Aug. 7, 2008  24  US 2008/0188162 Al  embodiment, which will not be described below, are identical  to those of the previously-described embodiment shown in  FIG.  18,  and will not be described repetitively.  [0276]  As shown in FIG.  34,  sponges  687,  each serving as  a liquid-retaining member, are provided in through-holes  101a  of polishing pad  101.  These sponges  687  have lower  ends contacting base  654b  of support member  654,  and have  upper ends positioned above polishing surface of the polish› ing pad  101.  The sponges  687  are made from a deformable  material, so that polishing head  1,  holding the substrate W,  can compress the sponges  687  via the substrate W to allow the  substrate W to contact the polishing surface during polishing.  With this structure, the electrolytic solution is retained by the  sponges  687  during polishing. Hence, an amount of the elec› trolytic solution scattering off the polishing surface due to a  centrifugal force can be reduced.  [0277]  On the other hand, when dressing the polishing sur› face, the above-described clamp is removed, and as shown in  FIG.  35, lid 654a  is elevated so that the upper ends of the  sponges  687  are positioned below the polishing surface. In  this state, the lid  654a  and the base  654b  are fixed in position.  Then, while a pure-water supply nozzle  688  supplies pure  water onto the polishing surface, the dresser  218  dresses the  polishing surface. Because the dresser  218  does not contact  the sponges  687  during dressing, the sponges  687  are not  damaged by the dresser  218.  [0278]  Other than the sponge, a fibrous memberor an open› cell foam may be used for the liquid-retaining member.  An  example of a method of forming the open-cell foam includes  the steps of mixing fine particles of calcium carbonate with a  base material, injection-molding the base material mixed  with the calcium carbonate particles to form an injection› molded product, and immersing the injection-molded prod› uct into hydrochloric acid water to decompose and dissolve  the calcium carbonate particles. In this case, an amount of the  calcium carbonate particles, filling the base material, is  required to be large enough to allow the calcium carbonate  particles to be in contact with each other. As the base material,  polyurethane, polyolefin, or rubber can be used.  [0279]  FIG.  36  is a schematic cross-sectional view showing  another example of this embodiment. As shown in FIG.  36,  in  this example, the electrolytic-solution path for directing the  electrolytic solution to the through-holes  101a  from below  the polishing pad  101  is not provided. Instead, the electrolytic  solution is supplied directly onto the polishing surface from  the electrolytic-solution supply nozzle  102.  Sponges  687,  each serving as the liquid-retaining member, are provided in  the through-holes  101a,  respectively, so that the electrolytic  solution, supplied from the electrolytic-solution supply  nozzle  102,  is retained by the sponges  687.  [0280]  In this example, it is preferable that the upper ends  of the sponges  687  be positioned below the polishing surface  so as not to interfere with dressing of the polishing surface.  An  arrangement of the liquid-retaining members is not limited to  the above examples in which the liquid-retaining members  are disposed in the through-holes  101a  which are uniformly  distributed over the polishing surface. For example, the pol› ishing surface may have grooves on its upper surface (i.e.,  polishing surface), and the liquid-retaining members may be  disposed in these grooves. In this case, the arrangements of  the liquid-retaining members as viewed from above include a  linear arrangement, a concentric circular arrangement, and a  fan-shaped arrangement.  [0281]  FIG.  37  and FIG.  38  are cross-sectional views each  schematically showing an example of a polishing pad  101  used in an electrochemical mechanical polishing apparatus  250  according to still another embodiment of the present  invention. Components and operations of this embodiment,  which will not be described below, are identical to those of the  previously-described embodiment shown in FIG.  18,  and will  not be described repetitively.  [0282]  In this embodiment, each of through-holes  101a  has  an upper opening with a smaller diameter than a diameter of  a lower opening thereof More specifically, in the example  shown in FIG.  37,  the diameter of each of the through-holes  101a  is gradually decreased from the lower opening to the  upper opening. In the example shown in FIG.  38,  each of the  through-holes  1  Ola  has two holes arranged vertically in series  with different diameters. Because the upper opening is  smaller than the lower opening, the electrolytic solution  retained in the through-holes  101a  is prevented from scatter› ing due to a centrifugal force. In this embodiment, the elec› trolytic-solution path for directing the electrolytic solution to  the through-holes  101a  from below polishing pad  101  may  not be provided. Instead, the electrolytic solution may be  supplied directly onto the polishing surface from electrolytic› solution supply nozzle  102  so that the through-holes  101a  retain the electrolytic solution therein.  [0283]  FIG.  39  is a schematic cross-sectional view showing  an electrochemical mechanical polishing apparatus  250  according to still another embodiment of the present inven› tion. Components and operations of this embodiment, which  will not be described below, are identical to those of the  previously-described embodiment shown in FIG.  18,  and will  not be described repetitively.  [0284]  As shown in FIG.  39,  an annular gas passage  690  is  provided so as to surround polishing pad  101.  This gas pas› sage  690  has a slit (i.e., gas ejection opening)  691  in an inner  circumferential surface thereof, so that a gas, flowing through  the gas passage  690,  is ejected through the slit  691  toward a  centerof polishing surface of the polishing pad  101.  With this  gas passage  690,  the gas can push back the electrolytic solu› tion that is about to flow out from the polishing surface by a  centrifugal force. The gas ejection opening is not limited to  the slit. Plural holes ( each having a diameter of not more than  1 mm, for example) may be provided as the gas ejection  opening. In this embodiment, the electrolytic-solution path  for directing the electrolytic solution to the through-holes  1  Ola  from below the polishing pad  101  may not be provided.  Instead, the electrolytic solution may be supplied directly  onto the polishing surface from electrolytic-solution supply  nozzle  102.  Further, a conductive pad may be used for the  polishing pad  101,  and the second electrode (electric supply  electrode) may be in contact with the conductive pad so as to  supply an electric current to the conductive film on the sub› strate via the conductive pad.  [0285]  FIG.  40  is a schematic side view showing an elec› trochemical mechanical polishing apparatus  250  according to  still another embodiment of the present invention. Compo› nents and operations of this embodiment, which will not be  described below, are identical to those of the previously› described embodiment shown in FIG.  18,  and will not be  described repetitively.  [0286]  As shown in FIG.  40,  two cylindrical rollers  693  and  694,  each rotatable about its own axis, are provided laterally  to polishing pad  101.  These rollers  693  and  694  are operable  to sandwich the overhanging polishing head  1  during polish-