FIELD OF THE INVENTION 
     The present invention relates to a polishing pad used for a material to be polished such as semiconductors, electronic components, and the like. More specifically, it relates to a polishing pad for use in a polishing machine utilizing chemical-mechanical polishing (CMP) technology wherein a transparent window member is formed on a part of the polishing pad so as to let a laser beam or visible light pass therethrough to detect the end point of polishing rate (the amount of wafer material removed by polishing during a unit time interval) of the wafer surface during polishing. 
     BACKGROUND OF THE INVENTION 
     In recent years, chip manufacturing has increasingly relied upon multi-layer structures to fabricate integrated circuits or ICs. During multi-layer IC circuit manufacturing, it is necessary that each layer of the IC circuit structure on a semiconductor wafer be planarized to maintain controlled electrical properties. 
     Planarization is performed by CMP (chemical mechanical planarization) also referred to as chemical-mechanical polishing using a polishing machine that comprises a lower platen having a circular rotating plate on which a polishing pad is attached; and an upper platen that presses a wafer onto the polishing pad; and a means for supplying a polishing slurry. 
     A polishing machine utilizing CMP technology employs a method for measuring the polishing rate while a wafer surface is being polished. The method requires that a laser beam be emitted from the rear side (platen side) of the polishing pad toward the wafer surface to be polished, which requires a transparent window member on a part of the polishing pad to allow the laser beam to pass therethrough. 
     To improve slurry dispersibility on the pad body surface, one can provide perforations, which are a group of minute openings, on the entire pad surface. This method has a drawback in that, if the openings are formed on a window member, slurry may leak through these openings or may agglomerate in the openings, which creates noise during measurement of the polishing rate of a wafer and adversely impacts accuracy of these measurements. Conventional technology has overcome this drawback by keeping the window member free from perforations. Nonetheless, the manufacturing methods required to produce these pads are inefficient. 
     In view of these concerns, there is a desire to manufacture a polishing pad in an effective manner that eliminates the cumbersome perforation steps of conventional technologies required to avoid puncturing the transparent window. 
     SUMMARY OF THE INVENTION 
     The invention provides a method of forming a transparent polishing pad. The first step forms a plurality of openings through a disk-shaped pad body. The plurality of openings is distributed about the disk-shaped pad body and a transparent window within a portion of the pad body and the transparent window. Then sealing the openings in the transparent window with a transparent material allows transport of polishing fluids through the openings in the disk-shaped pad body and prevents transport of the polishing fluids through the transparent window. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of working example 1 of the polishing pad. 
     FIG. 2 is a plan view of the polishing pad illustrated in FIG.  1 . 
     FIG. 3 is an enlarged cross section of the opening portion of the polishing pad illustrated in FIG.  2 . 
     FIG. 4 is an enlarged cross section of the opening portion of the polishing pad illustrated in FIG.  2 . 
     FIG. 5 is an enlarged cross section of the opening portion of an alternate working example of the polishing pad. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The polishing pad of the present invention has openings extending through the width of the polishing pad on about an entire surface of the polishing pad body. These openings optimize the slurry retention and discharge capabilities of the pad. The pad thus provides improved polishing uniformity with an increased polishing rate. Furthermore, the openings formed on a window member are sealed with a transparent material, which resolves the issue of slurry agglomeration in the openings. Sealing with a transparent material includes either filling the openings with the transparent material or covering the openings with a transparent film that is adhesively attached thereto. Consequently, accuracy of polishing rate measurements is not affected by the sealing. 
     As illustrated in FIGS. 1 and 2, polishing pad  100  comprises: a pad body  10  and a transparent window member  2  integrally formed with a part of pad body  10 . Pad body  10  is typically fabricated from a resin layer having minute pores. 
     Polishing pad  100  further comprises base layer  13  fabricated from a foamed layer and the like via pressure sensitive adhesive layer  12  on the rear side of pad body  10 . On its rear surface, base layer  13  is laminated with a separation sheet (not illustrated) via pressure sensitive adhesive layer  14 . The separation sheet is peeled so that pressure sensitive adhesive layer  14  can be stuck to a platen to prepare polishing pad  10  for planarization. 
     Pad body  10  is advantageously fabricated from one or more resins such as urethane, acrylic, polycarbonate, polyamide, polyester, and the like by a known casting or extrusion molding method, and the like. Most advantageously, pad body  10  is made of a thermoplastic resin among the above resins by the casting or extrusion molding method. However, it may also be made of a thermosetting resin by heating and curing the same. 
     Materials that window member  2  can be made of include those that pad body  10  advantageously include transparent resins such as polyvinyl chloride, poly (vinylidene fluoride). polyether sulfone, polystyrene, polyethylene, polytetrafluoroethylene, and the like. Any of these resins can be either cast molded or extrusion molded and cut into a desired size or thickness to provide window member  2 . 
     The openings  3  are formed about an entire surface of pad body  10  as described above. The desirable inner diameter of the openings  3  is 1-3 mm and the desirable density of the same is 2-5 openings/cm 2 . The openings in window member  2  are filled with a transparent material  4 . Transparent material  4  advantageously is a resin selected from the group consisting of polyurethane, polyester, acrylic, polycarbonate, nylon, polyvinyl chloride, poly (vinylidene fluoride), polyether sulfone, polyethylene, polystyrene, polytetrafuloloethylene, and the like. Alternatively, the same resin as that making up window member  2  may be filled into the openings  3  and cured to provide transparent material  4 . 
     As described, the openings  3  are filled with a transparent material  4  followed by sealing thereof. This keeps the openings  3  free from slurry migration so that agglomerated slurry will not cause noise when a laser beam passes through openings  3 . 
     Alternatively, a plurality of grooves may be formed on pad body  10  by a conventional method. The shape, size, or pattern of the grooves may be changed in accordance with one&#39;s objective. The grooves may be multiple concentric circles, for example. 
     Referring to FIGS. 3 and 4, a working example of the manufacturing method for the polishing pad is described herein. 
     Pad sheet materials may be obtained by the steps comprising: placing a block of transparent member constituting window member  2  in a mold; cast molding an opaque resin constituting pad body  10  in a mold to make a molded material; and slicing [sic, splitting] the molded material. Alternatively, when one intends to obtain a single polishing pad sheet in every batch, window member  2  may be poured in a mold followed by casting an opaque resin for pad body  10  in a mold. 
     The pad body  10  thus obtained is, then, perforated by a perforator in a manner such that the openings  3  are provided on an entire surface of pad body  10 . 
     Next, polishing pad body  10  is laminated in the order of pressure sensitive adhesive layer  12 , base layer  13 , pressure sensitive adhesive layer  14 , and a separation sheet to make polishing pad  100 . Base layer  13  is provided with an aperture  11  at the location of window member  2 . 
     Polishing pad  100  has many openings  3  that allow uniform distribution of polishing slurry supplied between the material to be polished with pad body  10  of polishing pad  100 . Uniform polishing is thus ensured, consequently eliminating the possibility of adversely affecting accurate measurements of polishing rate. 
     Note that in the above working example, the openings in window member  2  were filled with a resin; however, transparent film  5  such as a resin film, may also be adhesively attached to the front or rear surface of window member  2  as illustrated in FIG.  5 . Covering the front, rear or both surfaces of the window seals openings  3  protects the window member  2 . Most advantageously, the transparent film covers the front and rear of the window to prevent flow of the slurry into these openings. Transparent material  4  may also be used for transparent film  5 , which most advantageously is the same resin that window member  2  is made of. For example, when window member  2  is made of polyurethane, it is desirable that the transparent film  5  be made of polyurethane; and when window member  2  is made of polyester, it is advantageous that the transparent film  5  also be made of polyester resin film. 
     The present invention suppresses slurry agglomeration in the openings in a window member, and therefore does not affect the detection accuracy of polishing rate. Unlike polishing pads of conventional technology, the method does not require avoiding the window member when the pad body surface is perforated. This facilitates improved productivity for pad manufacturing.
The method forms a transparent polishing pad by first step forming a plurality of openings through a disk-shaped pad body. The plurality of openings is distributed about the disk-shaped pad body and a transparent window within a portion of the pad body and the transparent window. Then sealing the openings in the transparent window with a transparent material allows transport of polishing fluids through the openings in the disk-shaped pad body and prevents transport of the polishing fluids through the transparent window.