Abstract:
Wafer processing apparatuses and methods for polishing and cleaning semiconductor wafers with high productivity, small footprint, easy maintenance and low defectivity are provided. The apparatuses comprise a polishing apparatus and a cleaning apparatus. The polishing apparatus comprises at least one polishing module. Each module comprises at least one polishing surface, at least one polishing head, at least one wafer transfer station and a transport mechanism to transfer the at least one polishing head between the at least one polishing surface and the at least one wafer transfer station. The polishing module may comprise a shield member and fluid injection devices to protect the at least one polishing surface from foreign particles. The cleaning apparatus can comprise two or more dry chambers for high productivity. The wafer processing apparatuses can comprise two cleaning apparatuses for high productivity.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is entitled to the benefit of U.S. Provisional Patent Application Ser. Nos. 61/280,441 filed on Nov. 3, 2009, 61/283,324 filed on Dec. 2, 2009, 61/283,479 filed on Dec. 4, 2009, 61/283,694 filed on Dec. 8, 2009, 61/284,160 filed on Dec. 14, 2009, 61/284,448 filed on Dec. 21, 2009, and 61/399,096 filed on Jul. 6, 2010, which are all incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to semiconductor wafer processing equipments, and more particularly to apparatuses and methods for polishing and cleaning semiconductor wafers. 
       BACKGROUND OF THE INVENTION 
       [0003]    Local and global planarization of semiconductor wafers becomes increasingly important as more metal layers and interlayer dielectric layers are stacked on the wafers. A preferred method to planarize the wafers is a polishing method, where a surface of a semiconductor wafer is polished using a slurry solution supplied between the wafer and a polishing pad. The polished wafer is cleaned using chemicals and deionized (DI) water and then dried before the wafer is further processed in an apparatus for deposition of metallic or dielectric layers or photolithography. 
         [0004]    In general, a wafer processing apparatus for polishing semiconductor wafers includes a polishing apparatus and a cleaning apparatus. The polishing apparatus generally comprises multiple polishing tables where polishing pads are placed and multiple polishing heads that support and press the wafers against the polishing pads. The cleaning apparatus generally comprises multiple cleaning chambers for cleaning semiconductor wafers and a dry chamber for drying the cleaned wafers. The wafers polished in the polishing apparatus are cleaned sequentially through the multiple cleaning chambers and then dried in the dry chamber. 
         [0005]    One of the most important performance factors of a wafer processing apparatus for polishing and cleaning semiconductor wafers is productivity. For high productivity, a wafer processing apparatus can comprise two cleaning apparatuses because productivity of a wafer processing apparatus can be limited by low productivity of a single cleaning apparatus. When integrating two cleaning apparatuses with a polishing apparatus, the arrangement of the polishing apparatus and the cleaning apparatuses becomes important to efficiently polish and clean multiple semiconductor wafers. In addition, the footprint of a wafer processing apparatus must also be considered since a wafer processing apparatus with a large footprint requires a larger clean room to house the equipment, which translates into greater cost of operation. 
         [0006]    Another important performance factor of a wafer processing apparatus for polishing and cleaning semiconductor wafers is ease of maintenance. For easy maintenance, the arrangement of polishing and cleaning apparatuses in a wafer processing apparatus becomes important to provide enough space for engineers to access the polishing and cleaning apparatuses in order to maintain them. 
         [0007]    One of the most important performance factors of a cleaning apparatus used in a wafer processing apparatus for polishing and cleaning semiconductor wafers is productivity. For high productivity of a wafer processing apparatus, productivity of a cleaning apparatus needs to be improved because productivity of a wafer processing apparatus can be limited by low productivity of a cleaning apparatus. 
         [0008]    One of the most important performance factors of a polishing apparatus used in a wafer processing apparatus for polishing and cleaning semiconductor wafers is productivity. For higher productivity, a polishing apparatus typically requires more polishing tables and more polishing heads. As the numbers of polishing tables and polishing heads included in a polishing apparatus are increased, the efficient arrangement of the polishing tables and the polishing heads becomes important to design a polishing apparatus providing efficient polishing of semiconductor wafers with a small footprint. 
         [0009]    Another important performance factor of a polishing apparatus used in a wafer processing apparatus for polishing and cleaning semiconductor wafers is defectivity. Defectivity can be caused by large foreign particles dropping onto polishing pads from moving parts used to transfer polishing heads between the polishing pads. For low defectivity, a polishing apparatus requires an efficient design to protect polishing pads from the foreign particles. 
         [0010]    In view of these issues, what is needed is an apparatus and method for polishing and cleaning semiconductor wafers with high productivity, small footprint, sufficient maintenance space and low defectivity. 
       SUMMARY OF THE INVENTION 
       [0011]    An apparatus for polishing an object in accordance with an embodiment of the present invention comprises at least one polishing surface, at least one polishing head assembly comprising at least one polishing head, at least one object transfer station and a transport mechanism configured to transport the at least one polishing head assembly between the at least one polishing surface and the at least one object transfer station. The transport mechanism comprises a support structure comprising an opening disposed over the at least one polishing surface and the at least one object transfer station, at least one inner guide rail supported by the support structure, wherein the at least one inner guide rail is surrounded by the opening, at least one first guide block slidibly coupled to the at least one inner guide rail, at least one outer guide rail supported by the support structure, wherein the at least one outer guide rail surrounds the opening, at least one second guide block slidibly coupled to the outer guide rail, at least one head supporting member mounted to the at least one first guide block and the at least one second guide block, wherein the at least one head supporting member supports the at least one polishing head assembly, and at least one drive mechanism coupled to the at least one head supporting member, wherein the at least one drive mechanism is configured to transport the at least one polishing head assembly coupled to the at least one head supporting member between the at least one polishing surface and the at least one object transfer station. 
         [0012]    Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a top view of a polishing apparatus in accordance with an embodiment of the present invention. 
           [0014]      FIG. 2  is a top view of a polishing module used in the polishing apparatus of  FIG. 1 . 
           [0015]      FIG. 3  is a side view of the polishing module of  FIG. 2 . 
           [0016]      FIGS. 4(   a ) and  4 ( b ) are tops view of polishing apparatuses in accordance with embodiments of the present invention. 
           [0017]      FIG. 5  is a top view of a wafer processing apparatus in accordance with an embodiment of the present invention. 
           [0018]      FIG. 6  is a cross-sectional view of a cleaning apparatus used in the wafer processing apparatus of  FIG. 5 . 
           [0019]      FIG. 7  is a top view of a wafer processing apparatus in accordance with an embodiment of the present invention. 
           [0020]      FIGS. 8(   a ) and  8 ( b ) are top views of cleaning apparatuses in accordance with embodiments of the present invention. 
           [0021]      FIGS. 9 and 10  are top views of polishing apparatuses in accordance with embodiments of the present invention. 
           [0022]      FIGS. 11-13  are top views of wafer processing apparatuses in accordance with embodiments of the present invention. 
           [0023]      FIG. 14  is a top view of a polishing apparatus in accordance with an embodiment of the present invention. 
           [0024]      FIGS. 15(   a ) and  15 ( b ) are top views of a pivoting wafer transfer device and washing devices used in the polishing apparatus of  FIG. 14 . 
           [0025]      FIG. 16  is a top view of a wafer processing apparatus in accordance with an embodiment of the present invention. 
           [0026]      FIG. 17  is a vertical cross-sectional view of a rotation mechanism in accordance with an embodiment of the present invention. 
           [0027]      FIGS. 18 and 19  are plan views of the rotation mechanism of  FIG. 17  seen from cross sections  600 L 1  and  600 L 2  of the rotation mechanism of  FIG. 17 , respectively. 
           [0028]      FIG. 20  is a vertical cross-sectional view of the rotation mechanism in accordance with an embodiment of the invention. 
           [0029]      FIG. 21  is a plan view of the rotation mechanism of  FIG. 20  seen from a cross section  600 L 3  of the rotation mechanism of  FIG. 20 . 
           [0030]      FIG. 22  is a cross-sectional view of a guide rail, a guide block and air nozzles of the rotation mechanism of  FIG. 20  in accordance with an embodiment of the present invention. 
           [0031]      FIG. 23  is a top view of the rotation mechanism of  FIG. 20  seen from a cross section  600 L 4  of the rotation mechanism of  FIG. 20 . 
           [0032]      FIG. 24  is a perspective sectional side view of the rotation mechanism of  FIG. 20 . 
           [0033]      FIG. 25  is a top view of a polishing apparatus in accordance with an embodiment of the present invention. 
           [0034]      FIGS. 26(   a )- 26 ( h ) are sequential top views of the polishing apparatus of  FIG. 25  to show a sequence of polishing wafers in accordance with an embodiment of the present invention. 
           [0035]      FIG. 27-29  are top views of wafer processing apparatuses in accordance with embodiments of the present invention. 
           [0036]      FIG. 30  is a cross-sectional view of a cleaning apparatus in accordance with an embodiment of the present invention. 
           [0037]      FIGS. 31(   a )- 31 ( u ) are sequential top views of the cleaning apparatus of  FIG. 30  to show a method of processing wafers in accordance with an embodiment of the present invention. 
           [0038]      FIGS. 32(   a ) and  32 ( b ) are side views of a wafer output stage in accordance with an embodiment of the present invention. 
           [0039]      FIGS. 33-35  are top views of wafer processing apparatuses in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    With reference to  FIG. 1 , a polishing apparatus  5  in accordance with an embodiment of the present invention is described.  FIG. 1  is a top view of the polishing apparatus  5 . The polishing apparatus  5  comprises a first polishing module  10 , a second polishing module  10 ′ and a wafer transfer device  40 . The polishing apparatus  5  comprises an enclosure  11  to isolate the polishing modules  10  and  10 ′ from the environment. The first polishing module  10  comprises three polishing heads  20   a - 20   c , two polishing surfaces  14   a  and  14   b , and one wafer transfer station  18 . The second polishing module  10 ′ comprises three polishing heads  20   a ′- 20   c ′, two polishing surfaces  14   a ′ and  14   b ′, and one wafer transfer station  18 ′. The wafer transfer device  40  is a device to supply wafers to be polished from a wafer source to the wafer transfer stations  18  and  18 ′ and to transfer polished wafers from the wafer transfer stations  18  and  18 ′ to a wafer storage. The first and second polishing modules  10  and  10 ′ are situated in the polishing apparatus  5  such that they are substantially symmetric across an imaginary plane  410 . 
         [0041]    In the following description of the polishing apparatus  5 , only the components of the first polishing module  10  are described. The components of the second polishing module  10 ′ are not described separately because the components of the first polishing module are used in the same manner as the components of the second polishing module. The components used in the second polishing module  10 ′ are designated with an additional prime symbol (′) after the same reference numbers used to designate the components used in the first polishing module  10 , similar to the designations of the first and second polishing modules  10  and  10 ′. For example, the first polishing heads of the first and second polishing modules  10  and  10 ′ are designated as  20   a  and  20   a ′, respectively. 
         [0042]    With reference to  FIGS. 2 and 3 , the configuration of the polishing module  10  is further described.  FIGS. 2 and 3  are top and side views of the polishing module  10 , respectively. The polishing surfaces  14   a  and  14   b  of the first polishing module  10  are supported on respective polishing tables  13   a  and  13   b  and rotated by respective rotation mechanisms about respective rotational axes  15   a  and  15   b . Polyurethane pads can be used as the polishing surfaces  14   a  and  14   b  of the polishing module  10 . The polishing surfaces  14   a  and  14   b  are situated in the polishing module  10  such that an imaginary plane A connecting the rotational axes  15   a  and  15   b  is parallel to a depth direction of the polishing module  10 , as indicated in  FIG. 1 . 
         [0043]    As shown in  FIG. 3 , the first polishing head  20   a  is coupled to an end of a shaft  21   a . The other end of the shaft  21   a  is coupled to a rotational-and-vertical drive mechanism  22   a , which controls rotational and vertical motions of the first polishing head  20   a . The rotational-and-vertical drive mechanism  22   a  is coupled to an end of an arm  24   a . The other end of the arm  24   a  is coupled to a rotation mechanism  26 . The first polishing head  20   a , the shaft  21   a , and the rotational-and-vertical drive mechanism  22   a  form a first polishing head assembly. In the same manner as the first polishing head  20   a  is coupled to the rotation mechanism  26 , the second and third polishing heads  20   b  and  20   c  are coupled to the rotation mechanism  26  through respective shafts  21   b  and  21   c , respective rotational-and-vertical drive mechanisms  22   b  and  22   c  and respective arms  23   b  and  23   c . The second polishing head  20   b , the shaft  21   b , and the rotational-and-vertical drive mechanism  22   b  form a second polishing head assembly. The third polishing head  20   c , the shaft  21   c , and the rotational-and-vertical drive mechanism  22   c  form a third polishing head assembly. 
         [0044]    The rotation mechanism  26  is overhead mounted above the polishing tables  13   a  and  13   b  to a top frame structure (not shown in  FIGS. 2 and 3 ) of the polishing apparatus  5 . The rotation mechanism  26  is configured to rotationally transport the polishing heads  20   a - 20   c  about a rotation axis  28  between the wafer transfer station  18  and the polishing surfaces  14   a  and  14   b  along a circular path  28   a . Thus, the rotation mechanism  26  can be considered as a transport mechanism configured to transport polishing head assemblies, which include polishing heads. The circular path  28   a  is a trajectory of centers  23   a - 23   c  of the polishing heads  20   a - 20   c  during the rotation about the rotation axis  28  as shown in  FIGS. 1 and 2 . 
         [0045]    The wafer transfer station  18  and the first and second polishing surfaces  14   a  and  14   b  are disposed angularly about the rotation axis  28  such that angles from a center  18   c  of the wafer transfer station  18  to the respective rotation axes  15   a  and  15   b  of the first and second polishing surfaces  14   a  and  14   b  about the rotation axis  28  may be equal to each other and in the range from 100 to 110 degree. Any device that can transfer wafers with the polishing heads  20   a - 20   c  can be used as the wafer transfer station  18 . 
         [0046]    For polishing wafers, the polishing heads  20   a - 20   c  with the wafers are transferred to the polishing surfaces  14   a  and  14   b  about the rotation axis  28  by the rotation mechanism  26  and then pressed against the polishing surfaces  14   a  and  14   b . The polishing heads  20   a - 20   c  are rotated about the respective rotation axes  23   a - 23   c  and the polishing surfaces  14   a  and  14   b  are also rotated about the respective rotation axes  15   a  and  15   b . Slurry is supplied onto the polishing surfaces  14   a  and  14   b  during this polishing process. 
         [0047]    As shown in  FIGS. 1 and 2 , the polishing surfaces  14   a  and  14   b , the wafer transfer station  18  and the rotation axis  28  are configured and disposed in the polishing module  10  such that the polishing module  10  can have two polishing positions P 11  and P 12  on the first polishing surface  14   a  and two polishing positions P 21  and P 22  on the second polishing surface  14   b . In order to polish the wafers held by the polishing heads  20   a - 20   c  on the first polishing surface  14   a , each of the centers  23   a - 23   c  of the polishing heads  20   a - 20   c  is positioned on either the position P 11  or P 12 . In order to polish the wafers held by the polishing heads  20   a - 20   c  on the second polishing surface  14   b , each of the centers  23   a - 23   c  of the polishing heads  20   a - 20   c  is positioned on either the position P 21  or P 22 . 
         [0048]    Still referring to  FIG. 2 , the positions of P 11 , P 12 , P 21  and P 22  are further described using circumferences of the polishing heads  20   a - 20   c  and the polishing surfaces  14   a  and  14   b . As shown in  FIG. 2 , the polishing heads  20   a - 20   c  can be positioned on the first polishing surface  14   a  such that the circumferences of the polishing heads  20   a - 20   c  can have same tangents with the circumference of the first polishing surface  14   a  at two points  14 X and  14 X* wherein the point  14 X is adjacent to the wafer transfer station  18 , and the point  14 X* is opposite to the point  14 X. The points  14 X and  14 X* are points on the circumference of the first polishing surface  14   a . The polishing heads  20   a - 20   c  can be positioned on the second polishing surface  14   b  such that the circumferences of the polishing heads  20   a - 20   c  can have same tangents with the circumference of the second polishing surface  14   b  at two points  14 Y and  14 Y* wherein the point  14 Y* is adjacent to the wafer transfer station  18 , and the point  14 Y is opposite to the point  14 Y*. The points  14 Y and  14 Y* are points on the circumference of the second polishing surface  14   b . When the circumference of one of the polishing heads  20   a - 20   c  has a tangent at either the point  14 X or  14 X*, the center of that polishing head will be positioned at the polishing position P 11  or P 12  respectively on the first polishing surface  14   a . When the circumference of one of the polishing heads  20   a - 20   c  has a tangent at either the point  14 Y or  14 Y*, the center of that polishing head will be positioned at the polishing position P 21  or P 22  respectively on the second polishing surface  14   b.    
         [0049]    In the description of the polishing apparatus  5 , positioning the centers  23   a - 23   c  of the polishing heads  20   a - 20   c  at the polishing position P 11  means that the centers  23   a - 23   c  can be positioned on the circular path  28   a  within 1 inch distance range from P 11  toward P 12 ; positioning the centers  23   a - 23   c  at the polishing position P 12  means that the centers  23   a - 23   c  can be positioned on the circular path  28   a  within 1 inch distance range from P 12  toward P 21 ; positioning the centers  23   a - 23   c  at the polishing position P 21  means that the centers  23   a - 23   c  can be positioned on the circular path  28   a  within 1 inch distance range from P 21  toward P 22 ; and positioning the centers  23   a - 23   c  at the polishing position P 22  means that the centers  23   a - 23   c  can be positioned on the circular path  28   a  within 1 inch distance range from P 22  toward P 21 . During the polishing process on the polishing positions P 11 -P 22 , the centers  23   a - 23   c  of the polishing heads  20   a - 20   c  can be oscillated clockwise one inch and counterclockwise one inch to and from P 11 , P 12 , P 21  and P 22  respectively about the rotation axis  28  by the rotation mechanism  26 . 
         [0050]    Turning back to  FIG. 1 , the polishing surfaces  14   a - 14   b ′ of the polishing apparatus  5  are coupled with respective pad conditioning devices  80   a - 80   b ′ and respective slurry supply arms  90   a - 90   b ′. Each pad conditioning device  80 , i.e., each of the pad conditioning devices  80   a - 80   b ′, comprises a pivoting mechanism  82 , an arm  84  and a conditioning disc  86 . The pivoting mechanism  82  is configured to pivot the conditioning disc  86  between the center of the polishing surface  14  and a parking position  87  about an axis  81 . Each slurry supply arm  90 , i.e., each of the slurry supply arms  90   a - 90   b ′, comprises a pivoting mechanism  92  and an arm  94 . The pivoting mechanism  92  pivots the arm  94  to a central area of the polishing surface  14  about an axis  91 . 
         [0051]    Depending on the locations of the pad conditioning devices  80   a - 80   b ′ and the slurry arms  90   a - 90   b ′ relative to the polishing surfaces  14   a - 14   b ′, polishing positions on the polishing surfaces  14   a - 14   b ′ are determined. For example, the polishing apparatus  5  shown in  FIG. 1  is configured such that the first polishing module  10  uses P 11  and P 22  as its polishing positions on the first and second polishing surfaces  14   a  and  14   b  respectively; and the second polishing module  10 ′ uses P 11 ′ and P 22 ′ as its polishing positions on the first and second polishing surfaces  14   a ′ and  14   b ′ respectively. 
         [0052]    With different locations of the pad conditioning devices  80   a - 80   b ′ and the slurry arms  90   a - 90   b ′ relative to the polishing surfaces  14   a  and  14   b ′ and different arrangement of the polishing modules  10  and  10 ′, different polishing positions can be used as shown in  FIGS. 4(   a ) and  4 ( c ).  FIG. 4(   a ) shows a modified version of the polishing apparatus  5  in accordance with an embodiment of the present invention, which is configured such that the first polishing module  10  uses P 12  and P 21  as it polishing positions on the first and second polishing surfaces  14   a  and  14   b  respectively; and the second polishing module  10 ′ uses P 12 ′ and P 21 ′ as it polishing positions on the first and second polishing surfaces  14   a ′ and  14   b ′ respectively.  FIG. 4(   b ) shows another modified version of the polishing apparatus  5  in accordance with an embodiment of the present invention, which is configured such that the first polishing module  10  uses P 12  and P 21  as its polishing positions on the first and second polishing surfaces  14   a  and  14   b  respectively; and the second polishing module  10 ′ uses P 11 ′ and P 22 ′ as its polishing positions on the first and second polishing surfaces  14   a ′ and  14   b ′ respectively. 
         [0053]    With reference to  FIG. 5 , a wafer processing apparatus  100  in accordance with an embodiment of the present invention is described.  FIG. 5  is a top view of the wafer processing apparatus  100 . The wafer processing apparatus  100  comprises two cleaning apparatuses  120  and  120 ′, the polishing apparatus  5 , a factory interface  64 , a wafer input stage  16   a , two cleaner buffers  16   b  and  16   b ′ (equivalent to “cleaner interface stages” used in U.S. Provisional Patent Applications from which this application claims priority), and two wafer output stages  16   c  and  16   c′.    
         [0054]    The cleaner buffers  16   b  and  16   b ′ are devices where polished wafers are placed by the wafer transfer device  40 . The first cleaner buffer  16   b  is positioned at a first end  120   x  of the first cleaning apparatus  120  which is adjacent to the polishing apparatus  5 . The second cleaner buffer  16   b ′ is positioned at a first end  120   x ′ of the second cleaning apparatus  120 ′ which is adjacent to the polishing apparatus  5 . The cleaner buffers  16   b  and  16   b ′ may be enclosed in the respective cleaning apparatuses  120  and  120 ′ as one of the components of the respective cleaning apparatuses  120  and  120 ′. Respective second ends  120   y  and  120   y ′ of the first and second cleaning apparatuses  120  and  120 ′ are positioned adjacent to the factory interface  64 . The wafer output stages  16   c  and  16   c ′ are positioned at the respective second ends  120   y  and  120   y ′ of the first and second cleaning apparatuses  120  and  120 ′. 
         [0055]    The polishing apparatus  5  is disposed in the back side of the wafer processing apparatus  100  such that the respective imaginary planes A and A′ of the polishing modules  10  and  10 ′ are parallel to a depth direction of the wafer processing apparatus  100 . The cleaning apparatuses  120  and  120 ′ are disposed between the factory interface  64  and the polishing apparatus  5  such that longer sides  120   a  and  120   a ′ of the cleaning apparatuses  120  and  120 ′ are parallel to the depth direction of the wafer processing apparatus  100 . The cleaning apparatuses  120  and  120 ′ are disposed such that there is a space  120 S, which is surrounded by the factory interface  64 , the cleaning apparatuses  120  and  120 ′, and the polishing apparatus  5 . The wafer input stage  16   a  and the wafer transfer device  40  are positioned in the space  120 S. 
         [0056]    The factory interface  64  includes a cassette  60  and a wafer transfer device  50 . The cassette  60  is a device to store wafers to be processed and the wafers that have been processed. The wafer transfer device  50  transfer wafers from the cassette  60  to the wafer input stage  16   a  and from the wafer output stages  16   c  and  16   c ′ of the cleaning apparatuses  120  and  120 ′ to the cassette  60 . The factory interface  64  may further comprise a linear track  52 . The wafer transfer device  50  is coupled to the linear track  52  such that the wafer transfer device  50  can move linearly along the track  52 . The linear track  52  is positioned parallel to a width direction of the wafer processing apparatus  100 , as indicated in  FIG. 5 . 
         [0057]    The wafer input stage  16   a  is a device where wafers that will be transferred by the wafer transfer device  40  are placed by the wafer transfer device  50 . The wafer input stage  16   a  may be coupled to a stage transfer device  77  such that the wafer input stage  16   a  can move between a wafer receiving position RP 1  and a wafer release position RP 2  by the stage transfer device  77 . The wafer receiving position RP 1  is adjacent to the factory interface  64  such that the wafer input stage  16   a  can receive wafers from the wafer transfer device  50 . The wafer release position RP 2  is adjacent to the wafer transfer device  40  such that the wafer input stage  16   a  can release the wafers to the wafer transfer device  40 . 
         [0058]    The wafer transfer device  40  is positioned in a space surrounded by the wafer transfer stations  18  and  18 ′, the cleaner buffers  16   b  and  16   b ′, and the wafer release position RP 2 . The wafer transfer device  40  may be mounted to a linear track  42 . The linear track  42  is designed and disposed such that the wafer transfer device  40  can move between the wafer release position RP 2 , the cleaner buffers  16   b  and  16   b ′, and the wafer transfer stations  18  and  18 ′ of the polishing apparatus  5 . 
         [0059]    With reference to  FIG. 6 , the cleaning apparatuses  120  and  120 ′ are further described.  FIG. 6  is a cross sectional view of a cleaning apparatus  120  that can be used as the cleaning apparatuses  120  and  120 ′. The cleaning apparatus  120  comprises a cleaning module  124  and a fluid control system  126 . The fluid control system  126  controls supply and drain of chemical fluid to and from the cleaning module  124 . The cleaning module  124  comprises wafer stages  124   a - 124   d . Wafers are placed on the cleaner buffer  16   b  by the wafer transfer device  40 . An internal wafer transfer device  122  transfers the wafers from the cleaner buffer  16   b  to the wafer output stage  16   c  through the wafer stages  124   a - 124   d  sequentially. The cleaned and dried wafers are removed from the wafer output stage  16   c  by the wafer transfer device  50 . 
         [0060]    The internal wafer transfer device  122  comprises multiple grippers  162   a - 162   e  and a vertical-and-lateral transfer mechanism  164 . The first gripper  162   a  transfers a wafer from the cleaner buffer  16   b  through a first position CP 1  and a second position CP 2  to the first wafer stage  124   a . The second gripper  162   b  transfers the wafer from the first wafer stage  124   a  through the second position CP 2  and a third position CP 3  to the second wafer stage  124   b . The third gripper  162   c  transfers the wafer from the second stage  124   b  through the third position CP 3  and a fourth position CP 4  to the third wafer stage  124   c . The fourth gripper  162   d  transfers the wafer from the third stage  124   c  through the fourth position CP 4  and a fifth position CP 5  to the fourth wafer stage  124   d . The fifth gripper  162   e  transfers the wafer from the fourth stage  124   d  through the fifth position CP 5  and a sixth position CP 6  to the wafer output stage  16   c.    
         [0061]    Turning back to  FIG. 5 , a method of processing wafers in the wafer processing apparatus  100  is described. A first wafer W 1  is transferred from the cassette  60  to the wafer input stage  16   a  at the wafer receiving position RP 1  by the wafer transfer device  50 . The wafer input stage  16   a  is transferred from the wafer receiving position RP 1  to the wafer release position RP 2  by the stage transfer device  77 . The wafer W 1  is transferred from the wafer input stage  16   a  to the wafer transfer station  18  of the first polishing module  10  by the wafer transfer device  40 . The wafer W 1  is picked from the wafer transfer station  18  by the first polishing head  20   a  of the first polishing module  10 . The wafer W 1  is polished on the first and second polishing surfaces  14   a  and  14   b , and then placed on the wafer transfer station  18  by the first polishing head  20   a . The wafer W 1  is transferred from the wafer transfer station  18  to the cleaner buffer  16   b  of the first cleaning apparatus  120  by the wafer transfer device  40 , further transferred from there through the cleaning module  124  to the wafer output stage  16   c  by the internal wafer transfer device  122  and then transferred from the wafer output stage  16   c  to the cassette  60  by the wafer transfer device  50 . 
         [0062]    A second wafer W 2  is transferred from the cassette  60  to the wafer input stage  16   a  in the same way as the first wafer W 1 . The wafer W 2  is then transferred from the wafer input stage  16   a  at the wafer release position RP 2  to the wafer transfer station  18 ′ of the second polishing module  10 ′ by the wafer transfer device  40 . The wafer W 2  is picked from the wafer transfer station  18 ′ by the first polishing head  20   a ′ of the second polishing module  10 ′. The wafer W 2  is polished on the first and second polishing surfaces  14   a ′ and  14   b ′, and then placed on the wafer transfer station  18 ′ by the first polishing head  20   a ′. The wafer W 2  is transferred from the wafer transfer station  18 ′ to the cleaner buffer  16   b ′ of the second cleaning apparatus  120 ′ by the wafer transfer device  40 , further transferred from there through the cleaning module  124 ′ to the wafer output stage  16   c ′ by the internal wafer transfer device  122 ′ and then transferred from the wafer output stage  16   c ′ to the cassette  60  by the wafer transfer device  50 . 
         [0063]    In general, a first group of wafers such as the first wafer W 1  are processed through one of the polishing modules  10  and  10 ′ and one of the cleaning apparatuses  120  and  120 ′; and a second group of wafers such as the second wafer W 2  are processed through the other of the polishing modules  10  and  10 ′ and the other of the second cleaning apparatuses  120  and  120 ′. 
         [0064]    With reference to  FIG. 7 , a modified embodiment  100   a  of the wafer processing apparatus  100  is described.  FIG. 7  is a top view of the modified wafer processing apparatus  100   a . The wafer processing apparatus  100   a  is similar to the wafer processing apparatus  100  shown in  FIG. 5 . A difference is that the cleaning apparatuses  120  and  120 ′ are situated at the same side in the wafer processing apparatus  100   a  and the wafer input stage  16   a  and the wafer transfer device  40  are positioned at the opposite side. The cleaning apparatuses  120  and  120 ′ are situated such that both of the cleaner buffers  16   b  and  16   b ′ of the cleaning apparatuses  120  and  120 ′ are adjacent to the first polishing surface  14   a  of the first polishing module  10  of the polishing apparatus  5 . The wafer transfer device  40  is configured to transfer wafers from the wafer input stage  16   a  to the wafer transfer stations  18  and  18 ′; and from the wafer transfer stations  18  and  18 ′ to at least one of the first and second cleaner buffers  16   b  and  16   b′.    
         [0065]    In an embodiment, the cleaning apparatuses  120  and  120 ′ used in the wafer processing apparatuses  100   a  are configured to share the cleaner buffer  16   b  as described with reference to  FIG. 8(   a ), which is a top view of the cleaning apparatuses  120  and  120 ′. In this embodiment, the cleaning apparatuses  120  and  120 ′ comprise a stage transfer device  79  to which the shared cleaner buffer  16   b  is slidibly coupled. The stage transfer device  79  is configured to transfer the cleaner buffer  16   b  between a first transfer position TP 1  and a second transfer position TP 1 ′. The second transfer position TP 1 ′ is a position where the cleaner buffer  16   b  receives wafers from the wafer transfer device  40  and the internal wafer transfer device  122 ′ of the second cleaning apparatus  120 ′ receives the wafers from the cleaner buffer  16   b . The first transfer position TP 1  is a position where the internal wafer transfer device  122  of the first cleaning apparatus  120  receives the wafers from the cleaner buffer  16   b  after the cleaner buffer  16   b  receives the wafers at the second transfer position TP 1 ′ from the wafer transfer device  40  and then is transferred to the first transfer position TP 1  by the stage transfer device  79 . 
         [0066]    In an alternative embodiment of the stage transfer device  79 , a wafer relay device  172  can be used as shown in  FIG. 8(   b ), which is a top view of the cleaning apparatuses  120  and  120 ′. The wafer relay device  172  comprises a linear track  173 , a gripping device  174  and a pair of grippers  175   a  and  175   b . The grippers  175   a  and  175   b  are coupled to the gripping device  174 , which is configured to open and close the grippers  175   a  and  175   b . The gripping device  174  is coupled to the linear track  173  such that the gripping device  174  and therefore the grippers  175   a  and  175   b  can move between the cleaner buffers  16   b  and  16   b ′ on the linear track  173 . In an operation, the wafer transfer device  40  transfers a first wafer to the cleaner buffer  16   b ′ of the second cleaning apparatus  120 ′ from one of the wafer transfer stations  18  and  18 ′. The first wafer is then transferred from the cleaner buffer  16   b ′ by the internal wafer transfer device  122 ′ of the second cleaning apparatus  120 ′. After the first wafer is transferred from the cleaner buffer  16   b ′ by the internal wafer transfer device  122 ′ of the second cleaning apparatus  120 ′, the wafer transfer device  40  transfers a second wafer to the cleaner buffer  16   b ′ from the other of the wafer transfer stations  18  and  18 ′. The second wafer is then gripped by the grippers  175   a  and  175   b  and transferred to the cleaner buffer  16   b  of the first cleaning apparatus  120  by the wafer relay device  172  such that the internal wafer transfer device  122  of the first cleaning apparatus  120  can take the second wafer from the cleaner buffer  16   b.    
         [0067]    With reference to  FIG. 9 , a polishing apparatus  5   a  in accordance with an embodiment of the present invention is described.  FIG. 9  is a top view of the polishing apparatus  5   a . The polishing apparatus  5   a  is similar to the polishing apparatus  5  shown in  FIG. 1 . A difference is the orientation of the polishing modules  10  and  10 ′. In the polishing apparatus  5   a , the polishing modules  10  and  10 ′ are oriented such that the plane A of the first polishing module  10  is perpendicular to a depth direction of the polishing apparatus  5   a  and only the plane A′ of the second polishing module  10 ′ is parallel to the depth direction of the polishing apparatus  5   a , as indicated in  FIG. 9 . In another embodiment, an angle Q between the plane A and the plane A′ in the polishing apparatus  5   a  can be any angle in the range of 80 to 95 degree. In another embodiment, the angle Q can have be any angle in the range of 60 to 90 degree. In an embodiment, the first polishing module  10  in the polishing apparatus  5   a  uses P 12  and P 22  as its polishing positions on the first and second polishing surfaces  14   a  and  14   b  respectively; and the second polishing module  10 ′ in the polishing apparatus  5   a  uses P 12 ′ and P 22 ′ as its polishing positions on the first and second polishing surfaces  14   a  and  14   a ′ respectively. 
         [0068]    With reference to  FIG. 10 , a polishing apparatus  5   b  in accordance with a modified embodiment of the present invention is described.  FIG. 10  is a top view of the polishing apparatus  5   b . The polishing apparatus  5   b  is similar to the polishing apparatus  5   a  shown in  FIG. 9 . A difference is that the second polishing module  10 ′ may be disposed in the polishing apparatus  5   b  such that the rotation axis  15   b ′ of the second polishing surface  14   b ′ of the second polishing module  10 ′ is disposed further away from the plane A of the first polishing module  10  and closer to the wafer transfer station  18  of the first polishing module  10  than it is disposed in the polishing apparatus  5   a  in order to make the width of the polishing apparatus  5   b  smaller. Another difference is that the polishing apparatus  5   b  may use P 21 ′ as its polishing position on the second polishing surface  14   b ′ of the second polishing module  10 ′ while the polishing apparatus  5   a  uses P 22 ′. The polishing apparatuses  5   a  and  5   b  can be also configured to use other polishing positions that were used in the polishing apparatus  5  as described with reference to  FIGS. 1 and 2 . For example, the polishing apparatuses  5   a  and  5   b  can be configured to use P 11 , P 22 , P 11 ′ and P 22 ′; P 12 , P 21 , P 12 ′ and P 21 ′; and P 11 , P 22 , P 21 ′ and P 21 ′ as their polishing positions. 
         [0069]    The polishing apparatus  5   a  and  5   b  can be used in the wafer processing apparatus  100  as a replacement of the polishing apparatus  5  shown in  FIG. 1 . As an example, the wafer processing apparatus  100  comprising the polishing apparatus  5   a  is described with reference to  FIG. 11 , which is a top view of the wafer processing apparatus  100  comprising the polishing apparatus  5   a . The polishing apparatus  5   a  is situated in the wafer processing apparatus  100  such that the plane A′ of the second polishing module  10 ′ is parallel to the depth direction of the wafer processing apparatus  100 . In addition, the second polishing module  10 ′ which has the greater depth than the first polishing module  10  is situated adjacent to the first end  120   x ′ of the second cleaning apparatus  120 ′; and the first polishing module  10  which has the smaller depth than the second polishing module  10 ′ is situated at the opposite side. The wafer transfer device  40  and the wafer input stage  16   a  are positioned in the space  120 S between the first and second cleaning apparatuses  120  and  120 ′. Because the depth of the first polishing module  10  is smaller than the depth of the second polishing module  10 ′, there is an empty space  130  between the first polishing module  10  and the first cleaning apparatus  120 . Thus, an engineer can access the wafer transfer device  40  and the wafer input stage  16   a  disposed at the space  120 S through this empty space  130  to maintain them. 
         [0070]    The polishing apparatuses  5   a  and  5   b  can be used in the wafer processing apparatus  100   a  shown in  FIG. 7  as a replacement of the polishing apparatus  5 . As an example, the wafer processing apparatus  100   a  comprising the polishing apparatus  5   a  is described with reference to  FIG. 12 , which is a top view of the wafer processing apparatus  100   a  comprising the polishing apparatus  5   a . The second polishing module  10 ′ of the polishing apparatus  5   a  is situated adjacent to the first ends  120   x  and  120   x ′ of the first and second cleaning apparatuses  120  and  120 ′ such that the first and second cleaning apparatuses  120  and  120 ′ are situated between the second polishing module  10 ′ and the factory interface  64 . The wafer transfer device  40  can be mounted on the linear track  42  such that the wafer transfer device  40  can move between about the cleaner buffer  16   b  of the first cleaning apparatus  120  and about the wafer transfer stations  18  and  18 ′ of the polishing modules  10  and  10 ′. The wafer transfer device  40  transfers wafers from the wafer input stage  16   a  to the wafer transfer stations  18  and  18 ′; and from the wafer transfer stations  18  and  18 ′ to at least one of the cleaner buffers  16   b  and  16   b ′. An advantage of the wafer processing apparatus  100   a  comprising the polishing apparatus  5   a  is that there is a large space that can be used to maintain the wafer processing apparatus  100   a  between the first polishing module  10  and the factory interface  64 . In an embodiment, the cleaning apparatuses  120  and  120 ′ comprises the stage transfer device  79  or the wafer relay device  172 , which were described with reference to  FIGS. 8(   a ) and  8 ( b ). 
         [0071]    With reference to  FIG. 13 , a wafer processing apparatus  100   b  in accordance with an embodiment of the present invention is described.  FIG. 13  is a top view of the wafer processing apparatus  100   b . The wafer processing apparatus  100   b  comprises the cleaning apparatuses  120  and  120 ′ and a polishing apparatus such as the polishing apparatus  5   b  shown in  FIG. 10 . The cleaning apparatuses  120  and  120 ′ are disposed adjacent to each other between the first polishing module  10  of the polishing apparatus  5   b  and the factory interface  64  such that the second ends  120   y  and  120   y ′ of the cleaning apparatuses  120  and  120 ′ are adjacent to the factory interface  64  and the first ends  120   x  and  120   x ′ of the cleaning apparatuses  120  and  120 ′ face the first polishing module  10  of the polishing apparatus  5   b  across the wafer transfer device  40 . 
         [0072]    The polishing apparatus  5   b  is disposed such that there are a space  111   a  between the first polishing module  10  of the polishing apparatus  5   b  and the first ends  120   x  and  120   x ′ of the cleaning apparatuses  120  and  120 ′; a space  111   c  between the second polishing module  10 ′ of the polishing apparatus  5   b  and the factory interface  64 ; and a wafer transfer path  111   b  between the second polishing module  10 ′ of the polishing apparatus  5   b  and the first end  120   x ′ of the second cleaning apparatus  120 ′. The wafer transfer path  111   b  connects the spaces  111   a  and  111   c  for wafer transfer between the spaces  111   a  and  111   c . The polishing apparatus  5   b  may be disposed such that a distance  120 D* from the second polishing module  10 ′ to the factory interface  64  is shorter than a distance  120 D from the first ends  120   x  and  120   x ′ of the cleaning apparatuses  120  and  120 ′ to the factory interface  64 . 
         [0073]    The wafer transfer device  40  is disposed in the space  111   a  such that the wafer transfer device  40  can transfer wafers from the wafer transfer stations  18  and  18 ′ to at least one of the cleaner buffers  16   b  and  16   b ′ of the first and second cleaning apparatuses  120  and  120 ′. The space  111   a  also provides a space for an engineer to maintain the cleaning apparatuses  120  and  120 ′ and the polishing apparatus  5   b.    
         [0074]    A buffer  16   a * is disposed around the wafer transfer path  111   b  such that the wafer transfer device  40  can take wafers from the buffer  16   a *. The buffer  16   a * is a device to keep the wafers transferred by a second wafer transfer device  40 *. The buffer  16   a * may be configured to accommodate wafers vertically. 
         [0075]    The second wafer transfer device  40 * is disposed in the space  111   c . The second wafer transfer device  40 * is configured to transfer wafers to be polished from the wafer input stage  16   a  disposed adjacent to the factory interface  64  to the buffer  16   a *. The second wafer transfer device  40 * may be mounted to a linear track  42 *. 
         [0076]    In an operation of the wafer processing apparatus  100   b , wafers to be polished are transferred from the wafer input stage  16   a  to the buffer  16   a * by the second wafer transfer device  40 *; transferred from the buffer  16   a * to at least one of the wafer transfer stations  18  and  18 ′ of the polishing apparatus  5   b  by the wafer transfer device  40 ′; polished in the polishing apparatus  5   b  by at least one of the polishing heads  20   a - 20   c ′; transferred back to at least one of the wafer transfer stations  18  and  18 ′ by the at least one of the polishing heads  20   a - 20   c ′; and transferred from the at least one of the wafer transfer stations  18  and  18 ′ to at least one of the cleaner buffers  16   b  and  16   b ′ of the cleaning apparatuses  120  and  120 ′ by the wafer transfer device  40 . 
         [0077]    Alternatively, the wafer processing apparatus  100   b  may be configured such that the wafer transfer device  40  transfers the wafers polished in the polishing apparatus  5   b  back to the buffer  16   a * instead of transferring them to the cleaner buffers  16   b  and  16   b ′. In this embodiment, the wafer transfer device  40 * transfers the wafers from the buffer  16   a * to at least one of the cleaner buffers  16   b  and  16   b′.    
         [0078]    With reference to  FIG. 14 , a polishing apparatus  5   c  in accordance with an embodiment of the present invention is described. The polishing apparatus  5   c  is similar to the polishing apparatus  5  shown in  FIG. 1 . A difference is that the polishing apparatus  5   c  comprises a pivoting wafer transfer device  180  as a replacement of the wafer transfer stations  18  and  18 ′ of the polishing apparatus  5 . In addition, the polishing apparatus  5   c  can further comprise a first washing device  118  and a second washing device  118 ′. 
         [0079]    The pivoting wafer transfer device  180  is configured to transfer wafers with the polishing heads  20   a - 20   c  of the first polishing module  10  at a first transfer position  20 P; with the wafer transfer device  40  at a parking position; and with the polishing heads  20   a ′- 20   c ′ of the second polishing module  10 ′ at a second transfer position  20 P′. The first transfer position  20 P is a position where the wafer transfer station  18  of the first polishing module  10  was situated in the polishing apparatus  5  shown in  FIG. 1 ; the second transfer position  20 P′ is a position where the wafer transfer station  18 ′ of the second polishing module  10 ′ was situated in the polishing apparatus  5  shown in  FIG. 1 ; and the parking position is a position where a loader  188  of the pivoting wafer transfer device  180  is positioned among the wafer transfer device  40 , the first transfer position  20 P and the second transfer position  20 P′. 
         [0080]    The first washing device  118  is disposed about the transfer position  20 P and can spray DI water to the polishing heads  20   a - 20   c  and the wafers held by the polishing heads  20   a - 20   c  when the polishing heads  20   a - 20   c  are positioned at the transfer position  20 P. The second washing device  118 ′ is disposed about the transfer position  20 P′ of the second polishing module  10 ′ and can spray DI water to the polishing heads  20   a ′- 20   c ′ and the wafers held by the polishing heads  20   a ′- 20   c ′ when the polishing heads  20   a ′- 20   c ′ are positioned at the transfer position  20 P′. 
         [0081]    With reference to  FIGS. 15(   a ) and  15 ( b ), the pivoting wafer transfer device  180  and the wafer washing devices  118  and  118 ′ are further described.  FIGS. 15(   a ) and  15 ( b ) are side views of the pivoting wafer transfer device  180  and the washing devices  118  and  118 ′. In  FIG. 15(   a ), the loader  188  is positioned at the parking position and the polishing heads  20   a  and  20   a ′ are positioned at the first and second transfer positions  20 P and  20 P′ respectively over the respective washing devices  118  and  118 ′. In  FIG. 15(   b ), the loader  188  is positioned at the first transfer position  20 P under the first polishing head  20   a.    
         [0082]    The pivoting wafer transfer device  180  comprises the loader  188 , an arm  186 , a shaft  184 , a pivoting-and-vertical drive mechanism  182  and a pivoting axis  181 . The loader  188  is a device to transfer wafers with the polishing heads. The load  188  is coupled to an end of the arm  186 . The other end of the arm  186  is coupled to an end of the shaft  184  as shown in  FIGS. 15(   a ) and  15 ( b ). The other end of the shaft  184  is coupled to the pivoting-and-vertical drive mechanism  182 . The pivoting-and-vertical drive mechanism  182  is configured to move the loader  188  up and down by moving the shaft  184  up and down; and configured to pivot the loader  188  by pivoting the shaft  184  about the pivoting axis  181 . 
         [0083]    A procedure of transferring wafers to the polishing heads  20   a  and  20   a ′ by the loader  188  is described using the polishing head  20   a  as an example with reference to  FIGS. 14 ,  15 ( a ) and  15 ( b ). The procedure comprises steps of (1) transferring a first wafer from the wafer transfer device  40  to the loader  188  positioned at the parking position; (2) pivoting the loader  188  to the first transfer position  20 P; (3) moving the loader  188  upward to the polishing head  20   a ; (4) transferring the first wafer to the polishing head  20   a ; (5) moving the loader  188  down from the polishing head  20   a ; and (6) pivoting the loader  188  back to the parking position. The pivoting wafer transfer device  180  transfers a second wafer to the polishing head  20   a ′ in the same manner as the pivoting wafer transfer device  180  transferred the first wafer to the polishing head  20   a.    
         [0084]    In an embodiment, as shown in  FIG. 14 , in order to avoid interference between the loader  188  and the polishing heads  20   a - 20   c  and  20   a ′- 20   c ′ when the loader  188  is pivoted to the transfer positions  20 P and  20 P′, the polishing modules  10  and  10 ′ in the polishing apparatus  5   c  preferably uses P 12  and P 12 ′ as its polishing positions to polish the wafers on the first polishing surfaces  14   a  and  14   a ′ of the polishing modules  10  and  10 ′ respectively. 
         [0085]    The polishing apparatus  5   c  shown in  FIG. 14  can be used in the wafer processing apparatus  100   a  shown in  FIG. 7  as a replacement of the polishing apparatus  5 .  FIG. 16  is a top view of the wafer processing apparatus  100   a  comprising the polishing apparatus  5   c . The polishing apparatus  5   c  and the cleaning apparatuses  120  and  120 ′ are disposed in the wafer processing apparatus  100   a  such that the first polishing surface  14   a  of the polishing module  10  is adjacent to the first ends  120   x  and  120   x ′ of the cleaning apparatuses  120  and  120 ′. The wafer transfer device  40  is positioned adjacent to the loader  188  of the pivoting wafer transfer device  180  and the first end  120   x ′ of the cleaning apparatus  120 ′. The wafer transfer device  40  transfers wafers from the wafer input stage  16   a  to the loader  188 ; and from the loader  188  to at least one of the cleaner buffers  16   b  and  16   b′.    
         [0086]    With reference to  FIGS. 17 ,  18  and  19 , a rotation mechanism  600  that can be used as the rotation mechanism  26  of the polishing module  10  shown in  FIGS. 2 and 3  is described.  FIG. 17  is a vertical cross-sectional view of the rotation mechanism  600  in accordance with an embodiment of the present invention.  FIGS. 18 and 19  are plan views of the rotation mechanism  600  seen from cross sections  600 L 1  and  600 L 2  shown in  FIG. 17  respectively. 
         [0087]    Referring to  FIGS. 17 and 18 , the rotation mechanism  600  comprises a top support  600   a , an outer cylindrical support  600   b , an inner cylindrical support  600   c , and a circular bottom support  600   d . The supports  600   a ,  600   b  and  600   c  with or without the support  600   d  form a support structure of the rotation mechanism  600 . The outer and inner cylindrical supports  600   b  and  600   c  are mounted to and suspended from the top support  600   a  such that there is an annular shaped opening  650  between respective lower ends of the outer and inner cylindrical supports  600   b  and  600   c . The outer cylindrical support  600   b  comprises at least one opening  602 , through which the rotation mechanism  600  can be maintained and air can be exhausted from the rotation mechanism  600 . 
         [0088]    An annular gear  630  is mounted coaxially to the inner cylindrical support  600   c  about the rotation axis  28 . After the gear  630  is mounted, the circular bottom support  600   d  is mounted to the lower end of the inner cylindrical support  600   c  such that the bottom support  600   d  encloses a space  600 S surrounded by the inner cylindrical support  600   c . The inner space  600 S is used for fluid supply channels such as vacuum and pressurized air, electrical power supply cables and data communication cables. 
         [0089]    A first annular rim  605  is mounted to the lower end of the outer cylindrical support  600   b  such that the first annular rim  605  surrounds the annular opening  650 . An annular outer guide rail  640   a  is mounted to the first annular rim  605  and an annular inner guide rail  640   b  is mounted to the bottom support  600   d  such that the outer and inner annular guide rails  640   a  and  640   b  surround the annular opening  650 . Second and third annular rims  608   a  and  608   b  are mounted to the outer and inner guide rails  640   a  and  640   b  respectively such that they surround the annular opening  650 . 
         [0090]    A first group of nozzles  610   a  are mounted to the first annular rim  605  along the first annular rim  605  such that the first group of nozzles  610   a  can inject pressurized air toward an annular opening  655   a  (shown in  FIG. 17 ) between the outer cylindrical support  600   b  and an annular shield  655 . A second group of nozzles  610   b  are mounted to the second annular rim  608   a  along the second annular rim  608   a  such that the second group of nozzles  610   b  can inject pressurized air toward the annular opening  655   a  (through a space over the outer annular guide rail  640   a ). A third group of nozzles  610   c  are mounted to the third annular rim  608   b  along the third annular rim  608   b  such that the third group of nozzles  610   c  can inject pressurized air upwardly toward an annular opening  655   b  (shown in  FIG. 17 ) between the inner cylindrical support  610   c  and the annular shield  655  (through a space over the inner annular guide rail  640   b ). A fourth group of nozzles  610   d  are mounted to the bottom support  600   d  along a perimeter of the bottom support  600   d  such that the fourth group of nozzles  610   d  can inject pressurized air upwardly toward the annular opening  655   b . A fifth group of nozzles  610   e  may be mounted to the second annular rim  608   a  along the second annular rim  608   a  such that the fifth group of nozzles  610   e  can inject pressurized air toward the annular opening  650 . A sixth group of nozzles  610   f  may be mounted to the third annular rim  608   b  along the third annular rim  608   b  such that the sixth group of nozzles  610   f  can inject pressurized air toward the annular opening  650 . Each group of nozzles  610   a - 610   f  is connected to a source of the pressurized air (not shown in  FIG. 17 ) through a respective pressure control device such that pressure and flow rate of the pressurized air injected from each group of nozzles can be controlled individually. 
         [0091]    Referring to  FIG. 17  and  FIG. 19 , the annular shield  655  is disposed over the opening  650  as shown in  FIG. 17  such that it covers the opening  650 ; an outer radial end of the annular shield  655  is disposed over at least a portion of the outer rail  640   a ; and an inner radial end of the annular shield  655  is disposed over at least a portion of the inner rail  640   b . The annular shield  655  is mounted to the outer cylindrical support  600   b  through mounting plates  656  as shown in  FIG. 19 . The annular shield  655  is not connected to the inner cylindrical support  600   c . The annular shield  655  may be configured to have the openings  655   a  between the outer annular support  600   b  and the annular shield  655 . The openings  655   a  are used to exhaust air from the first and second groups of nozzles  610   a  and  610   b  as shown in  FIG. 17 . The annular shield  655  is also configured such that there is the annular opening  655   b  between the annular shield  655  and the inner annular support  600   c . The opening  655   b  is used to exhaust air from the third and fourth groups of nozzles  610   c  and  610   d  as shown in  FIG. 17 . The annular shield  655  and the first, second, third and fourth groups of nozzles  610   a - 610   d  are used to isolate the annular opening  650  from a space above the annular shield  655 . Air injected from the nozzles  610   a - 610   d  is used to protect dirty air from flowing into the opening  650  and to blow particles, which may be generated from the guide rails  640   a  and  640   b , to the openings  655   a  and  655   b.    
         [0092]    With reference to  FIGS. 20 and 21 , head supports  615   a - 615   c  of the rotation mechanism  600  are described.  FIG. 20  is a vertical cross sectional view of the rotation mechanism  600  along a vertical plane Z shown in  FIG. 21 .  FIG. 21  is a plan view of the rotation mechanism  600  seen from a cross section  600 L 3  shown in  FIG. 20 . The rotational-and-vertical drive mechanisms  22   a - 22   c  of the polishing heads  20   a - 20   c  described with reference to  FIGS. 2 and 3  are mounted to the head supports  615   a - 615   c  respectively. Thus, the head supports  615   a - 615   c  are used as head supporting members that support polishing head assemblies, which include polishing heads. As the head supports  615   a - 615   c  are similar to each other, details of the head supports  615   a - 615   c  are described using the first head support  615   a  as an example. 
         [0093]    The head support  615   a  is configured such that its outer radial end is positioned over the outer guide rail  640   a  and movably coupled to the outer guide rail  640   a  through at least one guide block  645   a . The guide block  645   a , which is fixedly mounted to the outer radial end of the head support  615   a , is movably coupled to the outer guide rail  640   a . The head support  615   a  is also configured such that its inner radial end is positioned over the inner guide rail  640   b  and movably coupled to the inner guide rail  640   b  through at least one guide block  647   a . The guide blocks  647   a , which is fixedly mounted to the inner radial end of the head support  615   a , is movably coupled to the inner guide rail  640   b . When the head supports  615   a - 615   c  are assembled to the rotation mechanism  600 , the annular opening  650  is exposed between the head supports  615   a - 615   c  as shown in  FIG. 21 . 
         [0094]    With reference to  FIG. 22 , the head support  615   a , the guide rail  640   a  or  640   b , the guide block  645   a  or  647   a  and the air nozzles  610   a ,  610   b  and  610   e  or  610   c ,  610   d  and  610   f  of the rotation mechanism  600  of  FIG. 20  are further described.  FIG. 22  shows a cross-sectional view of the head support  615   a , the guide rail  640   a  or  640   b , the guide block  645   a  or  647   a  and the air injection nozzles  610   a ,  610   b  and  610   e  or  610   c ,  610   d  and  610   f  of the rotation mechanism  600 . The head support  615   a  may be configured to comprise outer and inner portions  616  and  616 * downwardly extended from the outer and inner radial ends of the head support  615   a  respectively. The portions  616  and  616 * are mounted to the respective guide blocks  645   a  and  647   a . The portions  616  and  616 * comprise at least one opening  644  through the portions  616  and  616 * respectively. The outer portion  616  is positioned between the first and second groups of nozzles  610   a  and  610   b . The second group of nozzles  610   b  is configured to inject pressurized air through the openings  644 . The first group of nozzles  610   a  is configured to inject pressurized air upwardly. The inner portion  616 * is positioned between the third and fourth groups of nozzles  610   c  and  610   d . The third group of nozzles  610   c  is configured to inject pressurized air through the openings  644 . The fourth group of nozzles  610   d  is configured to inject pressurized air upwardly. The fifth and sixth group of nozzles  610   e  and  610   f  are configured to inject pressurized air toward the annular opening  650  in order to supply clean air to wafer processing area under the annular opening  650 . In an alternative embodiment, the first and fourth groups of nozzles  610   a  and  610   d  may be configured to suction the air injected from the second and third groups of nozzles  610   b  and  610   c  respectively. 
         [0095]    With reference to  FIGS. 20 and 23 , the rotation mechanism  600  is further described.  FIG. 23  is a plan view of the rotation mechanism  600  seen from a cross section  600 L 4  shown in  FIG. 20 . The annular shield  655  is disposed over the head supports  615   a - 615   c . Thus, the annular shield  655  is used as a shield member that shields the opening  650  from the gear  630 . A servo motor  642   a , which is used to rotate the first head support  615   a  about the rotation axis  28 , is mounted to the first head support  615   a  as shown in  FIG. 20 . A gear  643   a  which is attached to a spinning part of the motor  642   a  is coupled to the gear  630 . When the motor  642   a  rotates the gear  643   a , the gear  643   a  revolves around the gear  630 . A revolution force of the gear  643   a  is transmitted to the head support  615   a  such that the head support  615   a  rotates around the gear  630  on the guide rails  640   a  and  640   b  about the rotation axis  28 . Respective gears  643   b  and  643   c  of servo motors  642   b  and  642   c  to drive the head supports  615   b  and  615   c  are also coupled with the gear  630  as shown in  FIG. 23  such that the head supports  615   b  and  615   c  can rotate around the gear  630  on the guide rails  640   a  and  640   b  about the rotation axis  28 . Thus, the servo motor  642   a  with the gear  642   a  and the gear  630  can be considered as one drive mechanism to rotate or transport the connected polishing head assembly. Angular positions of the head supports  615   a - 615   c  relative to the rotation axis  28  are controlled individually by a controller  670 . 
         [0096]    Referring to  FIG. 20 , the rotation mechanism  600  is further described. The inner cylindrical support  600   c  comprises outlet port  680   a . The outlet port  680   a  provides an interface with a channel assembly  682   a . The channel assembly  682   a  is connected to fluid sources such as vacuum and pressurized air, electric power source and a controller through the outlet port  680   a . The outlet port  680   a  is connected to an inlet port  680   a *, which is mounted to the head support  615   a , through the channel assembly  682   a . The inlet port  680   a * provides an interface with the servo motor  642   a  and the rotational-and-vertical drive mechanism  22   a  which will be mounted to the head support  615   a.    
         [0097]    The channel assembly  682   a  is suspended from the top support  600   a  using at least one bendable support  684   a . When the head support  615   a  reciprocates clockwise and counterclockwise about the rotation axis  28  in order to transfer the polishing head  20   a  coupled to the rotational-and-vertical drive mechanism  22   a  between the polishing surfaces  14   a  and  14   b  and the wafer transfer station  18 , the bendable support  684   a  supports the channel assembly  682   a  in a bendable manner such that stretching of the channel assembly  682   a  is not disturbed by the support  684   a . The outlet and inlet ports and the channel assemblies of the second and third head supports  615   b  and  615   c  have similar configuration with those of the first head support  615   a.    
         [0098]    With reference to  FIG. 24 , the rotation mechanism  600  having the polishing heads  20   a - 20   c  is described.  FIG. 24  is a perspective sectional side view of the rotation mechanism  600 . The polishing heads  20   a - 20   c  are coupled to the head supports  615   a - 615   c  respectively through the respective shafts  21   a - 21   c  and the respective rotational-and-vertical drive mechanisms  22   a - 22   c . Therefore the first polishing head assembly comprising the rotational-and-vertical drive mechanism  22   a  and the first polishing head  20   a  is coupled to the first head support  615   a ; the second polishing head assembly comprising the rotational-and-vertical drive mechanism  22   b  and the second polishing head  20   b  is coupled to the second head support  615   b ; and the third polishing head assembly comprising the rotational-and-vertical drive mechanism  22   c  and the third polishing head  20   c  is coupled to the third head support  615   c.    
         [0099]    The polishing heads  20   a - 20   c  can be transferred among the first and second polishing surfaces  14   a  and  14   b  and the wafer transfer station  18  by rotating the respective gears  643   a - 643   c  using the respective motors  642   a - 642   c . The inlet ports  680   a *- 680   c * are coupled to the respective rotational-and-vertical drive mechanisms  22   a - 22   c  and the respective polishing heads  20   a - 20   c  to supply vacuum, pressurized air and electrical power and to communicate with them. 
         [0100]    With reference to  FIG. 25 , a polishing apparatus  5   c * in accordance with an embodiment of the present invention is described.  FIG. 25  is a top view of the polishing apparatus  5   c *. The polishing apparatus  5   c * comprises a single polishing module  110  and the wafer transfer device  40 . The polishing module  110  is modified from the polishing module  10  shown in  FIGS. 2 and 3  such that the polishing module  110  further comprises a third polishing surface  14   c , a fourth polishing head  20   d  and a second wafer transfer station  18 * over the polishing module  10 . 
         [0101]    The three polishing surfaces  14   a - 14   c  and the two wafer transfer stations  18  and  18 * of the polishing module  110  are angularly disposed about the rotation axis  28  in a sequence of the first wafer transfer station  18 , the first polishing surface  14   a , the second polishing surface  14   b , the third polishing surface  14   c  and the second wafer transfer station  18 *. The second wafer transfer station  18 * is disposed such that the center  18   c * of the second wafer transfer station  18 * is also positioned on the circular path  28   a . The polishing module  110  is configured such that the polishing heads  20   a - 20   d  can transfer wafers with any of the wafer transfer stations  18  and  18 * and polish wafers on any of the polishing surfaces  14   a - 14   c . The wafer transfer device  40  transfers the wafers with the first and second wafer transfer stations  18  and  18 *. 
         [0102]    In an operation of the polishing apparatus  5   c *, the wafer transfer device  40  sequentially supplies wafers to the first transfer station  18 ; the polishing heads  20   a - 20   d  are sequentially transferred from the second wafer transfer station  18 * to the first wafer transfer station  18  in order to sequentially load the wafers from the first transfer station  18 ; the polishing heads  20   a - 20   d  are sequentially transferred from the first wafer transfer station  18  through the polishing surfaces  14   a - 14   c  after loading the wafers; the wafers held by the polishing heads  20   a - 20   d  are sequentially polished on the polishing surfaces  14   a - 14   c ; the polishing heads  20   a - 20   d  are sequentially transferred from the third polishing surface  14   c  to the second wafer transfer station  18 *; the wafers are sequentially unloaded from the polishing heads  20   a - 20   d  to the second transfer station  18 *; and the wafers are sequentially removed from the second transfer station  18 * by the wafer transfer device  40 . 
         [0103]    With reference to  FIGS. 26(   a )- 26 ( h ), another method of processing wafers in the polishing apparatus  5   c * is described.  FIGS. 26(   a )- 26 ( h ) are sequential top views of the polishing apparatus  5   c * to show a sequence of polishing wafers in accordance with an embodiment of the present invention. The method comprises steps of: 
         [0104]    (1) positioning the first, second, third and fourth polishing heads  20   a - 20   d  at the first wafer transfer station  18 , the second wafer transfer station  18 *, the third polishing surface  14   c  and the second polishing surface  14   b  respectively; transferring a first wafer W 1  to the first wafer transfer station  18  by the wafer transfer device  40 ; and loading the wafer W 1  to the first polishing head  20   a  from the first wafer transfer station  18  as shown in  FIG. 26(   a ); 
         [0105]    (2) transferring the first polishing head  20   a  from the first wafer transfer station  18  to the first polishing surface  14   a ; transferring the second polishing head  20   b  from the second wafer transfer station  18 * to the first wafer transfer station  18  such that the second wafer transfer station  18 * is cleared to receive the third polishing head  20   c ; polishing the wafer W 1  on the first polishing surface  14   a  by the first polishing head  20   a ; and transferring a second wafer W 2  to the second wafer transfer station  18 * by the wafer transfer device  40  as shown in  FIG. 26(   b ); 
         [0106]    (3) transferring the third polishing head  20   c  to the second wafer transfer station  18 *; and loading the wafer W 2  to the third polishing head  20   c  from the second wafer transfer station  18 * as shown in  FIG. 26(   c ); 
         [0107]    (4) transferring the third polishing head  20   c  from the second wafer transfer station  18 * to the third polishing surface  14   c ; transferring the second polishing head  20   b  from the first wafer transfer station  18  to the second wafer transfer station  18 * such that the first wafer transfer station  18  is cleared to receive the first polishing head  20   a ; and polishing the wafer W 2  on the third polishing surface  14   c  by the third polishing head  20   c  as shown in  FIG. 26(   d ); 
         [0108]    (5) transferring the first polishing head  20   a  from the first polishing surface  14   a  to the first wafer transfer station  18 ; and unloading W 1  from the first polishing head  20   a  to the first wafer transfer station  18  as shown in  FIG. 26(   e ); 
         [0109]    (6) transferring the wafer W 1  from the first wafer transfer station  18  by the wafer transfer device  40 ; supplying a third wafer W 3  to the first wafer transfer station  18  by the wafer transfer device  40 ; and loading the wafer W 3  to the first polishing head  20   a  as shown in  FIG. 26(   f ); 
         [0110]    (7) transferring the first polishing head  20   a  from the first wafer transfer station  18  to the first polishing surface  14   a ; transferring the second polishing head  20   b  from the second wafer transfer station  18 * to the first wafer transfer station  18 ; and polishing W 3  on the first polishing surface  14   a  by the first polishing head  20   a  as shown in  FIGS. 26(   g ); and 
         [0111]    (8) transferring the third polishing head  20   c  from the third polishing surface  14   c  to the second wafer transfer station  18 *; and unloading the wafer W 2  from the third polishing head  20   c  to the second wafer transfer station  18 * as shown in  FIG. 26(   h ). 
         [0112]    The wafer W 2  is then transferred from the second wafer transfer station  18 * by the wafer transfer device  40  and a fourth wafer W 4  is supplied to the second wafer transfer station  18 * by the wafer transfer device  40 . The wafer W 4  is processed in the same way as the wafer W 2  was processed on the third polishing surface  14   c  by the third polishing head  20   c.    
         [0113]    As understandable from the method described with reference to  FIGS. 26(   a )- 26 ( h ), the polishing apparatus  5   c * is configured to carry out the above method by positioning the fourth polishing head  20   d  over the second polishing surface  14   b  during the entire process; by reciprocating the first polishing head  20   a  between the first wafer transfer station  18  and the first polishing surface  14   a  in order to polish a first group of wafers on the first polishing surface  14   a  by the first polishing head  20   a ; by reciprocating the third polishing head  20   c  between the second wafer transfer station  18 * and the third polishing surface  14   c  in order to polish a second group of wafers on the third polishing surface  14   c  by the third polishing head  20   c ; and by reciprocating the second polishing head  20   b  between the first and second wafer transfer stations  18  and  18 * such that the second polishing head  20   b  dose not disturb the reciprocating motions of the first and third polishing heads  20   a  and  20   c.    
         [0114]    The polishing apparatus  5   c * shown in  FIG. 25  can be used in the wafer processing apparatus  100   a  shown in  FIG. 12  as a replacement of the polishing apparatus  5   a .  FIG. 27  is a top view of the wafer processing apparatus  100   a  comprising the polishing apparatus  5   c *. In the wafer processing apparatus  100   a , the polishing apparatus  5   c * is disposed such that the third and second polishing surfaces  14   c  and  14   b  are aligned to the cleaning apparatuses  120  and  120 ′ in the depth direction of the wafer processing apparatus  100   a ; and the third polishing surface  14   c  is positioned adjacent to the first ends  120   x  and  120   x ′ of the cleaning apparatuses  120  and  120 ′. The wafer transfer device  40  and the wafer input stage  16   a  are disposed at the opposite side of the cleaning apparatuses  120  and  120 ′. The wafer transfer device  40  may be mounted on the linear track  42  such that the wafer transfer device  40  can be transferred between the wafer input stage  16   a  and the wafer transfer stations  18  and  18 * of the polishing apparatus  5   c *. The wafer transfer device  40  transfers wafers from the wafer input stage  16   a  to the wafer transfer stations  18  and  18 * and from the wafer transfer stations  18  and  18 * to at least one of the cleaner buffers  16   b  and  16   b′.    
         [0115]    The polishing apparatus  5   c * shown in  FIG. 25  can be also used in the wafer processing apparatus  100   b  shown in  FIG. 13  as a replacement of the polishing apparatus  5   b .  FIG. 28  is a top view of the wafer processing apparatus  100   b  comprising the polishing apparatus Sc*. The polishing apparatus  5   c * is disposed in the wafer processing apparatus  100   b  such that the wafer transfer device  40  disposed adjacent to the first ends  120   x  and  120   x ′ of the cleaning apparatuses  120  and  120 ′ is surrounded by the first ends  120   x  and  120   x ′ of the cleaning apparatuses  120  and  120 ′, the first and second wafer transfer stations  18  and  18 * of the polishing apparatus  5   c * and the buffer  16   a *. The buffer  16   a * is disposed between the first end  120   x ′ of the cleaning apparatus  120 ′ and the polishing apparatus Sc*. The polishing apparatus  5   c * is also disposed in the wafer processing apparatus  100   b  such that the third polishing surface  14   c  faces the factory interface  64  across the second wafer transfer device  40 * disposed in the space  111   c . In an operation, the second wafer transfer device  40 * transfers wafers from the wafer input stage  16   a  to the buffer  16   a *; the wafer transfer device  40  transfers the wafers from the buffer  16   a * to the wafer transfer stations  18  and  18 * of the polishing apparatus  5   c * and from the wafer transfer stations  18  and  18 * to at least one of the cleaner buffers  16   b  and  16   b ′ of the cleaning apparatuses  120  and  120 ′. 
         [0116]    With reference to  FIG. 29 , a wafer processing apparatus  200  in accordance with an embodiment of the present invention is described.  FIG. 29  is a top view of the wafer processing apparatus  200 . The wafer processing apparatus  200  comprises the factory interface  64 , two cleaning apparatuses  120 V and  120 V′, two polishing modules  110   a  and  110   a ′, the wafer transfer device  40 , and the wafer input stage  16   a . Each of the two polishing modules  110   a  and  110   a ′ is modified from the polishing module  110  shown in  FIG. 25  by removing the second wafer transfer station  18 * from the polishing module  110 . Each of the polishing modules  110   a  and  110   a ′ may comprise one, two or three polishing heads instead of comprising all of the four polishing heads  20   a - 20   d.    
         [0117]    The wafer input stage  16   a  is disposed between a first end  120 Vx of the first cleaning apparatus  120 V and a second end  120 Vy′ of the second cleaning apparatus  120 V′ such that the wafer transfer device  50  of the factory interface  64  can transfer wafers to the wafer input stage  16   a . The wafer input stage  16   a  may be configured to accommodate the wafers vertically or horizontally. 
         [0118]    The wafer transfer device  40  transfers wafers to be polished from the wafer input stage  16   a  to wafer transfer stations  18  and  18 ′ of the polishing modules  110   a  and  110   a ′ and transfers polished wafers from the wafer transfer stations  18  and  18 ′ to respective cleaner buffers  16 Vb and  16 Vb′ of the cleaning apparatuses  120 V and  120 V′. The wafer transfer device  40  may be mounted on the linear track  42  which extends between the wafer transfer stations  18  and  18 ′ and the wafer input stage  16   a.    
         [0119]    The first cleaning apparatus  120 V is disposed adjacent to the factory interface  64  such that (1) its longer side  120 Va is parallel to a longer side  64   a  of the factory interface  64  and therefore parallel to a width direction of the wafer processing apparatus  200 ; and (2) the first end  120 Vx of the first cleaning apparatus  120 V is adjacent to the wafer input stage  16   a  and a second end  120 Vy of the first cleaning apparatus  120 V which is opposite to the first end  120 Vx is disposed adjacent to a second end  64   y  of the factory interface  64 . 
         [0120]    The cleaner buffer  16 Vb of the first cleaning apparatus  120 V is disposed in the first end  120 Vx of the first cleaning apparatus  120 V such that the wafer transfer device  40  can transfer wafers to the cleaner buffer  16 Vb; and a wafer output stage  16 Vc is disposed in the second end  120 Vy of the first cleaning apparatus  120 V such that the wafer transfer device  50  of the factory interface  64  can transfer the wafers from the wafer output stage  16 Vc. 
         [0121]    The second cleaning apparatus  120 V′ is disposed either in the left side or in the right side of the wafer processing apparatus  200  such that (1) its longer side  120 Va′ is parallel to a depth direction of the wafer processing apparatus  200 ; and (2) a second end  120 Vy′ of the second cleaning apparatus  120 V′ is disposed adjacent to a first end  64   x  of the factory interface  64  such that the wafer transfer device  50  of the factory interface  64  can transfer wafers from a wafer output stage  16 Vc′ disposed in the second end  120 Vy′ of the second cleaning apparatus  120 V′. A cleaner buffer  16 Vb′ of the second cleaning apparatus  120 V′ is disposed in a first end  120 Vx′ of the second cleaning apparatus  120 V′ which is opposite to the second end  120 Vy′ of the cleaning apparatus  120 V′ such that the wafer transfer device  40  can transfer wafers to the cleaner buffer  16 Vb′. 
         [0122]    With reference to  FIG. 30 , the cleaning apparatus  120 V is further described. The cleaning apparatus  120 V can be used as the second cleaning apparatus  120 V′. That is, the second cleaning apparatus  120 V′ can be identical to the cleaning apparatus  120 V.  FIG. 30  shows a cross sectional view of the cleaning apparatus  120 V in accordance with an embodiment of the present invention. The cleaning apparatus  120 V comprises a cleaning module  124 V to clean and dry the wafers. The cleaning module  124 V comprises cleaning chambers  125 Va- 125 Vd and two dry chambers  125 Vx and  125 Vy. The cleaning chambers  125 Va- 125 Vd are configured to clean wafers by spraying DI water and chemicals to the wafers placed on respective wafer stages  124 Va- 124 Vd. The dry chambers  125 Vx and  125 Vy are configured to dry the wafers placed on respective wafer stages  124 Vx and  124 Vy by spinning the wafers or using isopropyl alcohol (IPA) chemical. The cleaning apparatus  120 V further comprises a fluid control system  126 V under the cleaning module  124 V. The fluid control system  126 V controls supply and drain of chemical fluid to and from the cleaning module  124 V. 
         [0123]    The cleaning apparatus  120 V further comprises two internal wafer transfer devices  122   a  and  122   b . The first internal wafer transfer device  122   a  comprises four gripping devices  70   a - 70   d . Each gripping device comprises a gripper  71  and a vertical-and-gripping drive mechanism  72 . The vertical-and-gripping drive mechanism  72  is configured to move the gripper  71  vertically as shown in  FIG. 30  by the arrow V and to open and close the gripper  71  to hold a wafer W and release the wafer W. The gripping devices  70   a - 70   d  are fixedly mounted to a supporting member  73   a , which is coupled to a linear drive mechanism  74   a.    
         [0124]    The linear drive mechanism  74   a  is configured to reciprocate the supporting member  73   a  between a wafer taking position WT 1  and a wafer release position WT 2  as shown in  FIG. 30  by the arrow L 1 . When the supporting member  73   a  is positioned at WT 1 , the gripping devices  70   a - 70   d  are positioned at gripper positions C 1 -C 4  respectively. When the supporting member  73   a  is positioned at WT 2 , the gripping devices  70   a - 70   d  are positioned at gripper positions C 2 -C 5  respectively. The gripper positions C 1 -C 5  are vertically aligned to the cleaner buffer  16 Vb and the wafer stages  124 Va- 124 Vd of the cleaning chambers  125 Va- 125 Vd respectively. 
         [0125]    The second internal wafer transfer device  122   b  comprises two gripping devices  70   x  and  70   y . The gripping devices  70   x  and  70   y  are fixedly mounted to respective supporting members  73   x  and  73   y , which are slidibly coupled to a liner drive mechanism  74   b . The linear drive mechanism  74   b  is configured to reciprocate the supporting member  73   x  and therefore the gripping device  70   x  between fifth, sixth and seventh gripper positions C 5 -C 7  and a parking position  70   xp  as shown in  FIG. 30  with the arrow L 2 ; and to reciprocate the supporting member  73   y  and therefore the gripping device  70   y  between the sixth, seventh and eighth gripper positions C 6 -C 8  and a parking position  70   yp  as shown in  FIG. 30  with the arrow L 3 . The linear drive mechanism  74   b  is configured to transfer the gripping devices  70   x  and  70   y  individually. Alternatively, each of the gripping devices  70   x  and  70   y  can be coupled to respective linear drive mechanism instead of being coupled to the same linear drive mechanism  74   b  such that the gripping devices  70   x  and  70   y  can be controlled by the respective linear drive mechanisms. When the gripping devices  70   x  and  70   y  are positioned at C 5 -C 8 , the gripping devices  70   x  and  70   y  are vertically aligned to the wafer stage  124 Vd of the fourth cleaning chamber  125 Vd, wafer stages  124 Vy and  124 Vx of the second and first dry chambers  125 Vy and  125 Vx, and the wafer output stage  16 Vc respectively. 
         [0126]    With reference to  FIGS. 31(   a )- 31 ( u ), a method of transferring and cleaning wafers in the cleaning apparatus  120 V is described.  FIGS. 31(   a )- 31 ( u ) are sequential top views of the cleaning apparatus  120 V. The method comprises steps of: 
         [0127]    (1) positioning the supporting member  73   a  of the first internal wafer transfer device  122   a  at the position WT 1 ; positioning the gripping devices  70   x  and  70   y  at the respective parking positions  70   xp  and  70   yp ; transferring a first wafer W 1  to the cleaner buffer  16 Vb by the wafer transfer device  40  (not shown in  FIGS. 31(   a )- 31 ( u )); lowering the gripping device  70   a  to the cleaner buffer  16 Vb; gripping the wafer W 1  from the cleaner buffer  16 Vb; and moving the gripping device  70   a  upward as shown in  FIG. 31(   a ); 
         [0128]    (2) transferring the supporting member  73   a  to the position WT 2 ; transferring a second wafer W 2  to the cleaner buffer  16 Vb by the wafer transfer device  40 ; lowering the gripping device  70   a  to the first cleaning chamber  125 Va; placing the wafer W 1  to the first cleaning chamber  125 Va; moving the gripping device  70   a  upward; and cleaning the wafer W 1  in the first cleaning chamber  125 Va as shown in  FIG. 31(   b ); 
         [0129]    (3) returning the supporting member  73   a  to the position WT 1 ; lowering the gripping devices  70   b  and  70   a  to the first cleaning chamber  125 Va and the cleaner buffer  16 Vb respectively; gripping the wafers W 1  and W 2  from the first cleaning chamber  125 Va and the cleaner buffer  16 Vb respectively; and moving the gripping devices  70   b  and  70   a  upward as shown in  FIG. 31(   c ); 
         [0130]    (4) transferring the supporting member  73   a  to the position WT 2 ; transferring a third wafer W 3  to the cleaner buffer  16 Vb by the wafer transfer device  40 ; lowering the gripping devices  70   b  and  70   a  to the second and first cleaning chambers  125 Vb and  125 Va respectively; placing the wafers W 1  and W 2  to the second and first cleaning chambers  125 Vb and  125 Va respectively; moving the gripping devices  70   b  and  70   a  upward; and cleaning the wafers W 1  and W 2  in the respective cleaning chambers as shown in  FIG. 31(   d ); 
         [0131]    (5) returning the supporting member  73   a  to the position WT 1 ; lowering the gripping devices  70   c - 70   a  to the second and first cleaning chambers  125 Vb and  125 Va and the cleaner buffer  16 Vb respectively; gripping the wafers W 1 -W 3  from the second and first cleaning chambers  125 Vb and  125 Va and the cleaner buffer  16 Vb respectively; and moving the gripping devices  70   c - 70   a  upward as shown in  FIG. 31(   e ); 
         [0132]    (6) transferring the supporting member  73   a  to the position WT 2 ; transferring a fourth wafer W 4  to the cleaner buffer  16 Vb by the wafer transfer device  40 ; lowering the gripping devices  70   c - 70   a  to the third, second and first cleaning chambers  125 Vc- 125 Va respectively; placing the wafers W 1 -W 3  to the third, second and first cleaning chambers  125 Vc- 125 Va respectively; moving the gripping devices  70   c - 70   a  upward; and cleaning the wafers W 1 -W 3  in the respective cleaning chambers as shown in  FIG. 31(   f ); 
         [0133]    (7) returning the supporting member  73   a  to the position WT 1 ; lowering the gripping devices  70   d - 70   a  to the third, second and first cleaning chambers  125 Vc- 125 Va and the cleaner buffer  16 Vb respectively; gripping the wafers W 1 -W 4  from the third, second and first cleaning chambers  125 Vc- 125 Va and the cleaner buffer  16 Vb respectively; and moving the gripping devices  70   d - 70   a  upward as shown in  FIG. 31(   g ); 
         [0134]    (8) transferring the supporting member  73   a  to the position WT 2 ; lowering the gripping devices  70   d - 70   a  to the fourth, third, second and first cleaning chambers  125 Vd- 125 Va respectively; placing the wafers W 1 -W 4  to the fourth, third, second and first cleaning chambers  125 Vd- 125 Va respectively; moving the gripping devices  70   d - 70   a  upward; and cleaning the wafers W 1 -W 4  in the respective cleaning chambers as shown in  FIG. 31(   h ); 
         [0135]    (9) returning the supporting member  73   a  to the position WT 1 ; transferring the gripping device  70   x  of the second internal wafer transfer device  122   b  to the position C 5 ; lowering the gripping devices  70   x  and  70   d - 70   b  to the fourth, third, second and first cleaning chambers  125 Vd- 125 Va respectively; gripping the wafers W 1 -W 4  from the fourth, third, second and first cleaning chambers  125 Vd- 125 Va respectively; and moving the gripping devices  70   x  and  70   d - 70   b  upward as shown in  FIG. 31(   i ); 
         [0136]    (10) transferring the supporting member  73   a  of the first internal wafer transfer device  122   a  to the position WT 2 ; transferring the gripping device  70   x  of the second internal wafer transfer device  122   b  to the position C 7 ; lowering the gripping devices  70   x  and  70   d - 70   b  to the first dry chamber  125 Vx, the fourth, third and second cleaning chambers  125 Vd- 125 Vb respectively; placing the wafers W 1 -W 4  to the respective chambers; moving the gripping devices  70   x  and  70   d - 70   b  upward; and drying the wafer W 1  and cleaning the wafers W 2 -W 4  in the respective chambers as shown in  FIG. 31(   j ); 
         [0137]    (11) returning the supporting member  73   a  of the first internal wafer transfer device  122   a  to the position WT 1 ; transferring the gripping device  70   x  to the position C 5 ; lowering the gripping devices  70   x ,  70   d  and  70   c  to the fourth, third and second cleaning chambers  125 Vd- 125 Vb respectively; gripping the wafers W 2 -W 4  from the respective chambers; and moving the gripping devices  70   x ,  70   d  and  70   c  upward as shown in  FIG. 31(   k ); 
         [0138]    (12) transferring the supporting member  73   a  to the position WT 2 ; transferring the gripping device  70   x  to the position C 6 ; lowering the gripping devices  70   x ,  70   d  and  70   c  to the second dry chamber  125 Vy, the fourth cleaning chamber  125 Vd and the third cleaning chamber  125 Vc respectively; placing the wafers W 2 -W 4  to the respective chambers; moving the gripping devices  70   x ,  70   d  and  70   c  upward; and drying the wafer W 2  and cleaning the wafers W 3  and W 4  in the respective chambers as shown in  FIG. 31(   l ); 
         [0139]    (13) returning the supporting member  73   a  to the position WT 1 ; transferring the gripping device  70   x  to the position C 5 ; transferring the gripping device  70   y  of the second internal wafer transfer device  122   b  to the position C 7 ; lowering the gripping devices  70   y ,  70   x  and  70   d  to the first dry chamber  125 Vx and the fourth and third cleaning chambers  125 Vd and  125 Vc respectively; gripping the wafers W 1 , W 3  and W 4  from the respective chambers; and moving the gripping devices  70   y ,  70   x  and  70   d  upward as shown in  FIG. 31(   m ); 
         [0140]    (14) transferring the supporting member  73   a  to WT 2 ; transferring the gripping device  70   y  to C 8 ; transferring the gripping device  70   x  to C 7 ; lowering the gripping devices  70   y ,  70   x  and  70   d  to the wafer output stage  16 Vc, the first dry chamber  125 Vx and the fourth cleaning chamber  125 Vd respectively; placing W 1 , W 3  and W 4  to the wafer output stage  16 Vc, the first dry chamber  125 Vx and the respective chambers respectively; moving the gripping devices  70   y ,  70   x  and  70   d  upward; and drying W 3  in the first dry chamber  125 Vx and cleaning W 4  in the fourth cleaning chamber  125 Vd as shown in  FIG. 31(   n ); 
         [0141]    (15) returning the supporting member  73   a  to the position WT 1 ; transferring the gripping device  70   x  to C 5 ; transferring the gripping device  70   y  to the position C 6 ; lowering the gripping devices  70   y  and  70   x  to the second dry chamber  125 Vy and the fourth cleaning chamber  125 Vd respectively; gripping the wafers W 2  and W 4  from the respective chambers; moving the gripping devices  70   y  and  70   x  upward; and transferring the wafer W 1  from the wafer output stage  16 Vc by the wafer transfer device  50  (not shown in  FIGS. 31(   a )- 31 ( u )) as shown in  FIG. 31(   o ); 
         [0142]    (16) transferring the gripping device  70   y  to the position C 8 ; transferring the gripping device  70   x  to the position C 6 ; lowering the gripping devices  70   y  and  70   x  to the wafer output stage  16 Vc and the second dry chamber  125 Vy respectively; placing the wafers W 2  and W 4  to the wafer output stage  16 Vc and the second dry chamber  125 Vy respectively; moving the gripping devices  70   y  and  70   x  upward; and drying the wafer W 4  in the second dry chamber  125 Vy as shown in  FIG. 31(   p ); 
         [0143]    (17) transferring the gripping device  70   x  to its parking position  70   xp ; transferring the gripping device  70   y  to the position C 7 ; lowering the gripping device  70   y  to the first dry chamber  125 Vx; gripping the wafer W 3  from the first dry chamber  125 Vx; moving the gripping device  70   y  upward; and transferring the wafer W 2  from the wafer output stage  16 Vc by the wafer transfer device  50  as shown in  FIG. 31(   q ); 
         [0144]    (18) transferring the gripping device  70   y  to the position C 8 ; lowering the gripping device  70   y  to the wafer output stage  16 Vc; placing the wafer W 3  to the wafer output stage  16 Vc; and moving the gripping device  70   y  upward as shown in  FIG. 31(   r ); 
         [0145]    (19) transferring the gripping device  70   y  to the position C 6 ; lowering the gripping device  70   y  to the second dry chamber  125 Vy; gripping the wafer W 4  from the second dry chamber  125 Vy; moving the gripping device  70   y  upward; and transferring the wafer W 3  from the wafer output stage  16 Vc by the wafer transfer device  50  as shown in  FIG. 31(   s ); 
         [0146]    (20) transferring the gripping device  70   y  to the position C 8 ; lowering the gripping device  70   y  to the wafer output stage  16 Vc; placing the wafer W 4  to the wafer output stage  16 Vc; and moving the gripping device  70   y  upward as shown in  FIGS. 31(   t ); and 
         [0147]    (21) transferring the gripping device  70   y  to its parking position  70   yp ; and transferring the wafer W 4  from the wafer output stage  16 Vc by the wafer transfer device  50  as shown in  FIG. 31(   u ). 
         [0148]    In the method described above, placing the wafers to the dry and cleaning chambers  125 Vx,  125 Vy and  125 Vd- 125 Va means placing the wafers on the respective wafer stages  124 Vx,  124 Vy and  124 Vd- 124 Va of the dry and cleaning chambers. 
         [0149]    In this sequential manner, a first group of the wafers cleaned in the cleaning chambers  125 Va- 125 Vd are dried in the first dry chamber  125 Vx and a second group of the wafers cleaned in the cleaning chambers  125 Va- 125 Vd are dried in the second dry chamber  125 Vy. 
         [0150]    In an embodiment, the cleaning apparatus  120 V may comprise more than two dry chambers between the wafer output stage  16 Vc and the last cleaning chamber such as the fourth cleaning chamber  125 Vd. In this embodiment, the gripping device  70   x  of the second internal wafer transfer device  122   b  transfers wafers from the last cleaning chamber to the plurality of dry chambers, and the gripping device  70   y  of the second internal wafer transfer device  122   b  transfers the wafers from the plurality of dry chambers to the wafer output stage  16 Vc. 
         [0151]    In an embodiment, the second internal wafer transfer device  122   b  comprises either one of the gripping devices  70   x  and  70   y  and is configured such that the one of the gripping devices can transfer wafers from the fourth cleaning chamber  125 Vd to the dry chambers  125 Vy and  125 Vx and from the dry chambers  125 Vy and  125 Vx to the wafer output stage  16 Vc. 
         [0152]    In an embodiment, the cleaner buffer  16 Vb may be also disposed in a cleaning chamber configured to spray DI water or chemicals to a wafer placed on the cleaner buffer  16 Vb. 
         [0153]    In an embodiment, the cleaning apparatus  120 V may comprise two, three or five cleaning chambers between the dry chamber  125   y  and the cleaner buffer  16 Vb, In this embodiment, the first internal wafer transfer device  122   a  comprises two, three or five gripping devices  70  respectively. 
         [0154]    In the wafer processing apparatuses  100 ,  100   a  and  100   b  described with reference to  FIGS. 5 ,  7 ,  11 - 13 ,  17 ,  27  and  28 , the cleaning apparatuses  120  and  120 ′ configured to transfer and process the wafers with the surfaces of the wafers laid horizontal as shown in  FIG. 6  were used. However, it is also possible that a cleaning apparatus configured to transfer and process the wafers with the surfaces of the wafers standing vertical such as the cleaning apparatus  120 V can be used as replacements of the cleaning apparatuses  120  and  120 ′. 
         [0155]    Turning back to  FIG. 29 , the wafer processing apparatus  200  is further described. In an embodiment, the wafer output stage  16 Vc′ of the second cleaning apparatus  120 V′ shown in  FIG. 29  may further comprise a pivoting device  16 P as shown in  FIGS. 32(   a ) and  32 ( b ), which are side views of the wafer output stage  16 Vc′ comprising the pivoting device  16 P when a wafer is positioned at first and second angles respectively. The pivoting device  16 P is configured to pivot the wafer placed on the wafer output stage  16 Vc′ between the first and second angles about a pivoting axis  16   cx  which passes vertically through a diameter of the wafer. In an operation, the wafer output stage  16 Vc′ receives the wafer from the internal wafer transfer device  122 V′ of the second cleaning apparatus  120 V′ at the first angle as shown in  FIG. 32(   a ) and then the wafer is pivoted to the second angle by the pivoting device  16 P about the pivoting axis  16   cx  as shown in  FIG. 32(   b ). The wafer transfer device  50  transfers the wafer from the wafer output stage  16 Vc′ after the wafer is positioned at the second angle. A difference between the first and second angles may be 90 degree. 
         [0156]    The cleaner buffer  16 Vb′ of the second cleaning apparatus  120 V′ may also comprise the pivoting device  16 P. The cleaner buffer  16 Vb′ receives a wafer from the wafer transfer device  40  at a third angle and then is pivoted to the first angle by the pivoting device  16 P. The internal wafer transfer device  122 V′ of the second cleaning apparatus  120 V′ transfers the wafers from the cleaner buffer  16 Vb′ after the cleaner buffer  16 Vb′ changes the orientation to the first angle from the third angle. 
         [0157]    Referring to  FIG. 29 , the layout of the polishing modules  110   a  and  110   a ′ in the wafer processing apparatus  200  is further described. The second polishing module  110   a ′ is disposed in the back side of the wafer processing apparatus  200  such that (1) the first polishing surface  14   a ′ is adjacent to the first end  120 Vx′ of the second cleaning apparatus  120 V′; (2) the second polishing surface  14   b ′ is disposed at a corner of the wafer processing apparatus  200  in the back side of the wafer processing apparatus  200 ; (3) the third polishing surface  14   c ′ is disposed in the back side of the wafer processing apparatus  200  such that it faces the first polishing surface  14   a  of the first polishing module  110   a  across a line  200 L; and (4) the wafer transfer station  18 ′ faces the wafer transfer station  18  of the first polishing module  110   a  across the line  200 L. 
         [0158]    The first polishing module  110   a  is disposed in the opposite side of the second polishing module  110   a ′ across the line  200 L such that (1) the second and third polishing surfaces  14   b  and  14   c  face the first cleaning apparatus  120 V across a space SP 1 ; (2) the third polishing surface  14   c  faces the second cleaning apparatus  120 V′ across a space SP 2 ; (3) the first polishing surface  14   a  faces the third polishing surface  14   c ′ of the second polishing module  110   a ′ across the line  200 L; and (4) the wafer transfer station  18  is adjacent to the wafer transfer station  18 ′ of the second polishing module  110   a ′ and the wafer transfer device  40 . 
         [0159]    The space SP 1  is disposed between the first cleaning apparatus  120 V and the first polishing module  110   a  such that an engineer can access to the first cleaning apparatus  120 V through the space SP 1  to maintain the first cleaning apparatus  120 V. The space SP 2  is disposed between the first polishing module  110   a  and the second cleaning apparatus  120 V′. The space SP 2  is surrounded by the wafer input stage  16   a , the second cleaning apparatus  120 V′, the first polishing module  110   a , the first cleaning polishing apparatus  120 V and the space SP 1 . The wafer transfer device  40  is disposed in the space SP 2 . 
         [0160]    Still referring to  FIG. 29 , a method of processing wafers in the wafer processing apparatus  200  is described. The method comprises steps of (1) transferring a first wafer W 1  from the cassette  60  to the wafer input stage  16   a  by the wafer transfer device  50 ; (2) transferring the wafer W 1  from wafer input stage  16   a  to the wafer transfer station  18  of the first polishing module  110   a  by the wafer transfer device  40 ; (3) loading the wafer W 1  from the wafer transfer station  18  to the first polishing head  20   a  of the first polishing module  110   a ; (4) transferring the first polishing head  20   a  from the wafer transfer station  18  to the polishing surfaces  14   a - 14   c  sequentially about the rotation axis  28  in order to polish the wafer W 1  on the polishing surfaces  14   a - 14   c ; (5) transferring the first polishing head  20   a  to the wafer transfer station  18  after polishing the wafer W 1 ; (6) unloading the wafer W 1  to the wafer transfer station  18 ; (7) transferring the wafer W 1  from the wafer transfer station  18  to the cleaner buffer  16 Vb of the first cleaning apparatus  120 V by the wafer transfer device  40 ; (8) transferring the wafer W 1  from the cleaner buffer  16 Vb to the wafer output stage  16 Vc of the first cleaning apparatus  120 V through the cleaning module  124 V by the internal wafer transfer device  122 V of the first cleaning apparatus  120 V in order to clean and dry the wafer W 1 ; and (9) transferring the wafer W 1  from the wafer output stage  16 Vc to the cassette  60  by the wafer transfer device  50 . 
         [0161]    The method further comprises steps of (1) transferring a second wafer W 2  from the cassette  60  to the wafer input stage  16   a  by the wafer transfer device  50 ; (2) transferring the wafer W 2  from wafer input stage  16   a  to the wafer transfer station  18 ′ of the second polishing module  110   a ′ by the wafer transfer device  40 ; (3) loading W 2  from the wafer transfer station  18 ′ to the first polishing head  20   a ′ of the second polishing module  110   a ′; (4) transferring the first polishing head  20   a ′ from the wafer transfer station  18 ′ to the polishing surfaces  14   a ′- 14   c ′ sequentially about the rotation axis  28 ′ in order to polish the wafer W 2  on the polishing surfaces  14   a ′- 14   c ′; (5) transferring the first polishing head  20   a ′ to the wafer transfer station  18 ′ after polishing W 2 ; (6) unloading the wafer W 2  to the wafer transfer station  18 ′; (7) transferring the wafer W 2  from the wafer transfer station  18 ′ to the cleaner buffer  16 Vb′ of the second cleaning apparatus  120 V′ by the wafer transfer device  40 ; (8) transferring the wafer W 2  from the cleaner buffer  16 Vb′ to the wafer output stage  16 Vc′ of the second cleaning apparatus  120 V′ through the cleaning module  124 V′ by the internal wafer transfer device  122 V′ of the second cleaning apparatus  120 V′ in order to clean and dry the wafer W 2 ; and (9) transferring the wafer W 2  from the wafer output stage  16 Vc′ to the cassette  60  by the wafer transfer device  50 . 
         [0162]    According to a modified embodiment of the wafer processing apparatus  200 , the wafer input stage  16   a  may be disposed inside the first cleaning apparatus  120 V such that the wafer input stage  16   a  is disposed between the second end  120 Vy′ of the second cleaning apparatus  120 V′ and the cleaner buffer  16 Vb of the first cleaning apparatus  120 V. In an embodiment the wafer input stage  16   a  may be positioned over or under the cleaner buffer  16 Vb of the first cleaning apparatus  120 V. 
         [0163]    In another modified embodiment, the wafer processing apparatus  200  may further comprises the second wafer transfer device  40 * and the buffer  16   a *, which are shown in  FIG. 28 , in the space SP 2  of the polishing apparatus  200  shown in  FIG. 29 . The second wafer transfer device  40 * is disposed between the wafer input stage  16   a  and the buffer  16   a *, and configured to transfer wafers from the wafer input stage  16   a  to the buffer  16   a * and from the buffer  16   a * to the cleaner buffer  16 Vb of the first cleaning apparatus  120 V. The buffer  16   a * is disposed between the first and second wafer transfer devices  40  and  40 * such that the buffer  16   a * can be also reached by the first wafer transfer device  40 . The buffer  16   a * accommodates wafers transferred by the first and second wafer transfer devices  40  and  40 * vertically or horizontally. 
         [0164]    In an operation of the wafer processing apparatus  200  further comprising the second wafer transfer device  40 * and the buffer  16   a *, wafers to be polished are transferred from the wafer input stage  16   a  to the buffer  16   a * by the second wafer transfer device  40 * and then transferred from there to the wafer transfer stations  18  and  18 ′ of the polishing modules  110   a  and  110   a ′ by the wafer transfer device  40 . After the wafers are polished at one of the polishing modules  110   a  and  110   a ′, a first group of the polished wafers are transferred from one of the wafer transfer stations  18  and  18 ′ to the buffer  16   a * by the wafer transfer device  40  and then further transferred from the buffer  16   a * to the cleaner buffer  16 Vb of the first cleaning apparatus  120 V by the second wafer transfer device  40 * in order to clean and dry the wafers in the first cleaning apparatus  120 V. A second group of the polished wafers are transferred from the other of the wafer transfer stations  18  and  18 ′ to the cleaning buffer  16 Vb′ of the second cleaning apparatus  120 V′ by the wafer transfer device  40  in order to clean and dry the wafers in the second cleaning apparatus  120 V′. 
         [0165]    With reference to  FIG. 33 , a wafer processing apparatus  300  in accordance with an embodiment of the present invention is described.  FIG. 33  is a top view of the wafer processing apparatus  300 . The wafer processing apparatus  300  comprises the factory interface  64 , the wafer transfer device  40  and a polishing apparatus  305 . The polishing apparatus  305  comprises two polishing modules  110   a  and  110   a ′ used in the wafer processing apparatus  200  shown in  FIG. 29 . At least one cleaning and dry chambers (not shown in  FIG. 33 ) can be disposed between the factory interface  64  and the polishing apparatus  305  in order to clean and dry wafers polished in the polishing apparatus  305 . 
         [0166]    The polishing surfaces  14   a - 14   c ′ of the polishing modules  110   a  and  110   a ′ are disposed such that a line N 1  connecting the rotational axes  15   a  and  15   b  of the first and second polishing surfaces  14   a  and  14   b  of the first polishing module  110   a  is substantially parallel to a depth direction of the wafer processing apparatus  300 ; a line N 2  connecting the rotational axes  15   b  and  15   c  of the second and third polishing surfaces  14   b  and  14   c  of the first polishing module  110   a  is substantially parallel to a width direction of the wafer processing apparatus  300 ; a line N 3  connecting the rotational axes  15   a ′ and  15   b ′ of the first and second polishing surfaces  14   a ′ and  14   b ′ of the second polishing module  110   a ′ is substantially parallel to the width direction; a line N 4  connecting the rotational axes  15   b ′ and  15   c ′ of the second and third polishing surfaces  14   b ′ and  14   c ′ of the second polishing module  110   a ′ is substantially parallel to the depth direction; the polishing surfaces  14   a ′ and  14   b ′ of the second polishing module  110   a ′ are disposed opposite to the factory interface  64  in the back side of the wafer processing apparatus  300 ; the first polishing surface  14   a  of the first polishing module  110   a , the third polishing surface  14   c ′ of the second polishing module  110   a ′ and the wafer transfer stations  18  and  18 ′ are disposed between the line N 2  and the line N 3 ; and the third polishing surface  14   c  of the first polishing module  110   a , the first polishing surface  14   a ′ of the second polishing module  110   a ′ and the wafer transfer stations  18  and  18 ′ are disposed between the line N 1  and the line N 4 . 
         [0167]    The wafer transfer device  40  is disposed around the third polishing surfaces  14   c  and  14   c ′ of the first and second polishing modules  110   a  and  110   a ′ such that the wafer transfer device  40  can transfer wafers to and from the wafer transfer stations  18  and  18 ′ of the polishing modules  110   a  and  110   a ′ through a space G 2  between the respective third polishing surfaces  14   c  and  14   c ′ of the first and second polishing modules  110   a  and  110   a′.    
         [0168]    With reference to  FIG. 34 , a wafer processing apparatus  500  in accordance with an embodiment of the invention is described.  FIG. 34  is a top view of the wafer processing apparatus  500 . The wafer processing apparatus  500  comprises a cleaning apparatus  520 , two polishing modules  10   a  and  10   a ′, the factory interface  64 , the wafer transfer device  40 , a wafer transfer device  40 C, the wafer input stage  16   a , the buffer  16   a *, and the cleaner buffer  16   b . The polishing module  10  shown in  FIG. 1  can be used as the polishing modules  10   a  and  10   a′.    
         [0169]    The cleaning apparatus  520  comprises three cleaning chambers  125   a - 125   c  and two dry chambers  125   x  and  125   y . However, the cleaning apparatus  520  may comprise six cleaning chambers  125   a - 125   c  and  125   a ′- 125   c ′ and four dry chambers  125   x ,  125   y ,  125   x ′ and  125   y ′ (the cleaning chambers  125   a ′- 125   c ′ and the dry chambers  125   x ′ and  125   y ′ are not shown in  FIG. 34 ). The cleaning chambers  125   a ′- 125   c ′ may be stacked on the cleaning chambers  125   a - 125   c . The dry chambers  125   x ′ and  125   y ′ may be stacked on the dry chambers  125   x  and  125   y.    
         [0170]    The cleaning apparatus  520  is disposed adjacent to the factory interface  64  such that a longer side  520   a  of the cleaning apparatus  520  is parallel to the longer side  64   a  of the factory interface  64 ; and the cleaning apparatus  520  is sandwiched between the factory interface  64  and a linear track  42 C which is also disposed parallel to the longer side of the factory interface  64 . The wafer transfer device  40 C is mounted on the linear track  42 C such that the wafer transfer device  40 C can transfer wafers from the cleaner buffer  16   b  to the cleaning chambers  125   a - 125   c  and from the cleaning chambers  125   a - 125   c  to the dry chambers  125   x  and  125   y . The wafer transfer device  40 C is configured to comprise first and second arms  41   a  and  41   b  such that the first arm  41   a  is used to transfer wafers to be cleaned from the cleaner buffer  16   b  to the cleaning chambers  125   a - 125   c  and the second arm  41   b  is used to transfer wafers cleaned in the cleaning chambers  125   a - 125   c  to the dry chambers  125   x  and  125   y . The wafer transfer device  40 C is also configured to transfer wafers from the wafer input stage  16   a  to the buffer  16   a *. The wafer input stage  16   a  is disposed between the cleaning chamber  125   a  and the dry chamber  125   x  which are adjacent to each other or disposed over any of the cleaning chambers  125   a - 125   c  and the dry chambers  125   x  and  125   y  such that the wafer transfer device  50  of the factory interface  64  can transfer wafers to the wafer input stage  16   a  and the wafer transfer device  40 C can transfer wafers from the wafer input stage  16   a.    
         [0171]    The cleaning chambers  125   a - 125   c  and the dry chambers  125   x  and  125   y  are configured to have respective first openings toward the wafer transfer device  40 C such that the cleaning chambers  125   a - 125   c  and the dry chambers  125   x  and  125   y  can receive wafers from the wafer transfer device  40 C through the respective first openings. The dry chambers  125   x  and  125   y  are further configured to have respective second openings toward the wafer transfer device  50  such that the wafer transfer device  50  can take the wafers from the dry chambers  125   x  and  125   y  through the respective second openings. 
         [0172]    The polishing modules  10   a  and  10   a ′ and the wafer transfer device  40  are disposed opposite to the factory interface  64  across the wafer transfer device  40 C. The buffer  16   a * and the cleaner buffer  16   b  are disposed between the wafer transfer device  40 C and the wafer transfer device  40 . The wafer transfer device  40  transfers wafers from the buffer  16   a * to the wafer transfer stations  18  and  18 ′ of the polishing modules  10   a  and  10   a ′ and from the wafer transfer stations  18  and  18 ′ to the cleaner buffer  16   b.    
         [0173]    The first polishing module  10   a  is disposed such that a line connecting the rotation axes  15   a  and  15   b  of the polishing surfaces  14   a  and  14   b  is substantially parallel to a depth direction of the wafer processing apparatus  500 , the first polishing surface  14   a  is adjacent to the linear track  42 C, and the wafer transfer station  18  is adjacent to the wafer transfer station  18 ′ of the second polishing module  10   a ′ and the wafer transfer device  40 . 
         [0174]    The second polishing module  10   a ′ is disposed in the back side of the wafer processing apparatus  500  such that a line connecting the rotation axes  15   a ′ and  15   b ′ of the polishing surfaces  14   a ′ and  14   b ′ is substantially parallel to a width direction of the wafer processing apparatus  500 ; distances from the rotational axes  15   a ′ and  15   b ′ of the polishing surfaces  14   a ′ and  14   b ′ of the second polishing module  10   a ′ to the factory interface  64  is greater than a distance from the rotation axis  15   b  of the second polishing surface  14   b  of the first polishing module  10   a  to the factory interface  64 ; the wafer transfer station  18 ′ faces the wafer transfer device  40 ; and there is a space SP 4  between the second polishing module  10   a ′ and the linear track  42 C. The space SP 4  provides a space for the wafer transfer device  40 , the buffer  16   a * and the cleaner buffer  16   b . The space SP 4  also provides a space through which an engineer can access the polishing modules  10   a  and  10   a ′ and the cleaning apparatus  520  in order to maintain them. 
         [0175]    With reference to  FIG. 35 , a wafer processing apparatus  600  in accordance with an embodiment of the present invention is described.  FIG. 35  is a top view of the wafer processing apparatus  600 . The wafer processing apparatus  600  comprises two cleaning apparatuses  620  and  620 ′, the factory interface  64  and the wafer transfer device  40 C. The wafer transfer device  40 C is mounted on the linear track  42 C. 
         [0176]    Each of the cleaning apparatuses  620  and  620 ′ comprises the cleaner buffer  16   b , multiple cleaning chambers  125   a - 125   c , the dry chamber  125   x  and multiple internal wafer transfer devices  127 . The cleaning chambers  125   a - 125   c  are disposed between the cleaner buffer  16   b  and the dry chamber  125   x . The internal wafer transfer devices  127  are disposed and configured to transfer wafers between the cleaner buffer  16   b  and the cleaning and dry chambers  125   a - 125   c  and  125   x.    
         [0177]    The first cleaning apparatus  620  is disposed adjacent to the factory interface  64  such that a longer side  620   a  of the cleaning apparatus  620  is substantially parallel to the longer side  64   a  of the factory interface  64 ; and the first cleaning apparatus  620  is sandwiched between the factory interface  64  and the linear track  42 C which is also disposed parallel to the longer side of the factory interface  64 . The second cleaning apparatus  620 ′ is disposed such that the linear track  42 C is sandwiched between the first and second cleaning apparatuses  620  and  620 ′; and a longer side  620   a ′ of the second cleaning apparatus  620 ′ is substantially parallel to the longer side  620   a  of the first cleaning apparatus  620 . 
         [0178]    The wafer processing apparatus  600  further comprises the wafer input stage  16   a , the buffer  16   a *, the wafer output stage  16   c , a second buffer  16   b * and the wafer transfer device  40 . The wafer input stage  16   a  and the wafer output stage  16   c  are disposed about the first cleaning apparatus  620  such that the wafer transfer device  50  of the factory interface  64  can transfer wafers to the wafer input stage  16   a  and from the wafer output stage  16   c ; and the wafer transfer device  40 C can transfer wafers from the wafer input stage  16   a  and to the wafer output stage  16   c . The wafer input stage  16   a  and the wafer output stage  16   c  may be disposed over any of the wafer stages  16   b ,  124   a - 124   c  and  124   x  of the first cleaning apparatus  620 . 
         [0179]    The buffer  16   a * and the second buffer  16   b * are disposed about the second cleaning apparatus  620 ′ such that the wafer transfer device  40 C can transfer wafers to the buffer  16   a * and from the second buffer  16   b *; and the wafer transfer device  40  can transfer wafers from the buffer  16   a * and to the second buffer  16   b *. The buffer  16   a * and the second buffer  16   b * may be disposed over any of the wafer stages  16   b ′,  124   a ′- 124   c ′ and  124   x ′ of the second cleaning apparatus  620 ′. 
         [0180]    The wafer processing apparatus  600  uses the same polishing modules  10   a  and  10   a ′ used in the wafer processing apparatus  500  shown in  FIG. 34 . The wafer transfer device  40  transfers wafers from the buffer  16   a * to the wafer transfer stations  18  and  18 ′ of the polishing modules  10   a  and  10   a ′ and from there to the second buffer  16   b * and the cleaner buffer  16   b ′ of the second cleaning apparatus  620 ′. 
         [0181]    A method of processing wafers in the wafer processing apparatus  600  comprises steps of: 
         [0182]    (1) transferring a first wafer W 1  from the cassette  60  to the wafer input stage  16   a  by the wafer transfer device  50 ; transferring the wafer W 1  from the wafer input stage  16   a  to the buffer  16   a * by the wafer transfer device  40 C; and transferring the wafer W 1  from the buffer  16   a * to the wafer transfer station  18  of the first polishing module  10   a  by the wafer transfer device  40 ; 
         [0183]    (2) loading the wafer W 1  to the first polishing head  20   a  of the polishing module  10   a  from the wafer transfer station  18 ; transferring the first polishing head  20   a  to the first and second polishing surfaces  14   a  and  14   b ; returning the first polishing head  20   a  to the wafer transfer station  18 ; and unloading the wafer W 1  from the first polishing head  20   a  to the wafer transfer station  18 ; 
         [0184]    (3) transferring the wafer W 1  from the wafer transfer station  18  to the second buffer  16   b * by the wafer transfer device  40 ; and transferring W 1  from the second buffer  16   b * to the cleaner buffer  16   b  of the first cleaning apparatus  620  by the first arm  41   a  of the wafer transfer device  40 C; 
         [0185]    (4) transferring the wafer W 1  from the cleaner buffer  16   b  through the cleaning chambers  125   a - 125   c  to the dry chamber  125   x  by the internal wafer transfer devices  127  in order to clean the wafer W 1  in the cleaning chambers  125   a - 125   c  and dry W 1  in the dry chamber  125   x ; and 
         [0186]    (5) transferring the wafer W 1  from the dry chamber  125   x  of the first cleaning apparatus  620  to the cassette  60  by the wafer transfer device  50 . 
         [0187]    The method of processing wafers in the wafer processing apparatus  600  further comprises steps of: (1) transferring a second wafer W 2  from the cassette  60  to the buffer  16   a * in the same manner as the first wafer W 1  is transferred to the buffer  16   a *; and transferring W 2  from the buffer  16   a * to the wafer transfer station  18 ′ of the second polishing module  10   a ′ by the wafer transfer device  40 ; 
         [0188]    (2) loading the wafer W 2  to the first polishing head  20   a ′ of the polishing module  10   a ′ from the wafer transfer station  18 ′; transferring the first polishing head  20   a ′ to the first and second polishing surfaces  14   a ′ and  14   b ′; returning the first polishing head  20   a ′ to the wafer transfer station  18 ′; and unloading the wafer W 2  from the first polishing head  20   a ′ to the wafer transfer station  18 ′; 
         [0189]    (3) transferring the wafer W 2  from the wafer transfer station  18 ′ to the cleaner buffer  16   b ′ of the second cleaning apparatus  620 ′ by the wafer transfer device  40 ; and transferring the wafer W 2  from the cleaner buffer  16   b ′ through the cleaning chambers  125   a ′- 125   c ′ to the dry chamber  125   x ′ by the internal wafer transfer devices  127  in order to clean the wafer W 2  in the cleaning chambers  125   a ′- 125   c ′ and dry the wafer W 2  in the dry chamber  125   x ′; and 
         [0190]    (4) transferring the wafer W 2  from the dry chamber  125   x ′ to the wafer output stage  16   c  by the second arm  41   b  of the wafer transfer device  40 C; and transferring the wafer W 2  from the wafer output stage  16   c  to the cassette  60  by the wafer transfer device  50 . 
         [0191]    While the present invention has been described with reference to the embodiments thereof, it will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described above, but it is intended to cover modifications within the inventive concept. As an example, although various apparatuses and methods have been described for polishing and cleaning semiconductor wafers, these apparatuses and methods may be used to polish and clean objects other than semiconductor wafers.