Abstract:
A polishing pad is placed on a polishing apparatus including a polishing platen which is rotatable and on which the polishing pad is placed, a substrate retaining mechanism, and a supplying mechanism for supplying a polishing agent on an upper surface of the polishing pad, the polishing pad having grooves extending from the center of the polishing pad to the outer edge thereof, the groove becoming gradually deeper from the center of the polishing pad toward the outer edge portion thereof so that the depth of the groove is the largest at the outer edge portion, thereby allowing a slurry to be smoothly discharged from the upper surface of the polishing platen.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a polishing apparatus for polishing a surface of a semiconductor substrate by a chemical mechanical polishing (CMP) method, a polishing pad for use in the polishing apparatus, and a polishing method using the polishing pad. 
         [0003]    2. Description of the Related Art 
         [0004]    In order to flatten irregularities on a surface of a semiconductor substrate in a manufacturing process of the semiconductor substrate or a manufacturing process of a semiconductor device, a chemical mechanical polishing (CMP) method is performed. For the chemical mechanical polishing method, a CMP apparatus  2  as shown in  FIGS. 1 and 2  is used. The CMP apparatus  2  includes a polishing platen  4 , a spindle carrier  8 , a spindle  10 , and a slurry nozzle  14 . To an upper surface of the polishing platen  4 , a polishing pad  6  is adhered. The spindle carrier  8  retains a wafer  12 , that is, a semiconductor substrate, and presses the wafer  12  to the polishing pad  6  at a constant load. The slurry nozzle  14  drops the muddy slurry  16  including a polishing agent on an upper surface of the polishing pad  6 . The polishing platen  4  and the spindle  10  are rotated by a rotation mechanism (not shown). The CMP apparatus  2  includes two sets of the spindle carriers  8  and the spindles  10  such that two wafers  12  can be polished at the same time. The two spindles  10  are connected to a structural body called a bridge  18 . 
         [0005]    In a polishing process for a surface of the wafer  12 , the polishing agent in the slurry  16  is kept in minute holes (around 10 to 50 μm in diameter) on the surface of the polishing pad  6  and irregularities on the surface of the wafer  12  are smoothed by the polishing agent. 
         [0006]      FIG. 3  is a top view of the polishing pad  6 .  FIG. 4  is a sectional view of the polishing pad  6 . The polishing pad  6  has a disk shape and is made of a synthetic resin such as polyurethane. The polishing pad  6  has pad grooves  20  formed in a grid like fashion.  FIG. 4  is the sectional view taken along the line A-A′ of  FIG. 3 . A sectional shape of the pad grooves  20  is a U-shape. A pad groove base portion  20   a  is a plane. A pad groove wall  20   b  is a wall perpendicular to the pad groove base portion  20   a.    
         [0007]    A width W 1  of the pad groove  20  and a depth D 1  of the pad groove  20  have the same dimensions independent of the position on the pad. Further, a pitch P 1  of the pad grooves  20  is constant, and the pad grooves  20  are formed in grid like fashion. 
         [0008]    Note that, the polishing pad  6  is composed of two layers, that is, an upper layer polishing pad  6   a  and a lower layer polishing pad  6   b . The upper layer polishing pad  6   a  is formed with the pad grooves  20 . 
         [0009]    By performing polishing, the minute holes on the surface of the polishing pad  6  are worn out. Accordingly, the surface of the polishing pad  6  is ground by a disk plate on which diamond particles are electrodeposited, thereby creating a new surface having minute holes. This is an operation for eliminating clogging on the surface of the polishing pad  6 . Thus, this operation enables to polish the wafer  12  accurately in a stable manner. 
         [0010]    Further, as long as the slurry  16  on the pad is fresh and frequently replaced with supplying slurry, it is possible to polish the wafer  12  in a stable manner. In other words, when the slurry  16  which has been supplied from the nozzle remains on the surface of the polishing pad  6  and is not replaced with the fresh slurry  16  to be supplied later, the wafer  12  cannot be polished. Further, for accurately polishing the wafer  12 , it is also important to discharge the shavings produced during polishing smoothly from the top surface of the polishing pad  6  to an outside through an outer edge of the polishing pad  6 . 
         [0011]    JP 2001-121405 A discloses a polishing pad having a structure in which a polishing surface of the polishing pad is formed with grooves extending from an initial point in the vicinity of a central portion of the polishing surface to an end point on an outer edge of the polishing surface. The cross section of a groove on the polishing pad varies between the initial point and the end point, the cross section reaches the maximum value at a point between the initial point and the end point. 
         [0012]    JP 2005-183711 A discloses a polishing pad having a plurality of parallel groove groups including substantially straight grooves which are in parallel with each other in a polishing surface. At least one of the grooves has different depths within the same groove. 
         [0013]    JP 2000-117620 A, JP 2004-327567 A, and U.S. Pat. No. 6,093,651 each discloses a technology of changing a depth of a groove concentrically with respect to a polishing pad from a center to an outer periphery thereof. 
         [0014]    However, the inventor of the present invention has noticed that there are the following problems with use in those polishing pads. 
         [0015]    In a case where a surface of the polishing pad  6  is roughly divided from a center  6   c  toward an outer edge into a central portion, a middle portion, and an outer edge portion, when an operation of periodically grinding the polishing pad  6  with the disk plate as described above and a normal operation of polishing the wafer  12  are performed, the middle portion is worn down to a maximum degree, so the surface of the polishing pad  6  corresponding to the middle portion is recessed. In particular, in the operation of grinding the polishing pad  6  with the disk plate, the middle portion of the surface of the polishing pad  6  is worn down more than in the other operation. 
         [0016]    When the middle portion of the polishing pad  6  is worn, the slurry  16  and the shavings produced by the polishing pad  6  are not discharged to the outside, and remain in the middle portion. As a result, the shavings generate minute flaws (micro scratches) on the surface of the wafer  12 . Further, when the slurry  16  which is not discharged but remains on the pad, the slurry  16  is dried and then the polishing agent included in the slurry  16  becomes coarse. The coarse polishing agent may scratch the surface of the wafer  12 , thereby causing the micro scratches. Accordingly, in order to ensure accuracy of a polished surface of the wafer  12  and to obtain the uniform polished surface of the wafer  12 , it is important to improve discharging efficiency of the slurry  16 . 
         [0017]    However, in a case where the polishing pad  6  as shown in  FIG. 3  or  4  is used, the discharging efficiency of the slurry  16  is not satisfactory. Therefore, there is a demand for the polishing pad  6 , the CMP apparatus  2 , and the polishing method by which the discharging efficiency of the slurry  16  is more satisfactory. 
       SUMMARY 
       [0018]    According to the present invention, a polishing pad has grooves extending from a center of the polishing pad to an outer edge thereof, the groove becoming gradually deeper from the center of the polishing pad toward an outer edge thereof such that a depth of the groove is the largest at an outer edge portion. Further, the polishing pad is placed on a polishing apparatus including a rotatable polishing platen on which the polishing pad is placed, a substrate retaining mechanism, and a supplying mechanism for supplying a polishing agent on an upper surface of the polishing pad, the polishing pad having the grooves extending from the center of the polishing pad to the outer edge thereof, the groove becoming gradually deeper from the center of the polishing pad toward the outer edge portion thereof such that the depth of the groove is the largest at the outer edge portion, thereby allowing a slurry to be smoothly discharged from the upper surface of the polishing platen. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a schematic perspective view illustrating a CMP apparatus; 
           [0021]      FIG. 2  is a schematic side view illustrating the CMP apparatus; 
           [0022]      FIG. 3  is a top view of a polishing pad; 
           [0023]      FIG. 4  is a sectional view of a polishing pad according to a conventional technique; 
           [0024]      FIG. 5A  is a sectional view of a polishing pad according to a first embodiment of the present invention; 
           [0025]      FIG. 5B  is a sectional view of the polishing pad according to the first embodiment of the present invention; 
           [0026]      FIGS. 6A and 6B  are views for describing one-mode of pad groove walls of the polishing pad according to the present invention; 
           [0027]      FIG. 7  is a sectional view of a polishing pad according to a second embodiment of the present invention; 
           [0028]      FIG. 8  is a top view of a polishing pad according to a third embodiment of the present invention; 
           [0029]      FIG. 9  is a sectional view of the polishing pad according to the third embodiment of the present invention; 
           [0030]      FIG. 10  is a top view of a polishing pad according to a fourth embodiment of the present invention; and 
           [0031]      FIG. 11  is a sectional view of the polishing pad according to the fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
       First Embodiment 
       [0033]      FIGS. 5A and 5B  show sectional views of a polishing pad  30  according to a first embodiment of the present invention. The polishing pad  30  is made of a synthetic resin such as polyurethane. Further, the polishing pad  30  has pad grooves  32  formed in grid like fashion like in a polishing pad  6  shown in  FIG. 3 . The pad grooves  32  are formed by mechanical machining. Further,  FIG. 5A  is a sectional view taken along the line A-A′ of  FIG. 3 .  FIG. 5B  is a sectional view taken along the line B-B′ of  FIG. 3 . Further, a sectional shape of the pad groove  32  is a U-shape. A pad groove base portion  32   a  is a flat plane. Pad groove walls  32   b  are walls perpendicular to the pad groove base portion  32   a . This sectional shape is one example as described after. 
         [0034]    A dimension of a groove width W 30  of the pad groove  32  is the same as that of the pad groove  32  in any place on the pad. Further, a pitch P 30  of the pad grooves  32  is also constant. 
         [0035]    From a center  30   c  of the polishing pad  30  toward an outer edge thereof, a depth of the pad groove  32  increases. That is, in the vicinity of the center  30   c  of the polishing pad  30 , the pad groove  32  has a depth D 2 , in a middle portion between the center  30   c  and the outer edge, the pad groove  32  has a depth D 3 , and in the outer edge, the pad groove  32  has a depth D 4 . As shown in  FIG. 5B , when a surface of any pad grooves  32  is viewed in section, it is understood that the pad grooves  32  has an inclined surface  32   a ′ toward the outer edge of the polishing pad  30  with the center  30   c  of the polishing pad  30  being a highest point. 
         [0036]    Note that, the polishing pad  30  is composed of two layers, that is, an upper layer polishing pad  30   a  and a lower layer polishing pad  30   b . The pad grooves  32  are formed in the upper layer polishing pad  30   a.    
         [0037]    As described above, the polishing pad  30  has a structure in which the depth of the pad groove  32  increases from the center  30   c  toward the outer edge. Accordingly, with a centrifugal force caused by rotation of a polishing platen  4  and also with a function of the inclined surface  32   a ′ of the pad groove base portion  32 , a slurry  16  and shavings produced by the polishing pad  30  can easily be discharged. The outer edge of the polishing pad  6  corresponds to lower portions of the inclined surface  32   a ′, so the slurry  16  and the shavings flow toward the outer edge. When the slurry  16  and the shavings are easily discharged, anew slurry  16  supplied from a slurry nozzle  14  is supplied to a polishing surface of a wafer  12 , thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves  32  formed in the polishing pad  30 , holes may further be formed therein. 
         [0038]    A CMP apparatus  2  including the polishing pad  30  is used to polish the wafer  12  in the following manner. First, the polishing pad  30  is adhered on an upper surface of the polishing platen  4 . A spindle carrier  8  retains the wafer  12  and the spindle carrier  8  presses the wafer  12  to the polishing pad  30  at a constant load. Through the slurry nozzle  14 , from a storage container (not shown) of the slurry  16 , the slurry  16  is supplied to the upper surface of the polishing pad  30  continuously or intermittently. The polishing platen  4  rotates at a constant rotation speed and the spindle carrier  8  also rotates at a constant rotation speed. 
         [0039]      FIGS. 6A and 6B  are views for describing another example of pad groove walls of the polishing pad  30  according to the present invention.  FIGS. 6A and 6B  are examples of pad groove  41  illustrating a shallow pad groove  44  and deep pad groove  46 . In correspondence with the above description made with reference to  FIGS. 5A and 5B , the shallow pad groove  44  having a depth D 2 ′ indicates the pad groove  41  in the vicinity of the center  30   c  of the polishing pad  32  and the deep pad groove  46  having a depth D 4 ′ indicates the pad groove  41  in the vicinity of the outer edge of the polishing pad  30 . A width W 3  of a base portion of the shallow pad groove  44  is smaller than a width W 2  of an upper portion thereof, and pad groove walls  44   a  form inclined surfaces. Further, a width W 5  of a base portion of the deep pad groove  46  is smaller than a width W 4  of an upper portion thereof, and pad groove walls  46   a  form inclined surfaces. In this case, the width W 2  and the width W 4  of the upper portions have the same dimension. The pad grooves  41  are formed by mechanical machining. 
         [0040]    As described above, the pad groove walls  44   a  and  46   a  of the pad grooves  41  form the inclined surfaces, thereby making the slurry  16  and the shavings produced by the polishing pad  30  difficult to remain in the pad grooves  41  and easily discharged. That is, the inclined surfaces of the pad groove walls  44   a  and  46   a  have an effect of preventing generation of the micro scratches on the wafer  12 . 
       Second Embodiment 
       [0041]      FIG. 7  shows a sectional view of a polishing pad  40  according to a second embodiment of the present invention. The polishing pad  40  is made of a synthetic resin such as polyurethane. Further, the polishing pad  40  has pad grooves  42  formed in a grid like fashion like in the polishing pad  6  shown in  FIG. 3 . The pad grooves  42  are formed by mechanical machining. Further,  FIG. 7  is a sectional view taken along the line A-A′ of  FIG. 3 . Further, a sectional shape of the pad groove  42  is a U-shape. A pad groove base portion  42   a  is a plane. Pad groove walls  42   b  are walls perpendicular to the pad groove base portion  42   a . Note that, as shown in  FIG. 6 , in a sectional shape of the pad groove  42 , the pad groove walls  42   b ′ may form the inclined surfaces. 
         [0042]    A dimension of a groove width W 40  of the pad groove  42  is the same as that of the pad groove  42  in any place. Further, a pitch P 40  of the pad grooves  42  is also constant. 
         [0043]    The polishing pad  40  has a structure in which the pad grooves  42  are divided from an outer edge side into groups of a first pad grooves  40   d , a second pad grooves  40   e , a third pad grooves  40   f , a fourth pad grooves  40   g , and a fifth pad grooves  40   h , and a groove depth of the each group is set for each group. A depth D 5  of the first pad grooves  40   d  is the largest. The nearer the group is to a center  40   c , the smaller the groove depth is. For example, the third pad grooves  40   f  have a depth D 6 . A depth D 7  of the fifth pad grooves  40   h  is the smallest. 
         [0044]    Note that, the polishing pad  40  is composed of two layers, that is, an upper layer polishing pad  40   a  and a lower layer polishing pad  40   b . The pad grooves  42  are formed in the upper layer polishing pad  40   a . Each of the upper layer polishing pad  40   a  and the lower layer polishing pad  40   b  has a thickness of about 1 to 2 mm. The depth D 5  of the first pad grooves  40   d  is 80% of a thickness of the upper layer polishing pad  40   a . The depth D 6  of the third pad grooves  40   f  is 60% of the thickness of the upper layer polishing pad  40   a . The depth D 7  of the fifth pad grooves  40   h  is 40% of the thickness of the upper layer polishing pad  40   a.    
         [0045]    As described above, the polishing pad  40  has a structure in which the depth of the pad grooves  42  stepwisely increases from the center  40   c  towards the outer edge. Accordingly, with a centrifugal force caused by rotation of the polishing platen  4  and also with a function of the depth of the pad grooves  42  increasing stepwisely, the slurry  16  and shavings produced by the polishing pad  40  can easily be discharged. When the slurry  16  and the shavings are easily discharged, a new slurry  16  supplied from the slurry nozzle  14  is supplied to the polishing surface of the wafer  12 , thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves  42  formed in the polishing pad  40 , holes may further be formed therein. 
       Third Embodiment 
       [0046]      FIG. 8  is a top view of a polishing pad  50  according to a third embodiment of the present invention. The polishing pad  50  is made of a synthetic resin such as polyurethane. Pad grooves  52  are arranged so as to extend radially from a center of the polishing pad  50 . The pad grooves  52  are formed by mechanical machining. Further, the pad grooves  52  has a U-shaped section (not shown). The pad grooves section may be inclined surface as shown in  FIGS. 6A and 6B  but U-shaped section. 
         [0047]      FIG. 9  is a sectional view of the polishing pad  50  according to the third embodiment of the present invention.  FIG. 9  is a sectional view taken along the line C-C′ of  FIG. 8 . From a center  50   c  of the polishing pad  50  toward an outer edge of the polishing pad  50 , a pad groove base portion  52   a  forms an inclined surface. Note that, the polishing pad  50  is composed of two layers, that is, an upper layer polishing pad  50   a  and a lower layer polishing pad  50   b . The pad grooves  52  are formed in the upper layer polishing pad  50   a.    
         [0048]    As described above, the polishing pad  50  has a structure in which a depth of the pad groove  52  increases from the center  50   c  toward the outer edge. Accordingly, with a centrifugal force caused by rotation of the polishing platen  4  and also with a function of the pad groove  52  having the depth increasing, the slurry  16  and shavings produced by the polishing pad  50  can easily be discharged. When the slurry  16  and the shavings are easily discharged, a new slurry  16  supplied from the slurry nozzle  14  is supplied to the polishing surface of the wafer  12 , thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves  52  formed in the polishing pad  50 , holes may further be formed therein. 
       Fourth Embodiment 
       [0049]      FIG. 10  is a top view of a polishing pad  60  according to a fourth embodiment of the present invention. The polishing pad  60  is formed of a synthetic resin such as polyurethane. Pad grooves  62  are arranged so as to extend spirally from a center of the polishing pad  60 . The pad grooves  62  are formed by mechanical machining. Further, the pad groove  62  has a U-shaped section (not shown). However, as shown in  FIG. 6 , pad groove walls may form inclined surfaces. 
         [0050]      FIG. 11  is a sectional view of the polishing pad  60  according to the fourth embodiment of the present invention.  FIG. 11  is a sectional view taken along the line D-D′ of  FIG. 10 . From a center  60   c  of the polishing pad  60  toward an outer edge of the polishing pad  60 , a pad groove base portion  62   a  forms an inclined surface. Note that, the polishing pad  60  is composed of two layers, that is, an upper layer polishing pad  60   a  and a lower layer polishing pad  60   b . The pad grooves  62  are formed in the upper layer polishing pad  60   a.    
         [0051]    As described above, the polishing pad  60  has a structure in which from the center  60   c  to the outer edge, a depth of the pad groove  62  increases. Accordingly, with a centrifugal force caused by the rotation of the polishing platen  4  and also with a function of the pad groove  62  having the depth increasing, the slurry  16  and shavings produced by the polishing pad  60  are easily discharged. When the slurry  16  and the shavings are easily discharged, a new slurry  16  supplied by the slurry nozzle  14  is supplied to the polishing surface of the wafer  12 , thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves  62  formed in the polishing pad  60 , holes may further be formed therein. 
         [0052]    In the above description, the first to fourth embodiments are described. However, the first to fourth embodiments may be employed in any combination.