Abstract:
An apparatus and method for polishing a workpiece including a polishing pad; at least one polishing arm for holding a workpiece to be polished on the polishing pad; at least one conditioning arm for conditioning the polishing pad; and, a slurry dispenser. The slurry dispenser is disposed between the at least one polishing arm and the at least one conditioning arm so that slurry dispensed by the slurry dispenser contacts the at least one conditioning pad before it contacts the at least one polishing pad.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fabrication of semiconductor devices, and in particular, to a method and apparatus for polishing semiconductor wafers. 
     DESCRIPTION OF THE RELATED ART 
     Chemical mechanical planarization (“CMP”) processes remove material from the surface of a semiconductor wafer in the production of ultra-high density integrated circuits. In a typical CMP process, a wafer is pressed against a polishing pad in the presence of a slurry under controlled chemical, pressure, velocity, and temperature conditions. The slurry solution generally contains small, abrasive particles that abrade the surface of the wafer, and chemicals that etch and/or oxidize the surface of the wafer. The polishing pad is generally a planar pad made from a relatively soft, porous material such as polyurethane. Thus, when the pad and/or the wafer moves with respect to the other, material is removed from the surface of the wafer by the abrasive particles (mechanical removal) and by the chemicals (chemical removal) in the slurry. 
     FIGS. 1 and 2 show a conventional polishing apparatus  10 . The apparatus  10  includes a polishing pad  20  and three polishing stations  30 ,  40 ,  50  for polishing semiconductor wafers  60 . Preferably, the polishing pad  20  spins counter-clockwise to accomplish the polishing of the wafers  60 , as shown by directional arrow A in FIG.  2 . Each station  30 ,  40 ,  50  includes a polishing arm  31 ,  41 ,  51  which holds the wafers  60  during the polishing process. Each polishing arm  31 ,  41 ,  51  includes a U-shaped member for holding vacuum chucks  32 ,  42 ,  52 . Each polishing arm  31 ,  41 ,  51  includes one such vacuum chuck  32 ,  42 ,  52 . The vacuum chucks  32 ,  42 ,  52  are coupled to U-shaped members through bearings  35 ,  45 ,  55 . The bearings  35 ,  45 ,  55  allow the vacuum chucks  32 ,  42 ,  52  to rotate with respect to the respective polishing arms  31 ,  41 ,  51 . The vacuum chucks  32 ,  42 ,  52  operate to hold the wafers  60  during the polishing process. Each of the vacuum chucks  32 ,  42 ,  52  includes an upper end  33 ,  43 ,  53  which may be coupled to a vacuum device (not shown) to provide a vacuum to the vacuum chucks. As can be clearly seen in FIG. 1, in the conventional polishing apparatus  10 , the polishing stations  30 ,  40  each hold wafers  60 , while the polishing station  50  is left empty (i.e. no wafer  60  is polished there). The polishing apparatus  10  also includes a slurry dispenser  70  which produces slurry which is dispensed onto a top surface  21  of the polishing pad  20 . 
     A problem associated with the conventional apparatus  10  discussed above is that the slurry dispensed from slurry dispenser  70  often gathers in clumps on the top surface  21  of the polishing pad  20 . Since the slurry is dispensed from the slurry dispenser  70  in droplet form, when the droplets hit the rotating polishing pad  20  they stay in droplet form and do not spread out. This clumping of the slurry results in uneven polishing of the wafers  60 . In particular, when a droplet of slurry contacts a wafer  60 , the initial area of the wafer that the slurry contacts is polished down further than the other areas of the wafer. 
     Therefore, there is currently a need for an improved polishing apparatus which provides an even distribution of slurry. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus and method for polishing a workpiece including, a polishing pad; at least one polishing arm for holding a workpiece to be polished on the polishing pad; at least one conditioning arm for conditioning the polishing pad; and, a slurry-producing device, the slurry-producing device being disposed between the at least one polishing arm and the at least one conditioning arm so that slurry dispensed by the slurry-producing device contacts the at least one conditioning pad before it contacts the at least one polishing pad. 
     The above and other advantages and features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a conventional polishing apparatus. 
     FIG. 2 is a side elevation view of the conventional polishing apparatus shown in FIG.  1 . 
     FIG. 3 is a top plan view of a polishing apparatus according to the exemplary embodiment of the present invention. 
     FIG. 4 is a side elevation view of the polishing apparatus shown in FIG.  3 . 
     FIG. 5 shows a top plan view of the polishing apparatus of FIG. 3, including a conditioning pad. 
     FIG. 6 is a side elevation view of the polishing apparatus shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 3 and 4, there is shown a polishing apparatus  100  according to an exemplary embodiment of the present invention. The apparatus  100  includes a polishing pad  120  and a conditioning station  130  for conditioning the polishing pad  120 , and two polishing stations  140 ,  150  for polishing semiconductor wafers  160 . In the exemplary embodiment, the polishing pad  120  rotates counter-clockwise to accomplish a polishing of the wafers  160 , as shown by directional arrow A in FIG.  4 . The polishing pad  120  may be substantially circular, as shown in FIG. 3, or may be of any other suitable shape known to those skilled in the art. Further, the conditioning station  130  and the polishing stations  140 ,  150  may be disposed at different radial positions about the periphery of the polishing pad  120 , as shown in FIG.  3 . The conditioning station  130  includes an arm  131  for conditioning the surface of the polishing pad by spreading out a slurry which becomes disposed on a top surface of the polishing pad  120 , as explained below. The polishing stations  140 ,  150  each include an arm  141 ,  151  with a U-shaped member which holds respective vacuum chucks  142 ,  152 . The conditioning station  130  also includes an arm  131  with a U-shaped member which holds a vacuum chuck  132 . The vacuum chucks  132 ,  142 ,  152  are coupled to the respective arms  131 ,  141 ,  151  through bearings  135 ,  145 ,  155 , which are preferably made of plastic, but may also be made of metal. The bearings  135 ,  145 ,  155  allow the vacuum chucks  132 ,  142 ,  152  to rotate with respect to the respective polishing arms  131 ,  141 ,  151 . As can be clearly seen in FIG. 2, in the exemplary polishing apparatus  100 , the polishing stations  140 ,  150  each hold wafers  160 , while the conditioning station  130  is left empty (i.e. no wafer  60  is polished there). In the exemplary polishing apparatus  100 , the vacuum chucks  142 ,  152  operate to hold the wafers  160  during the polishing process, and the vacuum chuck  132  operates to condition the surface of the polishing pad  120 . Each of the vacuum chucks  132 ,  142 ,  152  includes an upper end  133 ,  143 ,  153  which may be coupled to a vacuum device (not shown) to provide a vacuum to the vacuum chucks. In the exemplary polishing apparatus  100 , although all three vacuum chucks  132 ,  142 ,  152  may be coupled to a vacuum device, vacuum chuck  132  has no vacuum applied thereto, as it is used only for conditioning and not for holding a wafer  160 . The polishing apparatus  100  also includes a slurry dispenser  170  which produces slurry which is dispensed onto a top surface  121  of the polishing pad  120 . 
     In operation, the wafers  160  are applied to the rotating polishing pad  120  to accomplish a polishing of the wafers. In FIG. 4, the vacuum chucks  142 ,  152  of the polishing stations  140 ,  150  are shown in a position such that the wafers  160  are lowered against the polishing pad  120 . Additionally, the vacuum chuck  132  of the conditioning station  130  is shown in a lowered position and disposed against the polishing pad  120 . As noted above, the slurry produced by the slurry dispenser  170  assists in the polishing process. It should be noted that in the exemplary embodiment of the present invention the slurry-producing device  170  is disposed at a position in between the conditioning station  130  and the polishing station  150 . Thus, when slurry is dispensed by the slurry dispenser  170 , it strikes the polishing pad  120  and immediately contacts the conditioning station  130 . The vacuum chuck  132  of the conditioning station  130 , which is in contact with the polishing pad  120 , spreads out the droplets of slurry, which allows a more even polishing of the wafers  160  at the polishing stations  140 ,  150 . In particular, the slurry hits the polishing pad  120  in droplet form at a radial position before the conditioning station  130 . Then, as the polishing pad  120  rotates counter-clockwise (as shown by the arrows), the droplets of slurry are moved radially towards the conditioning station  130  and the associated vacuum chuck  132 . When the droplets disposed on the polishing pad  120  come into contact with the vacuum chuck  132 , they are spread out due to the collision. Thus, by the time the slurry reaches the polishing stations  140  and  150  it has already been spread out, and therefore the wafers  160  disposed at those positions are polished evenly. Alternatively, as shown in FIGS. 5 and 6 (polishing apparatus  100 ′), a conditioning pad  136  may be attached to the vacuum chuck  132  which serves to further condition the surface of the polishing pad  120  as well as spread out the slurry. It should be noted that the conditioning pad  136  may be coupled to the vacuum chuck through either a vacuum through the chuck, or through the use of an attachment means, such as for example, screws, or an adhesive means, such as for example, glue. 
     Thus, utilizing the above apparatus  100 , a more even polishing of wafers  160  can be accomplished. By using the conditioning station  130  disposed in the path of the slurry, the slurry is transformed from droplet form to a spread out form before it reaches the wafers  160 . Accordingly, the wafers  160  are polished evenly on all sides. 
     Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.