Abstract:
The polishing apparatus is capable of transferring a work piece to a top ring without moving the work piece from the center and capable of precisely polishing the work piece. The polishing apparatus has a transfer unit for transferring the work piece to the top ring. The transfer unit comprises: a guide member having a receiving section, which centers the work piece; a mounting table vertically moving with respect to the guide member, the mounting table having a mounting section, which receives the centered work piece; and a supporting mechanism supporting the mounting table and allowing the mounting table to move downward. The mounting table is relatively moved close to the top ring and presses the work piece onto the top ring so as to transfer the work piece to the top ring.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a polishing apparatus for polishing work pieces, e.g., wafer.  
         [0002]     Many types of polishing apparatuses are known.  
         [0003]     An ordinary polishing apparatus has a polishing plate, whose upper face is covered with polishing cloth, and a top ring, which has a lower face for holding a work piece and presses a lower face of the work piece onto the polishing cloth. The polishing plate and the top ring are relatively moved so as to polish the lower face of the work piece.  
         [0004]     Generally, the work piece is conveyed to a transfer unit by a robot hand, the transfer unit centers the work piece, and the top ring is moved to the transfer unit to receive the work piece.  
         [0005]     A conventional polishing apparatus having a transfer unit is disclosed in Japanese Patent Gazette No. 11-347922.  
         [0006]     The transfer unit comprises: a pusher stage having a supporting face, on which a work piece, e.g., a semiconductor wafer, will be mounted; an elevating unit for vertically moving the pusher stage; and a guide member, which is located in a periphery of the pusher stage and which has a guide face, which is a female-tapered face.  
         [0007]     The semiconductor wafer is conveyed to the pusher stage by the robot hand and mounted onto the supporting face of the pusher stage. Then, the pusher stage is moved downward together with the wafer. The wafer enters the guide member, and an outer circumferential face of the wafer contacts the guide face of the guide member, so that the wafer can be centered. The pusher stage is moved upward, received the centered wafer and presses the centered wafer onto a lower face of the top ring, so that the wafer can be held by the top ring.  
         [0008]     After polishing the wafer, the polished wafer is conveyed from the top ring to the transfer unit by the backward process, then the wafer is conveyed from the transfer unit to an external place by the robot hand.  
         [0009]     However, in the conventional transfer unit, the work piece is moved from the pusher stage to the female-tapered guide face so as to perform centering of the work piece. When the work piece is transferred to the top ring, the pusher stage is moved upward so as to receive the work piece and press the work piece onto the top ring. Therefore, the centered work piece is vibrated while the pusher stage is moved toward the top ring, thereby the work piece will be easily moved from the center. If the work piece is moved or shifted from the center, the work piece will be damaged or broken.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention was conceived to solve the above described problems.  
         [0011]     An object of the present invention is to provide a polishing apparatus, which is capable of transferring a work piece to a top ring without moving the work piece from the center and capable of precisely polishing the work piece.  
         [0012]     To achieve the object, the present invention has following structures.  
         [0013]     Namely, the polishing apparatus of the present invention comprises:  
         [0014]     a polishing plate having an upper face covered with polishing cloth;  
         [0015]     a top ring having a lower face for holding a work piece and pressing a lower face of the work piece onto the polishing cloth, the top ring being relatively moved with respect to the polishing plate so as to polish the lower face of the work piece; and  
         [0016]     a transfer unit being located at a work piece transfer position, at which the work piece is transferred to the top ring,  
         [0017]     wherein the transfer unit comprises: 
        a guide member having a receiving section, which guides an outer edge of the transferred work piece so as to perform centering of the work piece;     a mounting table being relatively vertically moving with respect to the guide member, the mounting table having a mounting section, which receives the centered work piece from the guide member with an upper face projecting upward; and     a supporting mechanism supporting the mounting table and allowing the mounting table to move downward, and        
 
         [0021]     wherein the mounting table is relatively moved close to the top ring and presses the work piece onto the lower face of the top ring so as to transfer the work piece to the top ring.  
         [0022]     In the polishing apparatus, the top ring may be moved downward and moves the work piece, which has been centered on the mounting table, together with the mounting table so as to transfer the work piece to the top ring.  
         [0023]     In the polishing apparatus, the guide member may be a plurality of pins, each of which has a tapered upper end acting as a guide section for centering the work piece.  
         [0024]     In the polishing apparatus, the mounting section of the mounting table may be circularly projected upward from an outer circumferential edge of the mounting table.  
         [0025]     In the polishing apparatus, a mounting face of the mounting section may be a female tapered face, whose internal diameter is gradually made smaller toward a lower end.  
         [0026]     In the polishing apparatus, an elastic member may be provided to a base, and  
         [0027]     the elastic member may elastically support the mounting table and allow the mounting table to move downward.  
         [0028]     In the polishing apparatus, the elastic member may be a coil spring, which is extended downward from the mounting table, attached on a shaft piercing through the base and elastically clamped between the mounting table and the base.  
         [0029]     In the polishing apparatus, a part of the shaft, which downwardly projects from the base, may be a first screw section,  
         [0030]     a nut may be screwed with the first screw section,  
         [0031]     a part of the shaft, which pierces through the base, may be covered with a screw cylinder whose outer circumferential face includes a second screw section screwed with the base, and  
         [0032]     a height of the mounting table with respect to the base and an elastic force of the coil spring can be adjusted by adjusting a screwing position of the screw cylinder with respect to the base and a screwing position of the nut.  
         [0033]     In the polishing apparatus, the mounting table may be vertically moved along a guide rod with maintaining a horizontal situation with respect to the base.  
         [0034]     In the polishing apparatus, an elevating member, which is vertically moved by a driving unit, may be provided to the base, and  
         [0035]     the guide member may be provided in the elevating member.  
         [0036]     In the polishing apparatus, the guide rod may guide not only the mounting table but also the elevating member.  
         [0037]     In the polishing apparatus, the transfer unit may further comprise:  
         [0038]     a supporting member supporting the mounting table, the supporting member having an elastic member, which allows the mounting table to move downward; and  
         [0039]     a plurality of positioning pieces being provided to the supporting member so as to contact an outer edge of the work piece, which has been centered on the mounting table, and position the work piece.  
         [0040]     By using the polishing apparatus of the present invention, the work piece can be transferred to the top ring without shifting from the center, so that the work piece can be polished with high polishing accuracy.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]     Embodiments of the present invention will now be described by way of examples and with reference to the accompanying drawings, in which:  
         [0042]      FIG. 1  is an explanation view of a first embodiment of the polishing machine of the present invention;  
         [0043]      FIG. 2  is a sectional view of a top ring;  
         [0044]      FIG. 3  is an explanation view showing the top ring, a work piece and a mounting section;  
         [0045]      FIG. 4  is a sectional view of a transfer unit, in which the work piece is centered by pins;  
         [0046]      FIG. 5  is an explanation view showing an arrangement of guide rods, shafts and the pins;  
         [0047]      FIG. 6  is a sectional view of the transfer unit, in which the pins are moved downward;  
         [0048]      FIG. 7  is a sectional view of the transfer unit when the top ring is moved downward so as to hold the work piece;  
         [0049]      FIG. 8  is a sectional view of the transfer unit of a second embodiment;  
         [0050]      FIG. 9  is a plan view showing an arrangement of positioning pieces of the transfer unit of the second embodiment; and  
         [0051]      FIG. 10  is an explanation view showing the positioning piece, a template and the work piece. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0052]     Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  
         [0053]      FIG. 1  is an explanation view of a polishing apparatus  10  of a first embodiment of the present invention.  
         [0054]     In  FIG. 1 , polishing cloth  13  is adhered on an upper face of a polishing plate  12  by, for example, adhesive. The polishing plate  12  is rotated about a spindle  14  in a horizontal plane. The spindle  14  is rotated by a known means (not shown).  
         [0055]     A top ring  16  is attached to a lower end of a rotary shaft  17 . The rotary shaft  17  is rotated about its own axis and vertically moved by a known mechanism (not shown). The top ring  16  is moved between a first position, which is located above the polishing plate  12 , and a second position X, which is located outside of the polishing plate  12 . The second position X is a work piece transfer position.  
         [0056]     A transfer unit  18  for transferring a work piece is located at the work piece transfer position X. A conveyor unit  19  has a robot hand (not shown). The conveyor unit  19  conveys the work piece to be polished into the transfer unit  18  and takes out the polished work piece threrefrom.  
         [0057]     The work piece is transferred from the transfer unit  18  to a lower face of the top ring  16 , the top ring  16  presses the work piece onto the polishing cloth  13  of the polishing plate  12 , and the polishing plate  12  and the top ring  16  are rotated, so that the work piece can be polished. After completing the polish, the work piece is transferred from the top ring  16  to the transfer unit  18 , then the work piece is taken out from the transfer unit  18  by the robot hand.  
         [0058]      FIG. 2  is a sectional view of the top ring  16 . The top ring  16  is a known top ring, so its structure will be briefly explained.  
         [0059]     A head proper  20  includes a ceiling section  21 , which is fixed to the shaft  17 , and a cylindrical section  22 , which is fixed to a lower outer circumferential edge of the ceiling section  21 .  
         [0060]     A holding plate  24  is located under the head proper  20  and capable of moving upward and downward with a ring-shaped diaphragm  25 . An outer circumferential edge of the diaphragm  25  is fixed to a lower face of the cylindrical section  22  by a fixing member  26 ; an inner circumferential edge of the diaphragm  25  is fixed to an outer circumferential edge of the holding plate  24  by a fixing member  27 .  
         [0061]     A first chamber  29 , which is tightly closed by the diaphragm  25 , is formed between the head proper  20  and the holding plate  24 . A pressurized fluid is introduced into the first chamber  29  from a fluid source (not shown) via a joint  30 . With this structure, the work piece can be pressed onto the polishing cloth  13 .  
         [0062]     Coaxial second chambers  31  are formed in the holding plate  24 . The second chambers  31  are mutually communicated by grooves (not shown) extended in radial directions. Many small holes  32 , which are communicated to the second chambers  31 , are evenly opened in a lower face of the holding plate  24 .  
         [0063]     A pressurized fluid is introduced into the second chambers  31  from the fluid source (not shown) via a joint  34  and a pipe  35  and jetted downward from the small holes  32  of the holding plate  24 . As shown in  FIG. 3 , a backing pad  36  having fine holes is provided on the lower face of the holding plate  24 , and a ring-shaped template  37  is provided to a lower outer circumferential edge of the backing pad  36 . The pressurized fluid, which has been jetted downward from the lower face of the holding plate  24 , is further jetted downward from the fine holes of the backing pad  36 . Therefore, the work piece W is further pressed onto the polishing cloth  13  by the jetted fluid.  
         [0064]     To hold the work piece, the fluid in the second chambers  31  is sucked, so that the work piece W is drawn to and held on a lower face of the backing pad  36 .  
         [0065]     Note that, an inner face of the cylindrical section  22  and an outer face of the fixing member  27  are tapered faces  38 , which are mutually fit, so that the holding plate  24  is correctly centered without falling out from the cylindrical section  22 .  
         [0066]     The characteristic point of the present invention is the transfer unit  18 .  
         [0067]      FIG. 4  is a sectional view of the transfer unit  18  of the first embodiment.  
         [0068]     An elevating table (an elevating member)  42 , which is vertically moved by a cylinder unit (a driving unit)  41 , is provided to a base  40 . The elevating member  42  is connected with a piston rod  41   a , and guide rods  43  are respectively guided by guide bushings  44 . By driving the cylinder unit  41 , the elevating member  42  is vertically moved with maintaining the horizontal situation.  
         [0069]     The elevating member  42  is a circular plate. Six pins (guide members)  45 , which are extended upward, are provided to an outer circumferential edge of the elevating member  42  and arranged in the circumferential direction at regular intervals (see  FIG. 5 ).  
         [0070]     As shown in  FIG. 3 , each of the pins  45  has a lower pin section  46 , which is a thicker section, and an upper pin section  47 , which is a tapered part. A border section between the lower pin section  46  and the upper pin section  47  has a tapered face  48 , whose diameter is gradually made greater toward a lower end. And, the upper pin section  47  also has a tapered face  49 , whose diameter is gradually made greater toward a lower end. Note that, a lower end of the upper pin section  47  is a columnar part  50  having a fixed diameter and connected with an upper end of the tapered border section  49 .  
         [0071]     Outer circumferential faces of the upper pin sections  47  of the six pins  47  act as receiving sections for guiding the work piece W. A known robot hand H (see  FIG. 5 ) holds an outer circumferential edge of the work piece W and conveys the work piece W into a space between the six upper pin sections  47 , then the robot hand H releases the work piece W. With this action, the outer circumferential edge of the work piece W is guided by the outer circumferential face of the upper pin sections  47 , so that the work piece W falls into a space between the six columnar parts  50 . Therefore, the work piece W is centered and mounted on upper parts of the tapered faces  48 . Clearances between the outer circumferential faces of the columnar parts  50  and the outer circumferential face of the work piece W are about 0.5 μm.  
         [0072]     In  FIG. 4 , sensors  51 , each of which has a light emitting section and a light receiving section, detect if the work piece W passes through a space between the upper pin parts  47  of the pins  45  or not.  
         [0073]     A mounting table  53  is a circular plate, and a ring-shaped mounting section  54 , which is extended upward, is provided along the outer circumferential edge of the mounting table  53 . By moving the pins  45  downward, the work piece W is transferred from the pins  45  to the mounting section  54 . The mounting section  54  has a mounting face  54   a  is a female tapered face, whose internal diameter is gradually made smaller toward a lower end. As shown in  FIG. 3 , when the work piece W is transferred to the mounting face  54   a , a height of an upper face of the work piece W is a height of a top end of the mounting face  54   a . Namely, sizes of the work piece W and the mounting face  54   a  are designed so as to project the work piece W upward. As shown in  FIG. 3 , the projected height of the work piece W is designed so as to prevent the template  37  from interfering with an upper part of the mounting section  54  when the top ring  16  is moved downward to press the work piece W with the backing pad  36 .  
         [0074]     As shown in  FIG. 5 , the mounting section  54  has notches  54   b , which have semicircular shapes, and an inner half part of each pin  45  can be passed thorough each notch  54 .  
         [0075]     The mounting table  53  is elastically supported by coil springs (elastic members) and allowed to move downward with respect to the base  40 . The supporting mechanism for supporting the mounting table  53  will be explained.  
         [0076]     Four guide rods  43  and four shafts  56  are extended downward from a lower face of the mounting table  53 , and they are alternately arranged on the same circle. Lower parts of the guide rods  43  and the shafts  56  pierce through the base  40 , and they are further extended downward. Their arrangement is shown in  FIG. 5  by solid lines.  
         [0077]     The guide rods  43  pierce through the base  40  with guide bushings  57 . Namely, the guide rods  43  guide not only the elevating member  42  but also the mounting table  53 . The mounting table  53  can be moved upward and downward with maintaining the horizontal situation.  
         [0078]     Upper parts of the shafts  56  are large diameter parts  56   a , whose diameters are larger than those of lower parts.  
         [0079]     Parts  56   b  of the shafts  56 , which are projected downward from the base  40 , are first screw sections, and nuts  58  are screwed with the first screw sections  56   b . Parts of the shafts  56 , which pierce through the base  40 , are respectively covered with screw cylinders  60 , whose outer circumferential faces include second screw sections  60   a  screwed with the base  40 . A tool can be engaged with engage sections  60   b  of the screw cylinders  60  so as to turn the screw cylinders  60 . By turning the screw cylinders  60 , positions of the screw cylinders  60  with respect to the base  40  can be adjusted. The positions of the screw cylinders  60  can be fixed by nuts  62 .  
         [0080]     The coil springs  64  cover parts of the shafts  56 , each of which is located between an upper end of the screw cylinder  60  and a lower face of the large diameter part  56   a . Therefore, the mounting table  53  is supported by the four coil springs  64 . When the mounting table  53  is pressed downward, the coil springs  64  are compressed downward (see  FIG. 7 ).  
         [0081]     With this structure, a height of the mounting table  53  with respect to the base  40  and elastic forces of the coil springs  64  can be adjusted by adjusting screwing positions of the screw cylinders  60  with respect to the base  40  and a screwing positions of the nuts  58 .  
         [0082]     The transfer unit  18  of the first embodiment has the above described structure. Successively, action of the transfer unit  18  will be explained.  
         [0083]     In  FIG. 4 , the elevating table  42  has been moved upward, and the upper pin sections  47  of the pins  45  locate at positions fully above an upper face of the mounting section  54  of the mounting table  53 .  
         [0084]     In this state, the robot hand H holds the outer edge of the work piece W, which has been accommodated in, for example, a magazine (not shown) and conveys the work piece W into the space between the six upper pin sections  47 . Then, the robot hand H releases the work piece W. The work piece W is guided by the outer circumferential faces of the upper pin sections  47  and falls onto the upper parts of the tapered faces  48 , so that the work piece W can be correctly positioned (see  FIG. 4 ).  
         [0085]     Next, as shown in  FIG. 6 , the cylinder unit  41  moves the elevating table  42  downward together with the pins  45 . With this action, the work piece W is transferred onto the mounting face  54   a  of the mounting section  54 . As described above, the height of the upper face of the work piece W is higher than the height of the upper end of the mounting face  54   a , so the work piece W is projected upward when the work piece W is transferred to the mounting face  54   a  (see  FIG. 3 ).  
         [0086]     Then, as shown in  FIG. 7 , the top ring  16  is moved downward, and the backing pad  36  contacts the upper face of the work piece W. In this state, the top ring  16  is further moved downward against the elastic forces of the coil springs  64 . The coil springs  64  are compressed, so the the coil springs  64  presses the work piece W onto the lower face of the backing pad  36  with the prescribed elastic forces. The fluid, e.g., air, in the second chambers  31  is sucked, so that the work piece W is drawn toward and held by the lower face of the backing pad  36 . Then, the top ring  16  is moved upward, moved toward the position above the polishing plate  12 , and moved downward. With this action, the work piece W is pressed onto the polishing cloth  13 . By rotating the polishing plate  12  and the top ring  16 , the lower face of the work piece W can be polished.  
         [0087]     After completing the polish, the work piece W is conveyed into the transfer unit  18  (see  FIG. 4 ), then conveyed to an external place by the robot hand H.  
         [0088]     In the first embodiment, the work piece W, which has been centered by the pins  45 , is transferred onto the mounting table  53  in that state, and sucked and held by the top ring  16 , which is moved downward, at that position. Therefore, the work piece W can be held by the top ring  16  without displacement of the work piece W.  
         [0089]     Note that, the top ring  16  is moved downward so as to hold the work piece W on the lower face of the top ring  16 , but the transfer unit  18  may be moved upward so as to transfer the work piece W to the top ring  16 . In this case, the transfer actions performed by the pusher stage, which is used in the conventional polishing apparatus, is not performed, so that displacement of the work piece W can be prevented.  
         [0090]     A second embodiment of the transfer unit  18  is shown in  FIGS. 8-10 . Note that, the structural elements explained in the first embodiment are assigned the same symbols, and explanation will be omitted.  
         [0091]     A supporting table (a supporting member)  70  is provided under the mounting table  53  and allowed to move downward.  
         [0092]     Namely, a plurality of supporting shafts  71  are fixed to the lower face of the mounting table  53  and extended downward. The supporting shafts  71  pierce through the supporting table  70  and extended downward therefrom. Washers  72  are respectively fixed lower parts of the supporting shafts  71  by nuts  73 . Coil springs (elastic members)  74  respectively covers the supporting shafts  71 . The coil springs  74  are elastically provided between the lower face of the supporting table  70  and the washers  72 .  
         [0093]     With this structure, the supporting table  70  can be moved downward together with the mounting table  53  and can be separately moved downward with respect to the mounting table  53 .  
         [0094]     Note that, guide rods  76  are provided to the lower face of the mounting table  53 . Guide bushings  77  are provided to the supporting table  70 .  
         [0095]     The supporting table  70  is formed into a circular shape or a radial shape. A plurality of positioning pieces  80 , which are extended upward, are provided to an outer edge or edges of the supporting table  70 .  
         [0096]     As shown in  FIG. 9 , the four positioning pieces  80  are circularly arranged at regular angular intervals. The positions of the positioning pieces  80  are different from those of the pins  45 . The positioning pieces  80  are respectively extended upward from notches  54   c  of the ring-shaped mounting section  54 . As shown in  FIGS. 4 and 10 , projected sections  80   a , which enclose the outer circumferential face of the work piece W so as to correctly position the work piece W without displacement when the work piece W is mounted on the mounting face  54   a  of the mounting section  54 , are respectively provided to upper parts of the positioning pieces  80 .  
         [0097]     When the projected sections  80   a  of the positioning pieces  80  contact the outer circumferential face of the work piece W, even if the pins  45  are moved downward, the work piece W is not displaced. When the top ring  16  is moved downward, the template  37  firstly contacts and presses the projected sections  80   a , so the positioning pieces  80  are moved downward together with the supporting plate  70 . Then, the top ring  16  is further moved downward, the backing pad  36  contacts the upper face of the work piece W, and the mounting table  53  is moved downward as well. Therefore, the work piece W is pressed onto the lower face of the backing pad  36  with the prescribed force, and the top ring  16  sucks and holds the work piece W. Note that, even if the projected sections  80   a  are moved downward, the template  37  holds the outer edge of the work piece W instead of the projected sections  80   a , so that displacement of the work piece W can be prevented.  
         [0098]     The invention may be embodied in other specific forms without departing from the spirit of essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.