Patent Publication Number: US-7210984-B2

Title: Shaped polishing pads for beveling microfeature workpiece edges, and associated systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 10/913,028, filed Aug. 6, 2004 now U.S. Pat. No. 7,066,792, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to shaped polishing pads for beveling microfeature workpiece edges, along with associated systems and methods. 
     BACKGROUND 
     Microfeature workpieces (e.g., round wafers) are typically provided to microfeature device manufacturers with beveled edges. A variety of techniques are used to bevel the edges, including applying plasma jets to the workpiece, running a polishing tape along the edges, and contacting the edges with a conical abrasive surface. During the course of processing, layers of materials are built up on the microfeature workpiece and then planarized using mechanical and chemical-mechanical planarization and polishing processes (collectively “CMP”). As a result of these processes, the initially beveled edges of the microfeature workpiece also receive deposits, which can reduce or eliminate the beveled shape of these edges. During subsequent planarization operations, these edges can be a source for defects. In particular, the deposited layers at and near the edge of the workpiece may tend to peel or delaminate, causing defects in the edge region of the microfeature workpiece. Defects in the edge region can migrate to other portions of the microfeature workpiece during subsequent processing steps, so that the defects are not necessarily limited to only the peripheral region of the workpiece. Furthermore, particles released from the edge region can cause scratch defects at the parts of the workpiece as the particles are dragged across the workpiece surface during processing. 
     One proposed solution to the foregoing problem is to use the same beveling tools that initially bevel the edges of the workpiece to also bevel the workpiece at selected points during microfeature device fabrication.  FIG. 1A  illustrates a tool  10  configured for such a purpose. The tool  10  can include a plurality of processing stations  12  (e.g., beveling stations) housed in an enclosure  11 . Input/output stations  13  are used to transfer microfeature workpieces into and out of the enclosure  11 . A control and display panel  14  is used to control the motion of the workpieces within the enclosure  11  and the processes taking place at the processing stations  12 . 
       FIG. 1B  illustrates components of one such processing station  12 . The components can include a wafer carrier  60  carrying a wafer  50  having two edges  54 . A shaft  42  carries a conical support  40  having a conical, concave surface. An abrasive liner  20  is attached to the conical support  40  and both the conical support  40  and the wafer carrier  60  are rotated, as indicated by arrows R. The wafer  50  is then brought into contact with the spinning abrasive liner  20  to bevel one edge  54 . Optionally, the remaining edge  54  can also be beveled after the wafer  50  is inverted on the carrier  60 . 
     One drawback with the foregoing approach is that the tool  10 , while effective for beveling workpiece edges, can be expensive. In particular, the tool can be expensive to acquire and, because it occupies a relatively large amount of clean-room floor space, can be expensive to own and maintain. Furthermore, the risk of damage to microfeature workpieces as they are shuttled back and forth between an edge bevel tool  10  and a CMP tool can further increase the overall cost of using such a tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrate a tool for beveling the edges of microfeature workpieces in accordance with the prior art. 
         FIG. 2  is a partially schematic, cross-sectional illustration of a system for beveling the edges of a microfeature workpiece in accordance with an embodiment of the invention. 
         FIG. 3  is a partially schematic, cross-sectional illustration of a system for removing material from both the edges and faces of microfeature workpieces, in accordance with another embodiment of the invention. 
         FIGS. 4A and 4B  illustrate a polishing pad having a curved surface for controlling the shape of a bevel applied to a microfeature workpiece, in accordance with another embodiment of the invention. 
         FIG. 5  illustrates a polishing pad assembly that includes a generally rigid support carrying a polishing pad material, in accordance with another embodiment of the invention. 
         FIG. 6  illustrates a tool having multiple polishing pads to remove material from both the edges and the faces of workpieces, in accordance with another embodiment of the invention. 
         FIGS. 7A and 7B  illustrate a web-format polishing tool and pad configured in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed toward systems and methods for beveling microfeature workpiece edges. A system in accordance with one aspect of the invention is configured to remove material from a microfeature workpiece having a first face, a second face facing opposite from the first face, an edge surface between the first and second faces, and an edge at a juncture between the edge surface and one of the first and second faces. The system can include a carrier positioned to carry the microfeature workpiece with the first and second faces generally normal to an axis. The system can further include a first polishing pad having a support surface and a polishing surface facing generally away from the support surface. The polishing surface can have a first shape, with at least one portion oriented at an acute angle relative to the axis and the support surface to remove material from the edge of the microfeature workpiece. A polishing pad support is positioned to carry the first polishing pad proximate to the carrier with the polishing surface facing toward the carrier. The polishing pad support can be configured to carry a second polishing pad in lieu of the first, the second polishing pad having a polishing surface with a second shape different than the first shape. The second shape can be configured to remove material from the first face of the microfeature workpiece while the microfeature workpiece rotates about the axis. 
     In a particular embodiment, the first polishing pad can have a generally circular planform shape, and the at least one portion of the pad can form a rim that extends circumferentially around at least part of the pad. In another embodiment, the at least one portion of the pad can include first and second portions facing at least partially toward each other, and a third portion (between the first and second portions) oriented generally normal to the axis. 
     A system in accordance with another aspect of the invention can include a carrier positioned to carry the microfeature workpiece with the first and second faces generally normal to an axis, a polishing pad support positioned proximate to the carrier, and a compliant polishing pad carried by the polishing pad support. The polishing pad can include a support surface facing toward the polishing pad support, and a polishing surface facing generally away from the support surface. The polishing surface can have at least one portion oriented at an acute angle relative to the axis and non-parallel to the support surface to remove material from the edge of the microfeature workpiece. 
     A system in accordance with yet another aspect of the invention includes a carrier positioned to carry a microfeature workpiece with the first face at a polishing plane. The system can further include a first polishing pad support, and a first polishing pad carried by the first polishing pad support. The first polishing pad can have a first polishing surface oriented generally parallel to the polishing plane. The system can further include a second polishing pad support carrying a second polishing pad. The second polishing pad can have a second polishing surface that is non-parallel to the polishing plane. 
     A method in accordance with yet another aspect of the invention includes positioning a microfeature workpiece at a processing tool, contacting the edge of the microfeature workpiece with a polishing surface of a polishing pad while the polishing surface is non-parallel to the first face of the workpiece, and removing material from the edge of the microfeature workpiece by rotating at least one of the microfeature workpiece and the polishing pad relative to the other about an axis generally normal to the first face of the workpiece while the edge contacts the polishing surface. The method can further include removing material from the first face of the workpiece without removing the workpiece from the processing tool. 
     As used herein, the terms “microfeature workpiece” and “workpiece” refer to substrates on and/or in which microfeature devices are integrally formed. Typical microfeature devices include microfeature circuits or components, thin-film recording heads, data storage elements, microfluidic devices, and other products. Micromachines and micromechanical devices are included within this definition because they are manufactured using much of the same technology that is used in the fabrication of integrated circuits. The substrates can be semiconductive pieces (e.g., doped silicon wafers and gallium arsenide wafers), nonconductive pieces (e.g., various ceramic substrates) or conductive pieces. In some cases, the workpieces are generally round, and in other cases the workpieces have other shapes, including rectilinear shapes. Several embodiments of systems and methods for removing material from the edges of microfeature workpieces are described below. A person skilled in the relevant art will understand, however, that the invention may have additional embodiments, and that the invention may be practiced without several of the details of the embodiments described below with reference to  FIGS. 2–7B . 
       FIG. 2  is a partially schematic, side elevational view of a system  200  having a polishing pad  220  shaped to bevel the edges of a microfeature workpiece  250 . The polishing pad  220  can be supported on an existing platen or pad support  240  that is also configured to carry existing CMP polishing pads. Accordingly, the polishing pad  220  can be installed and controlled using existing hardware. As will be described in greater detail below, this and other related features can provide a lower cost, more efficient way to remove material from the edges of the microfeature workpiece  250 . 
     The system  200  can include the polishing pad  220  carried on the polishing pad support  240 , with an optional underpad  241  positioned between the polishing pad  220  and the pad support  240 . A drive assembly  242  can rotate the pad support  240  and the polishing pad  220  (as indicated by arrow A). The drive assembly  242  can also reciprocate the pad support  240  and the polishing pad  220  (as indicated by arrow B). A polishing liquid  230  can be disposed on the polishing pad  220 , and the polishing pad  220  (with or without the polishing liquid  230 ) can form a polishing medium  231  for removing material from the microfeature workpiece  250 . 
     The microfeature workpiece  250  can include a first face  251 , a second face  252  facing generally opposite from the first face  251 , and an edge surface  253  between the first face  251  and the second face  252 . The edge surface  253  can form one edge  254  at its juncture with the first face  251  and another edge  254  at its juncture with the second face  252 . The edges  254  are shown as sharp 90° corners in  FIG. 5 , but can have other shapes in other embodiments and/or as the edges  254  are beveled. The beveled edges  254  can extend inwardly from the edge surface  253  by a distance of up to about three millimeters in one embodiment, and by other distances in other embodiments. The following discussion focuses on beveling the edge  254  between the first face  251  and the edge surface  253 , but it will be understood by those of ordinary skill in the art that the methods and systems described below in this context may apply equally to the edge  254  between the second face  252  and the edge surface  253 . 
     The microfeature workpiece  250  can be supported relative to the polishing pad  220  with a carrier  260 . Accordingly, the carrier  260  can include a carrier head  261  and, optionally, a resilient pad  264  that supports the workpiece  250  relative to the polishing pad  220 . The carrier  260  can include a carrier actuator assembly  262  that translates the carrier head  261  and the workpiece  250  (as indicated by arrow C) and/or rotates the carrier head  261  and the workpiece  250  (as indicated by arrow D). The carrier head  261  can include a vacuum chuck or other arrangement for releasably holding the microfeature workpiece  250 . An optional and independently actuatable retainer ring  263  can prevent the microfeature workpiece  250  from slipping out from under the carrier head  261 . The relative movement between the polishing pad  220  and the workpiece  250  chemically and/or chemically-mechanically removes material from the workpiece  250  during polishing and/or planarization, as described in greater detail below. 
     The polishing pad  220  can include a support surface  221  that directly engages a corresponding interface surface  243  of the pad support  240 , or engages an underpad  241  positioned between the pad support  240  and the polishing pad  220 . Accordingly, the support surface  221  faces generally toward the pad support  240 . The polishing pad  220  can further include a polishing surface  224  facing generally opposite from the support surface  221 . Some or all of the polishing surface  224  can be inclined at an acute angle X relative to the first face  251  of the microfeature workpiece  250 . Accordingly, these portions of the polishing surface  224  can also be oriented at an acute angle Y relative to an axis E that extends generally normal to the first and second faces  251 ,  252 . As a result, these portions of the polishing surface  224  can be positioned to bevel the edge  254  between the first face  251  and the edge surface  253 . 
     In a particular embodiment, the polishing surface  224  can include a first portion  222  that extends circumferentially around a peripheral region of the polishing pad  220  to form a rim  225 . The polishing surface  224  can also include a second portion  223  disposed annularly inwardly from the first portion  222  to form a generally conical, central surface. The carrier  260  can support the microfeature workpiece  250  so that the edge  254  contacts both the first portion  222  and the second portion  223 . As the carrier  260  and/or the pad support  240  rotate relative to each other, the first and second portions  222 ,  223  of the polishing surface  224  contact and bevel the edge  254  by removing material from the edge  254 . When the carrier  261  includes a retainer ring  263 , the retainer ring  263  can be elevated or removed so as not to interfere with the bevel process. Accordingly, the forces holding the microfeature workpiece  250  to the carrier head  261  can be strong enough to withstand the transverse force (e.g., directed out of the plane of  FIG. 2 ) applied to the microfeature workpiece  250  as it contacts the first and second portions  222 ,  223 . 
       FIG. 3  illustrates a system  310  having a polishing pad  320  configured in accordance with another embodiment of the invention. The polishing pad  320  can include a polishing surface  324  having an annular rim  325  that includes a first portion  322  facing at least partially toward a second portion  323 . The first and second portions  322 ,  323  can be oriented at an acute angle relative to the first face  251  of the microfeature workpiece  250 , in a manner generally similar to that described above with reference to  FIG. 2 . The polishing surface  324  can also include a third portion  326  positioned between the first portion  322  and the second portion  323  and oriented generally parallel to the first face  251  (e.g., at a polishing plane positioned to remove material from the first face  251 ). Accordingly, an operator can initially position the workpiece  250  with the edge  254  in contact with the first portion  322  of the polishing surface  324  to bevel the edge  254 . After material has been removed from the edge  254 , the operator can move the workpiece  250  (e.g., by moving the carrier  260 ) inwardly away from the rim  325 , as indicated by arrow F. With the microfeature workpiece  250  in this position, the operator can remove material from the first face  251 . Accordingly, the same polishing pad  320  can be used to remove material from both the edge  254  and the first face  251 . 
     In a particular aspect of an embodiment shown in  FIG. 3 , the polishing pad  320  can include one or more relief channels  327  positioned in the rim  325 . The relief channels  327  can be sized to receive material removed from the edge  254  of the microfeature workpiece  250 . Accordingly, this material can be conducted away from the polishing surface  324 . An advantage of this arrangement is that the material removed from the edge  254  can be less likely to be conveyed to the third portion  326  of the polishing surface  324 , where it can scratch or otherwise damage the first face  251  during CMP operations. 
     The operator can control the force applied to the workpiece  250  (as well as the orientation of the workpiece  250 ) to assist in selectively removing material from either the edge  254  or the first face  251 . For example, when the microfeature workpiece  250  is positioned against the rim  325 , the downforce applied to the workpiece  250  can be reduced so as to reduce or eliminate the amount of material removed from the first face  251  while material is being removed from the edge  254 . In a particular aspect of this embodiment, the gripping force applied to the workpiece  250  by the carrier  260  can be sufficient to allow the carrier  260  to force the edge  254  of the workpiece  250  laterally outwardly against the rim  325 , without applying a significant downforce on the workpiece  250 , and without causing the workpiece  250  to slip out from under the carrier head  261 . In some embodiments, the retainer ring  263  described above with reference to  FIG. 2  can help prevent the workpiece  250  from slipping out from under the carrier head  261 , so long as the retainer ring  263  does not interfere with the rim  325 . Alternatively, the gripping force between the carrier head  261  and the workpiece  250  can be sufficient to prevent the workpiece from slipping out, even without the presence of the retainer ring  263 . 
     In a further particular embodiment, the carrier  260  can lift the workpiece  250  above the third portion  326  of the polishing surface  324 , while engaging the workpiece edge  254  with the polishing pad rim  325 , thereby ensuring that material is not removed from the first face  251  while material is being removed from the edge  254 . An advantage of arrangements that limit or eliminate the amount of material removed from the first face  251  while material is being removed from the edge  254  is that the likelihood for damaging the first face  251  with material removed from the edge  254  can be reduced or eliminated. 
     In other arrangements, the composition of the polishing pad  320  (and in particular, the polishing surface  324 ) can be controlled to selectively remove material from the workpiece edge  254  more quickly than from the first face  251 . For example, the first and second portions  322 ,  323  can be formed from constituents that have a higher material removal rate than do constituents of the third portion  326 . In particular arrangements, the first and second portions  322 ,  323  can have a higher abrasiveness and/or hardness than the third portion  326 , and in other arrangements, other attributes of the polishing surface  324  can be selected to produce different polishing rates. 
     In the embodiments described above with reference to  FIGS. 2 and 3 , the rims of the polishing pads have generally flat, conical, inwardly facing surfaces. In another embodiment, the rim can have a curved surface so that the angle between the polishing surface and a line normal to the workpiece faces  251 ,  252  varies radially. For example, referring now to  FIG. 4A , a polishing pad  420  in accordance with another aspect of the invention can include a polishing surface  424  having a first portion  422  forming a rim  425  that has a curved cross sectional shape. An advantage of the curved polishing surface  424  is that it can be used to control the shape and size of the bevel applied to the edge of the workpiece  250 . For example, in an embodiment shown in  FIG. 4A , the workpiece  250  can be positioned so that contact with the polishing surface  424  produces a relatively gradual or shallow beveled edge  254   a . By moving the workpiece  250  outwardly, the edge can contact a steeper portion of the rim  425 . For example, referring now to  FIG. 4B , the workpiece  250  has been positioned further outward than is shown in  FIG. 4A . Accordingly, the edge  254   b  has a steeper bevel. Because the polishing pad  420  is compliant, the polishing surface  424  can flex at least somewhat as the workpiece  250  is moved outwardly, which can also steepen the bevel angle. In another embodiment, as described above, the workpiece  250  can be elevated above a central portion  426  to contact a steeper portion of the rim  425 . 
     In the embodiments described above with reference to  FIGS. 2–4B , the polishing pad, and in particular, the first portion, second portion and rim of the polishing pads, are self-supporting. Accordingly, these portions of the polishing pads can retain their shapes and positions when the polishing pads rest on the pad support. In other embodiments, the polishing pad can be so compliant that these portions of the pad are not self-supporting. For example, referring now to  FIG. 5 , a polishing pad assembly  520  in accordance with an embodiment of the invention includes a compliant non-self-supporting polishing pad material  528  that is attached to a generally rigid support  529 . The support  529  can extend upwardly adjacent to a rim  525  of the polishing pad material  528  to provide support for the polishing pad material  528  in this region. 
     Polishing pads configured in accordance with any of the embodiments described above with reference to  FIGS. 2–5  can be installed on tools and used in combination with other polishing pads to provide multiple functions for workpiece material removal. For example, referring now to  FIG. 6 , a system  600  can include a tool  610  having multiple stations  612  disposed within an enclosure  611  in accordance with an embodiment of the invention. For the purposes of illustration, the stations  612  are shown in  FIG. 6  as a first station  612   a  and a second station  612   b . The tool  610  can also include a robot  615  having an end effector  616  that is configured to releasably engage and disengage microfeature workpieces  250 . Accordingly, the robot  615  can move microfeature workpieces  250  from one station  612  to another. 
     The first station  612   a  can include a first polishing pad support  640   a  carrying a first polishing pad  620   a  having a configuration generally similar to the polishing pad  220  described above with reference to  FIG. 2 . Accordingly, the first polishing pad  620   a  can include a polishing surface  624   a  having a first portion that forms an outer, annular rim, and a second portion disposed annularly inwardly from the rim. The first polishing pad  620   a  can accordingly be used to remove material from the edge  254  of a microfeature workpiece  250 , as described above with reference to  FIG. 2 . 
     After material has been removed from the edge  254  of the microfeature workpiece  250 , the robot  615  can transfer the microfeature workpiece  250  to the second station  612   b  where material can be removed from the first face  251 , for example, using conventional CMP techniques. Accordingly, the second station  612   b  can include a second pad support  640   b  having a generally flat polishing pad  620   b  with a generally flat polishing surface  624   b  configured to remove material from the first face  251 . 
     An advantage of the system  600  describe above with reference to  FIG. 6  when compared with existing systems is that the same tool  610  can be used to remove material from both the edges and the faces of microfeature workpieces. Accordingly, the amount of time required to process the workpieces can be reduced because the workpieces need not be moved from one tool to another to perform these functions. The costs associated with manufacturing the workpieces can also be reduced because the edge removal function can be integrated into an existing tool, and accordingly, a separate tool need not be purchased and maintained by the operator. Still a further advantage of this arrangement is that it is versatile. For example, the polishing pad supports  640   a  and  640   b  can be identical or nearly identical, and yet can support polishing pads having different configurations and providing different functions. Accordingly, the operator need not retrofit significant features of the tool  610  and can instead place the desired polishing pad on an existing polishing pad support. If the operator later wishes to change the arrangement of polishing pads (e.g., by replacing the first polishing pad  620   a  with a more conventional second polishing pad  620   b , or replacing either of these pads with a polishing pad  320  generally similar to that shown in  FIG. 3 ), the operator need only remove the polishing pad from the corresponding polishing pad support and position the new polishing pad in its place. 
     The polishing pads described above with reference to  FIGS. 2–6  have generally circular planform shapes. In other embodiments, the polishing pads can have other shapes. For example, referring now to  FIG. 7A , a system  700  can include an elongated polishing pad  720  configured in accordance with another embodiment of the invention. In one aspect of this embodiment, the system  700  has a polishing pad support  740  with a top panel  741  at a work station where an operative portion “W” of the polishing pad  720  is positioned. The top panel  741  is generally a rigid plate to provide a flat, solid surface to which a particular section of the polishing pad  720  may be secured during polishing. 
     The system  700  can also have a plurality of rollers to guide, position and hold the polishing pad  720  over the top panel  721 . The rollers can include a supply roller  747 , first and second idler rollers  744   a  and  744   b , first and second guide rollers  745   a  and  745   b , and a take-up roller  746 . The supply roller  747  carries an unused or preoperative portion of the polishing pad  720 , and the take-up roller  746  carries a used or post-operative portion of the polishing  720 . Additionally, the first idler roller  744   a  and the first guide roller  745   a  can stretch the polishing pad  720  over the top panel  741  to hold the polishing pad  720  stationary during operation. A motor (not shown) drives at least one of the supply roller  747  and the take-up roller  746  to sequentially advance the polishing pad  720  across the top-panel  741 . Accordingly, clean pre-operative sections of the polishing pad  720  may be quickly substituted for used sections to provide a consistent surface for polishing the microfeature workpiece  250 . 
     The system  700  can also have a carrier assembly  760  that controls and protects the microfeature workpiece  250  during polishing. The carrier assembly  760  can include a head  761  to pick up, hold and release the microfeature workpiece  250  at appropriate stages of the polishing process. The carrier assembly  760  can also have a support gantry  765  carrying a drive assembly  770  that can translate along the gantry  765 . The drive assembly  770  can have an actuator  762 , a drive shaft  767  coupled to the actuator  762 , and an arm  768  projecting from the drive shaft  767 . The arm  768  carries the head  761  via a terminal shaft  769  such that the drive assembly  770  orbits the head  761  about an axis G—G (as indicated by arrow R 1 ). The terminal shaft  769  may also rotate the head  761  about its central axis H—H (as indicated by arrow R 2 ). 
       FIG. 7B  is a partially schematic, isometric top view of the polishing pad  720  shown in  FIG. 7A . In one aspect of an embodiment shown in  FIG. 7B , the polishing pad  720  can include a polishing surface  725  having a first portion  722 , a second portion  723  facing at least partially toward the first portion  722 , and a third portion  726  positioned between the first portion  722  and the second portion  723 . Accordingly, the polishing pad  720  can remove material from the edge(s) and face(s) of a microfeature workpiece, in a manner generally similar to that described above with reference to  FIG. 3 . In other embodiments, the polishing pad  720  can have other features generally similar to those described above. 
     From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, features described above in the context of particular embodiments of the invention can be combined or eliminated in other embodiments. Accordingly, the invention is not limited except as by the appended claims.