Patent Publication Number: US-6334810-B1

Title: Chemical mechanical polishing apparatus and method of using the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a chemical mechanical polishing (CMP) apparatus, and more particularly, to a chemical mechanical polishing apparatus containing cleaning fluid conduits for suppressing micro scratches on a wafer. 
     2. Description of the Related Art 
     As the integration of semiconductor devices increases and multi-layered interconnections become widely used, the importance of local and global planarization of an interlevel dielectric layer becomes more important. A preferred planarization method is a chemical mechanical polishing (CMP) method, where a surface of a semiconductor wafer is polished using chemical components of a slurry solution supplied between the wafer and a polishing pad. 
     In general, CMP equipment includes a polishing platen unit, a polishing head unit and a pad conditioning unit. The polishing platen unit includes a polishing platen connected to a drive motor and a polishing pad on the polishing platen. The drive motor rotates the polishing platen and the pad. 
     The polishing head unit includes a wafer carrier supporting and applying pressure to the semiconductor wafer, a first ring surrounding the wafer carrier to prevent lateral deviation of the semiconductor wafer during polishing, and a second ring surrounding the first ring. The second ring contacts the polishing pad to improve the polishing profile of an edge portion of the semiconductor wafer. 
     The pad conditioning unit contains a pad conditioner head connected to a motor shaft, which moves the head over the polishing pad. The pad conditioner head supports a disk holder which includes a diamond disk suspended above the polishing pad. The motor shaft lowers the head toward the polishing pad such that the diamond disk contacts the polishing pad to maintain and/or condition the surface of the polishing pad. 
     In the above CMP apparatus, the semiconductor wafer is attached to the wafer carrier with the surface of the semiconductor wafer to be polished facing the surface of the polishing pad. The polishing pad and the semiconductor wafer are rotated during polishing. A polishing slurry is supplied during the polishing operation. During polishing, pressure is appropriately applied by the polishing head unit on the semiconductor wafer contacting a first region of the polishing pad to polish the surface of the semiconductor wafer. Meanwhile, the pad conditioning unit is positioned over a second region of the polishing pad so that the surface of the polishing pad is appropriately conditioned and/or maintained by the diamond disk. 
     However, the prior art CMP apparatus suffers from the following problem. During polishing using the above CMP apparatus, the slurry supplied on the polishing pad may splash up and infiltrate into the gaps and/or holes in the polishing head unit and/or in the pad conditioning unit. For example, the slurry may infiltrate into the gaps between the first ring and the second ring, between the first ring and the wafer carrier, between the pad conditioner head and the disk holder and/or into the holes in the second ring. The infiltrated slurry rapidly solidifies into flakes or particles in the gaps and/or holes. 
     Although the polishing head unit, the polishing pad and the pad conditioning unit are cleaned from the outside after a polishing cycle, the slurry cannot be properly and completely removed from the gaps and/or holes. During the next polishing cycle, the solidified slurry particles drop away from the gaps and holes where they solidified onto the polishing pad. The solidified slurry particles on the polishing pad contact the wafer being polished and cause micro scratches (i.e., undesirable defects) on the surface of the wafer being polished. 
     The present invention is directed to overcoming or at least reducing the effects of the problem set forth above. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a chemical mechanical polishing apparatus, comprising a rotatable polishing pad, a wafer carrier facing in a direction of the polishing pad, at least one ring surrounding the wafer carrier and a first cleaning solution supply conduit located adjacent to the at least one ring for supplying a cleaning solution into at least one gap located in a region between the at least one ring and wafer carrier. 
     In accordance with another aspect of the present invention, there is provided a chemical mechanical polishing apparatus, comprising a rotatable polishing pad, a wafer carrier facing in a direction of the polishing pad and a pad conditioning unit, containing a pad conditioner head, a drive shaft connected to the pad conditioner head, a disk holder located below the pad conditioner head, such that a third gap is located between the disk holder and the pad conditioner head, a conditioning disk located below the disk holder and a second cleaning solution supply conduit for supplying a cleaning solution to the third gap. 
     In accordance with another aspect of the present invention, there is provided a method of polishing a substrate, comprising placing the substrate onto a carrier containing at least one ring, lowering the carrier to place the substrate in contact with a polishing pad, supplying a slurry to the polishing pad, rotating the polishing pad to remove a portion of the substrate and supplying a cleaning solution into at least one of (a) at least one gap located in a region between the at least one ring and the carrier to remove the slurry from the at least one gap and (b) a third gap located between a disk holder and a pad conditioner head of a pad conditioning unit to remove the slurry from the third gap. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above features and advantages of the invention will become apparent upon reference to the following detailed description of specific embodiments and the attached drawings, of which: 
     FIG. 1 is a cross-sectional view of a chemical mechanical polishing apparatus according to the present invention; 
     FIG. 2 is an enlarged cross-sectional view of the inner structure of portion A in FIG. 1; 
     FIG. 3 is a three-dimensional perspective view of the second ring shown in FIG. 1; and 
     FIG. 4 is a cross-sectional view of an inner structure of a pad conditioning unit shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Korean Application Number 99-12639, filed Apr. 10, 1999, discloses the same subject matter as the present application and is hereby incorporated by reference as if fully set forth herein. 
     The chemical mechanical polishing apparatus according to one embodiment of the present invention includes a polishing pad, a wafer carrier, a first ring, a second ring and a cleaning solution supply pipe. The polishing pad is rotatably installed and contacts a surface of a semiconductor wafer during polishing. The semiconductor wafer is loaded into the wafer carrier such that the surface of the semiconductor wafer to be polished faces the polishing pad. 
     The first ring surrounds the semiconductor wafer and the edge of the wafer carrier, and rotates together with the semiconductor wafer and the wafer carrier during polishing to reduce or prevent lateral deviation of the semiconductor wafer. The second ring surrounds the first ring, forming a gap between the second ring and the first ring. The second ring contains a plurality of holes passing from an outer surface to an inner surface, and a bottom surface for contacting a part of the polishing pad to improve a polishing profile of the outer region of the semiconductor wafer. 
     The cleaning solution supply pipe is connected to at least one of the holes in the second ring to supply the cleaning solution into the holes and the gaps between the first ring and the second ring and between the first ring and the wafer carrier. 
     A chemical mechanical polishing apparatus according to another embodiment of the present invention includes a rotatable polishing pad for polishing a surface of a semiconductor wafer and a polishing head unit for loading the semiconductor wafer to face the surface of the polishing pad. The polishing head unit is capable of moving vertically and horizontally. 
     The apparatus also contains a pad conditioning unit for maintaining the surface of the polishing pad during polishing. The pad conditioning unit comprises a conditioning disk, a disk holder and a pad conditioner head. The disk contacts part of the surface of the polishing pad during polishing to condition the polishing pad, while the disk holder supports the disk. The pad conditioner head supports the disk holder and contains a pipe for supplying a cleaning solution to a gap between the disk holder and the pad conditioner head. Preferably, the disk is formed of a diamond material, and the pipe is connected to the cleaning solution supply unit through a motor shaft and the pad conditioner head. 
     Referring to FIG. 1, the chemical mechanical polishing apparatus according to another embodiment of the present invention includes a polishing platen unit  100 , a polishing head unit  200  and a pad conditioning unit  400 . 
     The polishing platen unit  100  includes a polishing platen  130 , a drive motor  110  capable of rotating the polishing patent  130  about shaft Al in the direction of arrow  120 , and a polishing pad  140  installed on the polishing platen  130 . 
     The polishing head unit  200  includes a wafer carrier  220  supporting a semiconductor wafer  210  to be polished. The wafer carrier  220  may support one or more wafers  210 . A drive motor  230  rotates wafer carrier  220  about shaft A 2  in the direction of arrow  240 . However, a wafer carrier that lacks a drive motor for axial rotation is also within the scope of the present invention. The wafer carrier applies polishing pressure to the semiconductor wafer, as indicated by an arrow  250 . The wafer carrier  220  may also include an optional back film for adsorbing the semiconductor wafer  210  and for buffering the polishing pressure, and an optional backing plate, such as a ceramic plate (not shown). A polishing housing  260 , such as a metal housing, for supporting the wafer carrier  220  and for applying the polishing pressure, supports the wafer carrier  220 . However, the housing and the wafer carrier may comprise a single unit, if desired. 
     The CMP apparatus also contains at least one ring. Preferably, the apparatus contains at least two rings  270  and  280 . The first ring  270  may be used for guiding the semiconductor wafer  210  over the polishing pad  140 . The first ring may be installed around the wafer carrier  220 . A second ring  280  may be used for enhancing the polishing profile of the outer portion of the semiconductor wafer  210 . The second ring  280  may be installed around the first ring  270 . 
     Preferably, the first ring  270  rotates together with the wafer carrier  220  during polishing, while the second ring  280  remains stationary during polishing and contacts the polishing pad  140 . A first gap is formed between the first ring  270  and the second ring  280 , and a second gap is formed between first ring  270  and the wafer carrier  220 . Furthermore, the second ring  280  may contain holes in its outer surface. 
     A storage reservoir  310  is used to supply a slurry  300  to the polishing pad  140 . The slurry preferably comprises a chemical solvent and polishing particles for enhancing polishing of the wafer  210  by the polishing pad  140 . 
     The pad conditioning unit  400  includes a disk holder  420  supporting a diamond disk  410  and a pad conditioner head  430  supporting the disk holder  420 . A third gap is formed between the disk holder  420  and the head  430 . The conditioner head  430  is connected to a motor shaft  440 , preferably by its side surface. The motor shaft  440  is used to position the pad conditioner head over a predetermined region of the polishing pad  140  during polishing. 
     The polishing process using the CMP apparatus of FIG. 1 will now be described. First, the semiconductor wafer(s)  210  to be polished are stacked in a loading/unloading position in the polishing head unit, spaced apart from the polishing platen unit  100  by a predetermined distance. Then, the semiconductor wafer(s)  210  attached to the wafer carrier  220  are moved down to contact a first region of the polishing pad  140 . 
     The pad conditioning unit  400  also moves down over a second region of the polishing pad  140  such that the diamond disk  410  contacts the polishing pad  140 . The polishing platen unit  100  and the polishing head unit  200  are rotated by drive motors  110  and  230 , and the surface of the semiconductor wafer  210  contacting the polishing pad  140  is polished, while the diamond disk  410  maintains and/or conditions the polishing pad  140 . 
     As described above, during polishing, the slurry  300  may splash up from the surface of the polishing pad  140  and infiltrate into the first gap between the first ring  270  and the second ring  280 , the second gap between the wafer carrier  220  and the first ring  270 , the third gap between the disk holder  420  and the pad conditioner head  430  and/or into holes in the second ring  290 . The infiltrated glurry is quickly solidified into particles or flakes. The solidified slurry may fall down to the polishing pad  140  during the next polishing process, causing micro scratches on the surface of the wafer(s)  210  being polished. 
     According to an embodiment of the present invention, a cleaning solution supply conduit is connected to at least one ring of the polishing head unit  200  and/or to the pad conditioning unit  400 . The conduit is preferably a cleaning solution supply pipe and the cleaning solution is preferably purified or deionized water. However, other conduits or solutions may be used. The cleaning solution is used to remove the solidified slurry infiltrated into gaps or holes. 
     In a first preferred embodiment of the present invention, a first cleaning solution supply pipe  281  is connected to a hole (shown in FIGS. 2 and 3) in the second ring  280  where the slurry is easily infiltrated. In a second preferred embodiment of the present invention, a second cleaning solution supply pipe  450  is installed in the head  430  of the pad conditioning unit  400  (shown in FIG.  4 ). 
     FIG. 2 is an enlarged sectional view showing the inner structures of portion A of FIG. 1, i.e., the first and second rings  270  and  280 , and FIG. 3 is a three-dimensional perspective view of the second ring  280  of FIG.  1 . 
     Referring to FIGS. 2 and 3, the second ring  280  has a circular shape. The second ring  280  is preferably formed of a metallic material. The bottom surface of the second ring  280  may have an optional passivation layer  290  formed of a ceramic that contacts the polishing pad  140 , to protect the polishing pad  140  (shown in FIG. 1) from direct contact with the metal ring  280 . 
     The second ring  280  preferably contains a multiplicity of holes  283  that pass from the outer surface to the inner surface of the ring  280 . The cleaning solution supply pipe  281  is connected to at least one hole. The cleaning solution supply pipe  281  is completely connected to the entrance of a hole  283  by a connection unit  282 . 
     The method of operating the CMP apparatus according to the first preferred embodiment of the present invention will now be explained. First, the wafer(s)  210  are polished by contact with the polishing pad  140 , as described previously. The polishing head unit  200  of FIG. 1 then moves up to a loading/unloading position after the polishing process, and the cleaning solution is supplied to a hole  283  through the supply pipe  281 . The cleaning solution (i.e., deionized water) flows through the hole  283  into other holes  283  and into the first gap between the second ring  280  and  270  and the second gap between the first ring  270  and the wafer carrier  220 , as shown by an arrows in FIG.  2 . The flowing cleaning solution removes the slurry remaining in the holes  283  and in the first and second gaps. Thus, the solidified slurry is removed from the holes and the gaps, to thereby prevent it from falling onto the polishing pad  140  during a subsequent polishing step and to reduce or suppress the micro scratch defects in the wafer  210 . The polishing pad  140  may be cleaned between the polishing cycles. 
     Preferably, the cleaning solution is supplied through the cleaning solution supply pipe  281  at the same time as the cleaning of the outside of the polishing head unit  200  of FIG. 1, while the polishing head unit is raised up in the loading/unloading position. However, the cleaning solution may be supplied before or after the outside cleaning step. Furthermore, while not a preferred embodiment, the cleaning solution may be supplied intermittently or continuously through pipe  281  during the polishing of the wafer  210  to prevent the slurry from penetrating, sticking in and/or solidifying in the gaps and holes described above. This would prevent the slurry from solidifying in the gaps and/or holes and failing back onto the polishing pad  140  during the same polishing step. 
     In FIGS. 2 and 3, the cleaning supply pipe  281  is shown as preferably being connected to a hole  283  in the second ring. However, the cleaning supply pipe may be located above the first gap between the first ring  270  and the second ring and/or above the second gap between the first ring  270  and the wafer carrier  220 , to supply the cleaning solution directly into the gaps. Furthermore, there may be plural supply pipes  281 , or the cleaning solution supply conduit may have a ring or shower head shape to supply the cleaning solution to the ring shaped (i.e., circular) gaps. 
     In a second preferred embodiment of the present invention, a cleaning solution supply pipe  450  is installed to pass through the head  430  and the motor shaft  440  of the pad conditioning unit  400 , as shown in FIG.  4 . The cleaning solution supply pipe  450  is extended into the third gap between the disk holder  420  and the head  430  past the bottom surface of the head  430 . The slurry infiltrated into the gap between the disk holder  420  and the head  430  can be removed using the cleaning solution from the supply pipe  450 . 
     The method of operating the CMP apparatus according to the second preferred embodiment of the present invention will now be explained. First, the pad conditioning unit  400  of FIG. 1 is moved up away from the polishing pad  140  to a waiting position after the polishing step. At this time, the cleaning solution, i.e., pure or deionized water, is supplied through the cleaning solution supply pipe  450 . The supplied cleaning solution flows into the gap between the disk holder  420  and the pad conditioner head  430  through the cleaning solution supply pipe  450 . The cleaning solution removes the solidified slurry and prevents it from falling onto the polishing pad  140  during a subsequent polishing step, which reduces or suppresses the micro scratch defects on the wafer  210 . 
     Preferably the cleaning solution is supplied through the cleaning solution supply pipe  450  at the same time as the cleaning of the outside of the polishing head unit  200  of FIG. 1, while the polishing head unit is raised up in the loading/unloading position. However, the cleaning solution may be supplied before or after the outside cleaning step. Furthermore, while not a preferred embodiment, the cleaning solution may be supplied intermittently or continuously through pipe  450  during the polishing of the wafer  210  to prevent the slurry from penetrating, sticking in and/or solidifying in the third gap described above. This would prevent the slurry from solidifying in the third gap and falling back onto the polishing pad  140  during the same polishing step. 
     In FIG. 4, the supply pipe  450  is shown as extending through the motor shaft  440  and the pad conditioner head  430  to the third gap above the disk holder  420 . However, the supply pipe  450  may be located outside the motor shaft  440  and/or the pad conditioner head  430 , as long as it is able to supply the cleaning solution to the third gap. Furthermore, there may be plural supply pipes  450 , or the cleaning solution supply conduit may have a ring or shower head shape to supply the cleaning solution to the circular gap. 
     In a third preferred embodiment of the present invention, the CMP apparatus contains a cleaning solution supply conduit for supplying the cleaning solution to both the gaps and/or holes in the polishing head unit  200  and the pad conditioning unit  400 . The cleaning solution may be supplied to units  200  and  400  at the same or different times. 
     The CMP apparatus of the present invention may be used to polish a bare substrate, such as a semiconductor wafer, or to planarize isolation or interlevel insulating layer(s) (i.e., silicon oxide or nitride layers that separate various metallization layers) of a semiconductor device, such as a field effect or a bipolar transistor, formed on a semiconductor wafer. The scope of the present invention also includes a method of making the semiconductor device using the CMP apparatus and the semiconductor device made by the method. 
     Thus, a CMP apparatus and method of using the same has been described according to the present invention. While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and described in detail herein. However, it should be understood that the invention is not limited to the particular forms disclosed. Rather, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined in the appended claims.