Patent Publication Number: US-11642753-B2

Title: Polishing-pad laminated structure, polishing-pad positioning instrument, and method of attaching a polishing pad to a polishing table

Description:
BACKGROUND 
     Manufacturing processes of semiconductor devices include a process of polishing a dielectric film, e.g., SiO 2 , and a process of polishing a metal film, e.g., copper or tungsten. Manufacturing processes of backside illumination CMOS sensor and through-silicon via (TSV) include a process of polishing a silicon layer (silicon wafer), in addition to the polishing processes of the dielectric film and the metal film. 
     Wafer polishing is generally performed using a chemical mechanical polishing apparatus (or a CMP apparatus). This CMP apparatus is configured to polish a surface of the wafer by bringing the wafer into sliding contact with a polishing pad attached to a polishing table while supplying slurry onto the polishing pad. The polishing of the wafer is terminated when a thickness of a film (an insulating film, a metal film, a silicon layer, etc.), constituting the surface of the wafer, reaches a predetermined target value. Therefore, the film thickness is measured during polishing of the wafer. 
     An optical film-thickness measuring device is one example of a film-thickness measuring device. The optical film-thickness measuring device is configured to direct light to a surface of a wafer and analyze optical information contained in reflected light from the wafer to thereby measure a film thickness. The optical film-thickness measuring device includes a sensor head including a light emitter and a light receiver disposed in the polishing table. The polishing pad has a through-hole at the same position as the position of the sensor head. The light emitted from the sensor head is directed to the wafer through the through-hole of the polishing pad, and the reflected light from the wafer passes through the through-hole again to reach the sensor head. 
     The polishing pad wears gradually as polishing of wafers and dressing of the polishing pad are repeated. Therefore, if the wear of the polishing pad has progressed to some extent, it is replaced with a new polishing pad. A back surface of the polishing pad is composed of an adhesive surface, and the polishing pad is attached to the top surface of the polishing table. When attaching the polishing pad to the polishing table, it is important to accurately align the through-hole of the polishing pad with the sensor head disposed in the polishing table. This is because, if the through-hole of the polishing pad is not in alignment with the sensor head, the film-thickness measuring accuracy is lowered. 
     However, it is difficult to accurately align the through-hole of the polishing pad with the sensor head disposed in the polishing table. In particular, since the through-hole of the polishing pad are typically small, it takes a long time to properly attach the polishing pad to the polishing table, thus resulting in a decrease in operation rate of the polishing apparatus. 
     SUMMARY OF THE INVENTION 
     Therefore, according to one embodiment, there are provided a polishing-pad laminated structure and a polishing-pad positioning instrument which allow for easy alignment of a through-hole of a polishing pad with a sensor head installed in a polishing table. Further, according to one embodiment, there is provided a method of attaching a polishing pad to a polishing table using the polishing-pad positioning instrument. 
     The below-described embodiments relate to a polishing pad used in a polishing apparatus for polishing a substrate such as a wafer, and in particular, a polishing pad used in a polishing apparatus provided with a polishing table in which a film-thickness measuring device is disposed. 
     In an embodiment, there is provided a polishing-pad laminated structure comprising: a polishing pad having a through-hole located at a position corresponding to a position of a sensor head disposed in a polishing table; and a release sheet covering an adhesive surface of the polishing pad, the release sheet being divided into at least a first release sheet and a second release sheet, the first release sheet having a surface area smaller than a surface area of the second release sheet. 
     In an embodiment, the second release sheet has a through-hole at a same position as a position of the through-hole of the polishing pad. 
     In an embodiment, the polishing-pad laminated structure further comprises a release assisting projection connected to an edge of the second release sheet. 
     In an embodiment, there is provided a polishing-pad positioning instrument for positioning a polishing pad with respect to a polishing table, comprising: a positioning structure configured to be removably attached to the polishing table, the positioning structure including (i) a first positioning protrusion configured to be inserted into a table hole formed in a pad support surface of the polishing table, and (ii) a second positioning protrusion fixed to the first positioning protrusion, the second positioning protrusion having a cross-sectional shape corresponding to a cross-sectional shape of a through-hole formed in the polishing pad. 
     In an embodiment, a length of the second positioning protrusion along a central axis of the second positioning protrusion is not less than a thickness of the polishing pad. 
     In an embodiment, the polishing-pad positioning instrument further comprises a support structure supporting the second positioning protrusion, the support structure having a bottom surface perpendicular to a central axis of the second positioning protrusion. 
     In an embodiment, the second positioning protrusion is supported by the support structure such that the second positioning protrusion is movable along the central axis of the second positioning protrusion. 
     In an embodiment, the polishing-pad positioning instrument further comprises a spring disposed between the second positioning protrusion and the support structure, the positioning structure being forced by the spring in an extending direction of the central axis of the second positioning protrusion. 
     In an embodiment, there is provided a method of attaching a polishing pad to a pad support surface of a polishing table, comprising: (i) providing a polishing-pad laminated structure including the polishing pad and a release sheet, the polishing pad having a through-hole located at a position corresponding to a position of a sensor head disposed in the polishing table, the release sheet covering an adhesive surface of the polishing pad, the release sheet being divided into at least a first release sheet and a second release sheet, the first release sheet having a surface area smaller than a surface area of the second release sheet; (ii) providing a positioning structure including a first positioning protrusion and a second positioning protrusion, the first positioning protrusion being configured to be inserted into a table hole formed in the pad support surface of the polishing table, the second positioning protrusion being fixed to the first positioning protrusion, the second positioning protrusion having a cross-sectional shape corresponding to a cross-sectional shape of the through-hole of the polishing pad; (iii) placing the polishing-pad laminated structure, from which the first release sheet has been removed, on the pad support surface of the polishing table; (iv) inserting the first positioning protrusion into the table hole through the through-hole of the polishing pad; (v) inserting the second positioning protrusion into the through-hole of the polishing pad; (vi) removing the positioning structure from the polishing table and the polishing pad; and (vii) removing the second release sheet from the polishing pad and attaching the entire adhesive surface of the polishing pad to the pad support surface of the polishing table. 
     In an embodiment, there is provided a method of attaching a polishing pad to a pad support surface of a polishing table, comprising: (i) providing a polishing-pad laminated structure including the polishing pad and a release sheet, the polishing pad having a through-hole located at a position corresponding to a position of a sensor head disposed in the polishing table, the release sheet covering an adhesive surface of the polishing pad, the release sheet being divided into at least a first release sheet and a second release sheet, the first release sheet having a surface area smaller than a surface area of the second release sheet; (ii) providing a positioning structure including a first positioning protrusion and a second positioning protrusion, the first positioning protrusion being configured to be inserted into a table hole formed in the pad support surface of the polishing table, the second positioning protrusion being fixed to the first positioning protrusion, the second positioning protrusion having a cross-sectional shape corresponding to a cross-sectional shape of the through-hole of the polishing pad; (iii) inserting the first positioning protrusion into the table hole; (iv) placing the polishing-pad laminated structure, from which the first release sheet has been removed, on the pad support surface of the polishing table; (v) inserting the second positioning protrusion into the through-hole of the polishing pad; (vi) removing the positioning structure from the polishing table and the polishing pad; and (vii) removing the second release sheet from the polishing pad and attaching the entire adhesive surface of the polishing pad to the pad support surface of the polishing table. 
     According to the embodiments described above, the position of the polishing pad with respect to the polishing table is adjusted in a state where the first release sheet having a small surface area has been removed. Since the polishing-pad laminated structure can be moved relatively freely on the polishing table, the through-hole of the polishing pad can be precisely aligned with the sensor head disposed in the polishing table. Further, immediately after the alignment of the through-hole of the polishing pad with the sensor head is completed, the exposed portion of the adhesive surface of the polishing pad (i.e., the portion that has been covered with the first release sheet) is pressed against the polishing table, so that the relative position of the polishing pad with respect to the polishing table can be fixed. 
     Furthermore, according to the above-described embodiments, the positioning of the polishing pad with respect to the polishing table is completed by inserting the second positioning protrusion of the positioning structure into the through-hole of the polishing pad. Accordingly, the attachment work of the polishing pad can be easy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view showing an embodiment of a polishing apparatus; 
         FIG.  2    is a schematic cross-sectional view showing the polishing apparatus including an optical film-thickness measuring device; 
         FIG.  3    is a top view of a through-hole of a polishing pad shown in  FIG.  2   ; 
         FIG.  4    is a top view showing a polishing-pad laminated structure having a new polishing pad; 
         FIG.  5    is a backside view of the polishing-pad laminated structure shown in  FIG.  4   ; 
         FIG.  6    is a cross-sectional view taken along a line B-B in  FIG.  4   ; 
         FIG.  7    is a flow chart for explaining an attaching operation of a polishing pad to a polishing table; 
         FIG.  8 A  is a side view of a positioning structure used to position the polishing pad with respect to the polishing table; 
         FIG.  8 B  is a bottom view of the positioning structure shown in  FIG.  8 A ; 
         FIG.  9    is a cross-sectional view showing the positioning structure in a state in which a first positioning protrusion is inserted into a drain hole of the polishing table; 
         FIG.  10    is a diagram showing a process of attaching the polishing pad to the polishing table using the positioning structure; 
         FIGS.  11 A and  11 B  are diagrams each illustrating a process of attaching the polishing pad to the polishing table using the positioning structure; 
         FIG.  12    is a perspective view showing another embodiment of the polishing-pad positioning instrument; 
         FIG.  13    is a front view of the polishing-pad positioning instrument shown in  FIG.  12   ; 
         FIG.  14    is a cross-sectional view taken along a line C-C of  FIG.  13   ; 
         FIG.  15    is a view showing a process of attaching a polishing pad to a polishing table using the polishing-pad positioning instrument; 
         FIGS.  16 A and  16 B  are diagrams each showing a process of attaching the polishing pad to the polishing table using the polishing-pad positioning instrument; 
         FIG.  17    is a cross-sectional view showing a positional relationship among the positioning structure, the polishing-pad laminated structure, and the polishing table; 
         FIGS.  18 A and  18 B  are perspective views each showing still another embodiment of the polishing-pad positioning instrument; 
         FIGS.  19 A and  19 B  are diagrams each showing a process of attaching a polishing pad to a polishing table using the polishing-pad positioning instrument; 
         FIG.  20    is a view showing a process of attaching the polishing pad to the polishing table using the polishing-pad positioning instrument; 
         FIG.  21    is a cross-sectional view showing a positional relationship among the positioning structure, the polishing-pad laminated structure, and the polishing table; 
         FIG.  22    is a view showing a process of attaching the polishing pad to the polishing table using the polishing-pad positioning instrument; 
         FIG.  23    is a view showing a process of attaching the polishing pad to the polishing table using the polishing-pad positioning instrument; 
         FIG.  24    is a view showing a process of attaching the polishing pad to the polishing table using the polishing-pad positioning instrument; 
         FIG.  25    is a cross-sectional view showing a positional relationship among the positioning structure, the polishing-pad laminated structure, and the polishing table; 
         FIG.  26 A  is a top view showing another embodiment of a polishing-pad laminated structure, and  FIG.  26 B  is a backside view of the polishing-pad laminated structure shown in  FIG.  26 A ; 
         FIG.  27 A  is a top view showing still another embodiment of a polishing-pad laminated structure, and  FIG.  27 B  is a backside view of the polishing-pad laminated structure shown in  FIG.  27 A ; 
         FIG.  28    is a schematic cross-sectional view showing an embodiment of a polishing apparatus having a polishing table in which a plurality of sensor heads are arranged; 
         FIG.  29 A  is a top view showing an embodiment of a polishing-pad laminated structure used for the polishing table in which two sensor heads are arranged, and  FIG.  29 B  is a backside view of the polishing-pad laminated structure shown in  FIG.  29 A ; 
         FIG.  30    is a perspective view showing an embodiment of a polishing-pad positioning instrument suitable for the polishing-pad laminated structure shown in  FIGS.  29 A and  29 B ; 
         FIG.  31    is a front view of the polishing-pad positioning instrument shown in  FIG.  30   ; 
         FIG.  32    is a cross-sectional view taken along a line D-D of  FIG.  31   ; 
         FIGS.  33 A and  33 B  are perspective views each showing another embodiment of a polishing-pad positioning instrument suitable for the polishing-pad laminated structure shown in  FIGS.  29 A and  29 B ; 
         FIG.  34    is a perspective view showing another embodiment of a polishing-pad positioning instrument suitable for the polishing-pad laminated structure shown in  FIGS.  29 A and  29 B ; 
         FIG.  35    is a front view of the polishing-pad positioning instrument shown in  FIG.  34   ; 
         FIGS.  36 A and  36 B  are diagrams each showing a process of attaching a polishing pad to a polishing table using the polishing-pad positioning instrument; 
         FIG.  37    is a view showing a process of attaching the polishing pad to the polishing table using the polishing-pad positioning instrument; 
         FIG.  38    is a view showing a process of attaching the polishing pad to the polishing table using the polishing-pad positioning instrument; 
         FIG.  39 A  is a top view showing another embodiment of a polishing-pad laminated structure used for a polishing table in which two sensor heads are arranged, and  FIG.  39 B  is a backside view of the polishing-pad laminated structure shown in  FIG.  39 A ; 
         FIG.  40 A  is a top view showing still another embodiment of a polishing-pad laminated structure used for a polishing table in which two sensor heads are arranged, and  FIG.  40 B  is a backside view of the polishing-pad laminated structure shown in  FIG.  40 A ; 
         FIG.  41 A  is a top view showing an embodiment of a polishing-pad laminated structure used for a polishing table in which three sensor heads are arranged, and FIG.  41 B is a backside view of the polishing-pad laminated structure shown in  FIG.  41 A ; 
         FIG.  42 A  is a top view showing another embodiment of a polishing-pad laminated structure used for a polishing table in which three sensor heads are arranged, and  FIG.  42 B  is a backside view of the polishing-pad laminated structure shown in  FIG.  42 A ; 
         FIG.  43 A  is a top view showing still another embodiment of a polishing-pad laminated structure used for a polishing table in which three sensor heads are arranged, and  FIG.  43 B  is a backside view of the polishing-pad laminated structure shown in  FIG.  43 A ; and 
         FIG.  44    is a view showing another embodiment of a positioning structure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments will be described below with reference to the drawings.  FIG.  1    is a view showing an embodiment of a polishing apparatus. As shown in  FIG.  1   , the polishing apparatus includes a polishing table  3  to which a polishing pad  1  having a polishing surface  1   a  is attached, a polishing head  5  for holding a wafer W, which is an example of a substrate, and pressing the wafer W against the polishing pad  1  on the polishing table  3  to polish the wafer W, a polishing-liquid supply nozzle  10  for supplying a polishing liquid (e.g., slurry) onto the polishing pad  1 , and a polishing controller  12  for controlling polishing of the wafer W. 
     The polishing table  3  is coupled to a table motor  19  through a table shaft  3   a , so that the polishing table  3  is rotated by the table motor  19  in a direction indicated by arrow. The table motor  19  is located below the polishing table  3 . The polishing pad  1  is attached to a pad support surface  3   b  of the polishing table  3 . The pad support surface  3   b  is composed of an upper surface of the polishing table  3 . The polishing pad  1  has an upper surface, which provides a polishing surface  1   a  for polishing the wafer W. The polishing head  5  is secured to a lower end of a polishing head shaft  16 . The polishing head  5  is configured to be able to hold the wafer W on its lower surface by vacuum suction. The polishing head shaft  16  can be elevated and lowered by an elevating mechanism (not shown in the drawing). 
     Polishing of the wafer W is performed as follows. The polishing head  5  and the polishing table  3  are rotated in directions indicated by arrows, while the polishing liquid (or slurry) is supplied from the polishing-liquid supply nozzle  10  onto the polishing pad  1 . In this state, the polishing head  5  presses the wafer W against the polishing surface  1   a  of the polishing pad  1 . The surface of the wafer W is polished by a mechanical action of abrasive grains contained in the polishing liquid and a chemical action of the polishing liquid. 
     The polishing apparatus includes an optical film-thickness measuring device (film-thickness measuring apparatus)  25  for measuring a film thickness of the wafer W. This optical film-thickness measuring device  25  has a sensor module  42  for obtaining an optical signal that varies in accordance with the film thickness of the wafer W, and a processor  32  for determining the film thickness from the optical signal. The sensor module  42  is disposed in the polishing table  3 , and the processor  32  is coupled to the polishing controller  12 . The sensor module  42  includes a sensor head  31  configured to direct light to the surface of the wafer W and receive reflected light from the wafer W. The sensor head  31  rotates together with the polishing table  3  as indicated by arrow A, and obtains the optical signal of the wafer W held on the polishing head  5 . The sensor module  42  is coupled to the processor  32  so that the optical signal, obtained by the sensor module  42 , is sent to the processor  32 . 
       FIG.  2    is a schematic cross-sectional view showing the polishing apparatus having the optical film-thickness measuring device  25 . The polishing head shaft  16  is coupled to a polishing head motor  18  through a coupling device  17 , such as belt, so that the polishing head shaft  16  is rotated by the polishing head motor  18 . This rotation of the polishing head shaft  16  is transmitted to the polishing head  5  to rotate the polishing head  5  in the direction indicated by the arrow. 
     As described previously, the optical film-thickness measuring device  25  includes the sensor module  42  having the sensor head  31  and the processor  32 . The sensor module  42  includes an optical device  47  having at least a light source and a spectrometer, and optical fibers  48  coupled to the optical device  47 . The tip ends of the optical fibers  48  constitute the sensor head  31 , and the other ends of the optical fibers  48  are coupled to the optical device  47 . The optical device  47  is configured to emit light, which travels through the optical fibers  48  and is directed from the sensor head  31  to the surface, to be polished, of the wafer W. Reflected light from the wafer W is received by the sensor head  31  and is further transmitted to the optical device  47  through the optical fibers  48 . The optical device  47  is configured to resolve the reflected light according to wavelength and measure intensity of the reflected light over a predetermined wavelength range. 
     The polishing table  3  has a sensor hole  50 A and a drain hole  50 B formed in the upper surface of the polishing table  3 . The drain hole  50 B functions as a table hole used in positioning of the polishing pad  1  with respect to the polishing table  3  as described later. The polishing pad  1  has a through-hole  51  at a position corresponding to the holes  50 A and  50 B. The holes  50 A,  50 B are in communication with the through-hole  51 , and the through-hole  51  is located right above the holes  50 A,  50 B. The through-hole  51  has an upper open end lying in the polishing surface  1   a . The sensor hole  50 A is coupled to a liquid supply passage  53 . This liquid supply passage  53  is coupled to a liquid supply source  55  via a rotary join (not shown). The drain hole  50 B is coupled to a liquid discharge passage  54 . 
     The sensor head  31 , which is constituted by the tip ends of the optical fibers  48 , is located in the sensor hole  50 A, and is located close to the surface, to be polished, of the wafer W. The sensor head  31  is located so as to sweep across the surface, to be polished, of the wafer W held by the polishing head  5 . Each time the polishing table  3  rotates, the light is directed to a plurality of areas of the wafer W. 
     During polishing of the wafer W, the liquid supply source  55  supplies water (preferably pure water) as a transparent liquid into the sensor hole  50 A through the liquid supply passage  53 . The water fills a space formed between the lower surface of the wafer W and the sensor head  31 . The water further flows into the drain hole  50 B and is expelled therefrom through the liquid discharge passage  54 . The polishing liquid is discharged together with the water and thus a path of light is ensured. The liquid supply passage  53  is provided with a valve (not shown in the drawing) configured to operate in conjunction with the rotation of the polishing table  3 . The valve operates so as to stop the flow of the water or reduce the flow of the water when the wafer W is not located over the through-hole  51 . 
     During polishing of the wafer W, the sensor head  31  directs the light to the wafer W, and the sensor head  31  receives the reflected light from the wafer W. The optical device  47  measures the intensity of the reflected light at each of the wavelengths over a predetermined wavelength range, and transmits light intensity data obtained to the processor  32 . This light intensity data is an optical signal reflecting a film thickness of the wafer W, and contains the intensities of the reflected light and the corresponding wavelengths. The processor  32  produces, from the light intensity data, a spectral waveform representing the intensity of the light at each of the wavelengths. The processor  32  performs a Fourier transform process (e.g., fast Fourier transform process) on the spectral waveform to produce a frequency spectrum and determines a film thickness of the wafer W from the frequency spectrum. 
       FIG.  3    is a top view of the through-hole  51  of the polishing pad  1  shown in  FIG.  2   . The through-hole  51  of the polishing pad  1  has an elliptical cross section. The sensor hole  50 A and the drain hole  50 B are adjacent to each other, and are arranged along the rotational direction of the polishing table  3 . A width of the through-hole  51  of the polishing pad  1  is larger than a width of the sensor hole  50 A and a width of the drain hole  50 B, so that open ends of the sensor hole  50 A and the drain hole  50 B are located in the through-hole  51  of the polishing pad  1 . The sensor head  31  is arranged in the sensor hole  50 A. The water that has been supplied to the sensor hole  50 A through the liquid supply passage  53  and the polishing liquid (e.g., slurry) that has been used in polishing the wafer W are drained through the drain hole  50 B. 
     The polishing pad  1  gradually wears as polishing of wafers and dressing of the polishing pad  1  are repeated. Therefore, the polishing pad  1  is a consumable item. When the wear of the polishing pad  1  progresses to some extent, it is replaced with a new polishing pad. 
       FIG.  4    is a top view showing a polishing-pad laminated structure  60  including a new polishing pad  1 ,  FIG.  5    is a backside view of the polishing-pad laminated structure  60  shown in  FIG.  4   , and  FIG.  6    is a cross-sectional view taken along a line B-B in  FIG.  4   . The polishing-pad laminated structure  60  includes the new polishing pad  1  and a release sheet  62  covering an adhesive surface  1   b  constituting a back surface of the polishing pad  1 . The release sheet  62  is made of a flexible sheet material, such as paper or a resin film, which can be easily removed from the adhesive surface  1   b . The polishing pad  1  has the through-hole  51  at a position corresponding to the position of the sensor head  31  disposed in the polishing table  3 . The release sheet  62  has a through-hole  65  at the same position as the through-hole  51  of the polishing pad  1 . The through-hole  51  of the polishing pad  1  are aligned with the through-hole  65  of the release sheet  62 . 
     The release sheet  62  has the same size and the same shape as the polishing pad  1  and is attached to the entire adhesive surface  1   b  of the polishing pad  1 . In the present embodiment, the polishing pad  1  and the release sheet  62  are in a circular shape. The release sheet  62  is divided into a first release sheet  62 A and a second release sheet  62 B. The first release sheet  62 A and the second release sheet  62 B cover the entire adhesive surface  1   b  of the polishing pad  1 , and can be peeled off (or removed) from the adhesive surface  1   b . In the present embodiment, the first release sheet  62 A has a crescent shape. The first release sheet  62 A has a surface area smaller than that of the second release sheet  62 B. The first release sheet  62 A and the second release sheet  62 B are next to each other. In one embodiment, the release sheet  62  may be divided into three or more release sheets. 
     The through-hole  65  of the release sheet  62  are formed in the second release sheet  62 B. Three release assisting projections  67 B for assisting the removing of the second release sheet  62 B are connected to the second release sheet  62 B. One of the three release assisting projections  67 B is connected to an inner edge of the second release sheet  62 B, and the other two release assisting projections  67 B are connected to both outer edges of the second release sheet  62 B. It is noted, however, the arrangement of the release assisting projections  67 B is not limited to the present embodiment. In one embodiment, only one or only two of the three release assisting projections  67 B may be provided. In one embodiment, four or more release assisting projections  67 B may be connected to the second release sheet  62 B. A plurality of release assisting projections  67 B may be connected to the inner edge of the second release sheet  62 B, or three or more release assisting projections  67 B may be connected to the outer edge of the second release sheet  62 B. Furthermore, in one embodiment, the release assisting projection  67 B may not be provided. 
     The release assisting projection  67 B has a sheet or tape shape, and has a size that allows a user to pinch it. The release assisting projections  67 B may be integral with the second release sheet  62 B, or may be tape materials attached to the second release sheet  62 B by adhesives. In the present embodiment, no release assisting projection is connected to the first release sheet  62 A, but one or more release assisting projections for assisting the removing of the first release sheet  62 A may be connected to the first peeling sheet  62 A. 
     Next, operations of attaching the polishing pad  1  to the polishing table  3  will be described with reference to a flowchart of  FIG.  7   . 
     In step  1 , a user peels off the first release sheet  62 A from the adhesive surface (back surface)  1   b  of the polishing pad  1 . 
     In step  2 , the polishing-pad laminated structure  60  is placed on the pad support surface  3   b  of the polishing table  3  with the second release sheet  62 B covering the adhesive surface  1   b  of the polishing pad  1 . Although the first release sheet  62 A has been removed from the polishing pad  1 , at this stage an exposed portion of the adhesive surface  1   b  of the polishing pad  1  (i.e., a portion that has been covered by the first release sheet  62 A) does not adhere to the pad support surface  3   b  of the polishing table  3 . Therefore, the polishing-pad laminated structure  60  can be freely moved on the polishing table  3 . 
     In step  3 , the through-hole  51  of the polishing pad  1  is aligned with the sensor head  31  in the polishing table  3 . 
     In step  4 , with the through-hole  51  of the polishing pad  1  aligned with the sensor head  31 , the exposed portion of the adhesive surface  1   b  of the polishing pad  1  (i.e., the portion that has been covered by the first release sheet  62 A) is pressed strongly against the pad support surface  3   b  of the polishing table  3 , whereby the part of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
     In step  5 , the user grips the release assisting projections  67 B with fingers and peels the second release sheet  62 B from the adhesive surface  1   b  of the polishing pad  1 . Since the release assisting projections  67 B are connected to the edge of the second release sheet  62 B, peeling of the second release sheet  62 B begins at its edge, making it easy to remove the second release sheet  62 B. 
     In step  6 , a remaining part of the adhesive surface  1   b  of the polishing pad  1  is strongly pressed against the pad support surface  3   b  of the polishing table  3 , whereby the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
     According to the present embodiment, adjustment of the position of the polishing pad  1  with respect to the polishing table  3  is performed in a state where the first release sheet  62 A having a small surface area has been removed. Since the polishing-pad laminated structure  60  can be moved relatively freely on the polishing table  3 , the through-hole  51  of the polishing pad  1  can be precisely aligned with the sensor head  31  disposed in the polishing table  3 . In particular, according to the present embodiment, at the time of aligning the through-hole  51 , the adhesive layer  1   b  around the through-hole  51  remains covered with the second release sheet  62 B, and therefore fine adjustment of the position of the through-hole  51  can be easily conducted. Further, immediately after the alignment between the through-hole  51  of the polishing pad  1  and the sensor head  31  is completed, the exposed portion (i.e., the portion that has been covered with the first release sheet  62 A) of the adhesive surface  1   b  of the polishing pad  1  is pressed against the polishing table  3 , so that the relative position of the polishing pad  1  with respect to the polishing table  3  can be fixed. 
     In order to facilitate the operation of aligning the through-hole  51  of the polishing pad  1  with the sensor head  31  and to improve the alignment accuracy, in one embodiment, a positioning structure  75  shown in  FIGS.  8 A and  8 B  is used.  FIG.  8 A  is a side view of the positioning structure  75  used to position the polishing pad  1  with respect to the polishing table  3 , and  FIG.  8 B  is a bottom view of the positioning structure  75  shown in  FIG.  8 A . The positioning structure  75  includes a first positioning protrusion  77  configured to be able to be inserted into the drain hole  50 B (see  FIG.  2   ) as a table hole formed in the pad support surface  3   b  of the polishing table  3 , and a second positioning protrusion  78  fixed to the first positioning protrusion  77 . The second positioning protrusion  78  is located on the upper side of the first positioning protrusion  77 . 
     The positioning structure  75  is detachably attached to the pad support surface  3   b  of the polishing table  3 . The positioning structure  75  constitutes at least a part of a polishing-pad positioning instrument for positioning the polishing pad  1  with respect to the polishing table  3 . 
       FIG.  9    is a cross-sectional view showing the positioning structure  75  with its first positioning protrusion  77  inserted into the drain hole  50 B of the polishing table  3 . The first positioning protrusion  77  has a cross section that can be inserted into the drain hole  50 B as a table hole formed in the pad support surface  3   b  of the polishing table  3 . The length of the first positioning protrusion  77  is shorter than the length of the drain hole  50 B, so that the entire first positioning protrusion  77  can be inserted into the drain hole  50 B. In the present embodiment, the first positioning protrusion  77  has a pin shape. However, the shape and the length of the first positioning protrusion  77  are not limited to the present embodiment, and are determined based on the shape and the length of the table hole formed in the pad support surface  3   b.    
     In the present embodiment, the cross section of the first positioning protrusion  77  is smaller than the cross section of the second positioning protrusion  78 . In a case where the cross section of the table hole is large, the cross section of the first positioning protrusion  77  may have the same shape and the same size as those of the cross section of the second positioning protrusion  78 . Furthermore, in one embodiment, the cross section of the first positioning protrusion  77  may be larger than the cross section of the second positioning protrusion  78 . 
     When the first positioning protrusion  77  is placed in the drain hole  50 B, the second positioning protrusion  78  protrudes upward from the pad support surface  3   b  of the polishing table  3 . The second positioning protrusion  78  has the cross-sectional shape corresponding to the cross-sectional shape of the through-hole  51  of the polishing pad  1 . In the present embodiment, since the through-hole  51  of the polishing pad  1  has an elliptical cross section, the cross section of the second positioning protrusion  78  is in an elliptical shape slightly smaller than the cross section of the through-hole  51  of the polishing pad  1 . A length H of the second positioning protrusion  78  along a central axis CL of the second positioning protrusion  78  is equal to or greater than the thickness of the polishing pad  1 . 
     The polishing pad  1  is attached to the polishing table  3  as follows using the positioning structure  75  as a polishing-pad positioning instrument. First, as shown in  FIG.  10   , the polishing-pad laminated structure  60  from which the first release sheet  62 A has been removed is placed on the pad support surface  3   b  of the polishing table  3 . Next, as shown in  FIGS.  11 A and  11 B  and  FIG.  9   , the first positioning protrusion  77  of the positioning structure  75  is inserted into the drain hole  50 B of the polishing table  3  through the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. Further, the second positioning protrusion  78  is inserted into the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. The through-hole  51  of the polishing pad  1  is aligned with the sensor head  31  disposed in the polishing table  3  by the second positioning protrusion  78  inserted into the through-hole  51  of the polishing pad  1 . 
     Next, the exposed portion (i.e., the portion that has been covered by the first release sheet  62 A) of the adhesive surface (back surface)  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . Thus, the relative position of the polishing-pad laminated structure  60  with respect to the polishing table  3  is fixed. Thereafter, the positioning structure  75  is removed from the polishing table  3  and the polishing pad  1 . Furthermore, the second release sheet  62 B is peeled off from the polishing pad  1 , and the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
     According to the present embodiment, the positioning of the polishing pad  1  with respect to the polishing table  3  is completed by inserting the second positioning protrusion  78  of the positioning structure  75  into the through-hole  51  of the polishing pad  1 . Thus, the attaching work of the polishing pad  1  can be facilitated. 
     In one embodiment, the positioning structure  75  may be attached to the polishing table  3  before the polishing pad  1  is placed on the polishing table  3 . Specifically, first, the first positioning protrusion  77  of the positioning structure  75  is inserted into the drain hole  50 B of the polishing table  3 . Next, the polishing-pad laminated structure  60  from which the first release sheet  62 A has been removed is placed on the pad support surface  3   b  of the polishing table  3 . At this time, the second positioning protrusion  78  is inserted into the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. The through-hole  51  of the polishing pad  1  is aligned with the sensor head  31  disposed in the polishing table  3  by the second positioning protrusion  78  inserted into the through-hole  51  of the polishing pad  1 . Next, the exposed portion (i.e., the portion that has been covered by the first release sheet  62 A) of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . Thus, the relative position of the polishing-pad laminated structure  60  with respect to the polishing table  3  is fixed. Thereafter, the positioning structure  75  is removed from the polishing table  3  and the polishing pad  1 . Furthermore, the second release sheet  62 B is peeled off from the polishing pad  1 , and the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
       FIG.  12    is a perspective view showing another embodiment of a polishing-pad positioning instrument,  FIG.  13    is a front view of the polishing-pad positioning instrument shown in  FIG.  12   , and  FIG.  14    is a cross-sectional view taken along a line C-C of  FIG.  13   . In the present embodiment, a polishing-pad positioning instrument  80  includes a support structure  83  for supporting the second positioning protrusion  78  of the positioning structure  75 . The support structure  83  serves as a structure for preventing the entire positioning structure  75  from falling when the first positioning protrusion  77  is inserted into the drain hole  50 B of the polishing table  3 . The entire first positioning protrusion  77  and the lower portion of the second positioning protrusion  78  project downward from a bottom surface  83   a  of the support structure  83 . 
     In order to stabilize the posture of the positioning structure  75 , the bottom surface  83   a  of the support structure  83  is perpendicular to the central axis CL (see  FIG.  14   ) of the second positioning protrusion  78 . In the present embodiment, the support structure  83  has a cross shape. However, the entire support structure  83  may have another shape such as a flat plate shape or a disk shape, as long as the bottom surface  83   a  of the support structure  83  is perpendicular to the central axis CL of the second positioning protrusion  78 . In the present embodiment, a handle  86  is secured to the top of the support structure  83 . 
     As shown in  FIG.  14   , the support structure  83  has a vertical hole  83   b  extending perpendicularly to the bottom surface  83   a . The upper portion of the second positioning protrusion  78  is housed in the vertical hole  83   b . The second positioning protrusion  78  is supported by the support structure  83  so as to be movable along the central axis CL of the second positioning protrusion  78 . The polishing-pad positioning instrument  80  includes a spring  88  disposed between the second positioning protrusion  78  and the support structure  83 . The spring  88  is located in the vertical hole  83   b  and configured to force the positioning structure  75  in an extending direction of the central axis CL of the second positioning protrusion  78 . The structure and position of the spring  88  are not limited to this embodiment as long as the spring  88  can force the positioning structure  75  in the extending direction of the central axis CL of the second positioning protrusion  78 . In the present embodiment, the extending direction of the central axis CL of the second positioning protrusion  78  is parallel to the longitudinal direction of the first positioning protrusion  77 . 
     The polishing-pad positioning instrument  80  shown in  FIG.  12    is used as follows. First, as shown in  FIG.  15   , the polishing-pad laminated structure  60  from which the first release sheet  62 A has been removed is placed on the pad support surface  3   b  of the polishing table  3 . Next, as shown in  FIGS.  16 A and  16 B , the polishing-pad positioning instrument  80  is placed on the polishing pad  1 . At this time, as shown in  FIG.  17   , the first positioning protrusion  77  is inserted into the drain hole  50 B of the polishing table  3  through the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. Further, the second positioning protrusion  78  is inserted into the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. The through-hole  51  of the polishing pad  1  is aligned with the sensor head  31  disposed in the polishing table  3  by the second positioning protrusion  78  inserted into the through-hole  51  of the polishing pad  1 . 
     Next, while the polishing pad  1  is being pressed against the polishing table  3  by the support structure  83  of the polishing-pad positioning instrument  80 , the exposed portion (i.e., the portion that has been covered with the first release sheet  62 A) of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . Thus, the relative position of the polishing-pad laminated structure  60  with respect to the polishing table  3  is fixed. When the polishing-pad positioning instrument  80  is pressed against the upper surface (polishing surface)  1   a  of the polishing pad  1 , the support structure  83  is moved against the force of the spring  88 , until the bottom surface  83   a  of the support structure  83  is brought into contact with the upper surface (polishing surface)  1   a  of the polishing pad  1 . Therefore, the support structure  83  of the polishing-pad positioning instrument  80  can press the polishing pad  1  against the polishing table  3  while the first positioning protrusion  77  is inserted into the drain hole  50 B. 
     After the exposed portion of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 , the polishing-pad positioning instrument  80  is removed from the polishing table  3  and the polishing pad  1 . Further, the second release sheet  62 B is peeled off from the polishing pad  1 , and the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
       FIGS.  18 A and  18 B  are perspective views each showing still another embodiment of a polishing-pad positioning instrument  80 . The polishing-pad positioning instrument  80  includes a plate-shaped support structure  83  to which the positioning structure  75  is detachably attached. As shown in  FIG.  18 A , a slit  83   c  is formed in one edge of the support structure  83 . This slit  83   c  has a shape with which the second positioning protrusion  78  of the positioning structure  75  can engage. The second positioning protrusion  78  is slid into the slit  83   c , so that the positioning structure  75  is attached to the support structure  83  as shown in  FIG.  18 B . A string  90  is connected to the opposite edge of the support structure  83 . 
     The polishing-pad positioning instrument  80  shown in  FIGS.  18 A and  18 B  is used as follows. First, as shown in  FIGS.  19 A and  19 B , the bottom surface  83   a  of the support structure  83  is placed on the pad support surface  3   b  of the polishing table  3  while the first positioning protrusion  77  of the polishing-pad positioning instrument  80  is inserted into the drain hole  50 B of the polishing table  3 . Next, as shown in  FIG.  20   , the polishing-pad laminated structure  60  from which the first release sheet  62 A has been peeled off is placed on the pad support surface  3   b  of the polishing table  3  and the support structure  83 . At this time, as shown in  FIG.  21   , the second positioning protrusion  78  is inserted into the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. The through-hole  51  of the polishing pad  1  is aligned with the sensor head  31  disposed in the polishing table  3  by the second positioning protrusion  78  inserted into the through-hole  51  of the polishing pad  1 . 
     Next, the exposed portion (i.e., the portion that has been covered with the first release sheet  62 A) of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . Thus, the relative position of the polishing-pad laminated structure  60  with respect to the polishing table  3  is fixed. The string  90  is pulled in a direction of an arrow shown in  FIG.  20    to pull out the support structure  83  from the polishing table  3 , thereby leaving the positioning structure  75  on the polishing table  3  as shown in  FIG.  22   . Next, the positioning structure  75  is removed from the polishing table  3  and the polishing pad  1 . Further, the second release sheet  62 B is peeled off from the polishing pad  1 , and the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
     In one embodiment, the polishing-pad positioning instrument  80  shown in  FIGS.  18 A and  18 B  may be used as follows. First, as shown in  FIG.  23   , the polishing-pad laminated structure  60  from which the first release sheet  62 A has been removed is placed on the pad support surface  3   b  of the polishing table  3 . Next, as shown in  FIG.  24   , the polishing-pad positioning instrument  80  is placed on the polishing pad  1 . At this time, as shown in  FIG.  25   , the first positioning protrusion  77  is inserted into the drain hole  50 B of the polishing table  3  through the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. Further, the positioning protrusion  78  is inserted into the through-hole  51  of the polishing pad  1  and the through-hole  65  of the second release sheet  62 B. The through-hole  51  of the polishing pad  1  is aligned with the sensor head  31  disposed in the polishing table  3  by the second positioning protrusion  78  inserted into the through-hole  51  of the polishing pad  1 . 
     Next, while the polishing pad  1  is being pressed against the polishing table  3  by the support structure  83  of the polishing-pad positioning instrument  80 , the exposed portion (i.e., the portion that has been covered with the first release sheet  62 A) of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . Thus, the relative position of the polishing-pad laminated structure  60  with respect to the polishing table  3  is fixed. Thereafter, the polishing-pad positioning instrument  80  is removed from the polishing table  3 . Further, the second release sheet  62 B is peeled off from the polishing pad  1 , and the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
       FIG.  26 A  is a top view showing another embodiment of a polishing-pad laminated structure  60 , and  FIG.  26 B  is a backside view of the polishing-pad laminated structure  60  shown in  FIG.  26 A . Configurations, which are not particularly described, are the same as those of the embodiment described with reference to  FIG.  4    to  FIG.  6   , and will not be described in duplication. In the present embodiment, a release sheet  62  is divided into a first release sheet  62 A, a second release sheet  62 B, and a third release sheet  62 C. The first release sheet  62 A is located at the center of the polishing pad  1  and extends from one side to the opposite side of the polishing pad  1 . The second release sheet  62 B and the third release sheet  62 C are arranged to sandwich the first release sheet  62 A. The first release sheet  62 A has a band shape, and each of the second release sheet  62 B and the third release sheet  62 C has a half-moon shape. A surface area of the first release sheet  62 A is smaller than a surface area of the second release sheet  62 B and a surface area of the third release sheet  62 C. In the present embodiment, the through-hole  51  of the polishing pad  1  are covered with the first release sheet  62 A. No through-hole communicating with the through-hole  51  is formed in the release sheet  62  including the first release sheet  62 A, the second release sheet  62 B, and the third release sheet  62 C. In one embodiment, a through-hole communicating with the through-hole  51  may be formed in the release sheet  62 . 
     Three release assisting projections  67 B are connected to the second release sheet  62 B. One of the three release assisting projections  67 B is connected to an inner edge of the second release sheet  62 B, and the other two release assisting projections  67 B are connected to both outer edges of the second release sheet  62 B. It is noted, however, the arrangement of the release assisting projections  67 B is not limited to the present embodiment. In one embodiment, only one or only two of the three release assisting projections  67 B may be provided. In one embodiment, four or more release assisting projections  67 B may be connected to the second release sheet  62 B. A plurality of release assisting projections  67 B may be connected to the inner edge of the second release sheet  62 B, or three or more release assisting projections  67 B may be connected to the outer edge of the second release sheet  62 B. Further, in one embodiment, the release assisting projection  67 B may not be provided. 
     Three release assisting projections  67 C are connected to the third release sheet  62 C. One of the three release assisting projections  67 C is connected to an inner edge of the third release sheet  62 C, and the other two release assisting projections  67 C are connected to both outer edges of the third release sheet  62 C. It is noted, however, the arrangement of the release assisting projections  67 C is not limited to the present embodiment. In one embodiment, only one or only two of the three release assisting projections  67 C may be provided. In one embodiment, four or more release assisting projections  67 C may be connected to the third release sheet  62 C. A plurality of release assisting projections  67 C may be connected to the inner edge of the third release sheet  62 C, or three or more release assisting projections  67 C may be connected to the outer edge of the third release sheet  62 C. Further, in one embodiment, the release assisting projection  67 C may not be provided. 
     In the present embodiment, no release assisting projection is connected to the first release sheet  62 A. However, a release assisting projection for assisting the removing of the first release sheet  62 A may be connected to the first release sheet  62 A. 
     The attaching operation of the polishing pad  1  is performed in the same manner as the flowchart shown in  FIG.  7   . Specifically, a user peels off the first release sheet  62 A from the adhesive surface  1   b  of the polishing pad  1 . The polishing-pad laminated structure  60  is placed on the pad support surface  3   b  of the polishing table  3  with the second release sheet  62 B and the third release sheet  62 C covering the adhesive surface  1   b  of the polishing pad  1 . Although the first release sheet  62 A has been removed from the polishing pad  1 , at this stage the exposed portion of the adhesive surface  1   b  of the polishing pad  1  (i.e., the portion that has been covered by the first release sheet  62 A) does not adhere to the pad support surface  3   b  of the polishing table  3 . 
     In this embodiment, the adhesive surface  1   b  is exposed around the through-hole  51  of the polishing pad  1 . However, the exposed area of the adhesive surface  1   b  is small, and the exposed portion of the adhesive surface  1   b  is located between the second release sheet  62 B and the third release sheet  62 C. As a result, even when the polishing-pad laminated structure  60  is placed on the pad support surface  3   b  of the polishing table  3 , the exposed portion of the adhesive surface  1   b  is not likely to contact the pad support surface  3   b . Therefore, the polishing-pad laminated structure  60  can be freely moved on the polishing table  3 . 
     Next, the through-hole  51  of the polishing pad  1  is aligned with the sensor head  31  disposed in the polishing table  3 . As described above, since the polishing-pad laminated structure  60  can be freely moved on the polishing table  3 , the through-hole  51  of the polishing pad  1  can be precisely aligned with the sensor head  31 . With the through-hole  51  of the polishing pad  1  aligned with the sensor head  31 , the exposed portion of the adhesive surface  1   b  of the polishing pad  1  is strongly pressed against the pad support surface  3   b  of the polishing table  3 , whereby the portion of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . As a result, the relative position of the polishing-pad laminated structure  60  with respect to the polishing table  3  is fixed. 
     The user grips the release assisting projections  67 B with fingers and peels off the second release sheet  62 B from the adhesive surface  1   b  of the polishing pad  1 . A new exposed portion of the adhesive surface  1   b  of the polishing pad  1  is strongly pressed against the pad support surface  3   b  of the polishing table  3 . Further, the user grips the release assisting projections  67 C with fingers, and peels off the third release sheet  62 C from the adhesive surface  1   b  of the polishing pad  1 . Then, the remaining part of the adhesive surface  1   b  of the polishing pad  1  is strongly pressed against the pad support surface  3   b  of the polishing table  3 , whereby the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . In one embodiment, the third release sheet  62 C may be removed from the adhesive surface  1   b  of the polishing pad  1 , and then the second release sheet  62 B may be removed from the adhesive surface  1   b  of the polishing pad  1 . 
       FIG.  27 A  is a top view showing still another embodiment of a polishing-pad laminated structure  60 , and  FIG.  27 B  is a backside view of the polishing-pad laminated structure  60  shown in  FIG.  27 A . Configurations, which are not particularly described, are the same as those of the embodiment described with reference to  FIG.  4    to  FIG.  6   , and will not be described in duplication. A release sheet  62  is divided into a first release sheet  62 A, a second release sheet  62 B, and a third release sheet  62 C. In the present embodiment, the through-hole  51  of the polishing pad  1  are covered with the first release sheet  62 A. No through-hole communicating with the through-hole  51  is formed in the release sheet  62  including the first release sheet  62 A, the second release sheet  62 B, and the third release sheet  62 C. In one embodiment, a through-hole communicating with the through-hole  51  may be formed in the release sheet  62 . 
     The first release sheet  62 A has a rectangular shape. The entire first release sheet  62 A is surrounded by the second release sheet  62 B and the third release sheet  62 C. Each of the second release sheet  62 B and the third release sheet  62 C has a half-moon shape. A surface area of the first release sheet  62 A is smaller than a surface area of the second release sheet  62 B and a surface area of the third release sheet  62 C. 
     Three release assisting projections  67 B are connected to the second release sheet  62 B. One of the three release assisting projections  67 B is connected to an inner edge of the second release sheet  62 B, and the other two release assisting projections  67 B are connected to both outer edges of the second release sheet  62 B. It is noted, however, the arrangement of the release assisting projections  67 B is not limited to the present embodiment. In one embodiment, only one or only two of the three release assisting projections  67 B may be provided. In one embodiment, four or more release assisting projections  67 B may be connected to the second release sheet  62 B. A plurality of release assisting projections  67 B may be connected to the inner edge of the second release sheet  62 B, or three or more release assisting projections  67 B may be connected to the outer edge of the second release sheet  62 B. Further, in one embodiment, the release assisting projection  67 B may not be provided. 
     Three release assisting projections  67 C are connected to the third release sheet  62 C. One of the three release assisting projections  67 C is connected to an inner edge of the third release sheet  62 C, and the other two release assisting projections  67 C are connected to both outer edges of the third release sheet  62 C. It is noted, however, the arrangement of the release assisting projections  67 C is not limited to the present embodiment. In one embodiment, only one or only two of the three release assisting projections  67 C may be provided. In one embodiment, four or more release assisting projections  67 C may be connected to the third release sheet  62 C. A plurality of release assisting projections  67 C may be connected to the inner edge of the third release sheet  62 C, or three or more release assisting projections  67 C may be connected to the outer edge of the third release sheet  62 C. Further, in one embodiment, the release assisting projection  67 C may not be provided. 
     In the present embodiment, no release assisting projection is connected to the first release sheet  62 A. However, a release assisting projection for assisting the removing of the first release sheet  62 A may be connected to the first peeling sheet  62 A. 
     The attaching operation of the polishing pad  1  is performed in the same manner as the embodiment shown in  FIGS.  26 A and  26 B , and thus repetitive descriptions thereof will not be omitted. 
     Also in this embodiment, the adhesive surface  1   b  is exposed around the through-hole  51  of the polishing pad  1 , but the exposed area of the adhesive surface  1   b  is small, and the entire exposed portion of the adhesive surface  1   b  is surrounded by the second release sheet  62 B and the third release sheet  62 C. As a result, when the polishing-pad laminated structure  60  is placed on the pad support surface  3   b  of the polishing table  3 , the exposed portion of the adhesive surface  1   b  is not likely to contact the pad support surface  3   b . Therefore, the polishing-pad laminated structure  60  can be freely moved on the polishing table  3 . 
     The positioning structure  75  as the polishing-pad positioning instrument shown in  FIGS.  8 A and  8 B , the polishing-pad positioning instrument  80  shown in  FIG.  12   , and the polishing-pad positioning instrument  80  shown in  FIGS.  18 A and  18 B  can be used to attach the polishing pad  1  shown in  FIG.  26 A  and  FIG.  26 B  and the polishing pad  1  shown in  FIG.  27 A  and  FIG.  27 B  to the polishing pad  3 . 
     Although only one sensor head  31  is provided in the polishing table  3  in the embodiments described above, the present invention can be applied to a polishing apparatus including a polishing table  3  in which a plurality of sensor heads  31  are disposed as shown in  FIG.  28   . Two sensor heads  31  are arranged in the embodiment shown in  FIG.  28   , while the polishing apparatus may include three or more sensor heads  31 , and the polishing pad  1  may have three or more through-holes  51 . 
       FIG.  29 A  is a top view showing an embodiment of a polishing-pad laminated structure  60  used for the polishing table  3  in which two sensor heads  31  are disposed, and  FIG.  29 B  is a top view of the polishing-pad laminated structure  60  shown in  FIG.  29 A . Configurations, which are not particularly described, are the same as those of the embodiment described with reference to  FIG.  4    to  FIG.  6   , and will not be described in duplication. As shown in  FIG.  29 A , a polishing pad  1  has two through-holes  51  corresponding to the two sensor heads  31 . Positions of these two through-holes  51  correspond to positions of the two sensor heads  31  in the polishing table  3 . Further, as shown in  FIG.  29 B , a release sheet  62  has two through-holes  65  at the same positions as those of the through-holes  51  of the polishing pad  1 . 
     The attaching operation of the polishing pad  1  shown in  FIG.  29 A  is performed using a polishing-pad positioning instrument including two positioning structures  75 . More specifically, the attaching operation of the polishing pad  1  shown in  FIG.  29 A  is carried out in the same manner as the embodiment described with reference to the flowchart shown in  FIG.  7   , or the embodiment described with reference to  FIGS.  10  to  11 B , or the embodiment described with reference to  FIGS.  15  to  17   , or the embodiment described with reference to  FIGS.  19 A to  22   , or the embodiment described with reference to  FIGS.  23  to  25   . 
       FIG.  30    is a perspective view showing an embodiment of a polishing-pad positioning instrument  80  suitable for the polishing-pad laminated structure  60  shown in  FIGS.  29 A and  29 B ,  FIG.  31    is a front view of the polishing-pad positioning instrument  80  shown in  FIG.  30   , and  FIG.  32    is a cross-sectional view taken along a line D-D of  FIG.  31   . Configurations of the present embodiment, which are not particularly described, are the same as those of the embodiment described with reference to  FIGS.  12  to  14   , and thus repetitive descriptions will be omitted. 
     The polishing-pad positioning instrument  80  of the present embodiment includes two positioning structures  75 . The positions of these positioning structures  75  correspond to the positions of the two sensor heads  31  installed in the polishing table  3 . The method of using the polishing-pad positioning instrument  80  according to the present embodiment is the same as the embodiment described with reference to  FIGS.  15  to  17   , and thus repetitive descriptions will be omitted. 
       FIGS.  33 A and  33 B  are perspective views each showing another embodiment of a polishing-pad positioning instrument  80  suitable for the polishing-pad laminated structure  60  shown in  FIGS.  29 A and  29 B . Configurations of the present embodiment, which are not particularly described, are the same as those of the embodiment described with reference to  FIGS.  18 A and  18 B , and thus repetitive descriptions will be omitted. 
     The polishing-pad positioning instrument  80  of the present embodiment includes two positioning structures  75  detachably attached to a support structure  83 . More specifically, two slits  83   c , with which the second positioning protrusions  78  of the positioning structures  75  engage, are formed in one edge of the support structure  83 . The second positioning protrusions  78  of the respective positioning structures  75  are slid into the slits  83   c , so that the two positioning structures  75  are attached to the support structure  83 , as shown in  FIG.  33 B . The method of using the polishing-pad positioning instrument  80  according to the present embodiment is the same as the embodiment described with reference to  FIGS.  19 A to  22    or the embodiment described with reference to  FIGS.  23  to  25   , and thus repetitive descriptions will be omitted. 
       FIG.  34    is a perspective view showing another embodiment of a polishing-pad positioning instrument  80  suitable for the polishing-pad laminated structure  60  shown in  FIGS.  29 A and  29 B , and  FIG.  35    is a front view of the polishing-pad positioning instrument  80  shown in  FIG.  34   . Configurations of the present embodiment, which are not particularly described, are the same as those of the embodiment described with reference to  FIGS.  33 A and  33 B , and thus repetitive descriptions will be omitted. 
     The polishing-pad positioning instrument  80  of the present embodiment has a handle  86 . This handle  86  includes two pedestals  93  for supporting the second positioning protrusions  78  of the two positioning structures  75 , respectively, and a rod  94  extending between the pedestals  93 . Both ends of the rod  94  are fixed to the two pedestals  93 , respectively. Each pedestal  93  has a vertical hole  93   a  extending perpendicularly to a bottom surface thereof, so that the corresponding second positioning protrusion  78  can be fitted into the vertical hole  93   a . As shown in  FIG.  35   , the handle  86  is placed on the polishing-pad laminated structure  60 . The upper portions of the second positioning protrusions  78 , extending through the through-holes  51  of the polishing-pad laminated structure  60 , are inserted into the vertical holes  93   a  of the pedestals  93 , respectively. 
     The polishing-pad positioning instrument  80  shown in  FIG.  34    is used as follows. First, as shown in  FIGS.  36 A and  36 B , the bottom  83   a  of the support structure  83  is placed on the pad support surface  3   b  of the polishing table  3  while the first positioning protrusions  77  of the polishing-pad positioning instrument  80  are inserted into the drain holes  50 B of the polishing table  3 . Next, as shown in  FIG.  37   , the polishing-pad laminated structure  60  from which the first release sheet  62 A has been peeled off is placed on the pad support surface  3   b  of the polishing table  3  and the support structure  83 . At this time, the second positioning protrusions  78  are inserted into the through-holes  51  of the polishing pad  1  and the through-holes  65  of the second release sheet  62 B (see  FIG.  21   ). The through-holes  51  of the polishing pad  1  are aligned with the sensor heads  31 , respectively, disposed in the polishing table  3  by the second positioning protrusions  78  inserted into the through-holes  51  of the polishing pad  1 . 
     The exposed portion (i.e., the portion that has been covered with the first release sheet  62 A) of the adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . Thus, the relative position of the polishing-pad laminated structure  60  with respect to the polishing table  3  is fixed. As shown in  FIG.  38   , the handle  86  is attached to the positioning structures  75 . More specifically, the second positioning protrusions  78 , protruding upward from the polishing-pad laminated structure  60 , are inserted into the vertical holes  93   a  (see  FIG.  35   ) of the pedestals  93 . While the handle  86  is being pressed against the polishing-pad laminated structure  60  so that the positioning structures  75  do not fall down, the support structure  83  is pulled out of the polishing table  3  by pulling the string  90  in the direction of the arrow shown in  FIG.  38   . Next, the handle  86  and the positioning structures  75  are removed from the polishing-pad laminated structure  60 . Furthermore, the second release sheet  62 B is peeled off from the polishing pad  1 , and the entire adhesive surface  1   b  of the polishing pad  1  is attached to the pad support surface  3   b  of the polishing table  3 . 
       FIG.  39 A  is a top view showing another embodiment of a polishing-pad laminated structure  60  used for the polishing table  3  in which the two sensor heads  31  are arranged, and  FIG.  39 B  is a backside view of the polishing-pad laminated structure  60  shown in  FIG.  39 A . Configurations, which are not particularly described, are the same as those of the embodiment described with reference to  FIGS.  26 A and  26 B , and thus the description thereof will not be repeated. As shown in  FIG.  39 A , a polishing pad  1  has two through-holes  51  corresponding to the two sensor heads  31 . The positions of these two through-holes  51  correspond to the positions of the two sensor heads  31  in the polishing table  3 . As shown in  FIG.  39 B , a release sheet  62  is divided into a first release sheet  62 A, a second release sheet  62 B, and a third release sheet  62 C. 
       FIG.  40 A  is a top view showing still another embodiment of a polishing-pad laminated structure  60  used for the polishing table  3  in which the two sensor heads  31  are arranged, and  FIG.  40 B  is a backside view of the polishing-pad laminated structure  60  shown in  FIG.  40 A . Configurations, which are not particularly described, are the same as those of the embodiment described with reference to  FIGS.  27 A and  27 B , and thus the description thereof will not be repeated. As shown in  FIG.  40 A , a polishing pad  1  has two through-holes  51  corresponding to the two sensor heads  31 . The positions of these two through-holes  51  correspond to the positions of the two sensor heads  31  in the polishing table  3 . As shown in  FIG.  40 B , a release sheet  62  is divided into two first release sheets  62 A, a second release sheet  62 B, and a third release sheet  62 C. 
     The polishing-pad positioning instrument  80  shown in  FIG.  30   , the polishing-pad positioning instrument  80  shown in  FIGS.  33 A and  33 B , and the polishing-pad positioning instrument  80  shown in  FIGS.  34  and  35    can be used for attaching the polishing pad  1  shown in  FIG.  39 A  and the polishing pad  1  shown in  FIG.  40 A  to the pad support surface  3   b  of the polishing table  3 . 
     The number and positions of the through-holes  51  of the polishing pad  1  are determined based on the number and positions of the sensor heads  31  disposed in the polishing table  3 . The number and position of the sensor heads  31  are not limited to the embodiments described above. In one embodiment, three or more sensor heads  31  may be arranged. The same number of through-holes  51  of the polishing pad  1  is formed at the same positions of the sensor heads  31 . For example, as shown in  FIGS.  41 A,  41 B,  42 A,  42 B,  43 A, and  43 B , a polishing pad  1  may have three through-holes  51 . 
     The shape of the positioning structure  75  is not limited to the embodiments described above. In particular, the shape and the size of the first positioning protrusion  77  are determined based on the table hole provided in the polishing table  3 . For example, as shown in  FIG.  44   , the cross section of the first positioning protrusion  77  may have the same shape and the same size as those of the cross section of the second positioning protrusion  78 . Furthermore, in one embodiment, the cross section of the first positioning protrusion  77  may be larger than the cross section of the second positioning protrusion  78 . 
     The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.