Patent Publication Number: US-2007123154-A1

Title: Polishing apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a polishing apparatus for polishing a workpiece, such as a semiconductor wafer (e.g., silicon wafer), and more particularly to a polishing apparatus having a dresser for dressing a polishing surface of a polishing table.  
      2. Description of the Related Art  
      With a recent progress in semiconductor devices toward finer structure and higher integration, a distance between interconnects is becoming smaller and smaller. Especially, when forming a circuit pattern by optical lithography with a line width of not more than 0.5 μm, surfaces, on which pattern images are to be focused by a stepper, are required to be flat because depth of focus is small. Thus, in order to achieve flat surfaces, a polishing apparatus has been widely used to polish the surfaces.  
      This type of polishing apparatus includes a polishing table having a polishing pad attached to an upper surface thereof, and a top ring, serving as a substrate-holding mechanism, for holding a substrate to be polished. The polishing table and the substrate-holding mechanism are independently rotated at different speeds. The substrate is held by the top ring and pressed against a polishing surface of the polishing pad on the polishing table while a polishing liquid is supplied onto the polishing surface, whereby the substrate is polished to have a flat and mirror-finished surface. Some types of polishing apparatuses are designed to press a surface of a substrate with uniform pressure in order to achieve uniform polishing, as disclosed in Japanese laid-open patent publication No. 2004-249452. After polishing, the substrate is released from the top ring and is then transferred to a subsequent process, e.g., cleaning process.  
      In order to uniformly polish a surface of a substrate, it is necessary to perform conditioning, i.e., dressing, on the polishing surface of the polishing pad on the polishing table. There are two timings for performing dressing: one is dressing during polishing, and another is dressing after polishing, When dressing during polishing, it is important to prevent detachment of diamond particles from a dresser because the detached diamond particles would scratch the surface of the substrate to be polished. When dressing after polishing, a dressing speed is important. Generally, for the purpose of preventing detachment of the diamond particles, a dresser having small diamond particles, which are electrodeposited thereto and have rounded edges, is used, and a low load (i.e., small pressing force) is applied. As a result, the dressing speed is lowered.  
      Ideal dressing of the polishing surface of the polishing table is to keep the polishing surface in a best condition by dressing it during polishing, and to hold a shape of the polishing surface unchanged even after the polishing surface is scraped off. For example, on one hand, a dresser designed to dress a polishing surface at a low cut rate is suited to the former, and on the other hand, a dresser designed to dress a polishing surface at a high cut rate is suited to the latter. This means that it is difficult to achieve both of these effects with a single dresser.  
      Further, after replacing the polishing pad with a new one, dressing is typically performed for about 10 minutes, and then dummy polishing is performed using about 25 dummy wafers. This operation is performed in order to bring the polishing pad closer to a ready condition for practical use. However, dummy polishing requires cleaning of the dummy wafers and, as a result, downtime of the apparatus would be increased.  
      With regard to a removal rate (polishing rate), a state of the dressed polishing surface is important, as described above. In addition, a temperature of the polishing surface during polishing also affects the removal rate. In a polishing process that greatly depends on a temperature, e.g., in a case where the removal rate is lowered as the temperature increases, it is possible to prevent a decrease in removal rate during polishing by preventing an increase in temperature during polishing. Further, an increase in temperature of the polishing surface results in a decrease in hardness of the resin polishing pad forming the polishing surface, thus adversely affecting flattening capability.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a polishing apparatus which can maintain a polishing surface of a polishing table in suitable conditions during polishing, can hold a shape of the polishing surface unchanged even after the polishing surface is scraped off, and can polish a substrate at a high removal rate while suppressing an increase in temperature of the polishing surface.  
      Further, another object of the present invention is to provide a polishing apparatus which can shorten downtime of the apparatus required for bringing a new polishing pad closer to a ready condition for practical use after placement of a polishing pad.  
      In order to solve the above drawbacks, one aspect of the present invention provides a polishing apparatus comprising a polishing table having a polishing surface, a dresser for dressing the polishing surface, a substrate holder for holding and pressing a substrate against the polishing surface to polish the substrate with relative movement between the polishing surface and the substrate. The dresser includes a first dressing member and a second dressing member. The first dressing member has a circular or disk shape having a diameter larger than a diameter of the substrate. The second dressing member is shaped so as to surround the first dressing member. The first dressing member and the second dressing member are operable to come into contact with the polishing surface independently of each other.  
      According to the present invention described above, the first dressing member and the second dressing member can independently dress the polishing surface at different timings. The first dressing member can have a dressing surface with small diamond particles fixed thereto so that a cut rate is low. The second dressing member can have a dressing surface with large diamond particles fixed thereto so that a cut rate is high. In this case, the first dressing member dresses the polishing surface during polishing of the substrate, and the second dressing member dresses the polishing surface after polishing of the substrate. With this operation, the substrate is polished immediately after dressing, i.e., conditioning, by a dressed zone of the polishing surface which is slightly larger than a substrate-contacting zone. Accordingly, the substrate can be polished at a high removal rate. Further, after polishing, the second dressing member can quickly dress the polishing surface in its entirety at a high cut rate. In this manner, the first and second dressing members can be separately used.  
      In a preferred aspect of the present invention, the first dressing member and the second dressing member have rotating shafts, respectively. The rotating shafts of the first dressing member and the second dressing member are concentrically arranged and are rotatable independently of each other.  
      According to the present invention described above, the first dressing member and the second dressing member can be arranged along a vertical direction. Therefore, an arrangement space on the polishing surface can be small, and the dresser can be compact.  
      In a preferred aspect of the present invention, a cut rate of the polishing surface by the first dressing member is lower than that by the second dressing member.  
      According to the present invention described above, the substrate can be polished by the polishing surface immediately after the first dressing member dresses the polishing surface at a low cut rate, and therefore efficient polishing can be performed. Further, after polishing, the second dressing member can quickly dress the polishing surface in its entirety at a high cut rate.  
      In a preferred aspect of the present invention, the first dressing member is operable to dress the polishing surface of the polishing table during polishing of the substrate.  
      According to the present invention described above, the substrate can be polished by the polishing surface immediately after dressing. As a result, polishing can be performed at a high removal rate.  
      In a preferred aspect of the present invention, the first dressing member and the second dressing member are operable to control a pressing force applied to the polishing surface of the polishing table independently of each other.  
      According to the present invention described above, the first dressing member and the second dressing member can dress the polishing surface at different cut rates. For example, during polishing, the first dressing member can dress the polishing surface with a small pressing force, and after polishing, the second dressing member can quickly dress the polishing surface in its entirety with a large pressing force.  
      In a preferred aspect of the present invention, the first dressing member includes a fluid passage through which a cooling or heating medium circulates.  
      According to the present invention described above, the polishing surface can be dressed while cooled or heated by the medium. As a result, highly flat dressing can be achieved, and the substrate can be polished at a high removal rate.  
      In a preferred aspect of the present invention, the polishing apparatus further comprises a temperature controller for adjusting and controlling a temperature of the cooling or heating medium circulating the fluid passage.  
      According to the present invention described above, the dressed polishing surface can be maintained at an appropriate temperature. As a result, highly flat dressing can be achieved, and the substrate can be polished at a high removal rate.  
      Another aspect of the present invention provides a polishing apparatus comprising a polishing table having a polishing surface, a dresser for dressing the polishing surface, a substrate holder for holding and pressing a substrate against the polishing surface to polish the substrate with relative movement between the polishing surface and the substrate. The dresser includes a circular holding member for holding a circular dummy substrate, and a dressing member arranged around the circular holding member.  
      According to the present invention described above, the polishing surface can be dressed while the dummy substrate is pressed against the polishing surface. As a result, downtime of the apparatus can be shortened.  
      In a preferred aspect of the present invention, the circular holding member and the dressing member have rotating shafts, respectively, and the rotating shafts are concentrically arranged and are rotatable independently of each other.  
      According to the present invention described above, the circular holding member and the dressing member can be arranged along a vertical direction. Therefore, an arrangement space on the polishing surface can be small, and the dresser can be compact.  
      In a preferred aspect of the present invention, the circular holding member includes therein a fluid passage through which a cooling or heating medium circulates.  
      According to the present invention described above, heat of the dummy substrate is absorbed, and hence an increase in temperature thereof can be suppressed.  
      In a preferred aspect of the present invention, the circular holding member is operable to press the dummy substrate against the polishing surface of the polishing table during polishing of the substrate.  
      According to the present invention described above, the polishing surface can be maintained at an appropriate temperature. As a result, the substrate can be polished at a high removal rate.  
      In a preferred aspect of the present invention, the polishing surface of the polishing table comprises a surface of a polishing pad attached to an upper surface of the polishing table. The polishing apparatus is operable such that, after the polishing pad is replaced with a new polishing pad, the dummy substrate held by the circular holding member and the dressing member are pressed against a polishing surface of the new polishing pad to thereby break in the polishing surface of the new polishing pad.  
      According to the present invention described above, the polishing surface of the polishing pad can be in a ready condition for practical use in a short period of time.  
      In a preferred aspect of the present invention, a SiC wafer is used as the dummy substrate.  
      According to the present invention described above, the SiC water can be used for a long time as the dummy substrate.  
      In a preferred aspect of the present invention, the circular holding member is operable to press the dummy substrate against the polishing surface of the polishing table during polishing of the substrate.  
      According to the present invention described above, heat due to friction between the substrate and the polishing surface can be absorbed, and hence polishing efficiency can be improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a view showing a structural example of a polishing apparatus according to the present invention;  
       FIGS. 2A through 2C  are views showing a structural example of a first dressing member of the polishing apparatus according to the present invention,  FIG. 2A  being a plan view,  FIG. 2B  being a cross-sectional view taken along line A-A shown in  FIG. 2A ,  FIG. 2C  being an enlarged cross-sectional view showing a part of a dressing surface;  
       FIGS. 3A and 3B  are views showing a structure of a second dressing member of the polishing apparatus according to the present invention,  FIG. 3A  being a cross-sectional view of the second dressing member,  FIG. 3B  being an enlarged cross-sectional view showing a part of a dressing surface;  
       FIGS. 4A and 4B  are views showing a dresser of the polishing apparatus according to the present invention,  FIG. 4A  being a cross-sectional view illustrating a state in which the first dressing member performs dressing,  FIG. 4B  being a cross-sectional view illustrating a state in which the second dressing member performs dressing;  
       FIG. 5  is a view showing an arrangement of a substrate and the first dressing member on an upper surface of a polishing pad during polishing according to the present invention;  
       FIG. 6  is a view showing an arrangement of the substrate and the second dressing member on the upper surface of the polishing pad after polishing according to the present invention;  
       FIGS. 7A and 7B  are views showing an example of a dresser of the polishing apparatus according to the present invention,  FIG. 7A  being a cross-sectional view illustrating a state in which a circular holding member protrudes from the dressing member,  FIG. 7B  being a cross-sectional view illustrating a state in which the circular holding member is accommodated in a recessed portion of the dressing member;  
       FIG. 8  is a cross-sectional view illustrating an operating state of the dresser when starting up a polishing pad of the polishing apparatus according to the present invention;  
       FIG. 9  is a cross-sectional view illustrating an operating state of the dresser when breaking in a polishing surface of the polishing pad of the polishing apparatus according to the present invention;  
       FIG. 10  is a cross-sectional view illustrating an operating state of the dresser during polishing according to the present invention; and  
       FIG. 11  is a plan view showing the polishing surface of the polishing apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, embodiments of the present invention will be described with reference to the drawings.  FIG. 1  is a view showing a structural example of a polishing apparatus according to the present invention. In  FIG. 1 , a reference numeral  10  represents a polishing table. A polishing pad  11  is attached to an upper surface of the polishing table  10 . The polishing table  10  is rotated by a non-illustrated rotating mechanism in a direction indicated by arrow A.  
      A reference numeral  12  represents a substrate holder (top ring). This substrate holder  12  comprises a circular substrate-holding member  13  for attracting and holding a substrate (e.g., a silicon wafer) W to be polished. The substrate-holding member  13  has an attraction surface configured to attract the substrate W thereto, and this attraction surface has a plurality of openings  13   a  communicating with a space chamber  14  formed in the substrate-holding member  13 . The space chamber  14  is coupled to a vacuum source  15  via a valve  16 , so that the substrate W is held on the attraction surface by opening the valve  16  and is released from the attraction surface by closing the valve  16 .  
      The substrate holder  12  is coupled to a lower edge portion of a rotating shaft  17  via a universal coupling  18 , so that rotation of the rotating shaft  17  in a direction indicated by arrow B rotates the substrate holder  12  in the same direction. A reference numeral  19  represents a head member for rotatably supporting the rotating shaft  17 . This head member  19  is fixed to a support shaft  20 . A reference numeral  21  represents an air cylinder mounted on the head member  19 . This air cylinder  21  is operable to elevate and lower the substrate holder  12  via a piston member  22  and the rotating shaft  17 , and to bring the substrate W into contact with a polishing surface of the polishing pad  11  at a predetermined pressing force (load). A reference numeral  23  represents a bearing.  
      A reference numeral  24  represents a driving motor mounted on the head member  19 . A timing pulley  25  is coupled to a rotating shaft of the driving motor  24 . A timing belt  27  rides on the timing pulley  25  and a timing pulley  26  fixed to a circumferential surface of the rotating shaft  17 . By energizing the driving motor  24 , the substrate holder  12  is rotated in the direction B via the timing pulley  25 , the timing belt  27 , the timing pulley  26 , and the rotating shaft  17 . Rotation of the polishing table  10  in the direction A and rotation of the substrate holder  12  in the direction B provide relative movement between the substrate W and the polishing pad  11  to thereby polish the substrate W. A reference numeral  28  represents a guide ring for preventing the substrate W from being spun off from the substrate-holding member  13 .  
      The support shaft  20  is rotated through a certain angle by a non-illustrated rotating mechanism, so that the head member  19  is swung by rotation of the support shaft  20  to thereby allow the substrate holder  12  to move between a predetermined substrate-transfer position where the substrate W is transferred and a polishing position on the polishing pad  11 . The substrate holder  12  attracts and holds the substrate W at the substrate-transfer position, and is moved by swinging motion of the head member  19  to the polishing position. Then, the substrate holder  12  is moved downward to bring the substrate W into contact with the upper surface of the polishing pad  11  at a predetermined pressing force. The substrate holder  12  and the polishing table  10  are rotated to provide relative movement between the substrate W and the polishing pad  11  to thereby polish the substrate W. Thereafter, the substrate holder  12  is moved to the substrate-transfer position, and releases the polished substrate W. Such steps are repeated, whereby substrates W are polished.  
      A reference numeral  30  represents a dresser for dressing, i.e., conditioning, the polishing surface of the polishing pad  11  on the polishing table  10 . This dresser  30  comprises a first dressing member  31  and a second dressing member  32 . The first dressing member  31  has a circular or disk shape with a larger diameter than that of the substrate W, and has a lower surface serving as a dressing surface, which will be discussed later, with a large number of diamond particles fixed thereto for dressing the polishing surface of the polishing pad  11 . The second dressing member  32  has a disk-shape with a larger diameter than that of the first dressing member  31 . The second dressing member  32  has a recessed portion  32   a  at a central portion of a lower surface thereof, and the first dressing member  31  is accommodated in this recessed portion  32   a . A lower surface of the second dressing member  32  provides an annular belt-shaped surface serving as a dressing surface, which will be discussed later, with a large number of diamond particles fixed thereto for dressing the polishing surface of the polishing pad  11 .  
      The first dressing member  31  is fixed to a lower end of a rotating shaft  33 , and the second dressing member  32  is fixed to a lower end of a rotating shaft  34 . The rotating shaft  33  extends through the rotating shaft  34 , and is supported by bearings  35  and  36  that allow the rotating shaft  33  to be free to rotate in the rotating shaft  34 . The rotating shaft  33  is rotatably supported by a head member  37 , and the rotating shaft  34  is rotatably supported by a head member  38 . A reference numeral  39  represents an air cylinder mounted on the head member  37 . This air cylinder  39  is operable to elevate and lower the first dressing member  31  via a piston member  40  and the rotating shaft  33 , and to bring the first dressing member  31  into contact with the polishing surface of the polishing pad  11  at a predetermined pressing force (load). A reference numeral  41  represents a bearing. A reference numeral  42  represents an air cylinder mounted on the head member  38 . This air cylinder  42  is operable to elevate and lower the second dressing member  32  via a piston member  43  and the rotating shaft  34 , and to bring the second dressing member  32  into contact with the polishing surface of the polishing pad  11  at a predetermined pressing force (load). A reference numeral  44  represents a bearing.  
      A reference numeral  45  represents a driving motor mounted on the head member  37 . This driving motor  45  has a rotating shaft with a timing pulley  47  fixed thereto. A timing belt  49  rides on the timing pulley  47  and a timing pulley  48  fixed to a circumferential surface of the rotating shaft  33 . By energizing the driving motor  45 , the first dressing member  31  is rotated in a direction indicated by arrow C via the timing pulley  47 , the timing belt  49 , the timing pulley  48 , and the rotating shaft  33 . A reference numeral  50  represents a driving motor mounted on the head member  38 . This driving motor  50  has a rotating shaft with a timing pulley  51  fixed thereto. A timing belt  53  rides on the timing pulley  51  and a timing pulley  52  fixed to a circumferential surface of the rotating shaft  34 . By energizing the driving motor  50 , the second dressing member  32  is rotated in a direction indicated by arrow D via the timing pulley  51 , the timing belt  53 , the timing pulley  52 , and the rotating shaft  34 .  
      As described above, the first dressing member  31  and the second dressing member  32  have the rotating shaft  33  and the rotating shaft  34 , respectively, which have the same axis (they are concentrically arranged) and are rotated independently of each other in the directions indicated by arrows C and D. Further, the first dressing member  31  and the second dressing member  32  are elevated and lowered independently of each other by the air cylinder  39  and the air cylinder  42 , respectively, and are thus pressed against the polishing surface at desired pressing forces (loads). The head member  37  and the head member  38  have edge portions, respectively, which are fixed to a support shaft  54 . This support shaft  54  is rotated through a certain angle by a non-illustrated driving mechanism, so that the head members  37  and  38  are swung by rotation of the support shaft  54  to thereby allow the first dressing member  31  and the second dressing member  32  to move between predetermined waiting positions and dressing positions on the polishing pad  11 .  
      As shown in  FIGS. 2A through 2C , the first dressing member  31  comprises a disk-shaped body  31   a  having a lower surface. A large number of diamond particles  3   b  are fixed to the lower surface via a fixing layer (an electrodeposited layer)  31   c  formed on the lower surface to thereby form the dressing surface. A fluid passage  31   d  is formed in the disk-shaped body  31   a  so that a cooling medium circulates through the fluid passage  31   d . The rotating shaft  33  has therein a fluid-introduction passage  33   a  through which the cooling medium is introduced into the fluid passage  31   d , and further has therein a fluid-discharge passage  33   b  through which the cooling medium flows out from the fluid passage  31   d . The cooling medium  100  (see  FIG. 1 ), which has been introduced into the fluid-introduction passage  33   a , flows through the fluid passage  31   d  in the disk-shaped body  31   a  to thereby cool the disk-shaped body  31   a , and flows out from the fluid passage  31   d  through the fluid-discharge passage  33   b . Instead of the cooling medium for cooling the body  31   a , a heating medium for heating the body  31   a  may be introduced into the fluid passage  31   d .  FIG. 2A  is a plan view showing the first dressing member  31 ,  FIG. 2B  is a cross-sectional view taken along line A-A of  FIG. 2A , and  FIG. 2C  is an enlarged cross-sectional view showing a part of the dressing surface.  
      The second dressing member  32  comprises a disk-shaped body  32   b  having the recessed portion  32   a  at the center of the lower surface thereof for accommodating the first dressing member  31 . A large number of diamond particles  32   c  are fixed to the lower surface via a fixing layer (an electrodeposited layer)  32   d  formed around the recessed portion  32   a  to thereby form the dressing surface of an annular belt shape. A through-hole  34   a  is formed in the rotating shaft  34 , and the rotating shaft  33  of the first dressing member  31  extends through the through-hole  34   a .  FIG. 3A  is a cross-sectional view showing the second dressing member  32 , and  FIG. 3B  is an enlarged cross-sectional view showing a part of the dressing surface.  
      The diameters of the diamond particles  31   b  fixed to the lower surface of the first dressing member  31  are smaller than the diameters of the diamond particles  32   c  fixed to the lower surface of the second dressing member  32 . Further, the diamond particles  31   b  have more rounded shapes than the diamond particles  32   c . As shown in  FIG. 4A , the first dressing member  31 , rotating in the direction C, is pressed against the upper surface of the polishing pad  11  moved by the polishing table  10  in the direction A. Similarly, as shown in  FIG. 4B , the second dressing member  32 , rotating in the direction D, is pressed against the upper surface of the polishing pad  11  moved by the polishing table  10  in the direction A. Because the diamond particles  31   b  have smaller diameters and more rounded shapes than those of the diamond particles  32   c , a cut rate of the polishing pad  11  by the first dressing member  31  is lower than that by the second dressing member  32 .  FIGS. 4A and 4B  are views showing the dresser  30  of the polishing apparatus according to the present invention. More specifically,  FIG. 4A  is a cross-sectional view illustrating a state in which the first dressing member  31  performs dressing (conditioning), and  FIG. 4B  is a cross-sectional view illustrating a state in which the second dressing member  32  performs dressing (conditioning).  
      In the above polishing apparatus, the support shaft  54  is rotated to swing the head member  37  and the head member  38  to move the first dressing member  31  and the second dressing member  32  from the waiting positions to the dressing positions on the polishing surface of the polishing pad  11 , as shown in  FIG. 1 . In this state, the air cylinder  39  moves the first dressing member  31  downward to press the lower surface of the first dressing member  31 , rotating in the direction C, against the polishing surface of the polishing pad  11 , rotating in the direction A, at a predetermined pressing force to thereby dress the polishing surface, as shown in  FIG. 4A . On the other hand, in  FIG. 4B , the first dressing member  31  is accommodated in the recessed portion  32   a  of the second dressing member  32 , and the air cylinder  41  moves the second dressing member  32  downward to press the lower surface of the second dressing member  32 , rotating in the direction D, against the polishing surface of the polishing pad  11 , rotating in the direction A, at a predetermined pressing force to thereby dress the polishing surface.  
      As described above, there are two timings for dressing of the polishing surface of the polishing pad  11 : one is dressing during polishing of the substrate W, and another is dressing after polishing.  FIG. 4A  shows dressing during polishing of the substrate W, and  FIG. 4B  shows dressing after polishing. Because the diameter of the first dressing member  31  is larger than the diameter of the substrate W, when dressing in a manner shown in  FIG. 4A , a positional relationship on the polishing surface of the polishing pad  11  between the first dressing member  31  and the substrate W is such that the substrate W is positioned within a dressing zone  101  where dressing (conditioning) has been performed by the first dressing member  31 , as shown in  FIG. 5 . Further, because the diameter of the second dressing member  32  is larger than the diameter of the first dressing member  31 , the second dressing member  32  can dress the polishing surface in its entirety of the polishing pad  11  in a short period of time after polishing of the substrate W, as shown in  FIG. 6 .  
      Because the rotating shaft  33  of the first dressing member  31  and the rotating shaft  34  of the second dressing member  32  are concentrically arranged, and are moved up and down and rotated independently of each other as described above, the first dressing member  31  and the second dressing member  32  can be arranged along a vertical direction. Accordingly, the dresser  30  can be compact.  
      When performing dressing while polishing the substrate W as shown in  FIGS. 4A and 5 , the substrate W is polished by the polishing surface immediately after dressing. In addition, the first dressing member  31  is cooled by the cooling medium  100  flowing through the fluid passage  31   d  in the disk-shaped body  31   a , so that heat due to friction of the polishing surface and dressing is absorbed. As a result, the polishing surface can be maintained at an appropriate temperature, and the substrate W can thus be polished at a high removal rate. While dressing the polishing surface during polishing of the substrate W, the first dressing member  31  applies a smaller pressing force to the polishing surface than that of the second dressing member  32  applied after polishing. Therefore, heat value is low and the diamond particles are not detached from the dressing surface. When performing dressing after polishing of the substrate W as shown in  FIGS. 4B and 6 , the dressing surface of the second dressing member  32  is pressed against the polishing surface of the polishing pad  11  at a large pressing force to thereby dress the polishing surface at a high cut rate. Accordingly, the polishing surface of the polishing pad  11  can be rapidly and uniformly dressed.  
      Although not shown in the drawings, a temperature controller may be provided for adjusting and controlling a temperature of the cooling medium. In this case, the temperature controller can adjust and control the temperature of the cooling medium flowing through the fluid-discharge passage  33   b  after the cooling medium has flowed through the fluid passage  31   d  to cool or heat the first dressing member  31 . After the temperature is adjusted, the cooling medium can be returned to the fluid passage  31   d  through the fluid-introduction passage  33   a . With this structure, the polishing surface of the polishing pad  11  can be maintained at a predetermined temperature, and hence the substrate W can be polished at a high constant removal rate.  
       FIGS. 7A and 7B  are views showing another example of the dresser  30  of the polishing apparatus according to the present invention. This dresser  30  comprises a circular holding member  60  for attracting and holding a circular dummy substrate DW, and a dressing member  61  disposed around the circular holding member  60 . The circular holding member  60  has an attraction surface configured to attract the dummy substrate DW thereto, and this attraction surface has a plurality of openings  60   a  communicating with a space chamber  62  formed in the circular holding member  60 . The space chamber  62  is coupled to a vacuum source  64  via a vacuum passage  33   c  and a valve  63  provided in rotating shaft  33 . The circular holding member  60  is fixed to the rotating shaft  33 . By opening the valve  63  so as to communicate the vacuum source  64  with the space chamber  62 , the dummy substrate DW is attracted to and held on the attraction surface. The dummy substrate DW is released from the attraction surface by closing the valve  63  so as to isolate the space chamber  62  from the vacuum source  64 .  FIG. 7A  is a cross-sectional view illustrating a state in which the circular holding member  60  protrudes from the dressing member  61 , and  FIG. 7B  is a cross-sectional view illustrating a state in which the circular holding member  60  is accommodated in a recessed portion  61   a  of the dressing member  61 .  
      A diameter of the circular holding member  60  is larger than that of the substrate W. As with the first dressing member  31 , the circular holding member  60  has therein a fluid passage  60   b  for circulating a cooling medium. The rotating shaft  33  has therein fluid-introduction passage  33   a  through which the cooling medium is introduced into the fluid passage  60   b , and further has fluid-discharge passage  33   b  through which the cooling medium flows out from the fluid passage  60   b . The cooling medium  100  (see  FIG. 1 ), which has been introduced into the fluid-introduction passage  33   a , flows through the fluid passage  60   b  to thereby cool the circular holding member  60 , and flows out through the fluid-discharge passage  33   b . Although not shown in the drawings, a temperature controller may be provided for adjusting and controlling a temperature of the cooling medium circulating through the fluid passage  60   b  in the circular holding member  60 , as with the first dressing member  31 , so that the circular holding member  60  can be maintained at a predetermined temperature.  
      The dressing member  61  has the same structure as that of the second dressing member  32  shown in  FIGS. 3A and 3B . More specifically, the dressing member  61  has the recessed portion  61   a  at a center of a lower surface thereof for accommodating the circular holding member  60 . The dressing member  61  has an annular belt-shaped surface at a lower end thereof, and a large number of diamond particles are fixed to the annular belt-shaped surface for dressing the polishing surface of the polishing pad  11 . Vertical movement and rotating motion of the circular holding member  60  are performed in the same manner as those of the first dressing member  31 , and will not be described. Further, vertical movement and rotating motion of the dressing member  61  are performed in the same manner as those of the second dressing member  32 , and will not be described. As with the rotating shaft  33  of the first dressing member  31  and the rotating shaft  34  of the second dressing member  32 , the rotating shaft  33  of the circular holding member  60  and the rotating shaft  34  of the dressing member  61  have the same axis (i.e., they are concentrically arranged), and are moved up and down and rotated independently of each other.  
      After the polishing pad  11  on the polishing table  10  is replaced with a new one, starting up of the new polishing pad is performed. Specifically, as shown in  FIG. 8 , the dressing member  61  is rotated in the direction D, and the lower surface thereof, i.e., the dressing surface with a large number of diamond particles fixed thereto, is pressed against a polishing surface (upper surface) of the new polishing pad  11  moving in the direction A with rotation of the polishing table  10 . Simultaneously, a dummy semiconductor substrate (e.g., silicon wafer) DW is attracted to the attraction surface of the circular holding member  60 , and is pressed against the polishing surface of the polishing pad  11  at a predetermined pressing force. With this operation, downtime of the polishing apparatus can be shortened. The circular holding member  60  is cooled by the cooling medium flowing through the fluid passages  60   b . Therefore, heat due to friction of the dummy semiconductor substrate DW is absorbed, and hence an increase in temperature is suppressed. As the dummy semiconductor substrate DW, a SiC wafer having a higher wear resistance than the silicon wafer may be used.  
      After the polishing pad  11  on the polishing table  10  is started up, a dummy semiconductor substrate (e.g., silicon wafer) DW is held by the circular holding member  60  of the dresser  30 , and is rotated in the direction C, as shown in  FIG. 9 . Then, the dummy semiconductor substrate DW is pressed at a predetermined pressing force (load) against the polishing surface (upper surface) of the polishing pad  11  moving in the direction A with rotation of the polishing table  10 , whereby break-in is performed. During this operation, the cooling medium circulates through the fluid passage  60   b  of the circular holding member  60 . As a result, frictional heat of the dummy semiconductor substrate DW is absorbed by the cooling medium, and hence an increase in temperature of the dummy semiconductor substrate DW can be suppressed.  
      Further, while polishing the substrate W held by the substrate holder  12  (see  FIG. 1 ), the lower surface of the circular holding member  60 , rotating in the direction C, is pressed against the polishing surface of the polishing pad  11  moving in the direction A with rotation of the polishing table  10 , as shown in  FIG. 10 . In this case, the openings  60   d  for attracting the dummy semiconductor substrate DW and the space chamber  62  may not be formed, although shown in  FIG. 10 . The cooling medium circulates through the fluid passage  60   b  to cool the circular holding member  60 , so that heat of the polishing surface of the polishing pad  11 , which is held in contact with the circular holding member  60 , is absorbed by the cooling medium. More specifically, as shown in  FIG. 11 , an increase in temperature of a zone  102  contacting the circular holding member  60  is suppressed, and hence a temperature suitable for polishing can be maintained. As a result, the substrate W can be polished at a high removal rate.  
      Furthermore, while polishing the substrate W, the dummy semiconductor substrate DW, held by the circular holding member  60 , is kept in contact with the upper surface of the polishing pad  11  as shown in  FIG. 9 , so that the upper surface (polishing surface) of the polishing pad  11  is cooled by the cooling medium via the dummy semiconductor substrate DW. Accordingly, as with the above case, the substrate W can be polished at a high removal rate.  
      Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of claims for patent, and the scope of the technical concept described in the specification and drawings.