Abstract:
A polishing method and a polishing system are provided. By means of adjusting a rotational center of a polishing article corresponding to positions of a polishing pad or polishing pads, a polishing rate of the polishing article surface has a better uniformity, resulted from compensation of polishing rates at the rotational center of the polishing article.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 100109552, filed Mar. 21, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a polishing method and a polishing system. More particularly, the invention relates to a polishing system capable of providing better polishing uniformity on a surface of a polishing article and a polishing method of the same. 
     2. Description of Related Art 
     With the progress in the industry, the planarization process is often adopted for fabricating various devices. In the planarization process, the chemical mechanical polishing (CMP) process is often applied in the industry. Generally, the chemical mechanical polishing process is performed by supplying a slurry having chemical mixtures on a polishing pad, applying a pressure on the polishing article to be polished to press it on the polishing pad, and providing a relative motion between the polishing article and the polishing pad. Through the mechanical friction generated by the relative motion and the chemical effect of the polishing slurry, a portion of the surface of the planarization. 
     The conventional polishing pad includes a plurality of concentric circular grooves used to accommodate or remove residues or by-products generated from the polishing process, and enable a polishing article to be easily detached away from the circular polishing pad when the polishing process is completed. During the polishing process, not only does the polishing pad rotate, but the polishing article in contact with the surface of the polishing pad also rotates. However, as the concentric circular grooves on the conventional polishing pad are right circular grooves, and the polishing article rotates along an axis passing through the center point thereof as a rotational axis. Thus, when the direction between a particular point and the center point of the polishing article is perpendicular to the tangential direction of the grooves, the particular point will constantly contact a groove position or a non-groove position. For example, if the particular point contacts the groove position, points adjacent to the particular point would constantly contact the non-groove positions, thus affecting the polishing uniformity. Moreover, the above problem gets worse at positions closer to the central portion of the polishing article, as the central portion of the polishing article almost constantly contacts a specific position (for example, the groove position or the non-groove position) on the polishing pad during the whole polishing process. Therefore, the polishing rate of the central portion of the polishing article is lower or higher than the polishing rates of the other near portions, depending on whether the central portion constantly contacts the groove position or the non-groove position. The problem of non-uniform polishing rate of the polishing article may eventually degrade the reliability of the device. 
     Therefore, a polishing method and a polishing system are required to provide a better polishing uniformity. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a polishing method and a polishing system capable of providing a better polishing uniformity on the surface of a polishing article. 
     The invention is directed to a polishing method including the following. A first polishing pad and a second polishing pad are provided. The first polishing pad has a plurality of first high polishing rate regions and a plurality of first low polishing rate regions. The second polishing pad has a plurality of second high polishing rate regions and a plurality of second low polishing rate regions. A polishing article is set on the first polishing pad to perform a first polishing process. Thereafter, the polishing article is moved onto the second polishing pad to perform a second polishing process. Here, a rotational center of the polishing article corresponds to one of the first high polishing rate regions during the first polishing process and corresponds to one of the second low polishing rate regions during the second polishing process. Or, the rotational center of the polishing article corresponds to one of the first low polishing rate regions during the first polishing process and corresponds to one of the second high polishing rate regions during the second polishing process. 
     The invention is also directed to a polishing method including the following. A polishing pad having a plurality of high polishing rate regions and a plurality of low polishing rate regions is provided. A polishing article is set on the polishing pad to perform a first polishing process. Thereafter, the polishing article is moved to perform a second polishing process. Herein, a rotational center of the polishing article corresponds to one of the first high polishing rate regions during the first polishing process and corresponds to one of the low polishing rate regions during the second polishing process. Or, the rotational center of the polishing article corresponds to one of the low polishing rate regions during the first polishing process and corresponds to one of the high polishing rate regions during the second polishing process. 
     The invention is further directed to a polishing method including the following. A polishing pad having a plurality of high polishing rate regions and a plurality of low polishing rate regions is provided. A polishing article is set on the polishing pad to perform a first oscillatory polishing process. When performing the first oscillatory polishing process, a rotational center of the polishing pad and a rotational center of the polishing article have a first shortest distance D 1  therebetween. A second oscillatory polishing process is then performed. When performing the second oscillatory polishing process, the rotational center of the polishing pad and the rotational center of the polishing article have a second shortest distance D 2  therebetween, and D1−D 2 =P×N+P×(30%˜70%), where P represents a distance between two adjacent low polishing rate regions and N represents an integer. 
     The invention is additionally directed to a polishing system suitable for polishing a polishing article. The polishing system includes a first polishing pad and a second polishing pad. The first polishing pad has a plurality of first high polishing rate regions and a plurality of first low polishing rate regions. The second polishing pad has a plurality of second high polishing rate regions and a plurality of second low polishing rate regions. Particularly, when the polishing article is set on the first polishing pad to perform a first polishing process, a rotational center of the polishing article corresponds to one of the first high polishing rate regions, and when the polishing article is moved onto the second polishing pad to perform a second polishing process, the rotational center of the polishing article corresponds to one of the second low polishing rate regions. Or, when the polishing article is set on the first polishing pad to perform a first polishing process, a rotational center of the polishing article corresponds to one of the first low polishing rate regions, and when the polishing article is moved onto the second polishing pad to perform a second polishing process, the rotational center of the polishing article corresponds to one of the second high polishing rate regions. 
     The invention is further directed to a polishing system including a polishing pad and a polishing article. The polishing pad includes a plurality of high polishing rate regions and a plurality of low polishing rate regions. The polishing article is set on the polishing pad. Especially, when the polishing article is set on the polishing pad to perform a first polishing process, a rotational center of the polishing article corresponds to one of the high polishing rate regions, and when the polishing article is set to the polishing pad to perform a second polishing process, the rotational center of the polishing article corresponds to one of the low polishing rate regions. Or, when the polishing article is set on the polishing pad to perform a first polishing process, a rotational center of the polishing article corresponds to one of the low polishing rate regions, and when the polishing article is set on the polishing pad to perform a second polishing process, the rotational center of the polishing article corresponds to one of the high polishing rate regions. 
     The invention is further directed to a polishing system including a polishing pad and a polishing article. The polishing pad has a plurality of high polishing rate regions and a plurality of low polishing rate regions. The polishing article is set on the polishing pad. In particular, when a first polishing process is performed for the polishing article on the polishing pad, a rotational center of the polishing pad and a rotational center of on the polishing pad, a rotational center of the polishing pad and a rotational center of the polishing article have a first shortest distance D 1  therebetween. Moreover, when a second polishing process is performed for the polishing article on the polishing pad, the rotational center of the polishing pad and the rotational center of the polishing article have a second shortest distance D 2  therebetween. Herein, D1−D 2 =P×N+P×(30%˜70%), and P represents a distance between two adjacent low polishing rate regions and N represents an integer. 
     In light of the foregoing, in the invention, the polishing rates at the rotational center of the polishing article can be compensated by one another through adjusting positions of the rotational center of the polishing article corresponding to the polishing pad, such that the polishing rate at the surface of the polishing article has a better uniformity. 
     In order to make the aforementioned and other features and advantages of the invention more comprehensible, several embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  illustrates a schematic top view of a polishing system according to an embodiment of the invention. 
         FIG. 2  illustrates a schematic side view of a polishing system according to an embodiment of the invention. 
         FIG. 3  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when the polishing system in  FIGS. 1 and 2  performs a polishing process. 
         FIG. 4  illustrates a schematic top view of a polishing system according to an embodiment of the invention. 
         FIG. 5A  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when applying the polishing system in  FIG. 4  to perform a first polishing process according to another embodiment of the invention. 
         FIG. 5B  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when applying the polishing system in  FIG. 4  to perform a second polishing process according to another embodiment of the invention. 
         FIG. 6  illustrates a schematic top view of a polishing system according to an embodiment of the invention. 
         FIG. 7  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when the polishing system in  FIG. 6  performs a polishing process. 
         FIG. 8  illustrates a schematic top view of a polishing system according to another embodiment of the invention. 
         FIG. 9  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when applying the polishing system in  FIG. 8  to perform a polishing process according to an embodiment of the invention. 
         FIGS. 10A and 10B  are schematic top views illustrate a polishing system according to another embodiment of the invention. 
         FIG. 11  is a graph showing a relationship of positions of a rotational center of a polishing article versus time when applying the polishing system in  FIGS. 10A and 10B  to perform a polishing process according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  illustrates a schematic top view of a polishing system according to an embodiment of the invention.  FIG. 2  illustrates a schematic side view of a polishing system according to an embodiment of the invention. Referring to  FIGS. 1 and 2  simultaneously, the polishing system includes a first polishing pad  100 , a second polishing pad  200 , and a polishing article  10 . According to the present embodiment, the polishing system further includes a first platen  120 , a second platen  220 , and a carrier  130 . 
     The first polishing pad  100  has a plurality of first high polishing rate regions  104  and a plurality of first low polishing rate regions  102 . According to the present embodiment, at least one first groove  102   a  (as shown in  FIG. 2 ) is disposed in the first low polishing rate regions  102  of the first polishing pad  100 . Also, the first high polishing rate regions  104  of the first polishing pad  100  has a first polishing layer surface  104   a . In addition, the first high polishing rate regions  104  and the first low polishing rate regions  102  are concentric circular regions respectively, and the first high polishing rate regions  104  and the first low polishing rate regions  102  are disposed alternately. 
     In the present embodiment, the first polishing pad  100  is formed by, for example, a polymer base material. The polymer base material may be synthesized by a thermosetting resin or a thermoplastic resin. In addition to the polymer base material, the first polishing pad  100  may further include conductive materials, abrasive particles, micro-spheres, or soluble additives embedded in the polymer base material. Thus, the first polishing layer surface  104   a  in the first high polishing rate regions  104  is the polymer base material surface aforementioned. Further, the first grooves  102   a  in the first low polishing rate regions  102  are, for example, concentric circular grooves mainly used to transport and distribute a polishing slurry. 
     The first polishing pad  100  is set on the first platen  120 . In the present embodiment, the first platen  120  is a circular rotary disc. When the first platen  120  rotates, the first polishing pad  100  fixed on the surface of the first platen  120  is driven, such that the first polishing pad  100  rotates at the same time. 
     The second polishing pad  200  has a plurality of second high polishing rate regions  204  and a plurality of second low polishing rate regions  202 . According to the present embodiment, at least one second groove  202   a  (as shown in  FIG. 2 ) is disposed in the second low polishing rate regions  202  of the second polishing pad  200 . Also, the second high polishing rate regions  204  of the second polishing pad  200  has a second polishing layer surface  204   a  (as depicted in  FIG. 2 ). The second high polishing rate regions  204  and the second low polishing rate regions  202  are concentric circular regions respectively, and the second high polishing rate regions  204  and the second low polishing rate regions  202  are disposed alternately. 
     Similarly, in the present embodiment, the second polishing pad  200  is formed by, for example, a polymer base material. The polymer base material may be synthesized by a thermosetting resin or a thermoplastic resin. In addition to the polymer base material, the second polishing pad  200  may further include conductive materials, abrasive particles, micro-spheres, or soluble additives embedded in the polymer base material. Thus, the second polishing layer surface  204   a  in the second high polishing rate regions  204  is the polymer base material surface aforementioned. Further, the second grooves  202   a  in the second low polishing rate regions  202  are, for example, concentric circular grooves mainly used to transport and distribute a polishing slurry. 
     The second polishing pad  200  is set on the second platen  220 . In the present embodiment, the second platen  220  is a circular rotary disc. When the second platen  220  rotates, the second polishing pad  200  fixed on the surface of the second platen  220  is driven, such that the second polishing pad  200  rotates at the same time. 
     The carrier  130  is disposed above the first platen  120  or the second platen  220 , and used to accommodate the polishing article  10  and apply a pressure thereon to press the polishing article  10  onto a surface of the first polishing pad  100  or the second polishing pad  200 . Consequently, a surface to be polished in the polishing article  10  contacts with the first polishing pad  100  or the second polishing pad  200 . According to an embodiment, the carrier  130  enables the polishing article  10  to rotate on the first polishing pad  100  or the second polishing pad  200 , and drives an oscillatory movement shifting the polishing article  10  back and forth on the first polishing pad  100  or the second polishing pad  200 . Therefore, the contact between the polishing article  10  and the first polishing pad  100  or the second polishing pad  200  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. 
     Accordingly, steps of a polishing method performed using the polishing system mentioned above are provided below. 
     Firstly, the polishing article  10  is pressed by the carrier  130  onto the first polishing pad  100  to perform a first polishing process. Then, the carrier  130  moves the polishing article  10  onto the second polishing pad  200  to perform a second polishing process. Herein, in the beginning of the first polishing process, a rotational center C 2  of the polishing article  10  corresponding to a position of the first polishing pad  100  has to be set. Also, in the beginning of the second polishing process, the rotational center C 2  of the polishing article  10  corresponding to a position of the second polishing pad  200  has to be set. It is noted that different corresponding positions of the rotational center C 2  of the polishing article  10  respectively generate different polishing rates of the rotational center C 2  of the polishing article  10 . For example, when the rotational center C 2  of the polishing article  10  corresponds to the high polishing rate region, the rotational center C 2  of the polishing article  10  is then polished with a higher polishing rate. On the contrary, when the rotational center C 2  of the polishing article  10  corresponds to the low polishing rate region, the rotational center C 2  of the polishing article  10  is then polished with a lower polishing rate. It is specially noted that the polishing rates of the polishing article  10  in the first and second polishing processes can be compensated, so that an overall surface of the polishing article  10  (including the rotational center and other portions) has a better uniformity upon completion of the entire polishing process. In details, when the rotational center C 2  of the polishing article  10  is selectively set corresponding to the first high polishing rate region  104  in the first polishing process, the rotational center C 2  of the polishing article  10  has to be set corresponding to the second low polishing rate region  202  in the second polishing process. Conversely, when the rotational center C 2  of the rotational article  10  is selectively set corresponding to the first low polishing rate region  102  in the first polishing process, the rotational center C 2  of the polishing article  10  has to be set corresponding to the second high polishing rate region  204  in the second polishing process. In the detailed description below, the corresponding position of the rotational center C 2  of the polishing article corresponds to the first high polishing rate region  104  in the first polishing process and corresponds to the second low polishing rate region  202  in the second polishing process. However, the scope of the invention is not limited thereto. 
     In the present embodiment, the rotational center C 2  of the polishing article  10  is set corresponding to one of a plurality of high polishing rate regions  104  in the first polishing process. Specifically, when performing the first polishing process, the first platen  120  enables the first polishing pad  100  to rotate along a direction R 1 . Here, rotating along the direction R 1  is, for example, rotating in a counter-clockwise direction along a rotational center C 1  of the first polishing pad  100 . The carrier  130  enables the polishing article  10  to rotate along a direction R 2 . Here, rotating along the direction R 2  is, for example, rotating in a counter-clockwise direction along the rotational center C 2  of the polishing article  10 . During the first polishing process, the rotational center C 2  of the polishing article  10  constantly corresponds to the first high polishing rate region  104  of the first polishing pad  100  (that is, the polishing layer surface  104   a ). Since the rotational center C 2  of the polishing article  10  almost constantly contacts the same position during the first polishing process, the rotational center C 2  of the polishing article  10  polishes at a relatively higher polishing rate in the first polishing process. 
     After the first polishing process is completed, the carrier  130  moves the polishing article  10  to the second polishing pad  200  to perform the second polishing process. Here, the rotational center C 2  of the polishing article  10  is set corresponding to one of a plurality of second low polishing rate regions  202 . Specifically, when performing the second polishing process, the second platen  220  enables the second polishing pad  200  to rotate along a direction R 1 . Here, rotating along the direction R 1  is, for example, rotating in a counter-clockwise direction along a rotational center C 3  of the second polishing pad  200 . The carrier  130  enables the polishing article  10  to rotate along a direction R 2 . Here, rotating along the direction R 2  is, for example, rotating in a counter-clockwise direction along the rotational center C 2  of the polishing article  10 . During the second polishing process, the rotational center C 2  of the polishing article  10  constantly corresponds to the second low polishing rate region  202  of the second polishing pad  200  (that is, the groove  202   a ). Since the rotational center C 2  of the polishing article  10  almost constantly contacts the same position during the second polishing process, the rotational center C 2  of the polishing article  10  polishes at a relatively lower polishing rate in the second polishing process. 
       FIG. 3  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when the polishing system in  FIGS. 1 and 2  performs a polishing process. According to an embodiment of the invention, referring to  FIG. 3 , the polishing article  10  is disposed on the first polishing pad  100  to perform the first polishing process with a polishing time T 1 , and the polishing article  10  is disposed on the second polishing pad  200  to perform the second polishing process with a polishing time T 2 . Particularly, the polishing time T 1  in the first polishing process accounts for 30%-70% (or 40%-60%, or even 50%) of a total polishing time T 1 +T 2 . 
     Accordingly, as shown in  FIG. 3 , the rotational center C 2  of the polishing article  10  polishes at a relatively higher polishing rate during the first polishing process (that is, in the polishing time T 1  interval). This is due to that the rotational center C 2  of the polishing article  10  almost constantly contacts the first high polishing rate region  104  of the first polishing pad  100  (that is, the polishing layer surface  104   a ) during the first polishing process. The rotational center C 2  of the polishing article  10  polishes at a relatively lower polishing rate during the second polishing process (that is, in the polishing time T 2  interval). This is due to that the rotational center C 2  of the polishing article  10  almost constantly contacts the second low polishing rate region  202  of the second polishing pad  200  (that is, the groove  202   a ) during the second polishing process. In other words, the polishing rate of the rotational center C 2  of the polishing article  10  in the first polishing process and the polishing rate of the rotational center C 2  of the polishing article  10  in the second polishing process can compensate each other. Therefore, after the first and the second polishing processes are performed, the polishing rate of the rotational center C 2  of the polishing article  10  approaches the polishing rates at other positions of the polishing article  10 , such that a better uniformity of the polishing rate on the surface of the polishing article  10  is attained. 
       FIG. 4  illustrates a schematic top view of a polishing system according to another embodiment of the invention. Referring to  FIG. 4 , a polishing system in  FIG. 4  is similar to the polishing system in  FIGS. 1 and 2 , and the same elements as those in  FIGS. 1 and 2  are denoted with the same notations and the details are omitted hereinafter. The polishing system in  FIG. 4  and the polishing system in  FIGS. 1 and 2  are different in that an oscillatory polishing step is further performed for the polishing article  10  (also for the carrier  130 ) in the polishing process. In other words, when performing the first polishing process on the first polishing pad  100 , the polishing article  10  (the carrier  130 ) further performs an oscillatory polishing step O 1 ; that is, the polishing article rotates along the direction R 2  and oscillates back and forth between a position  10   a  and a position  10   b  for polishing. When the polishing article  10  oscillates back and forth between the position  10   a  and the position  10   b , the rotational center thereof also oscillates back and forth between a position C 2 - 1  and a position C 2 - 2 . 
     Similarly, when the polishing article  10  (the carrier  130 ) is moved to the second polishing pad  200  to perform the second polishing process, an oscillatory polishing step O 2  is further performed for the polishing article  10  (also for the carrier  130 ). That is, the polishing article  10  rotates along the direction R 2  and oscillates between the position  10   a  and the position  10   b  for polishing. When the polishing article  10  oscillates back and forth between the position  10   a  and the position  10   b , the rotational center thereof also oscillates back and forth between the position C 2 - 1  and the position C 2 - 2 . 
       FIG. 5A  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when applying the polishing system in  FIG. 4  to perform the first polishing process according to an embodiment of the invention.  FIG. 5B  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when applying the polishing system in  FIG. 4  to perform the second polishing process according to an embodiment of the invention. 
     Referring to  FIG. 5A , in the present embodiment, the first polishing process performed for the polishing article  10  on the first polishing pad  100  includes an initial polishing step and an oscillatory polishing step. In other words, when the first polishing process is performed for the polishing article  10  on the first polishing pad  100 , the initial polishing step is first performed in the first time interval T 1 . At this time, as the rotational center C 2  of the polishing article  10  almost constantly contacts the first high polishing rate region  104  of the first polishing pad  100  (that is, the polishing layer surface  104   a ), the rotational center C 2  of the polishing article  10  polishes at a relatively higher polishing rate in the first time interval T 1 . Thereafter, the oscillatory polishing step O 1  is performed in the second time interval T 2 . At this time, since the rotational center of the polishing article  10  oscillates back and forth between the position C 2 - 1  and the position C 2 - 2 , the rotational center C 2  of the polishing article  10  then contacts the first high polishing rate region  104  (that is, the polishing layer surface  104   a ) and the first low polishing rate region  102  (that is, the groove  102   a ) repetitively for polishing in the second time interval T 2 . 
     After the second time interval T 2 , a final polishing step is further performed in a third time interval T 3 . In the third time interval T 3 , as the rotational center C 2  of the polishing article  10  almost constantly contacts the first high polishing rate region  104  of the first polishing pad  100  (that is, the polishing layer surface  104   a ), the rotational center C 2  of the polishing article  10  polishes at a relatively higher polishing rate in the third time interval T 3 . 
     Accordingly, after the first polishing process is performed for the polishing article  10  on the first polishing pad  100 , the polishing article  10  is then moved to the second polishing pad  200  to perform the second polishing process. 
     Referring to  FIG. 5B , in the present embodiment, the second polishing process performed for the polishing article  10  on the second polishing pad  200  also includes an initial polishing step and an oscillatory polishing step. In other words, when the second polishing process is performed for the polishing article  10  on the second polishing pad  200 , the initial polishing step is first performed in the first time interval T 1 . At this time, as the rotational center C 2  of the polishing article  10  almost constantly contacts the second low polishing rate region  202  of the second polishing pad  200  (that is, the groove  202   a ), the rotational center C 2  of the polishing article  10  polishes at a relatively lower polishing rate in the first time interval T 1 . Thereafter, the oscillatory polishing step O 2  is performed in the second time interval T 2 . At this time, since the rotational center C 2  of the polishing article  10  oscillates back and forth between the position C 2 - 1  and the position C 2 - 2 , the rotational center C 2  of the polishing article  10  then contacts the second high polishing rate region  204  and the second low polishing rate region  202  repetitively for polishing in the second time interval T 2 . 
     After the second time interval T 2 , a final polishing step is further performed in the third time interval T 3 . In the third time interval T 3 , as the rotational center C 2  of the polishing article  10  almost constantly contacts the second low polishing rate region  202  of the second polishing pad  200  (that is, the groove  202   a ), the rotational center C 2  of the polishing article  10  polishes in a relatively lower polishing rate in the third time interval T 3 . 
     In the embodiments of  FIGS. 4, 5A and 5B , the rotational center C 2  of the polishing article  10  almost always polishes at a relatively higher polishing rate in the initial polishing step (and the final polishing step) of the first polishing process. Also, the rotational center C 2  of the polishing article  10  almost always polishes at a relatively lower polishing rate in the initial polishing step (and the final polishing step) of the second polishing process. Therefore, after the first and the second polishing processes are performed, the polishing rates of the rotational center C 2  of the polishing article  10  compensate each other and the compensated polishing rate approaches the polishing rates of other positions of the polishing article  10 , such that a better uniformity of the polishing rate on the surface of the polishing article  10  is attained. 
     Second Embodiment 
       FIG. 6  illustrates a schematic top view of a polishing system according to an embodiment of the invention. Referring to  FIG. 6 , the polishing system in the present embodiment includes a polishing pad  600  and a polishing article  20 . According to the present embodiment, the polishing system further includes a platen (not shown) configured to carry the polishing pad  600  and a carrier (not shown) configured to hold the polishing article  20 . 
     The polishing pad  600  has a plurality of high polishing rate regions  604  and a plurality of low polishing rate regions  602 . According to the present embodiment, at least one groove (similar to the groove  102   a  in  FIG. 2 ) is disposed in the low polishing rate regions  602  of the polishing pad  600 , and the high polishing rate regions  604  of the polishing pad  600  have a polishing layer surface (similar to the polishing layer surface  202   a  in  FIG. 2 ). In addition, the high polishing rate regions  604  and the low polishing rate regions  602  are concentric circular regions respectively, and the high polishing rate regions  604  and the low polishing rate regions  602  are disposed alternately. In the present embodiment, the material used for forming the polishing pad  600  and the type of the grooves in the low polishing rate regions  602  are identical or similar to those described in the first embodiment, and the details thereof are thus omitted hereinafter. 
     The polishing pad  600  is driven by the platen, so that the polishing pad  600  rotates along a direction R 3 . The polishing article  20  is pressed onto the polishing pad  600  through the carrier. The carrier enables the polishing article  20  to rotate on the polishing pad  600 , and drives an oscillatory movement shifting the polishing article  20  back and forth on the first polishing pad  600 . Therefore, the contact between the polishing article  20  and the polishing pad  600  may not be confined within a certain region. 
     Accordingly, detailed steps of a polishing method performed using the polishing system mentioned above are provided below. 
     Firstly, the polishing article  20  is pressed onto the polishing pad  600  to perform a first polishing process. Particularly, a rotational center C 6  of the polishing article  20  corresponds to one of the high polishing rate regions  604 . In details, the polishing pad  600  rotates along the direction R 3  during the first polishing process. Here, rotating along the direction R 3  is, for example, rotating in a counter-clockwise direction along a rotational center C 4  of the polishing pad  600 . Moreover, the polishing article  20  rotates along the direction R 5 . Herein, rotating along the direction R 5  is, for example, rotating in a counter-clockwise direction along a rotational center C 6  of the polishing article  20 . In the first polishing process, the rotational center C 6  of the polishing article  20  constantly corresponds to the high polishing rate region  604  of the polishing pad  600 . Since the rotational center C 6  of the polishing article  20  almost constantly contacts the same position during the first polishing process, the rotational center C 6  of the polishing article  20  polishes at a relatively higher polishing rate in the first polishing process. 
     Upon completion of the first polishing process, the carrier moves the polishing article  20  to a position  20   a , such that the rotational center C 5  is set corresponding to one of the low polishing rate regions  602  when the polishing article  20  is in position  20   a  to perform a second polishing process. More specifically, the polishing pad  600  rotates along the direction R 3  and the polishing article  20  rotates along the direction R 5  in the position  20   a  during the second polishing process. In the second polishing process, the rotational center C 5  of the polishing article  20  at the position  20   a  constantly corresponds to the low polishing rate region  602  of the polishing pad  600 . Since the rotational center C 5  of the polishing article  20  in the position  20   a  almost constantly contacts the same position during the second polishing process, the rotational center C 5  of the polishing article  20  in the position  20   a  polishes at a relatively lower polishing rate in the second polishing process. 
       FIG. 7  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when the polishing system in  FIG. 6  performs a polishing process. According to an embodiment of the invention, referring to  FIG. 7 , a polishing time of the polishing article  20  performing the first polishing process on the polishing pad  600  is T 1 , and a polishing time of the polishing article  20  performing the second polishing process on the polishing pad  600  is T 2 . Particularly, the polishing time T 1  in the first polishing process accounts for 10%-90% (or 20%-80%, 30%-70%, 40%-60%, or even 50%) of a total polishing time T 1 +T 2 . 
     Accordingly, as shown in  FIG. 7 , the rotational center of the polishing article  20  polishes at a relatively higher polishing rate during the first polishing process (that is, in the polishing time T 1  interval). This is due to that the rotational center of the polishing article  20  almost constantly contacts the high polishing rate region  604  of the polishing pad  600  during the first polishing process. The rotational center of the polishing article  20  polishes at a relatively lower polishing rate during the second polishing process (that is, in the polishing time T 2  interval). This is due to that the rotational center of the polishing article  20  almost constantly contacts the low polishing rate region  602  of the polishing pad  600  during the second polishing process. In other words, the polishing rate of the rotational center of the polishing article  20  in the first polishing process can be compensated with the polishing rate of the rotational center of the polishing article  20  in the second polishing process. Therefore, after the first and the second polishing processes are performed, the polishing rate of the rotational center of the polishing article  20  approaches the polishing rates at other positions of the polishing article  20 , such that a better uniformity of the polishing rate on the surface of the polishing article  20  is attained. 
       FIG. 8  illustrates a schematic top view of a polishing system according to another embodiment of the invention. Referring to  FIG. 8 , a polishing system in  FIG. 8  is similar to the polishing system in  FIG. 6 , and the same elements as those in  FIG. 6  are denoted with the same notations and the details are omitted hereinafter. The polishing system in  FIG. 8  and the polishing system in  FIG. 6  are different in that an oscillatory polishing step is further performed for the polishing article  20  in the polishing process. According to the present embodiment, after performing the first polishing process and before performing the second polishing process, an oscillatory polishing step O 3  is further performed for the polishing article  20 . In the oscillatory polishing step O 3 , the polishing article  20  rotates along the direction R 2  and oscillates back and forth between a position  20  and a position  20   a  for polishing.  FIG. 9  is a graph showing a relationship of a polishing rate at a rotational center of a polishing article versus time when applying the polishing system in  FIG. 8  to perform a polishing process according to an embodiment of the invention. Referring to  FIG. 9 , in the present embodiment, when the first polishing process is performed for the polishing article  20  on the polishing pad  600  (that is, in the first time interval T 1 ), as the rotational center of the polishing article  20  almost constantly contacts the high polishing rate region  604  of the polishing pad  600 , the rotational center of the polishing article  20  then polishes at a relatively higher polishing rate in the first time interval T 1 . Afterwards, the oscillatory polishing step is performed in the second time interval T 2 . At this time, the rotational center of the polishing article  20  oscillates back and forth between a position. C 6  and a position C 5 . Consequently, the rotational center of the polishing article  20  then contacts the high polishing rate region  604  and the low polishing rate region  602  repetitively for polishing in the second time interval T 2 . After the oscillatory polishing step (that is, the second time interval T 2 ) is performed, the second polishing process (that is, the third time interval T 3 ) is carried out. In the second polishing process (that is, the third time interval T 3 ), as the rotational center of the polishing article  20  almost constantly contacts the low polishing rate region  602  of the polishing pad  600 , the rotational center of the polishing article  20  thus polishes at a relatively lower polishing rate in the third time interval T 3 . 
     In the embodiments of  FIGS. 8 and 9 , the rotational center of the polishing article  20  almost always polishes at a relatively higher polishing rate in the first polishing process. Also, the rotational center of the polishing article  20  almost always polishes at a relatively lower polishing rate in the second polishing process. Therefore, after the first polishing process, the oscillatory polishing process, and the second polishing processes are performed, the polishing rate of the rotational center of the polishing article  20  approaches the polishing rates at other positions of the polishing article  20 , such that a better uniformity of the polishing rate on the surface of the polishing article  20  is attained. 
     In the embodiments aforementioned, the rotational center of the polishing article  20  polishes at a relatively higher polishing rate in the first polishing process and the rotational center of the polishing article  20  polishes at a relatively lower polishing rate in the second polishing process. Nevertheless, the invention is not limited thereto. In another optional embodiment, the rotational center of the polishing article  20  polishes at a relatively lower polishing rate in the first polishing process, and the rotational center of the polishing article  20  polishes at a relatively higher polishing rate in the second polishing process. In particular, the polishing rate of the rotational center of the polishing article  20  in the first polishing process can be compensated with the polishing rate of the rotational center of the polishing article  20  in the second polishing process. Therefore, after the first and the second polishing processes are performed, the polishing rate of the rotational center of the polishing article  20  approaches the polishing rates at other positions of the polishing article  20 , such that a better uniformity of the polishing rate on the surface of the polishing article  20  is attained. 
     Third Embodiment 
       FIGS. 10A and 10B  illustrate schematic top views of a polishing system according to another embodiment of the invention. Referring to  FIGS. 10A and 10B , a polishing system in  FIGS. 10A and 10B  is similar to the polishing system in  FIG. 6 , and the same elements as those in  FIG. 6  are denoted with the same notations and the details are omitted hereinafter. The polishing system in  FIGS. 10A and 10B  is different from the polishing system in  FIG. 6  in that polishing processes of the polishing article are all oscillatory polishing processes. 
     In details, when a first polishing process is performed for the polishing article  20  on the polishing pad  600 , the first polishing process is a first oscillatory polishing process O 4 , so that the polishing article  20  oscillates back and forth between a position  20 - 1  and a position  20 - 2  and the rotational center of the polishing article  20  oscillates between a position C 5 - 1  and a position C 5 - 2 . 
     In the first oscillatory polishing process O 4 , the rotational center C 4  of the polishing pad  600  and the rotational center of the polishing article  20  have a first shortest distance D 1  and a first longest distance D 3  therebetween. In other words, when the polishing article  20  oscillates to the position  20 - 1 , the rotational center of the polishing article  20  also shifts to the position C 5 - 1 . At this time, the rotational center C 4  of the polishing pad  600  and the rotational center C 5 - 1  of the polishing article  20  have the distance D 1  therebetween. When the polishing article  20  oscillates to the position  20 - 2 , the rotational center of the polishing article  20  also shifts to the position C 5 - 2 . Here, the rotational center C 4  of the polishing pad  600  and the rotational center C 5 - 2  of the polishing article  20  have the distance D 3  therebetween. 
     After the first oscillatory polishing process illustrated in  FIG. 10A  is performed, a second polishing process is subsequently performed for the polishing article  20  on the same polishing pad  600 . The second polishing process is a second oscillatory polishing process as shown in  FIG. 10B . In details, when a second oscillatory polishing process O 5  is performed for the polishing article  20  on the polishing pad  600 , the polishing article  20  then oscillates between the position  20 - 1  and the position  20 - 2 . Moreover, the rotational center of the polishing article  20  also oscillates between a position C 6 - 1  and a position C 6 - 2 . 
     In the second oscillatory polishing process O 5 , the rotational center C 4  of the polishing pad  600  and the rotational center of the polishing article  20  have a second shortest distance D 2  and a second longest distance D 4  therebetween. In other words, when the polishing article  20  oscillates to the position  20 - 1 , the rotational center of the polishing article  20  also shifts to the position C 6 - 1 . At this time, the rotational center C 4  of the polishing pad  600  and the rotational center C 6 - 1  of the polishing article  20  have the distance D 2  therebetween. When the polishing article  20  oscillates to the position C 6 - 2 , the rotational center C 4  of the polishing article  20  also shifts to the position C 6 - 2 . Here, the rotational center C 4  of the polishing pad  600  and the rotational center C 6 - 2  of the polishing article  20  have the distance D 4  therebetween. 
     Especially, when the polishing article  20  undergoes the first oscillatory polishing process O 4  and the second oscillatory polishing process O 5 , the shortest distance D 1  or D 2  between the rotational center C 4  of the polishing pad  600  and the rotational center (C 5 - 1 , C 6 - 1 ) of the polishing article  20  satisfies the following relation:
 
 D 1 −D 2 =P×N+P ×(30%˜70%)
 
     P is a distance between two adjacent low polishing rate regions  602   
     N is an integer 
     In the above relation, the percentage interval ranges from 30% to 70%; however, the scope of the invention is not limited thereto. The percentage interval can be adjusted depending on the distance P or the width of the low polishing regions  602  (that is, the width of the grooves). When the width of the low polishing rate regions  602  accounts for a small percentage of the distance P (that is, the width of the grooves is far smaller than the distance P), the percentage interval in the relation is then optionally 20%-80%, or even 10%-90%. On the contrary, when the width of the low polishing rate regions  602  accounts for a large percentage of the distance P, the percentage interval in the relation is then optionally 40%-60% or even 50%. 
     Furthermore, when the polishing article  20  undergoes the first oscillatory polishing process O 4  and the second oscillatory polishing process O 5 , the longest distance D 3  or D 4  between the rotational center C 4  of the polishing pad  600  and the rotational center (C 5 - 2 , C 6 - 2 ) of the polishing article  20  satisfies the following relation:
 
 D 3 −D 4 =P×N+P ×(30%˜70%).
 
     P is a distance between two adjacent low polishing rate regions  602   
     N is an integer 
     In the above relation, the percentage interval ranges from 30% to 70%; however, the scope of the invention is not limited thereto. The percentage interval can be adjusted depending on the distance P or the width of the low polishing regions  602  (that is, the width of the grooves). When the width of the low polishing rate regions  602  accounts for a small percentage of the distance P (that is, the width of the grooves is far smaller than the distance P), the percentage interval in the relation is then optionally 20%-80%, or even 10%-90%. On the contrary, when the width of the low polishing rate regions  602  accounts for a large percentage of the distance P, the percentage interval in the relation is then optionally 40%-60% or even 50%. 
     In other words, when the polishing article  20  in the present embodiment performs the first oscillatory polishing process (as shown in  FIG. 10A ) and the second oscillatory polishing process (as shown in  FIG. 10B ), oscillatory positions of the rotational center thereof are not overlapped (that is, are staggered) as depicted in  FIG. 11 .  FIG. 11  is a graph showing a relationship of positions of a rotational center of a polishing article versus time when applying the polishing system in  FIGS. 10A and 10B  to perform a polishing process according to an embodiment of the invention. In  FIG. 11 , when the polishing article  20  performs the first oscillatory polishing process (as shown in  FIG. 10A ), the position of the rotational center oscillates back and forth between a position P 1  and a position P 3 . When the polishing article  20  performs the second oscillatory polishing process (as shown in  FIG. 10B ), the position of the rotational center oscillates back and forth between a position P 2  and a position P 4 . 
     As illustrated in  FIG. 11 , the position P 1  of the rotational center of the polishing article  20  during the first oscillatory polishing process and the position P 2  of the rotational center of the polishing article  20  during the second oscillatory polishing process are not overlapped. The distance between the position P 1  and the position P 2  is the value of D1−D 2  aforementioned, which equals to P×N+P×(30%˜70%). Similarly, the position P 3  of the rotational center of the polishing article  20  during the first oscillatory polishing process and the position P 4  of the rotational center of the polishing article  20  during the second oscillatory polishing process are not overlapped. The distance between the position P 3  and the position P 4  is the value of D 3 −D 4  aforementioned, which equals to P×N+P×(30%˜70%). 
     In the present embodiment, as the position P 1  of the rotational center of the polishing article  20  during the first oscillatory polishing process and the position P 2  of the rotational center of the polishing article  20  during the second oscillatory polishing process are not overlapped, the polishing rates of the rotational center of the polishing article  20  in the first and the second oscillatory polishing processes can be compensated. The polishing rate of the rotational center of the polishing article  20  therefore approaches the polishing rates at other positions of the polishing article  20 , such that a better uniformity of the polishing rate on the surface of the polishing article  20  is attained. 
     According to another embodiment of the invention, the embodiments in the  FIGS. 10A and 10B  can also be applied in combination with the second embodiment ( FIGS. 6 and 8 ). In other words, in the present embodiment, the above-mentioned polishing process includes the first oscillatory polishing process and the second oscillatory polishing process shown in  FIGS. 10A and 10B , and can optionally determine an initial position of the polishing article  20  in the first polishing process and an initial position of the polishing article in the second polishing process. In other words, the initial position of the polishing article  20  in the first polishing process is fixed for the rotational center C 5  of the polishing article  20  to be set corresponding to one of the low polishing rate regions  602  (grooves). Additionally, the initial position of the polishing article  20  in the second polishing process is fixed for the rotational center C 6  of the polishing article  20  to be set corresponding to one of the high polishing rate regions  604  (the polishing layer surface). 
     Hence, the position P 1  of the rotational center of the polishing article  20  during the first oscillatory polishing process (as shown in  FIG. 10A ) and the position P 2  of the rotational center of the polishing article  20  during the second oscillatory polishing process (as shown in  FIG. 10B ) are not overlapped. Further, the initial position of the polishing article  20  in the first polishing process is fixed for the rotational center C 5  of the polishing article  20  to be set corresponding to one of the low polishing rate regions  602 . The initial position of the polishing article  20  in the second polishing process is fixed for the rotational center C 6  of the polishing article  20  to be set corresponding to one of the high polishing rate regions  604 . Therefore, the polishing rates of the rotational center of the polishing article  20  in the first polishing process and the second polishing process can be compensated by adopting the polishing system and the polishing method of the present embodiment. As a result, the polishing rate of the rotational center of the polishing article  20  approaches the polishing rates at other positions of the polishing article  20 , such that a better uniformity of the polishing rate on the surface of the polishing article  20  is attained. 
     In the embodiment above, the first polishing process is illustrated with  FIG. 10A  and the second polishing process is illustrated with  FIG. 10B . However, the scope of the invention is not limited thereto. In another optional embodiment, the first polishing process can be changed to the process displayed in  FIG. 10B  while the second polishing process is changed to the process shown in  FIG. 10A . Specifically, the polishing rates of the rotational center of the polishing article  20  in the first polishing process and the second polishing process can be compensated, so that the polishing rate of the rotational center of the polishing article  20  approaches the polishing rates at other positions of the polishing article  20 , such that a better uniformity of the polishing rate on the surface of the polishing article  20  is attained. 
     The polishing system and the polishing method in the embodiments aforementioned can be applied in the polishing apparatuses used in the fabrications of devices involved in semiconductors, integrated circuits, micro-electromechanics, communication, optics, storage disks, and displays and also the fabrication processes thereof. The polishing articles used for fabricating the devices include semiconductor wafers, group III-V wafers, storage device carriers, ceramic substrates, high polymer substrate, glass substrate, and so on; however, the scope of the invention is not limited thereto. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.