Patent Publication Number: US-2012031147-A1

Title: Method and Apparatus for Machining Thin-Film Layer of Workpiece

Description:
TECHNICAL FIELD 
     The present invention relates to a method for machining a thin-film layer of a workpiece and a thin-film layer machining apparatus for machining a thin-film layer of a workpiece, which is a transparent glass on which a thin-film layer is disposed on the top surface. 
     BACKGROUND ART 
     As a transparent glass on which a thin-film layer is disposed on the top surface, a solar battery, for example, is known.  FIG. 29  is a plan view showing a process for manufacturing a solar battery. In  FIG. 29 , a solar battery, which is a workpiece  101 , is a transparent glass  102  on which a plurality of thin-film layers are formed on the surface. The plurality of thin-film layers are formed across the entire surface of the glass  102 . Subsequently, a portion of the thin-film layers on the periphery of the glass  102  is removed (Edge Deletion). This removed portion is referred to as a removed portion  107 . 
       FIG. 30  is a cross-sectional view for explaining the process for manufacturing the solar battery.  FIG. 30(   a ) shows a first step,  FIG. 30(   b ) shows a second step,  FIG. 30(   c ) shows a third step, and  FIG. 30(   d ) shows a final step. In the process for manufacturing the solar battery, first, as shown in  FIG. 30(   a ), a first thin-film layer (rear surface electrode layer)  104  is disposed on the transparent glass  102 . Subsequently, a first line groove P 1  for insulating between a thin-film layer  1041  and a thin-film layer  1042  is formed. Next, as shown in  FIG. 30(   b ), a second thin-film layer (light absorbing layer)  105  is disposed on top of the thin-film layer  104 . Subsequently, a second line groove P 2  for insulating between a thin-film layer  1051  and a thin-film layer  1052  is formed. Next, as shown in  FIG. 30(   c ), a third thin-film layer (top surface electrode layer)  106  is disposed on top of the thin-film layer  105 . Subsequently, a third line groove P 3  for insulating between a thin-film layer  1061  and a thin-film layer  1062  of the thin-film layer  106  is formed. The third line groove P 3  has a depth reaching the top surface of the thin-film layer  104 . Finally, as shown in  FIG. 30(   d ), portions of the three layers (thin-film layers  104 ,  105 , and  106 ) on the periphery of the transparent glass  102  are removed. Hereinafter, the periphery portion from which the thin-film layers  104  to  106  are removed will be referred to as the removed portion  107 . The width of the removed portion  107  is 10 to 15 mm. Further, the line spacings between the adjacent first line grooves P 1 , between the adjacent second line grooves P 2 , and between the adjacent third line grooves P 3  are each 10 to 15 mm. Further, the spacing between the adjacent first line groove P 1  and second line groove P 2  and the spacing between the second line groove P 2  and third line groove P 3  are each 100 to 200 μm. In other words, the first to third line grooves P 1 , P 2 , and P 3 , which are arranged at spacings of 100 to 200 μm, are formed at spacings of 10 to 15 mm. 
       FIG. 31  is a perspective view showing a main part of a configuration of an apparatus for machining a thin-film layer that has been conventionally used. In the conventional thin-film layer machining apparatus, the workpiece is placed with the thin-film layer facing upwards and the thin-film layer is machined from the top surface side so that the thin-film layer is not damaged during machining and transporting the workpiece. In  FIG. 31 , the thin-film layer machining apparatus includes a bed  114 , an X movement mechanism  110 , and a Y movement mechanism  117 . The X movement mechanism  110  is disposed on the bed  114 . The X movement mechanism  110  includes a guide roller mechanism  113  which supports the bottom surface of the workpiece and a guide mechanism  112 . The guide mechanism  112  clamps the workpiece  101  being fit to the bottom surface of the workpiece  101 . The guide mechanism  112  reciprocally moves in the X direction (one axial direction on an orthogonal X-Y plane parallel to the surface of the bed  114 ) by means of a drive device (not shown) with supporting the side surface of the workpiece  101 . 
     The Y movement mechanism  117  is disposed on a column  115  fixed to the bed  114 . The Y movement mechanism  117  reciprocally moves in the Y direction along the column  115  by means of a Y driving mechanism (not shown). The Y direction is the direction of the other axis on the XY plane that is orthogonal to the X axis. A machining head  118  and an optical delivery system (not shown) are disposed on the Y movement mechanism  117 . The machining head  118  reciprocally moves in the Z direction (direction that is perpendicular to the XY plane) by means of a Z driving mechanism (not shown). 
     The steps for forming the first to third line grooves P 1  to P 3  are as follows: 
     (1) A position in the Y direction of the machining head  118  is determined by the Y movement mechanism  117 . 
     (2) After determining the position in the Y direction, the position in the Z direction (height) of the machining head  118  is determined. 
     (3) While moving the workpiece  101  in the X direction by means of the X movement mechanism  110 , a laser beam is emitted from the machining head  118  to form the first to third line grooves P 1  to P 3 . 
     (3-1) The first thin-film layer  104  is machined with a laser beam having a wavelength of  1064  nm. 
     (3-2) The second and third thin-film layers  105  and  106  are machined with a laser beam having a wavelength of 532 nm. 
     (4) After forming the third line groove P 3 , the periphery portion of the workpiece  101  is machined with a laser beam having a wavelength of 1064 nm to form the removed portion  107 . 
     The first to third line grooves P 1  to P 3  and the removed portion  107  are machined by dedicated machining devices. In order to increase the machining efficiency, the line groove machining devices are respectively dedicated, while being arranged in a line. In the formation of the first to third line grooves P 1  to P 3 , a beam of a spot diameter D is shifted by a fixed pitch  1 , and the depths of the line grooves are controlled by the overlap ratio [(D−1)/D] %. Therefore, the total energy introduced into the overlap portion on the bottom of the groove is (the number of overlaps)×(the pulse energy). Thus, the injected energy discretely changes depending on the location within a range of from the beam energy itself to the beam energy multiplied by the number of overlaps. 
     The invention disclosed in Patent Document 1 is publicly known as this type of technology. An object of this invention is to machine with accuracy by maintaining the focal point of a laser beam at a fixed position when scribing an integrated solar battery by a laser beam. In the method for manufacturing a solar battery of this invention, an electrode layer is formed on an insulating substrate, and irradiated with a laser beam. Thereby the electrode layer is divided and patterned. A photoelectric conversion layer is layered on the electrode layer, and then irradiated with a laser beam. Thereby, the photoelectric conversion layer is divided and patterned. A aspect of this invention is that, when patterning the photoelectric conversion layer, the divided line edge in the electrode layer on the insulating substrate is used as a reference for the focal point of the laser beam, and thereby, the divided line in the electrode layer and the dividing line of the photoelectric conversion layer are overlapped each other. 
     Patent Document 1: JP-A-10-303444  
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     The machining in the conventional thin-film layer machining apparatus has a problem in that it is difficult to maintain the irradiation position for the laser beam at a fixed position. In other words, the tolerance of the board thickness of the workpiece  101  is ±0.5 mm, and the tolerance of the warp or deformation is ±1 mm. As mentioned above, in a conventional apparatus, the bottom surface of the workpiece  101  is supported by the guide roller mechanism  113 . Therefore, the position of the top surface of the workpiece may change by ±1.5 mm, which is the sum of the tolerance of the board thickness and the tolerance of the warp or deformation. If the focusing height of the laser beam deviates from the design position, the machining is carried out in a defocused condition. Thus, the spot diameter varies. In this case, the groove widths of the first to third line grooves P 1  to P 3  cannot satisfy the permissible variation (±10% or less), or the target layer is not removed and remains due to insufficient energy density. 
     Further, there is also a problem related to restrictions of the pulse period (1/pulse frequency) of the laser beam. Basically, if the pulse period is shortened, the temperature of the beam overlap portion increases due to thermal conduction of the thin-film layer or glass. Consequently, detachment at the groove side walls from the substrate easily occurs. Thus, it has been necessary to set the pulse period to 0.04 ms or greater (a pulse frequency of 25 kHz or less). The pulse frequency at which the maximum output of a laser oscillator can be achieved is 80 to 120 kHz. In spite of this, the pulse frequency had to be decreased to 25 kHz or less, and thus the output utilization efficiency of the laser beam could not be enhanced. 
     A method of machining with a laser entering from the underside has been attempted (Patent Document 1), but this method did not reach practical application. The reason this method could not be practically utilized is that debris produced by the machining could not be sufficiently removed, and thus the insulation resistance decreased to approximately 50 MΩ due to the debris in the grooves. Therefore, the ideal insulation resistance of 2000 MΩ could not be obtained. 
     Therefore, a first problem to be solved by the present invention is to enable the irradiation position for the laser beam to be held in place, and thereby allow machining to be carried out such that the groove width satisfies the permissible variation, leading to an improvement in the quality of the worked portion. 
     Further, a second problem to be solved is to enhance the output utilization efficiency of the laser beam. 
     Solutions to the Problems 
     In order to overcome the above-described problems, a first means is a method of machining a thin-film layer of a workpiece, which is a transparent glass on which a thin-film layer is disposed on the top surface thereof, including machining the thin-film layer on the top surface side with a laser beam entering through the underside of the workpiece in a state in which the workpiece is supported in the vertical direction by a compressed air and held by a clamp device which is movable to follow the movement of the workpiece in the vertical direction. 
     A second means is a method of machining a thin-film layer of a workpiece, which is a transparent glass on which a thin-film layer is disposed on the top surface thereof, wherein machining is carried out while a cooling medium is blown onto a machining portion. 
     A third means is an apparatus for machining a thin-film layer of a workpiece, which is a transparent glass on which a thin-film layer is disposed on the top surface thereof, the apparatus including a support device which supports the workpiece in the vertical direction by a compressed air, a clamp device which holds the workpiece and is movable to follow the movement of the workpiece in the vertical direction, and a laser machining head which machines the thin-film layer by a laser beam, wherein the laser device machines the thin-film layer on the top surface side by irradiation with a laser beam entering through the underside of the workpiece. 
     A fourth means is an apparatus for machining a thin-film layer of a workpiece, which is a transparent glass on which a thin-film layer is disposed on the top surface thereof, the apparatus including a nozzle for delivering a cooling medium, and a laser machining head which machines the thin-film layer by a laser beam, wherein during machining, the cooling medium is blown by the nozzle disposed by the thin-film layer side to a position at which the laser emitted from the laser machining head is incident on the thin-film layer. 
     EFFECTS OF THE INVENTION 
     According to the present invention, the irradiation position for the laser beam can be held in place. Therefore, the machining can be carried out such that the groove width satisfies the permissible variation. As a result, the quality of the machined portion can be enhanced. 
     In addition, the thin-film layer can be machined from the underside while a cooling medium is blown on the top surface side. Therefore, even if the pulse period is shortened, enough insulation resistance can be obtained, and thus the output utilization efficiency of the laser beam can be enhanced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram showing a configuration of a thin-film layer machining apparatus according to an embodiment of the present invention. 
         FIG. 2  is a perspective view for explaining the configuration of the thin-film layer machining apparatus main body shown in  FIG. 1 . 
         FIG. 3  is a view showing the details of a workpiece-underside support mechanism shown in  FIG. 2 . 
         FIG. 4  is a view showing a modified embodiment 1 of the workpiece-underside support mechanism shown in  FIG. 3 . 
         FIG. 5  is a view showing a modified embodiment 2 of the workpiece-underside support mechanism shown in  FIG. 3 . 
         FIG. 6  is a view showing a modified embodiment 3 of the workpiece-underside support mechanism shown in  FIG. 3 . 
         FIG. 7  is a view showing a modified embodiment 4 of the workpiece-underside support mechanism shown in  FIG. 3 . 
         FIG. 8  is a view showing the details of a workpiece side clamp mechanism shown in  FIG. 2 . 
         FIG. 9  is a view showing a modified embodiment of the workpiece side clamp mechanism shown in  FIG. 8 . 
         FIG. 10  is a view showing the details of a workpiece front end surface clamp mechanism shown in  FIG. 2 . 
         FIG. 11  is a view showing the details of a workpiece rear end surface clamp mechanism shown in  FIG. 2 . 
         FIG. 12  is a plan view showing a first arrangement example of the clamp mechanisms in the embodiment of the present invention. 
         FIG. 13  is a plan view showing a second arrangement example which is a modified embodiment of the first arrangement example of the clamp mechanisms shown in  FIG. 12 . 
         FIG. 14  is a plan view showing a third arrangement example of the clamp mechanisms in the embodiment of the present invention. 
         FIG. 15  is a plan view showing a fourth arrangement example of the clamp mechanisms in the embodiment of the present invention. 
         FIG. 16  is a plan view showing a fifth arrangement example of the clamp mechanisms in the embodiment of the present invention. 
         FIG. 17  is a plan view showing a sixth arrangement example of the clamp mechanisms in the embodiment of the present invention. 
         FIG. 18  is a view for explaining a first dust collector for machining the line grooves according to the embodiment of the present invention. 
         FIG. 19  is a side view showing the main parts of a column equipped with the first dust collector shown in  FIG. 18 . 
         FIG. 20  is a view for explaining a second dust collector for machining the line grooves according to the embodiment of the present invention. 
         FIG. 21  is a side view showing the main part of a column equipped with the second dust collector shown in  FIG. 20 . 
         FIG. 22  is an explanatory view of a third dust collector used in the case of forming a removed portion around the periphery of the workpiece in the embodiment of the present invention. 
         FIG. 23  is a vertical cross-sectional view of guide roller units disposed on both side surfaces in the X direction of an upper dust collection chamber. 
         FIG. 24  is an explanatory view of a fourth dust collector used in machining of a center portion in the embodiment of the present invention. 
         FIG. 25  is a side view showing the main parts of a column equipped with the fourth dust collector shown in  FIG. 24 . 
         FIG. 26  is a schematic view showing a dust prevention mechanism of an optical system in the embodiment of the present invention. 
         FIG. 27  is a view showing a configuration of the main parts of the optical system in the embodiment of the present invention. 
         FIG. 28  is a view showing a configuration of the optical system in the embodiment of the present invention when carrying out machining to remove the periphery of the workpiece by a high output laser. 
         FIG. 29  is a plan view showing a process for manufacturing a solar battery carried out in a related art. 
         FIG. 30  is a cross-sectional view for explaining the process for manufacturing a solar battery carried out in the related art. 
         FIG. 31  is a main perspective view showing main part of a configuration of an apparatus for machining a thin-film layer that has been used in a related art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present invention relates to a technology for machining a workpiece, which is a transparent glass on which a thin-film layer is disposed on the top surface thereof, in consideration of the machining accuracy and machining efficiency. Basically, in the present invention, the workpiece is supported in the vertical direction by a compressed air, and the workpiece is held by a clamping device which follows the movement of the workpiece in the vertical direction. In this state, the thin-film layer on the top surface side is machined by a laser light entering through the underside of the workpiece. Hereinafter, an embodiment of the present invention will be explained with reference to the drawings. 
     1. Overall Configuration 
       FIG. 1  is a functional block diagram showing the configuration of the thin-film layer machining apparatus according to an embodiment of the present invention. In 
       FIG. 1 , the thin-film layer machining apparatus according to the present embodiment includes a thin-film layer machining apparatus main body SA, a main controller SB, and a sub controller SC. The thin-film layer machining apparatus main body SA is comprised of an XYZ positioning mechanism of a laser beam, a machining head, a laser oscillator, a vacuum device, a mist generating device, and the like. A laser controller, a motor driver, a pulse shaper driver, a galvanometer scanner driver, and the like are mounted in the sub controller SC. The main controller SB and the sub controller SC each include a CPU, ROM, and RAM. Each of the CPUs loads a program stored in their respective ROMs into their respective RAMs. Then each CPU executes a prescribed control defined by the program while using each RAM as a work area and data buffer. 
       FIG. 2  is a perspective view for explaining the configuration of the thin-film layer machining apparatus main body. The left side of a center line CL is omitted from the drawing. In  FIG. 2 , the thin-film layer machining apparatus main body SA is comprised of a frame mechanism bed A 1 , an X movement mechanism A 2 , a Y movement mechanism A 3 , a machining head A 4 , a laser oscillator A 5 , and a column A 6 . The X movement mechanism A 2  is disposed on the bed A 1 . The Y movement mechanism A 3  is similarly disposed on the bed A 1  in an orthogonal fashion relative to the X movement mechanism A 2 . The machining head A 4  is united with a Z movement mechanism disposed on the Y movement mechanism A 3 . The column A 6  is fixed on top of the bed A 1 . A dust collection mechanism disposed on the machining head, a position monitoring camera, and a height detection device for detecting the height are disposed on the column A 6 . 
     The X movement mechanism A 2  is comprised of a first X driving mechanism (the details of this mechanism are omitted) E 1 , a second X driving mechanism (the details of this mechanism are omitted) E 2 , and a pair of connecting plates  3 . The first X driving mechanism E 1  is movable in the X direction by a motor (not shown). The second X driving mechanism E 2  is movable parallel to the first X driving mechanism E 1 . One end of the connecting plate  3  is fixed to the first X driving mechanism E 1 . The other end of the connecting plate  3  is connected to the second X driving mechanism E 2 . With this configuration, the first and second X driving mechanisms E 1  and E 2  move simultaneously. The connecting part of the connecting plate  3  to the second X driving mechanism E 2  are configured to slide in only the Y direction, in order not to load the second X driving mechanism E 2  in the Y direction. 
     A workpiece side clamp mechanism  6  is provided to each of the first and second X driving mechanisms E 1  and E 2 . As will be explained later, the workpiece side clamps  6  is movable (follower type) in the vertical direction even during the clamping operation of the workpiece  101 . Further, a workpiece front end surface clamp mechanism  7  and a workpiece rear end surface clamp mechanism  8  are provided to the first X driving mechanism E 1 . The former determines the position of the front end surface of the workpiece  101 , and the latter determines the position of the rear end surface of the workpiece  101 , and both are retracted during unclamping. A workpiece side surface pressing mechanism  9  is provided to the second X driving mechanism E 2 . 
     A workpiece-underside support mechanism  4  is disposed on the bed A 1  via a support frame  5 . The workpiece-underside support mechanism  4  has a function to lift the workpiece and a function to suck the workpiece, in order to support the workpiece  101  without contact. The workpiece-underside support mechanism  4  is also disposed on the not-illustrated side of the center line CL in the drawing. A pair of guide rollers  10  is disposed on each end of the bed A 1  in the X direction. The guide rollers  10  regulate any displacement in the Y direction when sending the workpiece  101  in the X direction up to an input standby position (clamp position). The guide rollers  10  rise to a position which is the same level as the end surface of the workpiece  101  only during loading of the workpiece  101 . When the workpiece  101  reaches the clamp position, the guide rollers  10  drop down and enter standby. A support roller  11  is provided to the support frame  5 . The support rollers  11  are disposed such that the peak height of their outer diameters is 0.1 mm higher than the top surface height of the supports  46 . The support rollers  11  support the workpiece  101  when the workpiece-underside support mechanism  4  is inoperable, and enables the workpiece  101  to be moved manually. 
     2. Workpiece-Underside Support Mechanism 
     2.1 Basic Configuration The workpiece  101  is supported in a floating state on an air cushion from the bottom surface side. The mechanism for this support is the workpiece-underside support mechanism  4 .  FIG. 3  is a view showing the details of the workpiece-underside support mechanism  4 .  FIG. 3(   a ) is a plan view of the main parts, and  FIG. 3(   b ) is a cross-sectional view. 
     As shown in  FIG. 3 , the workpiece-underside support mechanism  4  has a floatation mechanism  41  and a suction mechanism  42 . The mechanisms  41  and  42  are disposed on a planar support  46 . The floatation mechanism  41  is a flat air bearing having an orifice array which is disposed in a plurality of concentric circles and formed by several tens of first orifices  43  having a diameter of about 0.2 mm. A space  45  is provided in the back of the first orifices  43 . Air is fed to the spaces  45  from an air source (not shown) via a first air passage  44 . The air is released from the first orifices  43 . In this way, the floatation mechanism  41  is a mechanism for floating via air pressure (hereinafter, this will be referred to as an air floatation mechanism). 
     In the air floatation mechanism  41 , if air having a pressure of 5 kgf/cm 2  is fed to the space  45  (arrow D 1 ), the workpiece  101  is pushed up in the direction of arrow D 2 . Simultaneously, the distance (gap) g between the bottom surface of the workpiece  101  and the top surface of the support  46  is corrected by a static pressure reduction effect due to a high speed flow generated by the combination of the air floatation mechanism  41  and the suction mechanism  42  to be explained below. For example, consider a case in which the interval in the XY directions of the air floatation mechanisms  41  is 300 mm, and the workpiece  101  is a glass having a size of 300 mm×1100 mm and a thickness of 5 mm. In this case, the distance g between the bottom surface of the workpiece  101  and the top surface of the support  46  can be maintained at 0.2 to 0.3 mm. 
     The suction mechanism  42  is positioned on the outer periphery of the array of the first orifices  43  of the air floatation mechanism  41 . The suction mechanism  42  includes an annular groove  48  and a second air passage  47  formed concentrically, and is connected to a vacuum source (not shown). By drawing air via the second air passage  47  (arrow D 3 ), the workpiece  101  can be sucked (arrow D 4 ). In this way, the floating position of the workpiece  101  is stabilized to a position at which the suction force by drawing air through the groove  48  and the lifting force by blowing air through the orifices  43  balance each other out. For example, if the air supply passage  44  between the bottom surface of the first workpiece  101  and the top surface of the support  46  is connected with the suction mechanism  42  at a negative pressure of 0.3 kgf/cm 2 , for example, the floating distance g of the workpiece  101  from the support  46  can be maintained at a fixed distance (for example, 0.2 mm) apart. Further, a workpiece warps within ±1.0 mm can be corrected by the workpiece-underside support mechanism  4 . Thereby, changes in height of the workpiece surface can be suppressed to a range of ±0.05 mm. Therefore, high quality machining for forming a uniform groove width can be carried out. 
     The reason that the workpiece warps within ±1.0 mm can be corrected, and thereby changes in height of the workpiece surface can be suppressed to a range of ±0.05 mm, is that the suction force by drawing air through the groove  48  and the lifting force by blowing air through the orifices  43  balance each other out. Thereby, the forces act on the workpiece to make it flat. Further, the distance g is stably maintained by the static pressure reduction effect due to a high speed flow generated by the combination with the suction mechanism  42 . 
     2.2 Modified Embodiment 1 
       FIG. 4  is a view showing a modified embodiment 1, which is one modified embodiment of the workpiece-underside support mechanism  4  shown in  FIG. 3 .  FIG. 4(   a ) is a plan view of the main parts, and  FIG. 4(   b ) is a cross-sectional view. 
     In the modified embodiment 1, the groove  48  in  FIG. 3  is substituted with an array of second orifices  482  having a small diameter. The array of second orifices  482  is formed concentrically with the array of first orifices  43  and arranged on the outer periphery of the array of first orifices  43 . The array of second orifices  482  is in communication with a groove space  481  within the support  46 . The groove space  481  is in communication with the second air passage  47 . In this embodiment, the diameter of the second orifices is preferably approximately 1.5 mm, for example. By this structure, the modified embodiment 1 can lift and hold the workpiece  101  similar to the embodiment shown in  FIG. 3 . 
     The other members which have not been particularly explained have the same configuration and equivalent function to those in the workpiece-underside support mechanism  4  shown in  FIG. 3 . 
     2.3 Modified Embodiment 2 
       FIG. 5  is a view showing a modified embodiment 2 of the workpiece-underside support mechanism  4  shown in  FIG. 3 .  FIG. 5(   a ) is a plan view of the main parts, and  FIG. 5(   b ) is a cross-sectional view. 
     In the modified embodiment 2, the functions of the first and second air passages  44  and  47  in the modified embodiment shown in  FIG. 4  are reversed. In other words, in the modified embodiment  2 , the first air passage  44  is provided on the suction side, whereas the second air passage  47  is provided on the supply side. In the modified embodiment 2, the diameter of the second orifices  482  is preferably about 0.2 mm, and the diameter of the first orifices  43  is preferably approximately 1.5 mm. Thereby, the second orifices  482  are used for floating the workpiece  101 . On the other hand, the first orifices  43  are used for sucking the workpiece  101 . 
     In the workpiece-underside support mechanism  4  shown in  FIG. 3 , a suction force cannot be immediately obtained even if the workpiece  101  reaches the groove  48 , because the opening area of the groove  48  is large. The suction force sharply increases from the time at which the opening is covered. In contrast, in the workpiece-underside support mechanisms  4  of the modified embodiments 1 and 2 shown in  FIGS. 4 and 5 , when the workpiece  101  reaches the orifices having a sucking function, the number of orifices facing the workpiece increases in accordance with the position of the workpiece  101 . Therefore, the suction force gradually increases. Further, when the workpiece goes away from the orifices having a suction function, the suction force gradually decreases. Thereby, compared to the embodiment in  FIG. 3 , since changes in the suction force are reduced, the suction force can be averaged. Therefore, the suction force can be stabilized during movement of the workpiece  101 . 
     The other members which have not been particularly explained have the same configuration and equivalent function to those in the workpiece-underside support mechanism  4  shown in  FIG. 3 . 
     2.4 Modified Embodiment 3 
       FIG. 6  is a view showing a modified embodiment 3 of the workpiece-underside support mechanism  4  shown in  FIG. 3 .  FIG. 6(   a ) is a plan view of the main parts, and  FIG. 6(   b ) is a cross-sectional view. 
     In the embodiments shown in  FIGS. 3 to 5 , the air floatation mechanism  41  and the suction mechanism  42  are arranged concentrically. However, the air floatation mechanism  41  and the suction mechanism  42  can be constituted as a separated structure and arranged alternately at each distance L. Further, as shown in  FIG. 6 , a circular cavity  484  may be used instead of the groove  48 . 
     The other members which have not been particularly explained have the same configuration and equivalent function to those in the workpiece-underside support mechanism  4  shown in  FIG. 3 . 
     2.5 Modified Embodiment 4 
       FIG. 7  is a view showing a modified embodiment 4 of the workpiece-underside support mechanism  4  shown in  FIG. 3 .  FIG. 7(   a ) is a plan view of the main parts, and  FIG. 7(   b ) is a cross-sectional view. 
     In the case of the modified embodiment  3 , since the area of the cavity  484  is large similar to the workpiece-underside support mechanism  4  shown in  FIG. 3 , the sucking force changes rapidly. Thus, in the modified embodiment 4 shown in  FIG. 7 , an array of third orifices  485  is arranged concentrically as an air inlet. The array of third orifices  485  is in communication with a space  486  within the support  46 . The space  486  is in communication with the second air passage  47 . Thereby, compared to the modified embodiment 3, since rapid pressure changes can be reduced, the pressure can be averaged. 
     In all of the workpiece-underside support mechanisms of the basic configuration and the modified embodiments 1 to 4 explained above with reference to  FIGS. 3 to 7 , the air pressure fed to the air floatation mechanism  41  may be changed according to the disposal location. Alternatively, in addition to changing the air pressure, the diameter of the first to third orifices  43 ,  482 , and  485  can be changed according to the disposal location. Thereby, the floating distance g of the workpiece  101  from the top surface of the support  46  can be controlled. Thus, for example, if the distance g is controlled so that it is at a maximum at the machining portion (at the center line CL), there will be almost no effect from warping even if the workpiece  101  warps  1  mm or more. Therefore, the machining precision can be enhanced. 
     3. Workpiece Clamp Mechanism 
     The workpiece  101  is supported so that it is movable in the Z direction in a state in which it is floated on an air cushion. Therefore, it is necessary to hold the workpiece in this state. Thus, in the present embodiment, a workpiece side clamp mechanism  6 , a workpiece front end surface clamp mechanism  7 , and a workpiece rear end surface clamp mechanism  8  are provided as a workpiece clamp mechanism 
     3.1 Workpiece Side Clamp Mechanism 
     3.1.1 Basic Configuration 
       FIG. 8  is a view showing the details of the workpiece side clamp mechanism  6 .  FIG. 8(   a ) is a plan view, and  FIG. 8(   b ) is a side view. 
     In  FIG. 8 , the workpiece side clamp mechanism  6  is comprised of upper and lower clamp arms  61  and  62 , link supports  63 , clamp pins  64  and  65 , links  66  and  67 , a connecting plate  68 , a drive cylinder  69 , and the like. 
     The link supports  63  and the drive cylinder  69  are connected with the connecting plate  68  between. The link supports  63  are provided in a pair (an upper and lower in  FIG. 8(   a )) in a parallel manner in the X direction. A link fitting  611  is connected to the piston rod of the drive cylinder  69  through the connecting plate  68 . A pair of links  610  is rotatably held on a side surface of the link fitting  611  by a clamp pin  651 . The link  67  and a pair of L-shaped links  66  are rotatably held on the inside of the pair of links  610  by a clamp pin  65 . Another pair of links  66  is rotatably held on the other side of the link  67  by a clamp pin  65 . The center parts of the four links  66  are rotatably supported by the clamp pins  64  on the link support  63 . The other ends of the four links  66  are rotatably supported by clamp pins  55  on the upper clamp arm  61 . The four links  66 , the link  67 , and the upper clamp arm  61  form a link mechanism. Therefore, the upper clamp arm  61  is lowered while keeping its horizontality, by moving the link fitting  611  toward the left in the drawing by operating the drive cylinder  69 . The lower clamp arm  62  is fixed to the link support  63 . The upper clamp arm  61  is prevented from interfering with the clamp pin  64  by a clearance hole  614  formed in the upper clamp arm  61 . 
     The workpiece side clamp mechanism  6  explained above is supported so that it is movable in the vertical direction with a retaining device  80  comprised of an upper support  615 , a lower support  616 , and the link support  63 , as well as four guide shafts  617  which pass through these in the vertical direction. A spring  618  supported by the lower support  616  supports the workpiece side clamp mechanism  6 . The retaining device  80  is supported on the first X movement mechanism  1  by a support device (not shown). Thereby, the workpiece holding surface  622  of the lower clamp arm  62  is 0.5 mm lower relative to the bottom surface of the workpiece  101  installed into the device. 
     In the above configuration, when the drive cylinder  69  is activated, a workpiece holding surface  612  of the upper clamp arm  61  lowers while keeping its horizontality, and presses the workpiece  101  to the workpiece holding surface  622  of the lower clamp arm  62 . Even if the workpiece  101  does not move in a downward direction, the workpiece  101  can be held, since the lower clamp arm  62  rises relatively. In other words, even if there is a deformation in the workpiece  101 , the workpiece  101  can be securely held. Further, the vertical balanced load can be maintained not more than 1 kg by the spring  618 . Therefore, the workpiece  101  does not deform. The workpiece  101  which is supported by the workpiece side clamp mechanism  6  is fixed in the X direction, and is supported to be movable in the Z direction. The spring  618  has a function of making the load applied to the workpiece  101  1 kg or less by receiving empty weight of the clamp mechanism  6 . In this way, by balancing the load applied to the workpiece along the vertical direction at 1 kg or less, deformations or height variations of the workpiece  101  that occur when large forces act on the workpiece  101  can be prevented. Thus, the clamp mechanism including the spring  618  has a function of holding the workpiece while following it in the vertical direction. 
     3.1.2 Modified Embodiment 
       FIG. 9  is a view showing a modified embodiment of the workpiece side clamp mechanism  6  shown in  FIG. 8 .  FIG. 9(   a ) is a plan view, and  FIG. 9(   b ) is a side view. 
     In the workpiece side clamp mechanism  6  according to the modified embodiment shown in  FIG. 9 , not only the upper clamp arm  61 , but also the lower clamp arm  62  can move up and down using the link mechanism shown in  FIG. 8 . In this modified embodiment, the link fitting  611  is constituted integrally with a connecting member  620  for driving the upper and lower links  66  and  67  simultaneously. Thereby, the link fitting  611  transmits the reciprocal movement of the drive cylinder  69  to the upper and lower links  67 . Thereby, the clamping action and clamping release action of the upper and lower clamp arms  61  and  62  become possible. These actions are substantially the same as the actions shown using  FIG. 8 . Therefore, members which are identical to those shown in  FIG. 8  are given the same reference numerals and explanations thereof are omitted. 
     In the case of this modified embodiment, the position of the abutting surface of the lower clamp arm  62  relative to the bottom surface of the workpiece  101  during the installation can be lowered compared to the case using the embodiment in  FIG. 8 . In other words, a large gap can be provided between both surfaces. 
     3.2 Workpiece Front End Surface Clamp Mechanism 
       FIG. 10  is a view showing the details of a workpiece front end surface clamp mechanism  7 .  FIG. 10(   a ) is a front view, and  FIG. 10(   b ) is a cross-sectional side view. 
     A rotary cylinder  71  rotates a clamp arm  72  in the direction of the arrow in  FIG. 10  via an arm rotating mechanism  73 . The front end surface of the workpiece  101  is then positioned in the X direction at the position of the clamp arm  72 ′ shown by the dashed dotted line. 
     3.3 Workpiece Rear End Surface Clamp Mechanism 
       FIG. 11  is a view showing the details of a workpiece rear end surface clamp mechanism  8 .  FIG. 11(   a ) is a front view, and  FIG. 11(   b ) is a cross-sectional side view. 
     The workpiece rear end surface clamp mechanism  8  has the same as the workpiece front end surface clamp mechanism  7  and a movement mechanism  81  which carries the workpiece front end surface clamp mechanism  7  and moves the workpiece front end surface clamp mechanism  7  in the X direction. The workpiece rear end surface clamp mechanism  8  determines the position of the rear end surface of the workpiece  101  in the X direction. 
     3.4 Arrangement 
     In the thin-film layer machining apparatus main body SA, the clamp mechanisms explained above can have not only the arrangement shown in  FIG. 2 , but can also be arranged in various ways. In the present embodiment, for example, an arrangement as described below is utilized. 
     3.4.1 First Arrangement Example 
       FIG. 12  is a plan view showing a first arrangement example of the clamp mechanisms in the present embodiment.  FIG. 12  corresponds to  FIG. 2 . The air floatation mechanism, the suction mechanism (vacuum suction mechanism), and the like are omitted from this drawing. 
     In  FIG. 12 , the machining apparatus includes a first X driving mechanism E 1 , a second X driving mechanism E 2  (when the workpiece size is small, a follower mechanism without a driving part is also possible), a slide mechanism E 3 , a workpiece side clamp mechanism E 4  including a mechanism for movement in the arrow direction, a workpiece side positioning roller mechanism E 5  including a mechanism for movement in the arrow direction, a workpiece side pressure roller mechanism E 6  including a mechanism for movement in the arrow direction, a workpiece front end positioning mechanism E 7  including a mechanism for movement in the arrow direction, and a workpiece rear end positioning mechanism E 8  including a mechanism for movement in the arrow direction. The double circles in  FIG. 12  show the positions of the respective machining heads A 4 . 
     The first arrangement example is for a large workpiece (for example, 2600 mm×2200 mm). Thus, the workpiece front end positioning mechanism E 7  and the workpiece rear end positioning mechanism E 8  are arranged at a center position in the Y direction. 
     In the case of this arrangement example, when the side surface clamping by the side clamp mechanism E 4  has been completed, only the pressure roller E 5  is retracted. Machining is carried out while the workpiece side pressure roller mechanism E 6 , the workpiece front end positioning mechanism E 7  and the workpiece rear end positioning mechanism E 8  are pressing. 
     3.4.2 Second Arrangement Example 
       FIG. 13  is a plan view showing a second arrangement example, which is a modified embodiment of the first arrangement example of the clamp mechanisms shown in  FIG. 12 . 
     In this arrangement example, the workpiece side pressure roller E 6  shown in  FIG. 12  is replaced with a workpiece side clamp mechanism E 9 , and the X driving mechanism E 2  is replaced with a follower mechanism E 2 ′. Further, the workpiece front end positioning mechanism E 7 , the workpiece rear end positioning mechanism E 8 , and the slide mechanism E 3  are eliminated. The other members are the same as the members in the first arrangement example shown in  FIG. 12 . 
     By constituting the arrangement in this way, the structure of the clamp mechanisms is simplified. Further, the clamps can be stabilized on the workpiece. Therefore, clamping imperfections do not easily occur. 
     3.4.3 Third Arrangement Example 
       FIG. 14  is a plan view showing a third arrangement example of the clamp mechanisms. 
     The third arrangement example is for a large (or medium) workpiece (2600 mm×2200 mm) A Y-axis direction movement mechanism is disposed on the first X driving mechanism E 1 . On the movement part thereof, the workpiece side clamp mechanism E 4  and the workpiece side pressure roller mechanism E 5  are mounted. Thereby, the workpiece is moved in the XY directions. Thus, a predetermined range on the workpiece  101  can be machined without moving the machining head A 4 . Further, an air floatation and suction mechanism  12  is provided on the upper surface of the second X driving mechanism E 2 . Further, a groove for clearance  13  which prevents interference of the pressure roller E 6  is formed on the top surface. In addition, the end portions of the connecting plates  3  are connected by a connecting plate  14 . By using the side pressure roller mechanism E 6  on the connecting plate  14 , the workpiece can be pressed even during machining. 
     Until this point, the present invention has been explained with regard to a case in which it is applied to an apparatus for machining the first to third line grooves P 1  to P 3  as in  FIG. 30 . However, by arranging the mechanisms E 4  to E 7  as described below, the present invention can also be applied to a workpiece periphery machining apparatus which removes a range of 10 to 12 mm from the outer periphery of the workpiece  101  by a high power laser having a wavelength of 1064 nm in a removed portion machining step. 
     3.4.4 Fourth Arrangement Example 
       FIG. 15  is a plan view showing a fourth arrangement example of the clamp mechanisms. 
     The fourth arrangement example is for a large workpiece (2600 mm×2200 mm). In this arrangement example, a mechanism which moves the workpiece side clamp mechanism E 4  in the arrow direction is disposed on two connecting plates  3 . The position of the workpiece in the Y direction is determined by the side positioning roller mechanism E 5  and the side pressure roller mechanism E 6  disposed on the bed. After the workpiece is clamped by the clamp mechanism E 4 , the side positioning roller mechanism E 5  and the side pressure roller mechanism E 6  are retracted. Subsequently, the workpiece is machined. After the longer edge side of the workpiece is machined, the workpiece is rotated by 90° on an air cushion at a position in the left side of the center line CL ( FIG. 2 ). Subsequently, the shorter edge side of the workpiece is machined. After the shorter edge side is machined, the workpiece is returned to its original position by rotating by 90°, and then the workpiece is discharged. The other members are constituted in the same way as those of the first arrangement example shown in  FIG. 12 . 
     In the present arrangement example, both sides can be machined in one spot and the center can be machined in two spots by using the laser head shown in  FIG. 28(   a ) to be explained later. 
     3.4.5 Fifth Arrangement Example 
       FIG. 16  is a plan view showing a fifth arrangement example of the clamp mechanisms. 
     The fifth arrangement example is for a medium workpiece (1400 mm×1100 mm). The workpiece side clamp mechanism E 4  explained above is disposed with a vertical movement mechanism and a front-back movement mechanism on the two connecting plates  3 , which are connected to the follower mechanism E 2 ′ to the slide mechanism E 3 . The other members are constituted in the same way as those of the first arrangement example shown in  FIG. 12 . 
     By arranging as explained in this arrangement example, the configuration shown in  FIG. 28(   b ) to be explained later can be used as the laser head. Therefore, the both sides can be machined simultaneously. 
     3.4.6 Sixth Arrangement Example 
       FIG. 17  is a plan view showing a sixth arrangement example of the clamp mechanisms. 
     The sixth arrangement example is for a medium or small workpiece (1400 mm×1100 mm or less). In this arrangement example, the second X driving mechanism E 2  is not used. Instead, flat air bearings E 21  are disposed on the end portions of the connecting plates  3 . The flat surface air bearings E 21  are constituted to slide on the surface of a flat guide. In addition, a workpiece rear end positioning mechanism  15  is disposed on the first X driving mechanism E 1 . In this arrangement example, by moving the connecting plate on the rear side in the X direction, workpieces of various sizes can be adjusted. The other members are constituted in the same way as those of the first arrangement example shown in  FIG. 12 . 
     By arranging as explained in this arrangement example, the configuration shown in  FIG. 28(   b ) to be explained later can be used as the laser head. Therefore, both sides can be machined simultaneously. 
     4. Dust Collector for Line Groove Machining 
     4.1 Embodiment of First Dust Collector 
       FIG. 18  is a view for explaining a first dust collector (hereinafter referred to as the “dust collector DC 1 ”) for machining the line grooves according to the embodiment of the present invention.  FIG. 18(   a ) is a plan view,  FIG. 18(   b ) is a cross-sectional view along line I-I of  FIG. 18(   a ), and  FIG. 18(   c ) is a cross-sectional view along line II-II of  FIG. 18(   a ). 
     The dust collector DC 1  includes a dust collection chamber  16 , a dust collection duct  17 , nozzles  18  and  19 , and an air floatation groove  20 . The plurality of nozzles  18  and  19  (in  FIG. 18 , there are 3 of each) are disposed in the dust collection chamber  16  so that they are facing each other in the X direction. The dust collection chamber  16  is connected to the dust collection duct  17 . The nozzles  18  and  19  deliver a cooling medium such as air, mist, or liquid (herein, water or sprayed water). The air floatation groove  20 , which is formed on the bottom surface (the surface facing the workpiece  101 ) of the dust collection chamber  16 , is connected to a compressed air source (not shown). As will be explained later, the dust collector DC 1  is pressed against the workpiece  101  with a preset pressure. 
     Air delivered from the air floatation groove  20  forms a layer of air between the workpiece  101  and the dust collector DC 1 . The air layer floats the dust collector DC 1 . The workpiece  101  is biased in the Z direction. As a result, warps of the workpiece  101  are corrected. Thereby, height variations of the surface of the workpiece can be minimized. 
     In  FIG. 18(   c ), if the workpiece  101  is moved in the direction of arrow D 5  shown by a solid line, the cooling medium is delivered from the nozzle  18  to a machining portion  21 . If the workpiece  101  is moved in the direction of arrow D 6  shown by a dashed line, the cooling medium is delivered from the nozzle  19  to a machining portion  22 . In other words, the nozzle used is switched so that the cooling medium is delivered towards the direction in which the workpiece is proceeding. As a result, debris generated by the machining are cooled down by the cooling medium and carried to a not-yet-machined portion. Therefore, the debris can be easily removed by an air blow or the like after machining since they adhere only weakly to the surface of the workpiece  101 . 
       FIG. 19  is a side view showing the main parts of a column A 6  provided with the dust collector DC 1 . 
     In  FIG. 19 , air cylinders  23  are fixed on a carriage  24 . The carriage  24  is movable in the Y direction on the column A 6 . The dust collector DC 1  is fixed to a piston rod of the air cylinder  23 . The piston rod is usually elastically biased by a spring  25  toward the upward direction in  FIG. 19 . During machining, the air cylinder  23  pushes the dust collector DC 1  toward the workpiece  101  with a preset pressure. Therefore, warps of the workpiece are corrected. The spring  25  prevents the dust collector DC 1  from dropping onto the workpiece  101  if the air supplied to the air cylinders  23  is stopped. 
     Air flows at high speed from the air floatation groove  20  toward the inside of the dust collection chamber  16 . Therefore, the cooling medium, even in case of using a mist or water as the cooling medium, is collected from the dust collection duct  17  even if the workpiece  101  is warped. Thus, there are no leaks of the cooling medium to the outside of the dust collection chamber  16 . Further, if the workpiece  101  is mounted on an XY table, the air cylinders  23  can be directly fixed to the column A 6 . 
     4.2 Embodiment of Second Dust Collector 
       FIG. 20  is a plan view for explaining a second dust collector (hereinafter referred to as the “dust collector DC 2 ”) for machining the line grooves according to the embodiment of the present invention.  FIG. 20(   a ) is a plan view,  FIG. 20(   b ) is a cross-sectional view along line I-I of  FIG. 20(   a ), and  FIG. 20(   c ) is a cross-sectional view along line II-II of  FIG. 20(   a ). Members which are identical to those shown in  FIGS. 18 and 19  are given the same reference numerals and explanations thereof are omitted. 
     Guide rollers  31  are supported in a rotatable manner on the side surface in the X direction of the dust collection chamber  16 . The position of the guide rollers  31  in the Z direction is determined such that the underside of the dust collection chamber  16  can maintain a spacing (approximately 0.5 mm) from the top surface of the workpiece  101 . The position of the guide rollers  31  in the Y direction is determined so that the line grooves P 1  to P 3  do not overlap with each other. 
       FIG. 21  is a side view showing the main parts of the column A 6  equipped with the dust collector DC 2 . In  FIG. 21 , the length of the dust collector DC 2  in the Y direction is approximately the same as the width of the workpiece  101 . Therefore, in the configuration of  FIG. 21 , the dust collector DC 2  is pressed by four air cylinders  23 . In the dust collector DC 2 , the air cylinders  23  are fixed to the column A 6 . This is because it is not necessary for the cylinders to move in the Y direction. 
     4.3 Embodiment of Third Dust Collector 
       FIG. 22  is an explanatory view of a third dust collector (hereinafter referred to as the “dust collector DC 3 ”) used in the case of forming a removed portion  107  around the periphery of the workpiece.  FIG. 22(   c ) is a front view,  FIG. 22(   a ) is a cross-sectional view along line I-I of  FIG. 22(   c ), and  FIG. 22(   b ) is a cross-sectional view along line II-II of  FIG. 22(   c ). 
     In  FIG. 22 , an upper dust collection chamber (upper chamber)  32  includes a plurality of nozzles  323  (three in the case of  FIG. 22 ) similar to the dust collection chamber  16 . The cooling medium, which is supplied through a passage  324 , is delivered toward the workpiece  101  at a preset pressure from the nozzles  323 . The delivered cooling medium is discharged from a dust collection duct  37  through a cavity  325 . On the bottom surface, in addition to grooved air blowing outlets  326  and  328  and the floatation groove  20 , a plurality of circular air blowing outlets  327  are provided. The inside of the upper dust collection chamber  32  is barriered off from the outside by the air. The nozzles  323  are disposed on the upper dust collection chamber  32  so that their blowing outlets are facing the Y direction. The nozzles  323  deliver cooling medium similar to the nozzles  18  and  19 . A machining laser beam B 1  is incident on the workpiece  101 . Upon passing through the workpiece  101 , a laser beam b 1  is incident on the upper dust collection chamber  32 . As will be explained below, a beam damper  329  which absorbs the laser beam b 1  is disposed at the irradiation position for the laser beam b 1  in the upper dust collection chamber  32 . Flanges  321  are provided on both side surfaces in the X direction of the upper dust collection chamber  32 . A pair of bearings (linear guide devices)  35  are fixed to the flanges  321 . Guide roller units R are also disposed on both side surfaces in the X direction of the upper dust collection chamber  32 .  FIG. 23  is a vertical cross-sectional view of the guide roller units R. 
     As shown in  FIG. 23 , the guide roller unit R is basically comprised of a holder  366 , an inner housing  365 , a slider  361 , a shaft  362 , and a guide roller  36 . The holder  366  is fixed to the dust collection chamber  16 . The guide roller  36  is integrated with the ball spline slider  361 . The shaft  362  is rotatably supported on the holder  366  by a bearing  364 . The slider  361  is rotatably supported on the inner housing  365  by a bearing  363 . Further, the slider  361  is supported so that it is movable in the axial direction relative to the shaft  362 . The inner housing  365  is fixed to a cylinder rod of a cylinder  367  fixed to the holder  366 . 
     In the above-described configuration, the guide roller  36  moves in the Y direction by moving the cylinder rod. Thereby, the workpiece can be positioned. Here, it is practical to make the movement stroke of the guide roller  36  larger than ½ of the machining width of the removed portion  107 . That is, for example, the guide roller  36  is positioned at the center of the machined width to begin the machining. When the machining reaches the center position, the guide roller  36  is moved slightly in front of the machining completion position. In this way, the thin-film layer of the workpiece  101  will not be damaged by the guide roller  36 . Further, a structure which disposes the guide roller  36  (inner housing  365 ) at a desired position by a motor can also be achieved. The position of the guide roller  36  in the Z direction is determined so that the lower end of the guide roller  36  projects from the lower end of the upper dust collection chamber  32  by a distance of S 1  (for example, 0.5 mm). 
     As shown in  FIG. 22(   b ), a lower dust collection chamber (lower chamber)  33  has an L-shape. Flanges  331  are provided on both side surfaces in the X direction of this chamber. Tracks  34  which engage with bearings (linear guide devices)  35  are fixed to the flanges  331 . The lower dust collection chamber  33  covers the end of the workpiece  101  by combining with the upper dust collection chamber  32 . A through opening  336  for transmitting an incident machining laser beam B 1  is provided on the bottom surface of the lower dust collection chamber  33 . Further, the air floatation groove  20  is provided on the side of the lower dust collection chamber  33  facing the workpiece  101 . 
     In order to prevent the cooling medium from leaking to the outside from the opening  336 , rectangular air blow outlets  332  and  333 , having a long side along the X direction, are provided. The air blow outlets  332  and  333  are connected to a compressed air source (not shown) via a passage  334 . Further, an air blow outlet is also provided at a position facing an air blow outlet  327  on the upper surface of the lower dust collection chamber  33 . The lower dust collection chamber  33  is fixed to a column by a means (not shown). At this time, the top end of the lower dust collection chamber  33  is separated from the bottom surface of the workpiece  101  by a distance S 2  (for example, 0.3 mm). The upper dust collection chamber  32  moves in the vertical Z direction relative to the lower dust collection chamber  33 . 
     Now, the distances (gaps) S 3 , S 4 , and S 5  shown in  FIG. 22(   b ) will be explained. The distance S 3  is determined by the width of the removed portion  107 , and is normally 10 to 15 mm. The distance S 4  is determined by the board thickness of the workpiece  101 , and is the board thickness of the workpiece  101  plus 0.2 to 0.5 mm. The distance S 5  is 0.1 mm or less so that the dust collection effect does not decrease. The lower dust collection chamber  33  is connected to the dust collection duct  37 . The spot height of the machining beam B 1  is set to match the surface of the machining portion by a Z-axis mechanism (not shown). 
     4.4 Embodiment of Fourth Dust Collector 
       FIG. 24  is an explanatory view of a fourth dust collector (hereinafter referred to as the “dust collector DC 4 ”) used in machining of a center portion.  FIG. 24(   a ) is a plan view,  FIG. 24(   b ) is a cross-sectional view along line I-I of  FIG. 24(   a ), and  FIG. 24(   c ) is a cross-sectional view along line II-II of  FIG. 24(   a ). 
     For example, in the case of a workpiece size of 2600×2200 mm, the workpiece is divided up into four parts to be used. Therefore, not only is the periphery removed, but a removed portion having a cross shape (hereinafter referred to as a “cross-shaped removed portion”) is also formed in the center. The removal width of the cross-shaped removed portion needs to be twice the width of the removed portion  107 . In the dust collector DC 4  illustrated in  FIG. 24 , the spacing between the two nozzles  18  is ½ of the machining width. A groove is formed along the X direction using two beams simultaneously. In this way, the machining efficiency can be enhanced. The delivering direction of the nozzles  18  can also be in the Y direction. Further, if guide rollers are provided to the front and back of the dust collector DC 4 , deformation of the workpiece can be more effectively corrected. 
       FIG. 25  is a side view showing the main parts of a column A 6  equipped with the dust collector DC 4 . The dust collector DC 4  shown in  FIG. 25  is mounted on a peripheral thin-film layer removal apparatus for a large workpiece. 
     In the case of using the dust collectors DC 1  to DC 4 , after completion of the machining, in the discharge step, it is preferable to dry the workpiece with a dryer. 
     The method for delivering a cooling medium onto the worked portion is also effective in the case of machining by irradiation with the laser from the thin-film layer side. 
     In the dust collectors DC 1  to DC 4 , a cooling medium such as air, mist, or liquid is delivered from the nozzles  18  and  19 . In regards to this, the reason for delivering, for example, mist or water onto the worked portion will be shown below. 
     That is, the insulation resistance required by the removed portion  107  (portion formed by removing the thin-film layer around the periphery of the workpiece) is 2000 MΩ or greater in the case that DC 500 V is applied. In normal machining of the workpiece  101 , the laser wavelength is 1064 nm, the average output is 300 W or greater, and the pulse frequency is 5 to 10 kHz. In this case, the spot diameter is 400 to 600 μm, and the necessary energy density is 16 J/cm 2  or greater. The thin-film layer component is scattered by the laser beam irradiation. However, at this time, the removed portion  107  momentarily enters a vacuum state. Therefore, the worked component instantaneously returns and adheres to the surface which is in a melted state. Further, spatters and debris are produced in large amounts, ionized to plasma of high temperature, and scatter on the periphery of the removed portion  107 , and adhere onto the glass surface and solidify. Therefore, the insulating resistance becomes approximately 30 MΩ or less. However, if mist or water is sprayed onto the worked portion, the glass surface is covered by water. The temperature of the high temperature spatters and debris also decreases when the spatters and debris reach the glass surface. As a result, the spatters and debris are prevented from adhering onto the glass surface. In other words, the problem of worked components adhering onto the removed portion  107  is overcome. Thereby, the requirement of an insulating resistance of 2000 MΩ or greater can be achieved. Further, even in machining which uses overlapping spots in subsequent pulses, the occurrence of cracks in the glass surface due to rising temperatures at portions on the glass where the beams overlap each other can be eliminated. 
     5. Optical System 
     5.1 Dust Prevention Mechanism 
       FIG. 26  is a schematic view showing a dust prevention mechanism of an optical system in the embodiment of the present invention. The arrow direction is the direction of movement of the workpiece. 
     In the optical system in the embodiment shown in  FIG. 26 , dust is removed from the workpiece  101  by a UV lamp  144  for static elimination. The removed dust drops into a dust collection duct  145  which also serves as a reflecting plate of the UV lamp  144 . Afterwards, the dust is collected by a dust collector (not shown). A rotating static brush  142  is provided on the downstream side from the UV lamp  144  in the movement direction of the workpiece. The rotating anti-static brush  142  cleans the underside of the workpiece  101 . A dust collection duct  143  is disposed on the outer periphery of the anti-static brush  142 . Dust removed from the workpiece  101  by the anti-static brush  142  is collected by the dust collection duct  143 . Subsequently, the dust is collected by a dust collector (not shown). 
     The position of the laser beam B 1  in the XY directions is determined by a beam positioning mechanism  38 . The laser beam B 1  impinges on the workpiece  101  after passing through a condenser lens (fθ lens)  39  and being reflected by a mirror  40 . The beam positioning mechanism  38  is supported so that it can be freely positioned in the Z direction relative to the machining head A 4 . An air blower  141  delivers air toward the reflective surface of the mirror  40 . Therefore, even if glass dust falls from the workpiece  101 , the glass dust will not remain on the reflective surface of the mirror  40 . 
     In actual machining, high productivity, good machining quality, and high reliability of the machining are required. In order to accommodate these requirements, the laser properties are important. If a frequency near the pulse frequency at which maximum output can be obtained is used, output fluctuations of the laser will be reduced to a minimum. The beam mode (energy distribution) will also become stable in a good condition. On the other hand, in the case of using a laser oscillator for line groove machining, as is being used in the present invention, the actual capable value of the pulse frequency at which maximum output can be obtained is 80 to 120 kHz. However, the limit of the table speed is 1 m/sec. In actual machining, the hole diameter which is used is 60 μm and the beam overlap ratio is 30 to 50%. Therefore, the pulse frequency is constrained to 25 to 40 kHz. Thus, the output utilization efficiency is 50% at maximum. 
     5.2 Optical System 
     In the present embodiment, in order to enhance the output utilization efficiency, an optical system as described below is utilized.  FIG. 27  is a view showing a configuration of the main parts of the optical system in the present embodiment. 
     In  FIG. 27 , a first corner mirror  147  is disposed at the entrance pupil position of an fθ lens  146  having a focal distance f. The angle of the corner mirror  147  is positioned to be 45° relative to the optical axis of the fθ lens  146 . A laser beam B 2  is incident so that it is coaxial with the optical axis of the fθ lens  146 . Two second corner mirrors are disposed at a position separated from the first corner mirror  147  by a distance  12 . These second corner mirrors are arranged such that the angles of the laser beams B 1  and B 3  are θ relative to the laser beam B 2 . The laser beams B 1 , B 2 , and B 3  have the same polarization. The pulse irradiation sequence of the laser beams is shifted by 1/F. The spacing l 1  is the line spacing (distance between the beam spots) at the removed portion  107 , and is l 1 =fθ. The beam spacing w at the position of the corner mirror  148  is calculated as w=l 2 ·tan θ. 
     For example, in the case of condensing the beam diameter of 10 mm using an fθ lens having a focal distance f of 10 mm, the angle θ necessary for obtaining a spot spacing l 1  of the machined portion (removed portion)=10 μm is approximately 5.7°. If the necessary effective diameter of the mirrors at the position of the second corner mirrors  148  is 20 mm, the mirror spacing l 2  for avoiding interference between the beam B 2  and the mirrors  148  is l 2 =200 mm. Therefore, by leading the three beams split from a beam of 80 to 120 kHz to the single fθ lens, machining at a table speed of 1 m/sec can be achieved. Thus, the output effective utilization ratio can be increased to 100%. 
     The output of a high output laser used in machining to remove the periphery of a workpiece is 500 W, and the pulse frequency thereof is 5 to 6 kHz. The spot size which has been formed into a rectangular beam is 600×600 and the overlap ratio is 30 to 50%. Therefore, the machining speed is 1.5 to 2.4 m/s. Thus, the output utilization efficiency is 66% at maximum, rate-determined by the table speed. In order to enhance the output utilization efficiency, a beam having a width of 2 W and a machining pitch of W/2, formed by aligning four rectangular beams of 300×300 μm next to each other, can be used. If machining is performed using this beam, the table speed can be decreased by ½ (50%). Thus, the output utilization efficiency can be increased two fold compared to the related art. 
       FIG. 28  is a view showing the configuration of the optical system in the present embodiment. This configuration is an example of an optical system for machining to remove the periphery of the workpiece by a high output laser. 
     In  FIG. 28 , a laser oscillator  49  emits an emission beam (having an output of, for example, 500 W)  50  having random polarization. The emission beam  50  is split into two beams having the same energy by a beam splitter  51 . The two split beams are each split into a P wave and an S wave by a first polarizing beam splitter  52 . The ratio (energy) of the P waves formed by splitting by the polarizing beam splitter  52  is adjusted by a ½λ, plate  53 . The ½λ plate  53  adjusts the ratio of P waves to S waves by a rotation angle. The P waves pass through a second polarizing beam splitter  54  and enter a micro-lens array (or rectangular fiber) beam shaper  56 . The ratio (energy) of the S waves formed by splitting by the polarizing beam splitter  52  is adjusted by the ½λ plate  53 . The ½λ, plate  53  adjusts the ratio of P waves to S waves by a rotation angle. The S waves pass through the second polarizing beam splitter  54  and enter the micro-lens array (or rectangular fiber) beam shaper  56 . The cross-section of the beams which have entered the beam shaper  56  is shaped into a rectangular shape, and then the beams are supplied to the removed portion  107  (worked portion) via an fθ lens  57 . The beams reflected by the second polarizing beam splitter  54  are absorbed by beam dampers  55 . 
     Reference numbers  58 ,  59 , and  60  in  FIG. 28(   a ) represent the arrangement of rectangular spots in the case that both ends are machined by one spot whereas the center is machined by two spots. Reference numbers  61  and  62  in  FIG. 28(   b ) show the arrangement of rectangular spots in the case that both sides are each machined by two rectangular spots. In order to form the beam cross-section into a rectangle, a plurality of prisms or a plurality of fiber emission outlets having a rectangular cross-section, or a fiber connector can be arranged next to each other. 
     A case using four beams has been explained above. However, for example, if eight beams are used and the rectangular beams are 210×210 μm, the table speed can be lowered to 35%. Further, in the above-described case, the outputs of B 1  to B 4  have been adjusted individually. However, if the first polarizing beam splitter  52 , the ½λ plate  53 , and the second polarizing beam splitter  54  are disposed at the position of the beam splitter  51  to adjust the output, the output error between the beams increases, but the number of polarizing beam splitters and ½λ plates can be decreased. 
     As explained above, according to the present embodiment, the following effects can be achieved: 
     (1) a mechanism for floating and sucking the workpiece and a workpiece clamp mechanism of a style which follows the vertical position of the workpiece are utilized. Thereby, height variations of the workpiece surface can be improved to ⅓ of that of the related art (from ±1.5 mm to ±0.05 mm). Therefore, the yield can be enhanced. 
     (2) The thin-film layer is worked from the underside while a cooling medium is delivered on the top surface side. Therefore, in machining of a first insulating layer and machining to remove the periphery of the workpiece, an insulating resistance of 2000 MΩ or greater can be achieved. As a result, the generating efficiency of a solar battery and the yield can be enhanced. 
     (3) Further, even if the pulse period is shortened (0.02 ms, pulse frequency 50 kHz), the insulating resistance can be secured and detachment at the entrance of a hole can be eliminated. Thus, it is possible to increase the speed. 
     (4) Reduced output machining of a maximum of 30% compared to the related art is possible. Thus, energy conservation can be achieved. 
     The above effects are achieved in this manner. 
     The present invention is not limited to the above embodiment, and various modifications are possible. The subject of the present invention encompasses all technical matters included in the technical concept of the inventions recited in the claims. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           1  . . . first X driving mechanism 
           2  . . . second X driving mechanism 
           3  . . . connecting plate 
           4  . . . workpiece-underside support mechanism 
           5  . . . support frame 
           6  . . . clamp device 
           7  . . . workpiece front end surface clamp mechanism 
           8  . . . workpiece rear end surface clamp mechanism 
           9  . . . workpiece side surface pressing mechanism 
           101  . . . workpiece 
           102  . . . transparent glass 
         A 1  . . . bed 
         A 2  . . . X movement mechanism 
         A 3  . . . Y movement mechanism 
         A 4  machining head 
         A 5  . . . laser oscillator 
         A 6  . . . column 
         SA . . . thin-film layer machining apparatus main body