Abstract:
Disclosed is a method for bonding semiconductor substrates, wherein an eutectic alloy does run off the bonding surfaces during the eutectic bonding. Also disclosed is an MEMS device which is obtained by bonding semiconductor substrates by this method. Specifically, a substrate ( 11 ) and a substrate ( 21 ) are eutectically bonded with each other by pressing and heating the substrate ( 11 ) and the substrate ( 21 ), while interposing an aluminum-containing layer ( 31 ) and a germanium layer ( 32 ) between a bonding part ( 30   a ) of the substrate ( 11 ) and a bonding part ( 30   b ) of the substrate ( 21 ) in such a manner that the aluminum-containing layer ( 31 ) and the germanium layer ( 32 ) overlap each other, with an outer edge ( 32   a ) of the germanium layer ( 32 ) being inwardly set back from the an outer edge ( 31   a ) of the aluminum-containing layer ( 31 ).

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a method of bonding by eutectic bonding of two semiconductor substrates and a MEMS device formed by the same. 
       BACKGROUND ART 
       [0002]    As a bonding method of these kinds of semiconductor substrates, a method has been known in which a silicon wafer formed with a MEMS structure has a germanium layer and a silicon wafer formed with integrated circuits has an aluminum containing layer, the germanium layer and the aluminum containing layer are faced to each other to be pressurized and heated, and an eutectic alloy made of the germanium and aluminum fixed to each other is formed (Patent Document 1).
   [Patent Document 1] U.S. Pat. No. 7,442,570   
 
       DISCLOSURE OF THE INVENTION 
     Problems that the Invention is to Solve 
       [0004]    In such a bonding method, in a case that the germanium layer and the aluminum containing layer are film-formed on a whole bonding surface of the semiconductor substrates, the eutectic alloy made of the germanium and the aluminum might be formed to be pressed out from the bonding surface by the pressurization. In other words, in this case, the eutectic alloy formed to be pressed out might be conducted to an electrode formed around the bonding surface of the semiconductor substrate, and there arises a problem such that a device is defective, making productivity lower. 
         [0005]    In view of the foregoing problem, it is an object of the invention to provide a method of bonding a semiconductor substrate without letting an eutectic alloy press out from a bonding surface in eutectic bonding and to provide a MEMS device formed by the same. 
       Means for Solving the Problems 
       [0006]    According to one aspect of the invention, there is provided a method of bonding a semiconductor substrate in which a first semiconductor substrate is bonded with a second semiconductor substrate by eutectic bonding with pressurization and heating, an aluminum containing layer primarily made of aluminum and a germanium layer in a polymer state being interposed between a bonding surface of the first semiconductor substrate and a bonding surface of the second semiconductor substrate. The method has a step of receding an outer end of the germanium layer inward with respect to an outer end of the aluminum containing layer as to the aluminum containing layer and the germanium layer in the polymer state. 
         [0007]    According to the structure above, since the outer end of the germanium layer is receded inward with respect to the outer end of the aluminum containing layer, a formed eutectic alloy does not protrude from the bonding surface even if the eutectic alloy in a melting state by the pressurization spreads to an outside. Therefore, undesirable conduction to an electrode can be avoided and productivity of the device can be improved. The length from the outer end of the aluminum containing layer to the receded outer end of the germanium layer is preferably equal to or less than 20 μm. Further, the aluminum containing layer and the germanium layer may be film-formed on either the first semiconductor substrate or the second semiconductor substrate. Still further, the aluminum containing layer and the germanium layer may be film-formed on a bonding surface of a same semiconductor substrate or on bonding surfaces of different semiconductor substrates. 
         [0008]    In this case, it is preferable that heating temperature and heating time of the pressurization and heating be controlled for alloying the germanium layer and the aluminum containing layer by eutectic bonding except an outer end portion of the aluminum containing layer. 
         [0009]    According to the structure above, it is possible to control an area where the eutectic alloy is formed accurately, and to efficiently avoid that the formed eutectic alloy protrudes from the substrates. 
         [0010]    In these cases, it is preferable that the aluminum containing layer and the germanium layer be film-formed on either the first semiconductor substrate or the second semiconductor substrate. 
         [0011]    According to the structure above, since a metal film does not need to be film-formed on the other semiconductor substrate, a film formation process before bonding the semiconductor substrate can be omitted, thereby a bonding process can be simplified. 
         [0012]    In this case, it is preferable that the aluminum containing layer be film-formed in a ring shape in planar view as having predetermined width, and the germanium layer have one or more strip layer sections film-formed in a ring shape in planar view on the aluminum containing layer. 
         [0013]    According to the structure above, since the eutectic alloy is formed consecutively in a direction orthogonal to an inner/outer direction of the semiconductor substrate, it is possible to bond the semiconductor substrate with high sealing characteristics. 
         [0014]    Further in this case, it is preferable that the aluminum containing layer be film-formed in a ring shape in planar view as having predetermined width, and the germanium layer have a strip layer section film-formed in a ring shape in planar view and a plurality of branch layer sections branched from the strip layer section on the aluminum containing layer. 
         [0015]    According to the structure above, since a total extension of a contact end of the germanium layer to the aluminum containing layer can be longer, the eutectic alloy formed by the heating and pressurization tends to fix on the first semiconductor substrate and bonding with high bonding strength can be performed. 
         [0016]    In these cases, it is preferable that the aluminum containing layer and the germanium layer be film-formed on the second semiconductor substrate and a pit be formed on the bonding surface of the first semiconductor substrate, in which a eutectic alloy generated by the pressurization and heating fills. 
         [0017]    According to the structure above, the eutectic alloy in the melting state formed in a vacuum by the heating and the pressurization fills in the pit by capillary phenomenon. This leads the eutectic alloy to spread in the pit thoroughly, thereby, since the eutectic alloy layer is formed to bite in the first semiconductor substrate, bonding strength of the bonding section can be increased. The pit formed in the first semiconductor substrate may be a plurality of apertures formed intermittently or a slit-like groove formed consecutively. 
         [0018]    According to the other aspect of the invention, there is provided a MEMS device bonded by the above bonding method of the semiconductor substrate. The first semiconductor substrate has a MEMS structure formed to be engraved at the bonding surface side thereof, and the second semiconductor substrate has an integrated circuit formed at the bonding surface side to control the MEMS structure. 
         [0019]    According to the structure, the substrates are bonded to avoid conduction to an undesired electrode, electric conducts of the MEMS structure, the integrated circuit and an outer circuit are maintained, and the MEMS structure and the integrated circuit are packaged integrally to protect against an outer environment such as moisture, temperature, dust and the like. Therefore, it is possible to provide a MEMS device having high precision. 
         [0020]    Further in this case, it is preferable that the MEMS sensor above is either one of an acceleration sensor, an angular velocity sensor, an infrared ray sensor, a pressure sensor, a magnetic sensor and a sonic sensor. 
         [0021]    According to the structure above, with the efficient package, it is possible to provide the acceleration sensor, the angular velocity sensor, the infrared ray sensor, the pressure sensor, the magnetic sensor and the sonic sensor having high precision. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIGS. 1A and 1B  are schematic appearance perspective views of a MEMS chip and a CMOS chip according to an embodiment. 
           [0023]      FIG. 2  is a schematic perspective view of a MEMS device according to the embodiment. 
           [0024]      FIGS. 3A and 3B  are cross sectional views illustrating film formation arrangement of an aluminum containing layer and a germanium layer according to the embodiment. 
           [0025]      FIG. 4  is a table describing film thickness of the aluminum containing layer and the germanium layer, a weight ratio of the germanium layer to the aluminum containing layer, and numeric values of a sealing ratio and share strength (bonding strength) of a bonding section. 
           [0026]      FIGS. 5A and 5B  are graphs illustrating relationships among a weight ratio of the germanium layer to the aluminum layer, the sealing ratio and the share strength of the bonding section after eutectic bonding. 
           [0027]      FIG. 6A  is an elevation view and  FIG. 6B  is a cross sectional view illustrating film formation arrangement of the aluminum containing layer and the germanium layer according to a first modification of the embodiment. 
           [0028]      FIG. 7A  is an elevation view and  FIG. 7B  is a cross sectional view illustrating film formation arrangement of the aluminum containing layer and the germanium layer according to a second modification of the embodiment. 
           [0029]      FIG. 8A  is an elevation view and  FIG. 8B  is a cross sectional view illustrating film formation arrangement of the aluminum containing layer and the germanium layer according to a third modification of the embodiment. 
           [0030]      FIG. 9A  is an elevation view and  FIGS. 9B and 9C  are cross sectional views illustrating film formation arrangement of the aluminum containing layer and the germanium layer according to the other embodiment. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0031]    Referring to the accompanying drawings, a method of bonding a semiconductor and a MEMS device according to one embodiment of the invention will be explained. In the method of bonding a semiconductor substrate according to the embodiment, a MEMS wafer having a number of sensing sections is faced to a CMOS wafer having a number of integrated circuits each of which controls each sensing section to bond by eutectic bonding via metal. In other words, in the invention, the formed MEMS sensor and the integrated circuits are formed in separate processes to face each other and are bonded by eutectic bonding. In the eutectic bonding, a wafer level package technology (WLP technology) is used, by which wafers are sealed collectively as they are, and then are cut off into each chip. 
         [0032]    A MEMS device according to the embodiment is fabricated by such eutectic bonding, and, for example, may be conceived as an acceleration sensor, an angular velocity sensor, an infrared ray sensor, a pressure sensor, a magnetic sensor and a sonic sensor. 
         [0033]      FIG. 1A  illustrates a piece in close-up of MEMS wafers (not illustrated) in which a plurality of sensing sections  12  are formed in a matrix shape. Hereinafter, a MEMS chip  10  as the piece will be explained for convenience. 
         [0034]    As illustrated, the MEMS chip  10  has a substrate  11  made of Silicon (Si) and a sensing section  12  formed at a center of the substrate  11  by micro fabrication technology. The sensing section  12  is formed to be engraved at the center of the substrate  11  and is composed of elements of an acceleration sensor, an angular velocity sensor, an infrared ray sensor, a pressure sensor, a magnetic sensor, a sonic sensor or the like. Further, the substrate  11  has a ring-shaped bonding section  30   a  in a planar view which surrounds the sensing section  12 . In the MEMS chip  10  in the embodiment, the sensing section  12  and the bonding section  30   a  are turned over to be upside down to face the CMOS chip  20  described later and the MEMS chip  10  is bonded with the CMOS chip  20 . Then, the bonding section  30   a  of the MEMS chip  10  is confronted with a bonding section  30   b  formed in the CMOS chip  20 , and both are bonded by eutectic bonding via a metal layer film-formed on the bonding section  30   b . The substrate  11  corresponds to a first semiconductor substrate and the sensing section  12  corresponds to a MEMS structure in claims. 
         [0035]      FIG. 1B  illustrates apiece in close-up from a CMOS wafer (not illustrated) in which a plurality of integrated circuits  22  are formed in a matrix shape. The CMOS chip  20  as the piece, similar to the MEMS chip  10 , will be explained. The CMOS chip  20  has a substrate  21  made of silicon and the integrated circuit formed by micro fabrication technology (semiconductor fabrication technology) on the substrate  21 . Further, the ring-shaped bonding section  30   b  in a planar view is disposed to surround a circuit central section  23  of the integrated circuit  22  facing the sensing section  12  of the MEMS chip  10  at the time of eutectic bonding. The integrated circuit  22  controls the sensing section  12  of the MEMS chip  10  and is connected to input/output signal lines from an outside. 
         [0036]    Further, the integrated circuit  22  has aluminum wirings, and an aluminum containing layer  31  film-formed at the time of aluminum wiring formation becomes a part of an eutectic alloy at the bonding. In other words, the bonding section  30   b  of the CMOS chip  20  is formed in a same shape approximately in a planar view with the bonding section  30   a  of the MEMS chip  10 . At the bonding section  30   b  of the CMOS chip  20 , the aluminum containing layer  31  as the eutectic alloy is film-formed on the substrate  11  and a germanium layer  32  as the eutectic alloy is film-formed on the aluminum containing layer  31  (for example, film formation by sputtering or vapor deposition technology). The substrate  21  corresponds to a second semiconductor substrate and the bonding section  30   b  corresponds to a bonding section of the second semiconductor substrate. 
         [0037]      FIG. 2  illustrates a MEMS device  1  formed by dicing or breaking the MEMS wafer and the CMOS wafer after the bonding (lamination bonding). As illustrated, the MEMS device  1  is made up of the bonded MEMS chip  10  and the CMOS chip  20  such that the sensing section  12  faces the circuit central section  23 . 
         [0038]    At the time of bonding, the MEMS chip  10  (MEMS wafer) and the CMOS chip  20  (CMOS wafer) are confronted, are heated from both sides, that is, from the MEMS chip  10  side and the CMOS chip  20  side under vacuum environment and are pressurized from the MEMS chip  10  side. Thus, the germanium layer film-formed at the bonding section  30   b  of the CMOS chip  20  develops eutectic reaction at a boundary surface with the aluminum containing layer  31 , and an aluminum-germanium alloy (hereinafter, refereed as eutectic alloy) is formed. Especially, the eutectic alloy in a melting state is pressed against a silicon surface of the bonding section  30   a  to be welded by the pressurization from the MEMS chip  10  side, and then, is fixed to be bonded solidly. Further, the eutectic bonding achieves electrical conduction between the substrates  11  and  21  and high sealing characteristics. Heating temperature at the time of bonding is preferably around 450° C. in consideration of heating damage to the sensing section  12  and the integrated circuit  22 . Further, the pressurization at the time of bonding may be performed from CMOS chip  20  side or from both the MEMS chip  10  side and the CMOS chip  20  side. Then, after the bonding, an individual MEMS device  1  is fabricated through separation process from a wafer to each chip. 
         [0039]    Referring to  FIGS. 3A and 3B , a film formation arrangement (film formation pattern) of the aluminum containing layer  31  and the germanium layer  32  will be explained.  FIGS. 3A and 3B  are enlarged views of the A-A line cross section in  FIG. 2 . As illustrated in  FIG. 3A , the aluminum containing layer  31  is evenly film-formed on the bonding section  30   b  of the CMOS chip  20  in a state before the eutectic bonding. Further, the germanium layer  32  on the aluminum containing layer  31  is film-formed such that an outer end  32   a  of the germanium layer  32  is receded inward with respect to an outer end  31   a  of the aluminum containing layer  31 . While, any metal layer is not film-formed at all on the bonding section  30   a  of the MEMS chip  10  and a silicon surface of the substrate  11  is barely formed. From this state, an eutectic alloy layer  33  is formed between the substrates  11  and  21  by the bonding method described above as illustrated in  FIG. 3B , and the MEMS chip  10  and the CMOS chip  20  are bonded by eutectic bonding. In the eutectic bonding of the embodiment, the pressurization and the heating is controlled appropriately, and a portion of the aluminum containing layer  31  which is not in contact with the germanium layer  32  remains without eutectic action (residual portion  34 ). In this case, the germanium layer  32  is preferably film-formed thinner than the aluminum containing layer  31  for the purpose of effective eutectic reaction. 
         [0040]    Thus, in a case that a metal layer is not film-formed at the MEMS chip  10  side before the bonding, a film formation process can be simplified after forming the sensing section  12  and undesired effect such as deformation, adhesion and breakage by film formation on a movable structure of the sensing section  12  as a thin film can be avoided. Further, since the aluminum containing layer  31  utilizes aluminum wirings of the integrated circuit  22 , metal film formation needed for actual bonding is only the germanium film formation on the bonding section  30   b  of the CMOS chip  20 , thereby bonding process can be simplified. Still further, since the bonding section  30  is disposed to surround the sensing section  12  and the circuit central section  23  and the eutectic alloy layer  33  is formed in such away as to be orthogonal in an inner/outer direction of the facing MEMS chip  10  and the CMOS chip  20 , the MEMS chip  10  and the CMOS chip  20  can be bonded with high sealing characteristics and bonding strength. The aluminum containing layer  31  and the germanium layer  32  may be film formed on either bonding section of the MEMS chip  10  or of the CMOS chip  20 , and they may be film-formed on a bonding section of a same substrate or on bonding sections of different substrates. 
         [0041]    Further, since the germanium layer  32  is film-formed such that the outer end  32   a  of the germanium layer  32  is receded inward with respect to the outer end  31   a  of the aluminum containing layer  31 , the formed eutectic alloy is formed without being pressed out from the bonding section  30  even if the eutectic alloy in the melting state expands to an outer side by pressurization at the time of bonding, thereby undesired conduction to an electrode can be avoided and productivity (an yield rate) of a device can be enhanced. Length from the outer end  31   a  of the aluminum containing layer  31  to the outer end  32   a  of the receded germanium layer  32  is preferably equal to or less than 20 μm. 
         [0042]    Referring to  FIGS. 4 to 5B , a weight ratio of the germanium layer  32  to the aluminum containing layer  31  at the time of bonding will be explained. In the bonding method of the embodiment, heating temperature and heating time as well as heating pressure is controlled for eutectic reaction between the whole germanium layer  32  and a part of the aluminum containing layer  31  in mutual bonding surfaces (see  FIG. 3B ). In practice, the weight ratio of the germanium layer  32  to the aluminum containing layer  31  is controlled by mainly a film thickness ratio of the germanium layer  32  to the aluminum containing layer  31 . Therefore, the germanium layer  32  and the portion of the aluminum containing layer  31  in contact therewith directly react by eutectic reaction, and the residual portion of the aluminum containing layer  31  remains as it is (see  FIG. 3B ). 
         [0043]      FIGS. 4 to 5B  illustrates a test result of eutectic bonding in which film thickness of the germanium layer  32  is changed arbitrary while film thickness of the aluminum containing layer  31  is set fixedly (800 nm).  FIG. 4  illustrates relationships among film thickness of the aluminum containing layer  31  and the germanium layer  32  film-formed before the eutectic bonding, a weight ratio of the germanium layer  32  to the aluminum containing layer  31 , and a sealing ratio and share strength (bonding strength) of the bonding section after the eutectic bonding. While,  FIG. 5A  is a graph of the weight ratio of the germanium layer  32  to the aluminum containing layer  31  versus the sealing ratio of the bonding section after the eutectic bonding, and  FIG. 5B  is a graph of the weight ratio of the germanium layer  32  to the aluminum containing layer  31  versus the share strength (bonding strength) of the bonding section after the eutectic bonding. 
         [0044]    As illustrated in  FIG. 5A , when the weight ratio of the germanium layer  32  to the aluminum containing layer  31  is between 27 wt % and 57 wt %, the sealing ratio of the bonding section after the eutectic bonding is equal to or more than about 50%. Further,  FIG. 5B  illustrates that the bonding strength (share strength) of the bonding section after the eutectic bonding is equal to or more than about 30 N when the weight ratio of the germanium layer  32  is between 27 wt % and 52 wt %. Still further, when the weight ratio of the germanium layer  32  is between 33 wt % and 42 wt %, the sealing ratio is 100% and the share strength (bonding strength) is between 41.6 N and 56.3 N (see  FIG. 4 ). In short, it becomes apparent by the test result that the bonding is performed with the highest sealing ratio and highest bonding strength when the eutectic bonding is performed by the method above with the weight ratio of the germanium layer  32  to the aluminum containing layer  31  as having 33 wt % to 42 wt %. This also indicates that good eutectic bonding can be obtained when the germanium layer  32  in the embodiment (film thickness of the aluminum containing layer  31 =800 nm) is film-formed between 200 nm and 300 nm thickness (see  FIG. 4 ). 
         [0045]    Referring to  FIGS. 6A to 8B , a modification of the film formation arrangement of the aluminum containing layer  31  and the germanium layer  32  according to the embodiment will be explained.  FIG. 6A  illustrates a portion of the bonding section  30   b  of the CMOS chip  20  before the eutectic bonding, and  FIG. 6B  illustrates a cross section of the bonding section  30  before the eutectic bonding (a first modification). As illustrated, the aluminum containing layer  31  is evenly film-formed on the bonding section  30   b  of the CMOS chip  20  and the germanium layer  32  is film-formed on the aluminum containing layer  31  in a plurality of strips shape. In short, the germanium layer  32  is made up of a plurality of concentric strip layer sections  35  which have an identical shape. 
         [0046]    In this kind of eutectic bonding, it has been known that the bonding strength is high at the end portion of the germanium layer  32 . Therefore, as the modification above, a total area of the end portion in the germanium layer  32  (strip layer sections  35 ) can be increased by film-forming the germanium layer  32  as the strip layer sections  35 , and strong eutectic bonding can be achieved without increasing an area of the bonding section  30 . Further, since the plurality of strip-shaped germanium layers  32  are disposed to be orthogonal in the inner/outer direction of the bonding section  30 , the MEMS chip  10  and the CMOS chip  20  can be bonded as having higher sealing characteristics and bonding strength. 
         [0047]      FIGS. 7A and 7B  illustrate a second modification of the film formation arrangement of the aluminum containing layer  31  and the germanium layer  32  according to the embodiment. As illustrated, in the film formation arrangement of the second modification, as the first modification, the aluminum containing layer  31  is evenly film-formed on the bonding section  30  of the CMOS chip  20 , and the germanium layer  32  film-formed on the aluminum containing layer  31  is integrally formed with a single strip layer section  35  and a plurality of branch layer sections  36 . The strip layer section  35  is formed in a square ring-shape along the aluminum containing layer  31  at a center of the aluminum containing layer  31  in a width direction. While, the plurality of branch layer sections  36  are film-formed so as to branch from each section of the strip layer section  35  to both sides at aright angle. Thus, a total area of the end portion of the germanium layer  32  (strip layer section  35  and branch layer sections  36 ) can be increased by forming the plurality of branch layer sections  36  (germanium layer  32 ) in a branch shape (fish&#39;s bone shape), thereby strong eutectic bonding can be achieved. 
         [0048]      FIGS. 8A and 8B  illustrate a third modification of the film formation arrangement of the aluminum containing layer  31  and the germanium layer  32 . As illustrated, the film formation arrangement of the third modification has a configuration in which the first modification is combined with the second modification. In other words, in the third modification, the aluminum containing layer  31  is evenly film-formed on the bonding section  30   b  of the CMOS chip  20 , and the germanium layer  32  film-formed on the aluminum containing layer  31  is made up of a plurality of strip layer sections  35  and a plurality of branch layer sections  36 . More specifically, the germanium layer  32  is made up of concentric three strip layer sections  35  having an identical shape and the plurality of branch layer sections  36  which branch from each section of a centrally positioned strip layer section  35  to both side at a right angle. Thus, the MEMS chip  10  and the CMOS chip  20  can be bonded with higher sealing characteristics and bonding strength. 
         [0049]    Referring to  FIGS. 9A to 9C , the other embodiment (second embodiment) of the invention will be explained. Portions different from those of the above embodiment will be mainly explained and same numerals are labeled for similar elements. As illustrated in  FIGS. 9A and 9B , the aluminum containing layer  31  film-formed on the bonding section  30   b  of the CMOS chip  20  is made up of a plurality of aluminum ring-shaped layer sections  37 . The plurality of aluminum ring-shaped layer sections  37  are formed in a ring shape in a plan view concentrically with the bonding section  30   b , and are disposed to be orthogonal in the inner/outer direction of the bonding section  30   b . Further, a plurality of ring-shaped germanium layers  32  (germanium ring-shaped layer sections  38 ) are film-formed so as to fill in space of these aluminum ring-shaped layer sections  37 . In this case, the plurality of germanium ring-shaped layer sections  38  are film-formed to contact contact-ends of the plurality of aluminum ring-shaped layer sections  37  in a vertical direction and to slightly overlap thereon (overlap layer sections  40 ) in a horizontal direction. 
         [0050]    While, as illustrated in  FIG. 9B , a plurality of engraved pits  41  are formed on the bonding section  30   a  of the substrate  11 . The plurality of pits  41  are formed to correspond to positions (the overlap layer sections  40 ) where the plurality of germanium ring-shaped layer sections  38  overlap on the plurality of aluminum ring-shaped layer sections  38 , and an alloy in a melting state after being heated and pressurized gets into the plurality of pits  41 . The plurality of pits  41  may be newly formed on the substrate  11  after the sensing section  12  has been formed, or engraved portions formed in the formation process of the sensing section  12  may be used. Further, the pits  41  may have intermittent aperture shape or consecutive groove shape. 
         [0051]      FIG. 9C  illustrates the bonding section after eutectic bonding. A eutectic alloy in a melting state formed by heating spreads into the plurality of pits  41  thoroughly by capillary action in vacuum by pressurization. Then, the fixed eutectic alloy layer  33  is formed to bite into the bonding section  30  (substrate  11 ) of the MEMS chip  10 . In other words, as illustrated, since the eutectic alloy layer  33  is formed vertically with respect to a surface direction of the bonding section, bonding with higher bonding strength can be achieved. 
         [0052]    According to the structures, a semiconductor substrate can be bonded with high bonding strength and sealing characteristics at appropriate portions while adverse effect on the sensing section  12  is restrained. Further, such effective bonding enables the sensing section  12 , the integrated circuit  22  and the external circuit to conduct electrically, and high precision MEMS devices in which the sensing section  12  and the circuit central section  23  are integrally packaged can be provided while an external atmosphere such as moisture, temperature, dust and the like is avoided. 
         [0053]    In the embodiment, the silicon wafers formed with the sensing section  12  and the integrated circuit  22  controlling the sensing section is used, but structures formed in the silicon wafer may be any circuits, not being limited thereto. Still further, a semiconductor substrate (composite semiconductor) having other base material instead of silicon wafer formed by silicon may be used. It is preferable that either one of the bonded semiconductor substrates have aluminum wirings. 
       REFERENCE NUMERALS 
       [0054]      1  MEMS device  10  MEMS chip  12  sensing section  11 ,  12  substrate  20  CMOS chip  22  integrated circuit  31  aluminum containing layer  31   a ,  32   a  outer end  32  germanium layer  35  strip layer section  36  branch layer section  41  pit