Patent Publication Number: US-2010129546-A1

Title: Protective film forming method and apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a protective film forming method and apparatus for forming a protective film of resin on the front side of a wafer such as a semiconductor wafer and an optical device wafer. 
     2. Description of the Related Art 
     In a semiconductor device fabrication process, a plurality of crossing streets (division lines) are formed on the front side of a substantially disk-shaped semiconductor wafer to partition a plurality of areas where devices such as ICs, LSIs, liquid crystal drivers, and flash memories are respectively formed. The wafer is cut along the streets to divide these areas from each other along the streets, thereby producing the individual devices. Further, in an optical device wafer, the front side of a sapphire substrate or the like is partitioned into a plurality of areas by a plurality of crossing streets, and a gallium nitride compound semiconductor or the like is layered in each of these partitioned areas to thereby form an optical device. Such an optical device wafer is cut along the streets into a plurality of optical devices such as light emitting diodes and laser diodes, which are widely used for electrical equipment. 
     As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the streets, there has been proposed a method including the steps of applying a pulsed laser beam to the wafer along the streets to thereby form a plurality of laser processed grooves and next breaking the wafer along these laser processed grooves by using a mechanical breaking apparatus (see Japanese Patent Laid-open No. Hei 10-305420, for example). 
     Such laser processing has advantages over cutting such that a processing speed is higher and a wafer formed of a hard material such as sapphire can be processed relatively easily. However, when a laser beam is applied to the wafer along the streets, thermal energy is concentrated at a region irradiated with the laser beam, causing the generation of debris, and this debris may stick to bonding pads connected to the circuits, causing a degradation in quality of the chips. To solve this problem due to the debris, there has been proposed a laser processing method including the steps of coating the work surface of a wafer with a protective film formed of resin such as polyvinyl alcohol and next applying a laser beam through the protective film to the work surface of the wafer (see Japanese Patent Laid-open No. 2004-322168, for example). 
     Japanese Patent Laid-open No. 2004-322168 mentioned above discloses a spinner coating method including the steps of dropping a predetermined amount of liquid resin from a liquid resin supply nozzle to a central portion of a wafer held on a spinner table and rotating the spinner table at 3000 rpm, for example, thereby forming a protective film on the work surface of the wafer. However, since the affinity of the liquid resin such as polyvinyl alcohol to the wafer is low, the work surface of the wafer is partially uncoated with the liquid resin, so that it is difficult to form a protective film having a uniform thickness on the work surface of the wafer. Further, since the spinner table is rotated at a high speed of 3000 rpm, for example, 99% of the liquid resin dropped onto the work surface of the wafer scatters to be wasted. For example, in the case that 30 mL of polyvinyl alcohol is dropped onto the work surface of a wafer having a diameter of 300 mm and the spinner table is rotated at 3000 rpm for 15 seconds, a protective film having a thickness of 5 μm is formed on the work surface of the wafer. In this case, the proportion of the amount of polyvinyl alcohol formed into the protective film to the amount of polyvinyl alcohol dropped onto the work surface of the wafer is merely 1%. That is, 99% of the polyvinyl alcohol supplied is wasted. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a protective film forming method and apparatus which can form a protective film having a uniform thickness from liquid resin on the front side (work surface) of a wafer and can reduce the amount of usage of the liquid resin. 
     In accordance with an aspect of the present invention, there is provided a protective film forming method for forming a protective film of resin on a work surface of a wafer, comprising a wafer holding step of holding the wafer on a spinner table in the condition where the work surface is oriented upward; a spray coating step of spraying first liquid resin onto the work surface of the wafer as rotating the spinner table at a first rotational speed after performing the wafer holding step; a liquid resin supplying step of dropping a predetermined amount of second liquid resin onto a central area of the work surface of the wafer as rotating the spinner table at a second rotational speed lower than the first rotational speed after performing the spray coating step; and a spin coating step of rotating the spinner table at a third rotational speed higher than the first rotational speed after performing the liquid resin supplying step to thereby spread the second liquid resin dropped onto the central area of the work surface of the wafer, thus forming the protective film on the work surface of the wafer. 
     Preferably, the spray coating step is performed under the conditions where the first liquid resin has a viscosity of 3 to 5 cp, the first liquid resin is sprayed at a rate of 0.04 to 0.06 mL/sec for 60 to 90 seconds, and the first rotational speed of the spinner table is set to 50 to 70 rpm; the liquid resin supplying step is performed under the conditions where the second liquid resin has a viscosity of 50 to 70 cp, the second liquid resin is dropped at a rate of 4 to 6 mL/sec for two to four seconds, and the second rotational speed of the spinner table is set to 5 to 15 rpm; and the spin coating step is performed under the conditions where the third rotational speed of the spinner table is set to 400 to 600 rpm and the duration time is set to 20 to 40 seconds. 
     Preferably, the protective film forming method further comprises a spin drying step of rotating the spinner table at 2000 to 3000 rpm for 50 to 70 seconds after performing the spin coating step to thereby dry the protective film formed on the work surface of the wafer. 
     In accordance with another aspect of the present invention, there is provided a protective film forming apparatus for forming a protective film of resin on a work surface of a wafer, comprising a spinner table for holding the wafer thereon; rotational driving means for rotating the spinner table; spraying means for spraying first liquid resin onto the work surface of the wafer held on the spinner table; and liquid resin supplying means for dropping second liquid resin onto a central area of the work surface of the wafer held on the spinner table. 
     The protective film forming method according to the present invention includes the spray coating step, the liquid resin supplying step, and the spin coating step. By performing the spray coating step prior to the spin coating step, the affinity of the second liquid resin to the work surface of the wafer in the spin coating step can be improved. Accordingly, although the rotational speed of the spinner table holding the wafer thereon in the spin coating step is set lower than that in the conventional method mentioned above, the protective film can be uniformly formed on the work surface of the wafer. Accordingly, the rate of contribution of the second liquid resin to the protective film can be improved to thereby reduce the amount of usage of the second liquid resin. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a laser processing system including a protective film forming apparatus according to a preferred embodiment of the present invention; 
         FIG. 2  is a partially cutaway perspective view of the protective film forming apparatus included in the laser processing system shown in  FIG. 1 ; 
         FIG. 3  is a vertical sectional view of the protective film forming apparatus in the condition where a spinner table included therein is lifted to a work load/unload position; 
         FIG. 4  is a vertical sectional view of the protective film forming apparatus in the condition where the spinner table is lowered to a working position; 
         FIG. 5  is a diagrammatic sectional view showing an essential part of spraying means included in the protective film forming apparatus; 
         FIG. 6  is a diagrammatic sectional view showing an essential part of liquid resin supplying means included in the protective film forming apparatus; 
         FIG. 7  is a partially cutaway perspective view of cleaning means included in the laser processing system shown in  FIG. 1 ; 
         FIG. 8  is a vertical sectional view of the cleaning means in the condition where a spinner table included therein is lifted to a work load/unload position; 
         FIG. 9  is a vertical sectional view of the cleaning means in the condition where the spinner table is lowered to a working position; 
         FIG. 10  is a perspective view of a semiconductor wafer as a workpiece to be processed by the laser processing system shown in  FIG. 1 ; 
         FIG. 11  is a plan view for illustrating a spray coating step to be performed by the protective film forming apparatus included in the laser processing system shown in  FIG. 1 ; 
         FIG. 12  is a plan view for illustrating a liquid resin supplying step to be performed by the protective film forming apparatus included in the laser processing system shown in  FIG. 1 ; 
         FIG. 13  is an enlarged sectional view of an essential part of the semiconductor wafer obtained by performing a spin coating step to form a protective film on the semiconductor wafer by the protective film forming apparatus included in the laser processing system shown in  FIG. 1 ; 
         FIGS. 14A and 14B  are schematic views for illustrating a laser beam applying step by the laser processing system in  FIG. 1 ; and 
         FIG. 15  is an enlarged sectional view of an essential part of the semiconductor wafer processed by the laser beam applying step shown in  FIGS. 14A and 14B . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the protective film forming method and apparatus according to the present invention will now be described in detail with reference to the attached drawings. Referring to  FIG. 1 , there is shown a perspective view of a laser processing system including the protective film forming apparatus according to the present invention. 
     The laser processing system shown in  FIG. 1  has a substantially boxlike housing  2 . The housing  2  contains a chuck table  3  as work holding means for holding a workpiece. The chuck table  3  is movable in the direction shown by an arrow X as a work feeding direction. The chuck table  3  has a vacuum chuck support  31  and a vacuum chuck  32  mounted on the vacuum chuck support  31 . The vacuum chuck  32  has an upper surface for placing a workpiece such as a disk-shaped semiconductor wafer thereon. The workpiece placed on the upper surface of the vacuum chuck  32  is held by suction means not shown. Further, the chuck table  3  is rotatable by a rotating mechanism not shown. The vacuum chuck support  31  of the chuck table  3  is provided with a pair of clamps  33  for fixing an annular frame for a disk-shaped semiconductor wafer to be hereinafter described. 
     The laser processing system shown in  FIG. 1  includes laser beam applying means  4  for applying a laser beam to the workpiece held on the vacuum chuck  32  of the chuck table  3 . The laser beam applying means  4  includes a cylindrical casing  41  extending in a substantially horizontal direction. Although not shown, the casing  41  contains pulsed laser beam oscillating means including a pulsed laser beam oscillator and repetition frequency setting means. Examples of the pulsed laser beam oscillator include a YAG laser oscillator and a YVO4 laser oscillator. The laser beam applying means  4  further includes focusing means  42  for focusing the laser beam oscillated by the pulsed laser beam oscillating means. The focusing means  42  is mounted on the front end of the casing  41 . 
     The laser processing system shown in  FIG. 1  further includes imaging means  5  for imaging the upper surface of the workpiece held on the vacuum chuck  32  of the chuck table  3  to detect a region to be processed by the laser beam applied from the focusing means  42  of the laser beam applying means  4 . The imaging means  5  includes an ordinary imaging device (CCD) for imaging the workpiece by using visible light, infrared light applying means for applying infrared light to the workpiece, an optical system for capturing the infrared light applied by the infrared light applying means, and an imaging device (infrared CCD) for outputting an electrical signal corresponding to the infrared light captured by the optical system. An image signal output from the imaging means  5  is transmitted to control means not shown. The laser processing system shown in  FIG. 1  further includes displaying means  6  for displaying the image obtained by the imaging means  5 . 
     The laser processing system shown in  FIG. 1  further includes a cassette setting portion  13   a  for setting a cassette  13  storing a semiconductor wafer  10  as a workpiece to be processed. The cassette setting portion  13   a  is provided with a cassette table  131  vertically movable by lifting means not shown. The cassette  13  is set on the cassette table  131 . The semiconductor wafer  10  is attached to the upper surface of a protective tape  12  supported to an annular frame  11 . Thus, the semiconductor wafer  10  supported through the protective tape  12  to the annular frame  11  is stored in the cassette  13 . For example, the semiconductor wafer  10  is provided by a silicon wafer having a diameter of 300 mm. As shown in  FIG. 10 , the semiconductor wafer  10  has a front side  10   a  and a back side  10   b . The front side  10   a  of the semiconductor wafer  10  is partitioned into a plurality of rectangular regions by a plurality of crossing streets  101 , wherein a plurality of individual devices  102  such as ICs and LSIs are respectively formed in these plural rectangular regions. The back side  10   b  of the semiconductor wafer  10  is attached to the upper surface of the protective tape  12  supported to the annular frame  11  in the condition where the front side  10   a  of the semiconductor wafer  10  is oriented upward as shown in  FIG. 1 . 
     The laser processing system shown in  FIG. 1  further includes work ejecting/inserting means  14  for ejecting the semiconductor wafer  10  from the cassette  13  before processing and inserting the semiconductor wafer  10  into the cassette  13  after processing, a temporary setting table  15  for temporarily setting the semiconductor wafer  10  ejected by the work ejecting/inserting means  14  before processing, a protective film forming apparatus  7  for forming a protective film on the work surface of the semiconductor wafer  10  before processing, the protective film forming apparatus  7  being provided in a first carrying path where the semiconductor wafer  10  is carried from the temporary setting table  15  to the chuck table  3  before processing, and cleaning means  8  for cleaning off the protective film formed on the work surface of the semiconductor wafer  10  after processing, the cleaning means  8  being provided in a second carrying path where the semiconductor wafer  10  is carried from the chuck table  3  to the temporary setting table  15  after processing. 
     The laser processing system shown in  FIG. 1  further includes first carrying means  16  for carrying the semiconductor wafer  10  from the temporary setting table  15  to the protective film forming apparatus  7  before processing and for carrying the semiconductor wafer  10  from the cleaning means  8  to the temporary setting table  15  after processing, and second carrying means  17  for carrying the semiconductor wafer  10  from the protective film forming apparatus  7  to the chuck table  3  before processing and for carrying the semiconductor wafer  10  from the chuck table  3  to the cleaning means  8  after processing. 
     The protective film forming apparatus  7  will now be described with reference to  FIGS. 2 to 4 . The protective film forming apparatus  7  includes a spinner table mechanism  71  and spinner table accommodating means  72  provided so as to surround the spinner table mechanism  71 . The spinner table mechanism  71  includes a spinner table  711 , an electric motor  712  for rotationally driving the spinner table  711 , and a support mechanism  713  for vertically movably supporting the electric motor  712 . The spinner table  711  includes a vacuum chuck  711   a  formed of a porous material. The vacuum chuck  711   a  is connected to suction means not shown. Accordingly, the spinner table  711  functions to hold the semiconductor wafer  10  as a workpiece placed on the vacuum chuck  711   a  by using a vacuum produced by the suction means. 
     The spinner table  711  is provided with a pair of clamps  714  for fixing the annular frame  11  supporting the semiconductor wafer  10 . The electric motor  712  has a drive shaft  712   a , and the spinner table  711  is connected to the upper end of the drive shaft  712   a . The support mechanism  713  is composed of a plurality of (three in this preferred embodiment) support legs  713   a  and a plurality of (three in this preferred embodiment) air cylinders  713   b  operatively connected to the support legs  713   a , respectively. All of the air cylinders  713   b  are mounted on the electric motor  712 . The support mechanism  713  functions in such a manner that the air cylinders  713   b  are operated to vertically move the electric motor  712  and the spinner table  711  between the upper position shown in  FIG. 3  as a work load/unload position and the lower position shown in  FIG. 4  as a working position. 
     The spinner table accommodating means  72  includes a receptacle  721 , three support legs  722  for supporting the receptacle  721  (two of the three support legs  722  being shown in  FIG. 2 ), and a cover member  723  mounted on the drive shaft  712   a  of the electric motor  712 . As shown in  FIGS. 3 and 4 , the receptacle  721  is composed of a cylindrical outer wall  721   a , a bottom wall  721   b , and a cylindrical inner wall  721   c . The bottom wall  721   b  is formed with a central hole  721   d  for allowing the insertion of the drive shaft  712   a  of the electric motor  712 . The cylindrical inner wall  721   c  projects upward from the peripheral edge of the central hole  721   d . The cover member  723  is a cylindrical member having a closed top. The closed top of the cover member  723  is mounted to the upper end portion of the drive shaft  712   a  of the electric motor  712 , and a covering portion  723   a  projects downward from the outer circumference of the closed top of the cover member  723 . In the working position of the electric motor  712  and the spinner table  711  as shown in  FIG. 4 , the covering portion  723   a  of the cover member  723  is located so as to surround the cylindrical inner wall  721   c  of the receptacle  721  with a given gap defined therebetween. 
     The protective film forming apparatus  7  further includes spraying means  74  for spraying first liquid resin onto the front side  10   a  (work surface) of the semiconductor wafer  10  as a workpiece held on the spinner table  711  before processing. The spraying means  74  includes a spray nozzle  740  for spraying the first liquid resin toward the work surface of the wafer held on the spinner table  711  before processing. The spray nozzle  740  is composed of a horizontally extending nozzle portion  741  having a downward bent front end and a support portion  742  extending downward from the base end of the nozzle portion  741 . The support portion  742  is inserted through a hole (not shown) formed through the bottom wall  721   b  of the receptacle  721 . 
     As shown in  FIG. 5 , the nozzle portion  741  of the spray nozzle  740  includes a liquid resin passage  741   a  and an air passage  741   b . The liquid resin passage  741   a  is connected to first liquid resin supplying means  743 , and the air passage  741   b  is connected to air supplying means  744 . The first liquid resin supplying means  743  functions to supply polyvinyl alcohol as the first liquid resin. This polyvinyl alcohol as the first liquid resin preferably has a viscosity of 3 to 5 centipoise (cp). For example, this viscosity is set to 3.8 cp in this preferred embodiment. The air supplying means  744  functions to supply air under a pressure of 0.4 MPa, for example. Although not shown, a seal member is mounted to the peripheral edge of the insert hole not shown for allowing the insertion of the support portion  742  of the spray nozzle  740 , thereby sealing the gap between the support portion  742  and the bottom wall  721   b . The spraying means  74  further includes a reversible electric motor  745  for horizontally swinging the spray nozzle  740 . The reversible electric motor  745  is configured so as to rotate the support portion  742  of the spray nozzle  740  in opposite directions. 
     The protective film forming apparatus  7  further includes liquid resin supplying means  75  for dropping second liquid resin onto a central area of the front side  10   a  (work surface) of the semiconductor wafer  10  held on the spinner table  711  before processing. The liquid resin supplying means  75  includes a liquid resin supply nozzle  750  for supplying the second liquid resin toward the work surface of the wafer held on the spinner table  711  before processing. The liquid resin supply nozzle  750  is composed of a horizontally extending nozzle portion  751  having a downward bent front end and a support portion  752  extending downward from the base end of the nozzle portion  751 . The support portion  752  is inserted through a hole (not shown) formed through the bottom wall  721   b  of the receptacle  721 . 
     As shown in  FIG. 6 , the nozzle portion  751  of the liquid resin supply nozzle  750  includes a liquid resin passage  751   a . The liquid resin passage  751   a  is connected to second liquid resin supply means  753 . The second liquid resin supplying means  753  functions to supply polyvinyl alcohol as the second liquid resin. This polyvinyl alcohol as the second liquid resin preferably has a viscosity of 50 to 70 cp. For example, this viscosity is set to 60 cp in this preferred embodiment. Although not shown, a seal member is mounted to the peripheral edge of the insert hole not shown for allowing the insertion of the support portion  752  of the liquid resin supply nozzle  750 , thereby sealing the gap between the support portion  752  and the bottom wall  721   b . The liquid resin supplying means  75  further includes a reversible electric motor  755  for horizontally swinging the liquid resin supply nozzle  750 . The reversible electric motor  755  is configured so as to rotate the support portion  752  of the liquid resin supply nozzle  750  in opposite directions. 
     The cleaning means  8  will now be described with reference to  FIGS. 7 to 9 . The cleaning means  8  includes a spinner table mechanism  81  and cleaning water receiving means  82  provided so as to surround the spinner table mechanism  81 . The spinner table mechanism  81  is similar to the spinner table mechanism  71  of the protective film forming apparatus  7 . That is, the spinner table mechanism  81  includes a spinner table  811 , an electric motor  812  for rotationally driving the spinner table  811 , and a support mechanism  813  for vertically movably supporting the electric motor  812 . The spinner table  811  includes a vacuum chuck  811   a  formed of a porous material. The vacuum chuck  811   a  is connected to suction means not shown. Accordingly, the spinner table  811  functions to hold the semiconductor wafer  10  as a workpiece placed on the vacuum chuck  811   a  by using a vacuum produced by the suction means not shown. 
     The spinner table  811  is provided with a pair of clamps  814  for fixing the annular frame  11  supporting the semiconductor wafer  10 . The electric motor  812  has a drive shaft  812   a , and the spinner table  811  is connected to the upper end of the drive shaft  812   a . The support mechanism  813  is composed of a plurality of (three in this preferred embodiment) support legs  813   a  and a plurality of (three in this preferred embodiment) air cylinders  813   b  operatively connected to the support legs  813   a , respectively. All of the air cylinders  813   b  are mounted on the electric motor  812 . The support mechanism  813  functions in such a manner that the air cylinders  813   b  are operated to vertically move the electric motor  812  and the spinner table  811  between the upper position shown in  FIG. 8  as a work load/unload position and the lower position shown in  FIG. 9  as a working position. 
     The cleaning water receiving means  82  includes a cleaning water receptacle  821 , three support legs  822  for supporting the cleaning water receptacle  821  (two of the three support legs  822  being shown in  FIG. 7 ), and a cover member  823  mounted on the drive shaft  812   a  of the electric motor  812 . As shown in  FIGS. 7 and 8 , the cleaning water receptacle  821  is composed of a cylindrical outer wall  821   a , a bottom wall  821   b , and a cylindrical inner wall  821   c . The bottom wall  821   b  is formed with a central hole  821   d  for allowing the insertion of the drive shaft  812   a  of the electric motor  812 . The cylindrical inner wall  821   c  projects upward from the peripheral edge of the central hole  821   d . As shown in  FIG. 7 , the bottom wall  821   b  is formed with a waste fluid outlet  821   e , and a drain hose  824  is connected to the waste fluid outlet  821   e . The cover member  823  is a cylindrical member having a closed top. The closed top of the cover member  823  is mounted to the upper end portion of the drive shaft  812   a  of the electric motor  812 , and a covering portion  823   a  projects downward from the outer circumference of the closed top of the cover member  823 . In the working position of the electric motor  812  and the spinner table  811  as shown in  FIG. 9 , the covering portion  823   a  of the cover member  823  is located so as to surround the cylindrical inner wall  821   c  of the cleaning water receptacle  821  with a given gap defined therebetween. 
     The cleaning means  8  further includes cleaning water supplying means  84  for cleaning the wafer held on the spinner table  811  after processing. The cleaning water supplying means  84  includes a cleaning water nozzle  841  for supplying a jet of cleaning water toward the wafer held on the spinner table  811  after processing and a reversible electric motor  842  for horizontally swinging the cleaning water nozzle  841 . The cleaning water nozzle  841  is connected to a cleaning water supply source not shown. The cleaning water nozzle  841  is composed of a horizontally extending nozzle portion  841   a  having a downward bent front end and a support portion  841   b  extending downward from the base end of the nozzle portion  841   a . The support portion  841   b  is inserted through a hole (not shown) formed through the bottom wall  821   b  of the cleaning water receptacle  821  and is connected to the cleaning water supply source not shown. Although not shown, a seal member is mounted to the peripheral edge of this hole not shown for allowing the insertion of the support portion  841   b  of the cleaning water nozzle  841 , thereby sealing the gap between the support portion  841   b  and the bottom wall  821   b.    
     The cleaning means  8  further includes air supplying means  85  for supplying a jet of air toward the wafer held on the spinner table  811  after cleaning with the cleaning water mentioned above. The air supplying means  85  includes an air nozzle  851  for supplying a jet of air toward the wafer held on the spinner table  811  and a reversible electric motor (not shown) for horizontally swinging the air nozzle  851 . The air nozzle  851  is connected to an air supply source not shown. The air nozzle  851  is composed of a horizontally extending nozzle portion  851   a  having a downward bent front end (discharge opening) and a support portion  851   b  extending downward from the base end of the nozzle portion  851   a . The support portion  851   b  is inserted through a hole (not shown) formed through the bottom wall  821   b  of the cleaning water receptacle  821  and is connected to the air supply source. Although not shown, a seal member is mounted to the peripheral edge of this hole not shown for allowing the insertion of the support portion  851   b  of the air nozzle  851 , thereby sealing the gap between the support portion  851   b  and the bottom wall  821   b.    
     The first carrying means  16  and the second carrying means  17  will now be described with reference to  FIG. 1 . The first carrying means  16  is located equidistant from the temporary setting table  15 , the protective film forming apparatus  7 , and the cleaning means  8 . The first carrying means  16  may have the same configuration as that of any carrying means generally used. That is, the first carrying means  16  is composed of holding means  161  for holding the annular frame  11  under suction and supporting means  162  for supporting the holding means  161  so that the holding means  161  can be vertically moved and horizontally swiveled. The first carrying means  16  functions to carry the semiconductor wafer  10  (attached to the protective tape  12  supported to the annular frame  11 ) from the temporary setting table  15  to the protective film forming apparatus  7  before processing and also to carry the semiconductor wafer  10  (attached to the protective tape  12  supported to the annular frame  11 ) from the cleaning means  8  to the temporary setting table  15  after processing. 
     The second carrying means  17  is located equidistant from the chuck table  3 , the protective film forming apparatus  7 , and the cleaning means  8 . The second carrying means  17  may have substantially the same configuration as that of the first carrying means  16 . That is, the second carrying means  17  is composed of holding means  171  for holding the annular frame  11  under suction and supporting means  172  for supporting the holding means  171  so that the holding means  171  can be vertically moved and horizontally swiveled. The second carrying means  17  functions to carry the semiconductor wafer  10  (attached to the protective tape  12  supported to the annular frame  11 ) from the protective film forming apparatus  7  to the chuck table  3  before processing and also to carry the semiconductor wafer  10  (attached to the protective tape  12  supported to the annular frame  11 ) from the chuck table  3  to the cleaning means  8  after processing. 
     The operation of the laser processing system shown in  FIG. 1  will now be described. The semiconductor wafer  10  supported through the protective tape  12  to the annular frame  11  as shown in  FIG. 1  (which will be hereinafter referred to simply as the semiconductor wafer  10 ) is stored at a predetermined position in the cassette  13  in the condition where the front side  10   a  (work surface) of the semiconductor wafer  10  is oriented upward. The cassette table  131  is next lifted or lowered by the lifting means (not shown) to thereby move the semiconductor wafer  10  stored in the cassette  13  to an ejecting position where the semiconductor wafer  10  is ejected from the cassette  13 . The work ejecting/inserting means  14  is next operated to eject the semiconductor wafer  10  from the cassette  13  and to move the semiconductor wafer  10  from the ejecting position to the temporary setting table  15 . The semiconductor wafer  10  moved to the temporary setting table  15  is set to a predetermined central position (centrally positioning step). 
     The semiconductor wafer  10  thus centrally positioned on the temporary setting table  15  is next held under suction by the holding means  161  of the first carrying means  16  and carried onto the vacuum chuck  711   a  of the spinner table  711  of the protective film forming apparatus  7  by the swiveling action of the holding means  161  about the axis of the supporting means  162 . The semiconductor wafer  10  placed on the vacuum chuck  711   a  is held under suction on the vacuum chuck  711   a  by the suction means (wafer holding step). Further, the annular frame  11  is fixed by the clamps  714 . At this time, the spinner table  711  is set at the load/unload position shown in  FIG. 3 , and both of the spray nozzle  740  and the liquid resin supply nozzle  750  are set at their standby positions where they are retracted from the spinner table  711  as shown in  FIGS. 2 and 3 . 
     After performing the above-mentioned wafer holding step to hold the semiconductor wafer  10  on the spinner table  711  of the protective film forming apparatus  7 , a spray coating step is performed in such a manner that the first liquid resin is sprayed onto the work surface of the semiconductor wafer  10  held on the spinner table  711  as rotating the spinner table  711  at a first rotational speed. More specifically, the spinner table  711  is set to the working position shown in  FIG. 4 , and the electric motor  745  of the spraying means  74  is operated to swing the spray nozzle  740  about the axis of the support portion  742  so that the front end of the nozzle portion  741  comes to a position directly above the center of the front side  10   a  (work surface) of the semiconductor wafer  10  held on the spinner table  711  as shown in  FIG. 11 . Next, the electric motor  712  is operated to rotate the spinner table  711  at 50 to 60 rpm (the first rotational speed). Accordingly, the semiconductor wafer  10  held on the spinner table  711  (in the condition where the semiconductor wafer  10  is attached to the protective tape  12  supported to the annular frame  11 ) is rotated in the direction shown by an arrow  70  in  FIG. 11 . 
     In the condition where the semiconductor wafer  10  is being rotated as mentioned above, the first liquid resin supplying means  743  and the air supplying means  744  shown in  FIG. 5  are operated to spray the first liquid resin from the nozzle portion  741  of the spray nozzle  740  onto the front side  10   a  (work surface) of the semiconductor wafer  10 , thereby coating the front side  10   a  with the first liquid resin (spray coating step). More specifically, the first liquid resin supplying means  743  is operated to thereby supply polyvinyl alcohol having a viscosity of 3.8 cp as the first liquid resin to the spray nozzle  740  at a rate of 0.05 mL/sec. At the same time, the air supplying means  744  is operated to supply air to the spray nozzle  740  under a pressure of 0.4 MPa. As a result, the polyvinyl alcohol having a viscosity of 3.8 cp supplied to the spray nozzle  740  is atomized by the air supplied to the spray nozzle  740  at the front end of the nozzle portion  741  and directed toward the front side  10   a  of the semiconductor wafer  10 . In this spray coating step, the electric motor  745  is operated to swing the spray nozzle  740  in a predetermined angular range from the position where the front end of the nozzle portion  741  is located directly above the center of the front side  10   a  of the semiconductor wafer  10  as shown in  FIG. 11  to the position where the front end of the nozzle portion  741  is located directly above the outer circumference of the front side  10   a  of the semiconductor wafer  10 . This spray coating step is performed for 60 to 90 seconds (e.g., 80 seconds). Accordingly, in the case that the duration time of the spray coating step is 80 seconds, 4 mL of polyvinyl alcohol is sprayed in the spray coating step. As a result, polyvinyl alcohol having a viscosity of 3.8 cp as the first liquid resin can be uniformly sprayed onto the front side  10   a  (work surface) of the semiconductor wafer  10 , thereby improving the affinity of the second liquid resin to the semiconductor wafer  10  in the subsequent steps. 
     After performing the spray coating step mentioned above, a liquid resin supplying step is performed in such a manner that the second liquid resin in a predetermined amount is dropped onto the central area of the work surface of the semiconductor wafer  10  held on the spinner table  711  as rotating the spinner table  711  at a second rotational speed lower than the first rotational speed. More specifically, the electric motor  745  of the spraying means  74  is operated to return the spray nozzle  740  to the standby position shown in  FIG. 4 , and the electric motor  755  of the liquid resin supplying means  75  is operated to swing the liquid resin supply nozzle  750  about the axis of the support portion  752  so that the front end of the nozzle portion  751  comes to a position directly above the center of the front side  10   a  (work surface) of the semiconductor wafer  10  held on the spinner table  711  as shown in  FIG. 12 . Next, the electric motor  712  is operated to rotate the spinner table  711  at 5 to 15 rpm (e.g., 10 rpm) (the second rotational speed). 
     Accordingly, the semiconductor wafer  10  held on the spinner table  711  (in the condition where the semiconductor wafer  10  is attached to the protective tape  12  supported to the annular frame  11 ) is rotated in the direction shown by an arrow  70  in  FIG. 12 . In the condition where the semiconductor wafer  10  is being rotated as mentioned above, the second liquid resin supplying means  753  shown in  FIG. 6  is operated to drop the second liquid resin from the nozzle portion  751  of the liquid resin supply nozzle  750  onto the front side  10   a  (work surface) of the semiconductor wafer  10 . More specifically, the second liquid resin supplying means  753  is operated to thereby supply polyvinyl alcohol having a viscosity of 60 cp as the second liquid resin to the liquid resin supply nozzle  750  at a rate of 5 mL/sec. Accordingly, a predetermined amount of liquid resin  100  as the second liquid resin is dropped from the nozzle portion  751  onto the central area of the front side  10   a  (work surface) of the semiconductor wafer  10  (liquid resin supplying step). This liquid resin supplying step is performed for two to four seconds (e.g., three seconds). Accordingly, in the case that the duration time of the liquid resin supplying step is three seconds, 15 mL of polyvinyl alcohol is supplied in the liquid resin supplying step. 
     After performing the liquid resin supplying step mentioned above, a spin coating step is performed in such a manner that the spinner table  711  holding the semiconductor wafer  10  thereon is rotated at a third rotational speed higher than the first rotational speed to thereby spread the second liquid resin dropped onto the central area of the front side  10   a  (work surface) of the semiconductor wafer  10 . In this spin coating step, the spinner table  711  is rotated at 400 to 600 rpm (e.g., 500 rpm) (the third rotational speed) for 20 to 40 seconds (e.g., 30 seconds). As a result, a protective film  110  is formed on the front side  10   a  (work surface) of the semiconductor wafer  10  as shown in  FIG. 13 . The protective film  110  has a thickness of 5 μm in the case that the spray coating step, the liquid resin supplying step, and the spin coating step are performed on the semiconductor wafer  10  having a diameter of 300 mm. By performing the spray coating step prior to the spin coating step, the affinity of the second liquid resin to the front side  10   a  of the semiconductor wafer  10  can be improved. Accordingly, although the rotational speed of the spinner table  711  holding the semiconductor wafer  10  thereon in the spin coating step is set lower than that in the conventional method mentioned above, the protective film  110  can be uniformly formed on the front side  10   a  (work surface) of the semiconductor wafer  10 . Accordingly, the rate of contribution of the second liquid resin to the protective film  110  can be improved to thereby reduce the amount of usage of the second liquid resin. 
     After performing the spin coating step, a spin drying step is performed in such a manner that the spinner table  711  holding the semiconductor wafer  10  is rotated at 2000 to 3000 rpm for 50 to 70 seconds. By performing this spin drying step, the protective film  110  formed on the front side  10   a  (work surface) of the semiconductor wafer  10  can be quickly dried. Alternatively, this spin drying step may be replaced by a natural drying step. 
     After performing the spin drying step mentioned above, the spinner table  711  is lifted to the load/unload position shown in  FIG. 3  and the vacuum chuck to the semiconductor wafer  10  held on the spinner table  711  is canceled. Next, the semiconductor wafer  10  is held under suction by the holding means  171  of the second carrying means  17  and carried from the spinner table  711  to the vacuum chuck  32  of the chuck table  3  by the swiveling motion of the holding means  171  about the axis of the supporting means  172 . The semiconductor wafer  10  thus carried to the vacuum chuck  32  is held on the vacuum chuck  32  under suction. Next, the chuck table  3  holding the semiconductor wafer  10  is moved to a position directly below the imaging means  5  disposed at the laser beam applying means  4  by moving means not shown in the figures. 
     When the chuck table  3  is positioned directly below the imaging means  5  as mentioned above, the imaging means  5  and the control means not shown in the figures perform image processing such as pattern matching for aligning each street  101  extending in a first predetermined direction on the front side  10   a  of the semiconductor wafer  10  to the focusing means  42  of the laser beam applying means  4  for applying a laser beam along each street  101 . Thus, the alignment of a laser beam applying position to each street  101  extending in the first predetermined direction is performed. Similarly, the alignment of a laser beam applying position to each street  101  extending in a second predetermined direction perpendicular to the first predetermined direction is also performed. In the case that the protective film  110  formed on the front side  10   a  of the semiconductor wafer  10  is not transparent, infrared radiation for imaging may be applied to the front side  10   a  of the semiconductor wafer  10  to perform the alignment from the front side  10   a.    
     After performing the alignment of the laser beam applying position to detect all the streets  101  formed on the front side  10   a  of the semiconductor wafer  10  held on the chuck table  3 , the chuck table  3  is moved to a laser beam applying region where the focusing means  42  of the laser beam applying means  4  is located, and a predetermined one of the streets  101  extending in the first predetermined direction is positioned directly below the focusing means  42 . At this time, the semiconductor wafer  10  is set so that one end (left end as viewed in  FIG. 14A ) of this predetermined street  101  is positioned directly below the focusing means  42  as shown in  FIG. 14A . Thereafter, a pulsed laser beam having an absorption wavelength to the semiconductor wafer  10  is applied from the focusing means  42  of the laser beam applying means  4  to the front side  10   a  of the semiconductor wafer  10  as moving the chuck table  3  holding the semiconductor wafer  10  in the direction shown by an arrow X 1  in  FIG. 14A  at a predetermined feed speed (laser beam applying step). When the other end (right end as viewed in  FIG. 14B ) of the predetermined street  101  comes to a position directly below the focusing means  42  as shown in  FIG. 14B , the application of the pulsed laser beam is stopped and the movement of the chuck table  3  is also stopped. As shown in  FIG. 14A , the focal point P of the pulsed laser beam is set near the upper surface of the predetermined street  101 . 
     By performing this laser beam applying step, a laser processed groove  120  is formed along the predetermined street  101  as shown in  FIG. 15 . At this time, even when debris  130  is generated by the application of the pulsed laser beam as shown in  FIG. 15 , the debris  130  is blocked by the protective film  110 , so that the debris  130  is prevented from sticking to the devices  102  and bonding pads (not shown). This laser beam applying step is performed for all of the streets  101  formed on the front side  10   a  of the semiconductor wafer  10  to thereby form the laser processed groove  120  along each street  101 . 
     For example, the laser beam applying step is performed under the following processing conditions. 
     Light source of laser beam: YVO4 laser or YAG laser 
     Wavelength: 355 nm 
     Repetition frequency: 20 kHz 
     Power: 3 W 
     Focused spot diameter: 5 μm 
     Work feed speed: 100 mm/sec 
     After performing the laser beam applying step along all of the streets  101  of the semiconductor wafer  10 , the chuck table  3  holding the semiconductor wafer  10  thereon is returned to the initial position shown in  FIG. 1  and the vacuum chuck to the semiconductor wafer  10  is canceled. Thereafter, the semiconductor wafer  10  is held under suction by the holding means  171  of the second carrying means  17  and carried from the chuck table  3  to the vacuum chuck  811   a  of the spinner table  811  of the cleaning means  8  by the swiveling motion of the holding means  171  about the axis of the supporting means  172 . The semiconductor wafer  10  thus carried to the vacuum chuck  811   a  is held under suction. At this time, both of the cleaning water nozzle  841  and the air nozzle  851  are set at their standby positions retracted from the spinner table  811  as shown in  FIGS. 7 and 8 . 
     In the condition where the semiconductor wafer  10  is held on the spinner table  811  of the cleaning means  8  after processing, a cleaning step is performed in such a manner that the spinner table  811  is lowered to the working position shown in  FIG. 9  and the electric motor  842  of the cleaning water supplying means  84  is driven to move the front end of the nozzle portion  841   a  of the cleaning water supply nozzle  841  to the position directly above the center of the semiconductor wafer  10  held on the spinner table  811 . Thereafter, the spinner table  811  is rotated at 300 to 500 rpm, for example, and the cleaning water composed of pure water and air is discharged from the front end of the nozzle portion  841   a . The nozzle portion  841   a  is provided by a so-called two-fluid nozzle such that about 0.2 MPa of pure water and about 0.3 to 0.5 MPa of air are supplied and the pure water is sprayed by the pressure of the air to clean the front side  10   a  of the semiconductor wafer  10  processed. At this time, the electric motor  842  is driven to swing the nozzle portion  841   a  of the cleaning water supply nozzle  841  in a required angular range from the center of the semiconductor wafer  10  held on the spinner table  811  to the outer circumference thereof. As a result, the protective film  110  formed on the front side  10   a  of the semiconductor wafer  10  can be easily cleaned off by the cleaning water because the protective film  110  is formed of a water-soluble resin. At the same time, the debris  130  generated in the laser beam applying step is also removed with the protective film  110 . 
     After performing the cleaning step mentioned above, a drying step is performed in such a manner that the cleaning water supply nozzle  841  is returned to the standby position and the air nozzle  851  of the air supplying means  85  is swung from the standby position shown in  FIG. 7  so that the front end of the nozzle portion  851   a  comes to the position directly above the center of the semiconductor wafer  10  held on the spinner table  811 . Thereafter, the spinner table  811  is rotated at 2000 to 3000 rpm, for example, and air is discharged from the front end of the nozzle portion  851   a  for about 15 seconds. At this time, the nozzle portion  851   a  of the air nozzle  851  is swung about the axis of the support portion  851   b  in a required angular range from the center of the semiconductor wafer  10  to the outer circumference thereof. As a result, the front side  10   a  of the semiconductor wafer  10  is dried. 
     After performing the drying step mentioned above, the rotation of the spinner table  811  is stopped and the air nozzle  851  of the air supplying means  85  is returned to the standby position. Thereafter, the spinner table  811  is lifted to the load/unload position shown in  FIG. 8  and the vacuum chuck to the semiconductor wafer  10  held on the spinner table  811  is canceled. Thereafter, the semiconductor wafer  10  is carried from the spinner table  811  to the temporary setting table  15  by the first carrying means  16 . Finally, the semiconductor wafer  10  is carried from the temporary setting table  15  to the cassette  13  and inserted into the predetermined position of the cassette  13  by the work ejecting/inserting means  14 . 
     During the cleaning step and the drying step by the cleaning means  8 , the work ejecting/inserting means  14  is operated to eject the semiconductor wafer  10  to be next processed from the cassette  13  to the temporary setting table  15 , and the first carrying means  16  is next operated to carry this semiconductor wafer  10  from the temporary setting table  15  to the protective film forming apparatus  7 . Thereafter, this semiconductor wafer  10  is subjected to the spray coating step, the liquid resin supplying step, the spin coating step, and the spin drying step by the protective film forming apparatus  7 . Thereafter, this semiconductor wafer  10  is carried from the protective film forming apparatus  7  to the chuck table  3  by the second carrying means  17  to perform the laser beam applying step. During this laser beam applying step, the previous semiconductor wafer  10  is carried from the cleaning means  8  to the temporary setting table  15  by the second carrying means  17 . Thereafter, the present semiconductor wafer  10  is carried from the chuck table  3  to the cleaning means  8  by the second carrying means  17  to perform the cleaning step and the drying step. 
     While a specific preferred embodiment of the present invention has been described, the present invention is not limited to this preferred embodiment, but various modifications may be made within the scope of the present invention. For example, while the protective film forming apparatus  7  is incorporated in the laser processing system in this preferred embodiment, the protective film forming apparatus  7  may be configured as an independent apparatus. 
     The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.