Patent Publication Number: US-8118645-B2

Title: Polishing method, polishing pad, and polishing system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 97103481, filed on Jan. 30, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a polishing pad, a polishing system, and a polishing method, in particular, to a polishing pad, a polishing system, and a polishing method capable of achieving a better polishing uniformity for the surface of a workpiece. 
     2. Description of Related Art 
     With progress of industrial technology, planarization processes are usually adopted for producing various devices, and a polishing process is one of the planarization processes often employed in the industry. Generally, in the polishing process, a fixed workpiece is pressed on a polishing pad by a pressure applied to the workpiece, and capable of moving relative to the surface of the polishing pad. As such, the surface of the workpiece is partially removed through friction generated by the above relative movement, and thus gradually becomes planarized. 
       FIG. 1  is a schematic top view of a conventional circular polishing pad. The circular polishing pad  110  includes a plurality of concentric circular grooves  120 . The concentric circular grooves  120  are used to accommodate or remove residues or by-products generated by polishing, and enable a workpiece  130  to be easily detached away from the circular polishing pad  110  when the polishing process is completed. 
     During the polishing process, the circular polishing pad  110  rotates, and the workpiece  130  in contact with the surface of the circular polishing pad  110  rotates as well, expecting that every portion on the surface of the workpiece  130  may contact the concentric circular grooves  120 . However, each of the concentric circular grooves  120  on the conventional circular polishing pad  110  has a circular shape, and the workpiece  130  rotates around its central axis. Thus, when a particular point moves periodically to a position where a direction between the particular point and the center of the workpiece  130  is perpendicular to a tangential direction of the grooves, the particular point will be constantly at a groove position or a non-groove position. For example, if the particular point is at the groove position, points adjacent to the particular point would be constantly at the non-groove positions, thus affecting the polishing uniformity. Moreover, the above problem gets worse at positions closer to the central portion of the workpiece  130 , as the central portion of the workpiece  130  is almost constantly in contact with a specific position (for example, the groove position or the non-groove position) on the circular polishing pad  110  during the whole polishing process. Therefore, the polishing rate of the central portion of the workpiece  130  is lower or higher than the polishing rates of the other near portions, depending on whether the central portion is constantly in contact with the groove position or the non-groove position. The problem of non-uniform polishing rate of the workpiece  130  may eventually degrade the reliability of the device. 
     Therefore, a polishing pad and a polishing method are required to provide a better polishing uniformity. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a polishing method to achieve a workpiece with a flat surface. 
     The present invention is further directed to a polishing pad capable of achieving a uniform polishing rate for the surface of a workpiece. 
     The present invention is also directed to a polishing system capable of achieving a better polishing uniformity for every portion on the surface of a workpiece. 
     A polishing method including the following steps is provided. First, a polishing pad having a plurality of grooves is provided. A width of each groove is W, and a pitch between two adjacent grooves is P. Then, an oscillatory movement distance of a workpiece on the polishing pad is set. The oscillatory movement distance enables any particular point on the workpiece to cross the same number of grooves, when a direction between the particular point and the center of the workpiece is perpendicular to a tangential direction of the grooves. Afterward, a polishing process is performed on the workpiece with the oscillatory movement distance. 
     Another polishing method including the following steps is provided. First, a polishing pad having a plurality of grooves is provided. A width of each groove is W, and a pitch between two adjacent grooves is P. Then, an oscillatory movement distance of a workpiece on the polishing pad is set as D≅P×N−W, and N is a positive integer. Afterward, a polishing process is performed on the workpiece with the oscillatory movement distance. 
     A polishing pad for performing a polishing process on a workpiece is further provided. During the polishing process, the workpiece is set with an oscillatory movement distance D on the polishing pad. The polishing pad includes a plurality of grooves, a width W of each groove and a pitch P between two adjacent grooves satisfy D≅P×N−W, and N is a positive integer. 
     A polishing system including a polishing pad and a workpiece is also provided. The polishing pad has a plurality of grooves, a width of each groove is W, and a pitch between two adjacent grooves is P. The workpiece is disposed on the polishing pad, and the workpiece is set with an oscillatory movement distance D on the polishing pad. The oscillatory movement distance is D≅P×N−W, and N is a positive integer. 
     According to the polishing method, the polishing pad, and the polishing system provided by the present invention, relative relations between the oscillatory movement distance of the workpiece on the polishing pad, the width of each groove, and the pitch between two grooves can be adjusted to achieve a better polishing uniformity for the surface of the polished workpiece. 
     In order to make the aforementioned and other objectives, features, and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a portion of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic top view of a conventional circular polishing pad. 
         FIG. 2  is a schematic cross-sectional view of a polishing system according to an embodiment of the present invention. 
         FIG. 3  is a schematic top view of a polishing pad according to an embodiment of the present invention. 
         FIG. 4  is a schematic top view of a polishing pad according to another embodiment of the present invention. 
         FIG. 5  is a schematic cross-sectional view of a polishing system according to another embodiment of the present invention. 
         FIG. 6  is a schematic top view of a polishing pad according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 2  is a schematic cross-sectional view of a polishing system according to an embodiment of the present invention, and  FIG. 3  is a schematic top view of a polishing pad according to an embodiment of the present invention. It should be noted that, in order to simplify the drawing, the rotation of a workpiece and the structure of a workpiece carrier are omitted in  FIG. 3 , but it is not intended to limit the scope of the present invention. Referring to  FIG. 2 , a polishing system  300  includes a polishing platen  302 , a workpiece carrier  304 , a polishing pad  310 , and a workpiece  330 . The polishing platen  302  is, for example, used to sustain the polishing pad  310 . The workpiece carrier  304  is, for example, used to fix the workpiece  330  on a surface of the polishing pad  310 . Further, in an embodiment, the polishing system  300  is selectively provided with a polishing slurry or solution during the polishing process, such that the polishing system  300  becomes a chemical mechanical polishing (CMP) process. The polishing pad, the polishing system, and the polishing method of the present invention are applicable to the polishing process during the fabrication of devices, such as semiconductors, integrated circuits, micro-electromechanical systems, energy transforming devices, communication devices, optical devices, storage disks, displays, and other devices need to be fabricated using the polishing process. The workpieces  330  used to fabricate the above devices include, but not limited to, semiconductor wafers, III-V group wafers, storage device carriers, ceramic substrates, polymer substrates, and glass substrates. 
     The polishing pad  310  is, for example, adhered to a surface of the polishing platen  302  for polishing the workpiece  330 . The polishing pad  310  is, for example, formed by a polymer base material, and the polymer base material may be synthesized by a thermosetting resin or a thermoplastic resin. In addition to the polymer base material, the polishing pad  310  may further include conductive materials, abrasive particles, micro-spheres, or soluble additives embedded in the polymer base material. 
     Referring to  FIGS. 2 and 3 , the polishing pad  310  has a plurality of grooves  320 . In this embodiment, the polishing platen  302  is a circular rotary disc, the polishing pad  310  is a circular polishing pad, and the grooves  320  are, for example, concentric circular grooves. A width of each groove  320  is W, and a pitch between two adjacent grooves  320  is P. When the polishing platen  302  rotates, the polishing pad  310  adhered to the surface of the polishing platen  302  is driven to rotate. 
     The workpiece carrier  304  is disposed on the polishing platen  302 , for fixing the workpiece  330  and pressing the workpiece  330  on the surface of the polishing pad  310 , such that the surface of the workpiece  330  to be polished may contact the polishing pad  310 . In addition to enabling the workpiece  330  to rotate on the polishing pad  310 , the workpiece carrier  304  can also drive an oscillatory movement and make the workpiece  330  shift back and forth on the polishing pad  310 , such that the contact between the workpiece  330  and the polishing pad  310  may not be confined within a certain region. Thereby, the polishing rate and uniformity become more stable, and the polishing process will be more even. 
     It should be particularly illustrated that, the workpiece  330  has an oscillatory movement distance D due to the back and forth movement on the polishing pad  310 , and the oscillatory movement distance D satisfies an equation as below:
 
 D≅P×N−W , and  N  is a positive integer.
 
     In detail, an oscillatory movement is driven by the workpiece carrier  304  to shift the workpiece  330  back and forth on the polishing pad  310 , and a direction of the oscillatory movement is perpendicular to a tangential direction of the grooves  320 . Taking the concentric circular grooves for example, the direction of the oscillatory movement is a radial direction of the concentric circular grooves. In addition, the oscillatory movement distance D of the workpiece  330  is approximately equal to a difference obtained by subtracting the width W of the groove  320  from integer multiples of the pitch P between two adjacent grooves  320  on the polishing pad  310 . 
     For example, when a direction between a particular point and the center of the workpiece  330  is perpendicular to a tangential direction of the grooves, as shown in a partial enlarged view of a region M 1  in  FIG. 3 , before the workpiece  330  moving oscillatingly, a particular point A on the workpiece  330  contacts a groove position of the polishing pad  310 , and another particular point B on the workpiece  330  contacts a non-groove position of the polishing pad  310 . When N=1, i.e., the oscillatory movement distance D of the workpiece  330  on the polishing pad  310  is set as D≅P−W, the workpiece  330 , for example, shifts to a position  331 , the particular point A on the workpiece  330  moves to a position A 1  with the oscillatory movement of the workpiece  330 , and meanwhile the particular point B moves to a position B 1  with the oscillatory movement of the workpiece  330 . In the circumstance, the particular point A on the workpiece  330  originally located at a groove position may move to the non-groove position A 1 , and the particular point B on the workpiece  330  originally located at a non-groove position may move across a groove to the adjacent non-groove position B 1 . Therefore, when moving to the position  331  with the oscillatory movement of the workpiece  330 , the particular points A and B on the workpiece  330  respectively contact the grooves  320  on the polishing pad  310  once. As such, the particular portions on the workpiece  330  may alternately cross the groove and non-groove positions instead of being fixed at the groove or non-groove positions. 
       FIG. 4  is a schematic top view of a polishing pad according to another embodiment of the present invention. In  FIG. 4 , the same means as those in  FIG. 3  are represented by the same symbols, and the illustrations thereof are omitted. In another embodiment, for example, when N=2, the oscillatory movement distance D of the workpiece  330  on the polishing pad  310  is set as D≅2P−W. When a direction between a particular point and the center of the workpiece  330  is perpendicular to a tangential direction of the grooves, as shown in a partial enlarged view of a region M 2  in  FIG. 4 , and the workpiece  330  shifts to a position  332 , a particular point A on the workpiece  330  originally located at a groove position may move across another groove to a non-groove position A 2 , and a particular point B on the workpiece  330  originally located at a non-groove position may move across two grooves to an adjacent non-groove position B 2 . Moreover, when moving to the position A 2  with the oscillatory movement of the workpiece  330 , the particular point A on the workpiece  330  may contact the grooves  320  on the polishing pad  310  twice. When moving to the position B 2  with the oscillatory movement of the workpiece  330 , the particular point B on the workpiece  330  may contact the grooves  320  on the polishing pad  310  twice as well. Therefore, the particular points on the workpiece  330  may uniformly and alternately cross the groove and non-groove positions instead of being fixed at the groove or non-groove positions. 
     Similarly, when N=3, 4, . . . , or any other positive integer, the particular point A on the workpiece  330  originally located at a groove position may move across another N−1 grooves to a non-groove position A N  (not shown) with the oscillatory movement of the workpiece  330 , and the particular point B on the workpiece  330  originally located at a non-groove position may move across N grooves to a non-groove position B N  (not shown) with the oscillatory movement of the workpiece  330 . In addition, when shifting to the positions A N  and B N , the particular points A and B on the workpiece  330  respectively cross the same number of the grooves  320  on the polishing pad  310 , i.e., N grooves. As such, every particular point on the workpiece  330  may uniformly cross the groove and non-groove positions instead of being fixed at the groove or non-groove positions. 
     In this manner, during the whole polishing process, by adjusting the oscillatory movement distance D of the workpiece  330  on the polishing pad  310 , a particular point may not be fixed at a groove or non-groove position, when a direction between the particular point and the center of the workpiece  330  is perpendicular to a tangential direction of the grooves. Particularly, the central portion of the workpiece  330  may not constantly contact the specific position (for example, the groove position or the non-groove position) on the polishing pad  310  during the whole polishing process. Therefore, the polishing rate of the central portion of the workpiece  330  would be closer to the polishing rates of the other near portions of the workpiece  330 , thus achieving a better polishing uniformity for the surface of the workpiece  330 . 
     The above embodiment takes a circular polishing platen, a circular polishing pad, and concentric circular grooves as an example, but the present invention is not limited thereto. In addition to the above embodiment, the present invention also has other implementation aspects.  FIG. 5  is a schematic cross-sectional view of a polishing system according to another embodiment of the present invention, and  FIG. 6  is a schematic top view of a polishing pad according to another embodiment of the present invention. In  FIGS. 5 and 6 , illustrations of means similar to those in  FIG. 2  are omitted. Further, in order to simplify the drawing, the rotation of a workpiece and the structure of a workpiece carrier are omitted in  FIG. 6 , but it is not intended to limit the scope of the present invention. Referring to  FIGS. 5 and 6  together, in this embodiment, a polishing system  600  includes a polishing platen  602 , a workpiece carrier  604 , driving wheels  606 , a polishing pad  610 , and a workpiece  630 . In addition, in an embodiment, the polishing system  600  is selectively provided with a polishing slurry or solution during the polishing process, such that the polishing system  600  becomes a CMP process. 
     The polishing platen  602  is, for example, a fixed platen. The polishing pad  610 , for example, a strip polishing pad, is movably sustained on a surface of the polishing platen  602 . The polishing pad  610  is driven by the driving wheels  606  disposed on two sides of the polishing pad  610  to move like a conveyer belt linearly, i.e., in a moving direction  640  as shown in  FIGS. 5 and 6 . Moreover, the polishing pad  610  has a plurality of grooves  620 . In an embodiment, the groove  620  is a linear groove, and a longitudinal direction of each groove  620  is, for example, parallel to the moving direction  640  of the polishing pad  610 . The grooves  620  are, for example, arranged parallel to each other, a width of each groove  620  is W, and a pitch between two adjacent grooves  620  is P. 
     The workpiece carrier  604  for fixing the workpiece  630  on a surface of the polishing pad  610  is disposed on the polishing platen  602 . In addition to enabling the workpiece  630  to rotate on the polishing pad  610 , the workpiece carrier  604  can also drive an oscillatory movement to make the workpiece  630  shift back and forth on the polishing pad  610 , so as to improve the polishing uniformity. The direction of the back and forth oscillatory movement of the workpiece  630  on the polishing pad  610  is, for example, perpendicular to a tangential direction of the grooves  620 , i.e., perpendicular to the longitudinal direction of the linear grooves  620  in this embodiment. Further, the workpiece  330  has an oscillatory movement distance D satisfying an equation below on the polishing pad  610 :
 
 D≅P×N−W , and  N  is a positive integer.
 
     In detail, for example, when N=1, referring to  FIG. 6 , during the polishing process, the workpiece  630  shifts back and forth on the polishing pad  610  with an oscillatory movement distance D≅P−W to a position  631 . When a direction between a particular point and the center of the workpiece  630  is perpendicular to a tangential direction of the grooves  620 , as shown in a partial enlarged view of a region M 3  in  FIG. 6 , a particular point X on the workpiece  630  originally located at a groove position may move to a non-groove position X 1  with the oscillatory movement of the workpiece  630 , and meanwhile a particular point Y on the workpiece  630  originally located at a non-groove position may move across a groove to an adjacent non-groove position Y 1  with the oscillatory movement of the workpiece  630 . Therefore, when moving to the position  631  with the oscillatory movement of the workpiece  630 , the particular points X and Y on the workpiece  330  respectively contact the grooves  620  on the polishing pad  610  once. Therefore, the particular points on the workpiece  630  may alternately cross the groove and non-groove positions instead of being fixed at the groove or non-groove positions. 
     Similarly, when N=2, 3, . . . , and any other random positive integer, the particular point X on the workpiece  630  originally located at a groove position may move across another N−1 grooves to a non-groove position X N  (not shown) with the oscillatory movement of the workpiece  630 , and the particular point Y on the workpiece  630  originally located at a non-groove position may move across N grooves to a non-groove position Y N  (not shown) with the oscillatory movement of the workpiece  630 . In addition, when oscillating and shifting to the positions X N  and Y N , the particular points X and Y on the workpiece  630  respectively cross the same number of the grooves  620  on the polishing pad  610 , i.e., N grooves. As such, every particular point on the workpiece  630  may uniformly cross the groove and non-groove positions instead of being fixed at the groove or non-groove positions. 
     Moreover, in the above embodiment, if the direction of the back and forth oscillatory movement of the workpiece  630  on the polishing pad  610  is not perpendicular to a tangential direction of the grooves  620 , for example, having an angle of θ to the longitudinal direction of the linear grooves  620 , the workpiece  630  has an oscillatory movement distance D satisfying an equation below on the polishing pad  610 :
 
 D ×sin θ≅ P×N−W , and  N  is a positive integer.
 
     In this manner, in the polishing system  600 , by adjusting the oscillatory movement distance D of the workpiece  630  on the polishing pad  610 , the particular points of the workpiece  630  can alternately cross the groove and non-groove positions, so as to achieve a better polishing uniformity for the surface of the workpiece  630 . 
     Further, the polishing method provided by the present invention is suitable for polishing the surface of a workpiece. First, a polishing pad having a plurality of grooves is provided. A width of each groove is W, and a pitch between two adjacent grooves is P. The polishing pad is, for example, a circular polishing pad or a strip polishing pad. When the circular polishing pad is adopted, the grooves on the polishing pad are concentric circular grooves, and when the strip polishing pad is adopted, the grooves on the polishing pad are linear grooves. It should be noted that, the polishing pad used in the polishing method of the present invention may also be any type of polishing pad employed in the polishing system of the above embodiments, and the present invention is not limited thereto. Afterward, an oscillatory movement distance of the workpiece on the polishing pad is set. The oscillatory movement distance enables any particular point on the workpiece to cross the same number of grooves, when a direction between the particular point and the center is perpendicular to a tangential direction of the grooves. In an embodiment, the oscillatory movement distance D≅P×N−W, and N is a positive integer. Then, a polishing process is performed on the workpiece with the oscillatory movement distance. The particular points on the workpiece may not be fixed at the groove or non-groove positions by adjusting the oscillatory movement distance. Particularly, the central portion of the workpiece may not constantly contact the specific position (for example, the groove position or the non-groove position) on the polishing pad during the whole polishing process. Therefore, the polishing method of the present invention may achieve a better polishing uniformity. 
     It should be further illustrated that, in addition to adjusting the oscillatory movement distance D of the workpiece on the polishing pad through the configuration of the grooves on the polishing pad, the present invention may also be applied to a polishing system with a fixed oscillatory movement distance D of the workpiece on the polishing pad. In an embodiment, when the oscillatory movement distance D is fixedly set as 25.4 mm, a suitable polishing pad may be fabricated according to the fixed oscillatory movement distance D of the workpiece on the polishing pad. That is, the fabricated polishing pad has a groove width W and a pitch P between two adjacent grooves satisfying an equation of D≅P×N−W, where N is a positive integer. Taking a fixed groove width W=0.6 mm as an example, when N=4, the pitch P between two adjacent grooves is approximately 6.5 mm, and when N=5, the pitch P between two adjacent grooves is approximately 5.2 mm. 
     In view of the above, according to the polishing method, the polishing pad, and the polishing system of the present invention, by adjusting the oscillatory movement distance of the workpiece on the polishing pad and the configuration of the grooves on the polishing pad, the particular points on the workpiece may uniformly and alternately cross the groove and non-groove positions, so as to achieve a better uniformity for the surface of the polished workpiece. Optionally, the grooves of the polishing pad having above-mentioned configuration may only be disposed on a region corresponding to a part of a polishing track that the polished workpiece passes by, instead of being disposed on the whole surface of the polishing pad. For example, the disposed region is only in the middle part of the polishing track corresponding to the central portion of the workpiece, such as corresponding to within ±2R/3, ±R/2, ±R/3, ±R/4, ±R/5, ±R/10, or other certain range of the central portion of the workpiece, wherein R is radius of the workpiece. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.