102to cover the cavity104. The cavity104may be formed to pass through the substrate102, and the diaphragm132may be exposed downward through the cavity104.

In accordance with an embodiment of the present disclosure, the MEMS microphone100may include a first anchor portion138configured to surround the diaphragm132and fixing the diaphragm132on the substrate102. The diaphragm132may include a lower electrode layer134made of a conductive material. For example, the lower electrode layer134may have a disk shape, and the first anchor portion138may have a circular ring shape. In addition, the diaphragm132may have a ventilation path146connecting an air gap between the diaphragm132and the back plate162with an inner space of the cavity104. For example, the diaphragm132may include a ventilation region144having a circular ring shape and disposed between the lower electrode layer134and the first anchor portion138, and the ventilation path146may be formed through the ventilation region144. In particular, the ventilation path146may include a plurality of slits extending in a circumferential direction.

FIGS.3to8are schematic enlarged plan views illustrating examples of a ventilation path as shown inFIG.2.

Referring toFIG.3, the ventilation path146may include a plurality of inner slits148A adjacent to the lower electrode layer134and extending in the circumferential direction, and a plurality of outer slits148B adjacent to the first anchor portion138and extending in the circumferential direction. Further, the ventilation passage146may include a plurality of first intermediate slits148C disposed between the inner slits148A and the outer slits148B and extending in the circumferential direction. In particular, the inner slits148A and the outer slits148B may be arranged to correspond to each other in a radial direction, and the first intermediate slits148C and the inner slits148A may be arranged to have a zigzag shape in the circumferential direction. Further, the first intermediate slits148C and the outer slits148B may be arranged to have a zigzag shape in the circumferential direction. Accordingly, the elastic strength of the diaphragm132may be reduced by the ventilation region144, and thus the sensitivity of the MEMS microphone100may be improved.

Referring toFIGS.4and5, the ventilation path146may include second intermediate slits148D radially extending and connecting between the inner slits148A and the outer slits148B. Further, the ventilation path146may include third intermediate slits148E radially extending between the inner slits148A and the outer slits148B. In such case, the third intermediate slits148E may be formed to cross the first intermediate slits148C.

Referring toFIG.6, the ventilation path146may include inner slits148F adjacent to the lower electrode layer134and extending in the circumferential direction, and outer slits148G adjacent to the first anchor portion138and extending in the circumferential direction. In such case, the inner slits148F and the outer slits148G may be arranged to have a zigzag shape in the circumferential direction.

Referring toFIG.7, the ventilation path146may include first extending slits148H radially extending from ends of the inner slits148F toward the outer slits148G, and second extending slits148J radially extending from ends of the outer slits148G toward the inner slits148F.

Referring toFIG.8, the ventilation path146may include first branch slits148K radially extending from the inner slits148F toward the first anchor portion138, and second branch slits148L radially extending from the outer slits148G toward the lower electrode layer134.

Referring again toFIGS.1and2, the diaphragm132may include a plurality of convex portions136. The convex portions136may correspond to the air holes194and may protrude toward the back plate162. In particular, as shown inFIG.2, the convex portions136may protrude toward the air holes194of the back plate162. For example, the convex portions136protrude upward from the lower electrode layer134and may be made of the same material as the lower electrode layer134. As an example, the lower electrode layer134and the convex portions136may be formed of impurity-doped polysilicon.

The MEMS microphone100may include a first electrode pad140electrically connected to the lower electrode layer134. As shown inFIG.1, the lower electrode layer134and the first electrode pad140may be electrically connected through a first connection pattern142. For example, the first electrode pad140and the first connection pattern142may be made of the same material as the lower electrode layer134.

The first anchor portion138may be disposed on an upper surface of the substrate102. For example, the first anchor portion138and the ventilation region144may be formed of undoped polysilicon.

The back plate162may include a support layer180made of an insulating material, and an upper electrode layer164attached to a lower surface of the support layer180and made of a conductive material. In particular, the back plate162may be disposed above the diaphragm132so that the upper electrode layer164is separated from the lower electrode layer134by a predetermined distance. For example, the upper electrode layer164may be formed of impurity-doped polysilicon, and the support layer180may be formed of silicon nitride.

The MEMS microphone100may include a second anchor portion184for fixing the back plate162on the substrate102, and a second electrode pad166electrically connected to the upper electrode layer164. As shown inFIG.2, the second anchor portion184may be disposed on the upper surface of the substrate102and may be made of silicon nitride. As shown inFIG.1, the upper electrode layer164and the second electrode pad166may be electrically connected through a second connection pattern168. For example, the second electrode pad166and the second connection pattern168may be made of the same material as the upper electrode layer164.

The first anchor portion138may have a circular ring shape surrounding the cavity104, and the second anchor portion184may have a circular ring shape surrounding the first anchor portion138.

A lower insulating layer120may be disposed on the upper surface of the substrate102, and an upper insulating layer150may be disposed on the lower insulating layer120. In such case, the first electrode pad140may be disposed on the lower insulating layer120, and the second electrode pad166may be disposed on the upper insulating layer150. For example, the lower insulating layer120and the upper insulating layer150may be made of silicon oxide and may be formed to surround the second anchor portion184.

A first bonding pad190may be disposed on the first electrode pad140through the upper insulating layer150and the support layer180, and a second bonding pad192may be disposed on the second electrode pad166through the supporting layer180. In addition, the support layer180may include protrusions182extending downward through the upper electrode layer164. The protrusions182may be made of the same material as the support layer180and may be used to prevent the lower electrode layer134and the upper electrode layer164from contacting each other.

In accordance with an embodiment of the present disclosure, each of the convex portions136may have a hollow truncated cone or hollow truncated pyramid shape. In particular, each of the convex portions136may have an upper inclined surface136A adjacent to a lower edge portion of each of the air holes194. As a result, the area of the lower electrode layer134may be increased, and thus the capacitance of the MEMS microphone100may be increased, and the sensitivity of the MEMS microphone100may be improved.

FIG.9is a schematic cross-sectional view illustrating a MEMS microphone in accordance with another embodiment of the present disclosure.

Referring toFIG.9, the back plate may include a plurality of second convex portions196formed to surround air holes198, respectively, and protruding in the same direction as the convex portions136. Each of the second convex portions196may have a hollow truncated cone or hollow truncated pyramid shape, and may have a lower inclined surface196A corresponding to the upper inclined surface136A of the convex portions136. In such case, each of the air holes198may be formed to pass through an upper portion of each of the second convex portions196.

As a result, the area of the upper electrode layer164may be increased, and thus the capacitance of the MEMS microphone100may be increased, and the sensitivity of the MEMS microphone100may be improved.

FIGS.10to24are schematic cross-sectional views illustrating a method of manufacturing the MEMS microphone as shown inFIG.2.

Referring toFIG.10, a mask layer110for forming a diaphragm132may be formed on a substrate102. For example, the mask layer110may be made of silicon oxide and may include patterns112corresponding to convex portions136of the diaphragm132. For example, after forming a silicon oxide layer (not shown) on the substrate102through a thermal oxidation process or a chemical vapor deposition process, a photoresist pattern (not shown) may be formed on the silicon oxide layer. Then, the mask layer110may be formed from the silicon oxide layer by performing an anisotropic etching process using the photoresist pattern as an etching mask. After forming the mask layer110, the photoresist pattern may be removed through a stripping process and/or an ashing process.

Referring toFIG.11, a surface portion of the substrate102may be partially removed by performing an etching process using the mask layer110as an etching mask. For example, a single crystal silicon substrate may be used as the substrate102, and the surface portion of the substrate102may be removed by wet etching process. In particular, a recess114having a plurality of protrusions116may be formed in the surface portion of the substrate102by the wet etching process. The protrusions116may have inclined side surfaces due to a difference in etching rate according to the crystal direction of the substrate102. For example, the surface portion of the substrate102may be partially removed through wet etching using an aqueous solution of potassium hydroxide (KOH) as an etchant. In addition, although not shown, after forming the recess114, the mask layer110may be removed through an etching process.

Referring toFIG.12, a lower insulating layer120may be formed on the substrate102. For example, the lower insulating layer120may include silicon oxide and may be formed conformally, that is, to have a substantially uniform thickness through a chemical vapor deposition process. Then, a first anchor channel122having a circular ring shape surrounding the recess114may be formed by patterning the lower insulating layer120. For example, after forming a photoresist pattern exposing a portion where the first anchor channel122is to be formed on the lower insulating layer120, the first anchor channel122exposing a portion of an upper surface of the substrate102may be formed by performing an etching process using the photoresist pattern as an etching mask.

Referring toFIG.13, a lower silicon layer130may be conformally formed on the lower insulating layer120to have a substantially uniform thickness. For example, the lower silicon layer130may be a polysilicon layer formed through a chemical vapor deposition process. In particular, a portion of the lower silicon layer130formed in the first anchor channel122may be used as a first anchor portion138for fixing a diaphragm132to be formed subsequently on the substrate102. Further, convex portions136protruding upward may be formed in the lower silicon layer130by the protruding portions116in the recess114.

Referring toFIG.14, a portion of the lower silicon layer130may be formed into a lower electrode layer134having conductivity by performing an ion implantation process. In addition, a first electrode pad140and a first connection pattern142(refer toFIG.1) for connecting the lower electrode layer134and the first electrode pad140may be formed in the lower silicon layer130by the ion implantation process. In particular, a portion of the lower silicon layer130including the convex portions136may be formed into the lower electrode layer134, and thus the convex portions136may function as a part of the lower electrode layer134.

Referring toFIG.15, the lower silicon layer130may be patterned so that a diaphragm132including the lower electrode layer134, the first electrode pad140, and the first connection pattern142remain on the lower insulating layer120. Further, the first anchor portion138for fixing the diaphragm132on the substrate102may be formed on the portion of the substrate102exposed by the first anchor channel122by patterning the lower silicon layer130. In particular, a portion of the lower silicon layer130between the lower electrode layer134and the first anchor portion138may function as a ventilation region144, and a ventilation path146including a plurality of slits may be formed through the ventilation region144by patterning the lower silicon layer130. For example, after forming a photoresist pattern for forming the diaphragm132, the first anchor portion138, the first electrode pad140, the first connection pattern142, and the ventilation path146on the lower silicon layer130, an etching process using the photoresist pattern as an etching mask may be performed until the lower insulating layer120is exposed.

Referring toFIG.16, an upper insulating layer150may be formed on the diaphragm132, the first anchor portion138, the first electrode pad140, the first connection pattern142, and the lower insulating layer120. For example, the upper insulating layer150may include silicon oxide and may be formed conformally to have a substantially uniform thickness through a chemical vapor deposition process. Subsequently, an upper silicon layer160may be conformally formed on the upper insulating layer150to have a substantially uniform thickness. For example, the upper silicon layer160may be a polysilicon layer formed through a chemical vapor deposition process.

Referring toFIG.17, an ion implantation process may be performed to form the upper silicon layer160into a conductive layer (not shown), that is, a polysilicon layer doped with impurities. The conductive layer may be patterned to form an upper electrode layer164corresponding to the lower electrode layer134, a second electrode pad166, and a second connection pattern168(refer toFIG.1) for connecting the upper electrode layer164and the second electrode pad166. That is, remaining portions of the conductive layer other than the upper electrode layer164, the second electrode pad166, and the second connection pattern168may be removed. For example, after forming a photoresist pattern on the conductive layer to expose portions of the conductive layer except for portions where the upper electrode layer164, the second electrode pad166, and the second connection pattern168are to be formed, an etching process using the photoresist pattern as an etching mask may be performed until the upper insulating layer150is exposed.

Referring toFIG.18, a plurality of holes170for forming protrusions182(refer toFIG.2) extending toward the lower electrode layer134may be formed by removing portions of the upper electrode layer164and the upper insulating layer150. The holes170may have a predetermined depth extending into the upper insulating layer150through the upper electrode layer164. For example, after forming a photoresist pattern exposing portions of the upper electrode layer164where the holes170are to be formed, an anisotropic etching process using the photoresist pattern as an etching mask may be performed for a predetermined time.

Referring toFIG.19, the upper insulating layer150and the lower insulating layer120may be patterned to form a second anchor channel172having a circular ring shape surrounding the first anchor portion138. For example, after forming a photoresist pattern exposing portions of the upper insulating layer150where the second anchor channel172is to be formed, an anisotropic etching process using the photoresist pattern as an etching mask may be performed until the upper surface of the substrate102is exposed.

Referring toFIG.20, after forming the second anchor channel172, a support layer180may be conformally formed on the upper electrode layer164and the upper insulating layer150to have a substantially uniform thickness. As a result, a back plate162including the upper electrode layer164and the support layer180may be formed on the substrate102. For example, the support layer180may be a silicon nitride layer formed by a chemical vapor deposition process. In particular, the support layer180may be formed to fill the holes170, and thus the protrusions182extending downward from the support layer180through the upper electrode layer164may be formed. In addition, a portion of the support layer180formed in the second anchor channel172may be used as a second anchor portion184for fixing the support layer180on the substrate102.

Referring toFIG.21, a first opening186and a second opening188may be formed to expose the first electrode pad140and the second electrode pad166, respectively, by patterning the support layer180and the upper insulating layer150. For example, after forming a photoresist pattern exposing portions of the support layer180corresponding to the first electrode pad140and the second electrode pad166, the first opening186and the second opening188may be formed through an anisotropic etching process using the photoresist pattern as an etching mask.

Referring toFIG.22, a first bonding pad190and a second bonding pad192may be formed on the first electrode pad140and the second electrode pad166, respectively. For example, the first bonding pad190and the second bonding pad192may be made of metal such as aluminum and may be formed by forming an aluminum layer on the support layer180and then patterning the aluminum layer.

Referring toFIG.23, a plurality of air holes194may be formed by patterning the support layer180and the upper electrode layer164. In particular, the air holes194may be formed to correspond to the convex portions136, respectively. For example, after forming a photoresist pattern exposing portions of the supporting layer180where the air holes194are to be formed, the air holes194may be formed through an anisotropic etching process using the photoresist pattern as an etching mask.

Referring toFIG.24, a back grinding process for reducing the thickness of the substrate102may be performed, and a cavity104penetrating the substrate102may then be formed. The cavity104may be formed to correspond to the diaphragm132by an anisotropic etching process.

Referring again toFIG.2, after forming the cavity104, a portion of the lower insulating layer120and a portion of the upper insulating layer150formed inside the second anchor portion184may be removed through a wet etching process. In such case, while the wet etching process is performed, the etchant may be supplied between the diaphragm132and the back plate162through the air holes194and the ventilation path146.

As another example, as shown inFIG.9, the back plate162may include second convex portions196formed by the convex portions136, and air holes198may be formed through upper portions of the second convex portions196.

In accordance with the embodiments of the present disclosure as described above, the ventilation path146including the plurality of slits may be formed in the ventilation region144. Accordingly, the elastic strength of the diaphragm132may be reduced, thereby improving the sensitivity of the MEMS microphone100. Further, the diaphragm132may include the convex portions136corresponding to the air holes194formed through the back plate162, thereby increasing an area of the lower electrode layer134. In addition, the back plate162may include the second convex portions196corresponding to the convex portions136, thereby increasing an area of the upper electrode layer164. As a result, the capacitance of the MEMS microphone100may be increased, and thus the sensitivity of the MEMS microphone100may be significantly improved.

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.