Abstract:
A laser processing apparatus includes a first chuck table for holding a first workpiece, moving units for moving the first chuck table in X and Y directions, and a first focusing unit for focusing a first laser beam to the first workpiece. A second chuck table holds a second workpiece. Other moving units move the second chuck table in the X direction and Y directions, and a second focusing unit focuses a second laser beam to the second workpiece. A laser oscillator produces an original laser beam, and an optical system branches the original laser beam into the first laser beam and the second laser beam, and leads the first and second laser beams to the first and second focusing units, respectively.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    The present invention relates to a laser processing apparatus for processing a workpiece such as a semiconductor wafer by applying a laser beam thereto. 
         [0003]    Description of the Related Art 
         [0004]    In a process of manufacturing a plurality of semiconductor device chips by using a laser processing apparatus, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions where a plurality of semiconductor devices such as integrated circuits (ICs) and large scale integration (LSI) circuits are each formed. The semiconductor wafer is cut along the division lines by applying a laser beam to thereby divide the regions where the semiconductor devices are formed from each other, thus obtaining the individual semiconductor device chips. 
         [0005]    The laser processing apparatus includes a chuck table for holding a workpiece, laser beam applying means for applying a laser beam to the workpiece held on the chuck table, and feeding means for feeding the chuck table, wherein the laser beam applying means includes a laser oscillator for oscillating a laser beam, focusing means, focusing means for focusing the laser beam oscillated by the laser oscillator to thereby apply the focused laser beam to the workpiece held on the chuck table, and an attenuator provided between the laser oscillator and the focusing means for adjusting the power of the laser beam, thereby performing desired laser processing to the workpiece (see Japanese Patent Laid-open No. 2010-158691, for example). 
         [0006]    Further, in many cases, the laser oscillator used in the laser processing apparatus is so designed as to oscillate a laser beam having a relatively large power for the purpose of supporting various kinds of processing. Accordingly, the attenuator is generally used to adjust the power of the laser beam to a reduced power suitable for the workpiece. 
       SUMMARY OF THE INVENTION 
       [0007]    As described above, the laser beam generated from the laser oscillator in the laser processing apparatus is used after adjusting the power of the laser beam to a reduced power. For example, ½ or less of the power that can be originally exhibited by the laser oscillator is used for laser processing of the workpiece. In this case, ½ or more of the power of the laser beam oscillated by the laser oscillator is wasted. Thus, the performance of the laser oscillator cannot be sufficiently exhibited to cause poor economy. 
         [0008]    It is therefore an object of the present invention to provide a laser processing apparatus which can sufficiently exhibit the performance of a laser oscillator capable of oscillating a laser beam having a large power. 
         [0009]    In accordance with an aspect of the present invention, there is provided a laser processing apparatus including a first chuck table for holding a first workpiece; first X moving means for moving the first chuck table in an X direction; first Y moving means for moving the first chuck table in a Y direction perpendicular to the X direction; first focusing means for focusing a first laser beam to the first workpiece held on the first chuck table; a second chuck table for holding a second workpiece; second X moving means for moving the second chuck table in the X direction; second Y moving means for moving the second chuck table in the Y direction; second focusing means for focusing a second laser beam to the second workpiece held on the second chuck table; a laser oscillator for oscillating an original laser beam; and an optical system for branching the original laser beam oscillated by the laser oscillator into the first laser beam and the second laser beam and leading the first and second laser beams to the first and second focusing means, respectively. 
         [0010]    Preferably, the optical system includes a first optical path for leading the first laser beam to the first focusing means; a second optical path for leading the second laser beam to the second focusing means; a beam splitter for branching the original laser beam oscillated by the laser oscillator into the first laser beam and the second laser beam and leading the first and second laser beams to the first and second optical paths, respectively; a first beam shutter provided on the first optical path for interrupting the first laser beam; a first attenuator provided on the first optical path for adjusting the power of the first laser beam; a second beam shutter provided on the second optical path for interrupting the second laser beam; and a second attenuator provided on the second optical path for adjusting the power of the second laser beam. 
         [0011]    Preferably, the optical system further includes first wavelength setting means provided on the first optical path for setting the wavelength of the first laser beam; and second wavelength setting means provided on the second optical path for setting the wavelength of the second laser beam. 
         [0012]    According to the laser processing apparatus of the present invention, the power of the single laser oscillator is branched to configure substantially two laser processing apparatuses. Accordingly, the performance of the laser oscillator can be sufficiently exhibited and good economy can therefore be attained. Further, since the laser oscillator for generating a laser beam is expensive, the cost of the laser processing apparatus can be reduced to substantially the half. 
         [0013]    Further, the optical system constituting the laser processing apparatus of the present invention includes the beam splitter for dividing the original laser beam generated by the single laser oscillator into the first laser beam and the second laser beam. The first optical path of the first laser beam is provided with the first beam shutter and the first attenuator. Similarly, the second optical path of the second laser beam is provided with the second beam shutter and the second attenuator. Accordingly, the laser processing apparatus having the single laser oscillator can be used as one laser processing apparatus or two laser processing apparatuses. Further, in the case that the first and second optical paths are provided with the first and second wavelength setting means, respectively, the wavelengths of the first and second laser beams can be made different from each other and the first and second workpieces can therefore be laser-processed at the different wavelengths. 
         [0014]    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 a preferred embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of a laser processing apparatus according to a preferred embodiment of the present invention; 
           [0016]      FIG. 2  is a perspective view showing an essential part of the laser processing apparatus shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a block diagram of laser beam applying means included in the laser processing apparatus shown in  FIG. 1 ; 
           [0018]      FIG. 4  is a perspective view of first and second cassette table mechanisms included in the laser processing apparatus shown in  FIG. 1 ; 
           [0019]      FIG. 5  is a perspective view of first and second temporary setting means included in the laser processing apparatus shown in  FIG. 1 ; 
           [0020]      FIG. 6  is a perspective view of first and second handling means included in the laser processing apparatus shown in  FIG. 1 ; 
           [0021]      FIG. 7  is a perspective view of first and second transfer means included in the laser processing apparatus shown in  FIG. 1 ; 
           [0022]      FIG. 8  is a perspective view showing a condition where the first handling means is positioned so as to take a semiconductor wafer out of a first cassette set on the first cassette table mechanism in the laser processing apparatus shown in  FIG. 1 ; 
           [0023]      FIG. 9  is a view similar to  FIG. 8 , showing a condition where the semiconductor wafer handled by the first handling means is temporarily set on the first temporary setting means; 
           [0024]      FIG. 10  is a view similar to  FIG. 8 , showing a condition where the semiconductor wafer temporarily set on the first temporary setting means is held by the first transfer means; 
           [0025]      FIG. 11  is a view similar to  FIG. 8 , showing a condition where the semiconductor wafer held by the first transfer means is transferred and set on a first chuck table included in the laser processing apparatus shown in  FIG. 1 ; and 
           [0026]      FIG. 12  is a perspective view showing a condition where the laser processing apparatus shown in  FIG. 1  is enclosed by a housing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    A preferred embodiment of the laser processing apparatus according to the present invention will now be described in detail with reference to the attached drawings.  FIG. 1  is a perspective view of a laser processing apparatus  1  according to this preferred embodiment. The laser processing apparatus  1  shown in  FIG. 1  includes a stationary base  2 , a first chuck table mechanism  3  for holding a first workpiece, the first chuck table mechanism  3  being provided on the stationary base  2  so as to be movable in an X direction shown by an arrow X, a second chuck table mechanism  3 ′ for holding a second workpiece, the second chuck table  3 ′ being provided on the stationary base  2  in parallel to the first chuck table mechanism  3  so as to be movable in the X direction, and a laser beam applying unit  4  provided on the stationary base  2  in a central region defined between the first and second chuck table mechanisms  3  and  3 ′. A first laser mechanism  1   a  including the first chuck table mechanism  3  is formed on the front side as viewed in  FIG. 1 , and a second laser mechanism  1   b  including the second chuck table mechanism  3 ′ is formed on the rear side as viewed in  FIG. 1 . 
         [0028]      FIG. 2  is a perspective view for illustrating the structure of the laser processing apparatus  1  shown in  FIG. 1  in detail. That is,  FIG. 2  shows a condition obtained by demounting first and second cassette table mechanisms  7  and  7 ′, first and second temporary setting means  8  and  8 ′, first and second handling means  9  and  9 ′, and first and second transfer means  10  and  10 ′ from the stationary base  2 . As shown in  FIG. 2 , the laser beam applying unit  4  is provided at a substantially central position on the stationary base  2 , and the first chuck table mechanism  3  is provided on the front side of the laser beam applying unit  4  as viewed in  FIG. 2 . The first chuck table mechanism  3  includes a pair of parallel guide rails  31  provided on the stationary base  2  so as to extend in the X direction, a moving base  32  slidably provided on the guide rails  31  so as to be movable in the X direction, a slide block  33  slidably provided on the moving base  32  so as to be movable in a Y direction shown by an arrow Y perpendicular to the X direction, a cover table  35  supported by a cylindrical member  34  standing on the slide block  33 , and a first chuck table  36  (first holding means) for holding the first workpiece. The first chuck table  36  has a vacuum chuck  361  formed of a porous material. The first workpiece is adapted to be held under suction on the upper surface of the vacuum chuck  361  as a holding surface by operating suction means (not shown). The first chuck table  36  is rotatable by a pulse motor (not shown) provided in the cylindrical member  34 . The first chuck table  36  is provided with clamps  362  for fixing an annular frame F (see  FIG. 1 ) supporting a semiconductor wafer W as the first workpiece through a protective tape T. 
         [0029]    The lower surface of the moving base  32  is formed with a pair of guided grooves  321  for slidably engaging the pair of guide rails  31  mentioned above. A pair of parallel guide rails  322  are provided on the upper surface of the moving base  32  so as to extend in the Y direction. Accordingly, the moving base  32  is movable in the X direction along the guide rails  31  by the slidable engagement of the guided grooves  321  with the guide rails  31 . The first chuck table mechanism  3  further includes first X moving means  37  for moving the moving base  32  in the X direction along the guide rails  31 . The first X moving means  37  includes an externally threaded rod  371  extending parallel to the guide rails  31  so as to be interposed therebetween and a pulse motor  372  as a drive source for rotationally driving the externally threaded rod  371 . The externally threaded rod  371  is rotatably supported at one end thereof to a bearing block  373  fixed to the stationary base  2  and is connected at the other end to the output shaft of the pulse motor  372  so as to receive the torque thereof. The externally threaded rod  371  is engaged with a tapped through hole formed in an internally threaded block (not shown) projecting from the lower surface of the moving base  32  at a central portion thereof. Accordingly, the moving base  32  is moved in the X direction along the guide rails  31  by operating the pulse motor  372  to normally or reversely rotate the externally threaded rod  371 . 
         [0030]    The first chuck table mechanism  3  is provided with X position detecting means (not shown) for detecting the X position of the first chuck table  36 . The X position detecting means is so configured as to transmit a pulse signal of one pulse every 1 μm, for example, to control means (not shown). The control means counts the number of pulses as the pulse signal input from the X position detecting means to thereby detect the X position of the first chuck table  36 . In the case that the pulse motor  372  is used as the drive source for the first X moving means  37  as in this preferred embodiment, the number of pulses as a drive signal output from the control means to the pulse motor  372  may be counted by the control means to thereby detect the X position of the first chuck table  36 . In the case that a servo motor is used as the drive source for the first X moving means  37 , a pulse signal output from a rotary encoder for detecting the rotational speed of the servo motor may be sent to the control means, and the number of pulses as the pulse signal input from the rotary encoder into the control means may be counted by the control means to thereby detect the X position of the first chuck table  36 . 
         [0031]    The lower surface of the slide block  33  is formed with a pair of guided grooves  331  for slidably engaging the pair of guide rails  322  provided on the upper surface of the moving base  32  as mentioned above. Accordingly, the slide block  33  is movable in the Y direction along the guide rails  322  by the slidable engagement of the guided grooves  331  with the guide rails  322 . The first chuck table mechanism  3  further includes first Y moving means  38  for moving the slide block  33  in the Y direction along the guide rails  322 . The first Y moving means  38  includes an externally threaded rod  381  extending parallel to the guide rails  322  so as to be interposed therebetween and a pulse motor  382  as a drive source for rotationally driving the externally threaded rod  381 . The externally threaded rod  381  is rotatably supported at one end thereof to a bearing block  383  fixed to the upper surface of the moving base  32  and is connected at the other end to the output shaft of the pulse motor  382  so as to receive the torque thereof. The externally threaded rod  381  is engaged with a tapped through hole formed in an internally threaded block (not shown) projecting from the lower surface of the slide block  33  at a central portion thereof. Accordingly, the slide block  33  is moved in the Y direction along the guide rails  322  by operating the pulse motor  382  to normally or reversely rotate the externally threaded rod  381 . 
         [0032]    The first chuck table mechanism  3  is provided with Y position detecting means (not shown) for detecting the Y position of the first chuck table  36 . The configuration of the Y position detecting means is similar to that of the X position detecting means mentioned above. That is, the Y position detecting means is so configured as to transmit a pulse signal of one pulse every 1 μm, for example, to the control means. The control means counts the number of pulses as the pulse signal input from the Y position detecting means to thereby detect the Y position of the first chuck table  36 . In the case that the pulse motor  382  is used as the drive source for the first Y moving means  38  as in this preferred embodiment, the number of pulses as a drive signal output from the control means to the pulse motor  382  may be counted by the control means to thereby detect the Y position of the first chuck table  36 . In the case that a servo motor is used as the drive source for the first Y moving means  38 , a pulse signal output from a rotary encoder for detecting the rotational speed of the servo motor may be sent to the control means, and the number of pulses as the pulse signal input from the rotary encoder into the control means may be counted by the control means to thereby detect the Y position of the first chuck table  36 . 
         [0033]    As shown in  FIG. 2 , the second chuck table mechanism  3 ′ is provided on the rear side of the laser beam applying unit  4  located in the central region of the stationary base  2 . That is, the laser beam applying unit  4  is interposed between the first chuck table mechanism  3  and the second chuck table mechanism  3 ′ in the Y direction. As similar to the first chuck table mechanism  3 , the second chuck table mechanism  3 ′ includes a second chuck table  36 ′ (second holding means) for holding the second workpiece, second X moving means  37 ′ for moving the second chuck table  36 ′ in the X direction, and second Y moving means  38 ′ for moving the second chuck table  36 ′ in the Y direction. In  FIG. 2 , substantially the same parts as those of the first chuck table mechanism  3  are denoted by the same reference numerals with primes “′,”and the operation of the second chuck table mechanism  3 ′ is substantially the same as that of the first chuck table mechanism  3 , so that detailed description thereof will be omitted herein. 
         [0034]    The laser beam applying unit  4  includes a support member  41  provided on the stationary base  2  and a casing  42  supported to the support member  41 . The casing  42  includes a pair of branch portions  42   a  and  42   b  horizontally extending toward the first and second chuck table mechanisms  3  and  3 ′, respectively. An optical system constituting laser beam applying means  5  to be hereinafter described is stored in the branch portions  42   a  and  42   b . A pair of first and second focusing means  51  and  51 ′ constituting a part of the laser beam applying means  5  are provided on the branch portions  42   a  and  42   b , respectively. Further, a pair of first and second imaging means  6  and  6 ′ for detecting a target area to be laser processed are also provided on the branch portions  42   a  and  42   b , respectively, wherein the first and second imaging means  6  and  6 ′ are located in the vicinity of the first and second focusing means  51  and  51 ′, respectively. Each of the first and second imaging means  6  and  6 ′ includes illuminating means for illuminating a workpiece, an optical system for capturing an area illuminated by the illuminating means, and an imaging device (charge-coupled device (CCD)) for imaging the area captured by the optical system. An image signal output from each of the first and second imaging means  6  and  6 ′ is transmitted to the control means. 
         [0035]    The laser beam applying means  5  will now be described in more detail with reference to  FIG. 3 . The laser beam applying means  5  includes pulsed laser beam oscillating means  52 , a half-wave plate  53  provided on an optical path to be branched, a polarization beam splitter  54 , first and second beam shutters  55  and  59 , first and second attenuators  56  and  60 , first and second wavelength setting means  57  and  61 , first and second half-wave plates  58  and  62  provided on first and second optical paths branched, and the first and second focusing means  51  and  51 ′. 
         [0036]    The pulsed laser beam oscillating means  52  includes a laser oscillator and repetition frequency setting means (both not shown), wherein the pulsed laser beam oscillating means  52  oscillates a laser beam LB having a wavelength of 1064 nm and a repetition frequency of 50 kHz, for example. The laser beam LB is branched into a first laser beam LB 1  (first optical path) and a second laser beam LB 2  (second optical path) by the polarization beam splitter  54 , wherein the first laser beam LB 1  is S polarized light reflected by the polarization beam splitter  54 , and the second laser beam LB 2  is P polarized light transmitted through the polarization beam splitter  54 . 
         [0037]    The half-wave plate  53  is interposed between the pulsed laser beam oscillating means  52  and the polarization beam splitter  54 . The rotational angle of the half-wave plate  53  is adjusted by rotational angle adjusting means (not shown), thereby allowing rotation of the polarization plane of the light emerging from the half-wave plate  53 . Accordingly, by rotating the half-wave plate  53 , the ratio in intensity between the first laser beam LB 1  as S polarized light and the second laser beam LB 2  as P polarized light to be output from the polarization beam splitter  54  can be continuously changed. 
         [0038]    The first and second beam shutters  55  and  59  are provided on the optical paths of the first and second laser beams LB 1  and LB 2  output from the polarization beam splitter  54 , respectively. Each of the first and second beam shutters  55  and  59  is provided with a shutter driving apparatus (not shown), wherein the first beam shutter  55  can be driven to a position where the first laser beam LB 1  is interrupted and a position where the first laser beam LB 1  is not interrupted, and the second beam shutter  59  can be driven to a position where the second laser beam LB 2  is interrupted and a position where the second laser beam LB 2  is not interrupted. Accordingly, the first and second beam shutters  55  and  59  can be operated so as to suitably select a mode where only the first laser beam LB 1  is applied to the first workpiece, a mode where only the second laser beam LB 2  is applied to the second workpiece, or a mode where both the first and second laser beams LB 1  and LB 2  are applied to the first and second workpieces. 
         [0039]    The first and second laser beams LB 1  and LB 2  passed through the first and second beam shutters  55  and  59  are adjusted in intensity by the first and second attenuators  56  and  60 , respectively. Each of the first and second attenuators  56  and  60  may be provided by a variable attenuator for a laser beam known in the art, wherein the laser intensity can be variably adjusted according to the processing conditions required for each workpiece. 
         [0040]    The first and second wavelength setting means  57  and  61  are provided on the optical paths of the first and second laser beams LB 1  and LB 2  passed through the first and second attenuators  56  and  60 , respectively. For example, the wavelength (1064 nm) of the laser beam oscillated from the laser beam oscillating means  52  can be converted into a wavelength of 532 nm by passing the laser beam through a nonlinear crystal or converted into a wavelength of 355 nm by passing the laser beam through a single crystal. The first and second wavelength setting means  57  and  61  can be operated so as to suitably select a mode where the transmission wavelength (1064 nm) to each workpiece is used to form a modified layer inside each workpiece or a mode where the absorption wavelength (355 nm) to each workpiece is used to perform ablation to the upper surface of each workpiece. Accordingly, by providing the first and second wavelength setting means  57  and  61  on the first and second optical paths, the wavelengths of the first and second laser beams LB 1  and LB 2  can be set different from each other. 
         [0041]    The first and second half-wave plates  58  and  62  are provided on the optical paths of the first and second laser beams LB 1  and LB 2  passed through the first and second wavelength setting means  57  and  61 , respectively. Each of the first and second half-wave plates  58  and  62  is provided with rotational drive means (not shown). Accordingly, the first half-wave plate  58  can be rotated to adjust the direction of the polarization plane of the first laser beam LB 1  according to the material of the first workpiece. Similarly, the second half-wave plate  62  can be rotated to adjust the direction of the polarization plane of the second laser beam LB 2  according to the material of the second workpiece. 
         [0042]    The first and second laser beams LB 1  and LB 2  passed through the first and second half-wave plates  58  and  62  enter the first and second focusing means  51  and  51 ′ provided at the ends of the first and second optical paths, respectively. Each of the first and second focusing means  51  and  51 ′ includes a focusing lens. Accordingly, the first laser beam LB 1  is focused to the first workpiece held on the first chuck table  36  by the focusing lens of the first focusing means  51 . Similarly, the second laser beam LB 2  is focused to the second workpiece held on the second chuck table  36 ′ by the focusing lens of the second focusing means  51 ′. 
         [0043]    The optical system of the laser beam applying means  5  mentioned above is stored in the branch portions  42   a  and  42   b  of the casing  42  located at the substantially central position on the stationary base  2  so as to be interposed between the first and second chuck table mechanisms  3  and  3 ′. The first and second focusing means  51  and  51 ′ are provided at the ends of the branch portions  42   a  and  42   b  where the first and second focusing means  51  and  51 ′ can be opposed to the first and second chuck tables  36  and  36 ′, respectively. That is, the first and second focusing means  51  and  51 ′ are located so as to be opposed to first and second processing areas where laser processing is performed to the first and second workpieces held on the first and second chuck tables  36  and  36 ′, respectively. 
         [0044]    In this preferred embodiment, each of the X and Y moving means mentioned above includes an externally threaded rod parallel to a pair of guide rails, an internally threaded block including a tapped through hole provided on the lower surface of a moving base or a slide block and threadedly engaged with the externally threaded rod, and a pulse motor as a drive source for rotationally driving the externally threaded rod. However, this configuration is merely illustrative. For example, each of the X and Y moving means may be provided by a so-called linear shaft motor including a linear rail extending in the X direction or the Y direction in place of the externally threaded rod and a coil movable element movably engaged with the linear rail in such a manner that the linear rail is inserted through the coil movable element, wherein the coil movable element is mounted on a moving base or a slide block above which a chuck table is provided. 
         [0045]    Referring back to  FIG. 1 , there are provided on the stationary base  2  the first and second cassette table mechanisms  7  and  7 ′ for mounting first and second cassettes  70  and  70 ′ in which a plurality of first workpieces such as semiconductor wafers and a plurality of second workpieces such as semiconductor wafers are each stored, the first and second temporary setting means  8  and  8 ′ for temporarily setting the first and second workpieces taken out of the first and second cassettes  70  and  70 ′, the first and second handling means  9  and  9 ′ for taking the first and second workpieces out of the first and second cassettes  70  and  70 ′ before processing and for returning the first and second workpieces into the first and second cassettes  70  and  70 ′ after processing, and the first and second transfer means  10  and  10 ′ for transferring the first and second workpieces from the first and second temporary setting means  8  and  8 ′ to the first and second chuck tables  36  and  36 ′ before processing and for transferring the first and second workpieces from the first and second chuck tables  36  and  36 ′ to the first and second temporary setting means  8  and  8 ′ after processing. 
         [0046]    These cassette table mechanisms  7  and  7 ′, temporary setting means  8  and  8 ′, handling means  9  and  9 ′, and transfer means  10  and  10 ′ will now be described in detail. As shown in  FIGS. 1 and 4 , the first cassette table mechanism  7  is provided adjacent to a first standby area where the first workpiece is held on the first chuck table  36  of the first chuck table mechanism  3  before processing or unheld from the first chuck table  36  after processing. Similarly, the second cassette table mechanism  7 ′ is provided adjacent to a second standby area where the second workpiece is held on the second chuck table  36 ′ of the second chuck table mechanism  3 ′ before processing or unheld from the second chuck table  36 ′ after processing. The first and second cassette table mechanisms  7  and  7 ′ include first and second cassette tables  71  and  71 ′ for mounting the first and second cassettes  70  and  70 ′, respectively. Each of the first and second cassette tables  71  and  71 ′ is vertically movable by elevating means (not shown). 
         [0047]    The first and second temporary setting means  8  and  8 ′ will now be described with reference to  FIGS. 1 and 5 . The first and second temporary setting means  8  and  8 ′ are located adjacent to the first and second cassette table mechanisms  7  and  7 ′ in the X direction, respectively. More specifically, the first temporary setting means  8  is located directly above the first standby area where the first workpiece is held or unheld with respect to the first chuck table  36 . Similarly, the second temporary setting means  8 ′ is located directly above the second standby area where the second workpiece is held or unheld with respect to the second chuck table  36 ′. As shown in  FIG. 5 , the first temporary setting means  8  includes a pair of parallel, sectionally L-shaped support rails  81   a  and  81   b  extending in the X direction and support rail moving means  82  for supporting end portions of the support rails  81   a  and  81   b  so as to allow the movement of the support rails  81   a  and  81   b  in the Y direction, thereby changing the spacing between the support rails  81   a  and  81   b . Similarly, the second temporary setting means  8 ′ includes a pair of parallel, sectionally L-shaped support rails  81   a ′ and  81   b ′ extending in the X direction and support rail moving means  82 ′ for supporting end portions of the support rails  81   a ′ and  81   b ′ so as to allow the movement of the support rails  81   a ′ and  81   b ′ in the Y direction, thereby changing the spacing between the support rails  81   a ′ and  81   b ′. The spacing between the support rails  81   a  and  81   b  is set so that when the support rails  81   a  and  81   b  are moved toward each other, this spacing becomes smaller than the outer diameter of the annular frame F supporting the semiconductor wafer W as the first workpiece through the protective tape T (more specifically, this spacing is the spacing between horizontal portions of the support rails  81   a  and  81   b ), whereas when the support rails  81   a  and  81   b  are moved away from each other, this spacing becomes larger than the outer diameter of the annular frame F. Similarly, the spacing between the support rails  81   a ′ and  81   b ′ is set so that when the support rails  81   a ′ and  81   b ′ are moved toward each other, this spacing becomes smaller than the outer diameter of the annular frame F supporting the semiconductor wafer W as the second workpiece through the protective tape T (more specifically, this spacing is the spacing between horizontal portions of the support rails  81   a ′ and  81   b ′), whereas when the support rails  81   a ′ and  81   b ′ are moved away from each other, this spacing becomes larger than the outer diameter of the annular frame F. 
         [0048]    The first and second handling means  9  and  9 ′ will now be described with reference to  FIGS. 1 and 6 . The first handling means  9  includes a handling arm  91 , a catch member  92  provided at an end portion of the handling arm  91  on the side opposed to the first cassette table mechanism  7  for catching the annular frame F supporting the semiconductor wafer W as the first workpiece stored in the first cassette  70 , and arm moving means  93  for supporting the handling arm  91  so as to allow the movement of the handling arm  91  in the X direction. Similarly, the second handling means  9 ′ includes a handling arm  91 ′, a catch member  92 ′ provided at an end portion of the handling arm  91 ′ on the side opposed to the second cassette table mechanism  7 ′ for catching the annular frame F supporting the semiconductor wafer W as the second workpiece stored in the second cassette  70 ′, and arm moving means  93 ′ for supporting the handling arm  91 ′ so as to allow the movement of the handling arm  91 ′ in the X direction. Each of the catch members  92  and  92 ′ is driven by air pressure supplied from an air cylinder (not shown), thereby catching the annular frame F. 
         [0049]    The first and second transfer means  10  and  10 ′ will now be described with reference to  FIGS. 1 and 7 . The first transfer means  10  includes a plurality of suction pads  11  for holding the annular frame F supporting the semiconductor wafer W as the first workpiece under suction, a transfer arm  12  having a front end where the suction pads  11  are located, an operating rod  13  for vertically moving the transfer arm  12 , and elevating means  14  for vertically moving the operating rod  13 . Similarly, the second transfer means  10 ′ includes a plurality of suction pads  11 ′ for holding the annular frame F supporting the semiconductor wafer W as the second workpiece under suction, a transfer arm  12 ′ having a front end where the suction pads  11 ′ are located, an operating rod  13 ′ for vertically moving the transfer arm  12 ′, and elevating means  14 ′ for vertically moving the operating rod  13 ′. For example, each of the elevating means  14  and  14 ′ is provided by an air piston. In this preferred embodiment, four suction pads  11  are supported to the transfer arm  12 , and four suction pads  11 ′ are supported to the transfer arm  12 ′. Each of the suction pads  11  and  11 ′ is biased downward by a coil spring or the like and connected through a flexible pipe to a vacuum distributor (not shown), which is connected to suction means (not shown). 
         [0050]    All of the laser beam applying means  5 , the cassette table mechanisms  7  and  7 ′, the temporary setting means  8  and  8 ′, the handling means  9  and  9 ′, and the transfer means  10  and  10 ′ mentioned above are provided on the stationary base  2  as shown in  FIG. 1 . The operation of the first laser mechanism  1   a  including the first chuck table mechanism  3 , a part of the laser beam applying means  5 , the first cassette table mechanism  7 , the first temporary setting means  8 , the first handling means  9 , and the first transfer means  10  will now be described with reference to  FIG. 1  and  FIGS. 8 to 11 . The operation of the second laser mechanism  1   b  including the second chuck table mechanism  3 ′, a part of the laser beam applying means  5 , the second cassette table mechanism  7 ′, the second temporary setting means  8 ′, the second handling means  9 ′, and the second transfer means  10 ′ is substantially the same as that of the first laser mechanism  1   a , and the detailed description thereof will be omitted herein. 
         [0051]    As shown in  FIGS. 1 and 8 , the first cassette table mechanism  7  is located adjacent to the first chuck table mechanism  3  in the X direction. The first temporary setting means  8  is located directly above the first standby area where the first workpiece is held or upheld with respect to the first chuck table  36 . The first handling means  9  is located on one side of the first standby area, i.e., on one side of the first temporary setting means  8  in the Y direction. The first transfer means  10  is located on the other side of the first standby area in the Y direction, i.e., on the side opposite to the first handling means  9  with respect to the first chuck table mechanism  3 . 
         [0052]    There will now be described a wafer setting step of taking the semiconductor wafer W as the first workpiece out of the first cassette  70  and then setting the semiconductor wafer W on the first chuck table  36 . As shown in  FIG. 8 , the support rail moving means  82  of the first temporary setting means  8  is operated to move the support rails  81   a  and  81   b  toward each other, thereby reducing the spacing between the support rails  81   a  and  81   b  according to the outer diameter of the annular frame F supporting the semiconductor wafer W. Thereafter, the first cassette table  71  is vertically moved to adjust the height of the semiconductor wafer W stored in the first cassette  70  to the height of the catch member  92  of the first handling means  9  because the height of the catch member  92  is fixed. 
         [0053]    After adjusting the height of the semiconductor wafer W stored in the first cassette  70  to the height of the catch member  92 , the handling arm  91  is moved toward the first cassette  70  until the catch member  92  comes into engagement with the annular frame F supporting the semiconductor wafer W stored in the first cassette  70 . In this condition, the catch member  92  is driven by the air pressure supplied by the air cylinder (not shown), thereby catching the annular frame F. Thereafter, the arm moving means  93  is operated to move the handling arm  91  away from the first cassette table mechanism  7 , thereby taking the semiconductor wafer W out of the first cassette  70  and carrying it to the support rails  81   a  and  81   b  of the first temporary setting means  8  as shown in  FIG. 9 . Thereafter, the operation of the catch member  92  catching the annular frame F is canceled to temporarily set the semiconductor wafer W on the support rails  81   a  and  81   b.    
         [0054]    After temporarily setting the semiconductor wafer W on the support rails  81   a  and  81   b  of the first temporary setting means  8 , the elevating means  14  of the first transfer means  10  is operated to lower the operating rod  13 . As described above, the transfer arm  12  having the suction pads  11  at the front end is connected to the upper end of the operating arm  13 . Accordingly, when the operating rod  13  is lowered, the suction pads  11  provided at the front end of the transfer arm  12  come into abutment against the annular frame F supporting the semiconductor wafer W temporarily set on the first temporary setting means  8 . As described above, each suction pad  11  is biased downward by a coil spring (not shown), so that when each suction pad  11  comes into abutment against the annular frame F, each suction pad  11  is moved slightly upward relative to the transfer arm  12 . When the suction pads  11  come into abutment against the annular frame F, the lowering motion of the operating rod  13  is stopped and a vacuum is supplied through the vacuum distributor (not shown) to the suction pads  11 , thereby holding the semiconductor wafer W through the annular frame F to the suction pads  11  under suction. 
         [0055]    After holding the semiconductor wafer W through the annular frame F to the suction pads  11 , the support rail moving means  82  of the first temporary setting means  8  is operated to increase the spacing between the support rails  81   a  and  81   b  to a size greater than the outer diameter of the annular frame F as shown in  FIG. 11 . Thereafter, the operating rod  13  is further lowered to place the semiconductor wafer W on the upper surface of the first chuck table  36  set in the first standby area. Further, the supply of the vacuum to the suction pads  11  is stopped and the operating rod  13  is next raised to the retracted position shown in  FIG. 9 . Thereafter, the suction means (not shown) is operated to hold the semiconductor wafer W through the protective tape T on the upper surface of the first chuck table  36  under suction. Thereafter, the clamps  362  are operated to fix the annular frame F to the first chuck table  36 . Thereafter, the X moving means  37  of the first chuck table mechanism  3  is operated to move the first chuck table  36  to the first processing area directly below the first focusing means  51  of the laser beam applying unit  4 . 
         [0056]    Thus, the wafer setting step by the first laser mechanism  1   a  has been described. As described above, the second laser mechanism  1   b  has substantially the same configuration as that of the first laser mechanism  1   a , and the operation of the second laser mechanism  1   b  is similar to that of the first laser mechanism  1   a . That is, the second laser mechanism  1   b  includes the second chuck table mechanism  3 ′, a part of the laser beam applying means  5 , the second cassette table mechanism  7 ′, the second temporary setting means  8 ′, the second handling means  9 ′, and the second transfer means  10 ′. Accordingly, the description of a wafer setting step by the second laser mechanism  1   b  will be omitted herein. All of the cassette table mechanisms  7  and  7 ′, the temporary setting means  8  and  8 ′, the handling means  9  and  9 ′, and the transfer means  10  and  10 ′ are controlled by control signals output from an output interface (not shown) included in the control means. 
         [0057]    There will now be described a laser processing step by the first laser mechanism  1   a.    
         [0058]    When the first chuck table  36  holding the semiconductor wafer W is set in the first processing area, the first imaging means  6  and the control means perform an alignment step of detecting a target area of the semiconductor wafer W to be laser-processed. That is, the first imaging means  6  and the control means perform image processing such as pattern matching for making the alignment between the target lines extending in a first direction on the semiconductor wafer W and the first focusing means  51  of the laser beam applying means  5  for applying a laser beam along the target lines, thus performing the alignment step of detecting the target lines extending in the first direction. Similarly, this alignment step is performed for the other target lines extending in a second direction perpendicular to the first direction on the semiconductor wafer W, thereby detecting the target lines extending in the second direction. 
         [0059]    After performing the alignment step to detect all of the target lines formed on the semiconductor wafer W held on the first chuck table  36 , the first chuck table  36  is moved to position one end of a predetermined one of the target lines directly below the first focusing means  51 . Thereafter, the focused spot of a pulsed laser beam to be focused by the focusing lens of the first focusing means  51  is set at a predetermined height inside the semiconductor wafer W, wherein the pulsed laser beam has a transmission wavelength to the semiconductor wafer W. Thereafter, the pulsed laser beam is applied from the first focusing means  51  to the semiconductor wafer W, and at the same time the first chuck table  36  is moved at a predetermined speed in the X direction shown in  FIG. 1 . When the other end of the predetermined target line has reached the position directly below the first focusing means  51 , the application of the pulsed laser beam is stopped and the movement of the first chuck table  36  is also stopped. As a result, a modified layer is formed inside the semiconductor wafer W along the predetermined target line. After performing such laser processing along the predetermined target line, the Y moving means  38  is operated to move the first chuck table  36  in the Y direction, and the laser processing is repeated along all of the other target lines extending in the first direction. Thereafter, the laser processing is similarly performed along all of the target lines extending in the second direction. A laser processing step by the second laser mechanism  1   b  is substantially the same as that by the first laser mechanism  1   a  mentioned above, so the detailed description thereof will be omitted herein. 
         [0060]    After finishing the laser processing step, the semiconductor wafer W held on the chuck table  36  is returned to the original position in the first cassette  70  in the following procedure reverse to that of the wafer setting step described with reference to  FIGS. 8 to 11 . That is, after processing the semiconductor wafer W in the first processing area, the first chuck table  36  holding the semiconductor wafer W is moved from the first processing area to the first standby area shown in  FIG. 11  by operating the X moving means  37 . Thereafter, the operating rod  13  of the first transfer means  10  is lowered until the suction pads  11  come into abutment against the annular frame F supporting the semiconductor wafer W held on the chuck table  36 . Thereafter, a vacuum is applied to the suction pads  11  to hold the semiconductor wafer W under suction. Thereafter, the suction holding of the semiconductor wafer W is canceled and the fixed condition of the annular frame F by the clamps  362  is also canceled. Thereafter, the operating rod  13  is raised to a vertical position higher than the support rails  81   a  and  81   b  of the first temporary setting means  8 . 
         [0061]    Thereafter, the support rail moving means  82  of the first temporary setting means  8  is operated to reduce the spacing between the support rails  81   a  and  81   b  according to the outer diameter of the annular frame F. Thereafter, the operating rod  13  of the first transfer means  10  is lowered to place the semiconductor wafer W held by the suction pads  11  onto the support rails  81   a  and  81   b  as shown in  FIG. 10 . Thereafter, the vacuum applied to the suction pads  11  is canceled to thereby temporarily set the semiconductor wafer W on the support rails  81   a  and  81   b . Thereafter, the operating rod  13  is raised to the highest vertical position, i.e., the retracted position shown in  FIG. 9 . 
         [0062]    Finally, the handling arm  91  of the first handling means  9  is moved from the position shown in  FIG. 9  to the position shown in  FIG. 8 . At this time, the annular frame F supporting the semiconductor wafer W is pushed by the handling arm  91 , so that the operation of the catch member  92  is not required. Thus, the semiconductor wafer W is pushed by the handling arm  91  and thereby returned to the original position in the first cassette  70  as shown in  FIG. 8 . 
         [0063]    As shown in  FIG. 12 , the laser processing apparatus  1  including the laser mechanisms  1   a  and  1   b  shown in  FIG. 1  has a housing  200  for covering the laser mechanisms  1   a  and  1   b . The housing  200  has a side wall opposed to the cassette table mechanisms  7  and  7 ′ in the X direction (see  FIG. 1 ). This side wall of the housing  200  is provided with a first door  201  opposed to the first cassette table mechanism  7  and a second door  204  opposed to the second cassette table mechanism  7 ′. The first and second doors  201  and  204  are arranged in parallel in the Y direction. The first and second doors  201  and  204  are configured like a so-called double door such that the first door  201  is adapted to open to the left and the second door  204  is adapted to open to the right as viewed in  FIG. 12 . When the first door  201  is opened, an operator can make access to the first standby area defined by the first cassette table mechanism  7  of the first laser mechanism  1   a  and the position where the first workpiece is held or unheld with respect to the first chuck table  36 . Similarly, when the second door  204  is opened, the operator can make access to the second standby area defined by the second cassette table mechanism  7 ′ of the second laser mechanism  1   b  and the position where the second workpiece is held or unheld with respect to the second chuck table  36 ′. That is, the first and second doors  201  and  204  are used in loading/unloading the first and second cassettes  70  and  70 ′ to/from the first and second cassette tables  71  and  71 ′, respectively. 
         [0064]    The first door  201  is provided with a first operation panel  202  for operating the first laser mechanism  1   a . Similarly, the second door  204  is provided with a second operation panel  205  for operating the second laser mechanism  1   b . These operation panels  202  and  205  are adapted to be operated by the operator to conduct various kinds of setting to the control means. That is, the first laser mechanism  1   a  and the second laser mechanism  1   b  can be operated independently. Accordingly, there is no possibility that when the first door  201  is in an open condition in loading the first cassette  70  to the first cassette table  71 , the operator may erroneously operate the first operation panel  202  to start the first laser mechanism  1   a . Similarly, there is no possibility that when the second door  204  is in an open condition in loading the second cassette  70 ′ to the second cassette table  71 ′, the operator may erroneously operate the second operation panel  205  to start the second laser mechanism  1   b.    
         [0065]    The first operation panel  202  is pivotably mounted on the first door  201  so as to be opened to the left as viewed in  FIG. 12 . Similarly, the second operation panel  205  is pivotably mounted on the second door  204  so as to be opened to the right as viewed in  FIG. 12 . In the laser processing apparatus  1  according to this preferred embodiment, it is assumed that the operator operates the operation panels  202  and  205  as confirming the operations of the laser mechanisms  1   a  and  1   b . Accordingly, the left side wall of the housing  200  is provided with a first inspection window  203  for allowing the operator to see the first laser mechanism  1   a  as shown in  FIG. 12 . Similarly, the right side wall of the housing  200  is provided with a second inspection window  206  for allowing the operator to see the second laser mechanism  1   b.    
         [0066]    Accordingly, the operator can operate the first operation panel  202  in its open condition as seeing the first laser mechanism  1   a  through the first inspection window  203 . Similarly, the operator can operate the second operation panel  205  in its open condition as seeing the second laser mechanism  1   b  through the second inspection window  206 . By providing these inspection windows  203  and  206  and the operation panels  202  and  205 , there is no possibility that the operation panels  202  and  205  may be confusingly operated in operating the first and second laser mechanisms  1   a  and  1   b.    
         [0067]    The present invention is not limited to the details of the above described preferred embodiment. 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.