Abstract:
A scribing apparatus simultaneously performs scribing processes for a TFT substrate and a C/F substrate in the same location, thereby efficiently utilizing equipment spaced and achieving enhanced productivity. A substrate cutting apparatus is equipped with the scribing apparatus, and a substrate cutting method uses the substrate cutting apparatus. The scribing apparatus includes a stage for attracting a first mother substrate including first and second conjoined substrates, a scribing belt for holding a second mother substrate including conjoined third and fourth substrates, and a head unit for forming cracks in the second substrate of the first mother substrate or in the third substrate of the second mother substrate

Description:
This application claims priority under 35 U.S.C. 119 of Korean Patent Application No. P2004-89706, filed on Nov. 5, 2004 which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a scribing apparatus for a liquid crystal display that occupies little space and enhances productivity, a substrate cutting apparatus equipped with the scribing apparatus, and a substrate cutting method using the substrate cutting apparatus. 
     2. Discussion of the Related Art 
     LCD devices display a desired image by individually supplying image data signals according to liquid crystal cells arranged in a matrix array, thereby controlling respective light transmittances of the liquid crystal cells. 
     The manufacture of such LCD devices utilizes a large-area mother substrate on which thin film transistor (TFT) array substrates are formed. Another large-area mother substrate, on which color filter (C/F) substrates are formed, is used. In order to achieve an improvement in throughput, the mother substrates are joined together to simultaneously form multiple of liquid crystal panels. Then, it is necessary to perform a process to cut the joined mother substrates into unit liquid crystal panels. 
     The liquid crystal panel cutting process generally includes a scribing process to form a crack to a desired depth in a surface of a mother substrate by using a scribing wheel made of a diamond material having a hardness higher than that of the mother substrate, which is made of, for example, glass. A breaking process applies a mechanical force to the mother substrate, thereby cutting the mother substrate. 
       FIG. 1  shows a sectional view illustrating a related art LCD device. This LCD device is manufactured in accordance with the following method. For simplicity, the following description will be given only in conjunction with one pixel region. 
       FIG. 1  shows a gate electrode  11  made of a conductive material such as metal that is initially formed on a first transparent substrate  10  at a predetermined region. A gate insulating film  12  made of a silicon nitride (SiNx) or silicon oxide (SiO 2 ) is then formed over the entire upper surface of the first substrate  10  including the gate electrode  11 . 
     Thereafter, an active layer  13  made of amorphous silicon is formed on the gate insulating film  12  at a region corresponding to the gate electrode  11 . An ohmic contact layer  14  is formed on the active layer  13  at regions corresponding to respective lateral edge portions of the active layer  13 . The ohmic contact layer  14  is formed from doped amorphous silicon. 
     Source and drain electrodes  15  and  16  are made of a conductive material such as metal and are subsequently formed on the ohmic contact layer  14 . The gate electrode  11  together with the source and drain electrodes  15  and  16  constitute a thin film transistor T. 
     Although not shown, the gate electrode  11  connects to a gate line, and the source electrode  15  connects to a data line. The gate line and data line cross each other and define a pixel region. 
     A protective film  17  is then formed over the entire upper surface of the first substrate  10  including the source and drain electrodes  15  and  16 . The protective film  17  is made from silicon nitride, silicon oxide, or an organic insulating material. The protective film  17  has a contact hole  18  that exposes a predetermined portion of the surface of the drain electrode  16 . 
     Thereafter, a pixel electrode  19  made of a transparent conductive material is formed on the protective film  17  at the pixel region. The pixel electrode  19  connects to the drain electrode  16  via the contact hole  18 . 
     A first orientation film  20  is then formed over the entire upper surface of the first substrate  10  including the pixel electrode  19 . The first orientation film  20  is made of, for example, polyimide, and has a surface on which the molecules of the first orientation film  20  orient in a predetermined direction. 
     A second transparent substrate  31  is arranged over the first substrate  10  while being vertically spaced apart from the first substrate  10  by a predetermined distance. 
     A black matrix  32  is formed on a lower surface of the second substrate  31  at a region corresponding to the thin film transistor T of the first substrate  10 . Although not shown, the black matrix  32  also covers a region other than the pixel electrode  19 . 
     A color filter  33  is then formed on the second substrate  31  beneath the black matrix  32 . Color filters are usually arranged in the form of repeated filter patterns of red (R), green (G), and blue (B), each of which corresponds to one pixel region. 
     A common electrode  34  made of a transparent conductive material is subsequently formed on the second substrate  31  beneath the color filter  33 . A second orientation film  35  is then formed on the second substrate  31  beneath the common electrode  34 . The second orientation film  35  is made of, for example, polyimide, and has a surface on which the molecules of the second orientation film  35  orient in a predetermined direction. 
     The first orientation film  20  and the second orientation film  35 A seal a liquid crystal layer  40  between them. 
     Manufacturing the above-described LCD device uses an array substrate fabrication process involving the formation of thin film transistors and pixel electrodes on a substrate to fabricate an array substrate, a color filter substrate fabrication process involving formation of color filters and a common electrode on another substrate to fabricate a color filter substrate, a liquid crystal panel fabrication process involving arrangement of the fabricated substrates, injection and sealing of a liquid crystal material, and attachment of polarizing plates to fabricate a liquid crystal panel. 
       FIG. 2  shows a flow chart illustrating a related art LCD manufacturing method. 
       FIG. 2  shows that in this method, a thin film transistor (TFT) array substrate including TFTs, and a color filter substrate including color filters are first prepared (S 1 ). 
     The TFT array substrate is fabricated by repeatedly performing processes of depositing a thin film and pattering the deposited thin film. In this case, the number of masks used for patterning of thin films in the fabrication of the TFT array substrate corresponds to the number of processes used in the fabrication of the TFT array substrate. Currently, research is underway to reduce the number of masks to thus reduce the manufacturing costs. 
     The color filter substrate is fabricated by sequentially forming a black matrix for preventing light from leaking through a region other than pixel regions, R, G, and B color filters, and the common electrode. The color filters may be formed using a dyeing method, a printing method, a pigment dispersion method, an electro-deposition method, or the like. Currently, the pigment dispersion method finds wide use. 
     Afterwards, an orientation film is formed over each substrate to determine the initial alignment direction of the liquid crystal molecules (S 2 ). 
     Coating a polymer thin film, and treating the surface of the polymer thin film such that the molecules of the polymer thin film on the treated surface orient in a predetermined direction form the orientation film. Generally, polyimide-based organic materials are used for the orientation film. For the orientation method, a rubbing method is generally used. 
     In the rubbing method, the orientation film is rubbed in a predetermined direction using a rubbing cloth. This rubbing method is suitable for mass production because of the ease of the orientation treatment. Also, the rubbing method advantageously achieves stable orientation and easy control of the pretilt angle. 
     An optical orientation method has recently been developed and practically used that achieves orientation using polarized beams. 
     Next, a seal pattern is formed at one of the two substrates (S 3 ). The seal pattern is arranged around the region where the image is to be displayed. The seal pattern has a port for injection of a liquid crystal material, and the seal pattern prevents the injected liquid crystal material from leaking. 
     The seal pattern is made by forming a thermosetting resin layer having a predetermined pattern. A screen printing method uses a screen mask. A seal dispenser method using a dispenser may be used. 
     The screen printing method, which has process convenience, is mainly used. However, the screen printing method also has drawbacks in that poor quality product may be produced because the screen mask may come into contact with the orientation film. Furthermore, the screen mask cannot easily cope with increasing substrate sizes. For this reason, there is a gradual substitution of a seal dispenser method for the screen printing method. 
     Subsequently, spacers of a predetermined size are sprayed on one of the either TFT array substrate or the color filter substrate to maintain an accurate and uniform space between the two substrates (S 4 ). 
     The methods for spraying spacers include a wet spray method where spacer material is sprayed while being mixed with alcohol, and a dry spray method where spacer material is sprayed undiluted. For the dry spray method, there includes an electrostatic spray method using static electricity, and an ionic spray method using pressurized gas. Since LCDs are easily damaged by static electricity, the ionic spray method is mainly used. 
     Thereafter, the two substrates of the LCD, i.e., the TFT array substrate and color filter substrate, are arranged such that the seal pattern becomes interposed between the substrates. In this state, the seal pattern is cured under pressure to join the substrates (S 5 ). In this case, the orientation films of the substrates face each other, and the pixel electrodes and color filters have a one-to-one correspondence. 
     Next, the joined substrates are cut into single liquid crystal panels (S 6 ). 
     Multiple liquid crystal panels, each of which will become one LCD device, are generally formed on one substrate sheet and are then separated into individual panels in order enhance manufacturing efficiency and reduce manufacturing costs. 
     The liquid crystal panel cutting process includes a scribing process to form a crack in a surface of each substrate using a scribing wheel made of a diamond material having a hardness higher than that of the substrate. The substrate can be made of, for example, glass. Then, a breaking process positions a breaking bar at a portion of the substrate where the crack is formed and applies a predetermined pressure to the breaking bar, thereby cutting the substrate in the direction along which the crack extends. 
     Subsequently, a liquid crystal material is injected between the two substrates of each liquid crystal panel (S 7 ). A vacuum injection method that utilizes a pressure difference between the interior and exterior of the liquid crystal panel is mainly used to inject the liquid crystal material. Micro air bubbles may be present in the liquid crystal material injected into the interior of the liquid crystal panel, and bubbles may thus be present in the interior of the liquid crystal panel, thereby causing the liquid crystal panel to have poor quality. In order to prevent such a problem, it is accordingly necessary to perform a de-bubbling process in which the liquid crystal is maintained under a vacuum for a prolonged time to remove bubbles by outgassing. 
     After the liquid crystal injection is complete, the injection port is sealed to prevent the liquid crystal from leaking out through the injection port. Coating an ultraviolet-setting resin over the injection port, and irradiating ultraviolet light at the coated resin to thereby set the coated resin achieve sealing the injection port. 
     Next, polarizing plates are attached to the outer surfaces of the liquid crystal panel, and driving circuits are then connected to the liquid crystal panel. Thus, an LCD device is completely manufactured (S 8 ). 
       FIGS. 3A to 3F  illustrate sequential steps of a related art process for cutting a mother substrate for separating the mother substrate into unit liquid crystal panels, using a related art substrate cutting apparatus, through sectional views and plan views. 
     The process for cutting a joined mother substrate (scribing and breaking processes) is usually carried out by using a substrate cutting apparatus. In  FIGS. 3A to 3F , a mother substrate (1,000 mm×1,200 mm) is illustrated on which six 18.1″ liquid crystal panels are arranged. 
     In the cutting process, a joined mother substrate  52  is first loaded on a table  51  included in a loader, as shown in  FIG. 3A . 
     The joined mother substrate  52  includes a TFT substrate  52   a  and a color filter (C/F) substrate  52   b.    
     In  FIG. 3A , the upper figure shows a sectional view illustrating the mother substrate  52  loaded on the table  51 , and the lower figure is a plan view illustrating the mother substrate  52  on the table  51  when viewed from the top. 
       FIG. 3B  shows that the mother substrate  52  is then inverted so that the TFT substrate  52   a  of the mother substrate  52  faces upward. 
     Then, a wheel  53  is aligned along a selected separation line on the TFT substrate  52   a . The wheel  53  is made of a diamond material having a hardness higher than that of the material of the substrate, for example, glass. The wheel  53  is then moved along the separation line while rotating to form a crack having a predetermined depth and extending in a long or short-axis direction (indicated by arrows in the drawing). This operation is repeated until cracks corresponding to all separation lines on the TFT substrate  52   a  are formed. 
     Thereafter, the mother substrate  52  is inverted such that the C/F substrate  52   b  of the mother substrate  52  faces upward, as shown in  FIG. 3C . A breaking bar  54  is then arranged on the C/F substrate  52   b.    
     Subsequently, a predetermined pressure is applied by the breaking bar  54 , thereby completely opening the cracks. As a result, the TFT substrate  52   a  cuts along the cracks, so that the TFT substrate  52   a  separates into unit liquid crystal panels. 
     Next, the wheel  53  is aligned with a selected separation line on the C/F substrate  52   b , as shown in  FIG. 3D . 
     The wheel  53  is then moved along the separation line while rotating to form a crack having a predetermined depth and extending in a long or short-axis direction (indicated by arrows in the drawing). This operation is repeated until cracks corresponding to all separation lines on the C/F substrate  52   b  are formed. 
     Thereafter, the mother substrate  52  is then inverted such that the TFT substrate  52   a  of the mother substrate  52  faces upward, as shown in  FIG. 3E . The breaking bar  54  is then arranged on the TFT substrate  52   a  of the inverted mother substrate  52 . A predetermined pressure is then applied to the breaking bar  54  to thereby cause the C/F substrate  52   b  to separate into the unit liquid crystal panels. 
     As shown in  FIG. 3F , separated pieces of the mother substrate corresponding to respective unit liquid crystal panels are then unloaded. That is, the separated substrate pieces are simultaneously lifted from the table  51  by using a suction cup assembly (not shown). The substrate pieces are then fed to a station for subsequent processing. 
       FIG. 4  illustrates the arrangement of scribing and breaking devices included in the conventional substrate cutting apparatus. 
       FIG. 4  shows the related art substrate cutting apparatus that includes a loader  70  for receiving a mother substrate, where the mother substrate includes a TFT substrate  60  and a C/F substrate  65  joined together. The mother substrate is loaded while being seated on the loader  70 . A first scriber  71  forms cracks in the mother substrate seated on the loader  70  along separation lines on the TFT substrate  60  of the mother substrate. A first breaker  72  applies a force to the cracks formed by the first scriber  71  at the side of the mother substrate opposite to the TFT substrate  60 , thereby cutting the TFT substrate  60 . The substrate cutting apparatus also includes a second scriber  73  for forming cracks in the mother substrate seated on the loader  70  along separation lines on the C/F substrate  65  of the mother substrate. A second breaker  74  applies a force to the cracks formed by the second scriber  73  at the side of the mother substrate opposite to the C/F substrate  65 , thereby cutting the C/F substrate  65  to completely separate the mother substrate into substrate pieces corresponding to unit liquid crystal panels. The substrate cutting apparatus further includes a suction cup assembly  75  for simultaneously lifting and feeding the separated substrate pieces, a separation table  76  for separating the separated substrate pieces from the suction cup assembly  75 , and an unloader  77  for transferring the separated substrate pieces from the separation table  76  to a station for subsequent processing. 
     The suction cup assembly  75  moves between the second breaker  74  and the separation table  76  to feed the substrate pieces, i.e., the unit liquid crystal panels, completely separated by the second breaker  74  to the separation table  76 . The substrate cutting apparatus further includes conveying rollers  78  and a robot  79  to feed the mother substrate to a desired station during the scribing and breaking processes. 
     However, the above-described related art substrate cutting apparatus and method have numerous problems. 
     That is, the recent trend of LCD devices is to provide a larger display, so that it is necessary to use scribing and breaking devices adapted to an increased size for the processing of larger substrates. As a result, these large scale scribing and breaking devices must occupy a large part of a clean room. To this end, scribing and breaking processes for cutting of TFT and C/F substrates are respectively carried out at different locations. As a result, excessive space is required and the productivity degrades. 
     SUMMARY OF THE INVENTION 
     Accordingly, the invention is directed to a scribing apparatus, a substrate cutting apparatus equipped with the scribing apparatus, and a substrate cutting method using the substrate cutting apparatus that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     One object of the invention, in part, is to provide a scribing apparatus that may simultaneously perform scribing processes for a TFT substrate and a C/F substrate in the same location, thereby efficiently securing a space for occupation of equipment and achieving enhanced productivity. A substrate cutting apparatus may be equipped with the scribing apparatus, and a substrate cutting method may use the substrate cutting apparatus. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     The invention, in part, pertains to a scribing apparatus that includes a stage for attracting a first mother substrate including conjoined first and second substrates; a scribing belt for holding a second mother substrate including conjoined third and fourth substrates; and a head unit for forming cracks in the second substrate of the first mother substrate or in the third substrate of the second mother substrate. 
     The invention, in part, pertains to a substrate cutting apparatus that includes a feeding robot for feeding a mother substrate that includes a conjoined first substrate and second substrate; a substrate conveyer for conveying the mother substrate fed from the feeding robot; a scriber for forming cracks having a predetermined depth in the first or second substrate of the mother substrate conveyed by the substrate conveyor along separation lines on the first or second substrate; a breaker for receiving the crack-formed mother substrate from the scriber, and separating the mother substrate into unit liquid crystal panels; and a panel inverter for inverting the separated liquid crystal panels. 
     The invention, in part, pertains to a substrate cutting method that includes placing a first mother substrate including first and second conjoined substrates over a vertically and laterally movable stage. The stage is fed to a scriber that forms first cracks in the second substrate of the first mother substrate along separation lines. Then the stage returns to an original position, a conveyor belt moves upward, and first mother substrate transfers to the conveyor belt. The conveyor belt moves downward, transferring the first mother substrate to a scribing belt of the scriber, and forming second cracks in the first substrate of the first mother substrate along separation lines. Then, the first mother substrate formed with the first and second cracks is fed to a breaking belt that separates the first mother substrate into unit liquid crystal panels. 
     It is to be understood that both the foregoing general description and the following detailed description of the invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  shows a sectional view illustrating a related art LCD device; 
         FIG. 2  shows a flow chart illustrating a related art LCD manufacturing method; 
         FIGS. 3A to 3F  illustrate sequential steps of a process for cutting a mother substrate for separation of the mother substrate into unit liquid crystal panels, using a related art substrate cutting apparatus, through sectional views and plan views; 
         FIG. 4  illustrates the arrangement of scribing and breaking devices included in a related art substrate cutting apparatus; 
         FIG. 5  shows a schematic view illustrating a scribing apparatus according to a preferred embodiment of the invention; 
         FIG. 6  shows a schematic view illustrating a substrate cutting apparatus according to a preferred embodiment of the invention; and 
         FIGS. 7A to 7H  show schematic views explaining a substrate cutting method carried out using the substrate cutting apparatus having the configuration of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 5  shows a schematic view illustrating a scribing apparatus according to a preferred embodiment of the invention. 
       FIG. 5  shows a scribing apparatus that includes a stage  110  for fixing first mother substrate  100  that includes a TFT substrate  100   a  and a C/F substrate  100   b  bonded to each other. The first mother substrate  100  is fixed in the stage  110  having the C/F substrate  100   b  downwardly exposed. The scribing apparatus also includes a scribing belt  120  for holding a second mother substrate  200  that includes a TFT substrate  200   a  and a C/F substrate  220   b  bonded to each other. The second mother substrate  200  is placed on the scribing belt  120  such that the TFT substrate  200   a  is upwardly exposed. The scribing apparatus further includes a head unit  130  for selectively irradiating a laser at the C/F substrate  100   b  of the first mother substrate  100  or the TFT substrate  200   a  of the second mother substrate  200 , thereby forming cracks having a predetermined depth. A laser generator  140  generates the laser beam, and directs the generated laser light to the head unit  130 . 
     The head unit  130  includes a first head  130   a  for forming cracks having a predetermined depth in the C/F substrate  100   b  of the first mother substrate  100 . A second head  130   b  for forms cracks having a predetermined depth in the TFT substrate  200   a  of the second mother substrate  200 . 
     The scribing apparatus also includes a reflector  150  for controlling the direction of the laser beam generated by the laser generator  140  to cause the laser beam to selectively irradiate through the first head  130   a  or second head  130   b . Also, the laser can irradiate through both heads simultaneously. 
     The reflector  150  includes a controller (not shown) to control the direction of the laser to selectively form cracks on the first mother substrate  100  or second mother substrate  200 . 
     Also, the first mother substrate  100  is fixed in the stage  110  having the C/F substrate  100   b  downwardly exposed. The scribing belt  120  holds the first mother substrate  100  such that the TFT substrate  100   a  of the first mother substrate  100  is upwardly exposed. The head unit  130  selectively irradiates the laser at the C/F substrate  100   b  of the first mother substrate  100  or the TFT substrate  100   a  of the first mother substrate  100 , thereby forming cracks having a predetermined depth. 
     The first head  130   a  forms cracks having a predetermined depth in the C/F substrate  100   b  of the first mother substrate  100  fixed in the stage  110 . The second head  130   b  forms cracks having a predetermined depth in the TFT substrate  100   a  of the first mother substrate  100  placed on the scribing belt  120 . 
     Meanwhile, the head unit  130  may be rotatable through an angle of 180°. In this case, the head unit  130  is rotated in accordance with a control signal from the controller so as to form cracks having a predetermined depth on a selected one of the first and second mother substrates  100  and  200  loaded on the scribing apparatus. 
     Although the head unit  130  has been described as a head unit adapted to irradiate a laser in the illustrated preferred embodiment of the invention, a head unit equipped with a diamond wheel may be used. Alternately, any appropriate scribing and cutting device may be used. 
       FIG. 6  illustrates a substrate cutting apparatus according to a preferred embodiment of the invention. 
       FIG. 6  shows a substrate cutting apparatus that includes a feeding robot  310  for feeding a mother substrate  300  that includes a TFT substrate  300   a  and a C/F substrate  300   b  joined to each other. A substrate conveyer  320  conveys the mother substrate  300  fed from the feeding robot  310 . The substrate cutting apparatus also includes a scriber  330  for forming cracks having a predetermined depth in the TFT substrate  300   a  and C/F substrate  300   b  of the mother substrate  300 , which is conveyed by the substrate conveyor  320  along separation lines on the TFT substrate  300   a  and C/F substrate  300   b . A breaker  340  receives the scribed mother substrate  300  from the scriber  330 , and the breaker  340  separates the mother substrate  300  into unit liquid crystal panels. Also, a panel inverter  350  inverts the separated liquid crystal panels. 
     A stage  321  is arranged over the substrate conveyor  320 . The stage  321  uses a vacuum to attract and adhere the mother substrate  300  fed by the feeding robot  310 , so as to fix the mother substrate  300 . The stage  321  is reciprocally laterally movable between a position over the substrate conveyor  320  and a position over the scriber  330  along a movement path  322 . The stage  321  is also vertically movable. 
     A conveyor belt  323  is arranged beneath the substrate conveyor  320 . The conveyor belt  323  vertically moves to receive the mother substrate  300 . The scriber  330  includes a scribing belt  331  for receiving the mother substrate  300  from the conveyor belt  323 . The scriber  330  moves the mother substrate  300  during the scribing process so that the mother substrate  300  is scribed. 
     A head unit  332  is arranged between the scribing belt  331  of the scriber  330  and the movement path  322  of the stage  321 . The head unit  332  is adapted to form cracks having a predetermined depth in the TFT substrate  300   a  and C/F substrate  300   b  of the mother substrate  300  along separation lines on the TFT substrate  300   a  and C/F substrate  300   b.    
     The head unit  332  is rotatable through an angle of 180°. Accordingly, the head unit  332  can form cracks having a predetermined depth in the C/F substrate  300   b  of the mother substrate  300 , which is adhering to the stage  321 , or the head unit  332  can form cracks having a predetermined depth in the TFT substrate  300   a  of the mother substrate  300  that is laid on the scribing belt  331 . 
     The head unit  332  may include a wheel made of a diamond material, may include a head adapted to irradiate a laser or may include any other appropriate scribing device. 
     Alternatively, the head unit  332  may include a first head  332   a  and a second head  332   b . In this case, the first head  332   a  forms cracks having a predetermined depth in the C/F substrate  300   b  of the mother substrate  300 , which is adhering to the stage  321 . The second head  130   b  forms cracks having a predetermined depth in the TFT substrate  300   a  of the mother substrate  300 , which is placed on the scribing belt  331 . 
     The head unit  332  connects to an external laser generator  360  that generates a laser beam. Accordingly, the head unit  332  receives a laser beam generated by the laser generator  360  and selectively irradiates through the first head  332   a  or second head  332   b  to thereby form cracks on the TFT substrate  300   a  or C/F substrate  300   b  of the mother substrate  300 . 
     The substrate cutting apparatus may further include a reflector  370  for controlling the direction of the laser beam generated by the laser generator  360  to cause the laser beam to selectively irradiate through the first head  332   a  or second head  332   b.    
     The reflector  370  may be controlled in accordance with an external control signal to cause the laser to be selectively irradiated through the first head  332   a  or second head  332   b , thereby causing cracks to be selectively formed on different mother substrates. 
     The breaker  340  includes a breaking belt  341  for receiving and holding the mother substrate  300  fed from the scribing belt  331 . A hot steam nozzle unit  342  for injects hot steam at the mother substrate  300  lying on the breaking belt  341 , thereby separating the mother substrate  300  into unit liquid crystal panels. The nozzle unit  342  is not restricted to steam, and any appropriate gas having sufficient heat capacity can be used. 
       FIGS. 7A to 7H  show schematic views explaining a substrate cutting method carried out using the substrate cutting apparatus having the configuration of  FIG. 6 . 
     In substrate cutting method according to a preferred embodiment of the invention, a first mother substrate  300 , which includes a conjoined TFT substrate  300   a  and a C/F substrate  300   b , is first fed to the substrate conveyor  320  using the feeding robot  310 , as shown in  FIG. 7A . 
     Afterwards, the stage  321 , which is vertically and laterally movable, is moved downward to the first mother substrate  300  fed to the substrate conveyor  320  by the feeding robot  310 . The stage  321  then picks up the first mother substrate  300  by using a vacuum, and moves the first mother substrate  300  upward, as shown in  FIG. 7B . 
     As shown in  FIG. 7C , the stage  321 , to which the first mother substrate  300  is vacuum-adhered, subsequently moves along the movement path  322  to feed the first mother substrate  300  to the scriber  330 . 
     Next, in the scriber  330 , to which the first mother substrate  300  has been fed along the movement path  322 , a laser beam irradiates through the first head  332   a  to the C/F substrate  300   b  of the first mother substrate  300  along the separation lines on the C/F substrate  300   b , thereby forming cracks having a predetermined depth in the C/F substrate  300   b . During this exposure process, the substrate  300   b  does not contact the stage  321 . 
     When using laser energy to form the cracks, a laser generated from the external laser generator  360  is used. The laser is also controlled to irradiate through the first head  332   a  by manipulating the reflector  370 . 
     Although utilization of a laser has been described in the illustrated preferred embodiment of the invention, cracks, i.e., scribes, may be formed using a wheel made of a diamond material. 
       FIG. 7D  shows that after completion of the scribing process for the C/F substrate  300   b  of the first mother substrate  300 , the stage  321  returns to an original position while the first mother substrate  300  remains attached to the stage  321 . 
     Following the return to the original position, the stage  321  moves upwardly above the conveyor belt  323  of the substrate conveyor  320 . While in this state, the feeding robot  310  is ready to load a second mother substrate  400  that includes a conjoined TFT substrate  400   a  and C/F substrate  400   b.    
     Thereafter, the conveyor belt  323  moves upward, as shown in  FIG. 7E . The stage  321  then releases (turns off) the suction force applied to the first mother substrate  300 , thereby causing the first mother substrate  300  to lie on the conveyor belt  323 . 
       FIG. 7F  shows that the conveyor belt  321  subsequently moves downwardly to transfer the first mother substrate  300  to the scribing belt  331  of the scriber  330 . 
     Next, in the scriber  330  where the first mother substrate  300  is laid on the scribing belt  331 , a laser irradiates through the second head  332   b  to the TFT substrate  300   a  of the first mother substrate  300  along the separation lines on the TFT substrate  300   a . Cracks are thereby formed having a predetermined depth in the TFT substrate  300   a.    
     Although the formation of cracks has been described as being achieved by using the first and second heads  332   a  and  332   b  in the illustrated preferred embodiment of the invention, cracks may also be formed on the substrate attracted to the stage  321  and the substrate laid on the scribing belt  331  by using a single head unit that can rotate through an angle of 180°. 
     Next, the feeding robot  310  loads the second mother substrate  400  onto the substrate conveyor  320 . The stage  321  of the substrate conveyor  320  then moves downward and picks up the second mother substrate  400  by using a vacuum. Meanwhile, the first mother substrate  300 , for which the process of scribing the TFT substrate  300   a  and C/F substrate  300   b  has been completed, is transferred to the breaking belt  341  of the breaker  340  by using a feeding operation of the scribing belt  331 , as shown in  FIG. 7G . 
     The stage  321 , to which the second mother substrate  400  is attracted, is subsequently fed to the scriber  330  along the movement path  322 . In the scriber  330 , a laser irradiates through the first head  332   a  to the C/F substrate  400   b  of the second mother substrate  400  along the separation lines on the C/F substrate  400   b . Cracks are thereby formed having a predetermined depth in the C/F substrate  400   b.    
     Meanwhile, a hot gas, preferably hot steam, is injected over the entire surface of the first mother substrate  300  fed to the breaker  340 , through the nozzle unit  342 , thereby separating the first mother substrate  300  into unit liquid crystal panels. 
       FIG. 7H  shows the first mother substrate  300 , for which the breaking process has been completed, being fed to the panel inverter  350 . Unnecessary separated substrate pieces are dropped into a storage unit  380  arranged at one side of the panel inverter  350 . 
     Subsequently, the feeding robot  310  is ready to load a third mother substrate  500  that includes a TFT substrate  500   a  and a C/F substrate  500   b  joined together. 
     In accordance with the invention, one may perform scribing processes for the TFT substrate of one mother substrate and the C/F substrates of another mother substrate in the scriber  330 , respectively, as the operations of  FIGS. 7A to 7H  are repeated. It is accordingly possible to remarkably reduce the area occupied by the scriber, as compared to related art technology. 
     The type of laser used for the laser generator  360  is not restricted, and a CO 2  laser, YAG laser, femtosecond laser or the like may be used. 
     As is apparent from the above description, the scribing apparatus, the substrate cutting apparatus equipped with the scribing apparatus, and the substrate cutting method using the substrate cutting apparatus according to the invention have numerous beneficial effects. 
     Namely, the invention renders it possible to use a single scriber to form cracks on a TFT substrate and a C/F substrate that are included in two identical mother substrates, respectively. Accordingly, it is possible to install an increased number of processing elements in a clean room that has a constant volume. One can thus secure space for equipment for the final cell processing in the clean room. As a result, an improved utilization of the clean room is achieved. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the spirit or scope of the inventions. Thus, it is intended that the invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.