Abstract:
A wafer-level package comprises: a first substrate; an electric element provided on the first substrate; a second substrate; an internal electrode pad; a well; and an external electrode pad. The second substrate is opposed to the first substrate with a predetermined gap therebetween. The electric element is provided between the first and second substrates. The internal electrode pad extends onto a first surface of one of the first and the second substrates. The inner electrode pad is connected to the electric element. The well penetrates the one of the first and the second substrates to the internal electrode. The external electrode pad is provided on a second surface of the one of the first and the second substrates and extends onto an inner wall of the well and being connected with the internal electrode pad.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-341982, filed on Sep. 30, 2003; the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a wafer-level package and its manufacturing method. More specifically, the invention relates to a wafer-level package which has a cavity inside the package and is suitable for a high frequency circuit or an analog circuit having small number of connecting pins, and its manufacturing method.  
         [0003]     Recently, a package has been highly desired to be small sized, thin and inexpensive. Particularly, in high frequency circuit, such a package has been needed for a small-sized mobile equipment in accordance with upgrading and diversifying of the wireless communication systems. For this reason, a wafer-level package is paid an attention, as an ultimate package, in which a thin film device is formed on a substrate wafer, the wafer is also used as a packaging member itself and the wafers can be assembled entirely.  
         [0004]     One of the major problems of the wafer-level package is how to connect internal bonding pads on a substrate surface to external electrode pads on an outer surface of the package.  
         [0005]     To solve the above problem, several methods are known. In the first method, external electrode pads through insulating layers are provided on peripheral areas of the substrate connected to internal connection pads by wires and the connecting portion is buried with resin. This method is disclosed in Japanese Patent Laid Open Publication No. 2002-9195 and Japanese Patent Laid Open Publication No. 2002-110855.  
         [0006]     In the second method, after a via hole is formed on the surface side of the substrate, a conductive material is buried in the via hole. Subsequently, the backside of the substrate is lapped, the conductive material in the via hole is exposed and an external electrode pad is formed on the backside of the substrate. This method is disclosed in Japanese Patent Laid Open Publication No. 2001-68616.  
         [0007]     In the third method, a cap wafer is fixed with a predetermined spacing on the substrate and the bonding pad on the substrate is connected via through hole provided on the cap wafer by bonding wire. This method is disclosed in Japanese Patent Laid Open Publication No. 2001-68580.  
         [0008]     However, by the above-mentioned first and third methods, when a frequency becomes over gigahertz-band, the problem that parasitic inductance degrades a band characteristics arise in a high frequency circuit. Thus, it is desirable that the wire-bonding is not used.  
         [0009]     By the second method, the trade-off between the formation of the via hole and embedment of the via metal becomes the problem. That is, in the case of the via hole of 100 micrometers depth which is equivalent to the substrate thickness after lapping, if the via hole has as large diameter as tens of micrometers, the etching becomes easy. On the other hand, if the via hole has several micrometers diameter and large aspect ratio, complicated process for forming the via hole is needed, such as repeating etching and forming protective layer of sidewalls of the via hole.  
         [0010]     Further, in the case of embedding a conductive layer (a part of which may be an insulator) in the via hole, if the via hole has a large diameter of tens of micrometers, a long processing time is needed, such as embedding the precise conductive layer of tens of micrometers thickness by a process for thin film including in thin film the conductive layer sputtering, CVD, and plating. On the other hand, if the via hole has several micrometers diameter, the via hole is relatively easy to be embedded in. Additionally, if the via hole has large diameter, a problem also occurs that an integration density of the via hole falls.  
         [0011]     Thus, the method of connecting internal bonding pads to external bonding pads has a problem that the via hole of small diameter is hard to be etched and the via hole of large diameter is hard to be embedded in.  
       SUMMARY OF THE INVENTION  
       [0012]     According to an embodiment of the invention, there is provided a wafer-level package comprising: 
        a first substrate;     an electric element provided on the first substrate;     a second substrate opposed to the first substrate with a predetermined gap therebetween, the electric element being provided between the first and second substrates;     an internal electrode pad extending onto a first surface of one or both of the first and the second substrates, the internal electrode pad being connected to the electric element;     a well penetrating the one of the first and the second substrates to the internal electrode; and     an external electrode pad provided on a second surface of the one of the first and the second substrates, the external electrode pad extending onto an inner wall of the well and being connected with the internal electrode pad.        
 
         [0019]     According to another embodiment of the invention, there is provided a method for manufacturing a wafer-level package comprising: 
        forming an electric element and an internal electrode pad connected to the electric element on a first surface of a first substrate;     bonding a second substrate to the first substrate by a bonding member so that the electric element and the internal electrode pad are placed between the first and second substrates;     forming a well extending from a second surface of the first substrate to the internal electrode pad;     forming an external electrode pad extending from the second surface of the first substrate to the internal electrode pad through an inner wall of the well.        
 
         [0024]     According to another embodiment of the invention, there is provided a method for manufacturing a wafer-level package comprising: 
        forming an electrical element on a first surface of a first substrate;     forming an internal electrode pad on a first surface of a second substrate;     arranging the first and the second substrates face to face so that the electric element on the first substrate is connected to the internal electrode on the second substrate by a bump;     forming a well extending from a second surface of the second substrate to the internal electrode pad; and     forming an external electrode pad extending from the second surface of the second substrate to the internal electrode pad through an inner wall of the well.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the embodiments of the invention. However, the drawings are not intended to imply limitation of the invention to a specific embodiment, but are for explanation and understanding only.  
         [0031]     In the drawings:  
         [0032]      FIG. 1  is a schematic diagram illustrating the cross-sectional structure of the wafer-level package according to the embodiment of the invention;  
         [0033]      FIG. 2  is an enlarged cross-sectional view of the well;  
         [0034]      FIG. 3  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0035]      FIG. 4  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0036]      FIG. 5  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0037]      FIG. 6  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0038]      FIG. 7  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0039]      FIG. 8  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0040]      FIG. 9  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0041]      FIG. 10  shows process step for manufacturing the wafer-level package according to the first example of the invention;  
         [0042]      FIG. 11  shows process step for manufacturing the wafer-level package according to the second example of the invention;  
         [0043]      FIG. 12  shows process step for manufacturing the wafer-level package according to the second example of the invention;  
         [0044]      FIG. 13  shows process step for manufacturing the wafer-level package according to the second example of the invention;  
         [0045]      FIG. 14  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0046]      FIG. 15  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0047]      FIG. 16  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0048]      FIG. 17  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0049]      FIG. 18  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0050]      FIG. 19  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0051]      FIG. 20  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0052]      FIG. 21  shows process step for manufacturing the wafer-level package according to the third example of the invention;  
         [0053]      FIG. 22  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0054]      FIG. 23  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0055]      FIG. 24  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0056]      FIG. 25  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0057]      FIG. 26  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0058]      FIG. 27  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0059]      FIG. 28  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0060]      FIG. 29  shows process step for manufacturing the wafer-level package according to the fourth example of the invention;  
         [0061]      FIG. 30  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0062]      FIG. 31  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0063]      FIG. 32  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0064]      FIG. 33  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0065]      FIG. 34  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0066]      FIG. 35  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0067]      FIG. 36  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0068]      FIG. 37  shows process step for manufacturing the wafer-level package according to the fifth example of the invention;  
         [0069]      FIG. 38  shows process step for manufacturing the wafer-level package according to the sixth example of the invention;  
         [0070]      FIG. 39  shows process step for manufacturing the wafer-level package according to the sixth example of the invention;  
         [0071]      FIG. 40  shows process step for manufacturing the wafer-level package according to the sixth example of the invention;  
         [0072]      FIG. 41  shows process step for manufacturing the wafer-level package according to the sixth example of the invention; and  
         [0073]      FIG. 42  shows process step for manufacturing the wafer-level package according to the sixth example of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0074]     Referring to drawings, some embodiments of the present invention will now be described in detail.  
         [0075]      FIG. 1  is a schematic diagram illustrating the cross-sectional structure of the wafer-level package according to the embodiment of the invention. The wafer level package of this embodiment has a structure in which a first substrate  11  and a second substrate  21  are facing each other and disposed with appropriate gap by adhesive resin  25 . That is, a cavity C is formed between these substrates  11  and  21 . A semiconductor device  12  is provided in a manner exposed to the cavity C or covered with the protective film etc. The semiconductor device  12  may be a device having various kinds of structures and functions, such as a transistor, a diode, a resistive element, an inductor, and a capacitor, a MEMS(Micro-Electro-Mechanical System) switch, a MEMS variable capacitor, and a FBAR(thin Film Bulk Acoustic wave Resonator) for example.  
         [0076]     The leads from the semiconductor device  12  are connected to the outside of the package through the external electrode pads  27 . That is, in the structure illustrated in this figure, the leads are connected between the semiconductor device  12  and the external electrode pads  27  through first internal electrode pads  13 , and stud bumps  24  and second internal electrode pads  23 . The external electrode pads  27  can be formed by depositing a conductive material in the well and on the underside of well  26  penetrating the substrate  21  and on the back of the substrate  21 . And the external electrode pads  27  extending to the back of the substrate  21  can be connected to external circuits, such as an assembly board (not shown), by surface mounting on a substrate electrode or wire bonding.  
         [0077]     One of the features of wafer-level package of this embodiment is that the “chamfered edges” are provided at the opening of the well  26  penetrating the substrate  21 .  
         [0078]      FIG. 2  is an enlarged cross-sectional view of the well. As illustrated in this figure, at the entry, the chamfered edges S are formed. The chamfered edges S are formed by inclining or rounding the corners of the opening. By providing such chamfered edges S, the “stepped cut” of the external electrode pads  27  covering the chamfered edges at the opening of the well can be suppressed. Consequently, the wires can be connected surely to the back side of the substrate  21  from the semiconductor device  12 , and can be connected with the external circuit which is not shown.  
         [0079]     Further, in this embodiment, the well  26  may be formed in a taper shape that the inside diameter becomes small gradually as it approaches to the substrate  11 , instead of perpendicular through hole. If the well  26  are formed in a taper shape, the external electrode pads  27  can be surely deposited to have sufficient thicknesses also on the walls of the well  26  by such method as a sputtering and vapor deposition, for example. Consequently, the “stepped cut” of the external electrode pads  27  on the walls of the well  26  can be prevented.  
         [0080]     The chamfered edge S and the well  26  in a taper shape explained above can be easily formed by the manufacturing method according to the embodiment. That is, in the invention, as explained in full detail later, after facing the first substrate  11  and the second substrate  21  each other, the well  26  are formed by etching the second substrate  21  from the back side of the substrate (the bottom in  FIG. 1  and  FIG. 2 ). Then, the well in a taper shape that the inside diameter becomes small as it approaches to the substrate  11  and having the chamfered edge S become easy to be formed with effects, such as the so-called “side etching” etc.  
         [0081]     Referring to examples, the wafer-level package and its manufacturing method of this embodiment will now be described in further detail.  
       FIRST EMBODIMENT  
       [0082]      FIG. 3  through  FIG. 10  show process steps for manufacturing the wafer-level package according to the first example of the invention.  
         [0083]     In  FIG. 3 , the first internal electrode pads  13  of Aluminum (Al) etc. and the semiconductor device  12  are provided on the surface of the first substrate  11  of silicon (Si) by a well-known method. The first substrate  11  may be an entire wafer or a divided wafer. It is desirable that the first substrate  11  has enough area to dispose a plurality of semiconductor chips thereon.  
         [0084]     In  FIG. 4 , a FBAR  22  and the second internal electrode pads  23  of Aluminum (Al) etc. are provided on the surface of the second substrate  21  of silicon (Si) prepared separately by a well-known method. The second substrate  21  may be an entire wafer or a divided wafer. The second substrate  21  is needed to have the same shape as the first substrate  11  substantially.  
         [0085]     In  FIG. 5 , stud bumps  24  are formed on the second internal electrode pads  23  using bonding wires of Au. And the adhesive resin  25  is coated using a dispenser along the periphery of the thin film piezoelectric resonator  22  and the second internal electrode pads  23 .  
         [0086]     In  FIG. 6 , the first substrate  11  and the second substrate  21  are facing, and the stud bumps  24  and the first internal electrode pads  13  are connected electrically by an ultrasonic bonding. At the same time, the first substrate  11  and the second substrate  21  are stuck with the adhesive resins  25 , and cured by heating.  
         [0087]     In  FIG. 7 , the first substrate  11  and the second substrate  21  are thinned up to the thickness of 200 micrometers by grinding them on their back sides.  
         [0088]     In  FIG. 8 , the well  26  of 200 micrometers inner diameter and depth which extends to the back sides of the second internal electrode pads  23  from the second substrate  21  are formed using a well-known photolithographic process and a reactive ion etching process. Even if a highly isotropic etching process such as a reactive ion etching is used, the chamfered edges S are formed at the corner of the opening ends of the well  26  in many cases. Moreover, it is also possible to form the chamfer parts S still more certainly by rounding the opening ends of the well  26  with a method of exposing lightly to a wet etchant, isotropic etching atmosphere, etc., after carrying out the opening of the well  26  by etching means, such as reactive ion etching.  
         [0089]     By the highly anisotropy etching method, when opening the well  26 , the well  26  whose sides are almost perpendicular to the major surface of the substrate are formed. On the other hand, by the etching method of a low anisotropy, when opening the well  26 , the well  26  are formed in a taper fashion in which the inner diameter becomes small as it approach to the substrate  11  from the opening ends (bottom in the figure). Thus, it becomes possible to suppress more surely the stepped cut of the external electrode pads deposited later.  
         [0090]     Thus, in  FIG. 9 , after opening the well  26 , Ti adhesion layer and Au electrode layer are deposited conformally in the walls and at the bottom of the well  26  and on the backside of the second substrate  21  by sputtering, for example. And the external electrode pads  27  are patterned by lithography and dry etching. For this process, the second internal electrode pads  23  and the external electrode pads  27  can be connected electrically.  
         [0091]     In  FIG. 10 , the portion stuck with adhesive resin  25  are separated for every chip by dicing.  
         [0092]     By the above-mentioned method, the wafer-level package in which the semiconductor device  12  or the thin film piezoelectric resonator  22  are sealed in the cavity C, and their wirings are connected to the back side of the substrate  21  is obtained. Thus, it is valuable that according to this embodiment, the package for surface mount in which the wafer can be in block sealed, which has thin and small size as same as a chip, and in which the thin film device and the semiconductor device are encapsulated inside the cavity can be formed.  
       SECOND EMBODIMENT  
       [0093]     Since the process steps of the second example before the process steps mentioned above in  FIG. 9  are the same as that of the first example, only the subsequent process steps will be explained.  
         [0094]      FIG. 11  through  FIG. 13  show process steps for manufacturing the wafer-level package according to the second example of the invention. In  FIG. 11 , after the process step shown in  FIG. 9 , the trenches  28  are formed by half-cutting the regions stuck with sealing resin  25  using a dicing saw of 200 micrometers width to the second substrate  21  from the back side of the first substrate  11 .  
         [0095]     In  FIG. 12 , the backside of the first substrate  11  is covered with the adhesive resin  29  and is cured.  
         [0096]     In  FIG. 13 , dicing is performed using the dicing saw of 30 micrometers width, and the central parts of the trenches  28  are separated for every chip.  
         [0097]     By such processes, in addition to the same effect as the first example, since the sides of the package are doubly covered with the adhesive resin  25  and the sealing resin  29 , environmental resistance improves further. Moreover, since the upper surface of the package is covered with the adhesive resin  29 , it becomes possible to mark on the surface. Therefore, the industrial value is very large.  
       THIRD EMBODIMENT  
       [0098]      FIG. 14  through  FIG. 21  are process steps for manufacturing method of the wafer-level package according to the third example of the invention.  
         [0099]     In  FIG. 14 , a microswitch  22  and the second internal electrode pads  23  of aluminum are provided on the surface of the second substrate  21  of Si by a well-known method. The second substrate  21  may be an entire wafer or a divided wafer. It is desirable that the second substrate  21  is the same shape as the first substrate  11 . Further, the adhesive resin  25  are printed by screen-print along the periphery of the microswitch  22  and the second internal electrode pads  23 .  
         [0100]     Moreover, in  FIG. 15 , the semiconductor device  12  and the first internal electrode pads  13  of aluminum are provided on the surface of the first substrate  11  of Si by a well-known method.  
         [0101]     In  FIG. 16 , conductive resin  14  is printed on the first internal electrode pads  13  using screen printing.  
         [0102]     Next, as shown in  FIG. 17 , the first substrate  11  and the second substrate  21  are facing so that the surfaces may face each other, and the first internal electrode pads  13  and the second internal electrode pads  23  are connected by conductive resin  14 . Simultaneously, the first substrate  11  and the second substrate  21  are stuck with adhesive resin  25 , and are sealed by cured with heating.  
         [0103]     In  FIG. 18 , the first substrate  11  and the second substrate  21  are thinned up to the thickness of 200 micrometers by grinding them on their backsides.  
         [0104]     In  FIG. 19 , well  26  of 200 micrometers inner diameter and depth which extend to the back sides of the second internal electrode pads  23  from the second substrate  21  are formed using a well-known photolithographic process and reactive ion etching process. Then, as mentioned above about the first example, the chamfered edges S can be formed surely and easily. Further, the well  26  may be opened in a taper shape.  
         [0105]     In  FIG. 20 , Ti adhesion layer and Au electrode layer are deposited conformally in the walls and at the bottom of the well  26  and on the backside of the second substrate  21  by a sputtering, for example. And the external electrode pads  27  are patterned by lithography and dry etching. For this process, the second internal electrode pads  23  and the external electrode pads  27  can be connected electrically.  
         [0106]     In  FIG. 21 , the portion stuck with adhesive resin  25  are separated for every chip by dicing. Thus, it is valuable that according to this embodiment, the package for surface mount in which the wafer can be collectively encapsulated, which has thin and small size as same as a chip, and in which the thin film device and the semiconductor device are sealed inside the cavity can be formed.  
         [0107]     In particular, according to this example, the internal electrode pads  13  and  23  can be connected electrically with the conductive resin  14 . The advantage that the conductive resin  14  has high manufacturability for being easily formed by screen printing etc. can be acquired.  
       FOURTH EMBODIMENT  
       [0108]      FIG. 22  through  FIG. 29  show process steps for manufacturing method of the wafer-level package according to the fourth example of the invention.  
         [0109]     In  FIG. 22 , the thin film piezoelectric resonator and the second internal electrode pads  23  of aluminum are provided on the surface of the first substrate  21  of glass by a well-known method.  
         [0110]     In  FIG. 23 , the adhesive resin  25  is coated by an ink-jet method along the periphery of the thin film piezoelectric resonator  22  and the second internal electrode pads  23 .  
         [0111]     In  FIG. 24 , Si oxide film is deposited on the surface of the second substrate  31  of glass prepared separately by the plasma CVD method. Bumps  32  are patterned by photolithography and reactive ion etching.  
         [0112]     In  FIG. 25 , the surfaces of the first substrate  21  and the second substrate  31  are opposed using the bumps  32  as stoppers, are stuck using the adhesive resin  25 , and are sealed by cured with heating.  
         [0113]     In  FIG. 26 , the first substrate  21  and the second substrate  31  are thinned up to the thickness of 200 micrometers by grinding them on their backsides.  
         [0114]     In  FIG. 27 , well  26  of 200 micrometers inner diameter and depth which extend to the back sides of the second internal electrode pads  23  from the second substrate  21  are formed using a well-known photolithographic process and reactive ion etching process. Then, as mentioned above about the first example, the chamfered edges S can be formed certainly and easily. Further, the well  26  maybe opened in a taper fashion. In  FIG. 28 , Ti adhesion layer and Au electrode layer are deposited conformally in the walls and at the bottom of the well  26  and on the backside of the second substrate  21  by methods, such as a sputtering. And the external electrode pads  27  are patterned by lithography and dry etching. For this process, the second internal electrode pads  23  and the external electrode pads  27  can be connected electrically. In  FIG. 29 , the portion stuck with adhesive resin  25  are separated for every chip by dicing.  
         [0115]     According to this example, elements, such as the thin film piezoelectric resonator, can be sealed between two glass substrates, and the space of the cavity can be prescribed by the bumps  32 .  
       FIFTH EMBODIMENT  
       [0116]      FIG. 30  through  FIG. 37  are process steps for manufacturing method of the wafer-level package according to the fifth example of the invention.  
         [0117]     In  FIG. 30 , a microswitch  42 , the first internal electrode pads  43  of aluminum, and first sealing pads  44  encompassing the internal electrode pads are provided on the surface of the first substrate  41  by a well known method. The first substrate  41  may be an entire wafer or a divided wafer. It is desired that the first substrate  41  has enough area to dispose a plurality of thin film device chips thereon.  
         [0118]     In  FIG. 31 , the bumps  45  of gold for internal connection and the bumps  46  for sealing are formed on the first internal bonding electrode pads  43  and the first sealing pads  44  by a lithography method and a selective plating method. In  FIG. 32 , the semiconductor device  52 , the second internal electrode pads  53  of gold, and the second sealing pads  54  encompassing the internal electrode pads are formed on the surface of the second substrate  51  of Si prepared before by a well known method. The second substrate  51  may be an entire Si wafer or a divided wafer. The second substrate is needed to have the same shape as the first substrate.  
         [0119]     In  FIG. 33 , the first bumps  45  for internal connection and the second internal electrode pads  53  are connected by facing the surfaces of the first substrate  41  and the second substrate  51  by thermocompression. Simultaneously, the bumps  46  for sealing and the second pads  54  for sealing are junctioned and sealed.  
         [0120]     In  FIG. 34 , the first substrate  41  and the second substrate  51  are thinned up to the thickness of 200 micrometers by grinding them on their backsides.  
         [0121]     In  FIG. 35 , well  47  of 200 micrometers inner diameter and depth which extend to the back sides of the first internal electrode pads  43  from the first substrate  41  are formed using a well-known photolithographic process and reactive ion etching process. Then, as mentioned above about the first example, the chamfered edges S can be formed surely and easily. Further, the well  47  may be opened in a taper shape. In  FIG. 36 , Ti adhesion layer and Au electrode layer are deposited conformally in the walls and at the bottom of the well  47  and on the backside of the second substrate  41  by a sputtering, for example. And the external electrode pads  48  are patterned by lithography and dry etching. By this process, the first internal electrode pads  43  and the external electrode pads  48  can be connected electrically. In  FIG. 37 , the perimeter of the bumps  46  for sealed are separated for every chip by dicing. The major steps of the wafer-level packaging is completed.  
         [0122]     According to this example, without using resin, the package is sealed forming the cavity between the substrate  41  and the substrate  51  by the bumps of soft metal for sealing. Since resin is not used, the wafer-level package having high hermeticity and relativity, such as high heat resistance can be provided.  
       SIXTH EMBODIMENT  
       [0123]     Next, as the sixth example of the invention, the wafer-level package where the well is opened in the semiconductor substrate and external electrode pads are connected will be explained.  
         [0124]      FIG. 38  through  FIG. 42  show process steps for manufacturing method of the wafer-level package of this example. The same symbols are given to the same elements as what were mentioned above with references to  FIG. 1  through  FIG. 37  about this figure, and detailed explanation will be omitted.  
         [0125]     First,  FIG. 38  corresponds to  FIG. 34  mentioned above about the fifth example. But, the non-insulation silicon substrate  61  is used instead of the insulating Si substrate  41 . And the nitride silicon (SiN x ) layer  62  is formed on the back side of the non-insulation silicon substrate  61 .  
         [0126]     In  FIG. 39 , well  67  of 200 micrometers inner diameter and depth which extend to the back sides of the first internal electrode pads  43  from the first substrate  61  are formed using a well-known photolithographic process and reactive ion etching process. Then, as mentioned above about the first example, the chamfered edges S can be formed certainly and easily. Further, the well  47  may be opened in a taper fashion.  
         [0127]     In  FIG. 40 , the inner walls of the well  67  are covered with the silicon-oxide (SiO x ) film  68  by forming the silicon-oxide (SiO x ) film on the backside of the substrate  61 .  
         [0128]     In  FIG. 41 , the silicon-oxide film  68  formed on the back of the substrate  61  and at the bottom of the well  67  is removed by etching. In this process, the anisotropic etching method, such as RIE (reactive ion etching) can be used.  
         [0129]     In  FIG. 42 , Ti adhesion layer and electrode layer of gold are formed conformaly as a film at the bottom and on the side of the well  67  by the sputtering method. The external electrode pads  69  are patterned by lithography and dry etching. Simultaneously, the first inside electrode  43  and external electrode pads  69  can be connected electrically.  
         [0130]     Then, as mentioned above about  FIG. 37 , the perimeter of the bumps  46  for sealed is separated for every chips by dicing. And the major steps of the wafer level package are completed.  
         [0131]     According to this example, it becomes possible to form via plug structure in the non-insulation silicon substrate  61  by providing appropriately insulating films, such as the nitride silicon film  62  and the silicon-oxide film  68 .  
         [0132]     Heretofore, the embodiments of the present invention have been explained, referring to the examples. However, the present invention is not limited to these specific examples. For example, conductivity, insulation, or half-conductivity is sufficient as a pair of substrates which are arranged in a facing fashion each other and form a cavity among them. Accordingly, it is intended to embrace all such variations, which fall within the scope of the present invention. Moreover, an element provided between pairs of the substrates can include electric element, such as a transistor, a diode, a resistive element, a capacitor, an inductor, an oscillation element, and a relay, and machine element and optical element, such as a micro actuator and a polygon mirror.  
         [0133]     Further, about the number and arrangement of the electric element contained in the wafer-level package and of well provided on the substrates may be appropriately selected by those skilled in the art with the known techniques to carry out the invention as taught in the specification and obtain equivalent effects.  
         [0134]     Further, also concerning the wafer-level package according to the invention, those skilled in the art will be able to carry out the invention appropriately selecting a material or a structure within known techniques.