Abstract:
A method for applying a resin film to the face of a semiconductor wafer, comprising: an assembly holding step of holding an assembly on the surface of chuck means, with the back of the assembly being opposed to the surface of the chuck means, the assembly including a frame having a mounting opening formed in a central portion of the frame, and a semiconductor wafer mounted in the mounting opening of the frame by sticking a mounting tape to the back of the frame and the back of the semiconductor wafer; a liquid droplet supply step of supplying liquid droplets of a solution having a resin dissolved therein onto the face of the semiconductor wafer in the assembly after the assembly holding step; and a spreading step of rotating the chuck means subsequently to the liquid droplet supply step, thereby spreading the liquid droplets throughout the face of the semiconductor wafer. The method further comprises a cleaning step of rotating the chuck means and also supplying a cleaning fluid to the surface of the frame after the spreading step, thereby cleaning the solution which has adhered to the surface of the frame.

Description:
FIELD OF THE INVENTION 
   This invention relates to a method for applying a resin film to the face of a semiconductor wafer. More specifically, the invention relates to a method for applying a resin film to the face of a semiconductor wafer by supplying liquid droplets of a solution of a resin to the face of a semiconductor wafer mounted on a frame via a mounting tape, and then rotating the frame and the semiconductor wafer mounted thereon, thereby spreading the liquid droplets to the entire face of the semiconductor wafer. 
   DESCRIPTION OF THE PRIOR ART 
   As is well known among people skilled in the art, it is common practice in the manufacture of a semiconductor device to partition the face of a semiconductor wafer into many rectangular regions by streets arranged in a lattice pattern, form a semiconductor circuit in each of the rectangular regions, and then divide the semiconductor water along the streets, thereby obtaining the individually separated rectangular regions, namely, semiconductor devices. As a mode of dividing the semiconductor wafer along the streets, a mode called laser dicing is put to practical use. In this laser dicing method, the face of the semiconductor wafer is irradiated with a laser beam along the street to melt the face of the semiconductor wafer along the street, thereby forming a groove along the street, followed by breaking the semiconductor wafer along the groove. 
   In the above-described laser dicing, when the face of the semiconductor wafer is melted along the street by irradiation with the laser beam, debris generated by melting scatters over the rectangular region, and may damage the semiconductor circuit formed in the rectangular region. Prior to laser dicing, therefore, it is necessary to apply a resin film to the face of the semiconductor wafer in order to protect the semiconductor circuit from the scattered debris. 
   Japanese Unexamined Patent Publication No. 2004-322168 discloses that a resin coating and cleaning apparatus is built into a dicer for performing laser dicing, the resin coating and cleaning apparatus being capable of applying a resin coating to the face of a semiconductor wafer before laser dicing, and also cleaning the face of the semiconductor wafer after laser dicing. The resin coating and cleaning apparatus comprises a rotationally driven chuck means, a liquid droplet supply means, a cleaning fluid supply means, and a drying gas supply means. The semiconductor wafer to be given the resin coating on the face thereof is handled in a state in which the semiconductor wafer is mounted on a frame via a mounting tape. In other words, the semiconductor wafer is handled as an assembly of the frame having a mounting opening in its central portion, and the semiconductor wafer mounted in the mounting opening of the frame by sticking the mounting tape to the back of the frame and the back of the semiconductor wafer. In applying the resin coating to the face of the semiconductor wafer, the assembly is mounted on the chuck means, with the back of the assembly (accordingly, the back of each of the semiconductor wafer, the frame, and the mounting tape) being opposed to the surface of the chuck means. Then, liquid droplets of a solution having resin dissolved therein are supplied to a central portion of the face of the semiconductor wafer. Then, the chuck means is rotated at a high speed, whereby the liquid droplets are spread throughout the face of the semiconductor wafer. 
   According to the experience of the inventors of the present application, the above-described method for applying the resin coating, disclosed in Japanese Unexamined Patent Publication No. 2004-322168, has been found to involve the following problem to the solved: When the chuck means is rotated at a high speed in order to spread the liquid droplets supplied to the central portion of the face of the semiconductor wafer, the solution scatters, although slightly, over the surface of the frame and adheres there. In transporting the assembly within the laser dicer, or carrying the assembly out of the laser dicer, a transport means equipped with a vacuum attraction type pad is usually used. The pad is pressed against the surface of the frame to attract the assembly under vacuum and, in this state, the assembly is transported to a required location. There, the vacuum of the pad is released to detach the assembly from the pad. If the solution adheres to the surface of the frame, however, there is a tendency toward the occurrence of a situation in which the frame, accordingly, the assembly, is not detached from the pad even upon release of the vacuum of the pad, owing to the tackiness of the solution. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention, therefore, to improve a method for applying a resin film to the face of a semiconductor wafer such that detachment of the assembly from the pad is not impeded. 
   According to the present invention, in order to attain the above object, after liquid droplets supplied to a central portion of the face of a semiconductor water are spread by rotation of a chuck means, a cleaning fluid is supplied to the surface of a frame, with the chuck means being rotated, whereby a solution which has scattered over the surface of the frame is cleaned. 
   That is, according to the present invention, there is provided, for attainment of the above object, a method for applying a resin film to the face of a semiconductor wafer, comprising: 
   an assembly holding step of holding an assembly on the surface of a chuck means, with the back of the assembly being opposed to the surface of the chuck means, the assembly including a frame having a mounting opening formed in a central portion of the frame, and a semiconductor wafer mounted in the mounting opening of the frame by sticking a mounting tape to the back of the frame and the back of the semiconductor wafer; 
   a liquid droplet supply step of supplying liquid droplets of a solution having a resin dissolved therein onto the face of the semiconductor wafer in the assembly after the assembly holding step; and 
   a spreading step of rotating the chuck means subsequently to the liquid droplet supply step, thereby spreading the liquid droplets throughout the face of the semiconductor wafer, 
   the method further comprising a cleaning step of rotating the chuck means and also supplying a cleaning fluid to the surface of the frame after the spreading step, thereby cleaning the solution which has adhered to the surface of the frame. 
   The cleaning fluid may be pure water. Preferably, in the cleaning step, the chuck means is rotated at 1 to 100 rpm, and the cleaning fluid is supplied for 5 to 30 seconds at a pressure of 0.1 to 0.3 MPa at a rate of 10 to 100 ml/min. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially cutaway perspective view showing a typical example of an apparatus for use in carrying out a preferred embodiment of the method according to the present invention. 
       FIG. 2  is a partial sectional view showing a main part of the apparatus of  FIG. 1 . 
       FIG. 3  is a perspective view showing an assembly having a semiconductor wafer mounted on a frame via a mounting tape. 
       FIG. 4  is a sectional view similar to  FIG. 2 , showing a mode of performing a liquid droplet supply step with the use of the apparatus of  FIG. 1 . 
       FIG. 5  is a sectional view similar to  FIG. 2 , showing a mode of performing a cleaning step with the use of the apparatus of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the method for applying a resin film to the face of a semiconductor wafer according to the present invention will be described in further detail by reference to the accompanying drawings. 
   Referring to  FIGS. 1 and 2  showing a typical example of an apparatus for performing the method of the present invention, the illustrated apparatus is equipped with a chuck means  2 . The chuck means  2  is composed of a disk-shaped chuck plate  4  formed from a porous material such as a porous ceramic, and an annular frame body  6  encircling the chuck plate  4 . The annular frame body  6  can be formed from stainless steel. An electric motor  8  is disposed below the chuck means  2 . An output shaft  10  of the electric motor  8  extends out upwardly and substantially vertically. The chuck means  2  is fixed to the upper end of the output shaft  10 , and is placed substantially horizontally. The electric motor  8  is mounted on a support base board (not shown) via three hydraulic cylinder mechanisms  12   a ,  12   b  and  12   c  extending in the vertical direction. In more detail, cylinders  14   a ,  14   b  and  14   c  of the three hydraulic cylinder mechanisms  12   a ,  12   b  and  12   c  are equally spaced in the circumferential direction and fixed to the outer periphery of the casing of the electric motor  8 , while the leading ends, namely, the lower ends, of pistons  16   a ,  16   b  and  16   c  of the three hydraulic cylinder mechanisms  12   a ,  12   b  and  12   c  are fixed on the substantially horizontal surface of the support base board. Thus, when the pistons  16   a ,  16   b  and  16   c  of the cylinder mechanisms  12   a ,  12   b  and  12   c  are expanded, the electric motor  8  and the chuck means  2  are raised. When the pistons  16   a ,  16   b  and  16   c  of the cylinder mechanisms  12   a ,  12   b  and  12   c  are contracted, the electric motor  8  and the chuck means  2  are lowered. Directly below the chuck means  2 , a cover member  18  is fixed to the output shaft  10  of the electric motor  8 . The cover member  18  has an annular top wall  20  whose central portion the output shaft  10  is inserted through, and a cylindrical wall  22  drooping from the peripheral edge of the top wall  20 . 
   The illustrated apparatus is also furnished with a stationary container  24  surrounding the chuck means  2 . The container  24  has an annular bottom wall  26 , an outer cylindrical wall  28  extending upward from the outer peripheral edge of the bottom wall  26 , and an inner cylindrical wall  30  extending upward from the inner peripheral edge of the bottom wall  26 . The outer diameter of the inner cylindrical wall  30  is somewhat smaller than the outer diameter of the cylindrical wall  22  of the cover member  18 . An outlet  32  is formed in the bottom wall  26 , and a discharge conduit  34  is connected to the outlet  32  (reference to  FIG. 1  is requested). The container  24  is fixed onto the surface of the support base board via three support legs  36  (only two of the support legs  36  are shown in  FIG. 1 ) disposed with equal spacing in the circumferential direction. 
   In the illustrated apparatus, a liquid droplet supply means  38 , a cleaning fluid supply means  40 , and a drying gas supply means  42  are further disposed. The liquid droplet supply means  38  is provided with a nozzle  44 , and the nozzle  44  has an upright portion extending along the inner peripheral surface of the outer cylindrical wall  28  of the container  24 , a horizontal portion extending substantially horizontally from the upper end of the upright portion, and a drooping portion extending downward from the leading end of the horizontal portion. The upright portion is inserted through the bottom wall  26  of the container  24 , projected downward, and coupled to an output shaft of an electric motor  46  ( FIG. 2 ) fixed to the lower surface of the bottom wall  26 . Thus, when the electric motor  46  is energized, the nozzle  44  is turned about a central axis of the upright portion thereof. The nozzle  44  is connected to a solution supply source (not shown) via a suitable communication means (not shown for avoiding complexity of the drawings). The solution supply source supplies the nozzle  44  with a solution which is preferably an aqueous solution having dissolved therein a water-soluble resin such as polyvinyl alcohol, polyethylene glycol, or polyethylene oxide. 
   The cleaning fluid supply means  40  is provided with a nozzle  48 , and the nozzle  48  has an upright portion extending along the inner peripheral surface of the outer cylindrical wall  28  of the container  24 , a horizontal portion extending substantially horizontally from the upper end of the upright portion, and a drooping portion extending downward from the leading end of the horizontal portion. The upright portion is inserted through the bottom wall  26  of the container  24 , projected downward, and coupled to an output shaft of an electric motor  50  ( FIG. 2 ) fixed to the lower surface of the bottom wall  26 . Thus, when the electric motor  50  is energized, the nozzle  48  is turned about a central axis of the upright portion thereof. The nozzle  48  is connected to a cleaning fluid supply source (not shown) via a suitable communication means (not shown for avoiding complexity of the drawings). The cleaning fluid supply source supplies the nozzle  48  with a cleaning fluid which may be pure water. If desired, a gas, which may be air, can be supplied to the nozzle  48 , together with the cleaning fluid which may be pure water. 
   The drying gas supply means  42  is provided with a nozzle  52 , and the nozzle  52  has an upright portion extending along the inner peripheral surface of the outer cylindrical wall  28  of the container  24 , a horizontal portion extending substantially horizontally from the upper end of the upright portion, and a drooping portion hanging downward from the leading end of the horizontal portion. The upright portion is inserted through the bottom wall  26  of the container  24 , projected downward, and coupled to an output shaft of an electric motor (not shown) fixed to the lower surface of the bottom wall  26 . Thus, when the electric motor is energized, the nozzle  52  is turned about a central axis of the upright portion thereof. The nozzle  52  is connected to a drying gas supply source (not shown) via a suitable communication means (not shown for avoiding complexity of the drawings). The drying gas supply source supplies the nozzle  52  with a drying gas which may be room temperature air or heated air. 
   The above-described apparatus may be substantially the same as the apparatus disclosed in the aforementioned Japanese Unexamined Patent Publication No. 2004-322168. Thus, a detailed description of the above-mentioned apparatus per se is omitted herein. 
     FIG. 3  shows an assembly  54  in which a semiconductor wafer  56  to be given a resin film on its face is mounted on a frame  60  via a mounting tape  58 . The frame  60 , which can be formed from a suitable metal such as aluminum or stainless steel or from a suitable synthetic resin, has a mounting opening  62  of a relatively large circular shape in a central portion thereof. The semiconductor wafer  56 , nearly disk-shaped, is positioned within the mounting opening  62  of the frame  60 . The mounting tape  58  extending across the mounting opening  62  is stuck to the back of the frame  60  and the back of the semiconductor wafer  56 , whereby the semiconductor wafer  56  is mounted in the mounting opening  62  of the frame  60 . Many rectangular regions  66  are defined on the face of the semiconductor wafer  56  by streets  64  arranged in a lattice pattern, and a semiconductor circuit is formed in each of the rectangular regions  66 . 
   The following is a detailed description of a preferred embodiment of the method for applying a resin film to the face of the semiconductor wafer  56  in the assembly  54  according to the present invention, the method being carried out with the use of the above-described apparatus. 
   First of all, an assembly holding step is performed. In this assembly holding step, the pistons  16   a ,  16   b  and  16   c  of the cylinder mechanisms  12   a ,  12   b  and  12   c  are expanded to bring the chuck means  2  to an ascent position shown in  FIG. 2 . The upper surface of the chuck means  2  located at the ascent position is advantageously at substantially the same height as the upper end of the outer cylindrical wall  28  of the container  24 . The assembly  54  is carried in onto the chuck means  2  by a suitable transport means (not shown), with the back of the assembly  54  being opposed to the surface of the chuck means  2 , accordingly, with the face of the semiconductor wafer  56  pointing upward. The transport means may be of the type having a plurality of vacuum attraction pads which are pressed against the frame  60  in the assembly  54 . When the assembly  54  disengaged from the transport means is placed on the chuck means  2 , the chuck plate  4  of the chuck means  2  is connected to a vacuum source (not shown) via a suitable communication passage (not shown), whereby the assembly  54  is attracted onto the chuck means  2  by suction. 
   Then, a liquid droplet supply step is performed. In this liquid droplet supply step, the pistons  16   a ,  16   b  and  16   c  of the cylinder mechanisms  12   a ,  12   b  and  12   c  are contracted to bring the chuck means  2  and the assembly  54  held on the surface thereof to a descent position shown in  FIG. 4 . Then, the nozzle  44  of the liquid droplet supply means  38  is moved to a position shown in  FIG. 4 , namely, a position where the tip of the nozzle  44  opposes the center of the semiconductor wafer  56  in the assembly  54 . Then, a required amount of liquid droplets is dropped through the nozzle  44 , and supplied onto the semiconductor wafer  56 . In  FIG. 4 , a liquid droplet  68  supplied onto the semiconductor wafer  56  is indicated by dashed double-dotted lines. The liquid droplet  68  is advantageously a relatively high viscosity solution having a water-soluble resin, such as polyvinyl alcohol, polyethylene glycol, or polyethylene oxide, dissolved in pure water. 
   Then, a spreading step is performed. In the spreading step, the electric motor  8  is energized to rotate the chuck means  2  and the assembly  54  held thereby, for example, at a speed of the order of 500 to 3,000 rpm for a time of the order of 30 to 120 seconds. By this rotation, the liquid droplets  68  are spread over the entire face of the semiconductor wafer  56  to apply a resin film to the face of the semiconductor wafer  56 . According to the experience of the inventors, in the spreading step, the solution constituting the liquid droplets  68  tends to scatter, although slightly, over the surface of the frame  60  in the assembly  54 . 
   With the method of the present invention, it is important that the above spreading step be followed by a cleaning step. In this cleaning step, as shown in  FIG. 5 , the nozzle  44  of the liquid droplet supply means  38  is returned to a non-operating position (the position shown in  FIG. 2 ) where the nozzle  44  is located close to the outer cylindrical wall  28  of the container  24 . On the other hand, the nozzle  48  of the cleaning fluid supply means  40  is moved to a position shown in  FIG. 5 , namely, a position where the tip of the nozzle  48  opposes the surface of the frame  60  in the assembly  54 . Then, the cleaning fluid is gushed through the nozzle  48 , and the electric motor  8  is energized to rotate the chuck means  2  and the assembly  54  held thereby. By so doing, the cleaning fluid acts on the surface of the frame  60  to clean the solution scattering over the surface of the frame. The cleaning fluid may be pure water, and is preferably supplied for 5 to 30 seconds at a pressure of 0.1 to 0.3 MPa at a rate of the order of 10 to 100 ml/min. If desired, pressurized air can be jetted, together with the cleaning fluid, through the nozzle  48 . The rotational speed of the chuck means  2  and the assembly  54  held thereby may be of the order of 1 to 100 rpm. After acting on the surface of the frame  60 , the gushed cleaning fluid flows down into the container  24 , and is discharged through the outlet  32  and the discharge conduit  34 . 
   After completion of the cleaning step, the electric motor  8  is deenergized to return the nozzle  48  of the cleaning fluid supply means  40  to a non-operating position (the position shown in  FIG. 2 ) where the nozzle  48  is located close to the outer cylindrical wall  28  of the container  24 . Then, the pistons  16   a ,  16   b  and  16   c  of the cylinder mechanisms  12   a ,  12   b  and  12   c  are expanded to bring the chuck means  2  to the ascent position shown in  FIG. 2 . Then, the chuck plate  4  of the chuck means  2  is cut off from the vacuum source, and the assembly  54  is carried out from above the chuck means  2  by the suitable transport means (not shown), and carried into a laser dicing zone, for example. 
   In cleaning the face of the diced semiconductor wafer  56  after completion of laser dicing, the assembly  54  is carried in onto the chuck means  2 , which is located at the ascent position shown in  FIG. 2 , by the suitable transport means (not shown), with the back of the assembly  54  opposing the chuck means  2  (even after dicing, the individually separated rectangular regions  66  of the semiconductor wafer  56  are stuck to the mounting tape  58 , and the assembly  54  is kept integrated). When the assembly  54  released from the transport means is placed on the chuck means  2 , the chuck plate  4  of the chuck means  2  is connected to the vacuum source (not shown) via the suitable communication passage (not shown). Thus, the assembly  54  is attracted onto the chuck means  2  by suction. Then, the pistons  16   a ,  16   b  and  16   c  of the cylinder mechanisms  12   a ,  12   b  and  12   c  are contracted to bring the chuck means  2  and the assembly  54  held on its surface to the descent position shown in  FIG. 4 . Then, the electric motor  8  is energized to rotate the chuck means  2  and the assembly  54  held thereby. Also, the cleaning fluid, or pressurized air together with the cleaning fluid, is gushed through the nozzle  48  of the cleaning fluid supply means  40 . On this occasion, the nozzle  48  is pivoted in a reciprocating manner within a required range corresponding to the face of the semiconductor wafer  56  to be cleaned. When the cleaning fluid, or pressurized air together with the cleaning fluid, is gushed toward the face of the semiconductor wafer  56 , the water-soluble resin present on the face of the semiconductor wafer  56  is dissolved, removed, and flowed down into the container  24  together with the cleaning fluid. 
   After completion of cleaning, the nozzle  48  of the cleaning fluid supply means  40  is returned to the non-operating position. Then, the nozzle  52  of the drying gas supply means  42  is pivoted in a reciprocating manner within a required range corresponding to the face of the semiconductor wafer  56 , and a drying gas is gushed through the nozzle  52 , whereby the semiconductor wafer  56  is dried. The drying gas may be room temperature air or heated air. 
   After completion of drying, the electric motor  8  is deenergized, and the nozzle  52  of the drying gas supply means  42  is returned to a non-operating position (position shown in  FIG. 2 ) where the nozzle  52  is located close to the outer cylindrical wall  28  of the container  24 . Then, the pistons  16   a ,  16   b  and  16   c  of the cylinder mechanisms  12   a ,  12   b  and  12   c  are expanded to bring the chuck means  2  to the ascent position shown in  FIG. 2 . Then, the chuck plate  4  of the chuck means  2  is cut off from the vacuum source, and the assembly  54  is carried out from above the chuck means  2  by the suitable transport means (not shown). 
   While the preferred embodiments of the method according to the present invention have been described in detail by reference to the accompanying drawings, it is to be understood that the invention is not limited to such embodiments, but various changes and modifications may be made without departing from the scope of the invention.