Abstract:
Systems and methods for preventing electrical leakage in a MEMS microphone. In one embodiment, the MEMS microphone includes a semiconductor substrate, an electrode, a first insulation layer, and a doped region. The first insulation layer is formed between the electrode and the semiconductor substrate. The doped region is implanted in at least a portion of the semiconductor substrate where the semiconductor substrate is in contact with the first insulation layer. The doped region is also electrically coupled to the

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/973,507, filed on Apr. 1, 2014 and titled “DOPED SUBSTRATE REGIONS IN MEMS MICROPHONES,” the entire contents of which is incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Embodiments of the invention relate to preventing electrical leakage between a semiconductor substrate and an electrode in a MEMS microphone. 
         [0003]    In a MEMS microphone, the overlap of an electrode (e.g., moveable membrane, stationary front plate) and a semiconductor substrate creates a susceptibility to electrical leakage from non-insulating particles (or other forms of leakage) that come into contact with the surfaces of both components. Insulating protection coatings are typically applied to MEMS microphones to prevent electrical leakage/shorts. However, conductive paths, caused by non-insulating particles, can be created during the manufacturing process prior to deposition of any coatings. 
       SUMMARY 
       [0004]    One embodiment of the invention provides a MEMS microphone. The MEMS microphone includes a semiconductor substrate, an electrode, a first insulation layer, and a doped region. The doped region is implanted in at least a portion of the semiconductor substrate where the semiconductor substrate is in contact with the first insulation layer. The doped region is electrically coupled to the electrode. In some implementations, the semiconductor substrate includes N-type majority carriers and the doped region includes P-type majority carriers. In other implementations, the semiconductor substrate includes P-type majority carriers and the doped region includes N-type majority carriers. In some implementations, the electrode includes at least one type of electrode selected from a group consisting of a moveable electrode and a stationary electrode. In some implementations, the MEMS microphone further includes an application specific integrated circuit. In some implementations, the doped region is electrically coupled to the application specific integrated circuit. In other implementations, the doped region is electrically coupled to an application specific integrated circuit that is external to the MEMS microphone. 
         [0005]    In another embodiment, a MEMS microphone with two insulation layers is provided. In one example, the MEMS microphone includes a semiconductor substrate, an electrode, a first insulation layer, a doped region, and a second insulation layer. The doped region is implanted in at least a portion of the semiconductor substrate where the semiconductor substrate is in contact with the first insulation layer. The doped region is electrically coupled to the electrode. The second insulation layer is formed between the semiconductor substrate and the doped region. The doped region includes a first plurality of majority carriers and the semiconductor substrate includes a second plurality of majority carriers. The first plurality of majority carriers and the second plurality of majority carriers include at least one type of majority carriers selected from a group consisting of P-type majority carriers and N-type majority carriers. In some implementations, the first plurality of majority carriers is a same type of majority carriers as the second plurality of majority carriers. In other implementations, the first plurality of majority carriers is a different type of majority carriers than the second plurality of majority carriers. 
         [0006]    The invention further provides a method for preventing electrical leakage in a MEMS microphone. In one embodiment, the method includes forming a first insulation layer between a semiconductor substrate and an electrode. The method also includes implanting a doped region into the semiconductor substrate such that the doped region is provided in at least a portion of the semiconductor substrate where the semiconductor substrate is in contact with the first insulation layer. The method further includes electrically coupling the electrode to the doped region. In some implementations, the method also includes implanting P-type majority carriers into the doped region and N-type majority carriers into the semiconductor substrate. In other implementations, the method also includes implanting N-type majority carriers into the doped region and P-type majority carriers into the semiconductor substrate. In some implementations, the electrode includes at least one type of electrode selected from a group consisting of a moveable electrode and a stationary electrode. In some implementations, the method further includes electrically coupling the doped region to an application specific integrated circuit that is internal to the MEMS microphone. In other implementations, the method further includes electrically coupling the doped region to an application specific integrated circuit that is external to the MEMS microphone. 
         [0007]    In another embodiment, the invention also provides a method for preventing electrical leakage in a MEMS microphone using, among other things, two insulation layers. In one example, the method includes forming a first insulation layer between a semiconductor substrate and an electrode. The method also includes implanting a doped region into the semiconductor substrate such that the doped region is provided in at least a portion of the semiconductor substrate where the semiconductor substrate is in contact with the first insulation layer. The method further includes electrically coupling the electrode to the doped region. The method also includes forming a second insulation layer between the semiconductor substrate and the doped region. In some implementations, the method further includes implanting a first plurality of majority carriers into the doped region and a second plurality of majority carriers into the semiconductor substrate. The first plurality of majority carriers and the second plurality of majority carriers include at least one type of majority carriers selected from a group consisting of P-type majority carriers and N-type majority carriers. In some implementations, the first plurality of majority carriers is a same type of majority carriers as the second plurality of majority carriers. In other implementations, the first plurality of majority carriers is a different type of majority carriers than the second plurality of majority carriers. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a cross-sectional side view of a conventional MEMS microphone. 
           [0010]      FIG. 2  is enlarged view of an area of  FIG. 1 . 
           [0011]      FIG. 3  is a cross-sectional side view of a MEMS microphone including a doped region. 
           [0012]      FIG. 4  is enlarged view of an area of  FIG. 3 . 
           [0013]      FIG. 5  is a cross-sectional side view of a MEMS microphone including a doped region. 
           [0014]      FIG. 6  is a cross-sectional side view of a MEMS microphone including a SOI layer. 
           [0015]      FIG. 7  is a cross-sectional side view of a MEMS microphone including a SOI layer. 
           [0016]      FIG. 8  is a cross-sectional side view of a MEMS microphone including an ASIC. 
           [0017]      FIG. 9  is a system level view of a MEMS microphone and an ASIC. 
           [0018]      FIG. 10  is a cross-sectional side view of a MEMS microphone including a doped region. 
           [0019]      FIG. 11  is a cross-sectional side view of a MEMS microphone including a doped region. 
           [0020]      FIG. 12  is a cross-sectional side view of a MEMS microphone including a doped region. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0022]    Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. 
         [0023]    It should also be noted that a plurality of different structural components may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific configurations illustrated in the drawings are intended to exemplify embodiments of the invention. Alternative configurations are possible. 
         [0024]      FIG. 1  illustrates a conventional MEMS microphone  100 . The conventional MEMS microphone  100  includes a moveable electrode  105  (e.g., membrane), a stationary electrode  110  (e.g., front plate), a semiconductor substrate  115 , a first insulation layer  120 , a second insulation layer  125 , and a third insulation layer  130 . The moveable electrode  105  overlaps the semiconductor substrate  115 . This overlaps creates a gap  135  between the moveable electrode  105  and the semiconductor substrate  115 . The gap  135  creates a susceptibility to electrical leakage from non-insulating particles that come into contact with the surfaces of both components and to or other forms of leakage. Non-insulating particles include, for example, small fragments or thin released beams of silicon from a sidewall of a hole in the semiconductor substrate  115  and organic particles from photoresist that is used in manufacturing the MEMS microphone  100 . 
         [0025]      FIG. 2  is an enlarged view of area  140  in  FIG. 1 . As illustrated in  FIG. 2 , an insulating protection coating  145  has been applied to the gap  135 . However, a non-insulating particle  150  is caught between the moveable electrode  105  and the semiconductor substrate  115 , causing a short. 
         [0026]    A MEMS microphone  300  includes, among other components, a moveable electrode  305 , a stationary electrode  310 , a semiconductor substrate  315 , a first insulation layer  320 , a doped region  325 , an inter-metal dielectric (“IMD”) layer  330 , and a passivation layer  335 , as illustrated in  FIG. 3 . The moveable electrode  305  overlaps the semiconductor substrate  315 . The stationary electrode  310  is positioned above the moveable electrode  305 . In some implementations, the first insulation layer  320  includes a field oxide. In other implementations, the first insulation layer  320  includes a different type of oxide. For example, the first insulation layer  320  may include a thermal or plasma-based oxide (e.g., low pressure chemical vapor deposition oxide, plasma-enhanced chemical vapor deposition oxide). The IMD layer  330  is positioned between the moveable electrode  305  and the stationary electrode  310 . The IMD layer  330  electrically isolates metal lines in a CMOS process. In some implementations, the IMD layer  330  includes un-doped tetraethyl orthosilicate. The passivation layer  335  is positioned adjacent to the IMD layer  330  and is coupled to the stationary electrode  310 . The passivation layer  335  protects the oxides from contamination and humidity. Contamination and humidity cause current leakage and degrades the electrical performance of transistors, capacitors, etc. In some implementations, the passivation layer  335  includes silicon nitride. In other implementations, the passivation layer  335  includes silicon dioxide. 
         [0027]    Acoustic and ambient pressures acting on the moveable electrode  305  cause movement of the moveable electrode  305  in the directions of arrow  345  and  350 . Movement of the moveable electrode  305  relative to the stationary electrode  310  causes changes in a capacitance between the moveable electrode  305  and the stationary electrode  310 . This changing capacitance generates an electric signal indicative of the acoustic and ambient pressures acting on the moveable electrode  305 . 
         [0028]      FIG. 4  is an enlarged view of area  340  in  FIG. 3 . The doped region  325  is implanted in the semiconductor substrate  315  such that it is in contact with the first insulation layer  320 . The doped region  325  is electrically coupled to the moveable electrode  305 . The semiconductor substrate  315  contains P-type majority carriers and the doped region  325  contains N-type majority carriers. In some implementations, the doped region  325  contains a concentration of approximately 1×10 16  cm −3  N-type majority carriers. In some implementations, the semiconductor substrate  315  contains N-type majority carriers and the doped region  325  contains P-type majority carriers. In some implementations, the doped region  325  contains a concentration of approximately 1×10 16  cm −3  P-type majority carriers. The doped region  325  prevents a non-insulating particle  345  from creating leakage paths in the gap  350  between the moveable electrode  305  and the semiconductor substrate  315 . P-type majority carriers include, for example, boron, aluminum, and any other group III element in the periodic table. N-type majority carriers include, for example, phosphorus, arsenic, and any other group V element in the periodic table. 
         [0029]    The concentration of majority carriers and the depth of the doped region  325  influences the maximum voltage and non-insulating particle size that the doped region  325  is capable of preventing electrical leakage from. For example, a 12 micrometer deep doped region  325  containing N-type majority carriers is able to prevent up to 100 volts of electrical leakage. In  FIG. 4 , the size of the non-insulating particle  345  is too small to create a leakage path between the moveable electrode  305  and the semiconductor substrate  315 .  FIG. 5  illustrates a non-insulating particle  355  that is large enough to create a leakage path between the moveable electrode  305  and the semiconductor substrate  315 . 
         [0030]    In some implementations, a MEMS microphone  600  includes, among other components, a moveable electrode  605 , a stationary electrode  610 , a semiconductor substrate  615 , a first insulation layer  620 , a doped region  625 , an IMD layer  630 , a passivation layer  635 , and a second insulation layer  640 , as illustrated in  FIG. 6 . The moveable electrode  605  is electrically coupled to the doped region  625 . The first insulation layer  620  includes a field oxide. The second insulation layer includes a silicon-on-insulator (“SOI”) wafer. The second insulation layer  640  is deposited between the semiconductor substrate  615  and the doped region  625 . The second insulation layer  640  provides electrical isolation between the semiconductor substrate  615  and the doped region  625 . Both the semiconductor substrate  615  and the doped region  625  contain P-type majority carriers. In some implementations, both the semiconductor substrate  615  and the doped region  625  contain N-type majority carriers. 
         [0031]    In some implementations, a MEMS microphone  700  includes, among other components, a moveable electrode  705 , a stationary electrode  710 , a semiconductor substrate  715 , a first insulation layer  720 , a doped region  725 , an IMD layer  730 , a passivation layer  735 , and a second insulation layer  740 , as illustrated in  FIG. 7 . The moveable electrode  705  is electrically coupled to the doped region  725 . The first insulation layer  720  includes a field oxide. The second insulation layer  740  includes an SOI wafer. The semiconductor substrate  715  contains P-type majority carriers and the doped region  725  contains N-type majority carriers. In some implementations, the semiconductor substrate  715  contains N-type majority carriers and the doped region  725  contains P-type majority carriers. 
         [0032]    In some implementations, a MEMS microphone  800  includes, among other components, a moveable electrode  805 , a stationary electrode  810 , a semiconductor substrate  815 , a first insulation layer  820 , a doped region  825 , an IMD layer  830 , a passivation layer  835 , and an application specific integrated circuit (“ASIC”)  840 , as illustrated in  FIG. 8 . The moveable electrode  805  is electrically coupled to the doped region  825 . The first insulation layer  820  includes a field oxide. The ASIC  840  is integrated into the MEMS microphone  800 , for example, in the IMD layer  830 . The ASIC  840  is electrically coupled to the doped region  825 . The doped region  825  can introduce parasitics (e.g., capacitance) between the doped region  825  and the semiconductor substrate  815 . In some implementations, the ASIC  840  is configured to support the added parasitics. In some implementations, the ASIC  840  is separate from the MEMS microphone  800 , as illustrated in  FIG. 9 . 
         [0033]    In some implementations, a MEMS microphone  1000  includes, among other components, a moveable electrode  1005 , a stationary electrode  1010 , a semiconductor substrate  1015 , a first insulation layer  1020 , a doped region  1025 , an IMD layer  1030 , and a passivation layer  1035 , as illustrated in  FIG. 10 . The first insulation layer  1020  includes a field oxide. The stationary electrode  1010  overlaps the semiconductor substrate  1015 . The moveable electrode  1005  is positioned above the stationary electrode  1010 . The stationary electrode  1010  is electrically coupled to the doped region  1025 . The IMD layer  1030  is positioned between the moveable electrode  1005  and the stationary electrode  1010 . The passivation layer  1035  is positioned adjacent to the IMD layer  1030  and is coupled to the moveable electrode  1005 . The semiconductor substrate  1015  contains P-type majority carriers and the doped region  1025  contains N-type majority carriers. In some implementations, the semiconductor substrate  1015  contains N-type majority carriers and the doped region  1025  contains P-type majority carriers. 
         [0034]    The MEMS microphones discussed above are designed for ASIC processes. Doped regions may also be used in a MEMS microphone  1100  designed for a non-ASIC process. In some implementations, the MEMS microphone  1100  includes, among other components, a moveable electrode  1105 , a stationary electrode  1110 , a semiconductor substrate  1115 , a first insulation layer  1120 , a doped region  1125 , and an IMD layer  1130 , as illustrated in  FIG. 11 . The moveable electrode  1105  is electrically coupled to the doped region  1125 . In some embodiments, the first insulation layer  1120  includes a field oxide. In other embodiments, the first insulation layer  1120  includes, for example, a different type of oxide, or a type of nitride. The moveable electrode  1105  overlaps the semiconductor substrate  1115 . The stationary electrode  1110  is positioned above the moveable electrode  1105 . The IMD layer  1130  is positioned between the moveable electrode  1105  and the stationary electrode  1110 . The IMD layer  1130  includes, for example, silicon oxide or nitride. 
         [0035]    In some implementations, the MEMS microphone  1200  includes, among other components, a moveable electrode  1205 , a stationary electrode  1210 , a semiconductor substrate  1215 , a doped region  1225 , and an IMD layer  1230 , as illustrated in  FIG. 12 . The moveable electrode  1205  does not overlap the semiconductor substrate  1215 . The moveable electrode  1205  is electrically coupled to the doped region  1205 . The stationary electrode  1210  is positioned above the moveable electrode  1205 . The IMD layer  1230  is positioned between the moveable electrode  1205  and the stationary electrode  1210 . The moveable electrode  1205  is physically coupled to the stationary electrode  1210  via the IMD layer  1230 . The IMD layer  1230  electrically isolates the moveable electrode  1205  from the stationary electrode  1210 . In some implementations, the IMD layer  1230  includes un-doped tetraethyl orthosilicate. In other implementations, the IMD layer  1230  includes, for example, silicon oxide or nitride. 
         [0036]    Thus, the invention provides, among other things, systems and methods of preventing electrical leakage in MEMS microphones. Various features and advantages of the invention are set forth in the following claims.