Abstract:
A flush system comprising a network of conduits, valves and screens that can be interposed between the process container and solvent re-claim tank components of a dry film photoresist (DFR) remover system, for example, that is used in the processing and packaging of integrated circuit chips. By operation of the valves in the flush system, DFR particles can be removed from the DFR remover system in order to prevent or minimize particle clogging of a particle filter in the DFR remover system. The screens in the flush system can be periodically cleaned by reverse flow of solvent or by operation of a nitrogen and DI (deionized) water purge system.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the packaging of semiconductor integrated circuits. More particularly, the present invention relates to an auto flush system for a dry film photoresist remover which is used to remove a photoresist film from a semiconductor chip after the formation of ball grid array (BGA) solder bumps on the chip.  
         BACKGROUND OF THE INVENTION  
         [0002]    One of the last processes in the production of semiconductor integrated circuits (IC) is multi-leveled packaging, which includes expanding the electrode pitch of the IC chips containing the circuits for subsequent levels of packaging; protecting the chip from mechanical and environmental stress; providing proper thermal paths for channeling heat dissipated by the chip; and forming electronic interconnections. The manner in which the IC chips are packaged dictates the overall cost, performance, and reliability of the packaged chips, as well as of the system in which the package is applied.  
           [0003]    Package types for IC chips can be broadly classified into two groups: hermetic-ceramic packages and plastic packages. A chip packaged in a hermetic package is isolated from the ambient environment by a vacuum-tight enclosure. The package is typically ceramic and is utilized in high-performance applications. A chip packaged in a plastic package, on the other hand, is not completely isolated from the ambient environment because the package is composed of an epoxy-based resin. Consequently, ambient air is able to penetrate the package and adversely affect the chip over time. Recent advances in plastic packaging, however, has expanded their application and performance capability. Plastic packages are cost-effective due to the fact that the production process is typically facilitated by automated batch-handling.  
           [0004]    A recent development in the packaging of IC chips is the ball grid array (BGA) package, which may be utilized with either ceramic packages or plastic packages and involves different types of internal package structures. The BGA package uses multiple solder balls or bumps for electrical and mechanical interconnection of IC chips to other microelectronic devices. For example, a very large scale integration (VLSI) or an ultra large scale integration (ULSI) chip may be electrically connected to a circuit board or other next level packaging substrate using the solder balls or bumps. The BGA technique is included under a broader connection technology known as “Controlled Collapse Chip Connection-C4” or “flip-chip” technology.  
           [0005]    As illustrated in FIG. 1, in BGA or “flip-chip” packaging technology, the IC chip substrate  1 , which often contains millions of integrated circuits, is initially layered with a fixture or solder resist material  2 , which may be a dry film photoresist (DFR) layer and which functions as a mold for subsequent formation of multiple solder bumps  4  on the chip substrate  1 . The DFR layer  2  is typically about 120 μm thick, and multiple apertures  3 , corresponding to the matrix array of solderable surfaces on the chip substrate  1 , extend through the PR layer  2 . Solder paste is then applied to the DFR layer  2  using a squeegee, and the solder paste fills the apertures  3 . As the solder paste is subsequently reflowed by heating, the solder paste forms mushroom-shaped solder bumps  4  which attach to solder pads on the surface of the chip substrate  1 . Finally, the DFR layer is removed, leaving the solder bumps  4  on the surface of the chip substrate  1  for connection of microelectronic devices thereto.  
           [0006]    [0006]FIG. 2 illustrates a typical conventional system for removal of dry film photoresist (DFR) polymer material. The system  10  includes a process container  11 , typically having an outer tank  12  connected in fluid communication with an inner tank  13 . A container outlet conduit  15  leads from the inner tank  13  to a solvent re-claim tank  16 , which is connected to a particle filter  18  by a tank outlet conduit  17 . The particle filter  18  is capable of filtering particles of about 0.1 μm wide and larger. A filter outlet conduit  19  connects the particle filter  18  to a circulation pump  20 , and a pump outlet conduit  21  connects the circulation pump  20  to the outer tank  12  of the process container  11 .  
           [0007]    [0007]FIG. 3 illustrates a typical process for removing the DFR polymer film  2  from the chip substrate  1  after formation of the solder bumps  4  thereon, using the system  10  of FIG. 2. After the chip substrate  1  is initially placed in the inner tank  13  of the process container  11 , organic solvent normally contained in the outer tank  12  is allowed to flow into the inner tank  13 . The chip substrate  1  is allowed to soak in the organic solvent for about 510 minutes, during which time DFR particles  6  begin to dislodge from the DFR layer  2  into the solvent. Finally, the chip substrate  1  is agitated in the inner tank  13 , such as by use of sonic waves, and the remaining DFR particles  6  are dislodged from the chip substrate  1  and into the solvent. The chip substrate  1  is then removed from the inner tank  13 , with the DFR layer  2  removed therefrom and the solder bumps  4  remaining thereon. The organic solvent is then drained from the outer tank  12  and into the solvent re-claim tank  16  and stored there until subsequent use of the solvent is required, at which time the solvent is distributed by operation of the circulation pump  20 , through the particle filter  18  and back into the outer tank  12  of the process container  11 .  
           [0008]    As it flows from the outer tank  12 , the solvent carries DFR particles having a variety of sizes to the solvent re-claim tank  16 , and subsequently, to the particle filter  18 , which effectively screens all particles having a size of typically about 0.1 μm and larger and prevents these particles from entering and clogging the circulation pump  20 . However, many of the particles screened by the particle filter  18  have a size of about 1.5 mm to about 2.0 mm, and these larger particles tend to clog the particle filter  18  to such a degree as to render the particle filter  18  inoperative after about 2 hours of operation. Consequently, the particle filter  18  must be cleaned or replaced after about 2 hour segments of operation of the system  10 , resulting in significant down-time for semiconductor chip processing.  
         SUMMARY OF THE INVENTION  
         [0009]    Therefore, an object of the present invention is to provide a flush system for flushing particles from a dry film photoresist remover system.  
           [0010]    Another object of the present invention is to provide a flush system which facilitates enhanced operating efficiency in a dry film photoresist remover system.  
           [0011]    Still another object of the present invention is to provide a self-cleaning flush system for removing particles from a dry film photoresist remover system.  
           [0012]    Yet another object of the present invention is to provide a flush system for removing particles from a dry film photoresist remover system, which flush system may be connected to a process controller for automatic operation of the flush system.  
           [0013]    A still further object of the present invention is to provide a flush system which is capable of facilitating increasing the wafer per hour (WPH) processing of semiconductor wafer chips in a semiconductor production facility.  
           [0014]    In accordance with these and other objects and advantages, the present invention is directed to a flush system comprising a network of conduits, valves and screens interposed between the process container and solvent re-claim tank components of a dry film photoresist (DFR) remover system that is used in the processing and packaging of integrated circuit chips. By operation of the valves in the flush system, DFR particles can be removed from the DFR remover system in order to prevent or minimize particle clogging of a particle filter in the DFR remover system. The screens in the flush system can be periodically cleaned by reverse flow of solvent or by operation of a nitrogen and DI (deionized) water purge system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The invention will now be described, by way of example, by reference to the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1 is a cross-sectional view of a portion of a semiconductor IC chip, illustrating a DFR (dry film photoresist) layer formed on the chip substrate and solder bumps formed on the substrate using the DFR layer as a mold;  
         [0017]    [0017]FIG. 2 is a schematic view of a conventional dry film photoresist layer remover system;  
         [0018]    [0018]FIG. 3 is a flow diagram illustrating removal of the DFR layer from the chip substrate after formation of solder bumps thereon;  
         [0019]    [0019]FIG. 4 is a schematic view illustrating the flush system of the present invention; and  
         [0020]    [0020]FIG. 5 is a side view, taken along section line  5  in FIG. 4, of a DI water and nitrogen gas purge system for the flush system of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The present invention has particularly beneficial utility in flushing particles from a solvent in a dry film photoresist remover system used in the processing of semiconductor IC chips. However, the invention is not so limited in application and while references may be made to such dry film photoresist remover systems, the invention is more generally applicable to flushing particles from liquids in a variety of industrial and product applications.  
         [0022]    Referring to FIGS. 4 and 5 of the drawings, a flush system of the present invention, suitable for implementation in a dry film photoresist (DFR) remover system used in the semiconductor production industry, is generally indicated by reference numeral  25 . The flush system  25  is interposed between the inner tank  13  of the upstream process container  11  and the downstream solvent re-claim tank  16  of the DFR remover system and is designed to prevent excessive clogging of a particle filter  18 , which is connected to the solvent re-claim tank  16  by means of a tank outlet conduit  17 , as described above with respect to the conventional DFR remover system  10  of FIG. 2. The particle filter  18  is connected to a circulation pump  20  by a filter outlet conduit  19 , and the circulation pump  20  is connected to the outer tank  12  of the process container  11  by a pump outlet conduit  21 , in conventional fashion. The flush system  25  of the present invention includes an elongated, sloped circulation conduit  26 , the rear, upstream or upper end of which is provided in fluid communication with a container outlet conduit  15  that drains the inner tank  13 , and the opposite front, downstream or lower end of which circulation conduit  26  is disposed in fluid communication with the solvent re-claim tank  16 . A flush loop  29  of the flush system  25  includes a flush loop intake conduit  30  which is connected to the circulation conduit  26  through a loop entry valve  35 ; a flush loop pump  31  provided in fluid communication with the flush loop intake conduit  30 ; a pump conduit  32  extending from the flush loop pump  31 ; and a circulation re-entry conduit  33  which extends from the pump conduit  32  and is connected to the circulation conduit  26 . A circulation valve  28  is provided in the circulation conduit  26 , between the loop entry valve  35  and the circulation re-entry conduit  33  of the flush loop  29 . A loop screen  34 , having screen openings or pore sizes of typically about 12 μm, is further provided in the circulation conduit  26 , between the circulation valve  28  and the circulation re-entry conduit  33 . A backflow valve  37  is provided in the circulation conduit  26 , between the discharge end of the circulation re-entry conduit  33  and the solvent re-claim tank  16 .  
         [0023]    The flush system  25  further includes a particle discharge unit  39 , having a vertical particle drain conduit  40  extending downwardly from a particle drain valve  41  which is provided in fluid communication with the circulation conduit  26 , at a point between the circulation valve  28  and the loop screen  34 . The horizontal bottom portion of the particle drain conduit  40  is fitted with an outlet valve  42  which is connected to the bottom end portion of a vertical particle screen conduit  44 . A particle screen  45 , having screen or pore sizes of typically about 12 μm, is mounted in the particle screen conduit  44 . A solvent re-entry valve  51  connects the upper end of the particle screen conduit  44  to the rear end of a horizontal solvent re-entry conduit  50 , the front end of which terminates in fluid communication with the circulation conduit  26 , just upstream of the entry point of the circulation conduit  26  into the solvent re-claim tank  16 . A particle discharge valve  46  connects the bottom end of the particle screen conduit  44  to a particle discharge conduit  48 .  
         [0024]    As illustrated in FIG. 5, a DI (deionized) water supply  55  and a nitrogen gas supply  58  are each connected to the interior of the vertical particle screen conduit  44 , by a water dispensing conduit  56  and a nitrogen dispensing conduit  59 , respectively. The discharge ends of the water dispensing conduit  56  and the nitrogen dispensing conduit  59  in the particle screen conduit  44  are disposed just above the particle screen  45 . The DI water supply  55  and the nitrogen supply  58  are operated to purge the particle screen  45  using water and nitrogen, respectively, as indicated by the arrows, and remove DFR particles  6  from the particle screen  45  as hereinafter further described.  
         [0025]    The flush system  25  of the present invention is operated as follows. After the chip substrate  1  is soaked in organic solvent and agitated in the inner tank  13  of the process container  11  to remove the DFR particles  6  therefrom, typically in the manner heretofore described with respect to the conventional DFR remover system  10  illustrated in FIGS.  1 - 3 , the chip substrate  1  is removed from the inner tank  11  for further processing or packaging. The DFR particles  6  removed from the chip substrate  1  tend to settle in the bottom of the inner tank  13 , and at least a substantial portion of the DFR particles  6  must be removed from the inner tank  13  prior to further processing of additional chip substrates  1  in the inner tank  13 . Accordingly, the circulation valve  28  and and backflow valve  37  are opened, and the organic solvent, in which the DFR particles  6  are suspended, is distributed from the inner tank  13 , through the circulation conduit  26  and into the solvent re-claim tank  16 , as indicted by the white arrows. The flowing solvent passes through the loop screen  34 , which removes from the solvent particles having a size on the order of reclaim about 12 μm and larger before the solvent proceeds through the remaining segment of the circulation conduit  26  and enters the solvent re-claim tank  16 . The solvent is then pumped, by operation of the circulation pump  20 , from the solvent re-claim tank  16 , through the particle filter  18  and back to the outer tank  12  of the process container  11 , as further illustrated by the white arrows. The particle filter  18  removes particles typically having a size on the order of about 0.1 μm and larger from the solvent before the solvent is pumped back to the outer tank  12 . The heretofore-described circulation of solvent from the inner tank  13 , through the solvent re-claim tank  16  and back to the outer tank  12  is continued for about 10 minutes, to remove most or all of the DFR particles  6  from the solvent. Accordingly, the loop screen  34  removes the larger-size (about 12 μm and larger) DFR particles  6  from the solvent before the solvent reaches the particle filter  18 , thereby significantly reducing clogging of the particle filter  18  and prolonging filtering time of the DFR remover system. The loop screen  34  and particle filter  18  together therefore remove most or all of the DFR particles  6  from the solvent, and most of the DFR particles  6  are removed from the inner tank  13  of the process container  11 , having been carried therefrom by the solvent before filtration.  
         [0026]    After the solvent-filtering operation heretofore described is run for about 10 minutes to remove most or all of the DFR particles  6  from the inner tank  13 , the flush system  25  is operated in a flush mode typically for about 5 minutes in order to remove and eliminate or flush the DFR particles  6  previously trapped by the loop screen  34  from the flush system  25 . This is accomplished by initially closing both the circulation valve  28  and the backflow valve  37  and opening the loop entry valve  35  of the flush loop  29 , as well as the particle drain valve  41 , the outlet valve  42  and the solvent re-entry valve  51  of the particle discharge unit  39 . The flush loop pump  31  of the flush loop  29  is then operated to pump solvent from the inner tank  13  through the loop entry valve  35  and the flush loop  29 , into the circulation conduit  26 , through the loop screen  34  and particle drain valve  41  and into the particle drain conduit  40  of the particle discharge unit  39 , as indicated by the black arrows. The weight of the solvent column in the particle drain conduit  40  then pushes the advancing front of the solvent into the particle screen conduit  44  through the outlet valve  42  and into the solvent re-entry conduit  50  through the solvent re-entry valve  51 . From the solvent re-entry conduit  50 , the solvent enters the circulation conduit  26  and is discharged from there into the solvent re-claim tank  16  for subsequent circulation through the particle filter  18  and back to the outer tank  12  by operation of the circulation pump  20 .  
         [0027]    As it flows backwards through the loop screen  34  upon exit from the flush loop  29 , as indicated by the black arrows, the solvent removes from the loop screen  34  the DFR particles  6  which had been previously trapped by the loop screen  34  upon forward pass of the solvent through the circulation conduit  26 . Upon subsequent upward flow of the solvent through the particle screen conduit  44 , the solvent passes through the particle screen  45  which, in turn, removes the DFR particles  6  previously flushed from the loop screen  34  by force of the backward-flowing solvent. The particle screen  45  removes particles typically having a size on the order of about 12 μm and larger, from the solvent. Consequently, most of the potential filter-clogging DFR particles  6  are removed from the solvent upon subsequent distribution of the solvent through the particle filter  18  during its transit back to the outer tank  12  of the process container  11 .  
         [0028]    After the flush mode of the flush system  25  heretofore described is continued typically for about 5 minutes to remove the previously-trapped DFR particles  6  from the loop screen  34 , the particle discharge unit  39  may be operated in a purge mode typically for about 5 minutes to remove from the particle screen  45  DFR particles  6  which had been trapped thereby during the flush mode. Accordingly, after the particle discharge valve  46  is opened, the DI water source  55  and the nitrogen gas supply  58  are operated either simultaneously or sequentially to discharge deionized water and nitrogen gas, respectively, through the water dispensing conduit  56  and the nitrogen dispensing conduit  59 , respectively, and against the particle screen  45 . The water and nitrogen gas dislodge all or most of the DFR particles  6  from the particle screen  45 , and the dislodged DFR particles  6  are discharged from the particle screen conduit  44 , through the open particle discharge valve  46  and into the particle discharge conduit  48 , from which the DFR particles  6  may be collected by a receptacle (not illustrated) or other waste elimination system.  
         [0029]    As further illustrated in FIG. 4, the various operating components of the flush system  25  may be operated automatically using a process controller  62 , having a microprocessor and enabling software and connected to the components typically by wiring  63 . In that case, the loop entry valve  35 , the circulation valve  28 , the backflow valve  37 , the particle drain valve  41 , the outlet valve  42 , the particle discharge valve  46  and the solvent re-entry valve  51  are typically electric.  
         [0030]    While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.