Abstract:
A fabrication method of a semiconductor device is disclosed. The method includes the following steps. First, a given number of projection electrodes are formed on each of a given number of semiconductor chips, and a thermosetting insulating adhesive is applied to areas of mounting parts where the semiconductor chips are to be mounted on a substrate. Second, the thermosetting insulating adhesive on the substrate is heated with a half-thermosetting temperature. Third, the semiconductor chips are aligned to the mounting parts of the substrate and a first fixing of the semiconductor chips is performed with a first pressure. Fourth, the substrate, on which the semiconductor chips are fixed, is heated with a thermosetting temperature of the thermosetting insulating adhesive, and a second fixing of the semiconductor chips is performed with a second pressure.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a method and a system for fabricating a semiconductor device, and more particularly, to a method and a system for fabricating a semiconductor device, in which a flip-chip connection is performed.  
         [0003]     Recently, according to a progress of a high-density integration of the semiconductor device, the flip-chip connection with bumps is frequently used to perform a high-density mounting of a semiconductor chip and to shorten a length of routing lines for requirement of a fast operation. Further, such a semiconductor device has to be fabricated with a low cost. To meet the above requirements, it is necessary to achieve a considerably precise alignment in the mounting of the semiconductor chip with the low cost.  
         [0004]     2. Description of the Prior Art  
         [0005]      FIGS. 1A  to  1 E show illustrations for explaining fabrication procedures of a conventional flip-chip-type semiconductor device. In  FIG. 1A , a given number of stud-bumps  14  (bonding balls only) are formed on aluminum pads of a semiconductor chip  11  by using a wire  13  (made of, for example, aluminum, copper, gold, etc.) with a wire-bonding technology.  
         [0006]     In heights of the stud-bumps  14 , there is generally a dispersion of about 20 μm. Therefore, in  FIG. 1B , to make the heights of the stud-bumps  14  uniform, the stud-bumps  14  of the semiconductor chip  11  are pressed against a flat glass plate  15  for leveling.  
         [0007]     In  FIG. 1C , in advance, a conductive adhesive  16  is skidded on a flat glass plate  15   a  (may be the flat glass plate in  FIG. 5B ), and a portion  16   a  of the conductive adhesive  16  on the flat glass plate  15   a  is adhered to an end of each stud-bump  14  by pressing the stud-bumps  14  against a surface of the conductive adhesive  16  for a given period.  
         [0008]     In  FIG. 1D , based on a number of the stud-bumps  14  on the semiconductor chip  11 , a thermosetting insulating adhesive  18  is applied on a substrate  17 , in which mounting pads  17   a  are formed, for reinforcement by a screen-printing method. And the semiconductor chip  11  which is absorbed by a bonding head (not shown) is moved over the substrate  17 .  
         [0009]     In  FIG. 1E , the stud-bumps  14  on the semiconductor chip  11  are aligned to the mounting pads  17   a  on the substrate  17 . And subsequently, these components are pressed and heated by the bonding head. In this way, the flip-chip connection and the mounting process of the semiconductor chip  11  to the substrate  17  are simultaneously performed.  
         [0010]     In this case, the bonding head is equipped with a heat source, and the insulating adhesive  18  is thermoset by the heat source to reinforce the flip-chip connection.  
         [0011]     As a method of heating, another method is known in Japanese Laid-Open Patent Application No. 5-67648, wherein the alignment, the heating, and the pressing are simultaneously performed by nozzles arranged around the bonding head to jet hot winds.  
         [0012]     Further, another heating method is known in Japanese Laid-Open Patent Application No. 3-184352. In this method, not shown in a drawing here, the bumps of the semiconductor chip are aligned and mounted by only the heating over the mounting pads of the substrate  17 . After that, the thermosetting insulating adhesive is applied and infiltrated into the mounting pads and the bumps. Then the insulating adhesive is thermoset by heating it in a heating block or thermostat.  
         [0013]     In  FIG. 1E , the mounting pads  17   a  and the stud-bumps  14  are not only aligned and pressed, but are also heated to thermoset the insulating adhesive  18 . However, a fabrication apparatus for performing such processes must have a considerably precise alignment mechanism and a heating mechanism. A cost of such a fabrication apparatus is high. Therefore, by spending time for thermosetting the insulating adhesive  18  with the high-cost fabrication apparatus, there is thus a problem that a mounting cost of the semiconductor chip is increased.  
         [0014]     On the other hand, in the Japanese Laid-Open Patent Application No. 3-184352, first the semiconductor chip is mounted by pressing only, and next it is heated. However, a difference (about 4 times) in thermal expansion between the semiconductor chip and the substrate makes the flip-chip connection imperfect.  
       SUMMARY OF THE INVENTION  
       [0015]     It is an object of this invention to provide a method and a system for fabricating a semiconductor device, in which a fabrication apparatus cost and a fabrication cost may be reduced, and a perfect flip-chip connection may be performed, in which the disadvantages described above are eliminated.  
         [0016]     The object described above is achieved by a fabrication method of a semiconductor device comprising the steps of: (a) forming a given number of projection electrodes on each of a given number of semiconductor chips, and applying a thermosetting insulating adhesive to areas of mounting parts where the semiconductor chips are to be mounted on a substrate; (b) heating the thermosetting insulating adhesive on the substrate with a half-thermoset temperature; (c) aligning the semiconductor chips to the mounting parts of the substrate and performing a first fixing of the semiconductor chips with a first pressure; and (d) heating the substrate, on which the semiconductor chip is fixed, with a thermosetting temperature of the thermosetting insulating adhesive, and performing a second fixing of the semiconductor chips with a second pressure.  
         [0017]     The object described above is also achieved by the fabrication method of the semiconductor device described above, wherein the first pressure is lower than the second pressure.  
         [0018]     The object described above is further achieved by the fabrication method of the semiconductor device described above, wherein the second fixing is simultaneously performed for each of semiconductor chips with the second pressure.  
         [0019]     In addition, the object described above is achieved by the fabrication method of the semiconductor device described above, wherein the given number of the projection electrodes are formed as studs by wire bonding, the studs being leveled.  
         [0020]     The object described above is further achieved by the fabrication method of the semiconductor device described above, wherein the step (a) further comprises the step (a- 1 ) of forming a conductive adhesive on the projection electrodes.  
         [0021]     The object described above is also achieved by the fabrication method of the semiconductor device described above, wherein in the step (a- 1 ), the conductive adhesive on the projection electrodes is formed by a conductive adhesive, which has been skidded on a plate, being transcribed onto the projection electrodes.  
         [0022]     The object described above is also achieved by a fabrication system of a semiconductor device comprising: a chip loading device forming a given number of projection electrodes on each of a given number of semiconductor chips; a substrate loading device loading a substrate having mounting parts on which the semiconductor chips are to be mounted; an adhesive-application device applying a thermosetting insulating adhesive to areas of the mounting parts of the substrate; an alignment-and-pressing device heating the thermosetting insulating adhesive on the substrate with a half-thermosetting temperature, aligning the semiconductor chips to the mounting parts of the substrate, and performing a first fixing of the semiconductor chips with a first pressure; and a pressing-and-heating device heating the substrate, on which the semiconductor chips are fixed, with a thermosetting temperature of the thermosetting insulating adhesive, and performing a second fixing of the semiconductor chips with a second pressure.  
         [0023]     According to the fabrication method of the semiconductor chip, first the semiconductor chip, on which the projection electrodes are formed, is aligned to the substrate, and is fixed in the first fixing by the pressing only. After that, the pressing and heating for thermosetting the insulating adhesive are performed. In such way, the first fixing is performed in a different process from the pressing and heating.  
         [0024]     In such a process, a less expensive apparatus may be individually applied for an alignment mechanism and a heating mechanism, so that a cost of fabrication apparatus may be reduced. And since at the final pressing and heating, the alignment is already finished, several processes, such as pressing, heating, and aligning, may be performed by a single process. Thus, throughput is improved, and, as a result, a fabrication cost may be also reduced.  
         [0025]     And according to the fabrication method of the semiconductor chip, the first pressure is lower than the second pressure. Therefore, when the semiconductor chip with the projection electrodes is fixed in the first fixing with the first pressure, a dispersion of a degree of collapse of the projection electrodes may be absorbed.  
         [0026]     Further according to the fabrication method of the semiconductor chip, the second fixing of the semiconductor chips is performed for each semiconductor chip with the second pressure. Therefore, multi-heads for pressing and heating become available, which leads to an improved mounting operation.  
         [0027]     Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIGS. 1A  to  1 E show illustrations for explaining fabrication procedures of a conventional flip-chip-type semiconductor device;  
         [0029]      FIG. 2  shows an overall block diagram of a fabrication system for realizing a fabrication method according to the present invention;  
         [0030]      FIG. 3  shows a flowchart explaining fabrication procedures of a semiconductor device according to the present invention;  
         [0031]      FIGS. 4A  to  4 F show illustrations for explaining the fabrication procedures of the semiconductor device according to the present invention; and  
         [0032]      FIG. 5  shows an overall illustration of the semiconductor device as a multi-chip module fabricated according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     First, a description will be given of first embodiment of a fabrication method of a semiconductor device according to the present invention, by referring to  FIG. 2 .  FIG. 2  shows an overall block diagram of a fabrication system  21  for realizing the fabrication method according to the present invention.  
         [0034]     In the fabrication system shown in  FIG. 2 , a chip loader  22  supplies a semiconductor chip on which a given number of electrode pads (e.g. aluminum pads) are formed, and a bonder  23  forms stud-bumps as projection electrodes on the semiconductor chip by means of a wire-bonding technology.  
         [0035]     A transcribing device  24  transcribes a conductive adhesive on a surface of the stud-bumps. A cure/alignment-and-pressing device  25  heats a substrate with an adhesive-half-thermosetting temperature, and aligns the semiconductor chip, on which stud-bumps are formed, to the substrate by a stepper to perform a first fixing with a first pressure.  
         [0036]     A substrate loader  26  supplies the substrate on which mounting pads as a mounting part are formed based of a number of the stud-bumps of each semiconductor chip. An adhesive-application device  27  applies, to the supplied substrate, a constant amount of a thermosetting insulating adhesive on areas of the mounting pads which correspond to each semiconductor chip, by using a dispenser, and then supplies the substrate to the cure/alignment-and-pressing device  25 .  
         [0037]     A pressing-and-heating device  28  presses the semiconductor chip fixed on the substrate with a second pressure, and heats it with a temperature by which the insulating adhesive is thermoset to perform a second fixing. An unloader  29  issues the substrate on which the semiconductor chip is mounted.  
         [0038]      FIG. 3  shows a flowchart explaining fabrication procedures of the semiconductor device according to the present invention, and  FIGS. 4A  to  4 F show illustrations for explaining the fabrication procedures of the semiconductor device according to the present invention. First, a semiconductor chip  31  is moved from the chip loader  22  to the bonder  23 , stud-bumps  34  are generated from a wire  33  (for example an aluminum wire, and for electrode pads made of copper or gold, a copper wire or a gold wire) by a capillary  32 , and subsequently, by means of a wire-bonding technology, the stud-bumps  34  are formed on electrode pads (not shown) which are formed on the semiconductor chip  31  (a step S 1  in  FIG. 3 ,  FIG. 4A ).  
         [0039]     In these stud-bumps  34  on the semiconductor chip  31 , there is a dispersion of height of about 20 μm. Therefore, to make their height uniform, the stud-bumps  34  are pressed to a flat glass plate  35  for leveling (a step S 2  in  FIG. 3 ,  FIG. 4B ). Then, the semiconductor chip  31  is moved to the transcribing device  24 .  
         [0040]     In the transcribing device  24 , in advance, a conductive adhesive  36  is skidded thinly on a flat glass plate  35   a . A conductive adhesive  36   a  is transcribed on surfaces of the stud-bumps  34  by pressing the stud-bumps  34  to the conductive adhesive  36  with heating (a step S 3  in  FIG. 3 ,  FIG. 4C ). The skidding of the conductive adhesive  36  on the flat glass plate  35   a  is performed by pushing out the conductive adhesive  36  onto the flat glass plate  35  with a rubber contacted with the conductive adhesive  36  using a skidder.  
         [0041]     On the other hand, in the substrate loader  26 , mounting pads  37   a  are formed on a substrate  37  based on a number of the stud-bumps of the semiconductor chip  31 , and this substrate  37  with the mounting pads  37   a  is supplied to the adhesive-application device  27 . In this device  27 , a thermosetting insulating adhesive  38  is applied in each area of the mounting pads  37   a  corresponding to each semiconductor chip  31  (a step S 4  in  FIG. 3 ). And subsequently, the substrate  37  is moved over a heat plate of the cure/alignment-and-pressing device  25  ( FIG. 4D ).  
         [0042]     This substrate  37  is precured at a temperature by which the insulating adhesive  38  is half-thermoset on the substrate  37 , by the heat plate  39  (a step S 5  in  FIG. 3 ). At a later step, when the substrate  37  on which the semiconductor chip  31  is mounted is moved to the pressing-and-heating device  28 , a positioning gap may happen due to a moving shock. For preventing an occurrence of such a positioning gap, this precuring process is implemented to obtain strong adhesion with the semiconductor chip  31  by half-thermosetting the insulating adhesive  38  (reducing a degree of viscosity and thixotropy).  
         [0043]     Then, in the device  25 , the semiconductor chip  31  is absorbed by a bonding head  40 , and each stud-bump  34  is aligned over a respective mounting pad  37   a  of the substrate  37 . At the same time, the bonding head  40  with the semiconductor chip  31  is pressed against the mounting pads  37   a  with the first pressure to perform a tentative fixing (a step S 6  in  FIG. 3 ,  FIG. 4E ). Then, the insulating adhesive  38  on the substrate  37  is cured by the heat plate  39 .  
         [0044]     The substrate  37 , onto which all of the semiconductor chip  31  is tentatively fixed, is moved to the pressing-and-heating device  28  by a transiting rail, etc., to dispose it on an adhesive-hardening stage  41  (a step S 7  in  FIG. 3 ). A heater block  42 , which is able to move freely in a vertical direction, is positioned over the adhesive-hardening stage  41 . And the heater block  42  is equipped with a given number of pressing-and-heating heads  42   a , the given number corresponding to a number of semiconductor chips  31  or a given number of semiconductor-chip groups. Each of the pressing-and-heating heads  42   a  has a function which can keep the heads  42   a  at the same vertical height.  
         [0045]     By heating the heater block  42 , heat of a temperature which the insulating adhesive  38  is thermoset is transmitted to the pressing-and-heating heads  42   a . When the heater block  42  is moved downward, the pressing-and-heating heads  42  are pressed against each semiconductor chip  31  with the second pressure, and simultaneously thermoset the insulating adhesive  38  to perform the second fixing (a step S 8  in  FIG. 3 ,  FIG. 4F ).  
         [0046]     In this case, the second pressure is set larger than the first pressure. This method may absorb a dispersion of a degree of collapse of the bumps  34 , and a dispersion of a thickness of the mounting pads  37   a  of the substrate  37 , which occur when the substrate  37  is pressed. This method may also absorb a difference of thermal expansion between the substrate  37  and the semiconductor chip  31  during heating. These procedures achieve an significantly improved flip-chip connection.  
         [0047]      FIG. 5  shows an overall illustration of the semiconductor device as a multi-chip module fabricated according to the present invention. As shown in  FIG. 5 , the semiconductor device  51  is a multi-chip module in which for example five semiconductor chips  31  are flip-chip-connected with the substrate  37  by the stud-bumps  34 , and are fixed to the substrate  37  with the thermosetting insulating adhesive  38 .  
         [0048]     In this fabrication method of the semiconductor device, a tentative-fixing process for alignment and a pressing-and-heating process are individually performed. Therefore, individual apparatuses for the respective processes may be prepared such as the cure/alignment-and-pressing device  25  for precise alignment and the pressing-and-heating device  28  for pressing and heating. Thus, an expensive apparatus which has both an alignment mechanism and a heating mechanism is unnecessary. The above advantages enable a fabrication apparatus cost to be reduced.  
         [0049]     Further, in the cure/alignment-and-pressing device  25 , the heating for thermosetting the insulating adhesive  38  is not carried out, but the semiconductor chip  31  is aligned and mounted on the substrate  37 . Therefore, it is easy to operate this fabrication apparatus for mounting many chips. This leads to a reduction of a fabrication cost.  
         [0050]     And a plurality of the pressing-and-heating heads  42   a  may be implemented in the pressing-and-heating device  28 , so that a mounting operation becomes also easier, and this also leads to a reduction of the fabrication cost.  
         [0051]     As described above, the present invention has the following features.  
         [0052]     According to the fabrication method of the semiconductor chip, first, the semiconductor chip, on which the projection electrodes are formed, is aligned to the substrate, and is fixed in the first fixing by the pressing only. After that, pressing and heating for thermosetting the insulating adhesive are performed. In such way, the first fixing for the precise alignment is performed in a different process from the pressing and heating.  
         [0053]     In such a process, a less expensive apparatus may be individually applied for an alignment mechanism and a heating mechanism, so that the cost of the fabrication apparatus may be reduced. And at the final pressing and heating, the alignment is already finished, therefore, several processes, such as pressing, heating, and aligning, may be performed by a the single process. Thus, the throughput is improved, and as a result, the fabrication cost may be also reduced.  
         [0054]     And according to the fabrication method of the semiconductor chip, the first pressure is lower than the second pressure. Therefore, when the semiconductor chip with the projection electrodes is fixed in the second fixing with the second pressure, the dispersion of the degree of collapse of the projection electrodes may be absorbed.  
         [0055]     Further according to the fabrication method of the semiconductor chip, the second fixing of the semiconductor chips is performed for each semiconductor chip with the second pressure. Therefore, multi-heads for pressing and heating become available, which leads to the improved mounting operation.  
         [0056]     Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention.