Abstract:
A method to protect an acoustic port of a microelectromechanical system (MEMS) microphone is provided. The method includes: providing the MEMS microphone; and forming a protection film, on the acoustic port of the MEMS microphone. The protection film has a porous region over the acoustic port to receive an acoustic signal but resist at least an intruding material. The protection film can at least endure a processing temperature of solder flow.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to microelectromechanical system (MEMS) microphone. More particularly, the present invention relates to the MEMS microphone with protection film from water, dust, et al. 
     2. Description of Related Art 
     MEMS chip, such as MEMS microphone, has a sensing diaphragm to sense the vibration of air pressure caused by acoustic signal, for example. The sensing diaphragm forms as a part of a sensing capacitor, so that the acoustic signal can be converted into electric signal. 
       FIG. 1  is a cross-sectional drawing, schematically illustrating a conventional MEMS chip. In  FIG. 1 , generally, a MEMS chip, such as a MEMS microphone, with diaphragm  58  is shown. The MEMS chip has a semiconductor substrate  40  and a dielectric structural layer  50  on the silicon substrate  40 . The semiconductor substrate  40  has a cavity  44  and several venting holes  48  in the active region  46 , which also serving a fixed electrode of a MEMS capacitor. The cavity  44  is connected with the chamber between the diaphragm  58  and the substrate  40  by the venting holes  48 , so that the diaphragm can vibrates with the acoustic signal, which is usually received by the cavity  44 . The dielectric structural layer  50  holds the diaphragm  58 . The diaphragm  58  senses the acoustic signal. The other circuit part  54  is also formed in the dielectric structural layer  50 . In fabrication, the dielectric structural layer  50  includes dielectric layer  52  and an etching stop layer  56  in multiple fabrication steps, to form the diaphragm  58  and the circuit part  54 . The A person with ordinary skill in the art can understand how the MEMS structure is formed by the fabrication process in multiple steps. 
     Generally, the MEMS chip is divided into two parts of backplate and diaphragm. Referring to  FIG. 1 , the basic structure of the backplate includes the substrate  40  and the diaphragm is formed in the dielectric structural layer  50 . In the following descriptions, the MEMS chip is then generally indicated by backplate and diaphragm as the two characteristic structures without showing the detail structure. 
       FIG. 2  is a drawing of cross-sectional view, schematically illustrating a conventional MEMS microphone. In  FIG. 2 , the MEMS chip  100  includes the backplate  102  and the diaphragm  104 . The backplate  102  has a cavity  106  at one side to receive acoustic signal. The diaphragm  104  is disposed over the backplate  102  at a side opposite to the cavity. The backplate has a venting-hole layer  108  with multiple venting holes. A chamber is formed between the venting-hole layer  108  and the diaphragm  104 , in which the space of the chamber is connected with the space of the cavity  106  by the venting holes. The MEMS chip  100  may be further implemented with a cap structure  110  as a MEMS microphone, in which the cap structure  110  can be formed over the diaphragm  104  by the adhesive layer  112 , such as the glue layer. The cap structure  110  also has an auxiliary chamber  110   a , so as to help the vibration of the diaphragm  104  in response to the acoustic signal received from the cavity  106 . 
       FIG. 3  is a drawing of cross-sectional view, schematically illustrating a conventional MEMS microphone. In  FIG. 3 , another type of the conventional MEMS microphones in different structure may include a packaging board  120 . A MEMS chip  100  and an application-specific integrated circuit (ASIC)  122  are disposed on the packaging board  120  and are electrically bounded by, for example, bonding wires or other bonding technology known in the art. Then a cap structure  114  on the packaging board  120  covers over the MEMS chip  100  and the ASIC  122 . In order to receive the acoustic signal, the cap structure  114  has an acoustic port  116  to receive the acoustic signal. The auxiliary chamber  118  inside the cap structure  114  allows the diaphragm for more-easily vibrating with the acoustic signal. 
       FIG. 4  is a drawing of cross-sectional view, schematically illustrating a conventional MEMS chip. In  FIG. 4 , another type of the conventional MEMS microphones in different structure may include a packaging board  120 . The packaging board  120  has an acoustic port  116 . A MEMS chip  100  and an ASIC  122  are disposed on the packaging board  120  and are electrically bounded by, for example, bonding wires. However, the cavity of the MEMS chip  100  is matched to the acoustic port  116  of the packaging board  120 , so the cavity can receive the acoustic signal. A cap structure  114  on the packaging board  120  covers over the MEMS chip  100  and the ASIC  122 . In this situation, the cap structure  114  may need not the acoustic port. The auxiliary chamber  118  inside the cap structure  114  allows the diaphragm for more-easily vibrating with the acoustic signal. 
     The conventional MEMS chip can be designed in various manners, but not limited to the types described above. It should be noted that the vibration amplitude of the diaphragm would determine the sensitivity. However, the conventional MEMS chip during the subsequent fabrication processes, such as the process to packaging in circuit board, may receive intruding material between the diaphragm and the venting-hole layer and then reduce the performance of the diaphragm. 
     SUMMARY OF THE INVENTION 
     The disclosure provides MEMS microphone with protection film. The protection film can receive the acoustic signal but resist at least an intruding material. The performance of the diaphragm can maintain, reducing the effect caused by the intruding material. 
     In an embodiment, a method to protect an acoustic port of a microelectromechanical system (MEMS) microphone is provided. The method includes: providing the MEMS microphone; and forming a protection film, on the acoustic port of the MEMS microphone. The protection film has a porous region over the acoustic port to receive an acoustic signal but resist at least an intruding material. The protection film can at least endure a processing temperature of solder flow. 
     In an embodiment, a method to form microelectromechanical system (MEMS) microphones at wafer level comprises: Ruining a plurality of MEMS microphones on a wafer, wherein each of the MEMS microphones has a cavity or an acoustic port to receive an acoustic signal; and forming a protection film, disposed over the wafer, covering the acoustic port or the cavity of each of the MEMS microphones. The protection film has a porous region over the acoustic port or the cavity to receive the acoustic signal but resist at least an intruding material. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a process flow diagram, schematically illustrating a face detection method according to a preferred embodiment of the invention. 
         FIG. 2  is a drawing of cross-sectional view, schematically illustrating a conventional MEMS microphone. 
         FIG. 3  is a drawing of cross-sectional view, schematically illustrating a conventional MEMS microphone. 
         FIG. 4  is a drawing of cross-sectional view, schematically illustrating a conventional MEMS chip. 
         FIG. 5  is a drawing of cross-sectional view, schematically illustrating a mechanism considered in the invention about affecting the performance of MEMS chip. 
         FIGS. 6A-6B  are drawings of cross-sectional view and top view, schematically illustrating a structure of MEMS microphone, according to an embodiment of the invention. 
         FIGS. 7A-7B  are drawings of cross-sectional view and top view, schematically illustrating a structure of protection film of the MEMS microphone, according to an embodiment of the invention. 
         FIG. 8  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone, according to another embodiment of the invention. 
         FIG. 9  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone, according to another embodiment of the invention. 
         FIG. 10  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone, according to another embodiment of the invention. 
         FIG. 11  is a drawing, schematically illustrating a structure of MEMS microphone at wafer level, according to another embodiment of the invention. 
         FIG. 12  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone at wafer level, according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the disclosure, multiple embodiments of MEMS microphone are provided for descriptions. However, the present invention is not limited to the embodiments provided. 
     For a MEMS microphone, a protection film is proposed to be formed with MEMS chip as the MEMS microphone. The MEMS microphone can be MEMS microphone or a MEMS chip with diaphragm to detect acoustic signal, for example. 
     The performance of a MEMS chip with diaphragm to detect variance of air pressure caused by the acoustic signal is very depending on the capability of vibration of the diaphragm. If the diaphragm of the MEMS chip cannot vibrate with the acoustic signal at the required sensibility, the performance of the MEMS chip is reduced or even failed.  FIG. 5  is a drawing of cross-sectional view, schematically illustrating a mechanism considered in the invention about affecting the performance of MEMS chip. 
     In  FIG. 5 , as investigated in the invention, the performance of a conventional MEMS chip, such as the MEMS microphone in  FIG. 2 , may be reduced because the intruding material  130  may enter the space between the diaphragm  104  and the venting-hole layer  108 , and reduce the capability of vibration of the diaphragm  104 . The intruding material  130  may be any one of dust, liquid, water, et al., which may enter the MEMS chip in later application, particularly during the subsequent fabrication process, for example. In the structure of  FIG. 5  as an example, the intruding material  130  first enters from the cavity  106  of the MEMS chip and then enters the space between the diaphragm  104  and the venting-hole layer  108  of the backplate  102  when the cap structure  110  is glued on the MEMS chip by the glue layer  112 . Here, the cavity  106  may also be referred as an acoustic port. 
       FIGS. 6A-6B  are drawings of cross-sectional view and top view, schematically illustrating a structure of MEMS microphone, according to an embodiment of the invention. In  FIG. 6A , the MEMS microphone includes a MEMS microphone, like the one in  FIG. 2 . In order to prevent the intruding material  130  from entering into the space between the diaphragm  104  and the venting-hole layer as shown in  FIG. 5 . Basically, the MEMS microphone of the embodiment includes a MEMS chip, which has a backplate  102  and a diaphragm  104 . The backplate  102  has a venting-hole layer  108  and a cavity  106  at a first side to receive an acoustic signal. The diaphragm  104  is disposed over the backplate  102  at a second side opposite to the second side. A protection film  140  is disposed on the first side of the backplate  102 , covering over the cavity  106 . The protection film  140  has a porous region over the cavity  106  to receive the acoustic signal but resist at least an intruding material  130  from the environment as indicated by arrow. The cap structure  110  is adhered over the backplate  102  over the diaphragm  104  from the other side. The cap structure  110  has the auxiliary chamber  110   a  to allow the diaphragm to be more-easily vibrated with the acoustic signal. 
     In  FIG. 6B , the top views for the MEMS chip and the protection film  140  are also shown. The cavity  106  is covered by the protection film  140 . The protection film  140 , as shown in  FIG. 6A  and  FIG. 6B , includes an adhesive layer  160  and a protection layer  150 . The adhesive layer  160  is disposed on the backplate  102  at the first side. The adhesive layer  160  has an opening  162  for exposing the cavity  106  of the backplate  102 . In the embodiment, the opening  162  may be precisely aligned to the cavity  106 . However, it is not absolutely required to precisely align the opening  162  to the cavity  106 . A rough alignment in  FIG. 8  as another embodiment will be described later. The protection layer  150  is disposed on the adhesive layer  160 , in which the protection layer  150  has the porous region with a plurality of acoustic holes  154  over the opening  162  to receive the acoustic signal but resist the intruding material  130 . 
     It can be noted that the protection film  140  composited with the adhesive layer  160  and the protection layer  150  may be separately formed and then adhered to the backplate  102 . It can also be noted that the porous region of the protection layer  150  may be just a part region over the cavity  106 . However, for easy fabrication, the protection layer  150  may be a mesh layer with the acoustic holes  154 . Alternatively, the protection layer  150  may be a glass-fiber layer to for the mesh layer, in which the multiple spaces between the glass fibers foci the acoustic holes  154  to allow the acoustic signal to passes. However, if the size of the acoustic holes  154  is too small, a portion of the acoustic signal may be blocked, so the size in width of the acoustic holes  154  may be at least half of the wavelength of the acoustic signal or larger. However, the size should be smaller than the size of the venting holes of the venting-hole layer  108  to resist the possible intruding material  130 . 
     Further, the protection layer  150  and the adhesive layer  160  should also be able to endure the operation temperature of solder flow during subsequent fabrication process to form the electronic apparatus. The max. solder flow is 260° C. In an embodiment, the protection layer  150  and the adhesive layer  160  can at least endure a processing temperature of solder flow of 260° C. 
       FIGS. 7A-7B  are drawings of cross-sectional view and top view, schematically illustrating a structure of protection film of the MEMS microphone, according to an embodiment of the invention. In  FIG. 7A  and  FIG. 7B , the protection film  140  may be formed separately from the fabrication of the MEMS microphones. However, it is not the only way to fabricate the protection film  140 . The protection  150  may be a mesh layer formed by glass-fiber layer with the acoustic holes  154  to allow the acoustic signal, as indicated by arrows, to pass the acoustic holes  154 . Here, the effect region is corresponding to the opening  162  of the adhesive layer  160 , so the region  164  other then the opening  162  may need no the acoustic holes  154 . However, for easy fabrication, the protection layer  150  may be a mesh layer in full region as an embodiment. In addition, the protection film  140  includes the protection layer  150  and the adhesive layer  160  together, each of which is also shown in  FIG. 7B  in top view. The protection layer  150 , as an example, is a glass-fiber mesh layer. The adhesive layer  160  may be a glue layer but there is the opening  162 , which is corresponding to the cavity of the MEMS microphone in the embodiment. 
       FIG. 8  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone, according to another embodiment of the invention. In  FIG. 8 , in comparing with  FIG. 6A , the adhesive layer  160  of the protection layer  140  has the opening  162 , which is not precitely aligned with the cavity  106  of the backplate  102 . However, since the opening  162  still exposes the cavity, it still has sufficient number of acoustic holes  154  to let the acoustic signal pass but the intruding material  130  is effectively resisted to enter the cavity  106 . 
       FIG. 9  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone, according to another embodiment of the invention. In  FIG. 9 , the MEMS microphone  200  is based on the conventional MEMS microphone in  FIG. 3 . The ASIC  122  and the MEMS chip  100  are disposed on the packaging board  120 . The cap structure  114  is also disposed on the packaging board  120  to cover the ASIC  122  and the MEMS chip  100 . The acoustic port  116  of the cap structure  114  receives acoustic signal. However, the intruding material would be resisted by the protection film  140 , which is disposed on the cap structure  114  to cover the acoustic port  116 . 
       FIG. 10  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone, according to another embodiment of the invention. In  FIG. 10 , the packaging board  120  has an acoustic port  116 . The MEMS chip  100  and the ASIC  122  are disposed on the packaging board  120  and are electrically bounded by, for example, bonding wires. 
     It should be noted that the MEMS chip  100  has been implement with the protection film  140 , as shown in  FIG. 6A  and  FIG. 6B . The cavity of the MEMS chip  100  is matched to the acoustic port  116  of the packaging board  120 , so the MEMS chip  100  can receive the acoustic signal from the acoustic port  116  but the intruding material may be resisted by the protection film  140 . In this embodiment, the cap structure  114  may need no another acoustic port. However, if the cap structure  114  in  FIG. 9  is taken, another protection film may also be implemented. 
     With the aspect of the protection film, used in the MEMS microphone, when the MEMS microphones is at the semi-finished stage, such as the wafer-level stage, the protection film have already applied to the MEMS microphones. 
       FIG. 11  is a drawing, schematically illustrating a structure of MEMS microphone at wafer level, according to another embodiment of the invention. In  FIG. 11 , the MEMS microphones in semi-finished stage of wafer level, multiple MEMS units  252  with the MEMS chip to be cut into MEMS microphones have already been formed on the wafer  250 . Then, the protection film  140  is formed over the MEMS units  252 . Here, the MEMS units  252  may be one of the structures shown in  FIGS. 6A-6B ,  8 ,  9  and  10 , or even other conventional MEMS microphone not described in the disclosure. 
       FIG. 12  is a drawing of cross-sectional view, schematically illustrating a structure of MEMS microphone at wafer level, according to another embodiment of the invention. Taking the MEMS microphone shown in  FIG. 6A  as the example, in  FIG. 12 , the wafer  250 , serving as the backplate, has been formed with the venting-hole layers  108  and diaphragm  104  within each MEMS units  252 , which is to be cut into MEMS microphones later. The cap structures  114  have also formed over the wafer  250  in each MEMS units  252 . Usually, the process to cut the wafer into MEMS microphones may produce a big amount of dust and involving auxiliary materials, such as cooling water or any other liquid, which are main part of the intruding material. The protection film  140  is formed before cutting the MEMS units  252  at the wafer level stage, so can at least effectively prevent the intruding material from entering into the MEMS chips  100 . 
     The protecting film  140  has been proposed in use for particularly fabricating the MEMS chip. The intruding material can be effectively resisted to enter the MEMS chip. Even in later application of the MEMS microphone in other electronic apparatus, the protection film can still effectively prevent the intruding material into the MEMS chip. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.