Abstract:
A substrate transfer processing apparatus capable of processing a substrate at high speed is provided. A mounting table on which a substrate is mounted includes a plate-shaped main body and a recessed part formed in a rear surface of the plate-shaped main body. Since the mounting table is lightweight as compared to the mounting table before the recessed part is formed therein, the load on a motor is small and the running cost is low even when the mounting table is moved at high speed. Because the plate-shaped main body is made of granite, the mounting surface can be made flat and smooth by polishing. Since the mounting surface is flat and smooth, the accuracy in positioning the substrate is high.

Description:
This application is a continuation of International Application No. PCT/JP2009/054857 filed Mar. 13, 2009, which claims priority to Japanese Patent Document No. 2008-071479, filed on Mar. 19, 2008. The entire disclosures of the prior applications are herein incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present invention relates to processing apparatuses which perform a substrate processing while transferring a substrate. 
     Conventionally, a substrate transfer apparatus (such as, a moving stage) has been used in performing a substrate processing while moving a processing unit such as a print head, and a substrate relative to each other. 
     In such a substrate transfer apparatus, the flatness and smoothness of a mounting surface for mounting a substrate is required in order to control a positional relationship between the processing unit and the substrate with high accuracy. Conventionally, the required flatness was around 100 μm, while in recent years a higher flatness (50 μm or less) has been required. 
     A method is known wherein a material (such as, granite) having a high hardness, is polished to form a substrate-mounting table. 
     However, granite is heavy in weight, and in order to move the substrate-mounting table at a high speed, a high-power moving unit and a control unit are required, thereby resulting in an increase in equipment cost and running cost (driving power or the like). Moreover, with an increase in the size of the substrate in recent years, the size of the mounting table has also increased; and thus, a reduction in the weight of the mounting table has been further required. 
     If the thickness of the mounting table made of granite is reduced, the strength of the mounting table decreases although the weight thereof can be reduced. Moreover, if the mounting table is thinned, the mounting table will bend when the mounting table is supported by a support shaft which is disposed upright on an air bearing (or wheel). 
     In order to improve the flatness of the mounting surface, prior to attaching the mounting table to the support shaft, the mounting table is usually disposed in a processing table, which is wider than the mounting table so as to polish the mounting surface. However, even if the flatness of the mounting surface is set 50 μm or smaller by polishing, and when the mounting table bends due to its attachment to the support shaft, the flatness of the mounting surface will exceed 50 μm. 
     Such problems are disclosed in, for example, JPA No. 07-311375 and JPA No. 2005-114882. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above-described problems. An object of the present invention is to provide a light-weight mounting table having high surface flatness. 
     In order to solve the above-described problems, according to an aspect of the present invention, a substrate transfer processing apparatus comprises a track for a substrate, a travel device for a substrate which moves along the track for a substrate and a mounting table which is attached to the travel device for a substrate and a substrate is disposed on a surface of the mounting table. The mounting table includes a plate-shaped main body made of granite and at least one recessed part which is formed by excavating a rear surface of the plate-shaped main body, and the mounting table is supported outside the recessed part, and the substrate is disposed on a surface of the plate-shaped main body opposite to a surface in which the recessed part is formed. 
     According to another aspect of the present invention, a substrate transfer processing apparatus further comprises a track for processing, a travel device for processing which moves along the track for processing and a processing unit attached to the travel device for processing, each of the track for a substrate and the track for processing being linear-shaped. A direction in which the track for a substrate extends and a direction in which the track for processing extends are perpendicular to each other; and an area where the substrate moves and an area where the processing unit moves overlap with each other. 
     According to yet another aspect of the present invention, there is provided a substrate transfer processing apparatus, wherein the processing unit includes a print head, and wherein the print head includes a discharge orifice which discharges a processing liquid toward the substrate disposed on the mounting table. 
     According to yet another aspect of the present invention, there is provided a substrate transfer processing apparatus such that the processing unit is an inspection unit for inspecting the substrate disposed on the mounting table. 
     The substrate transfer processing apparatus of the present invention is configured as described above, and the mounting table is lightweight as compared to a mounting table of which the recessed part is not formed because of the weight of the formed recessed part; and the equipment cost and running cost of a moving device for moving the mounting table are low. 
     Because a protruding part (rib) remains around the recessed part, the strength of the mounting table is higher than a case where the board thickness of the mounting table is simply reduced. 
     If the recessed part is formed in the mounting table, the mounting table is likely to bend when the mounting table is supported by a supporting member, as compared to a case where the recessed part is not formed. If the mounting table is left in the same state such that the mounting table is supported by the supporting member, and the surface of the mounting table on which a substrate is disposed is polished so as to be flat. Then, the surface of the mounting table is flat when the mounting table is actually supported by the supporting member. 
     Since the mounting table is lightweight, the mounting table can be easily handled and the facility cost and running cost of the moving device for moving the mounting table are also low. The strength of the mounting table is high as compared to a case where the thickness is simply reduced. Since the mounting table is made of granite, a flat and smooth mounting surface can be formed by polishing. Since the mounting surface is flat, the positional relationship between a substrate and the processing unit can be controlled with high accuracy and a desired position of the substrate can be processed accurately. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating an example of a substrate transfer processing apparatus of the present invention. 
         FIG. 2  is a cross-sectional view illustrating the example of the substrate transfer processing apparatus of the present invention. 
         FIG. 3  is a plan view illustrating a first example of a mounting table. 
         FIG. 4  is a plan view illustrating a second example of the mounting table. 
         FIG. 5  is a plan view illustrating a third example of the mounting table. 
         FIGS. 6(   a ) to  6 ( e ) are cross-sectional views illustrating the steps of manufacturing the mounting table. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a plan view of a substrate transfer processing apparatus  1  which is an example of a processing apparatus of the present invention; and  FIG. 2  is a cross-sectional view along line A-A of  FIG. 1 . 
     The substrate transfer processing apparatus  1  includes a pedestal  10 , a track  11  for a substrate disposed on the pedestal  10 , a travel device  21  for a substrate disposed on the track  11  for a substrate, and a mounting table  40  attached to the travel device  21  for a substrate. 
     Each track  11  for a substrate includes at least one rail  15 . 
     The rail  15  of the track  11  for a substrate linearly extends on the surface of the pedestal  10 . If the number of rails  15  of the track  11  for a substrate is two or more, the extension directions of the respective rails  15  are parallel to each other. 
     The travel device  21  for a substrate includes an air bearing  23  disposed on the rail  15  and a support shaft (support member)  25  having a lower end which is attached to the air bearing  23 . 
     The number of air bearings  23  is three or more, and one or more air bearings  23  are disposed in each rail  15 . 
     Accordingly, the number of support shafts  25  is also at least three, and at least one support shaft  25  is disposed above the rail  15 . 
     The mounting table  40  is attached in contact with the upper ends of three or more support shafts  25 , and is supported above the rail  15  by the support shaft  25 . 
     The air bearing  23  is connected to a gas supply system  17  (such as, an air compressor); and the gas of the gas supply system  17  is supplied to the air bearing  23 . 
     An ejection hole (not shown) is provided in the surface of the air bearing  23  on the rail  15  side; and the gas supplied to the air bearing  23  is ejected from the ejection hole toward the surface of the rail  15  so that the air bearing  23  floats from the rail  15  and the mounting table  40  floats while being supported by the support shaft  25 . 
     The surface of the rail  15  on which the air bearing  23  is disposed is horizontal. The gas supply amount of the gas supply system  17  is set so that each of the lower ends of the respective air bearings  23  floats by the same distance from the surface of the rail  15 . 
     The height from the lower end of each air bearing  23  to the upper end of the support shaft  25  is set to be identical; and accordingly, the upper end of the support shaft  25  (i.e., a portion where the support shaft  25  is in contact with the mounting table  40 ) is located within a horizontal plane parallel to the surface of the rail  15 . 
     The mounting table  40  includes a plate-shaped main body  41  and a recessed part  45  formed in one surface (rear surface  47 ) of the plate-shaped main body  41 , with a front surface (mounting surface  46 ) directed upward and the rear surface  47  directed downward; and the upper end of the support shaft  25  is attached in contact with the outer portion (the protruding part around the recessed part: rib) of the recessed part  45  in the rear surface  47 . 
     Even if the mounting table  40  bends when the mounting table  40  is supported by the support shaft  25 , the mounting surface  46  becomes flat as discussed later. Here, the mounting surface  46  is horizontal and the substrate  7  is horizontally disposed in close contact with the mounting surface  46 . 
     A groove  42  is formed in an area of the mounting surface  46  where the substrate  7  is disposed; and the substrate  7  is in close contact with an outer portion of the groove  42  of the mounting surface  46  so that the opening of the groove  42  is covered with the substrate  7 . The internal space of the groove  42  is connected to an exhaust system (not shown); and if the interior of the groove  42  is evacuated by the exhaust system, the substrate  7  is sucked to the mounting surface  46  due to a pressure difference. 
     The travel device  21  for a substrate travels by a moving device  31  while the mounting table  40  is horizontally supported. The moving device  31  includes a stationary magnet unit  33  and a movable magnet unit  35 , for example. The stationary magnet unit  33  includes a plurality of magnets disposed along the extension direction of the rail  15 ; and magnetic poles with different polarities are formed on the surfaces of adjacent magnets to each other. 
     The movable magnet unit  35  (motor coil) is attached to the mounting table  40 . The movable magnet unit  35  faces a part of the stationary magnet unit  33 . If an AC voltage is applied to the movable magnet unit  35  in a state such that the mounting table  40  is floated, the mounting table  40  moves along the extension direction of the track  11  for a substrate above the track  11  for a substrate. 
     The surface of the air bearing  23  is horizontal. The gas supply amount from the gas supply system  17  is set such that the distance between the air bearing  23  and the surface of the rail  15  always becomes constant. Accordingly, the mounting table  40  moves within the horizontal plane; and the substrate  7  also moves within the horizontal plane. If the application of an AC voltage to the movable magnet unit  35  is stopped, the mounting table  40  stops. 
     A track for processing  55  is disposed at a position above the mounting table  40 . The track for processing  55  includes at least one rail  56 ; and the extension direction of each rail  56  is perpendicular to the extension direction of the rail  15  of the track  11  for a substrate. 
     A travel device for processing  22  is disposed on the track for processing  55 , and a processing unit  50  (here, a print head) is attached to the travel device for processing  22 . The travel device for processing  22  travels on the rail  56  by a moving device  32 ; and the processing unit  50  moves along the extension direction of the rail  56 . Accordingly, the moving direction of the mounting table  40  is perpendicular to the moving direction of the processing unit  50 . 
     The track  11  for a substrate crosses the track for processing  55  under the track for processing  55  and both ends of the track  11  in the extension direction protrude from an area where the processing unit  50  moves. 
     Reference numeral  6  of  FIG. 1  denotes a processing area which is a part of an area where the processing apparatus  50  moves, and located right above the track  11  for the substrate. 
     Among two portions protruding from the processed area  6  of the track  11  for a substrate, one portion is defined as a start position and the other one is defined as a turn-back position, wherein the mounting table  40  moves back and forth between the start position and the turn-back position. 
     A substrate lifting mechanism (not shown) is disposed at the start position. For example, the substrate lifting mechanism includes a lifting pin (not shown); and the mounting table  40  has through-holes (not shown) into which the lifting pin can be inserted. The lifting pins move vertically inside the through-holes of the mounting table  40  which stands still at the start position; and the substrate  7  is placed on the upper end of the lifting pin and is detached from the mounting table  40 . 
     The substrate  7  is placed on the mounting surface  46  at the start position, and the mounting table  40  moves back and forth under the processed area  6 ; and then, the substrate  7  is removed after its return to the start position. Accordingly, an area where the substrate  7  travels overlaps with an area where the processing unit  50  travels; and the substrate  7  crosses the processed area  6  under the processed area  6 . 
     The track for processing  55  crosses the track  11  for a substrate above the track  11  for a substrate; and both ends thereof in the extension direction protrude from the track  11  for a substrate. The processing unit  50  moves back and forth between one of the portions of the track for processing  55  protruding from the track  11  for a substrate and the other portion; and the processing unit  50  faces the substrate  7  which crosses the processed area  6  while moving back and forth. 
     The processing unit  50  includes a head main body  51  and at least one print head  52 . The print head  52  includes at least one discharge orifice  53  and is attached to the head main body  51  with the discharge orifice  53  directed downward. 
     Each print head  52  is connected to a coating liquid supply system  58 ; and coating liquid (such as, ink, spacer dispersion liquid, or the like) supplied from the coating liquid supply system  58  is supplied to each print head  52  and is discharged from the discharge orifice  53 . 
     The substrate  7  faces the processing unit  50  under the processed area  6 ; and the coating liquid lands on the surface of the substrate  7  so as to coat the same. On the surface of the substrate  7 , a portion to be processed to which the coating liquid is to be applied is determined in advance. 
     The length of the portion to be processed along the moving direction of the processing unit  50  is longer than the length of an area where the processing unit  50  can apply the coating liquid at a time. 
     The substrate  7  is disposed under the travel area of the processing unit  50 , and the processing unit  50  is caused to travel so as to cross the travel area above the substrate  7  (forward movement) while discharging coating liquid, then the coating liquid is applied from one end of the portion to be processed in the moving direction of the processing unit  50  to the other end. 
     If the length of portion to be processed along the moving direction of the substrate  7  is longer than the length of an area where the processing unit  50  can apply the coating liquid at a time, after the processing unit  50  is moved forward, the substrate  7  is moved so as to dispose an unprocessed part in the portion to be processed to which the coating liquid has not been applied at just under the travel area of the processing unit  50 . 
     In such a state, when the processing unit  50  is caused to travel in the backward direction which is an inverse direction to the forward movement and crosses the portion to be processed (return movement) while discharging the coating liquid, the coating liquid is applied to the unprocessed part in the portion to be processed. 
     When the processing unit  50  crosses the portion to be processed and the movement of the substrate  7  are repeated, the coating liquid can be applied to the whole portion to be processed. 
     For the processing unit&#39;s  50  crossing of the portion to be processed, the processing unit  50  may be caused to travel while discharging the coating liquid, or the discharging of the coating liquid and the traveling of the processing unit  50  may be alternately repeated. 
     The printing unit is not limited in particular, and other coating unit (such as, a roll coater or a dispenser) can be used as long as it can apply the coating liquid while moving. Furthermore, the processing unit  50  is not limited to the printing unit; and the portion to be processed of the substrate  7  may be inspected (observed) using an inspection unit (such as, a microscope or a camera). 
     Next, the recessed part  45  of the mounting table  40  and an installation place of the support shaft  25  will be described in detail.  FIG. 3  to  FIG. 5  are plan views showing the recessed part  45  and an installation place P of the support shaft  25 . 
     As shown in  FIG. 3  and  FIG. 4 , the planar shape of the recessed parts  45 ,  62  may be rectangular (including square or rectangle), and as shown in  FIG. 5 , the planar shape of the recessed part  63  may be circular (including true circle or ellipse). Furthermore, the planar shape of the recessed part may be triangular or polygonal. 
     Moreover, as shown in  FIG. 5 , the recessed parts  45 ,  63  having different shapes may be formed in one plate-shaped main body  41 , and the recessed parts  45 ,  64  having different sizes may be formed in one plate-shaped main body  41 . 
     The number of recessed parts  45 ,  62 , and  63  may be plural as shown in  FIGS. 3 and 5 , or may be one as shown in  FIG. 4 . 
     It is preferable that the shape and size of the recessed part are determined in consideration of the center of gravity thereof and balance of the mounting table  40 . Specifically, the shape and size of the recessed part are determined so that the load on the support shafts  25  becomes uniform. Alternatively, they are preferably determined such that a rotation moment does not occur at the time of acceleration or deceleration. 
     The installation place where the support shaft  25  is installed is not limited in particular as long as it is in the rear surface of the plate-shaped main body  41 . However, the support shaft  25  is preferably provided in a protruding part on the outer side of the recessed part  45  because the bottom surface of the recessed part  45  is thin and its strength is poor. 
     As shown in  FIGS. 3 and 5 , if a place where protruding parts extending between the recessed parts  45  and  63  intersect with each other is set as the installation place P, the strength will increase. 
     In order to stably hold the mounting table  40 , at least three installation places P are necessary, and more preferably, four or more installation places P are required. In order to provide four or more installation places P in places where the protruding parts intersect with each other, nine or more recessed parts  45 ,  63  are required. 
     Next, a manufacturing process of the mounting table  40  will be described. 
       FIG. 6(   a ) shows the plate-shaped main body  41  before the recessed part  45  is formed therein. The plate-shaped main body  41  is made of a granite plate. 
     In one surface (rear surface  47 ) of the plate-shaped main body  41 , the installation place P of the support shaft  25  described above is determined in advance. In the rear surface  47  of the plate-shaped main body  41 , a portion excluding the installation place P and the edge part is excavated in order to form the recessed part  45 ; and the installation place P and edge part are left without being excavated ( FIG. 6  ( b )). It is noted that the depth of each recessed part  45  may be the same or may be different from each other. 
     The number of support shafts  25  attached to the mounting table  40  is determined in advance. The same number of support shafts for polishing (support member for polishing)  12  as the support shafts  25  are disposed upright so as to locate the upper end thereof within the same flat surface (the same horizontal plane), and the plate-shaped main body  41  is placed on the support shaft for polishing  12  such that each installation place P is in contact with the support shaft for polishing  12  ( FIG. 6(   c )). 
     Because the contact area between the support shaft for polishing  12  and the plate-shaped main body  41  is smaller than the rear surface of the plate-shaped main body  41 , a portion around the installation place P of the plate-shaped main body  41  drops below the installation place P and the plate-shaped main body  41  bends. 
     The shape and size of a portion (upper end) of the support shaft for polishing  12  where the support shaft for polishing  12  is in contact with the plate-shaped main body  41  have the same shape and size as that of the support shaft  25  of a portion (upper end) where the support shaft  25  is in contact with the plate-shaped main body  41 . Accordingly, the bend when the plate-shaped main body  41  is supported by the support shaft for polishing  12  is the same as that when the plate-shaped main body  41  is supported by the support shaft  25 . 
     In a state such that when the plate-shaped main body  41  is supported by the support shaft for polishing  12 , the mounting surface  46  is polished so as to set the flatness of the mounting surface  46  to be 16 μm or less (the height from a reference plane is in the range of +8 μm to −8 μm) (the lapping process in  FIG. 6(   d )). 
     When it is necessary to form the groove  42  and/or a hole for connecting groove  42  to the exhaust system or, the like, the mounting surface  46  is excavated so as to form groove  42  or the hole after the lapping process in a state such that the plate-shaped main body  41  is supported by the support shafts for polishing  12  ( FIG. 6(   e )). 
     The flatness of the surface of the mounting surface  46  is measured after the formation of the groove  42  or the hole. If needed, the mounting surface  46  is polished so as to set the flatness to be 16 μm or less (finish lapping process) in a state such that the plate-shaped main body  41  is supported by the support shaft for polishing  12 . It is noted that, if the groove  42  or the hole is formed in the mounting surface  46 , the flatness of a portion where the mounting surface  46  is in contact with the substrate  7  (i.e., the flatness of a portion of an outer part of the groove  42  or hole) is set to be 16 μm or less. 
     The support shaft for polishing  12  is removed from the installation place P of the mounting table  40  which has been manufactured in the above-discussed processes; and the upper end of each support shaft  25  is in contact with the installation place P, thereby the mounting table  40  being attached to the support shaft  25 . 
     As discussed above, the shape and size of a portion where the support shaft for polishing  12  is in contact with the mounting table  40  are similar to the shape and the size of the support shaft  25 ; and the installation place P where the support shaft for polishing  12  is attached to the mounting table  40  is also similar to the installation place P of the support shaft  25 . Accordingly, when the mounting table  40  is supported by the support shaft  25 , the mounting surface  46  has a flat surface having the flatness of 16 μm or less. 
     The grinding method in the lapping process and finish lapping process is not limited in particular. One example of such grinding method is a wet lapping method in which the polishing tool and the mounting surface  46  are rubbed with each other in a state such that a polishing liquid formed by dispersing abrasive grains into a solution (water, an organic solvent or the like) is interposed between a polishing tool (lapping tool) and the mounting surface  46 . 
     The abrasive grain is also not limited in particular, and a fine powder of diamond, silicon carbide, alumina, or the like, or a hydrophilic oxide-based abrasive grain (such as, silicon oxide, cerium oxide, zirconia, or chromium oxide) can be used. 
     The plate-shaped main body  41  used in the present invention is made of granite. 
     Metal has a high coefficient of thermal expansion and is likely to deform. If the plate-shaped main body  41  is made of a metal, even if the surface is polished to be flatten and smoothened, a deformation or a residual stress that has occurred during polishing causes a swell on the surface, and it cannot be eliminated. Moreover, ceramic is not suitable for the present invention because the surface thereof is difficult to be made flat and smooth by polishing. 
     Stone (mineral) (such as, granite) is most suitable for the material of the plate-shaped main body  41  of the present invention because it has a coefficient of thermal expansion lower than metal and can be polished easier than ceramic. 
     The material of the plate-shaped main body  41  is not limited in particular as long as it is a hard stone which does not cause a crack or the like by being excavated; and granite, marble, or the like can be used. However, granite is most suitable in terms ease in polishing. 
     If the plate-shaped main body  41  is made of granite, even when the recessed part  45  is excavated and also polished, the plate-shaped main body  41  will not be damaged; and further, the mounting surface  46  which is flatter and smoother than the one made of other materials can be obtained by the polishing. 
     The type of granite is not limited in particular, and various types (such as, China black, Indian black, Rustenburg, or Kurnool) can be used. 
     If a part of the plate-shaped main body  41  is made of a different material, the strength significantly decreases, and deformation is likely to occur due to a difference in the coefficients of thermal expansion. Therefore, in the plate-shaped main body  41 , all the parts from the mounting surface  46  to the rear surface  47  are preferably made of granite. 
     The substrate  7  can be held on the mouthing table  40  being pushed to the mounting surface  46  by a pressing member, instead of sucking. 
     The intersecting angle between the extension direction of the track  11  for a substrate and the extension direction of the track for processing  55  may not be the right angle as long as these extension directions intersect with each other. 
     The travel device for processing  22  attached to the processing unit  50  is not limited in particular. For example, similar to the travel device  21  for a substrate, the travel device for processing  22  includes the air bearing  24  disposed on the rail  56  and the support shaft (support member)  26  having its lower end attached to the air bearing  24 , the upper end of the support shaft  26  being attached to the processing unit  50 . 
     Moreover, the moving device  32  of the processing unit  50  is also not limited in particular; and for example, a stationary magnet unit  34  and movable magnet unit  36  similar to those of the moving device  31  of the mounting table  40  may be attached to the rail  56  and the processing unit  50 , respectively, so as to constitute the moving device  32 . 
     As discussed above, a case has been described where the mounting table  40  and the processing unit  50  are attached to the upper ends of the support shafts  25 ,  26  so as to travel on the rails  15 ,  56 , respectively. However, the present invention is not limited thereto. 
     For example, the sides of the support shafts  25 ,  26  and opposite side to the air bearings  23 ,  24  (or wheels) may be folded downward and upward, respectively; and on their folded ends, the mounting table  40  and the processing unit  50  may be placed so that the mounting table  40  and the processing unit  50  are disposed below the rails  15 ,  56 . 
     Also in this case, a full weight load of the mounting table  40  is applied to the support shaft  25 ; and therefore, when the mounting table  40  is manufactured, the support shaft for polishing  12  is attached to the installation place P, to which the support shaft  25  is to be attached, and polishing is performed in such a state that the mounting table  40  is supported by the support shaft for polishing  12 . 
     The configurations of the travel device  21  for a substrate and the travel device for processing  22  are also not limited in particular; and instead of the air bearings  23  and  24 , a wheel may be attached to the support shafts  25  and  26 , respectively. If the wheel is used instead of the air bearings  23  and  24 , the moving devices  31  and  32  are set as motors for rotating this wheel. 
     As discussed above, a case has been described such that each of the substrate  7  and the processing unit  50  is moved. However, the present invention is not limited thereto. For example, a rail is extended on the surface of the pedestal  10 , and the track  11  for a substrate is disposed so as to be perpendicular to this rail. If the track  11  for a substrate is moved along a rail perpendicular to the extension direction of the track  11 , then the substrate  7  will move in two directions (i.e., the direction along the track  11  for a substrate and the direction perpendicular to the track  11  for a substrate); and therefore, it is not necessary to move the processing unit  50 . 
     In order to prevent the occurrence of the derailment from the track  11  for a substrate, a derailment-preventing device  27  as shown in  FIG. 2  may be attached to the mounting table  40 . The derailment-preventing device  27  includes two or more air bearings  29  attached to the mounting table  40 , for example. Since the air bearing  29  is located on both sides of the rail  15  and is pushed against the rail  15  by a spring member  28  from both sides, the mounting table  40  does not derail from the rail  15 .