Patent Publication Number: US-2005127045-A1

Title: Laser crystallization apparatus and laser crystallization method

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a laser crystallization apparatus and a laser crystallization method.  
      2. Description of the Related Art  
      A liquid crystal display device includes an active matrix driving circuit including TFTs. Further, a system liquid crystal display device includes electronic circuits including TFTs in a peripheral region around a display region. Low-temperature Poly-Si is suitable for forming the TFTs in the liquid crystal display device and the TFTs in the peripheral region of the system liquid crystal display device. Further, the low-temperature Poly-Si is expected to be applied to pixel driving TFTs in an organic EL display or electronic circuits in a peripheral region of the organic EL display. The present invention relates to a semiconductor crystallization method and apparatus using a CW laser (continuous wave laser) for fabricating the TFTs from the low-temperature Poly-Si.  
      Conventionally, in order to form the TFTs of the liquid crystal display device from the low-temperature Poly-Si, an amorphous silicon film is formed on a glass substrate and the amorphous silicon film on the glass substrate is irradiated with excimer pulse laser to crystallize the amorphous silicon. Recently, a technique for crystallizing the amorphous silicon by irradiating the amorphous silicon film on the glass substrate with CW solid-state laser has been developed (for example, see Japanese Unexamined Patent Publication No. 2003-86505 and the Institute of Electronics, Information and Communication Engineers (IEICE) Transactions, Vol. J85-C No. 8, August 2002). The amorphous silicon is melted by a laser beam and then solidified, wherein the solidified portion turns into polysilicon.  
      While the mobility value in the silicon crystallization by the excimer pulse laser is about 150-300 (cm 2 /Vs), a mobility of about 400-600 (cm 2 /Vs) can be obtained in the silicon crystallization by the CW laser, which is advantageous in the formation of high-performance polysilicon.  
      In the silicon crystallization, an amorphous silicon film is scanned by a laser beam. In this case, a substrate having the silicon film is mounted on a movable stage so that the silicon film is scanned by moving the silicon film with respect to the fixed laser beam. In the case of the excimer pulse laser, for example, the scan operation can be performed by the laser beam having a beam spot of 27.5 cm×0.4 mm. On the other hand, in the case of the CW solid-state laser having a smaller beam spot, the laser beam is condensed as an elliptical spot by using an optical system such as a cylindrical lens. In this case, for example, the size of the beam spot is tens to hundreds of μm and the scanning operation is performed in a direction perpendicular to the major axis of the ellipse. Thus, the crystallization by the CW solid-state laser suffers from low throughput even though high-quality polysilicon can be obtained.  
      Because a CW laser has a small beam spot and, therefore, only a small area of amorphous silicon can be crystallized in one scan, a plurality of scans are performed successively to crystallize a required area of the amorphous silicon. In this case, a glass substrate is mounted on a movable stage and raster scanning is performed so that beam traces one scan in the forward direction and the next scan in the reverse direction to partially overlap each other. If the amount of overlap is small, a noncrystallized area may be formed between the two beam traces and therefore, the overlapping amount is determined with the addition of a positional tolerance. But, if the overlapping amount is large, the total width of the two beam traces is reduced and throughput is thus reduced.  
      In recent research, it has been found that the beam traces meander minutely. Though it can be said generally that the stage is moved linearly, the movement of the stage is in fact accompanied with minute meanderings even though the stage is controlled so that it is moved linearly and therefore, the beam trace crystallized in one scanning meanders as shown later. If there are meanderings, the overlapping amount between the two beam traces must be increased and as a result, the throughput is reduced.  
      Further, when a semiconductor layer in the peripheral region around the display region of the liquid crystal display device is crystallized, the scans must be performed in two directions orthogonal to each other. Therefore, the movable stage supporting the substrate on which the semiconductor layer is formed must be rotatable. The conventional rotary stage includes an XY stages and a rotary stage, wherein the substrate is attached to the rotary stage and the rotary stage can be rotated 90 degrees and, further, if it is rotated, the scannings can be performed in the two directions orthogonal to each other. However, the conventional rotary stage is provided also for the purpose of angular correction in final positioning of the substrate and, in this case, it must operate with high precision and accuracy of 0.1-0.2 seconds in the rotation range of several degrees. In order to achieve such precision, the conventional rotary stage is not designed to be rotated 90 degrees. Therefore, the stage must be redesigned as a whole so that the rotary stage can be rotated 90 degrees. Further, even when the rotary stage is manufactured so that it can be rotated 90 degrees, it must be designed to operate precisely for the final positioning of the substrate and therefore, the cost of the rotary stage will be high. As a result, when the scans are performed in two directions orthogonal to each other, an operator must pick up the substrate, turn it 90 degrees and reset it on the rotary stage by hand and, therefore, the operation becomes troublesome and the throughput is reduced.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a laser crystallization apparatus and a laser crystallization method that can achieve high throughput even when a CW laser is used.  
      A laser crystallization apparatus, according to the present invention, comprises a movable stage supporting a substrate having a semiconductor layer formed thereon, a device directing a laser beam to a plurality of optical paths in a time-division manner, and optical devices condensing and applying the laser beam passing through the optical paths to the semiconductor layer on the substrate supported by the stage.  
      Further, a laser crystallization method, according to the present invention, comprises the steps of directing a CW laser beam to at least two optical systems in a time-division manner, crystallizing a first region of a semiconductor layer formed on a substrate by using one of the optical systems to which the laser beam is directed, and crystallizing a second region of the semiconductor layer formed on the substrate that is spaced from the first region by using another of the optical systems to which the laser beam is directed.  
      In the laser crystallization apparatus and the laser crystallization method described above, the CW laser beam is directed to at least two optical systems in a time-division manner and different regions of the semiconductor layer are crystallized successively by using the respective optical systems. Therefore, a beam trace formed by the scan in one direction and another beam trace formed in the scan in the reverse direction do not overlap each other and it is possible to arrange such that only the beam traces formed in the scans in one specific direction overlap each other. As a result, the amount of overlap can be determined with a lower estimate of an effect of meandering in the beam traces resulted from the stage. Thus, a high throughput can be achieved even when a CW laser is used.  
      Also, a laser crystallization apparatus, according to the present invention, comprises a movable stage supporting a substrate having a semiconductor layer formed thereon, an optical device for applying a laser beam to the semiconductor layer on the substrate supported by the stage, a rotary device that is provided separately from the stage and can rotate the substrate, and a transporting device that can transport the substrate at least between the stage and the rotary device.  
      In this configuration in which the rotary device is provided separately from a rotary stage on XY stages, when scans are performed in two directions orthogonal to each other, first, a scan is performed in one direction while supporting the substrate having the semiconductor layer formed thereon, then the substrate is transported from the stage to the rotary device to rotate the substrate by 90 degrees and then, the substrate is transported from the rotary device to the stage to support the substrate on the stage to perform another scan in another direction. Thus, the scans can be performed successively in the two directions orthogonal to each other. Therefore, while the conventional stage with a limited rotation range but with high precision is used as it is, the scans can be performed without reduction of throughput by only newly providing the rotary stage that can be rotated 90 degrees. In this case, it is only required that the rotary device can be rotated 90 degrees or 90 plus some degrees but it does not have to provide high-precision and an accuracy of 0.1-1 degrees suffices (the precision is ensured by the rotary stage on the XY stages).  
      As described above, according to the present invention, throughput can be improved significantly because both forward and backward scans can be used for crystallization and, even if there are meanderings, the crystallization can be achieved only by either the forward or the backward scans in each crystallization region and therefore, the scanning pitch can be increased. Further, the present invention improves throughput of low-temperature polysilicon TFTs through crystallization by CW laser and as a result, contributes to development of devices including high-performance TFTs resulting from the low-temperature polysilicon technology, such as sheet computers, intelligent FPDs and low-cost CMOS. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic cross-sectional view showing a liquid crystal display device manufactured according to the present invention;  
       FIG. 2  is a schematic plan view showing the TFT substrate of  FIG. 1 ;  
       FIG. 3  is a schematic plan view showing a mother glass for fabricating the TFT substrate of  FIG. 2 ;  
       FIG. 4  is a schematic plan view showing a laser crystallization apparatus according to an embodiment of the present invention;  
       FIG. 5  is a perspective view showing the laser crystallization apparatus of  FIG. 4 ;  
       FIG. 6  is a side view showing the configuration of the optical device of  FIGS. 4 and 5 ;  
       FIG. 7  is a plan view showing an example of the device directing a laser beam to a plurality of optical paths in a time-division manner, of  FIGS. 4 and 5 ;  
       FIG. 8  is a perspective view showing a substrate supported by the stage;  
       FIG. 9  is a diagram showing an example of overlapping beam traces;  
       FIG. 10  is a diagram showing an example of a meandering beam trace;  
       FIG. 11  is a diagram showing an example of overlapping beam traces when the scanning according to the present invention is performed;  
       FIG. 12  is a diagram showing an example of overlapping beam traces when the reciprocating scanning is performed;  
       FIG. 13  is a side view showing a laser crystallization apparatus according to another embodiment of the present invention;  
       FIG. 14  is a perspective view showing an example of the stage;  
       FIG. 15  is a perspective view showing an example of the transporting device of  FIG. 13 ; and  
       FIG. 16  is a schematic plan view showing a variation of the laser crystallization apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention will now be described with reference to the drawings.  
       FIG. 1  is a schematic cross-sectional view showing a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device  10  comprises a pair of opposing glass substrates  12  and  14 , and a liquid crystal  16  inserted therebetween. The glass substrates  12  and  14  can be provided with electrodes and alignment films. One of the glass substrates  12  is a TFT substrate and the other of the glass substrates  14  is a color filter substrate.  
       FIG. 2  is a schematic plan view showing the glass substrate  12  of  FIG. 1 . The glass substrate  12  has a display region  18  and a peripheral region  20  around the display region  18 . The display region  18  includes a large number of pixels  22 . In  FIG. 2 , one of the pixels  22  is shown in a partly enlarged manner. The pixel  22  includes sub-pixel regions of three primary colors RGB and TFTs  24  are formed in respective sub-pixel regions of three primary colors. The peripheral region  20  has TFTs (not shown), wherein the TFTs in the peripheral region  20  are arranged more densely than the TFTs  24  in the display region  18 .  
      The glass substrate  12  of  FIG. 2  constitutes a 15 inch QXGA liquid crystal display device having 2048×1536 pixels  22 . In the direction (horizontal direction) in which the sub-pixel regions RGB of the three primary colors are aligned, 2048 pixels are aligned and, therefore, the number of the sub-pixel regions RGB is 2048×3. In the direction (vertical direction) perpendicular to that in which the sub-pixel regions RGB of the three primary colors are aligned (horizontal direction), 1536 pixels are aligned. In the semiconductor crystallization process, in the peripheral region  20 , the laser scanning is performed in the directions parallel to the sides thereof, whereas, in the display region  18 , the laser scanning is performed in the direction A or B.  
       FIG. 3  is a schematic plan view showing a mother glass  26  for fabricating the glass substrate  12  of  FIG. 2 . The mother glass  26  is configured so that a plurality of the glass substrates  12  can be obtained therefrom. Though four glass substrates  12  are obtained from one mother glass  26  in the example shown in  FIG. 3 , more than four glass substrates  12  may be obtained.  
       FIG. 4  is a schematic plan view showing a laser crystallization apparatus according to an embodiment of the present invention.  FIG. 5  is a perspective view showing the laser crystallization apparatus of  FIG. 4 . The laser crystallization apparatus  30  comprises a movable stage  62  supporting a substrate  66  having a semiconductor layer (an amorphous silicon film)  68  formed thereon ( FIG. 8 ), a laser source  32 , a device  36  directing the laser beam emitted from the laser source  32  to a plurality of optical paths  33  and  34  in a time-division manner, and optical devices  37  and  38  condensing and applying the laser beam passing through the optical paths  33  and  34  onto the semiconductor layer  68  on the substrate  66  supported by the stage  62 . The laser beam input to the device  36  may not only come directly from the laser source  32  but, for example, it may be one of sub-beams divided simultaneously by a half mirror as shown in  FIG. 16 . Further, inversely, outgoing light from the device  36  may be divided simultaneously into sub-beams.  
      The laser source  32  includes a CW laser (continuous wave laser) oscillator. The semiconductor layer  68  includes a region  1  and a region  2 . The semiconductor layer  68  does not have to be divided into the region  1  and the region  2  particularly but, here, it is merely so divided for convenience of description. In the shown embodiment, the optical paths  33  and  34  divided at the device  36  are oriented in opposite directions and mirrors  39  and  40  reflect the optical paths  33  and  34 , respectively, so that they are parallel to each other. The distance H between the center of the device  36  and the mirror  39  ( 40 ) can be changed so that the distance between the mirrors  39  and  40  or, in other words, the distance between the optical devices  37  and  38  can be adjusted. It is preferable that the mirror  39  and the optical device  37  are integrally supported by a first supporting means and the mirror  40  and the optical device  38  are integrally supported by a second supporting means so that the relative position between the first supporting means and the second supporting means can be changed by a single axis stage.  
       FIG. 6  is a side view showing the configuration of the optical device  37  of  FIGS. 4 and 5 . Though  FIG. 6  shows the configuration of the optical device  37  of  FIG. 5 , it is to be understood that the optical device  38  is also configured similarly. The optical device  37  comprises a mirror  42  that reflects the optical path of the laser beam from the horizontal direction to the vertical direction, a cylindrical lens  44  that is formed substantially as a semicylinder, a cylindrical lens  46  that is disposed orthogonal to the cylindrical lens  44  and formed substantially as a semicylinder, and a convex lens  48 . The mirror is preferably formed of a total reflection dielectric multilayer film. This optical device  37  ( 38 ) makes a beam spot BS of the laser beam elliptical on the semiconductor layer  68 . Further, a concave lens  50  is preferably disposed on the upstream side of the mirror  42 . However, the optical device  37  ( 38 ) does not have to include all these elements.  
       FIG. 7  is a plan view showing an example of the device  36  of  FIGS. 4 and 5  that directs the laser beam to the optical paths  33  and  34  in a time-division manner. The device  36  includes a galvanometer mirror  52 . The galvanometer mirror  52  is a mirror driven by a motor  54  and the motor  54  is connected to a control means  58  via a drive means (driving circuit)  56 . A stage drive means (driving circuit)  60  is also connected to the control means  58 . The control means  58  controls the galvanometer mirror  52  and the stage  62  to operate them in synchronization with each other. The galvanometer mirror  52  may be substituted by a polygon mirror.  
      The laser beam reflected by the galvanometer mirror  52  is directed to the mirror  39  or  40  depending on the position of the galvanometer mirror  52 . The galvanometer mirror  52  is driven so that the laser beam is directed along the optical path  33  or  34  alternately. In  FIG. 7 , the galvanometer mirror  52  is positioned so that the laser beam is reflected toward the mirror  40 , wherein the light emitted from the laser source  32  is reflected by the galvanometer mirror  52  to enter the optical path  34  and, then, is reflected by the mirror  40  to the mirror  42  in the optical device  37  of  FIG. 6 . At the next point in time, the galvanometer mirror  52  is displaced to the position to direct the laser beam to the mirror  39 , wherein the light emitted from the laser source  32  is reflected by the galvanometer mirror  52  to enter the optical path  33  and, then, reflected by the mirror  39  to the mirror  42  in the optical device  38 . In this connection,  FIGS. 4 and 5  show the optical paths  33  and  34  oriented to the opposite directions in a straight line, whereas  FIG. 7  shows the optical paths  33  and  34  oriented to the opposite directions at an angle. The important thing is that the laser beams, reflected by the mirrors  39  and  40  respectively, are parallel to each other.  
       FIG. 8  is a perspective view showing the substrate  66  supported by the stage  62 . The stage  62  includes an X stage  62 X, a Y stage  62 Y and a rotary stage (not shown in  FIG. 8 ). The X stage  62 X is disposed on a guide (not shown) so that the X stage  62 X can be moved in the X direction and it is driven in the X direction by a driving means such as a feed screw (not shown). The Y stage  62 Y is disposed on a guide (not shown), which is, in turn, provided on the X stage  62 X, so that the Y stage  62 Y is driven in the Y direction by a driving means such as a feed screw (not shown). The rotary stage is rotatably disposed on the Y stage  62 Y and rotatably driven by a driving means (not shown).  
      A suction table  64  is mounted on the rotary stage on the Y stage  62 Y. The suction table  64  forms a vacuum suction chuck having a plurality of vacuum suction holes and vacuum passages. The substrate  66  is, for example, the mother glass  26  shown in  FIG. 3  and the semiconductor layer  68  consisting of amorphous silicon is formed on the substrate  66  by a thin film manufacturing process. A laser beam LB is condensed and applied by the optical device  37  ( 38 ) shown in  FIG. 6  to the semiconductor layer  68 .  
      Scanning is performed in the state in which the laser beam LB illuminates a fixed position while the stage  62  is moved, so a strip-like portion of the semiconductor layer  68  is illuminated by the laser beam LB. A portion of the semiconductor layer  68  of amorphous silicon illuminated by the laser beam is melted, solidified and crystallized to turn into polysilicon. Within the strip-like portion illuminated by the laser beam in the semiconductor layer  68 , there is an effective melt width where the semiconductor layer  68  is melted sufficiently, but its opposite side portions are not melted sufficiently. Here, the portion of the semiconductor layer  68  included in the effective melt width is referred to as a beam trace.  
       FIG. 9  is a diagram showing an example of overlapping beam traces. Two beam traces  70  overlap each other with the overlapping amount of “I”. “J” indicates an effective melt width. Because the CW laser has a small beam spot and, therefore, only a small area of the semiconductor layer  68  can be crystallized in one scan, so a plurality of scans are performed successively allowing the beam traces to overlap each other so that a required area of the semiconductor layer  68  is crystallized.  
      In this case, as shown in  FIG. 4 , raster scanning is performed. In raster scanning, the Y stage  62 Y is moved in one direction (the forward direction) along the Y axis, the X stage  62 X is then moved in the direction along the X axis and the Y stage  62 Y is then moved in the reverse direction (the backward direction) along the Y axis. While the region  1  of the semiconductor layer  68  is crystallized in the scanning in the one direction (the forward direction), the region  2  of the semiconductor layer  68  is crystallized in the scanning in the opposite direction (the backward direction).  
      In  FIG. 4 , the first scanning is performed as shown by arrow al in the region  1  of the semiconductor layer  68 . The second scanning is performed as shown by arrow b 1  in the region  2  of the semiconductor layer  68 . The third scanning is performed as shown by arrow a 2  in the region  1  of the semiconductor layer  68 . The fourth scanning is performed as shown by arrow b 2  in the region  2  of the semiconductor layer  68 . As described above, by repeating the scanning in the opposite directions alternately, the portion required to be crystallized in the semiconductor layer  68  is crystallized.  
      The control means  58  controls the galvanometer mirror  52  and the stage  62  to operate them in synchronization with each other. In the forward scannings a 1 , a 2  and a 3 , the device  36  operates so that the laser beam passes through the optical path  33  whereas, in the backward scannings b 1  and b 2 , the device  36  operates so that the laser beam passes through the optical path  34 .  
      Regarding the forward scannings, the beam trace formed in the semiconductor layer  68  when the stage  62  ( 62 Y) is moved in the one direction al and the beam trace formed in the semiconductor layer  68  when the stage  62  ( 62 Y) is next moved in the same direction a 2  overlap each other. Regarding the backward scannings, the beam trace formed in the semiconductor layer  68  when the stage  62  ( 62 Y) is moved in the reverse direction b 1  and the beam trace formed in the semiconductor layer  68  when the stage  62  ( 62 Y) is next moved in the same direction b 2  overlap each other. Thus, the two beam traces  70  shown in  FIG. 9  represent the beam traces in the region  1  (region  2 ).  
      In this way, the present invention includes a mechanism for switching the laser beam between the different optical systems alternately in synchronization with the forward and backward scannings, in which these optical systems comprise optical focusing systems for illuminating the regions different from each other, and a function for scanning the condensed beam traces in an overlapping manner.  
      On the other hand, regarding the successive forward and backward scannings, the beam trace formed in the semiconductor layer  68  when the stage  62  ( 62 Y) is moved in the one direction al and the beam trace formed in the semiconductor layer  68  when the stage  62  ( 62 Y) is next moved in the reverse direction b 1  opposite are spaced from each other.  
       FIG. 10  is a diagram showing an example of a meandering beam trace. “K” indicates the amount of meandering. In the recent research, it has been found that the beam trace  70  minutely meanders. That is, the stage  62  ( 62 Y) is moved linearly, in general, but the movement of the stage  62  ( 62 Y) is in fact accompanied with meandering even though the stage is controlled so that it is moved linearly and, therefore, the beam trace  70  crystallized in one scanning meanders, as shown in  FIG. 10 .  
       FIG. 11  is a diagram showing an example of overlapping beam traces when the scanning is performed according to the present invention. For example,  FIG. 11  shows a beam trace  70  when the stage  62  ( 62 Y) is moved in the one direction al in  FIG. 4  and another beam trace  70  when the stage  62  ( 62 Y) is next moved in the same direction a 2  in  FIG. 4 , wherein these two beam traces overlap each other with the overlapping amount “I”. In the case of scanning in the same direction, the meanderings are in phase and, therefore, it is possible to reduce the overlapping amount.  
       FIG. 12  is a diagram showing an example of overlapping beam traces when the forward and backward scannings are performed. For example,  FIG. 12  shows a beam trace  70  when the stage  62  ( 62 Y) is moved in the one direction al and another beam trace  70  when the stage  62  ( 62 Y) is moved in the reverse direction b 1 , with these beam traces being brought closer to each other so that they overlap each other. In this case, because of meanderings in the both beam traces  70  that may occur independently of each other, if the amount of overlap is small, a noncrystallized area  70 X may be formed between the two beam traces  70 . Thus, if there are meanderings, the overlapping amount between the two beam traces  70  must be increased and, as a result, throughput is reduced.  
      In the preferred embodiment, an amorphous silicon film is crystallized by CW laser irradiation. A CW laser beam of 532 nm wavelength is obtained by using a DPSS laser of Nd: YVO4 and its harmonics (multiple waves). For example, using an elliptical beam spot, an amorphous silicon film having a thickness of about 100 nm is scanned at a laser power of 2.5 W and a laser scan speed of 2 m/s. As shown in  FIG. 10 , in one laser trace  70 , the effective melt width “J” is 20 μm and the amount of meandering “K” is 5 μm.  
      In the reciprocating scanning shown in  FIG. 12 , the overlapping amount “I” of about 10 μm, which is the sum of the amount of meandering “K” and a positioning tolerance of about 5 μm, is required. Assuming a case in which the overlapping amount “I” can be reduced to 0 in an ideal condition with no meandering and no positioning tolerance, throughput in the reciprocating scanning shown in  FIG. 12  is reduced to (20−10)/20=0.50 with respect to that in the ideal case.  
      In contrast to this, in the scanning shown in  FIG. 11  to which the present invention is applied, it is possible to effectively use the forward and backward scanning for crystallization and one directional scanning can be applied without including the amount of meandering “K”, throughput in the scanning shown in  FIG. 11  is improved to (20−5)/20=¾=0.75 with respect to that in the ideal case in which the overlapping amount “I” can be reduced to 0.  
      When laser power is limited or the thickness of the amorphous silicon film is large, the melt width is reduced. If the melt width is 15 μm, the throughput of the reciprocating scanning is (15−10)/15=⅓=0.33 with respect to that in the ideal case, but the throughput of the scannings according to the present invention is (15−5)/15=⅔=0.66.  
      When the raster scanning is not performed but the one directional scanning only, in either the forward or backward direction, is performed, the meanderings in the beam traces of a plurality of scannings are in phase as shown in  FIG. 11  and, therefore, the overlapping amount of only 5 μm corresponding to the positional tolerance mentioned above is sufficient, even though the width of meandering is 5 μm. Therefore, the overlapping amount can be reduced as shown in  FIG. 11 . However, in the one directional scanning only in the forward direction, (or in the one directional scannings only in the backward direction) the forward beam traces can be used for crystallization but, during the backward movement, the laser beam must be blocked by a shutter, which means that the half of the scanning time is wasted and, as a result, the throughput is reduced.  
       FIG. 13  is a side view showing a laser crystallization apparatus according to another embodiment of the present invention. The laser crystallization apparatus  72  of this embodiment comprises a movable stage  62  supporting a substrate  66  having a semiconductor layer  68  formed thereon (see  FIG. 8 ), a laser source  32 , an optical device  37  for applying a laser beam emitted from the laser source  32  to the semiconductor layer  68  on the substrate  66  supported by the stage  62 , a rotary device  74  that is provided separately from the stage  62  and that can rotate the substrate  66 , and a transporting device  76  that can transport the substrate  66  at least between the stage  62  and the rotary device  74 . Further, there is provided a substrate stacker (holder)  78  formed as a transporting cart and the transporting device  76  can transport the substrate  66  between the stage  62  and the substrate stacker (holder)  78 .  
      The stage  62  includes an X stage  62 X, a Y stage  62 Y and a rotary stage  62 R. The X stage  62 X is disposed on a guide (not shown) so that the X stage  62 X can be moved in the X direction and it is driven in the X direction by a driving means such as a feed screw (not shown). The Y stage  62 Y is disposed on a guide (not shown), which is, in turn provided on the X stage  62 X, so that the Y stage  62 Y is driven in the Y direction by a driving means such as a feed screw (not shown). The rotary stage  62 R is rotatably disposed on the Y stage  62 Y and rotatably driven by a driving means (not shown). A suction table  64  (see  FIG. 8 ) is provided on the rotary stage  62 R.  
       FIG. 14  is a perspective view showing an example of the stage  62 . The X stage  62 X comprising a plurality of split plates operates at low speed and has high position resolution. The Y stage  62 Y comprising one long plate operates at high speed and has relatively low position resolution.  
      The rotary stage  62 R is made to operate precisely in the rotation range of several degrees. That is, because the transporting device  76  takes out the substrate  66  from the substrate stacker  78  in a predetermined posture and puts it on the stage  62  in the predetermined posture, there is no particular need to rotate the substrate  66  on the stage  62  in this operational range. The rotary stage  62 R is provided for fine adjustment of the position of the substrate  66 .  
      On the other hand, as shown in  FIG. 2 , when the semiconductor layer  68  is crystallized in the preripheral region  20  around the display region  18  of the liquid crystal display device, the scanning must be performed in two directions (in the C and D directions) orthogonal to each other. Therefore, the substrate  66  must be rotated by 90 degrees. In this case, if the rotary device  74  is not provided, the substrate  66  should be manually rotated and put on the rotary table  62 R. Otherwise, the rotary table  62 R must be designed so that it can be rotated 90 degrees or more but manufacturing costs will be increased significantly if the rotary stage  62 R is fabricated so that it can be rotated 90 degrees or more while having high resolution.  
      The rotary device  74  comprises a rotary stage  74 R rotatably mounted on a stationary base  74 A and further includes a driving means for rotating the rotary stage  74 R. A vacuum suction chuck is provided on the rotary stage  74 R. The rotary stage  74 R can be rotated 90 degrees or more. It is not required that the rotary stage  74 R can perform positioning operation with high accuracy.  
       FIG. 15  is a perspective view showing an example of the transporting device  76  of  FIG. 13 . The transporting device  76  is constructed as a robot comprising a base  80 , a body  82  that can be moved in a vertical direction as shown by arrow E and rotated as shown by arrow F, a parallelogram link  84  attached to the body  82 , and a fork-like arm  86 . The parallelogram link  84  is extendable and retractable as shown by arrow G. The substrate  66  is transported while it is put on the arm  86 . The rotary stage  62 R of the stage  62  and the rotary stage  74 R of the rotary device  74  have respective lifting pins (not shown) so that the arm  86  can be inserted between the substrate  66  and either the rotary stage  62 R or the rotary stage  74 R.  
      In  FIG. 13 , the transporting device  76  takes out the substrate  66  in a predetermined posture and puts it on the stage  62  in the predetermined posture. The rotary stage  62 R of the stage  62  finely adjusts the position of the substrate  66 , and the semiconductor layer  68  is crystallized, for example, along one side of the peripheral region  20  in the direction of arrow C. Then, the transporting device  76  transports the substrate  66  from the rotary stage  62 R of the stage  62  to the rotary stage  74 R of the rotary device  74 . The rotary stage  74 R is rotated with the substrate  66  by 90 degrees and, the transporting device  76  then transports the substrate  66  rotated by 90 degrees from the rotary stage  74 R of the rotary device  74  to the rotary stage  62 R of the stage  62 . The rotary stage  62 R of the stage  62  finely adjusts the position of the substrate  66 , and the semiconductor layer  68  is crystallized, for example, along another side of the peripheral region  20  in the direction of arrow D. In this manner, the semiconductor layer can be crystallized with high throughput by providing the rotary device  74  of a simple construction.  
       FIG. 16  is a schematic plan view showing a variation of the laser crystallization apparatus. The laser crystallization apparatus  90  has a beam splitting means  92  such as a half mirror for splitting a laser beam emitted from the laser source  32  into two sub-beams. For each of the sub-beams divided by the beam splitting means  92 , the laser crystallization apparatus  90  comprises the device  36  shown in  FIGS. 4 and 5  that directs the laser beam to a plurality of optical paths  33  and  34  in a time-division manner and optical devices  37  and  38  condensing and applying the laser beams passing through the optical paths  33  and  34  to the semiconductor layer  68  on the substrate supported on the stage  62 . Thus, the area of the semiconductor layer  68  crystallized simultaneously can be increased.