Abstract:
A polishing pad having grooved window therein is provided. The polishing pad comprises a polishing layer and a window, wherein the polishing layer has at least one first groove therein and the window has at least one second groove therein. More particularly, the first groove is deeper than the second groove. The polishing pad having a grooved window therein has advantages of providing precise endpoint detection and thereby reducing or resolving defect problems.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefits of U.S. provisional application titled “Grooved Window Pad And Method Of Forming The Same” filed on Oct. 22, 2003, Ser. No. 60/514,092. All disclosure of this application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a polishing pad and a method of forming the same. More particularly, the present invention relates to a polishing pad having grooved window therein and a method of forming the same. 
     2. Description of Related Art 
     Endpoint detection techniques have been generally used for chemical-mechanical polishing (CMP) to ensure the polishing quality. Among those techniques, optical endpoint detection through a transparent detection window in a polishing pad provides a reliable result. 
     U.S. Pat. No. 5,893,796 discloses a method of forming a transparent window in a polishing pad by forming an aperture in a polishing layer first, and then a transparent window is fixed in the aperture with a layer of adhesive. Unfortunately, the slurry solution inevitably permeates through transparent window/polishing layer interface and leaks into the backside of the polishing pad, especially under the influence of the stress during polishing. Meanwhile, this would interfere with the optical signal and therefore the endpoint detection cannot be accurate. 
     U.S. Pat. No. 6,171,181 discloses a polishing pad with an integral window without above-mentioned slurry solution leakage problem. However, thereafter, during the process of forming grooves on the polishing pad with an integral window, grooves are also formed on the window portion with same groove depth as the grooves formed in the non-window portion. The non-smooth surface of the window portion, with grooves thereon, will lead to less light permeability and get lower reflected optical signal, which will degrade sensitivity of the endpoint detection. Besides, byproducts produced by reaction between polished materials and slurry and the slurry abrasive accumulated in the grooves on the window portion further makes endpoint detection difficult, even when the lifetime of the polishing pad is still within specification. 
     It is possible to form grooves by using mechanical techniques, such as cutting, only on the non-window portion of the polishing pad by controlling the distance between cutting tool and polishing pad, that is, the cutting tool lifts up only for the widow portion. However, the distance controlling stability for aligning to the window portion is challenging. Furthermore, there are some drawbacks of the polishing pad with no grooves formed on the window portion, firstly, sharp rising step of groove depth from grooved non-window portion to non-grooved widow portion will become a defect source when substrate moves relatively across window portion. Secondly, uneven friction and poor wettability of the window portion relative to non-window portion, due to absence of grooves on the entire window surface, makes the window itself become another defect source. 
     It would be desirable if a polishing pad having a transparent window therein that normally functions for endpoint detection can be utilized, while at the same time, the defects described above can be reduced or resolved. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a polishing pad having a grooved window therein and a method of forming the same, capable of providing good slurry transportation and normal endpoint detection. 
     According to an embodiment of the present invention, a polishing pad having a grooved window therein is provided. The polishing pad comprises a polishing layer and a window therein. The polishing layer has at least one first groove therein and the window has at least one second groove therein. More particularly, the first groove is deeper than the second groove. 
     According to another embodiment of the present invention, a method of forming a polishing pad having grooved window therein is provided. A window is formed in a polishing layer. Thereafter, at least one first groove is formed in the polishing layer and at least one second groove is formed in the window, wherein the first groove is deeper than the second groove. 
     According to an embodiment of the present invention, the second groove is formed in the window so as to improve the flow of slurry at the window portion. In addition, since the second groove formed in the window is shallower than the first groove formed in the polishing layer, the endpoint detection is precise. 
    
    
     
       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 part 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 showing a polishing pad having a transparent window therein according to an embodiment of the present invention. 
         FIG. 2  is a schematic cross-sectional view along I-I′ of  FIG. 1  showing the structure of the polishing pad. 
         FIG. 3  is a schematic cross-sectional view showing a method of forming first groove and second groove in a polishing pad according to an embodiment of the present invention. 
         FIG. 4  is a schematic cross-sectional view showing a method of forming first groove and second groove in a polishing pad according to another embodiment of the present invention. 
         FIG. 5A  and  FIG. 5B  are schematic cross-sectional views showing a method of forming first groove and second groove in a polishing pad according to another embodiment of the present invention. 
         FIG. 6A ,  FIG. 6B , and  FIG. 6C  are schematic cross-sectional views showing a polishing pad according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Reference will now be made in detail to the present preferred 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. 1  is a schematic top view showing a polishing pad with a transparent window according to an embodiment of the present invention.  FIG. 2  is a schematic cross-sectional view along I-I′ of  FIG. 1  showing the structure of the polishing pad. 
     As shown in  FIG. 1  and  FIG. 2 , a polishing pad  100  comprising a polishing layer  101  and a window  102  therein is provided. More particularly, at least one first groove  104   a  and at least one second groove  104   b  are formed in the polishing layer  101  and the window  102  respectively for improving the flow of slurry, wherein the first groove  104   a  is formed deeper than the second groove  104   b.  In other words, the depth (h 2 , h 3 ) of the second groove  104   b  formed in the window  102  is shallower relative to the depth (h 1 ) of the first groove  104   a  in the polishing layer  101 . In an embodiment of the present invention, the second groove  104   b  in the window  102  has different depths. Preferably, the profile of the depth of the second groove  104   b  is such that the depth gradually reduces from an edge area of the window  102  towards the central area of the window  102 . For example, the second groove  104   b  has a larger depth h 2  at the edge area of the window  102  compared to depth h 3  at the central area of the window  102 . 
     In an embodiment of the present invention, the polishing layer  101  is constituted of a polymer material. For example, the polymer material is selected from a group consisting of polyurethane (PU), epoxy resin, phenol formaldehyde (PF) resin, melamine resin, thermosetting resin and a combination thereof. The window  102  is a transparent window and is constituted of a transparent polymer, for example. 
     Accordingly, the polishing pad  100  of the present invention comprises a polishing layer  101  having the first groove  104   a  therein and a window  102  having the second groove  104   b  therein, wherein the first groove  104   a  is deeper than the second groove  104   b.  More particularly, the depth of the second groove  104   b  at the edge area of the window  102  is substantially deeper compared to that at the central area of the window  102  so that the slurry does not be retained in the second groove, and the endpoint detection is precise. 
     The method of forming the polishing pad  100  comprises, first, a window  102  formed in a polishing layer  101 . Thereafter, at least one first groove  104   a  is formed in the polishing layer  101  and at least one second groove  104   b  is formed in the window  102 , wherein the first groove  104   a  is deeper than the second groove  104   a.  In an embodiment of the present invention, the polishing layer  101  and the window  102  are formed with a molding process. For example, the window  102  is first disposed in a mold, and a polymer is injected into the mold to form the polishing layer  101 . After releasing the mold, a polishing pad  100  including the polishing layer  101  and the window  102  can be obtained. Alternatively, the polishing pad  100  including the polishing layer  101  and the window  102  can be formed using other suitable known methods. 
     After forming the polishing layer  101  and the window  102 , at least one first groove  104   a  is formed in the polishing layer  101  and at least one second groove  104   b  is formed in the window  102 . In an embodiment of the present invention, as shown in  FIG. 3 , the first groove  104   a  and the second groove  104   b  may be formed by chucking the polishing pad  100  with a chuck apparatus  200 , wherein the chuck apparatus  200  has a recession portion  202  corresponding to the window  102  so that the window  102  in the polishing layer  101  is deformed. The chuck apparatus  200  may be a vacuum chuck apparatus, an electrostatic chuck apparatus or other type, for example. Thereafter, the first groove  104   a  is formed in the polishing layer  101  and the second groove  104   b  is formed in the window  102 . The method for forming the first groove  104   a  and the second groove  104   b  may be performed by a mechanical process, such as using a mechanical cutting tool  250 , or a chemical process, such as chemical etching, or other known processes. As shown in  FIG. 3 , when the polishing pad  100  is chucked on the chuck apparatus  200 , the window  102  is deformed because of the recession portion  202  of the chuck apparatus  200 , and the upper surface of the deformed window  102  presents a concave surface. Hence, when performing the cutting process by using the mechanical cutting tool  250 , the first groove  104   a  formed in the polishing layer  101  can be deeper than the second groove  104   b  formed in the window  102 . Furthermore, since the upper surface of the deformed window  102  presents a concave surface when the polishing pad  100  is chucked on the chuck apparatus  200 , the second groove  104   b  formed in the window  102  has a larger depth h 2  at the edge area of the window  102  and has a less depth h 3  substantially at the central area of the window  102 . 
     In another embodiment of the present invention, as shown in  FIG. 4 , the first groove  104   a  and the second groove  104   b  are formed by chucking the polishing pad  100  with a chuck apparatus  200 . Further, a support layer  204  is disposed between the chuck apparatus  200  and the polishing pad  100 . More particularly, the support layer  204  has a recession portion  206  corresponding to the window  102  so that the window  102  in the polishing layer  101  is deformed. Similarly, the chuck apparatus  200  may be a vacuum chuck apparatus, an electrostatic chuck apparatus or other type apparatus, for example. Thereafter, the first groove  104   a  is formed in the polishing layer  101  and the second groove  104   b  is formed in the window  102 . The method for forming the first groove  104   a  and the second groove  104   b  may be performed by a mechanical process, such as using a mechanical cutting tool  250 , or a chemical process, such as chemical etching, or other known processes. 
     In another embodiment of the present invention, as shown in  FIGS. 5A and 5B , the first groove  104   a  and the second groove  104   b  formed by first forming a recession portion  208  in the backside of the window  102 , as shown in  FIG. 5A . Next, the polishing pad  100  is chucked with a chuck apparatus  200 , as shown in  FIG. 5B , wherein the window  102  in the polishing layer  101  is deformed because of the backside recession portion  208  of the window  102 . Similarly, the chuck apparatus  200  may be a vacuum chuck apparatus, an electrostatic chuck apparatus or other type, for example. Thereafter, the first groove  104   a  is formed in the polishing layer  101  and the second groove  104   b  is formed in the window  102  to obtain a polish pad  100 , in which the window  102  has a recession portion  208  in the backside of the window  102 , as shown in  FIG. 6A . The method for forming the first groove  104   a  and the second groove  104   b  may be performed by a mechanical process, such as using a mechanical cutting tool  250 , or a chemical process, such as chemical etching, or other known processes. In an embodiment of the present invention, the recession portion  208  in the backside of the window  102  is formed with a mechanical process, such as mechanical cutting, or a chemical process, such as chemical etching, for example. In another embodiment of the present invention, the recession portion  208  in the backside of the window  102  is formed through a molding process. For example, when forming the polishing layer  101  and the window  102  with a molding process, a sacrificial material is disposed within the mold stacking with the window  102 , and then a polymer is injected into the mold to form the polishing layer  101 . After releasing the mold, the sacrificial material is removed, and an integral unit comprising a polishing layer  101  and a window  102  with a backside recession portion  208  can be obtained. In the other embodiment of the present invention, the recession portion  208  in the backside of the window  102  may be formed through a molding process with a mold having a protrusion corresponding to the window position, and then a polymer is injected into the mold to form the polishing layer  101 . After releasing the mold, an integral unit comprising a polishing layer  101  and a window  102  with a backside recession portion  208  can be obtained. 
     It is should be noted that in the embodiment described with reference to  FIG. 5A ,  FIG. 5B , and  FIG. 6A , after forming the first grooves  104   a  and the second grooves  104   b , a step of leveling may be performed by forming a transparent material  600  at the recession portion  208  of the window  102  on the backside of the polishing pad to obtain a planar backside surface as shown in  FIG. 6B . Alternatively, as shown in  FIG. 6C , the step of leveling on the backside of the polishing pad to obtain a planar backside surface may be performed by removing the backside of the polishing layer  101  with a mechanical process, such as mechanical cutting. 
     According to the foregoing, by deforming the window, at least one second groove having different depths can be formed in the window. Particularly, the second groove at the edge area of the window has a substantially deeper depth compared to the second groove at the central area of the window. More particularly, the profile of the depth of the second groove is such that the depth gradually reduces from the edge area of the window towards the central area of the window. Therefore, slurry does not be retained within the second groove and the endpoint detection can be precise. 
     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.