Patent Publication Number: US-2023158633-A1

Title: Polishing pad with window and method of manufacturing the same

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. § 119(a) to Korean application number 10-2021-0160738, filed on Nov. 19, 2021, in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     Various embodiments generally relate to a window insert type polishing pad, more particularly, to a polishing pad with a window insert having accurate sensing without a leakage of water to be readily used in a chemical mechanical polishing process, and a method of manufacturing the window insert-type polishing pad. 
     2. Related Art 
     A polishing pad may be an indispensable part in a chemical mechanical polishing (CMP) process, which is one of a plurality of semiconductor fabrication processes. The CMP process may include attaching a wafer to a head, contacting the wafer with a surface of the polishing pad on a platen, supplying slurry to a surface of the wafer and rotating the platen and the head to remove any unnecessary portion or debris on the wafer, thereby planarizing the surface of the wafer. 
     Recently, an end point detection apparatus including a real time pressure control (RTPC) sensor may measure a thickness of a layer to determine the flatness of the wafer and to detect an end point of the CMP process in an in-situ process. Endpoint detection methods are used to measure the endpoint of the etching process to prevent etching through the overlayers by stopping the etching process before the overlayers are etched through. 
     A window insert type polishing pad may be capable of detecting the end point of the CMP process that polishes the wafer by using a window installed at the polishing pad and the RTPC sensor installed at the window. 
     However, water leakage may be easily generated through a gap between a polished layer and a window block so that failure of the CMP process may easily occur and the metal layer of the wafer may not be accurately sensed. Further, the polishing pads may need to be frequently replaced before reaching the end of service due to the fear of such failures, which would lead to an increase in the consumption rate of the polishing pads. 
     SUMMARY 
     According to embodiments of the disclosure, there may be provided a window insert type polishing pad. The window insert type polishing pad may include a top pad layer and a window block. The top pad layer may include a groove pattern formed on an upper surface of the top pad layer. A first hole may be formed through the top pad layer. The window block may be inserted into the first hole. The top pad layer and the window block may have a structure satisfying Formula 1. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   3. 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   1 
                 
               
             
           
         
       
     
     In Formula 1, the gap may indicate a height difference between an upper surface of the top pad layer and an upper surface of the window block, the Thk RTPC  may indicate a thickness of the window block, and the Thk grv  may indicate a depth of the groove pattern. 
     In example embodiments, the polishing pad may further include a sub-pad layer arranged under the top pad layer. The sub-pad layer may include a second hole formed through a portion of the sub-pad layer corresponding to a position of the first hole. The second hole may have an area smaller than an area of the first hole. 
     In example embodiments, the polishing pad may further include a third adhesive layer formed on a lower surface of the window block. The sub-pad layer may include a thermally fused portion formed at a portion of the sub-pad layer adjacent to the lower surface of the window block. 
     In example embodiments, the top pad layer and the window block may have a structure satisfying Formula 2. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   1.9 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   2 
                 
               
             
           
         
       
     
     According to example embodiments, there may be provided a method of manufacturing a window insert type polishing pad. In the method of manufacturing the window insert type polishing pad, a window block may be inserted into a first hole formed through a top pad layer. A gap-controlling film may be arranged on a surface of the window block. The upper surface of the gap-controlling film may then be pressed. A gap corresponding to a thickness of the gap-controlling film may be formed between an upper surface of the top pad layer and an upper surface of the window block. 
     According to example embodiments, there may be provided a method of manufacturing a window insert type polishing pad. In the method of manufacturing the window insert type polishing pad, a first hole may be formed through a top pad layer having a groove pattern. A window block may be installed at the first hole to form the polishing pad including the top pad layer and the window block. The top pad layer and the window block may be formed by following Formula 1. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   3. 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   1 
                 
               
             
           
         
       
     
     In Formula 1, the gap may indicate a height difference between an upper surface of the top pad layer and an upper surface of the window block, the Thk RTPC  may indicate a thickness of the window block, and the Thk grv  may indicate a depth of the groove pattern. 
     In example embodiments, installing the window block may include installing the window block at the first hole, arranging a gap-controlling film on a surface of the window block, and pressing the gap-controlling film. A gap corresponding to a thickness of the gap-controlling film may be formed between an upper surface of the top pad layer and an upper surface of the window block. 
     In example embodiments, the top pad layer and the window block may be formed by following Formula 2. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   1.9 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   2 
                 
               
             
           
         
       
     
     In example embodiments, the method may further include forming a first adhesive layer and a sub-pad layer on a lower surface of the top pad layer. The method may further include bonding a sheet for the sub-pad layer to a lower surface of a sheet for the top pad layer using adhesive to form a bond structure including the sub-pad layer, the first adhesive layer and the top pad layer sequentially stacked. The sheet for the sub-pad layer may have a second hole having a cross sectional area smaller than a cross sectional area of the first hole. A third hole may be formed through the first adhesive layer. The third hole may have an area substantially the same as the area of the second hole. A moisture-curable adhesive may be coated on an upper surface of the first adhesive layer around the third hole. A window block may be installed at the first hole of the bond structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and another aspects, features and advantages of the subject matter of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1 A and  1 B  are a plan view illustrating a polishing pad in accordance with an embodiment of the disclosure; 
         FIG.  2    is a cross-sectional view taken along a line A-A′ in  FIGS.  1 A and  1 B ; 
         FIG.  3    is a cross-sectional view illustrating a polishing pad in accordance with an embodiment of the disclosure; 
         FIG.  4    is a cross-sectional view illustrating a polishing pad in accordance with an embodiment of the disclosure; 
         FIG.  5    illustrates a method of manufacturing a polishing pad in accordance with an embodiment of the disclosure; 
         FIGS.  6 A and  6 B  are a cross-sectional view illustrating a polishing pad manufacturing by Example Embodiment 1 and Example Embodiments 2 to 6; 
         FIGS.  7 A and  7 B  are a cross-sectional view illustrating a polishing pad manufacturing by Comparative Embodiment 1 and Comparative Embodiments 2 to 4; and 
         FIGS.  8 A and  8 B  are a cross-sectional view illustrating a polishing pad manufacturing by Comparative Embodiment 5 and Comparative Embodiments 6 to 8. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  1 A and  1 B  are a plan view illustrating a polishing pad in accordance with an embodiment of the disclosure and  FIG.  2    is a cross-sectional view taken along a line A-A′ in  FIGS.  1 A and  1 B . 
     Referring to  FIGS.  1 A,  1 B, and  2   , a polishing pad  10  may include a top pad layer  100  and a window block  200 . The top pad layer  100  and the window block  200  may have a structure defined by the following Formula 1. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   3. 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   1 
                 
               
             
           
         
       
     
     In Formula 1, the ‘Gap’ may indicate a height difference between an upper surface of the top pad layer  100  and an upper surface of the window block  200 , the Thk RTPC  may indicate a thickness of the window block  200 , and the Thk grv  may indicate a depth of a groove pattern formed at the upper surface of the top pad layer  100 . 
     As shown in  FIG.  1 A , the window block  200  may be arranged at an edge portion of the top pad layer  100  between the center and an outside edge of the top pad layer  100 . Alternatively, as shown in  FIG.  1 B , the window block  200  may be arranged at a central portion of the top pad layer  100 . 
     The top pad layer  100  may closely contact a wafer to polish a surface of the wafer. As shown in  FIG.  2   , the window block  200  may be inserted into the top pad layer  100 . A first hole  110  may be formed through the top pad layer  100 . The first hole  110  may be used for measuring a reflectivity of the wafer to detect an end point. The first hole  110  may have various shapes. Particularly, the first hole  110  may have a circular shape having a diameter of about 10 mm to about 100 mm, or an elliptical shape. Alternatively, the first hole  110  may have a quadrangular shape having a lateral length of about 10 mm to about 100 mm and a longitudinal length of about 10 mm to about 100 mm. The polishing pad  10  may have a viewing angle for accurately measuring the reflectivity of the wafer. For example, the first hole  110  may have an area of about 1 cm 2  to about 70 cm 2 , and preferably, about 6 cm 2  to about 15 cm 2 . 
     A groove pattern P may be formed on the upper surface of the top pad layer  100 . The groove pattern P may include a plurality of protrusions R and a plurality concave grooves C that are alternately arranged. The groove pattern P may function to maintain and renew a chemical agent for polishing the surface of the wafer, such as slurry, deionized water, etc. The groove pattern P may have various shapes determined by a pitch, a width, a depth, etc., of the concave grooves C. 
     The top pad layer  100  may further include a supporting portion arranged under the groove pattern P to support the groove pattern P. The top pad layer  100  may have an overall thickness of about 0.5 mm to about 5 mm inclusive of the groove pattern P. The depth Thk grv  of the groove pattern P, i.e., a depth of the concave groove C, may be about 0.1 mm to about 3 mm. The width of the concave groove C may be about 0.1 mm to about 2.0 mm. The depth Thk grv  of the groove pattern P may correspond to a thickness of the groove pattern P. 
     In  FIGS.  2  to  4   , the groove pattern P may include the protrusions R and the concave grooves C that are alternately arranged in concentric circles from a center portion, but embodiments of this disclosure are not limited thereto. For example, the groove pattern P may include protrusions R and concave grooves C that are linearly and alternately arranged without reference to the window block  200 . The groove pattern P may include protrusions R and concave grooves C repeatedly arranged like comb pattern. In other embodiments, the groove pattern P may include annular protrusions R and annular concave grooves C concentrically arranged around the window block  200 . Further, the groove pattern P may each include a complex shape rather than a single shape. 
     The window block  200  may be inserted into the first hole  110  of the top pad layer  100 . 
     The window block  200  may include a material that allows a high degree of light transmission and that has few or no bubbles or cavities that impede high light transmittance. The material may be selected to prevent moisture from infiltrating into the window block  200 , which results in improved detection accuracy of the end point detection process and prevents damage of the light transmission region. 
     The light transmittance of the window block  200  may be about 60% to about 90%. The reflectivity of the window block  200  may be about 1.45 to about 1.60. For example, when the thickness of the window block  200  may be about 2.4 mm, the light transmittance of the window block  200  may be about 65% to about 75% and the reflectivity of the window block  200  may be about 1.53 to about 1.57. 
     The window block  200  may be surface-treated to have a roughness of the upper surface of about 2.0 μm to about 4.0 μm. 
     The surface treatment may prevent an error of the end point detection caused by wear of the window block  200  in a chemical mechanical polishing (CMP) process. The surface treatment may provide the window block  200  with the above-mentioned range of the roughness using various processes. For example, the surface treatment may be performed using sandpaper at a speed of about 100 rpm to about 1,000 rpm under a pressure of about 0.1 psi to about 3.0 psi to achieve a desired surface roughness. 
     The window block  200  may have a wear rate that is substantially equal to or slightly higher than a wear rate of the top pad layer  100 . Thus, after performing the CMP process, the top pad layer  100  and the window block  200  may be removed together to prevent scratching of the wafer that may be caused by a protrusion of the window block  200 . 
     The window block  200  may have a planar area that is substantially the same as the area of the first hole  110 . The window block  200  may have an overall thickness of about 0.2 mm to about 5 mm. 
     As shown in  FIG.  2   , the upper surface of the window block  200  may be lower than the upper surface of the top pad layer  100  so that the polishing pad  10  may have a gap around a first hole  110 . Alternatively, the upper surface of the window block  200  may be substantially coplanar with the upper surface of the top pad layer  100  so that the polishing pad  10  may not have a gap. That is, the Gap may correspond to a height difference between the upper surface of the window block  200  and the upper surface of the top pad layer  100 . The Gap may be about 0.001 mm to about 2 mm. 
     The window block  200  may include a recess  210 . The recess  210  may be formed at a lower surface of the window block  200 . The recess  210  may provide the window block  200  with a thinner upper thickness common to the first hole  110  to increase the detection accuracy of the end point detection. The recess  210  may have a depth of about 0.1 mm to about 4 mm. The Thk RTPC  in Formula 1, i.e., the thickness of an upper portion of the window block  200 , may be a distance between an inner surface of the recess  210  and the upper surface of the window block  200 . 
     The polishing pad  10  may include the top pad layer  100  and the window block  200  and may have a structure defined by Formula 1 to optimize the service life of the polishing pads  10  and to decrease the consumption rate of the polishing pads  10 . 
     The ‘Gap’ in Formula 1 may be the height difference between the upper surface of the top pad layer  100  and the upper surface of the window block  200 . The ‘Thk RTPC ’ in Formula 1 may be the thickness of an upper portion of the window block  200 . The ‘Thk grv ’ in Formula 1 may be the depth of the groove pattern P. 
     When the polishing pad  10  is used beyond its expected service life, the groove pattern P may be worn and the window block  200  may be broken so that the slurry, the deionized water, etc., may leak. Furthermore, when the window block  200  is broken, this leakage may cause a failure of the CMP apparatus and may result in an abnormal wafer. 
     When a gap does not exist between the window block  200  and the top pad layer  100 , the wafer may be damaged by the window block  200 , which also generates failures. In addition, when an excessive gap is formed between the window block  200  and the top pad layer  100 , or any other deviation that creates a leak path between them, the slurry or the deionized water may be leak and result in thickness errors in the wafer. 
     In contrast, embodiments of the disclosure include polishing pads  10  with a proper gap without leak pathways. The polishing pad may be designed using Formula 1 to obtain the optimal life for the polishing pads  10 . Waste is reduced by reducing the number of exchanges of the polishing pad  10  that may have a remaining serviceable life for a new polishing pad. 
     Particularly, an optimal life time of a new polishing pad  10  may be calculated using the depth of the groove pattern P (Thk grv ) and the upper portion thickness (Thk RTPC ) of the window block  200 . An optimal life time of the used polishing pad  10  may be inferred from remaining thicknesses of the groove pattern P and the window block  200  after the polishing pad  10  is put into service. Thus, by monitoring these parameters, the polishing pad  10  may be used for its optimal life time without leakage, which decreases the consumption rate of the polishing pad  10 . 
     According to an embodiment, the polishing pad is designed so that the sum of the Gap value and the Thk RTPC  value is 1.1 to 3.0 times of the Thk grv  value, and, as a result, the polishing pad  10  can be fully used within an appropriate use time. Preferably, the gap between the window block  200  and the top pad layer  100  may be uniform to accurately calculate the end point detection. 
     An optimal life time of a conventional polishing pad may be reached when the depth of the groove pattern decreases to about 80% of an initial depth of the groove pattern. For example, if the depth of the groove pattern is about 1 mm, then the polishing pad may be used until the depth of the groove pattern is about 0.2 mm. Here, the groove pattern at an edge portion of the polishing pad may be more worn than inner portions. Thus, the optimal life time of the polishing pad may be determined when the average depth of the groove pattern is about 0.2 mm to about 0.35 mm. 
     Thus, to prevent damage to the window block  200  during the life time of the polishing pad  10 , a value obtained by dividing the sum of the thickness of the upper portion of window block  200  and the Gap by the depth of the groove pattern may proportionally express the optimal life time of the window block  200  in the polishing pad  10 . The inventors have verified that the probability of breakage in the window block  200  is highest when the thickness of the upper portion of the window block  200  is about 200 μm to about 350 μm. 
     Therefore, the polishing pad  10  should be used until the thickness Thk RTPC  of the window block  200  is 0.2 mm to about 0.35 mm. The polishing pad  10  may then be exchanged for a new one when the thickness Thk RTPC  of the window block  200  may be about 0.2 mm to 0.35 mm. That is, the optimal life time of the polishing pad  10  may be a point at which the thickness Thk RTPC  of the window block  200  may be 0.2 mm to 0.35 mm in the polishing pad  10 , with a corresponding Gap used in Formula 1. 
     The polishing pad  10  may further include a sub-pad layer  300 . The sub-pad layer  300  may support the top pad layer  100  to help absorb and distribute impacts applied to the top pad layer  100 . The sub-pad layer  300  may include a material having a hardness that is lower than the hardness of the top pad layer  100 . 
     The sub-pad layer  300  may include a second hole  310 . The second hole  310  may be formed through a portion of the sub-pad layer  300  corresponding to the first hole  110 . The second hole  310  may be connected to the first hole  110  to form a structure configured to detect the end point through the window block  200 . 
     The second hole  310  may have an area that is smaller than the area of the first hole  110 . For example, the second hole  310  may have a circular shape having a diameter of about 5 mm to about 95 mm, or an elliptical shape. Alternatively, the second hole  310  may have a quadrangular shape having a lateral length of about 5 mm to about 95 mm and a longitudinal length of about 5 mm to about 95 mm. Thus, the polishing pad  10  may have an opening that allows a viewing angle for accurately measuring the reflectivity of the wafer. For example, in a plan view, the areas of the second hole  310  may be about 0.5 cm 2  to 50 cm 2 , and preferably, about 4 cm 2  to about 12 cm 2 . 
     The sub-pad layer  300  may have a thickness of about 0.1 mm to about 3.0 mm, and preferably, about 0.4 mm to about 2.0 mm. 
     The sub-pad layer  300  may be formed using a non-woven fabric or a porous pad. The sub-pad layer  300  may have a porous structure. 
     The pores in the sub-pad layer  300  may have an open cell structure. The pores in the sub-pad layer  300  may have a shape that extends in a thickness direction of the sub-pad layer  300 . A pores formation ratio of the sub-pad layer  300  may be higher than a pores formation ratio of the top pad layer  100 . That is, the sub pad layer  300  may have a structure in which more pores are formed than the top pad layer  100 . 
     Referring to  FIG.  4   , the thermally fused portion  330  may be formed by forming the second through hole  310  and then compressing portions of the sub pad layer  300  adjacent to the second hole  310  towards the window block  200 . Thermally fused portion  330  may be formed to overlap with the bottommost surface of the edge portion of the window block  200  in the vertical direction. The thermally fused portion  330  may be formed to have an area and shape sufficient to cover the entire bottommost surface of the edge portion of the window block  200 . For example, the thermally fused portion may be spaced apart by a distance of more than 0 and about 10 mm, which may correspond to a diameter of recess  210  of the window block. In particular, it is possible to cover gaps spaced apart by a distance of 0.5 to about 10 mm, or 1 to about 3 mm. 
     In  FIG.  4   , the thermally fused portion  330  may be thermally compressed to have a density higher than a density of a non-fused portion in the sub-pad layer  300 , to form a structure that prevents the introduction of slurry and deionized water into the top pad layer  100 . 
     A height difference between a lower surface of the thermally fused portion  330  and a lower surface of the non-fused portion may be about 0.1 mm to about 2.0 mm, and preferably 0.5 mm to about 1.5 mm. 
     The thermally fused portion  330  may be compressed to a thickness so that the infiltration of the slurry into the thermally fused portion  330  may be effectively prevented. As a result, a change of a polishing rate may be effectively decreased. 
     During performing the CMP process using the polishing pad  10 , the sub-pad layer  300  with the thermally fused portion  330  may prevent the infiltration of the slurry and the deionized water into the top pad layer  100 . This helps reduce any changes in compression rate of the top pad layer  100 , which is prevented from absorbing the slurry and the deionized water, to obtain a more uniform polishing rate. 
     In  FIG.  4   , the polishing pad  10  may further include a second adhesive layer  350  arranged on the lower surface of the sub-pad layer  300 . The second adhesive layer  350  may include a double-sided tape. The lower surface of the sub-pad layer  300  may be bonded to the platen through the second adhesive layer  350 . 
     Although not illustrated, the thermally fused portion  330  may be formed by compressing a portion of the sub-pad layer  300  with a portion of the second adhesive layer  350  at a temperature of about 100° C. to about 150° C. under a pressure of about 0.01 Mpa to about 5 Mpa for 60 seconds to about 600 seconds. 
     The polishing pad  10  may further include a first adhesive layer  400  arranged between the top pad layer  100  and the sub-pad layer  300  to bond the top pad layer  100  to the sub-pad layer  300 . 
     The first adhesive layer  400  may include a transparent film having coated an adhesive on both sides, theretofore example. 
     The first adhesive layer  400  may be formed using a hot-melt adhesive. 
     The first adhesive layer  400  may have a thickness of about 0.001 mm to about 3 mm. When the thickness of the first adhesive layer  400  is about 0.001 mm to about 3 mm, the first adhesive layer  400  may be melted at a low temperature to have strong adhesion force, thereby attaching the polishing layer to the supporting layer. 
     A third hole  410  may be formed through the first adhesive layer  400 . The third hole  410  may be connected to the first hole  110 . In a plan view, the third hole  410  may have an area that is smaller than the area of the first hole  110 . When the area of the third hole  410  is smaller than the area of the first hole  110 , the first adhesive layer  400  is configured to support the window block  200  inside the first hole  110  to effectively fix the window block  200  to the sub-pad layer  300 . 
     In a plan view, the third hole  410  may have a circular shape having a diameter of about 5 mm to about 95 mm, or an elliptical shape. Alternatively, the third hole  410  may have a quadrangular shape having a lateral length of about 5 mm to about 95 mm and a longitudinal length of about 5 mm to about 95 mm. 
     The diameter of the third hole  410  may be smaller than the diameter of the first hole  110 . The diameter of the third hole  410  may be substantially the same as the diameter of the second hole  310 . The diameter of the second hole  310  may be about 10% to about 95% of the diameter of the first hole  110 . 
     The second hole  310  and the third hole  410  may be aligned with each other. The second hole  310  and the third hole  410  may be formed simultaneously to ensure alignment of the second hole  310  and the third hole  410  to each other. 
     Referring to  FIGS.  3  and  4   , the polishing pad  10  may further include a third adhesive layer  230 . The third adhesive layer  230  may be arranged on the lowermost surface of the window block  200 . The third adhesive layer  230  may be attached to an upper surface of the first adhesive layer  400 . The third adhesive layer  230  may be partially arranged on the upper surface of the first adhesive layer  400 . The third adhesive layer  230  may be formed using a humidity-setting adhesive when the window block  200  is formed in the first hole  110 . The third adhesive layer  230  may be internally fused into the first adhesive layer  400  by heating and compressing the third adhesive layer  230 . Thus, the third adhesive layer  230  may function as a high-density region in the first adhesive layer  400 . The third adhesive layer  230  may be fused with the first adhesive layer  400 . The third adhesive layer  230  may prevent leakage between the window block  200  and the first hole  110  by blocking leak paths between the first hole  110  on the one hand, and on the other, recess  210  and second and third holes  310  and  410  in order to increase the sensing accuracy of the window block  200 . The third adhesive layer  230  may have a thickness of about 0.01 mm to about 0.5 mm. 
     As shown in  FIG.  2   , the polishing pad  10  may include the top pad layer  100 , the window block  200 , the sub-pad layer  300  and the first adhesive layer  400 . The groove pattern P and the first hole  110  may be formed at the top pad layer  100 . The window block  200  may be inserted into the first hole  110 . The window block  200  may include the recess  210 . The sub-pad layer  300  may be arranged below the lower surface of the top pad layer  100 . The second hole  310  may be formed through the sub-pad layer  300 . The first adhesive layer  400  may be arranged between the top pad layer  100  and the sub-pad layer  300 . The third hole  410  may be formed through the first adhesive layer  400 . 
       FIG.  3    is a cross sectional view illustrating a polishing pad in accordance with an embodiment of the disclosure. Referring to  FIG.  3   , a polishing pad  10  may include a top pad layer  100 , a window block  200 , a sub-pad layer  300 , a first adhesive layer  400  and a third adhesive layer  230 . The groove pattern P and the first hole  110  may be formed in the top pad layer  100 . The window block  200  may be inserted into a first hole  110 . The window block  200  may include a recess  210 . The sub-pad layer  300  may be arranged beneath the lower surface of the top pad layer  100 . A second hole  310  may be formed through the sub-pad layer  300 . The first adhesive layer  400  may be arranged between the top pad layer  100  and the sub-pad layer  300 . A third hole  410  may be formed through the first adhesive layer  400 . The third adhesive layer  230  may be arranged on the lowermost surface of the window block  200 . 
       FIG.  4    is a cross sectional view illustrating a polishing pad in accordance with an embodiment of the disclosure. Referring to  FIG.  4   , a polishing pad  10  may include a top pad layer  100 , a window block  200 , a sub-pad layer  300 , a first adhesive layer  400  and a second adhesive layer  350 . A groove pattern P and a first hole  110  may be formed in the top pad layer  100 . The window block  200  may be inserted into the first hole  110 . The window block  200  may include a recess  210 . The sub-pad layer  300  may be arranged beneath the lower surface of the top pad layer  100 . A second hole  310  may be formed through the sub-pad layer  300 . The sub-pad layer  300  may include a thermally fused portion  330 . The thermally fused portion  330  may be disposed at or near the top of second hole  310 , and may be disposed to overlap, in the vertical direction, the lowermost portion of the window block  200  and laterally adjacent portions of top pad layer  100 . The first adhesive layer  400  may be arranged between the top pad layer  100  and the sub-pad layer  300 . The third hole  410  may be formed through the first adhesive layer  400 . The third adhesive layer  230  may be arranged on the lower surface of the window block  200 . 
     According to embodiments of the disclosure, the polishing pads  10  that have the above-mentioned structures may exhibit the following effects with respect to problems caused by conventional polishing pads. 
     In the conventional polishing pad, when a gap Gap does not exist between the window block  200  and the top pad layer  100 , the wafer may be damaged by the window block  200 . Further, when an excessive gap is formed between the window block  200  and the top pad layer  100 , or when a deviation between the window block  200  and the top pad layer  100  is enough to create a leak path, leakage may cause sensing errors. In contrast, the polishing pad  10  of embodiments disclosed herein include a Gap between the window block  200  and the top pad layer  100 , and the gap between the window block  200  and the top pad layer  100  in the polishing pad  10  may be constantly controlled to stably sense the metal layer at the initial step of the CMP process. 
     Further, the leakage of water and air may be generated by the design and the fabrication processes, and leakage between the top pad layer  100  and the window block  200  may generate errors of the RTPC sensor. To remedy these problems, the polishing pad  10  may be manufactured by the thermal fusion and by adhesion processes, using the two adhesives to prevent the leakage of the water and the air. 
     In order to prevent the damage of the wafer caused by a broken window block  200 , a polishing pad having remaining life may be exchanged for new one, which increases the consumption rate of the polishing pad. The proper life time of the polishing pad  10  may be calculated from Formulas 1 to 3 (defined below) to decrease the consumption rate of the polishing pad  10 . 
     When the CMP process is performed using the polishing pad  10 , the window block  200  may be easily broken when the thickness of the window block  200  is from 200 μm to about 350 μm. Thus, the optical thickness of the window block  200  may be deduced. 
     When the polishing pad  10  defined by Formula 1 is manufactured using the Gap between the upper surfaces of the top pad layer  100  and the window block  200 , the thickness Thk RTPC  of the window block  200 , the depth Thk grv  of the groove pattern at the top pad layer  100 , the optimal life time of the polishing pad  10  may be more accurately predicted. 
     In some embodiments, the top pad layer  100  and the window block  200  of the polishing pad  10  may have a structure defined by the following Formula 2. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   1.9 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   2 
                 
               
             
           
         
       
     
     In some embodiments, the top pad layer  100  and the window block  200  of the polishing pad  10  may have a structure defined by the following Formula 3. 
     
       
         
           
             1.6 
             ≤ 
             
               
                 Gap 
                 + 
                 
                   Thk 
                   RTPC 
                 
               
               
                 Thk 
                 grv 
               
             
             ≤ 
             1.9 
           
         
       
     
     A polishing pad  10  having the above-mentioned structure may be used in various technologies for measuring the end point detection of the CMP process. 
     The measurement of the end point detection may utilize an optical microscope method using a light source to measure thickness changes, a current detection method of a driving motor using a frictional force, or an eddy current detection method using an induced electromotive force of a metal. The end point detection of the polishing pad  10  may be measured using the above-mentioned three methods. The eddy current detection method, which may detect an eddy current to terminate the CMP process at a desired thickness, i.e., the RTPC method, may be applied to the polishing pad  10 . 
     More particularly, when a gap exists between a signal detection sensor and a wafer, an RTPC type magnetic signal measurement method may generate an unstable signal in accordance with a height of the gap, states of the slurry and the deionized water, etc., to generate an error in a thickness of an initial layer. Thus, it may be important to set the height of the gap and the overall uniformity of the gap. The polishing pad  10  in embodiments of the disclosure may be capable of preventing leakage and accurately measuring a copper layer in the initial CMP process so that the polishing pad  10  may be readily used in RTPC type magnetic signal measurement methods. 
     The conventional polishing pad manufactured by a thermal fusion may have a strong bonding force between layers. However, leaks may be easily generated in the conventional polishing pad. Further, the conventional polishing pad manufactured using an adhesive may have good vapor permeability resistance. In contrast, because a height difference between the window block and the top pad layer may be irregular, the conventional polishing pad may have low sensing accuracy. 
     In contrast, the polishing pad  10  of embodiments of the disclosure may be manufactured while simultaneously using both the bonding method and the fusion method applied to the third adhesive layer to prevent the leakage and to have improved sensing accuracy. 
     The polishing pad  10  of embodiments of the disclosure, which may include a top pad layer  100  and a window block  200 , and which may be defined by any of Formulas 1 to 3, may be manufactured by following processes. 
     The polishing pad  10  may be manufactured by installing a window block  200  at a first hole, arranging a gap-controlling film on a surface of the window block  200  and pressing the gap-controlling film. 
     For example, the gap-controlling film may be arranged on a lower pressing pad of a compressor including an upper supporting pad. The window block may be inserted into the first hole of the top pad layer. The top pad layer with the window block may be reversed. The reversed top pad layer with the window block may then be loaded into the compressor. The window block may be arranged on the gap-controlling film on the lower pressing pad. The lower pressing pad may compress the top pad layer with the window block. The top pad layer  100  with the window block may be separated from the compressor to complete a polishing pad having a gap corresponding to the thickness of the gap-controlling film. 
     Alternatively, the gap-controlling film may be arranged on the upper surface of the window block  200 . The window block  200  with the gap-controlling film may be inserted into the first hole  110 . The upper surface of the gap-controlling film may be pressed until the upper surface of the gap-controlling film is substantially coplanar with the upper surface of the top pad layer  100 . The gap-controlling film may then be removed from the window block  200 . Further, the gap-controlling film may be arranged on the upper surface of the window block  200  in the first hole  110 . 
     The polishing pad  10  having a gap, which may be the height difference between the upper surface of the top pad layer and the upper surface of the window block, may be easily manufactured in great quantity. Further, the gap in the polishing pad may have a low level of manufacturing deviation and a uniform structure. 
     Particularly, the polishing pad  10  manufactured by the above-mentioned methods may have the gap (the height difference between the upper surface of the top pad layer and the upper surface of the window block) of about 0.001 mm to about 2 mm, an RTPC time variability of about ±1% to about 30% and a gap variability of about 10% to about 40%. Preferably, the polishing pad  10  of example embodiments may have the gap of about 0.001 mm to about 0.5 mm, an RTPC time variability of about ±5% to about 15% and a gap variability of about 25% to about 35%. The variability may be illustrated later in detail with reference to following Examples. 
     The polishing pad  10  having an above-mentioned structure may have low dispersion with respect to a polishing time and a high analysis value of a process capacity to have a predicted fraction defective of the CMP process of no more than about 5.7×10 −5 , thereby having good yield rate. 
     Thus, the gap-controlling film may have a thickness of about 0.001 mm to about 0.1 mm. The gap-controlling film may include at least one film to control the gap. 
     In a method of manufacturing the polishing pad  10  of embodiments of the disclosure, a first hole  110  may be formed through the top pad layer  100  with a groove pattern P. A window block  200  may be formed in the first hole  110  to form a polishing pad  10  including the top pad layer  100  and the window block  200 . The top pad layer  100  and the window block  200  may have a structure defined by the following Formula 1. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   3. 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   1 
                 
               
             
           
         
       
     
     In Formula 1, the Gap may indicate a height difference between an upper surface of the top pad layer  100  and an upper surface of the window block  200 , the Thk RTPC  may indicate a thickness of an upper portion of the window block  200 , and the Thk grv  may indicate a depth of a groove pattern formed at the upper surface of the top pad layer  100 . 
     In embodiments, the top pad layer and the window block of the polishing pad  10  may have a structure that is defined by the following Formula 2. 
     
       
         
           
             
               
                 
                   1.1 
                   ≤ 
                   
                     
                       Gap 
                       + 
                       
                         Thk 
                         RTPC 
                       
                     
                     
                       Thk 
                       grv 
                     
                   
                   ≤ 
                   1.9 
                 
               
               
                 
                   Formula 
                   ⁢ 
                       
                   2 
                 
               
             
           
         
       
     
     The top pad layer and the window block of the polishing pad  10  may have a structure defined by the following Formula 3. 
     
       
         
           
             1.6 
             ≤ 
             
               
                 Gap 
                 + 
                 
                   Thk 
                   RTPC 
                 
               
               
                 Thk 
                 grv 
               
             
             ≤ 
             1.9 
           
         
       
     
       FIG.  5    illustrates a method of manufacturing a polishing pad in accordance with an embodiment of the disclosure. The method of manufacturing the polishing pad may include forming a first hole through a sheet of material for the top pad layer. The first hole may be formed through a central portion of the sheet to have a set or predetermined size or area. 
     The first hole  110  may be formed by a press, a punch, or a polishing process using a cutting tool. Alternatively, the first hole  110  may be formed by pouring a material into a mold having a shape corresponding to the shape of the first hole  110  and then hardening the material. 
     The method of manufacturing the polishing pad may include installing the window block at the first hole to form the polishing pad including the top pad layer and the window block. 
     The window block may be formed with a recess and may be installed in the first hole. The gap-controlling film may be arranged on the surface of the window block. The upper surface of the gap-controlling film may then be pressed. 
     For example, the gap-controlling film may be arranged on a lower pressing pad of a pressor. The window block may be inserted into the first hole of the top pad layer. The top pad layer with the window block may be reversed. The reversed top pad layer with the window block may then be loaded onto the pressor. The window block may be arranged on the gap-controlling film on the lower pressing pad. The lower pressing pad may press the top pad layer with the window block. The top pad layer with the window block may be separated from the pressor to complete the polishing pad having a gap (the height difference between the upper surface of the top pad layer and the upper surface of the window block) that corresponds to the thickness of the gap-controlling film. 
     Alternatively, the gap-controlling film may be arranged on the upper surface of the window block  200 . The window block with the gap-controlling film may be inserted into the first hole  110 . The upper surface of the gap-controlling film may be pressed to position the upper surface of the gap-controlling film to be substantially coplanar with the upper surface of the top pad layer  100 . The gap-controlling film may then be removed from the window block. Further, the gap-controlling film may be arranged on the upper surface of the window block in the first hole. 
     The above-mentioned methods may include forming the basic structure of a polishing pad including a top pad layer  100  and a window block  200 . The methods of disclosed embodiments may further include forming the first adhesive layer  400  and the sub-pad layer  300  on the lower surface of the top pad layer  100 . 
     In embodiments of the disclosure, the method may include forming the first hole through a sheet of material for the top pad layer with the groove pattern. A sheet of material for the sub-pad layer may be bonded to the lower surface of the sheet for the top pad layer to form a bond structure that includes the sub-pad layer, the first adhesive layer and the top pad layer, sequentially stacked. A third hole may be formed through the first adhesive layer. A moisture-curable adhesive may be coated on an upper surface of the first adhesive layer. A window block may be installed in the first hole of the bond structure. 
     The bond structure may be formed by arranging the sheet with the second hole for the sub-pad layer on the lower surface of the sheet for the top pad layer, and by coating the adhesive between the sheets. In a plan view, the area of the second hole may be smaller than the area of the first hole. The second hole may be formed in the same manner used for forming the first hole. When the top pad layer  100  and the sub-pad layer  300  are bonded to each other, the first hole  110  of the top pad layer  100  and the second hole  310  of the sub-pad layer  300  may be aligned with each other in a plan view. 
     The sheet for the top pad layer and the sheet for the sub-pad layer may be attached to each other using the adhesive. The attachment may take place at no less than a melting point of the adhesive for the first adhesive layer. The adhesive may include a hot-melt adhesive. The attachment may be performed at a temperature of about 90° C. to about 130° C. 
     After forming the bond structure, the third hole may be formed through the first adhesive layer. In a plan view, the area of the third hole may be substantially the same as the area of the second hole. The first hole  110 , the second hole  310  and the third hole  410  may be aligned with each other. 
     The moisture-curable adhesive may coat the upper surface of the first adhesive layer. Because the size of the second and third holes may be smaller than the area of the first hole, the upper surface of the first adhesive layer may be partially exposed. The moisture-curable adhesive may be coated on the exposed portion of the first adhesive layer. The window block may be arranged in the first hole and the window block may be fixed to the first adhesive layer. The polishing pad may include an adhesive layer formed of the moisture-curable adhesive. 
     The window block  200  may be attached to the sub-pad layer  300  by thermal pressing. For example, after inserting the window block  200  into the first hole, the first adhesive layer  400  may attach the window block  200  to the sub-pad layer  300  by thermal pressing through the window block  200 . 
     Further, before inserting the window block  200 , the third adhesive layer  230  (see  FIG.  3   ) may be arranged on the lower surface of the window block  200 . That is, the window block  200  with the moisture-curable adhesive may be inserted into the first hole  110 . The third adhesive layer  230  may reinforce an adhesion force between the window block  200  and the sub-pad layer  300 . The third adhesive layer  230  may be hardened when the window block  200  is installed in the first hole  110  to fuse the first adhesive layer  400  by thermal pressing. Thus, a region having a high density may be formed in the first adhesive layer  400 . 
     The method of manufacturing the polishing pad  10  may further include forming a thermally fused portion on the sub-pad layer  300 . 
     In embodiments of the disclosure, the thermally fused portion  330  may formed through thermal pressing. For example, the thermally fused portion  330  may be formed at a temperature of about 100° C. to about 150° C. under a pressure of about 0.1 MPa to about 5 MPa. The thermally fused portion  330  may be formed at the region corresponding to an outer peripheral region on the lower surface of the window block  200 . The sub-pad layer  300  may be partially pressed to form the thermally fused portion  330 . The thermally fused portion  330  may have a high density that prevents leakage. 
     The polishing pad  10  may have improved sealing characteristics against moisture due to good sealing between the top pad layer  100  and the window block  200 , thereby suppressing leakage in the CMP process. The sub-pad layer  300  may include the thermally fused portion  330 . The thermally fused portion  330  may have low porosity to prevent the leakage of the water and/or the slurry in the polishing solution without an additional leakage-preventing layer. 
     Although slurry leakage may be generated between the window block  200  and the top pad layer  100 , the third adhesive layer  230  may secondarily prevent the slurry leakage. The third adhesive layer  230  may be formed at the sub-pad layer  300  corresponding to the outer peripheral region of the window block  200  to have good leakage-suppressing effect. The sub-pad layer  300  may be readily pressed and easily applied. 
     In embodiments of the disclosure, a sheet for the top pad layer may include a composition including a urethane-based prepolymer, a hardening agent, a reaction rate regulating agent, a chain extending agent and a pore forming agent. 
     The urethane-based prepolymer may include a high molecular compound having an NCO end formed by reacting polyhydric alcohol, isocyanate and the chain extending agent with each other. More particularly, the urethane-based prepolymer may be formed by polymerizing a mixture of the polyhydric alcohol containing polytetramethylene glycol, the hardening agent containing toluene diisocyanate and hexamethylene diisocyanate, the chain extending agent containing butanediol, the reaction rate regulating agent containing tertiary amine such as triethylenediamine and the pore forming agent. The urethane-based prepolymer may have a mean molecular weight of about 800 g/mol to about 1,000 g/mol. The pore forming agent may include a material for forming pores in the sheet for the top pad layer such as a solid pore forming agent, a liquefied pore forming agent, an inert gas, etc. 
     The sheet for the top pad layer may include a groove pattern formed on the upper surface of the sheet. The groove pattern may be formed by mechanical polishing, a forming process using a mold, etc., and methods are not limited to the above examples. 
     Therefore, the sheet for the top pad layer may have a structure including the groove pattern configured to facilitate flow of the polishing solution and the pores may be configured to assist in the flow to a smaller degree. 
     The window block may include a composition containing a urethane-based prepolymer, a hardening agent and a reaction rate regulator. The urethane-based prepolymer may include materials substantially the same as those for the top pad layer. A content of the hardening agent may be controlled to adjust hardness, thereby controlling a wear rate of the CMP process, i.e., loss probability. 
     The window block  200  may further include a recess  210  formed at a central portion of the window block  200 . The recess  210  may be formed by a router, a cutting, a compression, etc. 
     The sub-pad layer  300  may support the top pad layer  100 . The sub-pad layer  300  may absorb and distribute an impact applied to the top pad layer  100 . The sub-pad layer  300  may have hardness that is lower than the hardness of the top pad layer  100 . 
     In embodiments of the disclosure, the sub-pad layer  300  may be formed using a sheet for the sub-pad layer. The sheet for the sub-pad layer may be formed of a composition containing a non-woven fabric or a urethane-based prepolymer. 
     The first adhesive layer may include general adhesives for attaching sheets to each other. The first adhesive layer may include a hot-melt adhesive. Particularly, the hot-melt adhesive may include a polyurethane-based resin, a polyester-based resin, an ethylene-acetate vinyl-based resin, a polyamide-based resin, a polyolefin-based resin, a combination thereof, etc. 
     The first adhesive layer  400  may include the hot-melt adhesive having a melting point of about 110° C. to about 130° C. When the melting point of the first adhesive layer  400  is within the above range, the first adhesive layer  400  may have strong adhesion force and may prevent peeling between the top pad layer and the sub-pad layer and deformation and deterioration of the top pad layer and/or the sub-pad layer. 
     The moisture-curable adhesive, that is, the third adhesive may be cured by moisture in air. 
     The method of manufacturing the polishing pad may further include forming a second adhesive layer  350  on the lower surface of the sub-pad layer  300 . The second adhesive layer  350  may include double-sided tape. The second adhesive layer  350  may attach the lower surface of the sub-pad layer  300  to the platen. 
     The second adhesive layer may be formed of a film for a sub-pad layer and may be formed with an opening common to the second hole. Alternatively, a hole common to the second hole may be formed in the second adhesive layer after the film attached to the lower surface of the sub-pad layer. The film for forming the second adhesive layer may be a film in which an adhesive is coated on both sides. Alternatively, the film for forming the second adhesive layer may be a film using the same structure except attached a releasing film on one side. 
     Example 1 
     A polishing sheet was manufactured using the method in  FIG.  5   . 
     (1) Manufacturing a Sheet for a Top Pad Layer 
     A casting apparatus included a mixture supply line of a urethane-based prepolymer, a hardening agent and a solid pore forming agent. The urethane-based prepolymer containing a 9% by weight of a non-reacted NCO was supplied to a prepolymer tank of the casting apparatus. A bis(4-amino-3-chlorophenyl) methane (MOCA) was supplied to a hardening agent tank. A 3% by weight of the solid pore forming agent with respect to a 100% by weight of the urethane-based prepolymer was supplied to the prepolymer tank. 
     The urethane-based prepolymer and the MOCA were supplied and agitated into a mixing head. A ratio of a molecular equivalent of an NCO group of the urethane-based prepolymer to a molecular equivalent of a reactive group of the hardening agent was 1:1. The urethane-based prepolymer and the MOCA were supplied at a speed of 10 kg/min. 
     The agitated material was then supplied to a pre-heated mold of a temperature of 120° C. The material was formed using the mold to form a porous polyurethane sheet for the top pad layer. A surface of the porous polyurethane sheet was ground using a grinder. A groove pattern having a thickness Thk grv  was formed at the porous polyurethane sheet using a tip. 
     (2) Manufacturing a Window Block 
     A urethane-based prepolymer and a hardening agent were supplied to a mold having a lateral length of 1,000 mm, a longitudinal length of 1,000 mm and a height of 50 mm to form a cake for the window block. The same hardening agent was used to manufacture the sheet for the top pad layer for manufacturing the window block. 
     The urethane-based prepolymer was different from the urethane-based prepolymer used for manufacturing the sheet for the top pad layer. The urethane-based prepolymer used for the cake includes an 8.5% by weight of a non-reacted NCO produced by PUGL-500D of SKC Company. 
     The cake was cut and blanked to form a molded article having a size of 20 mm×60 mm×2.0 mm. The molded article was installed at a router. A recess was then formed at the molded article using the router to form the window block. The recess had a size of 12.5 mm×31.0 mm×1.0 mm. A distance between an inner surface of the recess and an upper surface of the window block, i.e., a thickness THK RTPC  was 1.0 mm. 
     (3) Manufacturing a Sub-Pad Layer 
     A sheet material having a thickness of 1.3 mm produced by ND-5400H of PTS was used to form a sheet for the sub-pad layer having a size of 1,000 mm×1,000 mm. A second hole having a size of 16 mm×56 mm was formed through the sheet for the sub-pad layer. 
     (4) Manufacturing a Polishing Pad 
     A first hole having a size of 20 mm×60 mm was formed through the sheet for the top pad layer. A hot-melt film was attached to the surface of the sheet for the sub-pad layer. The hot melt film was produced by TF-00 of SKC Company having an average thickness of 40 μm and a reflectivity of 1.5. Double-sided tape was then attached to the other surface of the sheet for the sub-pad layer. The sheets for the top pad layer and sub-pad layer were heated to a temperature of 120° C. to thermally fuse the sheets using the hot-melt film to form a four layers in a bond structure. The bond structure included the top pad layer, the sub-pad layer, the first adhesive layer having a thickness of 1.5 mm between the top pad layer and the sub-pad layer and a second adhesive layer attached to the lower surface of the sub-pad layer. 
     A second hole and a third hole each having a size of 16 mm×56 mm were formed through the first adhesive layer, the sub-pad layer and the second adhesive layer in alignment with the first hole. A hole having a size same as the size of the second hole was formed through the second adhesive layer. 
     A moisture-curable adhesive was coated on the upper surface of the sub-pad layer between the first hole and the second hole. The window block was inserted into the first hole of the top pad layer. The lower surface of the window block was thermally fused with the sub-pad layer to attach the window block to the sub-pad layer, thereby manufacturing the polishing pad in  FIG.  4   . The thermal fusion was performed at a temperature of 130° C. under a pressure of 0.5 MPa for three minutes. The upper surfaces of the window block and the top pad layer in the polishing pad were coplanar with each other so that a gap did not exist between the upper surfaces of the top pad layer and the window block in  FIG.  6 A . 
     Example 2 
     A polishing pad having a gap of 50 μm in  FIG.  6 B  was manufactured by processes used for manufacturing the polishing pad in Example 1 except for using a gap-controlling film. The gap-controlling film having a thickness of 50 μm was attached to the upper surface of the window block to form a window block structure. The first hole was formed through the window block structure. The window block structure was then pressed. The gap-controlling film was removed to form the gap between the upper surfaces of the window block and the top pad layer. 
     Example 3 
     A polishing pad having a gap of 150 μm in  FIG.  6 B  was manufactured by processes used for manufacturing the polishing pad in Example 2 except for using a gap-controlling film having a thickness of 150 μm. 
     Example 4 
     A polishing pad having a gap of 250 μm in  FIG.  6 B  was manufactured by processes used for manufacturing the polishing pad in Example Embodiment 2 except for using a gap-controlling film having a thickness of 250 μm. 
     Example 5 
     A polishing pad having a gap of 100 μm was manufactured by processes used for manufacturing the polishing pad in Example Embodiment 2 except for using a window block with a recess. The recess had a size of 12.5 mm×31.0 mm×0.6 mm. A distance between the inner surface of the recess and the upper surface of the window block, i.e., the thickness Thk RTPC  was 1.4 mm. 
     Example 6 
     A polishing pad having a gap of 200 μm was manufactured by processes used for manufacturing the polishing pad in Example Embodiment 5. 
     Comparative Example 1 
     A polishing pad without a gap in  FIG.  7 A  was manufactured by processes used for manufacturing the polishing pad in Example 1 except without the moisture-curable adhesive and the thermally fused portion. The window block was attached to the first adhesive layer on the upper surface of the sub-pad layer. The sheet for the top pad layer included the groove pattern having a thickness of 0.75 mm. 
     Comparative Example 2 
     A polishing pad with a gap of 50 μm was manufactured by processes used for manufacturing the polishing pad in Comparative Example 1 except for attaching a gap-controlling film having a thickness of 50 μm on the upper surface of the window block to form the window block structure, forming the first hole through the window block structure, pressing the window block structure and removing the gap-controlling film to form the gap between the upper surfaces of the top pad layer and the window block. 
     Comparative Example 3 
     A polishing pad with a gap of 150 μm in  FIG.  7 B  was manufactured by processes used for manufacturing the polishing pad in Comparative Example 2 except for using a gap-controlling film having a thickness of 150 μm. 
     Comparative Example 4 
     A polishing pad with a gap of 250 μm in  FIG.  7 B  was manufactured by processes used for manufacturing the polishing pad in Comparative Example 2 except for using a gap-controlling film having a thickness of 250 μm. 
     Comparative Example 5 
     A polishing pad without a gap in  FIG.  8 A  was manufactured by processes used for manufacturing the polishing pad in Example 1 except for following processes. The first adhesive layer and the window block were attached to the upper surface of the sub-pad layer. The window block was thermally fused to form the polishing pad with a first compression region  331  and a second compression region  333 . 
     Comparative Example 6 
     A polishing pad with a gap of 50 μm in  FIG.  8 B  was manufactured by processes used for manufacturing the polishing pad in Comparative Example 5 except for attaching a gap-controlling film having a thickness of 50 μm on the upper surface of the window block to form the window block structure, forming the first hole through the window block structure, pressing the window block structure and removing the gap-controlling block to form the gap between the upper surfaces of the top pad layer and the window block. 
     Comparative Example 7 
     A polishing pad with a gap of 150 μm in  FIG.  8 B  was manufactured by processes used for manufacturing the polishing pad in Comparative Example 6 except for using the gap-controlling film having a thickness of 150 μm. 
     Comparative Example 8 
     A polishing pad with a gap of 250 μm in  FIG.  8 B  was manufactured by processes used for manufacturing the polishing pad in Comparative Example 6 except for using the gap-controlling film having a thickness of 250 μm. 
     Experiment 1: Property Evaluation 1 
     (1) Evaluating Sensitivities at an Initial CMP Process 
     The polishing pads manufactured in the Examples and Comparative Examples were placed on the platen. The polishing solution including the slurry and the deionized water was supplied to the polishing pads to polish the surface of the wafer. The sensitivities for measuring thicknesses of copper layers on the wafer at the initial CMP process were evaluated as shown in following Table 1. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Groove 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 thickness in 
               
               
                   
                   
                   
                   
                 Formula 
                   
                 Water 
                 Air 
                 damage of 
               
               
                   
                 Gap 
                 Thk RTPC   
                 Thk grv   
                 value 
                 Sensitivity 
                 leakage 
                 leakage 
                 window block 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 0 
                 1,000 
                 850 
                 1.1765 
                 ◯ 
                 Good 
                 3.4 × 10 −4   
                 500 
               
               
                 Example 2 
                 50 
                 1,000 
                 850 
                 1.2353 
                 ◯ 
                 Good 
                 2.2 × 10 −4   
                 450 
               
               
                 Example 3 
                 150 
                 1,000 
                 850 
                 1.3529 
                 ◯ 
                 Good 
                 1.3 × 10 −4   
                 200 
               
               
                 Example 4 
                 250 
                 1,000 
                 850 
                 1.4706 
                 X 
                 Good 
                 1.2 × 10 −4   
                 150 
               
               
                 Example 5 
                 100 
                 1,400 
                 850 
                 1.7647 
                 ◯ 
                 Good 
                 1.4 × 10 −4   
                 0 
               
               
                 Example 6 
                 200 
                 1,400 
                 850 
                 1.8824 
                 ◯ 
                 Good 
                 2.4 × 10 −4   
                 0 
               
               
                 Comparative 
                 0 
                 1,000 
                 750 
                 1.3333 
                 ◯ 
                 Bad 
                 — 
                 400 
               
               
                 Example 1 
               
               
                 Comparative 
                 50 
                 1,000 
                 750 
                 1.4000 
                 ◯ 
                 Bad 
                 — 
                 330 
               
               
                 Example 2 
               
               
                 Comparative 
                 150 
                 1,000 
                 750 
                 1.5333 
                 ◯ 
                 Bad 
                 — 
                 200 
               
               
                 Example 3 
               
               
                 Comparative 
                 250 
                 1,000 
                 750 
                 1.6667 
                 X 
                 Bad 
                 — 
                 0 
               
               
                 Example 4 
               
               
                 Comparative 
                 0 
                 1,000 
                 850 
                 1.1765 
                 ◯ 
                 Bad 
                 2.1 × 10 −2   
                 200 
               
               
                 Example 5 
               
               
                 Comparative 
                 50 
                 1,000 
                 850 
                 1.2353 
                 ◯ 
                 Bad 
                 1.8 × 10 −2   
                 150 
               
               
                 Example 6 
               
               
                 Comparative 
                 150 
                 1,000 
                 850 
                 1.3529 
                 ◯ 
                 Bad 
                 3.5 × 10 −2   
                 180 
               
               
                 Example 7 
               
               
                 Comparative 
                 250 
                 1,000 
                 850 
                 1.4706 
                 X 
                 Bad 
                 5.1 × 10 −2   
                 110 
               
               
                 Example 8 
               
               
                   
               
            
           
         
       
     
     (2) Water Leakage Test 
     The polishing pads manufactured by Examples and Comparative Examples were placed on the platen. The polishing solution including the slurry and the deionized water was supplied to the polishing pads to polish the surface of the wafer. The leakage of the polishing solution into the top pad layer in each of the polishing pads was evaluated as shown in Table 1. 
     (3) Air Leakage Test 
     Air leakage (cc/minute) of the polishing pads manufactured by Examples and Comparative Examples were evaluated in Table 1. 
     (4) Depths of the Groove Pattern in the Top Pad Layer in Polishing Pad with Damaged Window Block 
     The polishing pads manufactured by Examples and Comparative Examples were placed on the platen. The polishing solution including the slurry and the deionized water was supplied to the polishing pads to polish the surface of the wafer. The polishing process was terminated when the window block was broken. The thicknesses of the groove patterns remaining on the top pad layer were measured as shown in Table 1. 
     (5) Result 1 
     It can be noted that the water leakage is not generated in the polishing pads in Examples 1 to 6, which have good leakage-proof capacity. In contrast, it can be noted that the water leakage is generated in the polishing pads manufactured by Comparative Examples 1 to 8, which have bad leakage-proof capacity. 
     Therefore, it can be noted that the third adhesive layer and the thermally fused portion function to improve the sealing capacity so that the good water leakage-proof capacity is provided to the polishing pads in the Examples. 
     Further, it can be noted that the air leakage in the polishing pads of the Examples is smaller than the air leakage in the polishing pads of Comparative Examples due to the third adhesive layer and the thermally fused portion. 
     Furthermore, it can be noted that the window block of each of the polishing pads in the Examples is not broken until the groove pattern is fully removed so that the polishing pads are used through their lifetime. 
     When characteristics of the polishing pad manufactured by Examples 5 and 6 were evaluated, values calculated by Formula 1 were 1.7647 and 1.8824. Thus, it can be noted that the polishing pad having a structure designed by the value of no less than 1.6 obtained from Formula 1 is successfully used in the CMP process. 
     Experiment 2: Property Evaluation 2 
     Capacities of the polishing pads in CMP processes manufactured by Example 5 and Comparative Example 6 were evaluated as shown following Table 2 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Comparative 
                   
               
               
                   
                 Example 6 
                 Example 5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 AVG 
                   32.5″ 
                      32.9 
               
               
                 Max 
                 37″ 
                 34″ 
               
               
                 Min 
                 27″ 
                 31″ 
               
               
                 RAN 
                 10″ 
                  3″ 
               
               
                 Cp 
                      0.70 
                      1.76 
               
               
                 Cpk 
                      0.64 
                      1.73 
               
               
                   
               
            
           
         
       
     
     In Table 2, AVG is an average of the RTPC times, Max is a maximum of the RTPC times, Min is a minimum of the RTPC times, RAN is dispersion, and Cp and Cpk are analysis values of the process capacities. A unit of the RTPC times is a second. 
     The twenty-three polishing pads of Comparative Example 6 and the eleven polishing pads of Example 5 were prepared. The Cp and the Cpk were obtained using Formulas 1 to 3. When the Cp and the Cpk are no less than 1.33, the capacity of the polishing pad is determined to be good based on Table 3. 
         Cp =allowable dispersion/actual dispersion 
         Cpk =(1− k )× Cp  
 
         K =difference between a standard center and an average/half of standard width 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Predicted 
               
               
                   
                 Predicted 
                 fraction 
               
               
                   
                 yield 
                 defective 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 1.34 &lt; Cp ≤ 1.67 
                 Very good 
                 No less than 
                 No more than 
               
               
                   
                   
                 99.999943% 
                 0.000057% 
               
               
                 1.00 &lt; Cp ≤ 1.33 
                 good 
                 No less than 
                 No more than 
               
               
                   
                   
                 99.9937% 
                 0.0063% 
               
               
                 0.68 &lt; Cp ≤ 1.00 
                 Ordinary 
                 No less than 
                 No more than 
               
               
                   
                   
                 99.73% 
                 0.27% 
               
               
                 0.00 &lt; Cp ≤ 0.67 
                 Very bad 
                 No more than 
                 No less than 
               
               
                   
                   
                 95.45% 
                 4.5% 
               
               
                   
               
            
           
         
       
     
     When a metal layer on the wafer may be polishing to a set thickness, the CMP process may be automatically terminated. The RTPC time may represent a time that the thickness of the metal layer may be reduced to the set thickness in polishing the wafers on which the same metal layers may be formed. For example, when a wafer on which a metal layer having a thickness of about 10,000 Å may be formed is polished to have the metal layer having a final thickness of about 3,000 Å, the CMP process may be terminated at the thickness of 7,000 Å in the polished metal layer. Thus, the RTPC time may represent the polishing time. 
     The same RTPC time may mean that a deviation of the polishing time until the metal layer may have the set thickness under same conditions may not be high or may be same. The range of the RTPC time, i.e., the CMP process and the environmental conditions may be stable in proportion to the smaller dispersion. 
     A reading of the thickness of the metal layer and a difference between the polishing times may be different in accordance with positions of the gap in the polishing pads. Thus, it may be required to maximumly decrease the range of the gap. The range of the gap may be dependent upon the structure of the window block in the polishing pad. That is, when the gap is increased, the range of the gap may also be increased. 
     Therefore, the ranges of the RTPC time and the gap may be an important factor affecting the capacity of the CMP process. 
     An average of the RTPC times in the polishing pad of Example 5 is 32.9 seconds. An average of the RTPC times in the polishing pad of Comparative Example 6 is 32.5 seconds. A maximum and a minimum of the RTPC times in the polishing pad of Example 5 are 34 second and 31 seconds, respectively. A maximum and a minimum of the RTPC times in the polishing pad of Comparative Example 6 are 37 second and 27 seconds, respectively. Thus, a dispersion of the polishing pad in Example 5 is 3 seconds. In contrast, a dispersion of the polishing pad in Comparative Example 6 is 10 seconds. Therefore, the range of the polishing pad in Example 5 is ±5% with respect to the average. In contrast, the range of the polishing pad in Comparative Example 6 is above ±30%. As a result, it can be noted that the polishing pad of Example 5 has a lower range of the RTPC time so that the polishing pad of Example 5 is reliably used. 
     The Cp and the Cpk of the polishing pad in Example 5 are 1.76 and 1.73, respectively. Thus, it can be noted that the predicted yield of the wafer polished by the polishing pad in Example 5 is very high due to good characteristics of the polishing pad. In contrast, the Cp and the Cpk of the polishing pad in the Comparative Example 6 are 0.70 and 0.64, respectively. Thus, it can be noted that the predicted yield of the wafer polished by the polishing pad in Comparative Example 6 is ordinary or very low due. 
     Further, the ranges of the gap and the RTPC time in the polishing pad in Example 5 are evaluated. The range of the gap may mean a deviation of the gap in the polishing pad manufactured by same processes. The low range of the gap may indicate a small shape difference between the gaps. 
     For example, when a designed polishing pad may have a designed gap of about 0.05 mm, an actual polishing pad may have a gap of about 0.035 mm to about 0.065 mm. The actual polishing pad may have about 30% of a gap range. That is, the actual gap may be lower than the target gap by about ±30%. 
     The polishing pad in Example 5 had a gap of about 0.001 mm to about 0.1 mm to have about a ±30% difference between the actual gap and the target gap so that the range of the RTPC time may be about ±5%. Thus, the polishing pad having the gap of about 0.001 mm to about 0.1 mm may be stably used in the CMP process. 
     In contrast, the polishing pad in Comparative Example 6 had a gap of about 0.01 mm to about 0.2 mm to have about a ±40% difference between the actual gap and the target gap so that the range of the RTPC time may be about ±15%. 
     According to examples, the polishing pad having the gap of about 0.01 mm to about 0.1 mm in Example 5 may be more stable and reliable in use when compared with the polishing pad in Comparative Example 6. 
     As a result, the polishing pads with uniform gaps in the Example may be manufactured in large quantity.