Patent Publication Number: US-6712678-B1

Title: Polishing-product discharging device and polishing device

Description:
TECHNICAL FIELD 
     The present invention relates to a mechanism for discharging debris produced when a workpiece such as semiconductor wafers, various hard disks, glass substrates, liquid crystal panels, etc. is polished, and a polishing apparatus. 
     BACKGROUND ART 
     A conventional CMP (Chemical Mechanical Polishing) apparatus for use in the process of fabricating semiconductor integrated circuit devices comprises a polishing cloth mounted on a turntable and a rotatable top ring for holding a substrate to be polished against the polishing cloth to polish a surface of the substrate (free abrasive polishing) while a polishing slurry is being supplied to the polishing cloth. However, the conventional CMP apparatus is problematic in that it may fail to sufficiently planarize a surface to be polished depending on the type of pattern on the surface or the state of steps (surface irregularities) on the surface. 
     There has been developed a bonded-abrasive polishing process, which is to be used instead of the CMP apparatus of the above structure. In the process, a substrate to be polished is pressed against a bonded-abrasive and the substrate and the bonded-abrasive are slid relatively to each other while an abrasive liquid (solution) is supplied to the surface of the bonded-abrasive, thereby polishing the substrate. 
     When the substrate is polished using the bonded-abrasive, however, debris produced by the polishing process, such as waste bits produced by the polishing process, large grain fragments separated from the bonded-abrasive when the bonded-abrasive is dressed, or diamond particles released from the dresser, remains on the surface of the bonded-abrasive, tending to make scratches (flaws) on the surface of the substrate to be polished. Almost no effective means for discharging such debris produced by the bonded-abrasive polishing process has yet been available. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above drawbacks. In particular, it is an object of the present invention to provide a mechanism for effectively discharging debris produced when a substrate is polished by a bonded-abrasive, and a polishing apparatus. 
     To achieve the above object, there is provided in accordance with the present invention a polishing apparatus for pressing a surface to be polished of a substrate against a bonded-abrasive surface and for moving the surface to be polished and the bonded-abrasive surface relative to each other to polish the surface to be polished. A mechanism is provided for discharging debris produced on the bonded-abrasive surface when the surface to be polished is polished. 
     With the above arrangement, debris produced when the substrate is polished, large grain fragments separated from the bonded-abrasive surface when the bonded-abrasive surface is dressed, or diamond particles released from a dresser used to dress the bonded-abrasive surface, can effectively be removed from the bonded-abrasive surface and the surface to be polished of the substrate. Thus, scratches (flaws) are effectively prevented from being made on the surface of the substrate being polished. 
     Preferably, the mechanism for discharging debris may comprise a debris discharging component for discharging the debris. The debris discharging component may comprise grooves defined in the bonded-abrasive surface for discharging the debris therethrough, and a fluid ejecting component for ejecting a liquid or gas in and along the grooves to discharge the debris out through the grooves. In a scroll-type polishing apparatus which incorporates the above mechanism, a liquid such as water, a chemical liquid, or the like can be supplied to a polishing surface provided by the bonded-abrasive surface from below the polishing surface to lubricate and cool the polishing surface and also to discharge the debris effectively out through the grooves. In a table-type polishing apparatus with a bonded-abrasive plate incorporating the above mechanism, debris can also be effectively discharged from a bonded-abrasive surface. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1A is a fragmentary schematic side elevational view of a polishing apparatus according to a first embodiment of the present invention, and FIGS. 1B and 1C are a fragmentary schematic plan view and a perspective view, respectively, showing the positional relationship of a bonded-abrasive and a trapping jig; 
     FIG. 2 is a view showing a modification of the structure shown in FIG. 1C; 
     FIG. 3 is a view showing another modification of the structure shown in FIG. 1B; 
     FIGS. 4A and 4B are views showing still another modification of the structure shown in FIG. 1C; 
     FIGS. 5A through 5C are views of a polishing apparatus according to a second embodiment of the present invention, FIG. 5A being a fragmentary schematic side elevational view of the polishing apparatus, FIG. 5B a fragmentary schematic plan view of the polishing apparatus, and FIG. 5C a fragmentary schematic plan view of a modification of the polishing apparatus; 
     FIGS. 6A through 6C are views of a polishing apparatus according to a third embodiment of the present invention, FIG. 6A being a fragmentary schematic side elevational view of the polishing apparatus, FIG. 6B a fragmentary schematic plan view of the polishing apparatus, and FIG. 6C a fragmentary schematic plan view of a modification of the polishing apparatus; 
     FIGS. 7A and 7B are views showing a bonded-abrasive  70  used in a polishing apparatus according to a fourth embodiment of the present invention, FIG. 7A being a plan view of the bonded-abrasive, and FIG. 7B a sectional side elevational view thereof, i.e., a cross-sectional view taken along line B—B of FIG. 7A; 
     FIGS. 8A,  8 B, and  8 C are views showing respective modifications of the bonded-abrasive; 
     FIGS. 9A through 9C are views showing a bonded-abrasive  80  according to a modification, FIG. 9A being a plan view of the bonded-abrasive, FIG. 9B an enlarged view of a groove  81  of the bonded-abrasive, illustrating the manner in which the bonded-abrasive operates, and FIG. 9C a view of the groove shown in FIG. 9B, taken along a line perpendicular to the plane of the view shown in FIG. 9B, illustrating the manner in which the bonded-abrasive operates; 
     FIGS. 10A through 10C are views showing a bonded-abrasive  90  according to another modification, FIG. 10A being a plan view of the bonded-abrasive, FIG. 10B an enlarged view of a groove  81  of the bonded-abrasive, illustrating the manner in which the bonded-abrasive operates, and FIG. 10C a view of the groove shown in FIG. 10B, taken along a line perpendicular to the plane of the view shown in FIG. 10B, illustrating the manner in which the bonded-abrasive operates; 
     FIG. 11 is a vertical cross-sectional view of a scroll-type polishing apparatus; 
     FIGS. 12A and 12B are views showing a scrolling motion, FIG. 12A being a plan view and FIG. 12B a cross-sectional view taken along line A—A of FIG. 12A; 
     FIGS. 13A through 13C are views showing the structure of grooves according to a fifth embodiment of the present invention, FIGS. 13A and 13B being cross-sectional views, and FIG. 13C a plan view; 
     FIGS. 14A through 14C are views showing sloping barriers, FIG. 14A being a cross-sectional view of the sloping barriers, FIG. 14B a plan view of the sloping barriers, and FIG. 14C a plan view showing the structure of sloping barriers with a discharge passage defined centrally therein; and 
     FIGS. 15A and 15B are views showing an automatically vertically movable barrier according to a modification, FIG. 15A being a cross-sectional view of the automatically vertically movable barrier when it is in use, and FIG. 15B a cross-sectional view of the automatically vertically movable barrier when it is not in use. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described in detail below with reference to the drawings. 
     First Embodiment 
     FIG. 1A is a fragmentary schematic side elevational view of a polishing apparatus according to a first embodiment of the present invention, and FIGS. 1B and 1C are fragmentary schematic plan and perspective views, respectively, showing the positional relationship of a bonded-abrasive and a trapping jig. 
     As shown in FIGS. 1A through 1C, the polishing apparatus has a disk-shaped bonded-abrasive element  10  mounted on a base  15 , a top ring  20  disposed on an upper surface (bonded-abrasive surface) of the bonded-abrasive element  10  for holding a semiconductor wafer (workpiece to be polished)  100 , a trapping jig  30  disposed on the upper surface of the bonded-abrasive element  10 , and a fluid ejection nozzle  43  and other members disposed above the upper surface of the bonded-abrasive element  10 . The components of the polishing apparatus will be described below. 
     The disk-shaped bonded-abrasive element  10  comprises abrasive particles, such as particles of CeO2, SiO2, Al2O3, ZrO2, MnO2, Mn2O3, or the like having an average diameter of 2 μm or less, which are bonded together by a binder, such as polyimide resin, phenolic resin, urethane, PVA (polyvinyl alcohol), or the like. The base  15  has an outer profile which is the same as the bonded-abrasive element  10 , and is fixedly mounted on a rotary plate  17 . 
     The semiconductor wafer  100  is mounted on the top ring  20  at a position horizontally spaced from the upper surface of the bonded-abrasive element  10 . Then, the top ring  20  is moved to the illustrated position on the bonded-abrasive element  10  by an actuating mechanism (not shown). 
     The trapping jig (debris trapping means)  30  comprises a cylindrical brush or sponge (which may be another resilient material), and has opposite ends supported by axial support rods  31 ,  33 . The trapping jig  30  is rotatable about its own axis by a motor  35  that is coupled to the axial support rod  33 . 
     The motor  35  and the axial support rod  31  are fixed to a support base  37 , which is suspended from an arm  39 . When an air cylinder  41  mounted on the arm  39  is actuated, the support base  37  is moved vertically. The fluid ejection nozzle (debris discharging component)  43  is attached to the support base  37  in the vicinity of the axial support rod  31 . 
     The semiconductor wafer  100  is polished at a position indicated by the dotted line in FIG.  1 B. The trapping jig  30  is disposed downstream of the polishing position (with respect to the rotation of bonded-abrasive element  10 ), and extends radially outwardly from the center of the bonded-abrasive element  10 . 
     The fluid ejection nozzle  43  is disposed immediately upstream of the trapping jig  30 , and ejects a fluid (e.g., water) radially outwardly from the center of the bonded-abrasive element  10  along the trapping jig  30 . 
     Operation of a mechanism for discharging debris produced when the semiconductor wafer  100  is polished will be described below. The semiconductor wafer  100  held by the top ring  20  is rotated and pressed against the rotating bonded-abrasive element  10  at its polishing position, and an abrasive liquid (water, a chemical liquid, or a liquid containing abrasive particles) is simultaneously supplied from an abrasive liquid supply mechanism to polish the surface of the semiconductor wafer  100  to be polished. Although not shown, before the semiconductor wafer  100  is polished or while the semiconductor wafer  100  is being polished, a dresser is pressed against the bonded-abrasive element  10  to dress the bonded-abrasive  10 . Debris produced at this time remains attached to the surface of the bonded-abrasive element  10 . 
     Then, the air cylinder  41  is actuated to lower the support base  37 . As shown in FIGS. 1A through 1C, the trapping jig  30  is pressed against the surface of the bonded-abrasive element  10 , and the motor  35  is simultaneously energized to rotate the trapping jig  30 . 
     The debris that has been attached to the surface of the bonded-abrasive element  10  when the semiconductor wafer  100  has been polished is trapped by the trapping jig  30 . The fluid ejection nozzle  43  ejects fluid to force the trapped debris off the surface of the bonded-abrasive element  10  and to discharge the trapped debris. The fluid may be ejected from the fluid ejection nozzle  43  all the time or intermittently while the trapping jig  30  is being pressed against the bonded-abrasive element  10 . The fluid should preferably be ejected from the fluid ejection nozzle  43  under a pressure of 5 kgf/cm 2  or higher. 
     In the present embodiment, the trapping jig  30  has a cylindrical shape and is rotatable about its own axis. However, the trapping jig  30  is not necessarily rotated, but may simply be pressed against the abrasive surface of the bonded-abrasive element  10 . In this modification, as shown in FIG. 2, a trapping jig  30 - 2  may be in the shape of a quadrangular prism. Alternatively, as shown in FIG. 3, a trapping jig  30 - 3  may be in the form of an arcuate rod. Further alternatively, as shown in FIGS. 4A and 4B, a trapping jig  30 - 4  may be in the form of a water wheel rotatable about its own central axis. In these modifications, fluid ejection nozzles  43 - 2 ,  3 ,  4  are placed in a position to discharge the trapped debris off of the surface of the bonded-abrasive element  10 . 
     The trapping jig is not limited to the above structures, but may be of any of various structures and may operate according to any of various ways insofar as it serves as the debris trapping component capable of trapping debris produced on the bonded-abrasive surface when the semiconductor wafer is polished. 
     The fluid ejection nozzle is not limited to the above structures, but may be of any of various structures and may operate according to any of various ways as long as it serves as the debris discharging mechanism capable of discharging the debris trapped on the bonded-abrasive element by the debris trapping component off of the surface of the bonded-abrasive. 
     Second Embodiment 
     FIGS. 5A through 5C are views of a polishing apparatus according to a second embodiment of the present invention, FIG. 5A being a fragmentary schematic side elevational view of the polishing apparatus, FIG. 5B a fragmentary schematic plan view of the polishing apparatus, and FIG. 5C a fragmentary schematic plan view of a modification of the polishing apparatus. 
     The polishing apparatus according to the second embodiment is identical to the polishing apparatus shown in FIGS. 1A through 1C in that the base  15  and the bonded-abrasive element  10  are mounted on the rotary plate  17  for rotation, and the semiconductor wafer  100  is held against the surface of the bonded-abrasive element  10  by a top ring (not shown) and rotated thereby. The details of these common structures will not be described below. 
     In the embodiment shown in FIGS. 5A and 5B, the polishing apparatus has a fluid applying component  50  for applying a fluid (a liquid or gas) to the surface of the bonded-abrasive element  10  while the semiconductor wafer  100  is being polished. 
     The fluid applying component  50  comprises a disk-shaped nozzle support plate  51  and a linear array of eight fluid ejection nozzles  53  attached centrally to a lower surface of the nozzle support plate  51 . The fluid ejection nozzles  53  eject water under high pressure or the like. The pressure of the ejected water should be at a level of a water jet, e.g., preferably about 2 MPa or higher. The nozzle support plate  51  can be rotated by a drive shaft  57 . 
     The polishing apparatus also has another main fluid ejection nozzle (debris discharging component)  55  disposed downstream of the fluid applying component  50 . The fluid ejection nozzle  55  is arranged to eject a fluid (e.g., water) radially outwardly from the center of the surface of the bonded-abrasive element  10 . 
     The semiconductor wafer  100  held by a top ring (not shown) is held against the bonded-abrasive element  10  at a position indicated by the dotted line, and is rotated. At the same time, the bonded-abrasive element  10  is rotated in the direction indicated by the arrow so as to polish the surface of the semiconductor wafer  100 . Alternatively, before the semiconductor wafer  100  is polished or while the semiconductor wafer  100  is being polished, the bonded-abrasive element  10  is dressed by a dresser. At this time, while the nozzle support plate  51  is being rotated in the direction indicated by the arrow, a fluid such as water is ejected under high pressure from the fluid ejection nozzles  53  to the surface of the bonded-abrasive element  10 . Debris which has been entrapped by small surface irregularities of the bonded-abrasive element  10  when the semiconductor wafer  100  has been polished and/or the bonded-abrasive element  10  has been dressed is lifted, and is discharged together with the fluid from the surface of the bonded-abrasive element  10 . 
     Since the fluid ejection nozzle  55  is disposed downstream of the fluid applying means  50  (with respect to the rotation of the bonded-abrasive element  10 ) and ejects the fluid radially outwardly of the bonded-abrasive element  10 , the debris is further effectively discharged from the surface of the bonded-abrasive element  10 . 
     As shown in FIG. 5C, a trapping jig  59  which is identical to the trapping jig according to the first embodiment may be disposed downstream of the fluid ejection nozzle  55  for more effectively discharging the debris. 
     In the present embodiment, the fluid ejection nozzle  55  and the trapping jig  59  may not necessarily be required, because the fluid applying component  50  alone is capable of discharging the debris. 
     The fluid applying component  50  is not limited to the above structure, and may be modified in various ways insofar as it applies a liquid or gas to the bonded-abrasive surface while the semiconductor wafer is being polished to remove the debris from the bonded-abrasive surface. 
     Third Embodiment 
     FIGS. 6A through 6C are views of a polishing apparatus according to a third embodiment of the present invention, FIG. 6A being a fragmentary schematic side elevational view of the polishing apparatus, FIG. 6B a fragmentary schematic plan view of the polishing apparatus, and FIG. 6C a fragmentary schematic plan view of a modification of the polishing apparatus. 
     The polishing apparatus according to the third embodiment is identical to the polishing apparatus shown in FIGS. 1A through 1C in that the base  15  and the bonded-abrasive element  10  are mounted on the rotary plate  17  for rotation, and the semiconductor wafer  100  is held against the bonded-abrasive element  10  by a top ring (not shown) and rotated thereby. The details of these common structures will not be described below. 
     The polishing apparatus shown in FIGS. 6A and 6B has a dressing component  60  disposed on the surface of the bonded-abrasive element  10 , for dressing the bonded-abrasive element  10  while the semiconductor wafer  100  is thereby being polished. 
     The dressing component  60  comprises a disk-shaped support plate  61  and a disk-shaped dressing plate  63  attached to a lower surface of the support plate  61 . The dressing plate  63  comprises a diamond of #400 electrodeposited on a surface of a metal sheet. The support plate  61  is rotatable by a drive shaft  67 . 
     The polishing apparatus also has a fluid ejection nozzle (debris discharging component)  65  disposed downstream of the dressing component  60 . 
     The semiconductor wafer  100  held by a top ring (not shown) is held against the bonded-abrasive element  10  at a position indicated by the dotted line and rotated to polish the surface of the semiconductor wafer  100  to be polished. At the same time, the dressing component  60  is rotated in the direction indicated by the arrow to dress the surface of the bonded-abrasive element  10 . 
     When the surface of the bonded-abrasive element  10  is dressed, debris which has been entrapped by small surface irregularities of the bonded-abrasive element  10  when the semiconductor wafer  100  has been polished is displaced onto the surface of the bonded-abrasive element  10 . The fluid ejection nozzle  65  disposed downstream of the dressing component  60  ejects the fluid radially outwardly with respect to the bonded-abrasive element  10 , discharging the debris together with the fluid effectively from the surface of the bonded-abrasive element  10 . 
     As shown in FIG. 6C, a trapping jig  69  which is identical to the trapping jig according to the first embodiment may be disposed downstream of the fluid ejection nozzle  65  for more effectively discharging the debris. 
     The dressing component  60  is not limited to the above structure, and may be of any structure as long as it is capable of dressing the bonded-abrasive surface. The fluid ejection nozzle  65  and the trapping jig  69  may have any structure capable of discharging the debris, which has been displaced onto the bonded-abrasive surface by the dressing component. 
     Fourth Embodiment 
     FIGS. 7A and 7B are views showing a bonded-abrasive element  70  used in a polishing apparatus according to a fourth embodiment of the present invention. FIG. 7A is a plan view of the bonded-abrasive element, and FIG. 7B is a sectional side elevational view thereof, i.e., a cross-sectional view taken along line B—B of FIG.  7 A. 
     The bonded-abrasive element  70  according to the present embodiment has a number of parallel grooves (debris discharging components)  71  for discharging debris which is lodged in the abrasive surface of the bonded-abrasive element  70 . 
     The bonded-abrasive element  70  has a disk shape and is attached to a disk-shaped base  75  by an adhesive  77 , the bonded-abrasive element  70  having substantially the same dimensions and shape as the base  75 . The bonded-abrasive element  70  and the adhesive  77  are cut along parallel lines to form the grooves  71 . The bonded-abrasive element  70  has a thickness of 5 mm and an outside diameter of 60 mm. The grooves  71  have a width of 2 mm each, and are spaced by a pitch ranging from 20 to 100 mm. 
     In the present embodiment, debris produced when the surface of a workpiece is polished can be discharged simply when an usual polishing process is carried out by pressing the workpiece against the abrasive surface of the bonded-abrasive element  70  and by moving the workpiece and the bonded-abrasive element  70  relative to each other. 
     Specifically, a semiconductor wafer (not shown) held by a top ring is pressed against the surface of the bonded-abrasive element  70 . While an abrasive liquid (solution) is being supplied to the abrasive surface of the bonded-abrasive element  70 , the bonded-abrasive element  70  is rotated and the semiconductor wafer is simultaneously rotated to polish the semiconductor wafer. Debris that is produced falls into the grooves  71 , and is discharged together with the abrasive liquid out of the grooves  71 . The grooves  71  may be arranged in a grid pattern as shown in FIG. 8A, a lozenge pattern as shown in FIG. 8B, or a radial pattern as shown in FIG.  8 C. 
     FIGS. 9A through 9C are views showing a bonded-abrasive element  80  according to a modification, FIG. 9A being a plan view of the bonded-abrasive element, FIG. 9B being an enlarged view of a groove  81  of the bonded-abrasive, illustrating the manner in which the bonded-abrasive operates, and FIG. 9C being a view of the groove shown in FIG. 9B, taken along a line perpendicular to the plane of the view shown in FIG. 9B, illustrating the manner in which the bonded-abrasive operates. 
     The bonded-abrasive element  80  according to the present embodiment has a number of parallel grooves  81  for discharging debris, which are defined in the abrasive surface of the bonded-abrasive element  80  that is attached to a base  85  by an adhesive  87 . The bonded-abrasive element  80  also has a fluid ejection nozzle (fluid ejecting nozzle)  83  disposed centrally in each of the grooves  81  for ejecting a fluid (a liquid or gas) in and through each groove  81  in opposite directions to discharge debris out of each groove  81 . 
     A semiconductor wafer (not shown) held by a top ring is pressed against the surface of the bonded-abrasive element  80 . While an abrasive liquid (solution) is being supplied to the abrasive surface of the bonded-abrasive element  80 , the bonded-abrasive element  80  is rotated and the semiconductor wafer is simultaneously rotated to polish the semiconductor wafer. Debris that is produced falls into the grooves  81 , and is discharged together with the abrasive liquid out of the grooves  81 . Since fluid such as water is simultaneously ejected from the fluid ejection nozzle  83  in and along each groove  81  in opposite directions, the debris in the grooves  81  can reliably be discharged from the grooves  81 . 
     The shape of the grooves  81 , and the shape, structure, and position of the fluid ejection nozzle may be modified in various ways. 
     FIGS. 10A through 10C are views showing a bonded-abrasive element  90  according to another modification, FIG. 10A being a plan view of the bonded-abrasive element, FIG. 10B being an enlarged view of a groove  91  of the bonded-abrasive element, illustrating the manner in which the taken along a line perpendicular to the plane of the view shown in FIG. 10B, illustrating the manner in which the bonded-abrasive operates. 
     The bonded-abrasive element  90  according to the present embodiment has a number of parallel grooves  91  for discharging debris which are defined in the abrasive surface of the bonded-abrasive element  90  that is attached to a base  95  by an adhesive  97 . The bonded-abrasive element  90  also has fluid ejection nozzles (fluid ejecting components)  93  disposed in the grooves  91  for ejecting a fluid (a liquid or gas) toward the surface to be polished of the semiconductor wafer  100  placed on the bonded-abrasive element  90 , i.e., vertically upwardly from the abrasive surface of the bonded-abrasive element  90 . The fluid ejection nozzles  93  are disposed in a ring pattern within the path along which the semiconductor wafer  100  is polished. 
     The semiconductor wafer  100  held by a top ring is pressed against the surface of the bonded-abrasive  90 . While an abrasive liquid (solution) is being supplied to the bonded-abrasive element  90 , the bonded-abrasive element  90  is rotated and the semiconductor wafer  100  is simultaneously rotated to polish the semiconductor wafer  100 . Debris that is produced falls into the grooves  91 , and is discharged together with the abrasive liquid out of the grooves  91 . Since fluid such as water is simultaneously ejected from the fluid ejection nozzle  93  to the surface of the semiconductor wafer  100  to be polished, the debris attached to the semiconductor wafer  100  can be washed off. Therefore, the debris can more effectively be discharged. 
     The fluid is intermittently ejected from the fluid ejection nozzles  93  only when the semiconductor wafer  100  is positioned immediately above the fluid ejection nozzles  93 . The shape of the grooves  91 , and the shape, structure and position of the fluid ejection nozzles  93  may be modified in various ways. 
     The mechanism for discharging debris produced when the workpiece is polished according to the fourth embodiment is applicable not only to the table-type polishing apparatus shown in FIGS. 1A through 1C, but also to a scroll-type polishing apparatus. The application of the mechanism to a scroll-type polishing apparatus will be described below. 
     FIGS. 11 and 12A,  12 B are views showing a circulatory translational motion mechanism of a scroll-type polishing apparatus. A circulatory translational motion (scrolling motion) is made by two surfaces which move in a circulatory pattern such as a circular pattern while in a translational pattern without changing their facing attitude. This mechanism allows a bonded-abrasive plate to be slightly greater than a substrate to be polished. Therefore, it is easy to manufacture a highly planar bonded-abrasive plate, a motor for actuating the bonded-abrasive plate may be small in size, and the mechanism may be compact and take up a small area. The mechanism comprises a translational table assembly  131  which provides a polishing tool surface that makes circulatory translational motion, and a top ring  132  for holding a wafer  100  with the surface to be polished being directed downwardly and pressing the wafer  100  against the polishing tool surface under a given pressure. 
     The translational table assembly  131  has a tubular casing  134  housing a motor  133  therein, an annular support plate  135  projecting inwardly from an upper portion of the tubular casing  134 , three or more supports  136  circumferentially spaced and mounted on the annular support plate  135 , and a reference plate  137  supported on the supports  136 . Upper surfaces of the supports  136  and a lower surface of the reference plate  137  have a plurality of recesses  138 ,  139  spaced at equal intervals in the circumferential direction, and bearings  140 ,  141  are mounted in the respective recesses  138 ,  139 . As shown in FIG. 12B, a joint  144  has two shafts  142 ,  143  that are displaced by a distance “e” from each other, and these shafts  142 ,  143  have ends mounted respectively in the bearings  140 ,  141 , allowing the reference plate  137  to make a circulatory translational motion along a circle having a radius “e”. 
     The reference plate  137  has a recess  148  defined centrally in a lower surface thereof and which houses a bearing  137  which supports a drive end  146  that is positioned eccentrically on the upper end of a main shaft  145  of the motor  133 . The drive end  146  is displaced eccentrically from the main shaft  145  by a distance “e”. The motor  133  is housed in a motor chamber  149  defined in the casing  134 , and the main shaft  145  thereof is supported by upper and lower bearings  150 ,  151 . Counterbalances  152   a ,  152   b  for bringing the eccentric load into balance are mounted on the main shaft  145 . 
     The reference plate  137  has a diameter which is slightly greater than the sum of the diameter of the wafer  100  to be polished and the distance “e”. The reference plate  137  comprises two plate members  153 ,  154  joined to each other with a space  155  defined therebetween for the passage therein of an abrasive liquid such as water, a chemical liquid, or the like to be supplied to the surface to be polished. The space  155  communicates with an abrasive liquid supply port  156  defined in a side of the reference plate  137  and also with a plurality of liquid outlet holes  157  defined in an upper surface of the reference plate  137 . A bonded-abrasive plate  159  is applied to the upper surface of the reference plate  137 . The bonded-abrasive plate  159  has a plurality of outlet holes  158  defined therein which are aligned with the respective liquid outlet holes  157  in the bonded-abrasive plate  159 . The outlet holes  157 ,  158  are usually distributed substantially uniformly over the entire surfaces of the reference plate  137  and the bonded-abrasive plate  159 . 
     The top ring  132 , which serves as a pressing device, is mounted on the lower end of a shaft  160  so as to be tiltable to a certain extent in conformity with the surface to be polished. A pressing force from an air cylinder (not shown) and a rotational force from a motor (not shown) are applied through the shaft  160  to the top ring  132 . The top ring  132  has a substrate holder  161  on its lower end with a resilient sheet  162  mounted therein. A retrieval tank  163  for retrieving a liquid supplied to the surface to be polished is disposed around an upper portion of the casing  134 . 
     A polishing process carried out by the polishing apparatus shown in FIGS. 11 and 12A,  12 B will be described below. When the motor  133  is energized, the reference plate  137  makes a translational circular motion, and the wafer  100  attached to the top ring  132  is pressed against the surface of the bonded-abrasive plate  159  attached to the reference plate  137 . An abrasive liquid is supplied via the abrasive liquid supply port  156 , the space  155 , and the outlet holes  157 ,  158  to the polishing surface. Specifically, the abrasive liquid is supplied via grooves in the surface of the bonded-abrasive plate  159  to the polishing surface thereof which is held against the wafer  100 . 
     At this time, a small relative translational circular motion having a radius “e” is developed between the polishing surface of the bonded-abrasive plate  159  and the surface to be polished of the wafer  100 , uniformly polishing the entire surface of the wafer  100 . If the surface to be polished and the polishing surface remain in the same positional relation to each other, then since the surface to be polished is affected by local variations of the polishing surface, the top ring  132  is gradually rotated about its own axis to prevent the surface of the wafer  100  from being polished only by one local region of the bonded-abrasive plate  159 . 
     Fifth Embodiment 
     Since the scroll-type polishing apparatus performs the polishing process with the scrolling motion, as described above, it suffices for the bonded-abrasive surface to move in a range of the scrolling motion with respect to the size of the wafer to be polished. However, it is difficult to supply a liquid required for the polishing process from an external source, as is the case with the table-type polishing apparatus. Consequently, a liquid required for the polishing process needs to be supplied to the polishing surface from the bonded-abrasive surface, which is located below the wafer. As shown in FIG. 13A, a base plate  201  has a plurality of liquid supply holes  202  defined therein for supplying a liquid therethrough to respective grooves  203  above the liquid supply holes  202 . To form grooves in a disk-shaped bonded-abrasive element, grooves may not be defined all the way through a bonded-abrasive element  204 , as shown in FIG. 13A, and shallow grooves  203  may be defined in the bonded-abrasive  204 , leaving bottoms therein, as shown in FIG.  13 B. Then flow passages for supplying a liquid to the grooves in the bonded-abrasive may be defined from the side of the base plate  201  in alignment with the shallow grooves  203 . 
     The grooves have a width ranging from 1 to 3 mm each, and are spaced by a pitch Y (distance between adjacent grooves) of about 20 mm. The grooves may be defined by slotting the disk-shaped bonded-abrasive element after the disk-shaped bonded-abrasive element is bonded to the base plate, and may alternatively be defined by producing plate-like bonded-abrasive pieces and applying them to the base plate. As shown in FIG. 13C, the pitch Y is the same as or smaller than twice the scrolling diameter e. If the pitch Y were greater than twice the scrolling diameter e, then there would be developed a region where no grooves pass over the surface to be polished even when the polishing surfaces make a scrolling motion. Stated otherwise, the surface to be polished would have a region which does not contact grooves at any time during the scrolling motion, and debris from the region of the surface to be polished would not be discharged into the groove. As a result, the debris that remains unremoved adversely affects the in-plane uniformity of the surface to be polished. 
     In the scroll-type polishing apparatus, the water or chemical liquid needs to be supplied to the interface between the bonded-abrasive surface and the surface to be polished of the wafer for promoting a chemical polishing action and also for reducing the frictional resistance to the polishing surface to suppress the problem of increased vibrations for thereby increasing the mechanical stability of the polishing apparatus. The abrasive liquid supplied to the polishing surface is also effective to cool the polishing surface. When the abrasive liquid is supplied to the bonded-abrasive surface, the groove configuration shown in FIG. 13A or  13 B allows the abrasive liquid to flow along the grooves  203  and out of the grooves  203 , failing to supply the abrasive liquid to the polishing surface of the bonded-abrasive when the wafer is polished thereby. If the lubricating and cooling action based on the abrasive liquid is lost when the wafer is polished, the polishing capability of the polishing apparatus is adversely affected, making it difficult to polish the wafer uniformly. If no liquid is present on the bonded-abrasive surface when it is dressed, then the bonded-abrasive surface cannot be dressed as desired. Therefore, it is necessary that an adequate amount of liquid be present on the polishing surface of the bonded-abrasive while the wafer is being polished and also while the bonded-abrasive element is being dressed. 
     FIGS. 14A and 14B are views of the bonded-abrasive element  204 , showing sloping barriers  207 A,  207 B on an end of each of the grooves  203  defined therein. The sloping barrier  207 A has a height reaching the bonded-abrasive surface and serves to provide a full-height blockade in the groove to the liquid in the groove  203 , while allowing the groove to overflow the barrier. The sloping barrier  207 B provides a half-height blockade in the groove  203 . When the groove  203  is supplied with the liquid from below the bonded-abrasive element, if the groove has a small width, then since the liquid tends to overflow the groove  203 , the barrier is not necessarily required. If the groove  203  has a large width, however, the barrier is required, and the barriers shown in FIGS. 14A and 14B are effective to block the fluid in the groove  203 . As described above, if the groove  203  is sufficiently small in width, then a sufficient amount of liquid can be supplied to the polishing surface without the need for barriers. However, if the groove  203  is wider and a sufficient amount of liquid cannot be supplied to the polishing surface from below the bonded-abrasive due to a shortage of liquid pressure, then the barriers  207 A,  207 B are effective to cause the liquid in the groove to overflow the groove  203  easily, thus supplying a sufficient amount of water, chemical liquid, or the like to the polishing surface when the wafer is polished, or supplying a sufficient amount of water or the like to the bonded-abrasive when the bonded-abrasive is dressed. Debris produced by the polishing process, such as waste bits produced by the polishing process, large grain fragments separated from the bonded-abrasive element when the bonded-abrasive element is dressed, or diamond particles released from the dresser, is discharged out by the liquid that is supplied to lubricate and cool the polishing surface. Since the barriers  207 A,  207 B have sloping surfaces, they allow the debris to be discharged easily together with the liquid out of the groove  203 . 
     FIG. 14C shows a modification of the sloping barriers  207 A,  207 B, which have a discharge passage  208  defined centrally therein. The discharge passage  208  is slotted partly in the sloping barriers  207 A,  207 B to promote the discharge of the debris from the groove  203 . The width of the discharge passage  208  needs to be selected depending on the width of the groove  203  and the amount of water to be supplied to the groove  203 . It is necessary that the liquid which has overflowed the groove be supplied in a sufficient amount to the polishing surface and the debris be discharged efficiently out of the groove. For example, the width of the discharge passage  208  should preferably be at most two-thirds of the width of the groove  203 . The barriers  207 A,  207 B may be produced by machining the bonded-abrasive element when the grooves are formed therein, or placing separate members shaped like the barriers  207 A,  207 B in grooves which have been formed through the bonded-abrasive. The separate members shaped like the barriers  207 A,  207 B may be made of a material which is the same as the bonded-abrasive, or a soft material that can easily be worn. 
     FIGS. 15A and 15B show an automatically vertically movable barrier  209  associated with the groove  203  according to a modification of the present invention. The groove  203  is supplied with liquid flowing through the liquid supply hole  202 , as is the case with the embodiments shown in FIGS. 14A through 14C. According to the modification, the automatically vertically movable barrier  209  is employed in place of the sloping barriers at each of the opposite ends of the groove  203 . The automatically vertically movable barrier  209  is actuated by a pneumatic actuator that can be turned on and off by a switch. When the automatically vertically movable barrier  209  is in use, it is lifted to block the groove  203 . When the automatically vertically movable barrier  209  is not in use, it is lowered to discharge debris from the groove  203 . The automatically vertically movable barrier  209  is preferably made of a soft material such as sponge so that it can easily be worn when the bonded-abrasive is dressed and the wafer is polished. The automatically vertically movable barrier  209  allows the liquid to be reliably stored in the groove  203  and reliably overflow the groove  203  so as to be supplied to the polishing surface when the wafer is polished, and also allows the debris to be reliably discharged from the groove  203 . 
     The polishing apparatus with any of the above mechanisms for discharging debris may be combined with a conventional CMP apparatus comprising a polishing cloth. Before and after a substrate is polished by the polishing apparatus with any of the above mechanisms, the substrate may be polished by the conventional CMP apparatus. 
     According to the above various embodiments of the present invention, since debris can effectively be removed and discharged from the surface of the bonded-abrasive element and the surface to be polished of the substrate, any scratches (flaws) are effectively prevented from being made on the surface being polished. 
     Industrial Applicability 
     The present invention relates to a polishing apparatus for polishing a workpiece such as semiconductor wafers, various hard disks, glass substrates, liquid crystal panels, etc. The present invention can be used in various industrial fields such as the field of fabrication of semiconductor devices.