Abstract:
A method of fabricating a semiconductor device includes a step of attaching a circuit substrate on a semiconductor wafer in alignment with each other, providing an electrical interconnection between the circuit substrate and semiconductor devices formed in the wafer, providing solder bumps on the circuit substrate, and dicing the semiconductor wafer together with the circuit substrate thereon along a scribe line.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention generally relates to semiconductor devices having a ball grid array (BGA) contact structure and more particularly to a so-called micro-BGA device in which a circuit substrate is provided on a semiconductor chip with a size smaller than an outer dimension of the semiconductor-chip.  
           [0002]    [0002]FIG. 1 shows a conventional semiconductor device having a BGA contact structure.  
           [0003]    Referring to FIG. 1, the semiconductor device includes a circuit substrate  36  and a semiconductor chip  32  provided on a top surface of the circuit substrate  36 . Further, electrodes on the semiconductor chip  32  are electrically interconnected to corresponding electrodes formed on the top surface of the circuit substrate  36  by way of a bonding wire  34 . The electrodes on the top surface of the circuit substrate  36  are in turn interconnected to respective corresponding electrodes on a bottom surface of the circuit substrate  36  via through-holes (not shown) provided in the circuit substrate  36 . The circuit substrate  36  further carries solder bumps  37  on the bottom surface in correspondence to the electrodes provided thereon. The semiconductor chip  32  on the top surface of the circuit substrate  36  is encapsulated by a resin package body  31  together with the bonding wire  34 .  
           [0004]    [0004]FIG. 2 shows another conventional BGA semiconductor device disclosed in the U.S. Pat. No. 5,148,265.  
           [0005]    Referring to FIG. 2, the BGA semiconductor device is distinct over the semiconductor device of FIG. 1 in that a circuit substrate  46  corresponding to the circuit substrate  36  of FIG. 1 is now provided on a top surface of a semiconductor chip  42  corresponding to the semiconductor chip  32 , with a size smaller than an outer size of the semiconductor chip  42 . Such a BGA device that uses a circuit substrate having an outer size smaller than the outer size of a semiconductor chip is called a micro-BGA device. In the micro-BGA device of FIG. 2, it should be noted that the solder bumps (not shown) are provided on electrodes  43  formed on the circuit substrate  46 .  
           [0006]    In the foregoing conventional BGA device of FIG. 1, there arises a problem in that, because of the lateral size of the circuit substrate exceeding the size of the semiconductor chip, the overall size of the semiconductor device tends to become excessively large and a high-density mounting of the device on an electronic apparatus is difficult.  
           [0007]    In the foregoing micro-BGA device of FIG. 2, on the other hand, it is necessary to bond the circuit substrate, of which size is smaller than a size of the semiconductor chip, on the semiconductor chip, while handling or alignment of such a small semiconductor chip or small circuit substrate is difficult and increases the number of fabrication steps as well as the cost of the semiconductor device.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, it is a general object of the present invention to provide a novel and useful semiconductor device and a fabrication process thereof wherein the foregoing problems are eliminated.  
           [0009]    Another and more specific object of the present invention is to provide a semiconductor device including a semiconductor chip and a circuit substrate, wherein the semiconductor device has an outer size substantially identical with an outer size of the semiconductor chip, and wherein the circuit substrate is attached to the semiconductor chip by a simple and easy process.  
           [0010]    Another object of the present invention is to provide a method of fabricating a semiconductor device, comprising the steps of:  
           [0011]    forming an electronic circuit on a wafer in a region defined by a scribe line, said wafer carrying a first electrode thereon;  
           [0012]    attaching a circuit substrate carrying thereon a predetermined conductor pattern, on said wafer, said circuit substrate carrying a second electrode and a third electrode, said step of attaching said circuit substrate including a step of aligning said circuit substrate with respect to said electronic circuit in said wafer;  
           [0013]    interconnecting said first electrode on said wafer and second electrode of said predetermined conductor pattern by a wire bonding process;  
           [0014]    forming a spherical electrode on said third electrode; and  
           [0015]    dicing said wafer along said scribe line.  
           [0016]    Another object of the present invention is to provide a semiconductor device, comprising:  
           [0017]    a semiconductor chip having a top surface, said semiconductor chip carrying a first electrode;  
           [0018]    a circuit substrate attached to a top surface of said semiconductor chip, said circuit substrate carrying thereon a predetermined conductor pattern including a second electrode and a third electrode;  
           [0019]    a resin layer intervening between said top surface of said semiconductor chip and said circuit substrate;  
           [0020]    a spherical electrode provided on said circuit substrate in correspondence to said third electrode;  
           [0021]    a bonding wire electrically interconnecting said second electrode of said predetermined conductor pattern on said circuit substrate and said first electrode on said semiconductor chip; and  
           [0022]    a resin potting encapsulating said bonding wire including said first and second electrodes,  
           [0023]    said chip and said resin potting being defined by a common edge surface substantially perpendicular to a principal surface of said substrate.  
           [0024]    Another object of the present invention is to provide a semiconductor device, comprising:  
           [0025]    a semiconductor chip having a top surface, said semiconductor chip carrying a first electrode;  
           [0026]    a circuit substrate attached to a top surface of said semiconductor chip, said circuit substrate carrying thereon a predetermined conductor pattern including a second electrode and a third electrode;  
           [0027]    a spherical electrode provided on said circuit substrate in correspondence to said third electrode;  
           [0028]    a bonding wire electrically interconnecting said second electrode of said predetermined conductor pattern on said circuit substrate and said first electrode on said semiconductor chip;  
           [0029]    a resin potting encapsulating said bonding wire including said first and second electrodes;  
           [0030]    a resin side wall cover covering a side wall of said circuit substrate;  
           [0031]    said chip having a side wall substantially flush to an outer surface of said resin side wall cover, said side wall of said chip being substantially perpendicular to a principal surface of said chip.  
           [0032]    According to the present invention, the semiconductor wafer, in which a number of semiconductor chips are formed as an integral monolithic body, is diced after the circuit substrate is attached thereto. Thereby, the adjustment for a proper positioning between the chip and the circuit substrate is achieved easily for each chip by merely conducting a positioning adjustment between the semiconductor wafer as a whole and a master circuit substrate that includes the circuit substrates with a large number in a mechanically interconnected state.  
           [0033]    Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0034]    [0034]FIG. 1 is a diagram showing the construction of a conventional semiconductor device;  
         [0035]    [0035]FIG. 2 is a diagram showing the construction of another conventional semiconductor device;  
         [0036]    [0036]FIG. 3 is a diagram showing the construction of a semiconductor device according to a first embodiment of the present invention;  
         [0037]    [0037]FIG. 4 is a diagram showing the construction of the semiconductor of FIG. 3 in an oblique view with a part thereof removed;  
         [0038]    FIGS.  5 A- 5 F are diagrams showing a fabrication process of the semiconductor device of the first embodiment;  
         [0039]    [0039]FIGS. 6A and 6B are diagrams showing a modified fabrication process of the semiconductor device of the first embodiment;  
         [0040]    [0040]FIG. 7 is a diagram showing a fabrication process of a semiconductor device according to a second embodiment of the present invention;  
         [0041]    [0041]FIG. 8 is a diagram showing the semiconductor device of the second embodiment in a cross-sectional view;  
         [0042]    [0042]FIG. 9 is a diagram showing the semiconductor of the second embodiment in an oblique view;  
         [0043]    [0043]FIG. 10 is a diagram showing the construction of a semiconductor device according to a third embodiment of the present invention; and  
         [0044]    FIGS.  11 A- 11 F are diagrams showing the fabrication process of the semiconductor device of the third embodiment.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0045]    [FIRST EMBODIMENT]  
         [0046]    [0046]FIG. 3 shows a semiconductor device  5  according to a first embodiment of the present invention in a cross-sectional view, while FIG. 4 shows the same semiconductor device  5  formed on a semiconductor wafer  2 A such as a Si wafer in an oblique view for a state before the semiconductor wafer  2 A is diced into individual semiconductor chips  2  along a scribe line  2 B.  
         [0047]    Referring to FIG. 3, the semiconductor device  5  is constructed on the semiconductor chip  2  and includes a circuit substrate  6  that is provided on the semiconductor chip  2 , with an intervening adhesive layer  3   a  that causes the circuit substrate  6  to adhere to the semiconductor chip  2  firmly. The chip  2  carries thereon an electrode pad  8   a  that is connected electrically to a corresponding electrode pad  8   b  on the circuit substrate  6  by way of a bonding wire  4 . Further, the bonding wire  4  is embedded in a resin potting  1 .  
         [0048]    In the construction of the semiconductor device  5  of the present embodiment, the electrical signal appearing on the electrode pad  8   a  of the chip  2  is forwarded to the electrode pad  8   b  on the circuit substrate  6  by way of a bonding wire  4  and further to an electrode pad  8   c  on the circuit substrate  6  by way of a conductor pattern  9  provided on the circuit substrate  6 . The electrode pad  8   c  carries thereon a spherical or semi-spherical solder bump  7  or a suitable spherical electrode. It should be noted that the conductor pattern  9  on the circuit substrate  6  is covered by a solder resist layer  3   b,  and the solder bump  7  projects outwardly from the solder resist layer  3   b  that covers the surface of the circuit substrate  6 . It should be noted that the layer  3   b  is not illustrated in FIG. 3.  
         [0049]    It should be noted that the semiconductor chip  2  is fabricated according to a standard fabrication process of an integrated circuit and supplies the output electrical signal to the electrode pad  8   a  provided thereon.  
         [0050]    On the other hand, the adhesive layer  3   a  is formed of an adhesive material constituted by a principal resin component and a solvent that dissolves a flexibilizer. For example, a reactive thermoplastic resin that contains a carboxyl group or a denatured maleic acid anhydride may be used for the principal resin, while a reactive silicone such as a silicone having an epoxy group may be used for the flexibilizer.  
         [0051]    More specifically, a bisphenol A-type epoxy resin may be used for a binder resin of the adhesive layer  3   a  in combination with a suitable amount of phenol novolak resin, which is used as a curing agent. The binder and the curing agent are then diluted by butylcellosolve acetate and mixed by a rolling process. Further, sieved Al particles having an average diameter in the range of 3-30 μm are added further to the mixture thus obtained, with a proportion such that the adhesive layer contains, in a completely cured state thereof, the Al particles with a proportion of about 30 vol %. The target adhesive is then obtained by adding triphenylphosphine further to the mixture as a cure accelerator, shortly before the end of the roll mixing process, with a proportion of about 2 wt % with respect to the 100 wt % of the epoxy resin.  
         [0052]    The bonding wire  4 , on the other hand, may be formed of a wire of gold or aluminum having a diameter of 25-30 μm and is bonded to the electrode  8   a  or  8   b  by using an ordinary wire bonding apparatus. In the present invention, a first bonding process is conducted to the electrode  8   a  on the chip, followed by a second bonding process that is conducted to the electrode  8   b,  for reducing the overall height of the semiconductor device  5 .  
         [0053]    The circuit substrate  6  is formed of a glass epoxy or polyimide and is bonded to the semiconductor chip  2  by way of the adhesive layer  3   a  as indicated in FIG. 3. It should be noted that the circuit substrate  6  carries thereon the conductor pattern  9 , such that the conductor pattern  9 , which may be formed of Cu, extends from the electrode  8   b  to the electrode  8   c  on which the solder bump  7  is formed. The conductor pattern  9  can be formed in any desired shape by conducting an etching process.  
         [0054]    The solder bump  7  is typically formed of an alloy containing 60 wt % of Sn and 40 wt % of Pb, wherein the composition of the solder bump  7  may be adjusted appropriately depending upon the necessary or desired characteristics of the solder bump. Thus, the solder bump  7  may contain other elements than Sn or Pb. Further, the solder bump  7  may be formed by plating a solder alloy around a spherical or semi-spherical core of Cu or a resin.  
         [0055]    FIGS.  5 A- 5 F show the fabrication process of the BGA device  5  of FIG. 3.  
         [0056]    Referring to FIG. 5A, the adhesive layer  3   a  is provided on a top surface of a semiconductor wafer  10 , wherein the semiconductor wafer  10  includes a number of electronic devices in respective regions each defined by a scribe line  51  and corresponding to a chip, as a monolithic integral body. The adhesive layer  3   a  is formed by a suitable process such as a screen printing process that uses a metal mask or a screen mask. Alternatively, the adhesive layer  3   a  may be formed by a potting process.  
         [0057]    Next, in the step of FIG. 5B, a master circuit substrate  6 A is mounted on the adhesive layer  3   a,  wherein the master circuit substrate  6 A includes a number of the circuit substrates  6  in a mechanically interconnected state by a bridging part  6 B. The master circuit substrate  6 A is thereby adjusted with respect to the electronic devices formed on the wafer  10  such that each of the circuit substrates  6  included in the master circuit substrate  6 A achieves a proper alignment to the corresponding electronic device on the wafer  10 . Thereafter, the adhesive layer  3   a  is cured and the master circuit substrate  6 A is firmly attached to the wafer  10  via the adhesive layer  3   a.  In the construction of FIG. 5B, it should be noted that there is formed a groove in correspondence to the scribe line  51  such that the top surface of the wafer  10  is exposed at the groove  51 .  
         [0058]    Of course, it is possible to form the master circuit substrate  6 A first and attach the semiconductor wafer  10  to the circuit substrate  6 A by interposing the adhesive layer  3   a  therebetween.  
         [0059]    Next, in the step of FIG. 5C, the electrode pads (not shown) on the wafer  10  exposed by the groove  51  are interconnected to corresponding electrode pads on the master circuit substrate  6 A by respective bonding wires  4 , by conducting a wire bonding process in each of the regions of the wafer  10  and in each of the circuit substrates  6  included in the master circuit substrate  6 A. Preferably, the wire bonding process of FIG. 5C is conducted first by bonding an end of the bonding wire  4  to an electrode pad on the wafer  10 , followed by bonding an opposite end of the bonding wire  4  to an electrode pad on the master circuit substrate  6 A. By doing so, it becomes possible to reduce the loop height of the bonding wire  4 .  
         [0060]    Next, in the step of FIG. 5D, the bonding wire  4  is embedded into the resin potting  1 , which is provided along the scribe line  51  as indicated in FIG. 5D, and the solder bumps  7  are formed on the top surface of the master circuit substrate  6 A as indicated in FIG. 5E. The solder bump  7  is formed easily by causing a reflowing of a solder ball which is placed on the electrode pad  8   c  shown in the oblique view of FIG. 4. By covering the solder ball by a flux layer and transferring the flux layer to the electrode pad  8   c,  the formation of the semi-spherical solder bump  7  is achieved successfully upon reflowing of the solder ball.  
         [0061]    The structure thus obtained is then diced in the step of FIG. 5F by applying a dicing saw  50  along the dicing line  51 , and the semiconductor device  5  of FIG. 3 is obtained. As a result of the foregoing dicing process, the semiconductor wafer  10  is divided into individual semiconductor chips  2 . Similarly, the master circuit substrate  6 A is divided into individual circuit substrates  6 .  
         [0062]    The semiconductor device  5  thus formed has a characteristic feature that the side wall of the semiconductor chip  2  forms a flush surface with a side wall of the resin potting  1  and that the side wall of the semiconductor chip  2  is substantially perpendicular to the principal surface of the semiconductor chip  2 . Further, the foregoing fabrication process, particularly the dicing process of FIG. 5F is advantageous for avoiding the problem of chipping of the semiconductor chip, by protecting the semiconductor wafer by the resin potting  1  along the scribe line  51 .  
         [0063]    [0063]FIG. 6A shows a preferable modification of the wire bonding process of FIG. 5C conducted by a bonding tool  52 , in which the master circuit substrate  6 A includes a depressed region adjacent to the scribe line  51 , and it can be seen that an electrode pad  8   b  is formed on such a depressed region. As indicated in FIG. 6A, the electrode pad  8   b  is connected to a corresponding electrode  8   a  on the wafer  10  by the bonding wire  4 . The construction of FIG. 6A is advantageous for reducing the loop height of the bonding wire  4 .  
         [0064]    [0064]FIG. 6B shows a part of the semiconductor device that is formed from the half-product of FIG. 6A.  
         [0065]    Referring to FIG. 6B, it can be seen that the semiconductor device has an advantageous feature in that the bonding wire  4 , and hence the resin potting  1  holding the bonding wire  4  therein, is substantially accommodated in the depression formed at the edge of the circuit substrate  6 A facing the scribe line  51 . Thus, the risk that the solder bumps  7  on the top surface of the circuit substrate  6 A failing to make a contact with an external electronic device due to the projection of the resin potting  1  is positively eliminated. Associated therewith, it should be noted that the size or diameter of the solder bumps  7  can be reduced without causing a problem of failure of contact with the external electronic device.  
         [0066]    As already noted, the present invention as set forth above with reference to the first embodiment successfully eliminates the complex and time-consuming alignment process for achieving a proper alignment between a semiconductor chip and a corresponding minute circuit substrate, and the efficiency of production of the BGA semiconductor device is improved substantially.  
         [0067]    [SECOND EMBODIMENT]  
         [0068]    [0068]FIG. 7 shows a fabrication process of a BGA semiconductor device  15  according to a second embodiment of the present invention.  
         [0069]    Referring to FIG. 7, the semiconductor wafer  10  carries an adhesive layer  13   a  corresponding to the adhesive layer  3   a,  and a master circuit substrate  16 A is provided on the adhesive layer  13   a  in correspondence to the master circuit substrate  6 A of FIG. 5F. Further, spherical or semi-spherical solder bumps  17  are provided on the top surface of the master circuit substrate  16 A in correspondence to the solder bumps  17 .  
         [0070]    In the present embodiment, the groove  51  formed in the master circuit substrate  16 A and exposing the top surface of the wafer  10  is not used for the scribe line, and the electrode pads on the exposed top surface of the wafer  10  along the groove  51  are connected electrically to corresponding electrode pads on the master circuit substrate  16 A by way of respective bonding wires  14 . The bonding wires  14  are further embedded into a resin potting  11 .  
         [0071]    In the present embodiment, a groove  61  is formed at a location bisecting the region of the master circuit substrate  16 A located between a first groove  51  and an adjacent groove  51 , and the dicing is conducted along the groove  61  by applying a dicing saw to the groove  61  in a state that the groove  61  is filled by a resin potting similar to the resin potting  1 .  
         [0072]    [0072]FIGS. 8 and 9 show the BGA semiconductor device  15  of the present embodiment in detail respectively in a cross sectional view and in an oblique view for a state after the dicing process is conducted.  
         [0073]    Referring to FIGS. 8 and 9, it should be noted that electrode pads  18   a  corresponding to the electrode pads  8   a  are provided on the exposed top surface of the chip  12 , wherein the chip  12  is formed as a result of dicing of the wafer  10  along the scribe lines  61  of FIG. 7.  
         [0074]    The electrode pads  18   a  are formed in the groove in a criss-cross pattern, and each electrode pad  18   a  is connected to a corresponding electrode pad  18   b  provided on the top surface of the circuit substrate  16 , which is obtained as a result of the dicing of the master circuit substrate  16 A, by a bonding wire  14 . The circuit substrate  16  further carries a number of conductor patterns  19  each extending between an electrode pad  18   a  and an electrode pad  18   c,  wherein the electrode pad  18   c  is provided on the top surface of the master circuit substrate  16 A and hence on the top surface of the circuit substrate  16  in correspondence to the electrode pad  8   c  of FIG. 4. Further, the top surface of the circuit substrate  16  is protected by a solder resist  13   b  except for the part where the solder bumps  17  are formed.  
         [0075]    In the BGA device of the present embodiment, the bonding wires  14  are used to connect the corresponding electrode pads  18   a  and the electrode pads  18   b  at a central part of the chip  12 , as indicated in FIG. 8. Further, the BGA semiconductor device of the present invention is laterally surrounded by the resin potting  1 .  
         [0076]    The fabrication process of the BGA device of the present invention is substantially identical with that of the BGA device of the first embodiment, except that there is a difference in the shape of the circuit substrate  16  or in the location of the groove in which the wire bonding is made.  
         [0077]    The present embodiment is advantageous in the point that it enables a saving of the area that is used for achieving the wire bonding process.  
         [0078]    [THIRD EMBODIMENT]  
         [0079]    [0079]FIG. 10 shows the construction of a BGA semiconductor device  25  fabricated according to a third embodiment of the present invention.  
         [0080]    Referring to FIG. 10, the semiconductor device  25  includes a circuit substrate  26  corresponding to the circuit substrate  6 , wherein the circuit substrate  26  is formed of a polyimide film carrying thereon a conductor pattern and is mounted on a semiconductor chip  22  corresponding to the semiconductor chip  2  without an intervening adhesive layer. The conductor pattern on the polyimide film  26  may be formed by an etching process. On the polyimide film  26 , there are provided a plurality of semi-spherical solder bumps  27  in correspondence to the solder bumps  7  on the circuit substrate  6 . The foregoing conductor pattern on the polyimide film  26  is connected to the electrode pads on the semiconductor chip  22  by way of bonding wires  24 . Further, the bonding wires  24  are embedded in a resin potting  21 , wherein it should be noted that the resin potting  21  further supports the polyimide film  26  on the top surface of the semiconductor chip  22 .  
         [0081]    Hereinafter, the fabrication process of the BGA device  25  of the present invention will be described with reference to FIGS.  11 A- 11 F.  
         [0082]    Referring to FIG. 11A, the polyimide film  26 , which carries thereon the conductor pattern, is aligned with respect to the Si wafer  10 . In FIG. 11A, it should be noted that the polyimide film  26  forms a continuous film as indicated by a broken line. On the other hand, the polyimide film  26  includes a cutout in correspondence to the broken line, and the top surface of the Si wafer  10  is exposed at the foregoing cutout. It should be noted that the polyimide film  26  is disposed on the wafer  10  such that the cutout is aligned with the scribe line  51  defined in the wafer  10 .  
         [0083]    The polyimide film  26  thus aligned is then fixed temporarily on the wafer  10  by a jig such as a clip as indicated in FIG. 11B, and a wire bonding process is conducted in the step of FIG. 11C by using the bonding wire  24 . Thereby, the length of the bonding wire  24  is set to be slightly larger than the length needed in the wire bonding process conducted in the state of FIG. 11C.  
         [0084]    Next, an injection of the resin  21  is conducted in the step of FIG. 11D along a periphery of the wafer  10 , and the polyimide film  26  is lifted in the upward direction from the wafer  10  as indicated in FIG. 11D as a result of such an injection of the resin  21 . Thereby, the length of the bonding wire  24  is chosen such that the polyimide film  26  can be lifted freely in the upward direction with a predetermined distance. Such an injection of the resin  21  is easily implemented by using an apparatus that is used conventionally in the mounting process of a flip-chip package device or a BGA package device for introducing an under-fill resin between the mounting substrate and the chip or a BGA package.  
         [0085]    After the step of FIG. 11D, the solder bumps  27  are formed on the corresponding electrode pads of provided on the polyimide film  26  as indicated in FIG. 11E, and the structure of FIG. 11E is diced in the step of FIG. 11F along the scribe lines by applying a dicing saw  50 . As a result of the dicing step of FIG. 11F, the BGA device  25  of FIG. 10 is obtained in which it should be noted that the chip  22  and the resin body  21  have a common, flush side wall perpendicular to the principal surface of the chip  22 .  
         [0086]    In the dicing step of FIG. 11F, it should be noted that the dicing of the semiconductor wafer  10  is conducted in the state that the wafer  10  is protected by the resin  21 . Thus, the problem of chipping of the diced semiconductor chip  22  is effectively avoided.  
         [0087]    In the present embodiment, too, it should be noted that the proper alignment between the individual chip  22  and the polyimide circuit substrate  26  is achieved easily, by conducting such an alignment process before the semiconductor wafer  10  is divided into individual semiconductor chips  22 . Further, the present embodiment can eliminate the process of applying an adhesive film on the wafer  10 .  
         [0088]    Further, the present invention is by no means limited to the embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention as set forth in claims.