Patent Publication Number: US-11658146-B2

Title: Bonding apparatus, bonding system, bonding method, and recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation application of U.S. patent application Ser. No. 16/347,856 filed on May 7, 2019, now U.S. Patent Number 11,094,667 B2, which is a U.S. national phase application under 35 U.S.C. § 371 of PCT Application No. PCT/JP2017/036657 filed on Oct. 10, 2017, which claims the benefit of Japanese Patent Application No. 2016-218579 filed on Nov. 9, 2016, the entire disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The various embodiments described herein pertain generally to a bonding apparatus configured to bond substrates, a bonding system equipped with the bonding apparatus, a bonding method using the bonding apparatus and a recording medium. 
     BACKGROUND ART 
     Recently, semiconductor devices are getting miniaturized. If a plurality of highly integrated semiconductor devices is placed on a horizontal plane and these semiconductor devices are connected by a wiring to be produced as a product, a wiring length is increased. As a result, resistance of the wiring is increased, and there is a concern that a wiring delay may be increased. 
     In this regard, there is proposed using a three-dimensional integration technique of stacking semiconductor devices three-dimensionally. In this three-dimensional integration technique, two sheets of semiconductor wafers (hereinafter, referred to as “wafers”) are bonded by using a bonding system described in, for example, Patent Document 1. By way of example, the bonding system is equipped with a surface modifying apparatus configured to modify to-be-bonded surfaces of wafers; a surface hydrophilizing apparatus configured to hydrophilize the surfaces of the wafers which are modified by the surface modifying apparatus; a bonding apparatus configured to bond the wafers having the surfaces which are hydrophilized by the surface hydrophilizing apparatus. In this bonding system, the surfaces of the wafers are modified in the surface modifying apparatus by performing a plasma processing on the surfaces of the wafers. Further, in the surface hydrophilizing apparatus, the surfaces of the wafers are hydrophilized by supplying pure water onto the surfaces thereof. Then, the wafers are bonded in the bonding apparatus by a Van der Waals force and a hydrogen bond (intermolecular force). 
     In the aforementioned bonding apparatus, one wafer (hereinafter, referred to as “upper wafer”) is held by using an upper chuck, and the other wafer (hereinafter, referred to as “lower wafer”) is held by a lower chuck provided under the upper chuck. While being held by these upper and lower chucks, the upper wafer and the lower wafer are bonded. Here, before the wafers are bonded, a position of the lower chuck with respect to the upper chuck in a horizontal direction is adjusted by moving the lower chuck in the horizontal direction with a moving device, and, also, a position of the lower chuck in a rotational direction (a direction of the lower chuck) is adjusted by rotating the lower chuck with a moving device.
     Patent Document 1: Japanese Patent Laid-open Publication No. 2015-018919   

     In the bonding apparatus of the aforementioned Patent Document 1, however, when adjusting the position of the lower chuck in the rotational direction after adjusting the position of the lower chuck in the horizontal direction, a rotation shaft may be deviated in the horizontal direction when rotating the lower chuck depending on control accuracy of the moving device. In such a case, the horizontal position of the lower chuck with respect to the upper chuck may be deviated, and, resultantly, the upper wafer and the lower wafer may be deviated from each other when they are bonded. In this regard, there is still a room for improvement in bonding the wafers. 
     SUMMARY 
     The purpose of exemplary embodiments described herein is to provide a technique capable of performing a bonding processing of bonding substrates appropriately by performing position adjustment of a first holder configured to hold a first substrate and a second holder configured to hold a second substrate appropriately. 
     In one exemplary embodiment, a bonding apparatus configured to bond substrates includes a first holder configured to vacuum-exhaust a first substrate to attract and hold the first substrate on a bottom surface thereof; a second holder disposed under the first holder and configured to vacuum-exhaust a second substrate to attract and hold the second substrate on a top surface thereof; a rotator configured to rotate the first holder and the second holder relatively; a moving device configured to move the first holder and the second holder relatively in a horizontal direction; a position measurement device disposed at the first holder or the second holder rotated by the rotator and configured to measure a position of the first holder or the second holder; and a controller configured to control the rotator and the moving device based on measurement results of the position measurement device, and the position measurement device comprises a first position measurement device, a second position measurement device and a third position measurement device, and a distance between the first position measurement device and the second position measurement device is same as a distance between the first position measurement device and the third position measurement device. 
     According to the exemplary embodiment, since the position of the first holder or the second holder is measured by using the three position measurement devices, eccentric amounts (deviation amounts) between the first holder and the second holder in the rotational direction, the X direction and the Y direction can be respectively calculated, and correction amounts for the first holder or the second holder in the rotational direction, the X direction and the Y direction can be calculated from the measurement results. By controlling the rotator and the moving device based on the calculation results, the relative position between the first holder and the second holder can be appropriately adjusted. Accordingly, the bonding between the first substrate held by the first holder and the second substrate held by the second holder can be carried out appropriately after the position adjustment. 
     In another exemplary embodiment, a bonding system equipped with a bonding apparatus comprises a processing station equipped with the bonding apparatus; and a carry-in/out station configured to place thereon multiple first substrates, multiple second substrates or multiple combined substrates each obtained by bonding the first substrate and the second substrate, and configured to carry the first substrates, the second substrates or the combined substrates into/from the processing station. The processing station comprises a surface modifying apparatus configured to modify surfaces of the first substrate or the second substrate to be bonded; a surface hydrophilizing apparatus configured to hydrophilize the surface of the first substrate or the second substrate modified by the surface modifying apparatus; and a transfer device configured to transfer the first substrates, the second substrates or the combined substrates with respect to the surface modifying apparatus, the surface hydrophilizing apparatus and the bonding apparatus. In the bonding apparatus, the first substrate and the second substrate having the surfaces hydrophilized by the surface hydrophilizing apparatus are bonded. 
     In still another exemplary embodiment, in a bonding method of bonding substrates by using a bonding apparatus, the bonding apparatus comprises a first holder configured to vacuum-exhaust a first substrate to attract and hold the first substrate on a bottom surface thereof; a second holder disposed under the first holder and configured to vacuum-exhaust a second substrate to attract and hold the second substrate on a top surface thereof; a rotator configured to rotate the first holder and the second holder relatively; a moving device configured to move the first holder and the second holder relatively in a horizontal direction; and a position measurement device disposed at the first holder or the second holder rotated by the rotator and configured to measure a position of the first holder or the second holder, and the position measurement device comprises a first position measurement device, a second position measurement device and a third position measurement device, and a distance between the first position measurement device and the second position measurement device is same as a distance between the first position measurement device and the third position measurement device. The bonding method comprises measuring the position of the first holder or the second holder by using the three position measurement devices; and adjusting a relative position between the first holder and the second holder by controlling the rotator and the moving device based on measurement results in the measuring of the position. 
     In yet another exemplary embodiment, there is provided a computer-readable recording medium having stored thereon computer-executable instructions that, in response to execution, cause the bonding apparatus to perform the bonding method. 
     According to the exemplary embodiments as described above, it is possible to perform the bonding processing of bonding the substrates appropriately by performing the position adjustment of the first holder configured to hold the first substrate and the second holder configured to hold the second substrate appropriately. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view schematically illustrating a configuration of a bonding system according to an exemplary embodiment. 
         FIG.  2    is a side view schematically illustrating an internal configuration of the bonding system according to the exemplary embodiment. 
         FIG.  3    is a side view schematically illustrating a configuration of an upper wafer and a lower wafer. 
         FIG.  4    is a transversal cross sectional view schematically illustrating a configuration of a bonding apparatus. 
         FIG.  5    is a longitudinal cross sectional view schematically illustrating the configuration of the bonding apparatus. 
         FIG.  6    is a longitudinal cross sectional view schematically illustrating an upper chuck, an upper chuck rotator and a lower chuck. 
         FIG.  7    is a plan view schematically illustrating a configuration of the upper chuck rotator. 
         FIG.  8    is an explanatory diagram showing individual dimensions when calculating an eccentric amount of the upper chuck with respect to the lower chuck. 
         FIG.  9    is a flowchart illustrating major processes of a wafer bonding processing. 
         FIG.  10    is an explanatory diagram illustrating a state in which a center of the upper wafer and a center of the lower wafer are pressed to be brought into contact with each other. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, various exemplary embodiments will be described with reference to accompanying drawings. Further, it should be noted that the exemplary embodiments are not intended to be anyway limiting. 
     1. Configuration of Bonding System 
     First, a configuration of a bonding system according to an exemplary embodiment will be discussed.  FIG.  1    is a plan view schematically illustrating a configuration of a bonding system  1 .  FIG.  2    is a side view schematically illustrating an internal configuration of the bonding system  1 . 
     In the bonding system  1 , two sheets of wafers W U  and W L  as substrates are bonded, for example, as shown in  FIG.  3   . Hereinafter, a wafer placed at an upper side is referred to as “upper wafer W U ” as a first substrate, and a wafer placed at a lower side is referred to as “lower wafer W L ” as a second substrate. Further, in surfaces of the upper wafer W U , a bonding surface to be bonded is referred to as “front surface W U1 ,” and a surface opposite to the front surface W U1  is referred to as “rear surface W U2 .” Likewise, in surfaces of the lower wafer W L , a bonding surface to be bonded is referred to as “front surface W L1 ,” and a surface opposite to the front surface W L1  is referred to as “rear surface W L2 .” In the bonding system  1 , a combined wafer W T  as a combined substrate is formed by bonding the upper wafer W U  and the lower wafer W L . 
     The bonding system  1  is equipped with, as depicted in  FIG.  1   , a carry-in/out station  2  and a processing station  3  connected as a single body. The carry-in/out station  2  is configured to carry cassettes C U , C L  and C T , which accommodates therein a plurality of wafers W U , a plurality of wafers W L  and a plurality of combined wafers W T , respectively, to/from the outside. The processing station  3  is equipped with various kinds of processing apparatuses configured to perform preset processings on the wafers W U  and W L  and the combined wafer W T . 
     The carry-in/out station  2  includes a cassette placing table  10 . The cassette placing table  10  is equipped with a multiple number of, for example, four cassette placing plates  11 . The cassette placing plates  11  are arranged in a horizontal X direction (up-and-down direction of  FIG.  1   ). When the cassettes C U , C L , C T  are carried to/from the outside of the bonding system  1 , the cassettes C U , C L , C T  are placed on these cassette placing plates  11 . In this way, the carry-in/out station  2  is configured to be capable of holding a multiple number of upper wafers W U , a multiple number of lower wafers W L  and a multiple number of combined wafers W T . Further, the number of the cassette placing tables  11  is not limited to the example shown in the present exemplary embodiment, and may be set as required. Furthermore, one of the cassettes may be used to collect abnormal wafers. That is, an abnormal combined wafer, which has suffered a problem in bonding between an upper wafer W U  and a lower wafer W L , is separately accommodated in a cassette to be separated from other normal combined wafers W T . In the present exemplary embodiment, one of the cassettes C T  is used for the collection of the abnormal wafers, and other cassettes C T  are used for the accommodation of the normal combined wafers W T . 
     The carry-in/out station  2  is equipped with a wafer transfer section  20  adjacent to the cassette placing table  10 . Provided in the wafer transfer section  20  is a wafer transfer device  22  configured to be movable along a transfer path  21  which is extended in the X direction. The wafer transfer device  22  is configured to be movable in a vertical direction and pivotable around a vertical axis (θ direction). The transfer device  22  is configured to transfer the wafers W U  and W L  and the combined wafer W T  between the cassettes C U , C L  and C T  placed on the cassette placing plates  11  and transition devices  50  and  51  of a third processing block G 3  of the processing station  3  to be described later. 
     A multiple number of, for example, three processing blocks G 1 , G 2  and G 3  equipped with various kinds of apparatuses are provided in the processing station  3 . For example, the first processing block G 1  is provided at a front side (negative X-directional side of  FIG.  1   ) of the processing station  3 , and the second processing block G 2  is provided at a rear side (positive X-directional side of  FIG.  1   ) of the processing station  3 . Further, the third processing block G 3  is provided near the carry-in/out station  2  (at a negative Y direction side of  FIG.  1   ) of the processing station  3 . 
     Provided in the first processing block G 1  is a surface modifying apparatus  30  configured to modify the surfaces W U1  and W L1  of the wafers W U  and W L . In the surface modifying apparatus  30 , an oxygen gas or a nitrogen gas as a processing gas is formed into plasma under a decompressed atmosphere to be ionized. These oxygen ions or nitrogen ions are irradiated to the surfaces W U1  and W L1  of the wafers W U  and W L , so the surfaces W U1  and W L1  are plasma-processed to be modified. 
     By way of example, in the second processing block G 2 , a surface hydrophilizing apparatus  40  and a bonding apparatus  41  are arranged in a horizontal Y direction in this sequence from the carry-in/out station  2 . The surface hydrophilizing apparatus  40  is configured to hydrophilize and clean the surfaces W U1  and W L1  of the wafers W U  and W L  with, for example, pure water. The bonding apparatus  41  is configured to bond the wafers W U  and W L . A configuration of the bonding apparatus  41  will be elaborated later. 
     In this surface hydrophilizing apparatus  40 , while rotating the wafer W U  (W L ) held by, for example, a spin chuck, the pure water is supplied onto the corresponding wafer W U  (W L ). The supplied pure water is diffused on the surface W U1  (W L1 ) of the wafer W U  (W L ), so that the surface W U1  (W L1 ) is hydrophilized. 
     By way of example, in the third processing block G 3 , the transition devices  50  and  51  for the wafers W U  and W L  and the combined wafer W T  are arranged in two levels in this order from the bottom, as illustrated in  FIG.  2   . 
     Further, as illustrated in  FIG.  1   , a wafer transfer region  60  is formed in an area surrounded by the first processing block G 1  to the third processing block G 3 . For example, a wafer transfer device  61  is disposed in the wafer transfer region  60 . 
     The wafer transfer device  61  is equipped with, for example, a transfer arm  61   a  which is configured to be movable in a vertical direction and a horizontal direction (Y direction and X direction) and pivotable around a vertical axis. The wafer transfer device  61  is moved within the wafer transfer region  60  and transfers the wafers W U  and W L  and the combined wafer W T  into preset apparatuses within the first processing block G 1 , the second processing block G 2  and the third processing block G 3  which are adjacent to the wafer transfer region  60 . 
     As depicted in  FIG.  1   , the bonding system  1  is equipped with a controller  70 . The controller  70  may be implemented by, for example, a computer and includes a program storage (not shown). The program storage stores therein programs for controlling processings on the wafers W U  and W L  and the combined wafer W T  in the bonding system  1 . Further, the program storage also stores therein programs for controlling operations of the aforementioned various kinds of the processing apparatuses and a driving system such as the transfer devices to thereby allow a wafer bonding processing to be described later to be performed in the bonding system  1 . Further, the programs are stored in, for example, a computer-readable recording medium H such as a hard disk (HD), a flexible disk (FD), a compact disk (CD), a magnet optical disk (MO) or a memory card, and may be installed to the controller  70  from the recording medium H. 
     2. Configuration of Bonding Apparatus 
     Now, a configuration of the bonding apparatus  41  will be explained. 
     &lt;2-1. Overall Configuration of Bonding Apparatus&gt; 
     As depicted in  FIG.  4   , the bonding apparatus  41  includes a processing chamber  100  having a hermetically sealable inside. A carry-in/out opening  101  for the wafers W U  and W L  and the combined wafer W T  is formed at a lateral side of the processing vessel  100  on the side of the wafer transfer region  60 . An opening/closing shutter  102  for the carry-in/out opening  101  is provided at the carry-in/out opening  101 . 
     The inside of the processing vessel  100  is partitioned into a transfer region T 1  and a processing region T 2  by an inner wall  103 . The aforementioned carry-in/out opening  101  is formed at the lateral side of the processing vessel  100  in the transfer region T 1 . Further, the inner wall  103  is also provided with a carry-in/out opening  104  for the wafers W U  and W L  and the combined wafer W T . 
     A transition  110  configured to temporarily place thereon the wafers W U  and W L  and the combined wafer W T  is provided at a positive Y-directional side of the transfer region T 1 . The transition  110  has, for example, two levels and is capable of holding any two of the wafers W U  and W L  and the combined wafer W T  at the same time. 
     A wafer transfer device  111  is provided within the transfer region T 1 . The wafer transfer device  111  is equipped with a transfer arm  111   a  configured to be movable in the vertical direction and the horizontal direction (X direction and Y direction) and also pivotable around a vertical axis, as shown in  FIG.  4    and  FIG.  5   . The wafer transfer device  111  is capable of transferring the wafers W U  and W L  and the combined wafer W T  within the transfer region T 1  or between the transfer region T 1  and the processing region T 2 . 
     A position adjusting device  120  configured to adjust a direction of the wafers W U  and W L  in the horizontal direction is provided at a negative Y-directional side of the transfer region T 1 . The position adjusting device  120  includes: a base  121  equipped with a holder (not shown) configured to hold and rotate the wafer W U  (W L ); and a detector  122  configured to detect a position of a notch of the wafer W U  (W L ). The position adjusting device  120  adjusts the position of the notch of the wafer W U  (W L ) by detecting the position of the notch with the detector  122  while rotating the wafer W U  (W L ) held by the base  121 . Accordingly, the horizontal positions of the wafer W U  (W L ) is adjusted. Further, a structure configured to hold the wafer W U  (W L ) in the base  121  is not particularly limited. By way of non-limiting example, various structures such as a pin chuck structure or a spin chuck structure may be utilized. 
     Furthermore, an inverting device  130  configured to invert a front surface and a rear surface of the upper wafer W U  is provided in the transfer region T 1 . The inverting device  130  is equipped with a holding arm  131  configured to hold the upper wafer W U . The holding arm  131  is extended in the horizontal direction (X direction). Further, the holding arm  131  is provided with holding members  132  respectively arranged at four positions. The holding members  132  are configured to hold the upper wafer W U . 
     The holding arm  131  is supported by a driver  133  including, for example, a motor or the like. The holding arm  131  is configured to be rotatable around a horizontal axis by the driver  133 . Further, the holding arm  131  is rotatable around the driver  133  and movable in the horizontal direction (X direction). Another driver (not shown) including, for example, a motor or the like is provided under the driver  133 . The driver  133  can be moved in the vertical direction along a vertically extended supporting column  134  by this another driver. The upper wafer W U  held by the holding members  132  can be rotated around the horizontal axis and can also be moved in the vertical direction and the horizontal direction by the driver  133 . Further, the upper wafer W U  held by the holding members  132  can be moved between the position adjusting device  120  and an upper chuck  140  to be described later by being rotated around the driver  133 . 
     The upper chuck  140  and a lower chuck  141  are disposed in the processing region T 2 . The upper chuck  140  serves as a first holder configured to attract and hold the upper wafer W U  on a bottom surface thereof, and the lower chuck  141  serves as a second holder configured to place the lower wafer W L  on a top surface thereof while attracting and holding the lower wafer W L . The lower chuck  141  is provided under the upper chuck  140  and is configured to be disposed to face the upper chuck  140 . That is, the upper wafer W U  held by the upper chuck  140  and the lower wafer W L  held by the lower chuck  141  can be arranged to face each other. 
     The upper chuck  140  is held by an upper chuck rotator  150  disposed above the upper chuck  140 . The upper chuck rotator  150  is configured to rotate the upper chuck  140  around a vertical axis as will be described later. Further, the upper chuck rotator  150  is provided at a ceiling surface of the processing vessel  100 . 
     The upper chuck rotator  150  is equipped with an upper imaging device  151  configured to image the front surface W L1  of the lower wafer W L  held by the lower chuck  141 . That is, the upper imaging device  151  is disposed adjacent to the upper chuck  140 . The upper imaging device  151  may be, by way of example, but not limitation, a CCD camera. 
     The lower chuck  141  is supported by a lower chuck stage  160  provided under the lower chuck  141 . The lower chuck stage  160  is equipped with a lower imaging device  161  configured to image the front surface W U1  of the upper wafer W U  held by the upper chuck  140 . That is, the lower imaging device  161  is disposed adjacent to the lower chuck  141 . The lower imaging device  161  may be, by way of example, but not limitation, a CCD camera. 
     The lower chuck stage  160  is supported by a first lower chuck mover  162  disposed under the lower chuck stage  160 . Further, the first lower chuck mover  162  is supported by a supporting table  163 . The first lower chuck mover  162  is configured to move the lower chuck  141  in the horizontal direction (X direction) as will be described later. Moreover, the first lower chuck mover  162  is configured to move the lower chuck  141  in the vertical direction. 
     The supporting table  163  is fastened to a pair of rails  164  which is disposed at a bottom side of the supporting table  163  to be elongated in the horizontal direction (X direction). The supporting table  163  is configured to be movable along the rails  164  by the first lower chuck mover  162 . Further, the first lower chuck mover  162  is moved by, for example, a linear motor (not shown) provided along the rails  164 . 
     The rails  164  are provided at a second lower chuck mover  165 . The second lower chuck mover  165  is fastened to a pair of rails  166  which is provided at a bottom side of the second lower chuck mover  165  to be elongated in the horizontal direction (Y direction). The second lower chuck mover  165  is configured to be movable along the rails  166 , that is, to move the lower chuck  141  in the horizontal direction (Y direction). The second lower chuck mover  165  is moved by, for example, a linear motor (not shown) provided along the rails  166 . The rails  166  are disposed on a placing table  167  provided at a bottom surface of the processing vessel  100 . 
     Further, in the present exemplary embodiment, the first lower chuck mover  162  and the second lower chuck mover  165  constitutes a moving device of the present disclosure. 
     &lt;2-2. Configuration of Upper Chuck and Upper Chuck Rotator&gt; 
     Now, a detailed configuration of the upper chuck  140  and the upper chuck rotator  150  of the bonding apparatus  41  will be described. 
     The upper chuck  140  is of a pin chuck type, as shown in  FIG.  6   . The upper chuck  140  has a main body  170  having a diameter larger than a diameter of the upper wafer W U  when viewed from the top. A plurality of pins  171  configured to be brought into contact with the rear surface W U2  of the upper wafer W U  is provided at a bottom surface of the main body  170 . Further, an outer rib  172  having the same height as the pins  171  and configured to support a periphery of the rear surface W U2  of the upper wafer W U  is provided at a periphery of the bottom surface of the main body  170 . The outer rib  172  is annularly formed at an outside of the pins  171 . 
     Further, an inner rib  173  having the same height as the pins  171  and configured to support the rear surface W U2  of the upper wafer W U  is provided at an inside of the outer rib  172  on the bottom surface of the main body  170 . The inner rib  173  is formed in a ring shape to be concentric with the outer rib  172 . A region  174  inside the outer rib  172  (hereinafter, sometimes referred to as “suction region  174 ”) is partitioned into a first suction region  174   a  inside the inner rib  173  and a second suction region  174   b  outside the inner rib  173 . 
     First suction openings  175   a  for vacuum-exhausting the upper wafer W U  in the first suction region  174   a  are formed at the bottom surface of the main body  170 . The first suction openings  175   a  are formed at, for example, four positions in the first suction region  174   a . The first suction openings  175   a  are connected to first suction lines  176   a  which are provided within the main body  170 . Further, the first suction lines  176   a  are connected with a first vacuum pump  177   a.    
     In addition, second suction openings  175   b  for vacuum-exhausting the upper wafer W U  in the second suction region  174   b  are formed at the bottom surface of the main body  170 . The second suction openings  175   b  are formed at, for example, two positions within the second suction region  174   b . The second suction openings  175   b  are connected to second suction lines  176   b  provided within the main body  170 . Further, the second suction lines  176   b  are connected with a second vacuum pump  177   b.    
     By vacuum-exhausting the suction regions  174   a  and  174   b  formed by being surrounded by the upper wafer W U , the main body  170  and the outer rib  172  through the suction openings  175   a  and  175   b , respectively, the suction regions  174   a  and  174   b  are decompressed. At this time, since an atmosphere at the outside of the suction regions  174   a  and  174   b  is under an atmospheric pressure, the upper wafer W U  is pressed toward the suction regions  174   a  and  174   b  by the atmospheric pressure as much as a decompressed amount, so that the upper wafer W U  is attracted to and held by the upper chuck  140 . Further, the upper chuck  140  is configured to be capable of vacuum-exhausting the upper wafer W U  through the first suction region  174   a  and the second suction region  174   b  individually. 
     In this case, since the outer rib  172  supports the periphery of the rear surface W U2  of the upper wafer W U , the upper wafer W U  is appropriately vacuum-exhausted, including the periphery thereof. Therefore, the entire surface of the upper wafer W U  is attracted to and held by the upper chuck  140 , and flatness of the upper wafer W U  can be reduced and the upper wafer W U  can thus be flattened. 
     Furthermore, since the heights of the pins  171  are uniform, flatness of the bottom surface of the upper chuck  140  can be further reduced. In this way, by flattening the bottom surface (by reducing the flatness of the bottom surface) of the upper chuck  140 , the upper wafer W U  held by the upper chuck  140  can be suppressed from suffering from a deformation in the vertical direction. 
     Further, since the rear surface W U2  of the upper wafer W U  is supported by the pins  171 , it is easy for the upper wafer W U  to be separated from the upper chuck  140  when releasing the vacuum-exhaust of the upper wafer W U  by the upper chuck  140 . 
     The upper chuck  140  is provided with a through hole  178  which is formed through a center of the main body  170  in a thickness direction of the main body  170 . The center of this main body  170  corresponds to a center of the upper wafer W U  held by and attracted to the upper chuck  140 . A leading end of the actuator  191  of a pressing member  190  to be described later is inserted through this through hole  178 . 
     The upper chuck rotator  150  is equipped with an upper chuck stage  180  provided on a top surface of the main body  170  of the upper chuck  140  and configured to hold the upper chuck  140 , as depicted in  FIG.  6    and  FIG.  7   . The upper chuck stage  180  has an open top and has a hollow cylindrical shape. When viewed from the top, the upper chuck stage  180  has the substantially same shape as the main body  170 . Provided at an outer circumferential surface of the upper chuck stage  180  is a supporting member  181  configured to support the upper chuck stage  180  and mounted to the ceiling surface of the processing vessel  100 . A slight gap is formed between the outer circumferential surface of the upper chuck stage  180  and an inner circumferential surface of the supporting member  181 . 
     The pressing member  190  configured to press the center of the upper wafer W U  is provided on a bottom surface within the upper chuck stage  180 . The pressing member  190  has the actuator  191  and a cylinder  192 . 
     The actuator  191  is configured to generate a constant pressure in a certain direction by air supplied from an electro-pneumatic regulator (not shown), and is capable of generating the pressure constantly regardless of a position of a point of application of the pressure. The actuator  191  is capable of controlling a pressing load applied to the center of the upper wafer W U  by the air from the electro-pneumatic regulator while the actuator  191  comes into contact with the center of the upper wafer W U . Further, the leading end of the actuator  191  is vertically movable up and down through the through hole  178  by the air from the electro-pneumatic regulator. 
     The actuator  191  is supported by the cylinder  192 . The cylinder  192  is capable of moving the actuator  191  in the vertical direction by a driver having, for example, a motor embedded therein. 
     As stated above, the pressing member  190  controls the pressing load with the actuator  191  and controls the movement of the actuator  191  with the cylinder  192 . The pressing member  190  is capable of pressing the center of the upper wafer W U  and a center of the lower wafer W L  when bonding of the wafers W U  and W L  to be described later is performed. 
     The supporting member  181  is equipped with, as depicted in  FIG.  7   , a rotating device  200  configured to rotate the upper chuck stage  180  (and the upper chuck  140 ). The rotating device  200  is in contact with the outer circumferential surface of the upper chuck stage  180  and is capable of rotating the upper chuck state  180  with a driver which has, for example, a motor embedded therein. 
     Further, the supporting member  181  is provided with fixing parts  210  configured to hold the upper chuck stage  180  in place. The fixing parts  210  are equi-spaced at four positions along the outer circumferential surface of the upper chuck stage  180 . Each fixing part  210  blows air toward the outer circumferential surface of the upper chuck stage  180 , thus achieves centering of the upper chuck stage  180  and holds the upper chuck stage  180  in place. 
     Further, the supporting member  181  is equipped with linear scales  221  to  223  as position measurement devices each configured to measure a position of the upper chuck stage  180 , that is, a position of the upper chuck  140 . The linear scales  221  to  223  include scales  221   a  to  223   a  provided at the outer circumferential surface of the upper chuck stage  180  and detection heads  221   b  to  223   b  configured to read the scales  221   a  to  223   a , respectively. Further, for the measuring method of the position of the upper chuck  140  by the linear scales  221  to  223 , a commonly known method may be utilized. 
     In the three linear scales  221  to  223 , the first linear scale  221  is disposed to face the rotating device  200  on a central line of the upper chuck stage  180 . Further, the second linear scale  222  and the third linear scale  223  are disposed at positions where they form a central angle of 90 degrees with respect to the first linear scale  221 , and are disposed to face each other on the central line of the upper chuck stage  180 . That is, a distance between the first linear scale  221  and the second linear scale  222  and a distance between the first linear scale  221  and the third linear scale  223  are same. 
     Furthermore, through the linear scale is used as the position measurement device in the present exemplary embodiment, the position measurement device is not limited thereto as long as it is capable of measuring the position of the upper chuck  140 . By way of non-limiting example, a displacement meter may be used as the position measurement device. 
     &lt;2-3. Position Adjustment of Upper Chuck&gt; 
     The first linear scale  221  is connected to a servo amplifier (not shown), and the servo amplifier is connected to the controller  70 . That is, the first linear scale  221  is used for a servo control (full close control), and a measurement result of the first linear scale  221  is used to adjust a position of the upper chuck  140  in the rotational direction ( 0  direction) around the vertical axis thereof, as will be described later. 
     Further, the second linear scale  222  and the third linear scale  223  are respectively connected to the controller  70 . Measurement results of the three linear scales  221  to  223  are used to adjust a position of the upper chuck  140  in the horizontal direction (X direction and Y direction) as will be described later, and also used, when required, to adjust the position of the upper chuck  140  in the rotational direction ( 0  direction). To elaborate, to adjust these positions of the upper chuck  140 , the eccentric amount (deviation amount) of the upper chuck  140  with respect to the lower chuck  141  is calculated from the measurement results of the three linear scales  221  to  223 . 
     Here, a method of calculating the aforementioned eccentric amount of the upper chuck  140  will be explained.  FIG.  8    is an explanatory diagram showing dimensions required to calculate the eccentric amount of the upper chuck  140 . In  FIG.  8   , a reference numeral  140   a  refers to a center point of the upper chuck  140  which is not eccentric, that is, located at a right position, and a reference numeral  140   b  indicates a center point of the upper chuck  140  which is eccentric. Measurement results L 1  to L 3  of the three linear scales  221  to  223  are respectively represented by the following expressions (1) to (3). Further, the measurement results L 1  to L 3  of the linear scales  221  to  223  are encoder values (absolute values) counted up in the clockwise direction.
 
 L 1= y+Rθ   (1)
 
 L 2=− x+Rθ   (2)
 
 L 3= x+Rθ   (3)
         L 1 : An encoder value of the first linear scale  221     L 2 : An encoder value of the second linear scale  222     L 3 : An encoder value of the third linear scale  223     x: An eccentric amount of the upper chuck  140  with respect to the lower chuck  141  in X direction   y: An eccentric amount of the upper chuck  140  with respect to the lower chuck  141  in Y direction   θ: An eccentric amount (rotation amount) of the upper chuck  140  with respect to the lower chuck  141     R: Radius of the upper chuck  140         

     If the expressions (1) to (3) are organized with respect to x, y and  0 , the following expressions (4) to (6) are derived.
 
 x =( L 3− L 2)/2  (4)
 
 y=L 1−( L 3+ L 2)/2  (5)
 
θ=( L 3+ L 2)/2 R   (6)
 
     &lt;2-4. Configuration of Lower Chuck&gt; 
     Now, a detailed configuration of the lower chuck  141  of the bonding apparatus  41  will be explained. 
     The lower chuck  141  is of a pin chuck type, the same as the upper chuck  140 , as shown in  FIG.  6   . The lower chuck  141  has a main body  230  having a diameter larger than a diameter of the lower wafer W L  when viewed from the top. A plurality of pins  231  configured to be brought into contact with the rear surface W L2  of the lower wafer W L  is provided at a top surface of the main body  230 . Further, an outer rib  232  having the same height as the pins  231  and configured to support a periphery of the rear surface W L2  of the lower wafer W L  is provided at a periphery of the top surface of the main body  230 . The outer rib  232  is annularly formed at an outside of the pins  231 . 
     Further, an inner rib  233  having the same height as the pins  231  and configured to support the rear surface W L2  of the lower wafer W L  is provided at an inside of the outer rib  232  on the top surface of the main body  230 . The inner rib  233  is formed in a ring shape to be concentric with the outer rib  232 . A region  234  inside the outer rib  232  (hereinafter, sometimes referred to as “suction region  234 ”) is partitioned into a first suction region  234   a  inside the inner rib  233  and a second suction region  234   b  outside the inner rib  233 . 
     A first suction opening  235   a  for vacuum-exhausting the lower wafer W L  in the first suction region  234   a  is formed at the top surface of the main body  230 . The first suction opening  235   a  is formed at, for example, a single position in the first suction region  234   a . The first suction opening  235   a  is connected to a first suction line  236   a  which is provided within the main body  230 . Further, the first suction line  236   a  is connected with a first vacuum pump  237   a.    
     In addition, second suction openings  235   b  for vacuum-exhausting the lower wafer W L  in the second suction region  234   b  are formed at the top surface of the main body  230 . The second suction openings  235   b  are formed at, for example, two positions within the second suction region  234   b . The second suction openings  235   b  are connected to second suction lines  236   b  provided within the main body  230 . Further, the second suction lines  236   b  are connected with a second vacuum pump  237   b.    
     By vacuum-exhausting the suction regions  234   a  and  234   b  formed by being surrounded by the lower wafer W L , the main body  230  and the outer rib  232  through the suction openings  235   a  and  235   b , respectively, the suction regions  234   a  and  234   b  are decompressed. At this time, since an atmosphere at the outside of the suction regions  234   a  and  234   b  is under the atmospheric pressure, the lower wafer W L  is pressed toward the suction regions  234   a  and  234   b  by the atmospheric pressure as much as a decompressed amount, so that the lower wafer W L  is attracted to and held by the lower chuck  141 . Further, the lower chuck  141  is configured to be capable of vacuum-exhausting the lower wafer W L  through the first suction region  234   a  and the second suction region  234   b  individually. 
     In this case, since the outer rib  232  supports the periphery of the rear surface W L2  of the lower wafer W L , the lower wafer W L  is appropriately vacuum-exhausted, including the periphery thereof. Therefore, the entire surface of the lower wafer W L  is attracted to and held by the lower chuck  141 , and flatness of the lower wafer W L  can be reduced and the lower wafer W L  can thus be flattened. 
     Furthermore, since the heights of the pins  231  are uniform, flatness of the top surface of the lower chuck  141  can be further reduced. In this way, by flattening the top surface (by reducing the flatness of the top surface) of the lower chuck  141 , the lower wafer W L  held by the lower chuck  141  can be suppressed from suffering from a deformation in a vertical direction. 
     Further, since the rear surface W L2  of the lower wafer W L  is supported by the pins  231 , it is easy for the lower wafer W L  to be separated from the lower chuck  141  when releasing the vacuum-exhaust of the lower wafer W L  by the lower chuck  141 . 
     The lower chuck  141  is provided with through holes (not shown) which are formed in a thickness direction of the main body  230  at, e.g., three positions in the vicinity of a center of the main body  230 . Elevating pins provided under the first lower chuck mover  162  are inserted through these through holes. 
     Guide members (not shown) are provided at a periphery of the main body  230  to suppress each of the wafers W U  and W L  and the combined wafer W T  from falling down by being bounced off or slid off the lower chuck  141 . The guide members are equi-spaced at plural positions, for example, four positions at the periphery of the main body  230 . 
     The operations of the individual components of the bonding apparatus  41  are controlled by the aforementioned controller  70 . 
     3. Bonding Method 
     Now, a bonding method for the wafers W U  and W L  performed by the bonding system  1  configured as described above will be explained.  FIG.  9    is a flowchart illustrating an example of main processes of such a wafer bonding processing. 
     First, a cassette C U  accommodating the upper wafers W U , a cassette C L  accommodating the lower wafers W L  and an empty cassette C T  are placed on the preset cassette placing plates  11  of the carry-in/out station  2 . Then, an upper wafer W U  is taken out of the cassette C U  by the wafer transfer device  22  and is transferred to the transition device  50  of the third processing block G 3  of the processing station  3 . 
     Subsequently, the upper wafer W U  is transferred into the surface modifying apparatus  30  of the first processing block G 1  by the wafer transfer device  61 . In the surface modifying apparatus  30 , an oxygen gas or a nitrogen gas as the processing gas is excited into plasma to be ionized under the preset decompressed atmosphere. The oxygen ions or the nitrogen ions are irradiated to the front surface W U1  of the upper wafer W U , and the front surface W U1  is plasma-processed. As a result, the front surface W U1  of the upper wafer W U  is modified (process S 1  of  FIG.  9   ). 
     Then, the upper wafer W U  is transferred into the surface hydrophilizing apparatus  40  of the second processing block G 2  by the wafer transfer device  61 . In the surface hydrophilizing apparatus  40 , pure water is supplied onto the upper wafer W U  while rotating the upper wafer W U  held by the spin chuck. The supplied pure water is diffused on the front surface W U1  of the upper wafer W U , and hydroxyl groups (silanol groups) adhere to the front surface W U1  of the upper wafer W U  modified in the surface modifying apparatus  30 , so that the front surface W U1  is hydrophilized. Further, the front surface W U1  of the upper wafer W U  is cleaned by the pure water (process S 2  of  FIG.  9   ). 
     Thereafter, the upper wafer W U  is transferred into the bonding apparatus  41  of the second processing block G 2  by the wafer transfer device  61 . The upper wafer W U  carried into the bonding apparatus  41  is then transferred into the position adjusting device  120  through the transition  110  by the wafer transfer device  111 . Then, the direction of the upper wafer W U  in the horizontal direction is adjusted by the position adjusting device  120  (process S 3  of  FIG.  9   ). 
     Then, the upper wafer W U  is delivered onto the holding arm  131  of the inverting device  130  from the position adjusting device  120 . Then, in the transfer region T 1 , by inverting the holding arm  131 , the front surface and the rear surface of the upper wafer W U  are inverted (process S 4  of  FIG.  9   ). That is, the front surface W U1  of the upper wafer W U  is turned to face downwards. 
     Thereafter, the holding arm  131  of the inverting device  130  is rotated around the driver  133  to be located under the upper chuck  140 . The upper wafer W U  is then transferred to the upper chuck  140  from the inverting device  130 . The rear surface W U2  of the upper wafer W U  is attracted to and held by the upper chuck  140  (process S 5  of  FIG.  9   ). To elaborate, by operating the vacuum pumps  177   a  and  177   b , the upper wafer W U  is vacuum-exhausted through the suction openings  175   a  and  175   b  in the suction regions  174   a  and  174   b , so that the upper wafer W U  is attracted to and held by the upper chuck  140 . 
     While the above-described processes S 1  to S 5  are being performed on the upper wafer W U , processings are performed on the lower wafer W L . First, the lower wafer W L  is taken out of the cassette C L  by the wafer transfer device  22  and transferred into the transition device  50  of the processing station  3 . 
     Subsequently, the lower wafer W L  is transferred into the surface modifying apparatus  30  by the wafer transfer device  61 , and the front surface W L1  of the lower wafer W L  is modified (process S 6  of  FIG.  9   ). Further, the modification of the front surface W L1  of the lower wafer W L  in the process S 6  is the same as the above-described process S 1 . 
     Thereafter, the lower wafer W L  is transferred into the surface hydrophilizing apparatus  40  by the wafer transfer device  61 , so that the front surface W L1  of the lower wafer W L  is hydrophilized and cleaned (process S 7  of  FIG.  9   ). The hydrophilizing and the cleaning of the front surface W L1  of the lower wafer W L  in the process S 7  are the same as those in the above-described process S 2 . 
     Afterwards, the lower wafer W L  is transferred into the bonding apparatus  41  by the wafer transfer device  61 . The lower wafer W L  carried into the bonding apparatus  41  is transferred into the position adjusting device  120  through the transition  110  by the wafer transfer device  111 . Then, the direction of the lower wafer W L  in the horizontal direction is adjusted by the position adjusting device  120  (process S 8  of  FIG.  9   ). 
     Then, the lower wafer W L  is transferred onto the lower chuck  141  by the wafer transfer device  111 , and the rear surface W L2  is attracted to and held by the lower chuck  141  (process S 9  of  FIG.  9   ). To elaborate, by operating the vacuum pumps  237   a  and  237   b , the lower wafer W L  is vacuum-exhausted through the suction openings  235   a  and  235   b  in the suction regions  234   a  and  234   b , so that the lower wafer W L  is attracted to and held by the lower chuck  141 . 
     Subsequently, the position adjustment of the upper wafer W U  held by the upper chuck  140  and the lower wafer W L  held by the lower chuck  141  is performed. 
     First, initial adjustment of the positions of the upper wafer W U  and the lower wafer W L  in the rotational direction (horizontal direction) is performed by using the upper imaging device  151  and the lower imaging device  161 . To elaborate, the lower chuck  141  is moved in the horizontal direction (X direction and Y direction) by the first lower chuck mover  162  and the second lower chuck mover  165 , and preset reference points (for example, two points at a periphery) on the front surface W L1  of the lower wafer W L  are imaged in sequence by using the upper imaging device  151 . Concurrently, preset reference points (for example, two points at a periphery) on the front surface W U1  of the upper wafer W U  are imaged in sequence by using the lower imaging device  161 . The obtained images are outputted to the controller  70 . Based on the images obtained by the upper imaging device  151  and the lower imaging device  161 , the controller  70  rotates the upper chuck  140  by the rotating device  200  to a position where the reference points of the upper wafer W U  and the lower wafer W L  are overlapped, that is, where the directions of the upper wafer W U  and the lower wafer W L  become identical. In this way, the positions of the upper wafer W U  and the lower wafer W L  in the rotational direction are initially adjusted (process S 10  of  FIG.  9   ). 
     Here, the position adjustment using the upper imaging device  151  and the lower imaging device  161  is performed only in this process S 10 , and the position adjustments in the subsequent processes S 11  and S 12  are performed by using the linear scales  221  to  223  as will be described later. Particularly, in the process S 11 , though the position of the upper chuck  140  in the rotational direction is adjusted by using the first linear scale  221 , initial states of the upper wafer W U  held by the upper chuck  140  and the lower wafer W L  held by the lower chuck  141  in the rotational direction cannot be observed with the first linear scale  221 . For this reason, in the aforementioned process S 10 , the positions of the upper wafer W U  and the lower wafer W L  in the rotational direction are initially adjusted. 
     After the process S 10 , the position of the upper chuck  140  is measured by using the first linear scale  221 . The measurement result of the first linear scale  221 , that is, the encoder value L 1  of the first linear scale  221  is outputted to the controller  70 . The controller  70  calculates a correction amount for the upper chuck  140  in the rotational direction based on the encoder value L 1  of the first linear scale  221  such that an eccentric amount θ of the upper chuck  140  with respect to the lower chuck  141  in the rotational direction falls within a preset threshold value, e.g., ±0.2 μrad. Then, the controller  70  controls the rotating device  200  based on this correction amount. As the upper chuck  140  is rotated by the rotating device  200  as much as the correction amount, the position of the upper chuck  140  with respect to the lower chuck  141  in the rotational direction is adjusted (process S 11  of  FIG.  9   ). 
     In the process S 11 , the first linear scale  221  spaced farthest from the rotating device  200  is used. By way of example, if the upper chuck  140  and the lower chuck  141  are deviated from each other in the rotational direction, an influence of this deviation is largely reflected in this encoder value L 1  of the first linear scale  221  as compared to an encoder value L 2  of the second linear scale  222  or an encoder value L 3  of the third linear scale  223 , for example. Accordingly, the position of the upper chuck  140  in the rotational direction can be adjusted more appropriately. 
     Further, in the process S 11 , when rotating the upper chuck  140  by the rotating device  200 , the upper chuck stage  180  is centered by the fixing parts  210 . 
     In addition, in the process S 11 , the rotating device  200  may be controlled such that the eccentric amount θ of the upper chuck  140  in the rotational direction becomes zero. Further, if the encoder value L 1  of the first linear scale  221  is found to fall within a preset threshold value as a result of the measurement by the first linear scale  221 , it may not be required to rotate the upper chuck  140  with the rotating device  200 . 
     In the above-described process S 11 , when rotating the upper chuck  140  by the rotating device  200 , a center point (rotation axis) of the upper chuck  140  may be deviated from the center point  140   a  to the center point  140   b  in the horizontal direction, as shown in  FIG.  8   . By way of example, in case that the control accuracy of the rotating device  200  is low, the center point of the upper chuck  140  is deviated in the horizontal direction. Further, though the upper chuck  140  is centered by the air from the four fixing parts  210 , the center point of the upper chuck  140  may be deviated in the horizontal direction depending on the air balance from these fixing parts  210 . 
     Thus, the horizontal position of the upper chuck  140  is then adjusted. To elaborate, the position of the upper chuck  140  is first measured by using the three linear scales  221  to  223 . The measurement results of the three linear scales  221  to  223 , that is, the encoder values L 1  to L 3  of the three linear scales  221  to  223  are outputted to the controller  70 . Based on the encoder values L 1  to L 3  of the linear scales  221  to  223 , the controller  70  calculates eccentric amounts x, y and θ of the upper chuck  140  with respect to the lower chuck  141  in the X direction, the Y direction and the θ direction, respectively, from the following expressions (4) to (6).
 
 x =( L 3− L 2)/2  (4)
 
 y=L 1−( L 3+ L 2)/2  (5)
 
θ=( L 3+ L 2)/2 R   (6)
 
     Further, the controller  70  calculates the correction amounts for the upper chuck  140  in the horizontal direction (X direction and Y direction) such that the eccentric amount x of the upper chuck  140  in the X direction and the eccentric amount y of the upper chuck  140  in the Y direction fall within a preset threshold value, e.g., 1 μm. Then, the controller  70  controls the first lower chuck mover  162  and the second lower chuck mover  165  based on these correction amounts. As the upper chuck  140  is moved by the first lower chuck mover  162  and the second lower chuck mover  165  as much as the correction amounts, the position of the upper chuck  140  with respect to the lower chuck  141  in the horizontal direction is adjusted (process S 12  of  FIG.  9   ). 
     In the process S 12 , since the distance between the first linear scale  221  and the second linear scale  222  is equal to the distance between the first linear scale  221  and the third linear scale  223 , simple expressions such as the aforementioned expressions (4) to (6) may be used. Here, if these distances are different, an equation for calculating the eccentric amounts of the upper chuck  140  would be complicated, resulting in a complicated control as well. In the present exemplary embodiment, the horizontal position of the upper chuck  140  can be adjusted through the simple control. 
     Furthermore, in the process S 12 , the first lower chuck mover  162  and the second lower chuck mover  165  may be controlled such that the eccentric amount x of the upper chuck  140  in the X direction and the eccentric amount y of the upper chuck  140  in the Y direction both become zero. Further, if each of the encoder values L 1  to L 3  of the linear scales  221  to  223  falls within the preset threshold value as a result of the measurement by the three linear scales  221  to  223 , it is not needed to move the upper chuck  140  in the horizontal direction by the first lower chuck mover  162  and the second lower chuck mover  165 . 
     Moreover, in the process S 12  of the present exemplary embodiment, the position of the upper chuck  140  in the horizontal direction is adjusted. By way of example, if the eccentric amount θ of the upper chuck  140  in the rotational direction calculated from the expression (6) does not fall within the preset threshold value, e.g., ±0.2 μrad, the position of the upper chuck  140  in the rotational direction may be further adjusted. To be specific, in the controller  70 , the correction amount for the upper chuck  140  in the rotational direction is calculated based on the eccentric amount θ of the upper chuck  140  in the rotational direction. Then, the upper chuck  140  is rotated by the correction amount with the rotating device  200 , so that the position of the upper chuck  140  with respect to the lower chuck  141  in the rotational direction is adjusted. 
     By performing the above-stated processes S 10  to S 12 , the position adjustment between the upper chuck  140  and the lower chuck  141  is performed, and the positions of the upper wafer W U  held by the upper chuck  140  and the lower wafer W L  held by the lower chuck  141  in the rotational direction and the horizontal direction are adjusted. 
     Thereafter, by moving the lower chuck  141  vertically upwards by the first lower chuck mover  162 , the position adjustment between the upper chuck  140  and the lower chuck  141  in the vertical direction is performed, so that the position adjustment between the upper wafer W U  held by the upper chuck  140  and the lower wafer W L  held by the lower chuck  141  in the vertical direction is carried out (process S 13  of  FIG.  9   ). Then, the upper wafer W U  and the lower wafer W L  are located at the preset positions while facing each other. 
     Subsequently, a bonding processing of bonding the upper wafer W U  held by the upper chuck  140  and the lower wafer W L  held by the lower chuck  141  is performed. 
     First, as depicted in  FIG.  10   , the actuator  191  is lowered by the cylinder  192  of the pressing member  190 . As the actuator  191  is moved down, the center of the upper wafer W U  is lowered while being pressed. At this time, the preset pressing load is applied to the actuator  191  by the air supplied from the electro-pneumatic regulator. The center of the upper wafer W U  and the center of the lower wafer W L  are pressed to be in contact with each other by the pressing member  190  (process S 14  of  FIG.  9   ). At this time, by stopping the operation of the vacuum pump  177   a , the vacuum-exhaust of the upper wafer W U  from the first suction openings  175   a  in the first suction region  174   a  is stopped, while carrying on the operation of the second vacuum pump  177   b  to vacuum-exhaust the second suction region  174   b  from the second suction openings  175   b . When pressing the center of the upper wafer W U  with the pressing member  190 , the periphery of the upper wafer W U  can still be held by the upper chuck  140 . 
     Accordingly, the bonding is started between the center of the upper wafer W U  and the center of the lower wafer W L  which are pressed against each other (as indicted by a bold line in  FIG.  10   ). That is, since the front surface W U1  of the upper wafer W U  and the front surface W L1  of the lower wafer W L  have been modified in the processes S 1  and S 6 , respectively, a Van der Waals force (intermolecular force) is generated between the front surfaces W U1  and W L1 , so that the front surfaces W U1  and W L1  are bonded. Further, since the front surface W U1  of the upper wafer W U  and the front surface W L1  of the lower wafer W L  have been hydrophilized in the processes S 2  and S 7 , respectively, hydrophilic groups between the front surfaces W U1  and W L1  are hydrogen-bonded (intermolecular force), so that the front surfaces W U1  and W L1  are firmly bonded. 
     Then, by stopping the operation of the second vacuum pump  177   b  while still pressing the center of the upper wafer W U  and the center of the lower wafer W L  with the pressing member  190 , the vacuum-exhaust of the upper wafer W U  from the second suction openings  175   b  in the second suction region  174   b  is stopped. Accordingly, the upper wafer W U  falls down on the lower wafer W L . The upper wafer W U  gradually falls on the lower wafer W L  to be in contact with each other, and the aforementioned bonding between the front surfaces W U1  and W L1  by the Van der Waals force and the hydrogen-bond is gradually expanded. Accordingly, the entire front surface W U1  of the upper wafer W U  and the entire front surface W L1  of the lower wafer W L  are brought into contact with each other, so that the upper wafer W U  and the lower wafer W L  are bonded (process S 15  of  FIG.  9   ). 
     In this process S 15 , since the rear surface W U2  of the upper wafer W U  is supported by the pins  171 , the upper wafer W U  is easily separated from the upper chuck  140  when the vacuum-exhaust of the upper wafer W U  by the upper chuck  140  is released. Thus, the expansion (bonding wave) of the bonding between the upper wafer W U  and the lower wafer W L  takes place in a circular shape, so that the upper wafer W U  and the lower wafer W L  are appropriately bonded. 
     Thereafter, the actuator  191  of the pressing member  190  is raised up to the upper chuck  140 . Further, by stopping the operation of the vacuum pumps  237   a  and  237   b  and thus stopping the vacuum-exhaust of the lower wafer W L  in the suction region  234 , the attracting and holding of the lower wafer W L  by the lower chuck  141  is stopped. At this time, since the rear surface W L z of the lower wafer W L  is supported by the pins  231 , the lower wafer W L  is easily separated from the lower chuck  141  when the vacuum-exhaust of the lower wafer W L  by the lower chuck  141  is released. 
     Thereafter, the combined wafer W T  obtained by the bonding of the upper wafer W U  and the lower wafer W L  is transferred to the transition device  51  by the wafer transfer device  61 , and then is transferred into the cassette C T  of the preset cassette placing table  11  by the wafer transfer device  22  of the carry-in/out station  2 . Through these processes, the series of operations of the bonding processing for the wafers W U  and W L  is completed. 
     According to the exemplary embodiment as described above, in the process S 11 , the position of the upper chuck  140  with respect to the lower chuck  141  in the rotational direction is adjusted by using the measurement result of the first linear scale  221 . At this time, by using the first linear scale  221  which is located at the farthest position from the rotating device  200 , the deviation of the upper chuck  140  and the lower chuck  141  in the rotational direction can be investigated more appropriately than in cases of using the other linear scales  222  and  223 . Thus, the position of the upper chuck  140  in the rotational direction can be appropriately adjusted. 
     Further, in the process S 12 , the horizontal position of the upper chuck  140  with respect to the lower chuck  141  is adjusted by using the measurement results of the three linear scales  221  to  223 . Accordingly, even if the horizontal position of the upper chuck  140  is deviated when adjusting the position of the upper chuck  140  in the rotational direction in the process S 11 , it is possible to correct and adjust the horizontal position of the upper chuck  140  appropriately in the process S 12 . 
     Furthermore, in this process S 12 , in case that the eccentric amount θ of the upper chuck  140  in the rotational direction is not within the preset threshold value, the position of the upper chuck  140  in the rotational direction can be appropriately adjusted. 
     Since the relative positions between the upper chuck  140  and the lower chuck  141  can be appropriately adjusted in the processes S 11  and S 12  as stated above, the bonding between the upper wafer W U  held by the upper chuck  140  and the lower wafer W L  held by the lower chuck  141  can be appropriately carried out. 
     Conventionally, in case of further performing the position adjustment after adjusting the positions of the upper wafer W U  and the lower wafer W L  by using the upper imaging device  151  and the lower imaging device  161  in the process S 10 , it takes time to accomplish this position adjustment as the upper imaging device  151  and the lower imaging device  161  are used again. According to the present exemplary embodiment, however, since this position adjustment is performed by using the linear scales  221  to  223  in the processes S 11  and S 12 , the position adjustment can be carried out in a short time. Therefore, a throughput of the wafer bonding processing can be bettered. 
     Moreover, since the bonding system  1  of the present exemplary embodiment is equipped with the surface modifying apparatus  30 , the surface hydrophilizing apparatus  40  and the bonding apparatus  41 , the bonding of the wafers W U  and W L  can be conducted efficiently within the single system. Therefore, the throughput of the wafer bonding processing can be further improved. 
     4. Other Exemplary Embodiments 
     Now, other exemplary embodiments of the present disclosure will be explained. 
     In the bonding apparatus  41  according to the above-described exemplary embodiment, the second linear scale  222  and the third linear scale  223  are disposed at the positions where they form the central angle of 90 degrees with respect to the first linear scale  221 , and are disposed to face each other on the central line of the upper chuck stage  180 . However, the arrangement of the second linear scale  222  and the third linear scale  223  is not limited thereto. The second linear scale  222  and the third linear scale  223  may be provided at positions where their central angle with respect to the first linear scale  221  forms an angel different from 90 degrees, e.g., 45 degrees, as long as the distance between the first linear scale  221  and the second linear scale  222  and the distance between the first linear scale  221  and the third linear scale  223  are same. If these distances are same even if the central angle is not 90 degrees, the eccentric amount of the upper chuck  140  can be calculated by using the simple equations as the expressions (4) to (6). Thus, the position adjustment of the upper chuck  140  can be carried out through the simple control. 
     Further, in the bonding apparatus  41  of the above-described exemplary embodiment, the upper chuck  140  is configured to be rotatable. However, the lower chuck  141  may be configured to be rotatable instead. In such a case, the three linear scales  221  to  223  are provided at the lower chuck  141 . Further, both the upper chuck  140  and the lower chuck  141  may be configured to be rotatable. In such a case, the three linear scales  221  to  223  may be provided at either the upper chuck  140  or the lower chuck  141 . 
     Moreover, in the bonding apparatus  41  according to the above-described exemplary embodiment, though the lower chuck  141  is configured to be movable in the horizontal direction, the upper chuck  140  may be configured to be movable in the horizontal direction instead, or both the upper chuck  140  and the lower chuck  141  may be configured to be movable in the horizontal direction. Likewise, though the lower chuck  141  is configured to be movable in the vertical direction, the upper chuck  140  may be configured to be vertically movable instead, or both the upper chuck  140  and the lower chuck  141  may be configured to be vertically movable. 
     In addition, in the bonding system  1  according to the above-stated exemplary embodiment, after the wafers W U  and the W L  are bonded in the bonding apparatus  41 , the obtained combined wafer W T  may be heated to a preset temperature (annealing processing). By performing this heating processing on the combined wafer W T , bonding interfaces can be firmly bonded. 
     From the foregoing, it will be appreciated that the exemplary embodiment of the present disclosure has been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the embodiment disclosed herein is not intended to be limiting. The scope of the inventive concept is defined by the following claims and their equivalents rather than by the detailed description of the exemplary embodiment. It shall be understood that all modifications and embodiments conceived from the meaning and scope of the claims and their equivalents are included in the scope of the inventive concept. In the present disclosure, the substrate is not limited to the wafer. The present disclosure is also applicable to various other types of substrates such as a FPD (Flat Panel Display), a mask reticle for photomask, and so forth. 
     The claims of the present application are different and possibly, at least in some aspects, broader in scope than the claims pursued in the parent application. To the extent any prior amendments or characterizations of the scope of any claim or cited document made during prosecution of the parent could be construed as a disclaimer of any subject matter supported by the present disclosure, Applicants hereby rescind and retract such disclaimer. Accordingly, the references previously presented in the parent applications may need to be revisited.
           1 : Bonding system     2 : Carry-in/out station     3 : Processing station     30 : Surface modifying apparatus     40 : Surface hydrophilizing apparatus     41 : Bonding apparatus     61 : Wafer transfer device     70 : Controller     140 : Upper chuck     141 : Lower chuck     150 : Upper chuck rotator     162 : First lower chuck mover     165 : Second lower chuck mover     200 : Rotating device     221 : First linear scale     222 : Second linear scale     223 : Third linear scale   W U : Upper wafer   W L : Lower wafer   W T : Combined wafer