Patent Publication Number: US-2011062641-A1

Title: Stage equipped with alignment function, processing apparatus having the stage equipped with alignment function, and method of aligning substrate

Description:
TECHNICAL FIELD  
     The present invention relates to a stage equipped with an alignment function, a processing apparatus having the stage equipped with an alignment function, and a method of aligning a substrate. The invention relates, in particular, to those which are used in an inkjet type of coating apparatus provided with coating heads which are disposed in a manner to be movable along an axis. 
     BACKGROUND ART  
     It is known to use an inkjet type of coating apparatus (hereinafter referred to as a “coating apparatus”) in order to directly form, on a substrate, electrically conductive fine patterns, and the like without going through a photolithography process. The apparatus is recently used in forming very fine source/drain electrode patterns of several μ mm in the step of manufacturing large-area thin film transistor substrates, and also in forming color filters, alignment layers and spacers for flat panel displays. 
     As this kind of coating apparatus, there is known one, in patent document 1, having the following arrangement. That is, the one described in patent document 1 is made up of: a stage which is capable of holding by sucking a substrate to be processed while leaving the surface to be processed open to access; and an inkjet means. The stage is movable along an X-axis guide by means of a feed screw having a motor. On the other hand, the inkjet means has: a portal supporting means which is disposed on a path of movement of the stage so as to bridge the stage; and at least one coating head for coating the substrate with a predetermined ink, the coating head being disposed on the supporting means so as to be movable in a Y-axis direction. 
     It is to be noted here that the above-mentioned coating apparatus has a possibility of positional deviation when the substrate is held by suction onto the stage or when the substrate is placed in position on the stage by a transfer robot. As a solution, prior to the coating of the ink, there is performed positioning (alignment) of the scanning surface of the substrate relative to the coating head. At this time, it is necessary to adjust the inclination of the substrate not only in the X-axis direction and Y-axis direction, but also in a θ direction by rotating the substrate on the same plane. 
     In this case, it is conceivable to arrange such that the alignment is performed by rotating the stage itself in a state in which the substrate is held sucked. However, in case the large-area substrate for use as a flat panel display as described above is the object to be processed, not only does the substrate weight increase accompanied by the increase in the substrate size, but also does the stage itself increase in size, and the weight thereof increases depending on the substrate size. Therefore, in the above-mentioned method, there will become needed a rotating mechanism (bearings and the like) so as to rotate the total weight of the substrate and a transfer table. As a result, the apparatus itself will necessarily have to be large in size. In addition, in order to align the stage at a high accuracy by rotating the stage, there will be needed a motor which is of high thrust force and high-performance, thereby resulting in a disadvantage of a higher cost. 
     On the other hand, it is conceivable to arrange, in stead of arranging the stage in a rotatable manner, the supporting means to support the coating heads to be rotatable so as to perform the alignment in the θ direction. This idea has, however, a disadvantage in that the transfer table must also be moved in the X-axis direction and in the Y-axis direction depending on necessity while rotating the supporting means at the time of alignment in the θ direction. The control to perform high-accuracy alignment will be remarkably complicated. 
     Patent Document 1: JP-A-2006-136770  
     DISCLOSURE OF THE INVENTION  
     Problems to be Solved by the Invention 
     In view of the above-mentioned problems, this invention has a problem of providing: a stage equipped with an alignment function which is capable of performing alignment especially in the θ direction at high accuracy and with ease even in case the weight of the object to be processed is large; a processing apparatus having the stage equipped with the alignment function; and a method of aligning a substrate. 
     Means of Solving the Problems 
     In order to solve the above problems, the invention according to claim  1  is a stage equipped with an alignment function, the stage having a stage main body for holding an object to be processed while leaving a processing surface thereof open to access. The stage comprises: a suction means capable of sucking an opposite surface of the object to be processed, the opposite surface lying counter to the processing surface; a gas supply means for supplying a gas to such a region of the object to be processed as is other than a portion sucked by the suction means; and a drive means for rotatably driving the suction means so as to rotate the object to be processed on the same plane by causing the suction means to serve as a center of rotation. 
     According to this invention, the object to be processed is placed in position on the stage while leaving the processing surface of the object to be processed open to access. The suction means is caused to suck an opposite surface of the object to be processed, the opposite surface lying counter to the processing surface. Then, the gas is supplied to such a region of the object to be processed as is other than a portion sucked by the suction means. In this state, the suction means is rotated by the drive means on the same plane by causing the suction means to serve as the center of rotation. Then, the object to be processed can be rotated by a predetermined angle integrally with the suction means. As a result, the substrate (object to be processed) can be rotated in the θ direction so as to perform the alignment. 
     As described above, this invention has employed an arrangement in which, by supplying the gas to the portion other than the region that is sucked by the suction means, the alignment in the θ direction is performed by rotating, integrally with the suction means, only the object to be processed in a state in which the portion other than the region sucked by the suction means is kept levitated or floated (in this case, it is sufficient if the frictional resistance is reduced at least between the portion in question and the upper surface of the stage). Therefore, even in case where, e.g., the object to be processed is large in weight, there is no need of a rotary mechanism such as a large-sized bearing, and the like. The apparatus can thus be prevented from getting large in size. In addition, since the object to be processed can be rotated with a small thrust force, a high-precision alignment can be performed without employing a high-performance motor, thereby contributing to the cost reduction. Still furthermore, the alignment in the θ direction can be performed without moving the processing means such as an inkjet means that is disposed so as to lie opposite to the objet to be processed held by the stage, thereby making it easy to control the alignment 
     Further, in order to solve the above problems, the invention according to claim  2  is a stage equipped with an alignment function. The stage has a holding tray for holding thereon an object to be processed while leaving a processing surface thereof open to access, and a stage main body for supporting the holding tray in a rotatable manner. The stage comprises: a gas supply means for supplying a gas to an opposite surface of the holding tray, the opposite surface lying counter to the processing surface; and a drive means for rotatably driving the holding tray so as to rotate the holding tray on a same plane. 
     This invention has employed an arrangement in which the substrate (object to be processed) is aligned in the θ direction by rotating with the drive means integrally with the suction means, the object to be processed in a state of being held on the tray while the tray is kept levitated (in a manner similar to the above case, it is sufficient if the frictional resistance is reduced at least between the holding tray and the upper surface of the stage). Therefore, like in the above case, there is no need of a rotary mechanism such as a large-sized bearing, and the like, thereby contributing to the lower cost. 
     The stage according to this invention preferably further comprises a guide means, and a moving means for moving the stage main body along the guide means. Then, the alignment in the direction of moving the stage main body can be performed only by changing the stopping position of the stage main body relative to the processing means such as a coating head which is disposed on an upper part of the guide means. 
     Further, the stage according to this invention preferably further comprises: a suction groove formed along a surface of contact of the stage main body or the holding tray with the object to be processed; and a vacuum pump for evacuating the suction groove in a state in which the object to be processed is mounted on the stage or the holding tray. Then, for example, when the stage main body is moved along the guide means, the object to be processed can advantageously be surely held by the stage main body or the holding tray. 
     In case the alignment in the θ direction is performed on the above-mentioned stage, not only is required the positioning accuracy (e.g., below 1μ radian), but also is strongly required the reduction in alignment time. In this case, preferably, the drive means comprises: a fine-adjustment mechanism for rotating the suction means within a predetermined micro-angle range; and a coarse-adjustment mechanism for rotating the suction means within an angle range larger than the angle range of the fine-adjustment mechanism. According to this arrangement, after driving the object to be processed, by the coarse-adjustment mechanism, at a high speed to the neighborhood of a target position, a high-precision positioning can thereafter be performed by the fine-adjustment mechanism. As a result, high-accuracy alignment can be materialized at a short time. 
     Preferably, the coarse-adjustment mechanism is coupled to the suction means. The fine-adjustment mechanism comprises an arm and a drive source for swinging the arm. The fine-adjustment mechanism and the coarse-adjustment mechanism are operatively coupled to each other such that, when the arm is swung by the drive source, the suction means is rotatably driven through the coarse-adjustment mechanism. Then, the rotary shaft to rotatably drive the suction means can be made in common with each other, thereby eliminating the complex structure of the drive means. In addition, at the time of performing alignment in the θ direction, switching can be made smoothly from the rotatable driving with the coarse-adjustment mechanism to the rotatable driving with the fine-adjustment mechanism. 
     Further, the arm of the fine-adjustment mechanism has a length to be extended at least to one side of the stage main body and is connected at a front end of the arm to the drive source. Then, the amount of displacement of the front end of the arm required for movement by a predetermined micro-angle range will become large. As a result, the resolution of the detection means such as an encoder to detect the amount of displacement can be improved to thereby materialize a higher precision alignment. 
     In order to solve the above problems, a processing apparatus according to this invention comprises: the stage equipped with an alignment function according to any one of claims  1  through  7 ; and a processing means for performing a predetermined processing on the object to be processed, the processing means being disposed to lie opposite to the object to be processed that is held by the stage. 
     In order to solve the above problems, the method of aligning a substrate (an object to be processed) comprises the steps of: mounting on a stage a substrate (the object) to be processed in a manner to leave a processing surface thereof open to access; causing a suction means to suck an opposite surface of the substrate (object to be processed), the opposite surface lying counter to the processing surface, the sucking means being disposed on the stage; supplying a gas to the opposite surface except for a region that is sucked by the suction means; and aligning the object to be processed by rotating the substrate (object to be processed) by a predetermined angle on the same plane by causing the suction means to serve as a center of rotation. 
     In this case, the step of aligning the object to be processed preferably comprises: rotating the suction means by a range of angle which is larger than a predetermined micro-angle range; and thereafter further rotating the suction means within the micro-angle range. 
     BEST MODE FOR CARRYING OUT THE INVENTION  
     With reference to the drawings, description will now be made of an example in which a substrate S made of glass and the like for directly forming thereon electrically conductive fine patterns and the like is defined as an object to be processed, and in which a stage equipped with an alignment function and for holding the substrate S according to an embodiment of this invention is applied to an inkjet type of coating apparatus. 
     The inkjet apparatus has a platform  1 , and on this platform  1  is disposed a base plate  2  which is rectangular parallelepiped in shape. The base plate  2  is made of granite and the like so as to secure smoothness on the top surface thereof. The top surface of the base plate  2  is provided with a pair of right and left rail members (guide means)  3 R,  3 L which are extended horizontally in the axial direction over the entire length of the base plate  2  (see  FIG. 2 ). 
     On the rail members  3 R,  3 L, a stage  4  which is equipped with an alignment function is disposed in a manner to be reciprocated, i.e., movable back and forth. The stage  4  has a stage main body  4   a  of a plate shape. On the bottom four corners of the stage main body  4   a,  there are mounted sliders (sliding members)  5  which are slidably engaged with the relevant rail members  3 R,  3 L. On the bottom surface of the stage main body  4   a , there are also disposed nut members (not illustrated). Each of the nut members is engaged in a threaded manner with a feed screw (not illustrated) which is disposed along the two rail members  3 R,  3 L within a range of extension of the rail members  3 R,  3 L. When a motor (not illustrated) coupled to one end of the feed screw is rotated, the stage  4  is moved back and forth along the rail members  3 R,  3 L (hereinafter, the direction of this back-and-forth movement is referred to as an X-axis direction). In this arrangement, the above-mentioned feed screw and the motor constitute a moving means in this embodiment. The moving means is not limited to the above example; for example, there may be used a linear motor which is made up of a moving part and a stator of a magnetic levitation system. 
     At a position in which the stage main body  4   a  is located at one side as seen in the X-axis direction of the rail members  3 R,  3 L (right-hand position in  FIG. 1 , i.e., a transfer position), it is so arranged that the transfer of the substrate S to the stage main body  4   a  is performed by an articulated transfer robot R of a known structure. For the purpose of transfer of this substrate S, there are provided: a lifting means  6  made up of a plurality of supporting rods  6   a  which are disposed vertically so as to penetrate through the base plate  2  in the vertical direction of the base plate  2 ; and air cylinders (not illustrated) for moving up and down the respective supporting rods  6   a.  It is thus so arranged that the substrate S can be supported at a predetermined elevated position above the upper surface of the stage main body  4   a  (see  FIG. 1 ). 
     On the other hand, at a position in which the stage  4  is located on the other side of the rail members  3 R,  3 L as seen in the X-axis direction (left-hand position in  FIG. 1 , i.e., a processing position), it is so arranged that a predetermined processing is performed while appropriately moving back and forth the stage main body  4   a  in the X-axis direction. In the inkjet type of coating apparatus according to this embodiment, an inkjet means  7  as the processing means is positioned substantially in the middle portion of the rail members  3 R,  3 L. The inkjet means  7  is made up of: a portal supporting member  7  which is disposed in a manner to bridge the stage main body  4   a  in a direction at right angles to the X-axis direction; and a plurality of coating heads  7   b  for coating the substrate S, held in position on the stage main body  4   a,  with the ink. 
     Each of the coating heads  7   b  is held by a holder  7   d  so that the front ends of the nozzles  7   c  are positioned on the same horizontal plane and at an equal distance from one another. The holder  7   d  is mounted on the upper horizontal portion of the supporting member  7   a  in such a manner that the coating heads  7   b  lie on the side of the processing position (left side in  FIG. 1 ). In this case, the holder  7   d  is engaged in a screwed manner with a motorized feed screw (not illustrated) which is housed inside the upper horizontal portion of the supporting means  7   a.  When the motor is driven to rotate the feed screw, each of the coating heads  3  is integrally moved back and forth in a direction at right angles to the X-axis direction (the direction of this back-and-forth movement is hereinafter referred to as a Y-axis direction). 
     Each of the coating heads  7   b  has a known structure, i.e., by appropriately driving a piezoelectric element disposed in an ink chamber, the ink contained in an ink tank  5  is caused to drop. The ink contained in the ink tank  5  is appropriately selected depending on what is going to be formed on the surface of the substrate S. For example, if the product is for forming a spacer for use in a flat panel display, there will be used an ink which is made from the spacer particles, binder, and solvent. 
     When the substrate S is handed over to the stage main body  4   a  by the transfer robot R as described above, there are cases where the substrate S gives rise to positional deviation relative to the stage main body  4   a.  Therefore, it is necessary to perform the positioning (alignment) of the substrate S relative to the coating heads  7   b  prior to the coating of the ink. At this time, not only the adjustment in the X-axis direction and the Y-axis direction, but also the adjustment of the inclination (inclination angle θ) of the substrate S relative to each of the coating heads  7   b  must also be made by rotating the substrate S on the same plane (the direction of this rotation is hereinafter referred to as θ direction, see  FIG. 2 ). 
     The stage  4  according to the first embodiment has: a suction means  8  which is capable of sucking a central region on the rear surface of the substrate S; a gas supply means  9  for supplying a gas to such a region of the substrate S as is other than a portion sucked by the suction means  8 ; and a drive means  10  for giving a rotating force to the suction means  8  so that the substrate S can be rotated in the θ direction on the same plane by causing the suction means  8  to serve as the center of rotation, i.e., so that the suction means  8  can be rotatably driven (see  FIG. 3 ). 
     The suction means  8  has a chuck plate  11  housed in a recessed portion  4   b  which is provided in the center of the stage main body  4   a  and which is rectangular in shape as seen in plan view. The chuck plate  11  is made, e.g., of a suction pad of known structure or of a disk of porous structure, and is connected to a vacuum pump through an evacuation pipe (not illustrated). When the vacuum pump is operated, the chuck plate  11  is arranged to suck, by an entire front surface thereof, the rear surface of the substrate S. Further, in the center on the rear side of the stage main body  4   a,  there is concentrically formed a through hole  4   c  which is in communication with the recessed portion  4   b.  The through hole  4   c  is provided with a sleeve member  12  and a ball bearing  13  so that a push member  14  can be supported by the ball baring  13 . In this case, the push member  14  and an inner race  13   a  of the ball bearing  13  are connected together by means, e.g., of a key connection using a parallel key or a spline connection (see  FIG. 4 ). 
     The push member  14  is coupled to a drive rod  15   a  of a direct acting type of actuator  15  of a known structure, disposed below the push member  14 . Depending on the size of the substrate, an air cylinder may be used in place of the direct acting actuator. In such a case, there may be employed an arrangement in which the air cylinder is operated by making use of the gas to be supplied by the gas supply means  9 , thereby simplifying the apparatus. When the actuator  15  is operated, the chuck plate  11  is movable between an elevated position in which the upper surface of the chuck plate  11  projects upwards beyond the upper surface of the stage main body  4   a,  and a lowered position in which the upper surface of the chuck plate  11  is at least flush with the upper surface of the stage main body. In addition, when the inner race  13   a  is given a rotating force by an arm which is described hereinafter, the push member  14  is rotatably driven. The chuck plate  11  and consequently the substrate S are rotated in the  0  direction by causing the push member  14 , which works as the rotary axis of the suction means  8 , to serve as the center of rotation. 
     The gas supply means  9  is made up of; a plurality of recessed grooves  16  which are formed in the X-axis direction substantially along the entire length of the upper surface of the stage main body  4   a;  air pads  17  which are each disposed in respective recessed grooves  16  at a predetermined distance from one another; and a gas pipe  18  which supplies each of the air pads  17  with gas such as compressed air from a compressor and the like (not illustrated) (see  FIGS. 2 and 4 ). In this case, the number of the recessed grooves  16  to be formed, and the number of air pads  17  to be disposed are appropriately set depending on the weight of the substrate S to be supported by the stage main body  4   a.    
     The drive means  10  is provided with a plate-shaped arm  19 . One end of the arm  19  is coupled by a pin to the inner race  13   a  in the center line of the arm  19 . The other end of the arm  19  is extended to the side surface of the stage main body and is connected to the drive source  20  disposed on the side surface thereof. The drive source  20  has a frame  20   a , and a feed screw  20   b  with a motor M is disposed inside the frame  20   a  in the X-axis direction. The feed screw  20   b  has engaged therewith in a screwed manner a movable member  20   c  having formed therein a screwed hole. On an upper part of the movable member  20   c,  there is engaged a slider part  20   d  in a manner to be slidable along a rail member  20   e  which is attached to the feed screw  20   b  on the upper inside of the frame  20   c.  According to this arrangement, when the motor M is operated to rotate the feed screw  20   b , the movable member  20   c  is movable back and forth in the X-axis direction depending on the direction of rotation of the motor M (see  FIGS. 2 and 5 ). 
     On the lower surface of the movable member  20   c,  there is formed a rail part  20   f  which is extended in the Y - axis direction. The rail part  20   f  has engaged therewith a supporting member  20   g  in a slidable manner. To the lower end of the supporting member  20   g,  there is coupled the other end of the arm  19  through a bearing  20   h.  When the feed screw  20   b  is rotated to move the movable member  20   c  along the rail member  20   e,  a rotating force is given to the push member  14  which serves as the rotary shaft of the suction means  8 , while the supporting member  20   g  moves along the rail part  20   f.    
     In this case, there is constituted a fine - adjustment mechanism which swings the arm  19  within a range of stroke of the back and forth movement of the movable member  20   c  to thereby rotatably drive the push member  14 , and consequently the suction means  9  by a predetermined micro-angle range (e.g., within 1 degree) (hereinafter, this fine-adjustment mechanism as the drive means is denoted by a reference numeral  10 ). The micro-angle range of this invention can be appropriately set depending on the precision and the like which is required at the time of aligning the substrate S. By changing the stroke of the back-and-forth movement of the movable member  20   c,  the micro-angle range can be adjusted. Further, the drive source  20  is provided with a detection means such as a photoelectric linear encoder (not illustrated) so that the amount of displacement of the movable member  20   c  can be detected. According to this arrangement, the amount of displacement of the movable member  20   c  when the arm  19  is moved by a micro-angle amount (e.g., by 1 degree) becomes larger than the amount in the case in which detection is made of the amount of rotary deviation by providing the push member  14  with detection means such as a rotary encoder and the like. As a result, the precision of the detection means which detects the amount of deviation can be increased, whereby a more precise alignment can be materialized. 
     When, e.g., the stage main body  4   a  is moved from the hand-over position to the processing position, if the substrate S is held by suction with the suction means  8  alone, there will occur a disadvantage in that, e.g., the substrate S will be detached off from the suction means  8  at the time of starting of, or stopping of, the movement of the stage main body  4   a.  As a solution, the stage main body  4   a  has formed on an upper surface thereof a plurality of suction grooves  21  which are communicated with the vacuum pump, the suction grooves being formed in a manner to be extended in the X-axis direction and Y-axis direction (see  FIG. 2 ). When the stage main body  4   a  is moved, the suction grooves  21  are evacuated. In this manner, the substrate S is arranged to be held by suction substantially over the entire surface of the substrate S. 
     A description will now be made of the alignment of the substrate S by means of the stage  4  equipped with an alignment function according to this invention. At the hand-over position of the stage main body  4   a,  each of the supporting rods  6   a  of the lifting means  6  is lifted. Thereafter, the substrate S is transferred by the transfer robot R and is disposed in position so that the substrate S can be supported by a front end of each of the supporting rods  6   a  (see  FIG. 1 ). Then, each of the supporting rods  6   a  is lowered to thereby place the substrate S on the stage main body  4   a.  The substrate S on which the ink is coated is provided with at least one mark R (about several tens microns through 0.1 mm in size) of a predetermined shape at a position which serves as an origin of the scanning surface at the time of ink coating (see  FIG. 2 ). 
     Once the substrate S has been placed on the stage main body  4   a , the suction grooves  21  are evacuated to thereby cause the substrate S to get sucked to the stage main body  4   a  substantially over the entire surface of the stage main body. In this state, a feed screw (not illustrated) is rotated to move the stage main body  4   a  to the processing position. When the stage main body  4   a  has reached the processing position, the substrate S is pictured by a picturing means such as a CCD camera and the like mounted on the supporting member  7   a  of the inkjet means  7 . The pictured image is analyzed by an image analyzing means of a known structure. The analyzed data is outputted to a control means (not illustrated) such as a microcomputer and the like which controls the operation of the inkjet type of coating apparatus. When the data is inputted into the control means, there is calculated an amount of displacement (correction value) in the direction of the X-axis direction, the Y-axis direction and the θ direction for the purpose of aligning the substrate position by causing the mark R on the substrate S to serve as a reference (or standard). When the correction value is calculated, control is made of the motor for the feed screw which moves the stage main body  4  and of the motor for moving the holder  7   d  of the inkjet means. Alignment is thus made first of all relative to the coating heads  7   a  in the X-axis direction and in the Y-axis direction. Then, the vacuum pump is stopped in operation and the suction of the substrate S is released. 
     Subsequently, when the actuator  15  is operated to lift the chuck plate  11 , the substrate is lifted off from the upper surface of the stage main body  4   a.  At this time, the vacuum pump which is in communication with the chuck plate  11  and the gas supply means  9  are operated. As a result, the substrate S is sucked at points of contact between the chuck plate  11  and the substrate S. At the same time, due to the gas to be ejected from each of the air pads  18  of the gas supply means  9 , the portion excluding the region which is sucked by the chuck plate  11  (i.e., peripheral portion of the substrate) is caused to be levitated. In this manner, when the central portion of the substrate S is held sucked and the periphery thereof is levitated, the motor M of the fine-adjustment mechanism  10  is driven to thereby appropriately rotate the feed screw depending on the correction value calculated by the control means. According to this arrangement, the rotating force is given to the chuck plate  11  through the arm  19  which swings about the actuator  15  as the center and through the push member  14 . Only the substrate S is rotated relative to the upper surface of the stage main body  4   a  by a predetermined micro-angle range in the θ direction depending on the above-mentioned correction value, whereby an alignment in the θ direction can be performed (see  FIG. 6 ). 
     Without lifting the chuck plate  11 , the gas may be supplied at the lowered position of the chuck plate  11  from the gas supply means  9 . Even in a state in which the portion except for the region that is sucked by the chuck plate is not levitated in a strict sense of the term, alignment in the θ direction can still be performed in a state in which the frictional resistance between the portion in question and the upper surface of the stage main body  4   a  is substantially reduced. For example, in case the substrate has a deflection, this solution is advantageous for accurate alignment. 
     The lifting of the substrate S can be confirmed: e.g., by a change in flow amount of an air flow sensor connected to the gas pipe  18  in communication with each of the air pads  18 ; or by the detection of the change in height as a result of direct scanning of the substrate surface by using a laser displacement meter and the like from the upper surface of the substrate. Then, by performing alignment in the θ direction upon confirmation of levitation, the rear surface of the substrate S can be prevented from getting into contact with the stage main body  4   a . Alignment can thus be performed without damaging the rear surface of the substrate S. Alternatively, by rotating the substrate S in a lowered position of the chuck plate  11 , the layer of the air to be supplied from the gas supply means  9  can prevent the rear surface of the substrate S from getting damaged. 
     In this manner, according to the embodiment of this invention, there has been employed an arrangement in which the alignment in the θ direction can be performed by rotating only the substrate S: in a state in which the portion except for the sucked region is kept levitated by the gas to be ejected from the air pads  18 ; or in a state in which the frictional resistance is substantially reduced between the portion at least exclusive of the sucked region and the upper surface of the stage main body  4   a . Therefore, even in case the weight of the substrate S is large, there is no need of a rotary mechanism such as a large bearing and the like, whereby the apparatus itself can be prevented from getting large in size. In addition, since the substrate S can be rotated with a small thrust force, a high-precision alignment becomes possible without using a high-performance motor, thereby contributing to the reduction in cost. Furthermore, while alignment in the θ direction is being performed, the inkjet means  7  and consequently the position of the coating heads  7   b  need not be moved. There is thus no need of a special control at the time of alignment of the substrate. 
     After the above-mentioned alignment has been finished, confirmation is made as to whether the substrate S has been moved in the X-axis direction, in the Y-axis direction, and in the θ direction in response to the amount of displacement (correction value) that was calculated to align the substrate position. In other words, the operation of the gas supply means  9  is stopped and also the actuator  15  is operated to lower the chuck plate  11 , and the operation of the vacuum pump in communication with the chuck plate  11  is stopped. Then, the suction grooves  21  are evacuated and the substrate S is sucked to the stage main body  4   a  substantially over the entire surface thereof. In this state, the substrate S is pictured in the same manner as noted above by a picturing means such as a CCD camera and the like. The pictured image is analyzed by the image analyzing means, and the analyzed data is outputted to the control means. In this manner, the above-mentioned confirmation is made by causing the mark R of the substrate S to serve as a reference. 
     By so arranging that confirmation is made in a state in which the substrate S is kept sucked to the stage main body  4   a  after completion of the alignment as described above, the above-mentioned confirmation can be made without being influenced by the positional deviation that may occur between the case in which the substrate S is on the stage main body  4   a  and the case in which the substrate S is levitated. 
     Subsequently, once the confirmation of alignment of the substrate S in the X-axis direction, in the Y-axis direction and in the θ direction has been finished, back-and-forth movements are appropriately made of the stage  4  in the X-axis direction and each of the coating heads  7   a  integrally in the Y-axis direction. During the above movements, each of the coating heads  7   b  is moved along the scanning surface of the substrate so that the substrate S is coated with ink in a pattern determined in advance. At this time, coating of the ink can be made in a state in which the center of the substrate S is lifted and that the peripheral portion of the substrate S is kept levitated by the gas to be ejected from the air pads  18 . On the other hand, ink coating may alternatively be made in a state in which the substrate S is placed on the stage main body  4   a  once again, and in which the suction grooves  21  are evacuated so that the substrate S can be kept sucked substantially over the entire surface of the stage main body  4   a.    
     In the above-mentioned embodiment, a description has been made of an example in which the substrate S is levitated only by the gas to be ejected out of the air pads  18 . Alternatively, there may be employed the following arrangement, i.e., in order to stably levitate the substrate, the substrate S is levitated by keeping an equilibrium in balance between the evacuation of the suction grooves  21  and the pressure of the gas to be ejected out of the air pads  18 . In addition, as the air pads  18 , those which are arranged to enable both the gas ejection and evacuation at the same time may also be employed. 
     Further, in the above-mentioned embodiment, a description was made of an example in which an arrangement was made to rotate only the substrate S in the θ direction. It may also be so arranged that the stage main body is provided with a rotatable holding tray which holds the substrate S with the processing surface thereof left open to access. 
     In concrete, with reference to  FIGS. 7 through 9 , a description will now be made of such an example. A stage  30  with an alignment function relating to the first modified example is disposed on the pair of the left and right rail members  3 R,  3 L provided on the upper surface of the base plate  2 , in the same manner as above, so as to be movable back and forth. The stage  30  has a stage main body  31  of plate shape. On the four corners of the lower surface of the stage main body  31 , there are provided sliders  32  which are slidably engaged with the rail members  3 R,  3 L. In the same manner as above, the stage main body  31  is movable back and forth by rotation of a feed screw (not illustrated) along the two rail members  3 R,  3 L. 
     The stage main body  31  is provided, in a rotatable manner, with a plate-shaped holding tray  33  which is capable of holding the substrate S by suction. On the rear surface of the holding tray  33 , there is formed a recessed space  33   b  of a dented shape at a plurality of positions so that there can be respectively formed therein a rib part  33   a  which maintains the strength of the holding tray  33  and, at the same time, guarantees the surface smoothness. On the rear central part of the holding tray  33 , there is formed a rotary shaft  33   c.  The rotary shaft  33   c  is supported by a ball bearing  35  which is disposed, through a sleeve member  34 , into a through hole formed in the center of the stage main body  31 . In this case, similar to the above example, the rotary shaft  33   c  and the inner race  35   a  of the ball bearing  35  are of a key connection using a parallel key or a spline connection. In a non-operating state of the gas supply means, which is described in detail hereinafter, the lower surface of the rib part  33   a  is in surface contact with the upper surface of the stage main body  31  (see FIG.  7 ). 
     The stage main body  31  is provided with: a gas supply means  36  which supplies the recessed space  33  of the holding tray  33  with a gas; and a fine-adjustment mechanism  37  which rotatably drives the holding tray  33  so that the holding tray  33 , that keeps holding the substrate S, can rotate on the same plane. 
     The gas supply means  36  is constituted by: recessed holes  36   a  which are each circular as seen in plan view and which are formed in a predetermined position on the upper surface of the stage main body  31 ; an air pad  36   b  which is porous in structure and which is housed inside each of the recessed holes  36   a;  and a gas pipe  36   c  which supplies each of the air pads  36   c  with a gas such as compressed air (see  FIG. 7 ). 
     The fine-adjustment mechanism  37  which serves as a drive means is provided with a frame  37   a  mounted on one side surface of the stage main body  31 . The frame  37   a  is provided with a feed screw  37   b  with a motor M, so as to be extended in the X-axis direction. The feed screw  37   b  gets engaged in a screwed manner with a movable member  37   c  having formed therein a screwed hole. At the lower part of the movable member  37   c,  there is formed a slider  37   d.  The slider part  37   d  is slidably engaged with a rail member  37   e  which is mounted in parallel with the feed screw  37   b  on the bottom inner side of the frame  37   a.  According to this arrangement, when the motor M is operated to thereby rotate the feed screw  37   b,  the movable member  37   c  becomes reciprocally movable in the X-axis direction depending on the direction of rotation of the motor M (see  FIG. 8 ). 
     Further, on an upper surface of the movable member  37   c,  there is formed a rail part  37   f  which is extended in the Y - axis direction. The rail part  37   f  has slidably engaged therewith a supporting member  37   g.  On an upper end of the supporting member  37   g,  there is attached an arm  37   i  through a bearing  37   h.  The arm  37   i  is coupled to a side surface of the holding tray  33 . When the feed screw  37   b  is rotated to thereby move the movable member  37   c  along the rail member  37   e,  the supporting member  37   g  moves along the rail part  37   f,  and the holding tray  33  is given a rotating force, thereby being rotatably driven. In this case, the arm  37   i  is swung within a range of the stroke of the reciprocating movement of the movable member  37   c,  whereby the holding tray  33  is rotatably driven within a predetermined micro-angle range (e.g., within one degree). In addition, between the supporting member  37   g  and the arm  37   i,  there may be interposed, in addition to the bearing  37   h,  a spring guide  37   j  which allows an up and down movement of the arm  37   i  relative to the supporting member  37   g.    
     There is employed an arrangement in which: on an upper surface of the holding tray  33 , there are appropriately formed suction grooves  38  in a manner to be extended in the X-axis direction and in the Y-axis direction, the suction grooves  38  being in communication with a vacuum pump; and by evacuating the suction grooves  38  the substrate S can be sucked and held substantially over the entire surface thereof (see  FIG. 9 ). 
     In case alignment is performed in the θ direction, each of the air pads  36   b  of the gas supply means  36  is supplied with gas such as compressed air in a state in which the substrate S is held sucked substantially over the entire surface thereof. According to this arrangement, there can be attained a state in which the holding tray  33  is kept levitated off from the upper surface of the stage main body  31  or a state in which the frictional resistance between the two has substantially been reduced due to the compressed air. At this time, since the holding tray  33  is levitated, there will give rise to a deviation (clearance) in the direction of height, between the fine-adjustment mechanism  37  coupled to the stage main body  31  and the holding tray  33 . However, the spline guide  37   i  will resolve the mechanical contradiction, i.e., the deviation can be absorbed. 
     Subsequently, the motor M of the fine-adjustment mechanism  37  is driven and, in the same manner as above, the feed screw  37   b  is appropriately rotated depending on the correction value calculated by the control means. According to this arrangement, the holding tray  33  is rotatably driven through the arm  37   i,  and the holding tray  33  that is holding the substrate S by suction will be rotated by a predetermined angle in the θ direction relative to the upper surface of the stage main body  31  by causing the rotation axis  33   c  to serve as the center of rotation. 
     As described above, according to the above-mentioned first modified example, there has been employed an arrangement in which the holding tray  33  that holds the substrate S is rotated. As a result of combined effects in: that the holding tray  33  is made lighter in weight by forming recessed space  33   b  on the rear surface of the holding tray  33 ; and that the portion of the substrate except for the part coupled to the rotary shaft  33   c  is kept levitated by supplying gas from the air pads  36   b,  there is no need of a rotary mechanism such as a large-size bearing, and the like. The apparatus itself can thus be prevented from getting large in size. Since the substrate S can be rotated at a small thrust force, high-precision alignment becomes possible without using a high-performance motor. 
     In the above-mentioned first modified example, a description has been made of an example in which the substrate S or the holding tray  33  that holds thereon the substrate S is rotated in the θ direction. However, there may be employed an arrangement in which the stage itself has further assembled thereto a drive apparatus provided, e.g., with a feed screw having a motor so as to be movable in the X-axis direction and in the Y-axis direction, whereby alignment in such directions can be performed. 
     Further, in the above-mentioned first modified example, a description has been made of an example in which the drive means is made up of the fine-adjustment mechanism  10 . However, the drive mechanism need not be limited thereto. In order to coat the substrate S with the predetermined ink while moving the substrate S, e.g., in the θ direction, the drive mechanism may be arranged by a coarse-adjustment mechanism which is capable of rotating the suction means  8  by an angle range larger than that of the fine-adjustment mechanism and which, depending on cases, is capable of rotating the substrate S by 90 degrees or 180 degrees. As a second modified example provided with such a coarse-adjustment mechanism, the coarse-adjustment mechanism  100  is made up, as shown in  FIG. 10 , of a worm wheel  101  which is mounted on a drive rod  15   a  of the actuator  15  and which is connected to an inner race  13   a  of the ball bearing  13 ; and a worm  102  which is supported by a housing fixed to a frame (not illustrated) and which is rotatably driven by a motor (not illustrated). The coarse-adjustment mechanism  100  need not be limited to the above, and alternatively other known arrangement such as a DD motor and the like may be employed. 
     On the other hand, as a third modified example, the drive means may be constituted, as shown in  FIGS. 11 and 12 , of; the fine-adjustment mechanism  10  which is provided with the arm  19  and the drive source  20 ; and the coarse-adjustment mechanism  100  which is provided with the worm wheel  101  and the worm  102 . In this case, the worm wheel  101  of the coarse-adjustment mechanism  100  is coupled to the inner race  13   a,  and one end of the arm  19  is fixed to the lower surface of the housing  103  which supports the worm  102  to be engaged with the worm wheel  101 . 
     In the above-mentioned drive means, when the worm  102  of the coarse-adjustment mechanism  100  is rotatably driven by a motor M disposed on the housing  103 , the worm wheel  101  is rotated and, as a result of rotation of the inner race  13   a  that is coupled to the worm wheel  101 , the push member  14  is rotated. Then, the chuck plate  11  is rotated and the substrate S is rotated in the θ direction within an angle range larger than that of the fine-adjustment mechanism  10 . At this time, there is no rotating force transmitted to the arm  19 . Then, when the drive source  20  is driven (see  FIGS. 1 and 2 ), the arm  19  will be swung by causing the actuator  15  to serve as the center of swinging or rotating movement. At this time, the worm  102  will be swung together with the housing  103  that is fixed to the arm  19 . As a result of rotation of the worm wheel  101  accompanied by the above, the push member  14  and the chuck plate  11  are rotated, and the substrate S will be rotated in the θ direction by a predetermined micro-angle. 
     According to the above-mentioned arrangement, since the suction means  8  is rotatably driven, the rotating force can be given to the push member  14  which serves as a common rotary shaft, from the fine-adjustment mechanism  10  and the coarse-adjustment mechanism  100 . As a result, the rotary shaft (push member  14 ) to rotatably drive the suction means  8  can be arranged in common with each other and, consequently, the drive means can be prevented from getting complicated in its structure. Further, at the time of performing alignment in the θ direction, switching from the rotatable driving by the coarse-adjustment mechanism  100  to the rotatable driving by the fine-adjustment mechanism  10  can also be made smooth. 
     In addition, at the time of picturing the substrate S by, e.g., a picturing means, in order to calculate the amount of displacement (correction value) in the θ direction so that the position of the substrate S is aligned with that mark R on the substrate S which serves as a standard or reference, there may be the following case, i.e., a case in which the mark R deviates beyond the picturing range of the picturing means, or a case in which the calculated correction value exceeds the micro-angle range that can be aligned by the fine-adjustment mechanism. In such a case, first, the substrate S is rotatably driven by means of the coarse-adjustment mechanism  100  at a high speed to the neighborhood of a target position (i.e., to an angle range that is capable of aligning by the fine - adjustment mechanism  10 ). Depending on the necessity, the substrate S is pictured again by the picturing means to thereby calculate the correction value by causing the mark R of the substrate S to serve as a standard. Subsequently, by means of the fine-adjustment mechanism  10 , high-accuracy positioning can be performed. According to this arrangement, highly accurate and short-time alignment can be materialized. 
     In the above-mentioned third modified example in which the drive means has the fine-adjustment mechanism  10  and the coarse-adjustment mechanism  100 , it is so arranged that the rotating force from each of the fine-adjustment mechanism  10  and the coarse-adjustment mechanism  100  is inputted into the push member  14 . It is however not limited thereto. As a fourth modified example, the following arrangement may be employed. In other words, as shown in  FIG. 13 , in a manner coaxial with the push member  14 , another hollow rotary shaft  201  is disposed through a bearing  201   a  for fine-adjustment driving. The lower surface of this hollow rotary shaft  201  may be connected to the upper surface of a housing  202  which houses therein the worm wheel  101  and the worm  102 . According to this arrangement, when the worm  102  of the coarse-adjustment mechanism  100  is rotatably driven, the push member  14  is rotated without transmitting the rotating force to the arm  19 . When the drive source  20  is driven, on the other hand, the arm  19  is swung by causing the actuator  15  to serve as the center of swinging or rotating movement, the hollow rotary shaft  201  coupled to the arm  19  through the housing  202  is rotated and, accompanied by this, the push member  14  is rotated through the worm wheel  101 . 
     Although not illustrated, as still another modified example, an arrangement may be made such that, in case the hollow rotary shaft  201  is disposed coaxially with the push member  14 , the rotating force from the fine-adjustment mechanism  10  is transmitted only to the hollow rotary shaft  201 . In this case, an actuator (not illustrated) to move the hollow rotary shaft  201  up and down may be added. In this manner, at the time of rotating the substrate S from the coarse-adjustment mechanism  100  through the push member  14 , the chuck plate  11  is moved up by pushing only the push member  14 . On the other hand, at the time of rotating the substrate S by the fine-adjustment mechanism  10  through the hollow rotary shaft  201 , the chuck plate  11  is moved up by pushing only the hollow rotary shaft  201 . In case there is added the actuator to move the hollow rotary shaft  201  up and down, the rotary shaft (push member) to which the rotating force is given from the fine-adjustment mechanism  10  need not be disposed coaxially with the rotary shaft (hollow rotary shaft) to which the rotating force is given from the coarse-adjustment mechanism  100 . 
     In the above-mentioned embodiment and each of the modified examples, descriptions have so far been made of examples in which the stage  4 ,  30  equipped with an alignment function was applied to a coating apparatus. Without being limited thereto, this invention may be applied to a case in which, like a back-grinding step to be performed, e.g., in the steps of manufacturing semiconductor devices, a predetermined processing is performed by cutting tools (processing means) to a wafer (an object to be processed) from a side opposite to the wafer, the wafer being disposed on a stage arranged in a movable manner. In this manner, alignment of the object to be processed can be made relative to the cutting tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of an inkjet type of coating apparatus provided with a stage equipped with an alignment function according to an embodiment of this invention; 
         FIG. 2  is a partial plan view of the inkjet type of coating apparatus explaining the stage main body; 
         FIG. 3  is a partial sectional view of the inkjet type of coating apparatus explaining the arrangement of the stage main body; 
         FIG. 4  is a partial sectional view showing an enlargement of the part IV in  FIG. 3 ; 
         FIG. 5  is a partial sectional view showing an enlargement of the part V in  FIG. 3 ; 
         FIG. 6  is a schematic plan view explaining the alignment of the substrate in the θ direction by the stage according to this invention; 
         FIG. 7  is a schematic side view explaining a first modified example of the stage equipped with the alignment function according to this invention; 
         FIG. 8  is a partial sectional view showing an enlargement of part VIII in  FIG. 7 ; 
         FIG. 9  is a plan view of the stage shown in  FIG. 7 ; 
         FIG. 10  is a partial sectional view explaining a second modified example of the stage equipped with the alignment function according to this invention; 
         FIG. 11  is a partial sectional view explaining a third modified example of the stage equipped with the alignment function according to this invention 
         FIG. 12  is a perspective view explaining by partially enlarging a drive means of the stage equipped with the alignment function relating to a third modified example; and 
         FIG. 13  is a partial sectional view explaining a fourth modified example of the stage equipped with the alignment function according to this invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS AND CHARACTERS  
     
         
           1   3 R,  3 L rail member (guide means) 
           4 ,  30  stage 
           4   a,    31  stage main body 
           8  suction means 
           9  gas supply means 
           10  fine-adjustment mechanism (drive means) 
           100  coarse-adjustment mechanism (drive means) 
           21  suction groove 
           33  holding tray 
         S substrate (object to be processed)