Patent Publication Number: US-8116893-B2

Title: Dicing method

Description:
TECHNICAL FIELD 
     The present invention relates to a dicing method for dividing, into chips, a workpiece such as a wafer on which semiconductor elements or electronic components are formed. 
     BACKGROUND ART 
     A dicing apparatus, which performs a cutting or groove-forming process on a workpiece such as a wafer on which semiconductor elements or electronic components are formed, includes at least: a rotary blade which is formed of a thin grindstone called a blade and is rotated by a spindle at high speed; a worktable which holds the workpiece; and X, Y, Z, and θ moving shafts which change a relative position between the worktable and the blade. At the time of processing the workpiece, a cutting fluid for cooling or lubrication is supplied from a nozzle to the rotating blade or a processing point at which the workpiece and the blade contact each other, and the cutting or groove-forming process is performed on the workpiece by the operations of the respective moving shafts. 
       FIG. 8  illustrates a conventional example of the dicing apparatus. A dicing apparatus  70  includes a processing part  75 . The processing part has: high-frequency motor built-in type spindles  72 ,  72  respectively equipped with a blade  71  and a wheel cover (not shown) on their tips, and disposed so as to be opposed to each other; a worktable  73  which adsorbs and holds a workpiece W; and an image pickup device  74  formed of a microscope, a CCD camera, or the like for picking up an image of the workpiece W. In addition to these components, the dicing apparatus  70  includes: a cleaning part  76  which spin-cleans the processed workpiece W which has been processed by the processing part  75 ; a load port  77  onto which a cassette that houses a large number of the workpieces W mounted on a frame F is set; a conveyance device  78  which conveys the workpiece W; a controller  79  which controls the operations of the respective parts; and the like. 
     As illustrated in  FIG. 9 , the structure of the processing part  75  includes an X table  83  which is guided by X guides  81 ,  81  provided to an X base  80  and is driven by a linear motor  82  in an X direction indicated by X-X of the figure. A worktable  85  is provided to the X table  83  via a rotary table  84  which rotates in a θ direction. 
     On the other hand, Y tables  88 ,  88  which are guided by Y guides  87 ,  87  and are driven by a stepper motor (not shown) and a ball screw (not shown) in a Y direction indicated by Y-Y of the figure are provided on a side surface of a Y base  86 . A Z table  89  which is driven by a drive device (not shown) in a Z direction indicated by Z-Z of the figure is provided to each of the Y tables  88 . The high-frequency motor built-in type spindle  72  which has the blade  71  on its tip is fixed to the Z table  89 . The processing part  75  has the structure as described above, and hence the blade  71  is step-fed (fed in a stepwise manner) in the Y direction and also is fed while cutting-in (cutting-in feed) in the Z direction, and the worktable  73  is fed while cutting (cutting feed) in the X direction. 
     The spindles  72  are both rotated at a high speed of 1,000 rpm to 80,000 rpm, and a supply nozzle (not shown) which supplies the cutting fluid into which the workpiece W is to be immersed is provided in the vicinity of the spindles  72 . 
     An electrodeposition blade obtained by electrodepositing diamond abrasive grains or CBN abrasive grains with nickel, a metal-resin bonding blade obtained by bonding with a resin mixed with a metal power, or the like is used as the blade  71 . The dimensions of the blade  71  are variously selected depending on the processing type. In a case where a general semiconductor wafer is diced into the workpiece, a blade having a diameter of approximately 50 mm and a thickness of approximately 30 μm is used. 
     In addition, the controller which controls the operations of the respective parts of the dicing apparatus  70  includes a CPU, a memory, an input/output circuit part, various control circuit parts, and the like, and is incorporated inside a pedestal of the dicing apparatus  70 . As the dicing apparatus having the above-mentioned structure, for example, a dicing apparatus disclosed in Patent Document 1 has been proposed. 
     In the dicing apparatus  70  having the above-mentioned structure, as a stage prior to the processing, an alignment operation is performed, in which an image of the workpiece W is picked up by the image pickup device  74  and the position of the workpiece W is aligned with the blade  71 . Also during the processing, if necessary, an image of the workpiece W is picked up by the image pickup device  74  as appropriate to check a processing condition. However, in the dicing apparatus  70 , only one worktable  73  onto which the workpiece W is set and only one image pickup device  74  which picks up an image of the workpiece are provided. Therefore, during the processing of one workpiece W, it is not possible to set another new workpiece W onto the worktable  73  to perform the alignment by the image pickup device  74 . Accordingly, the utilization rate of the image pickup device is low, and in addition, the utilization rate of the entire dicing apparatus is also deteriorated. 
     As a solution to such a problem, Patent Document 2 discloses a dicing apparatus in which two blades, two worktables, and two image pickup devices are provided. In this dicing apparatus, a workpiece which is set onto one worktable is aligned by one image pickup device, while a workpiece which is set onto another worktable is aligned by another image pickup device. Then, the workpiece which is set onto the one worktable is processed by one blade, while the workpiece which is set onto the another worktable is processed by another blade. Alternatively, the workpiece which is set onto the one worktable or the another worktable is processed by both the one blade and the another blade. In this manner, two workpieces are aligned individually by the two image pickup devices, and one workpiece is processed by the two blades, whereby the utilization rate of the dicing apparatus is improved.
     Patent Document 1: Japanese Patent Application Laid-Open No. 2002-280328   Patent Document 2: Japanese Patent Application Laid-Open No. 2006-156809   

     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     However, in the dicing apparatus as disclosed in Patent Document 2, images of two workpieces are picked up individually by the two image pickup devices. Therefore, for example, even in a case where, during the image pickup of one workpiece on the one worktable, the image pickup device needs to be used for another workpiece on the another worktable, an image of the another workpiece cannot be picked up by the two image pickup devices until the end of the image pickup of the one workpiece. As a result, the utilization efficiency of the dicing apparatus is deteriorated. 
     The present invention has been made in order to solve the above-mentioned problem, and therefore aims to provide a dicing method which achieves an increase in utilization rate of image pickup device and also an improvement in utilization rate of an entire apparatus. 
     Means for Solving the Problem 
     In order to achieve the above-mentioned object, according to an aspect of the present invention, there is provided a dicing method which is used for a dicing apparatus including a first worktable and a second worktable each of which can have a workpiece set thereon, a first image pickup device and a second image pickup device which pick up an image of the workpiece, and a first cutting device and a second cutting device which perform cutting of the workpiece, and the first cutting device and the second cutting device are moved for cutting by a moving device relative to the first worktable or the second worktable, the dicing method comprising: in a case where a control device detects, during an image pickup of the workpiece set onto the second worktable by the first image pickup device and the second image pickup device, that an image of the workpiece set onto the first worktable also needs to be picked up by the first image pickup device and the second image pickup device, determining, by the control device, a priority between an operation performed on the first worktable and an operation performed on the second worktable; and when it is determined that the operation performed on the first worktable has a higher priority, interrupting the image pickup of the workpiece set onto the second worktable, and moving the first image pickup device and the second image pickup device to pickup an image of the workpiece on the first worktable. 
     According to this aspect, first, a workpiece is set onto the first worktable, an image of the workpiece is picked up by the first image pickup device and the second image pickup device to perform the alignment, and the first cutting device and the second cutting device are moved for cutting relative to the first worktable by a moving device. When the processing of the workpiece set onto the first worktable is started, another workpiece is set also to the second worktable, and the alignment is started by the first image pickup device and the second image pickup device. 
     In a case where the control device included in the dicing apparatus detects, during the alignment operation of the workpiece on the second worktable, that an image of the workpiece on the first worktable during the processing needs to be picked up again by the image pickup device, in order to perform a realignment, a kerf checking, or a checking of diced chips, the control apparatus determines the priority between the operation which is currently performed on the workpiece on the second worktable and the operation which is performed on the workpiece on the first worktable. 
     Normally, it takes a longer time to finish the dicing process of the workpiece excluding the alignment than the alignment operation. Further, if the workpiece during the processing is left for a long time, there arises a problem that the cutting fluid used for the processing is dried on the workpiece. Therefore, the processing operation has a higher priority than the alignment operation. 
     Accordingly, the control device temporarily stops the alignment operation of the workpiece on the second worktable, stores all pieces of data used for the alignment and state control information (position, automatic focus, and illuminated condition) on the position at the time of the interruption with regard to the workpiece whose image is currently being picked up by the image pickup device, and moves the image pickup device to a position at which an image of the workpiece on the first worktable is picked up. When the control device recognizes that the image pickup of the workpiece on the first worktable is finished and the image pickup device becomes available, the image pickup device is moved back to the position above the workpiece set onto the second worktable, which is stored in the control device, and restarts the unfinished alignment operation. 
     In this manner, the image pickup device is preferentially used for the operation having a higher priority, and the interrupted operation is restarted at the position at the time of the interruption. Accordingly, it becomes possible to increase the utilization rate of the image pickup device and to improve the utilization rate of the entire apparatus. 
     In order to achieve the above-mentioned object, according to another aspect of the present invention, there is provided a dicing method which is used for a dicing apparatus including a first worktable and a second worktable each of which can have a workpiece set thereon, a first image pickup device and a second image pickup device which pick up an image of the workpiece, and a first cutting device and a second cutting device which perform cutting of the workpiece, and the first cutting device and the second cutting device are moved for cutting by a moving device relative to the first worktable or the second worktable, the dicing method comprising: in a case where a control device detects, during an image pickup of the workpiece set onto the second worktable by the first image pickup device and the second image pickup device, that an image of the workpiece set onto the first worktable also needs to be picked up by any one of the first image pickup device and the second image pickup device, determining, by the control device, a priority between an operation performed on the first worktable and an operation performed on the second worktable; and when it is determined that the operation performed on the first worktable has a higher priority, moving any one of the first image pickup device and the second image pickup device which are performing the image pickup of the workpiece set onto the second worktable, to a position at which an image of the workpiece on the first worktable is picked up, to pickup the image. 
     According to this aspect, first, the alignment of a workpiece set onto the first worktable is performed, and the processing of the workpiece is started after the alignment. When the processing of the workpiece set onto the first worktable is started, another workpiece is also set to the second worktable, and the alignment is started. 
     In a case where the control device detects, during the alignment operation of the workpiece on the second worktable, that an image of the workpiece on the first worktable during the processing needs to be picked up again by the image pickup device, the control apparatus determines the priority between the operation which is currently performed on the workpiece on the second worktable and the operation which is performed on the workpiece on the first worktable. 
     When the control device determines that the operation which is performed on the first worktable has a higher priority than the operation which is performed on the second worktable, the control device moves any one of the first image pickup device and the second image pickup device which are performing the image pickup of the workpiece set onto the second worktable, to a position at which an image of the workpiece on the first worktable is picked up, to pickup the image. 
     In this manner, the first image pickup device or the second image pickup device is assigned to the operation having a higher priority to be used. Accordingly, it becomes possible to increase the utilization rate of the image pickup device and to improve the utilization rate of the entire apparatus. 
     Advantage of the Invention 
     As described above, according to the dicing method of the present invention, it becomes possible to increase the utilization rate of the image pickup device and also to improve the utilization rate of the entire apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an external appearance of a dicing apparatus for which a dicing method of the present invention is carried out; 
         FIG. 2  is a perspective view illustrating a structure of a processing part of the dicing apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a cross sectional view illustrating a main part structure of the processing part illustrated in  FIG. 2 ; 
         FIG. 4  is a plan view illustrating an alignment state of a workpiece on a second worktable; 
         FIG. 5  is a plan view illustrating an alignment state of a workpiece on a first worktable; 
         FIG. 6  is a plan view illustrating a state where an image of the workpiece on the first worktable is picked up again; 
         FIG. 7  is a plan view illustrating a state where an image of the workpiece on the first worktable is picked up by one image pickup device; 
         FIG. 8  is a perspective view illustrating an external appearance of a conventional dicing apparatus; and 
         FIG. 9  is a perspective view illustrating a structure of a processing part of the dicing apparatus illustrated in  FIG. 8 . 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           1 ,  70  . . . dicing apparatus,  5 A . . . first image pickup device,  5 B . . . second image pickup device,  8  . . . controller (control device),  9  . . . rotary blade,  10  . . . spindle,  12  . . . first worktable,  14  . . . second worktable,  16 ,  18  . . . X table,  20  . . . oil pan,  22  . . . guide rail,  24  . . . ball screw,  26  . . . servomotor,  28  . . . ball nut,  30  . . . slider,  32  . . . θ table,  33  . . . fixture,  34  . . . accordion cover,  36  . . . guide rail,  38  . . . ball screw,  40  . . . servomotor,  44  . . . θ table,  46  . . . accordion cover,  48  . . . guide base,  50  . . . spindle Y guide,  52  . . . spindle Y table,  54  . . . spindle Z table,  56  . . . holder,  58 ,  60  . . . image pickup device drive device,  62  . . . image pickup device Y guide,  64 A,  64 B . . . image pickup device Y table,  66 A,  66 B . . . image pickup device Z table 
       
    
     Best Mode for Carrying out the Invention 
     Hereinafter, a preferred embodiment of a dicing method according to the present invention is described in detail with reference to the accompanying drawings. 
     First of all, the structure of a dicing apparatus for which the dicing method according to the present invention is described.  FIG. 1  is an overall perspective view of the dicing apparatus. 
     A dicing apparatus  1  of the embodiment illustrated in  FIG. 1  includes: a load port  2  where a cassette that houses a plurality of workpieces is transferred from an external device; a conveyance device  4  which includes an adsorption part  3  and conveys the workpiece to the respective parts of the apparatus; a first image pickup device  5 A and a second image pickup device  5 B, such as a microscope or a CCD camera, which observe an upper surface of the workpiece; a processing part  6 ; a spinner  7  which cleans and dries the processed workpiece; a controller  8  serving as a control device which controls the operations of the respective parts of the apparatus; and the like. 
     The processing part  6  includes two air-bearing or mechanical-bearing spindles  10 ,  10  of a high-frequency motor built-in type each of which has a blade  9  as a rotary blade and which are disposed so as to be opposed to each other. The spindles  10 ,  10  are rotated at high speed, and also are step-fed in a Y direction of the figure and fed while cutting-in in a Z direction of the figure independently of each other. The blade  9  is surrounded by a flange cover (not shown) which is opened on its front side and lower side, and a grinding fluid is supplied toward a processing point from a grinding nozzle provided to the flange cover. In addition, a cleaning nozzle (not shown) is provided to the flange cover, and a cleaning fluid is supplied toward the processing point from the cleaning nozzle. 
     The blade  9  is a thin disk-shaped grindstone, and an electrodeposition blade obtained by electrodepositing diamond abrasive grains or CBN abrasive grains with nickel, a metal-resin bonding blade obtained by bonding with a resin mixed with a metal power, or the like is used as the blade  9 . The dimensions of the blade  9  are variously selected depending on the processing type. In a case where a general semiconductor wafer is diced as the workpiece, a blade having a diameter of approximately 50 mm and a thickness of approximately 30 μm is used. 
     Further, the processing part  6  includes two worktables of first worktable  12  and second worktable  14  having an identical shape, on which the workpiece is adsorbed and set, and the first worktable  12  and the second worktable  14  are fed while grinding (grinding feed) in an X direction of  FIG. 1  by the movement of X tables  16 ,  18  serving as a moving device illustrated in  FIG. 2  which is described below. 
       FIG. 2  is a perspective view illustrating a main part of the processing part  6  of the dicing apparatus  1 . As illustrated in  FIG. 2 , a box-shaped oil pan  20  is horizontally disposed below the first worktable  12  and the second worktable  14  of the processing part  6  so as to sufficiently surround the two first worktable  12  and second worktable  14 . On a left side surface of the oil pan  20 , two paired guide rails (guide mechanism)  22 ,  22  are arranged along the arrow X direction of the figure. Between the guide rails  22 ,  22 , a ball screw  24  constituting a drive mechanism is arranged parallel to the guide rails  22 ,  22  and along the left side surface of the oil pan  20 . 
     In addition, a servomotor  26  which rotates the ball screw  24  is disposed on a deeper side of the oil pan  20  in a depth direction thereof. Further, the X table  16  which is guided by the guide rails  22 ,  22  and is driven in the X direction by the rotation of the ball screw  24  by the servomotor  26  is disposed in a longitudinal direction. It should be noted that the drive mechanism of the present invention may be a drive mechanism using a linear motor in addition to the drive mechanism using the ball screw  24 . 
     As illustrated in  FIG. 3 , the X table  16  includes a ball nut  28  which is screwed with the ball screw  24 , and sliders  30 ,  30  which are slidably engaged with the guide rails  22 ,  22 . Further, a θ table (θ-rotating shaft)  32  which θ-rotates about the Z direction (see  FIG. 1 ) as an axis is mounted on the X table  16 , and the first worktable  12  is attached to the θ table  32 . The θ table  32  (rotating shaft) has a bottom surface which is fixed to an L-shaped fixture  33  attached to the X table  16  so that the first worktable  12  rotates on a horizontal plane in the θ direction. 
     In addition, a pair of accordion covers (accordion members)  34 ,  34 , which expands and contracts by the movement of the X table  16  in the X direction and covers the guide rails  22 ,  22  and the ball screw  24 , is disposed on the left side surface of the oil pan  20 . One accordion cover  34  has one end which is fixed to a front side of the oil pan  20  in the depth direction thereof, and another end which is fixed to a front side edge of the X table  16  in the depth direction thereof. Another accordion cover  34  has one end which is fixed to a deeper side of the oil pan  20  in the depth direction thereof, and another end which is fixed to a deeper side edge of the X table  16  in the depth direction thereof. It should be noted that the another accordion cover  34  is omitted in  FIG. 2 . 
     On the other hand, as illustrated in  FIG. 2 , similarly on a right side surface of the oil pan  20 , two paired guide rails (guide mechanism)  36 ,  36  are arranged along the arrow X direction of  FIG. 1 . Also between the guide rails  36 ,  36 , a ball screw  38  constituting a drive mechanism is arranged parallel to the guide rails  36 ,  36  and along the right side surface of the oil pan  20 . 
     In addition, a servomotor  40  which rotates the ball screw  38  is disposed on the deeper side of the oil pan  20  in the depth direction thereof. Further, the X table  18  which is guided by the guide rails  36 ,  36  and is driven in the X direction by the rotation of the ball screw  38  by the servomotor  40  is disposed. 
     The X table  18  is provided with a ball nut (not shown) which is screwed with the ball screw  38 , and sliders (not shown) which are slidably engaged with the guide rails  36 ,  36 . Further, a θ table (θ-rotating shaft)  44  which θ-rotates about the Z direction (see  FIG. 1 ) as an axis is mounted on the X table  18 , and the second worktable  14  is attached to the θ table  44 . The θ table  44  (rotating shaft) has a bottom surface which is fixed to an L-shaped fixture (not shown) attached to the X table  18  so that the second worktable  14  rotates on a horizontal plane in the θ direction. 
     In addition, a pair of accordion covers (accordion members)  46 ,  46 , which expands and contracts by the movement of the X table  18  in the X direction and covers the guide rails  36 ,  36  and the ball screw  38 , is disposed on the right side surface of the oil pan  20 . One accordion cover  46  has one end which is fixed to the front side of the oil pan  20  in the depth direction thereof, and another end which is fixed to a front side edge of the X table  18  in the depth direction thereof. Another accordion cover  46  has one end which is fixed to the deeper side of the oil pan  20  in the depth direction thereof, and another end which is fixed to a deeper side edge of the X table  18  in the depth direction thereof. It should be noted that the another accordion cover  46  is omitted in  FIG. 2 . 
     In addition, as illustrated in  FIG. 4 , a gate-shaped guide base  48  is vertically disposed to the processing part  6 . A spindle Y guide  50  is attached to a left side surface of the guide base  48  in  FIG. 4 , horizontally to the arrow Y direction of the figure. In addition, two spindle Y tables  52 ,  52  serving as a moving device, which are guided by the spindle Y guide  50  and are step-fed by a drive mechanism (not shown) in the Y direction, are disposed. Each of the spindle Y guide tables  52 ,  52  has a spindle Z table  54  which serves as a moving device and is fed while cutting-in by a guide rail (not shown) and a drive mechanism (not shown) in the arrow Z direction of the figure. The spindle  10  is attached to each spindle Z table  54  via a holder  56 . 
     The two spindles  10 ,  10  are disposed so as to be opposed to each other and each have the rotary blade  9  attached to the tip thereof. With this mechanism, the two rotary blades  9 ,  9  are fed while cutting-in in the Z direction and step-fed in the Y direction independently of each other. In addition, a linear motor may be used as the drive mechanism for each of the spindle Y tables  52 ,  52  and the spindle Z tables  54 . Alternatively, a servomotor and a lead screw may be used as the drive mechanism therefor. 
     Two image pickup device drive devices  58 ,  60  are provided on a right side surface of the guide base  48  in  FIG. 4 . The image pickup device drive devices  58 ,  60  include: an image pickup device Y guide  62  which is attached to the right side surface of the guide base  48  and is disposed horizontally to the arrow Y direction of the figure; image pickup device Y tables  64 A,  64 B which are guided by the image pickup device Y guide  62  and are moved by a drive mechanism (not shown) in the Y direction; and image pickup device Z tables  66 A,  66 B which are fed in the arrow Z direction of the figure by a guide rail (not shown) and a drive mechanism (not shown) provided in the image pickup device Y tables  64 A,  64 B. 
     The first image pickup device  5 A and the second image pickup device  5 B which observe the upper surface of a workpiece W are attached to the image pickup device Z table  66 A and the image pickup device Z table  66 B, respectively. It should be noted that the image pickup device drive devices  58 ,  60  are not necessarily attached to the guide base  48  but may be attached to the image pickup device Y guide as another guide base which is disposed parallel to the guide base  48 . 
     The first image pickup device  5 A and the second image pickup device  5 B are fed in the Y direction and the Z direction of the figure by the image pickup device drive devices  58 ,  60  having the above-mentioned structure. It should be noted that known drive devices, such as the linear motor or the servomotor and the lead screw, may be similarly used as the drive mechanism for each of the image pickup device Y guide  62  and the image pickup device Z tables  66 A,  66 B. A CCD camera (not shown) is incorporated in each of the first image pickup device  5 A and the second image pickup device  5 B. An image of the workpiece W which is picked up by the CCD camera is subjected to a pattern matching process by an image processing apparatus provided in the controller  8  of  FIG. 1 , to thereby perform the alignment of the workpiece W. The control of the drive device for these respective parts, the control of the alignment operation, the control of the processing part  6 , the control of the conveyance device  4 , and the like are all performed by the controller  8 . 
     Next, a description is given of the dicing method according to the present invention which is carried out for the dicing apparatus  1  having the above-mentioned structure. 
     In the dicing method of the present invention, first, the cassette which is set onto the load port  2  of the dicing apparatus  1  houses a plurality of dicing tapes, and the workpieces W which are attached to a frame via the dicing tapes are pulled out one by one from the cassette by the conveyance device  4 , to be adsorbed by the first worktable  12 . 
     After that, as illustrated in  FIG. 5 , the first worktable  12  is moved to below the image pickup device Y guide  62 , and at the same time, the first image pickup device  5 A and the second image pickup device  5 B are conveyed by the image pickup device Y tables  64 A,  64 B to immediately above the workpiece. Here, the first image pickup device  5 A and the second image pickup device  5 B are brought into focus by the image pickup device Z tables  66 A,  66 B. Subsequently, an image of a pattern portion formed on the upper surface of the workpiece W is picked up by the CCD camera incorporated in each of the first image pickup device  5 A and the second image pickup device  5 B, and the alignment thereof is performed using a known pattern matching method. It should be noted that the next workpiece W is set onto the second worktable  14  during this alignment of workpiece. 
     The workpiece W after the alignment is conveyed to the processing part  6  by the first worktable  12  and is subjected to a dicing process. In this process, the two rotary blades  9 ,  9  are each fed while cutting-in to a necessary degree, and two lines of the processing region (street) are simultaneously processed by the grinding feed of the first worktable  12  in the X direction. Then, the rotary blades  9 ,  9  are step-fed by a necessary pitch in the Y direction to be positioned at the next street, and two lines of this street are similarly processed by the feeding for grinding of the first worktable  12  in the X direction. This operation is repeated, so that all the streets of the workpiece W in one direction are processed. After all the lines in one direction are processed, the workpiece W is rotated by 90 degrees by the rotation of the θ table  32 , and streets which are orthogonal to the first-processed streets are processed. 
     When the first workpiece W is being subjected to the processes (processing, cleaning, and the like) subsequent to the alignment by the processing part  6 , as illustrated in  FIG. 4 , the next workpiece W set onto the second worktable  14  is moved to below the image pickup device Y guide  62 , and the first image pickup device  5 A and the second image pickup device  5 B are conveyed by the image pickup device Y tables  64 A,  64 B to immediately above this next workpiece W. Similarly here, the first image pickup device  5 A and the second image pickup device  5 B are brought into focus by the image pickup device Z tables  66 A,  66 B. An image of a pattern portion formed on the upper surface of the next workpiece W is picked up by the CCD camera incorporated in each of the first image pickup device  5 A and the second image pickup device  5 B, and the alignment thereof is performed. 
     At this time, in a case where the controller  8  detects that an image of the first workpiece W which is being processed on the first worktable  12  needs to be picked up again by the first image pickup device  5 A and the second image pickup device  5 B in order to perform, for the first workpiece W, a realignment, a kerf checking, or a checking of the diced chips, the controller  8  determines the priority between the alignment operation which is currently performed on the workpiece W on the second worktable  14  and the dicing operation which is performed on the workpiece W on the first worktable  12 . 
     Normally, it takes a longer time to finish the dicing operation of the workpiece W excluding the alignment than the alignment operation. Further, if the workpiece during the processing is left for a long time, there arises a problem that the cutting fluid used for the processing is dried on the workpiece W. Therefore, the dicing operation has a higher priority than the alignment operation. 
     Accordingly, the controller  8  stores all pieces of data used for the alignment and state control information (position, automatic focus, and illuminated condition) on the position at the time of the interruption with regard to the workpiece W whose image is being picked up by the first image pickup device  5 A and the second image pickup device  5 B for the alignment operation, and temporarily interrupts the alignment operation. After the interruption, as illustrated in  FIG. 6 , the first image pickup device  5 A and the second image pickup device  5 B are moved to a position at which an image of the workpiece W on the first worktable  12  is picked up, and the workpiece W on the first worktable  14  whose processing is stopped is moved to below the first image pickup device  5 A and the second image pickup device  5 B. 
     Here again, the first image pickup device  5 A and the second image pickup device  5 B are brought into focus by the image pickup device Z tables  66 A,  66 B. An image of the upper surface of the workpiece W on the first worktable  12  whose processing is not finished is picked up by the CCD camera incorporated in each of the first image pickup device  5 A and the second image pickup device  5 B. Then, the realignment during the processing, the kerf checking, the checking of the cut chips, or the like is performed. 
     When the controller  8  recognizes that the image pickup of the workpiece W on the first worktable  12  is finished and thus the first image pickup device  5 A and the second image pickup device  5 B become available, as illustrated in  FIG. 4 , the first image pickup device  5 A and the second image pickup device  5 B are moved back to a position which is above the workpiece W set onto the second worktable  14  and is stored in the controller  8 , and start the alignment operation again, and at the same time, the processing of the workpiece W on the first worktable  12  is restarted. 
     In this manner, the first image pickup device  5 A and the second image pickup device  5 B are preferentially used for the operation having a higher priority, and the interrupted operation is restarted at the interruption position. Accordingly, it becomes possible to increase the utilization rates of the first image pickup device  5 A and the second image pickup device  5 B and also to improve the utilization rate of the entire dicing apparatus  1 . 
     It should be noted that, in this embodiment, both the first image pickup device  5 A and the second image pickup device  5 B are moved to above the workpiece W on the first worktable  12  whose image needs to be picked up again. Alternatively, as illustrated in  FIG. 7 , only the first image pickup device  5 A may be moved to above the workpiece W on the first worktable  12  to pick up an image of the workpiece W on the first worktable  12 , while the second image pickup device  5 B may continue the current image pickup to continue the alignment operation. 
     In this manner, the first image pickup device  5 A or the second image pickup device  5 B is assigned to the operation having a higher priority to be used. Accordingly, it becomes possible to increase the utilization rates of the first image pickup device  5 A and the second image pickup device  5 B and also to improve the utilization rate of the entire dicing apparatus  1 . 
     As described hereinabove, in the dicing method according to the present invention, the image pickup device is preferentially used for the operation having a higher priority, and the interrupted operation is restarted at the interruption position. Accordingly, it becomes possible to increase the utilization rate of the image pickup device and also to improve the utilization rate of the entire apparatus. 
     In this embodiment, the opposed spindles  10 ,  10  which have the blades  9  respectively attached to the opposed tips thereof are used as the cutting device. However, the present invention is not limited thereto, and can be preferably carried out for a dicing apparatus using a known cutting device such as a laser.