Abstract:
An apparatus for conditioning the polishing pad of a chemical mechanical planarization (CMP) system including an apertured conditioning disk that is formed to support a plurality of brush bristles in any desired configuration. The bristles are utilized to lift out debris and contaminants that have been lodged within the deep pores of polishing pads, particularly “soft” polishing pads (or polishing felts) that include relatively deep pores. The apertures in the conditioning disk are used to allow for the efficient evacuation of the effluent created during the conditioning process. The apertures may also be used to introduce conditioning fluids as the bristles are brushing the surface to assist in the conditioning process. The utilization of the apertures to evacuate the effluent (via an attached vacuum source) overcomes problems associated with the prior art by immediately removing the dislodged material from the pad surface before it has an opportunity to be re-incorporated into the polishing pad.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/728,126, filed Oct. 19, 2005 and herein incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to a conditioning brush for use in cleaning the polishing pad of a chemical mechanical planarization (CMP) apparatus and, more particularly, to a conditioning brush formed as disk to include an arrangement of both bristles and apertures to facilitate the cleaning operation.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the field of chemical mechanical planarization (CMP), a process known as “pad conditioning” or “pad dressing” is used to restore the surface of the polishing pad and remove surface glazing by dislodging particulates and spent polishing slurry from the pad. Pad conditioning may be performed “ex-situ” (i.e., conditioning the polishing pad between wafer polishing cycles) or “in-situ” (i.e., concurrent with, or during, a wafer polishing cycle). In a typical prior art “in-situ” pad conditioning process, a fixed abrasive conditioning disk is moved across the pad surface to remove a small amount of pad material and debris, thus creating new asperities in the pad surface to allow for the free flow of the polishing slurry. The removed pad material and debris then combine with the slurry dispensed during the polishing process and are passively carried away from the pad.  
         [0004]     Particulate generation is an on-going problem with known processes of conditioning CMP polishing pads, where particles from any one of the CMP apparatus, slurry, wafer, pad or conditioner remain on the pad&#39;s surface after conditioning. Any individual particle remaining on the pad may later scratch a wafer surface during polishing, creating a potential defect or contributing to polishing non-uniformity. For example, a particle disposed on the polishing pad may create a high spot that locally concentrates the forces between the polishing pad and the wafer. If large numbers of particles are present on the polishing pad, local disparities in polishing rates may result in polishing non-uniformities.  
         [0005]     In certain types of CMP, for example tungsten CMP or post-planarization buffing, a relatively porous polishing pad is utilized, where this type of pad is characterized by a microstructure exhibiting vertically oriented, open pores. Variously referred to as a “soft” polishing pad, fibrous polishing pad, and the like, such pads may consist of a poromeric coating over a felt substrate, the poromeric coating comprising vertically oriented large pores sitting on top of a smaller, microporous felt layer. The polishing slurry and debris that settles within the lower regions of the pores within these pads can become nearly stagnant and develop recirculating eddy flows that trap even more material and limit the polishing/buffing capabilities of the pad. Over time, the trapped/recirculated materials can resurface and damage the wafer, dilute the process materials, or both. The conventional diamond abrasive conditioning disk is not effective in removing this deeply-trapped material, and has the additional drawback of quickly wearing away the porous pad material. As an alternative, a conditioning “brush” may be used to scour the porous pad surface in a manner that is likely to dislodge deeply embedded particles and move them into the waste stream. Prior art CMP systems utilizing a conditioning brush, however, require a large amount of slurry and rinse waters in an attempt to displace these particulates.  
         [0006]     U.S. Pat. NO. 6,386,963 issued to S. Kenji et al. on May 14, 2002 discloses a conditioning element that is formed to support a combination of an abrasive surface and brush bristles. In the Kenji et al. structure, abrasive conditioning material is formed on a ring-shaped plate that is attached to the bottom surface of the conditioner head, leaving the center region of the element open. A plurality of brush bristles is formed on a small disk that is then attached to the center region of the abrasive ring. One problem with this particular arrangement, however, is that the limited positioning of the bristles in the central region of the conditioning element allows some particulate matter to be unaffected by the bristles and thus remain embedded within the pad. Further, the differential in height between the abrasive material and the bristles will likely result in inconsistent conditioning behavior and wear rates for the pad material.  
         [0007]     Another prior art arrangement is disclosed in U.S. Pat. No. 7,033,253, issued to F. L. Dunn on Apr. 25, 2006. In the Dunn arrangement, brush bristles are disposed in any desired pattern on the bottom surface of a conditioning element, with the remaining portion of the surface covered by an abrasive material. The relative hardness of the bristles and the abrasive material may be controlled to best condition a particular pad material.  
         [0008]     While both the Dunn and Kenji et al. arrangements provide an improvement in implementing a conditioning brush within a conventional CMP conditioning element, problems remain in that the material dislodged by the bristles (and the abrasive material) may be re-introduced to the pad surface before the conditioning process has an opportunity to flush the debris away.  
         [0009]     Thus, a need remains in the art for a conditioning arrangement that provides the brushing motion preferred for large pore, fibrous or soft polishing pads/felts, while efficiently removing the debris from the polishing pad surface.  
       SUMMARY OF THE INVENTION  
       [0010]     The need remaining in the prior art is addressed by the present invention, which relates to a conditioning brush for use in cleaning the polishing pad of a chemical mechanical planarization (CMP) apparatus and, more particularly, to a conditioning brush formed as a disk to include an arrangement of both bristles and apertures to facilitate the cleaning operation.  
         [0011]     In accordance with the present invention, an apertured conditioning disk is formed to support a plurality of brush bristles in any desired configuration. The apertures in the conditioning disk are used to allow for the efficient evacuation of the effluent created during the conditioning process, including both the debris dislodged by the bristles and slurry material remaining in the pores. The apertures may also be used to introduce conditioning fluids to assist in the conditioning process. The utilization of the apertures to evacuate the effluent (via an attached vacuum source) overcomes problems associated with the prior art by immediately removing the dislodged and/or accumulated material from the pad surface before it has an opportunity to be re-incorporated into the polishing pad.  
         [0012]     In one embodiment of the present invention, the conditioning disk is formed of a stiff material capable of supporting the bristles in position such that the bristles have a slight stand-off from the bottom surface of the disk, allowing for the conditioner head to maintain a vacuum seal while the bristles engage the pores of the pad material. In an alternative embodiment, the conditioning disk may be formed of an abrasive material to permit simultaneous abrading and brushing of the polishing pad surface. In yet another embodiment, the bristles themselves may be formed of an abrasive-filled composite material.  
         [0013]     Other and further embodiments and aspects of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Referring now to the drawings,  
         [0015]      FIG. 1  illustrates an exemplary CMP system including a conditioning brush formed in accordance with the present invention;  
         [0016]      FIG. 2  is a top view of system of  FIG. 1 ;  
         [0017]      FIG. 3  is a top view of an exemplary conditioner head/conditioning brush formed in accordance with the present invention, include a plurality of bristles and a separate plurality of apertures within the brush;  
         [0018]      FIG. 4  is a cut-away side view of the conditioning brush of  FIG. 3 ;  
         [0019]      FIG. 5  is a simplified view of the arrangement of  FIG. 4 , illustrating in particular the intrusion of the bristles within the pores of the polishing pad;  
         [0020]      FIG. 6  is a top view of an alternative embodiment of the present invention, with the bristles disposed in V patterns and the apertures disposed therebetween, the view of  FIG. 6  illustrating the placement of only a few bristles;  
         [0021]      FIG. 7  is a top view of the same embodiment as  FIG. 6 , in this case with a complete set of bristles in place; and  
         [0022]      FIG. 8  is a top view of yet another embodiment of a conditioning brush formed in accordance with the present invention, in this case, the bristles and apertures disposed as a plurality of arms configured in a spiral pattern from the center. 
     
    
     DETAILED DESCRIPTION  
       [0023]      FIG. 1  contains a perspective view of an exemplary CMP system  10  formed in accordance with the present invention for brushing the surface of a polishing pad used to polish/planarize surface S of a semiconductor wafer  12 . In operation, surface S of wafer  12  is positioned against a polishing pad  14  through an arrangement not shown (and not relevant to the subject matter of the present invention). Wafer  12  is rotated on polishing pad  14 , as shown by the arrow in  FIG. 1 . Polishing pad  14  itself is secured to a rotating, orbital or linear platen  16 . A stream of polishing slurry, generally containing an oxidizer, abrasive and/or ultrapure water (UPW) is poured on polishing pad surface  18  from a conventional polishing slurry delivery apparatus (not shown). The polishing slurry, in cooperation with the rotating motion of wafer  12  and pad  14 , acts to remove a portion of the wafer&#39;s surface unevenness.  
         [0024]     As mentioned above, it is necessary to “condition” or “redress” surface  18  of polishing pad  14  to remove the glaze/build-up of polishing slurry from the pad&#39;s surface, as well as to remove accumulated debris and other materials associated with the polishing process itself. In the arrangement as shown in  FIG. 1 , an end effector arm  20  is used to perform the conditioning process, where arm  20  moves in an arc A about a fixed shaft  21  and simultaneously provides a rotational motion R and a downward force F on an attached conditioner head  22 .  FIG. 2  shows, in a top view, the relative motions of arm  20 , conditioner head  22  and polishing pad  14 , illustrating in particular arc movement A of arm  20  across the surface of polishing pad  14 . In an alternative embodiment, the end effector can be configured to cover a full radius of polishing pad  14 , such that it conditions surface  18  without the need of the arc-based sweeping motion. The apertured conditioning brush of the present invention, as discussed in detail below, may be used with either embodiment. The apertured conditioning brush of the present invention is equally applicable for use in systems that include polishing felts instead of polishing pads, where the felts have the same deep nap configuration as the soft polishing pads discussed above. That is, the polishing pads and polishing felts best suited for conditioning with the apertured brush of the present invention are characterized by a microstructure exhibiting vertically oriented, open pores (e.g., poromeric coating), capable of trapping debris and fluids in recirculating eddies, as discussed above.  
         [0025]     Referring back to  FIG. 1 , conditioner head  22  is shown as further comprising an apertured conditioning brush  30 , formed in accordance with the present invention to perform the functions of: (1) brushing surface  18  of polishing pad  14  to loosen debris lodged deep within pad  14 ; (2) evacuating the conditioning fluid, dislodged debris and/or spent polishing fluid (hereinafter referred to as “effluent”) from the vicinity of polishing pad  14 ; and, possibly, (3) introducing conditioning fluids onto surface  18  of pad  14 . Conventional abrasive conditioning disks are not always successful in removing debris deeply embedded within the pores of some of the more fibrous polishing pads and polishing felts. A plurality of bristles, as described below, are included in contacting surface  31  of conditioning brush  30  and will enter the deep pores of the fibrous polishing pad to dislodge accumulated debris. Apertures formed within conditioning brush  30  provide a channel for the removal of effluent through a vacuum path, where in  FIG. 1  conditioner head  22  is illustrated as including a vacuum outlet port  37  coupled to a vacuum source  50 . Conditioning fluids may be used in combination with the surface brush to efficiently remove accumulated debris, where the conditioning fluids may be disposed onto the surface of polishing pad  18  through an inlet port  39  in conditioner head  22 .  
         [0026]      FIG. 3  contains a top view of an exemplary apertured conditioning brush  30  as fixed within conditioner head  22 , where illustrated surface  31  will contact the surface of a polishing pad during conditioning. There exist various arrangements for attaching conditioning brush  30  to conditioner head  22 , where a particularly suitable arrangement that maintains apertured alignment between brush  30  and the remaining components of conditioning disk  22 , using a magnetic-based hex key arrangement, is disclosed in co-pending application Ser. No. 10/819,754, filed Apr. 7, 2004, and assigned to the assignee of this application. Referring to  FIG. 3 , a plurality of apertures  34  are shown, where apertures  34  are surrounded by a plurality of bristles  40  that function to provide the soft pad brushing in accordance with the present invention. FIG.  4  is a cut-away side view of the arrangement of  FIG. 3 . Bristles  40  function to dislodge particulate matter from the fibrous pores below surface  18  of pad  14  (see  FIG. 5 ) and push the effluent through apertures  34  toward vacuum outlets  35  around the outer periphery of conditioner head  22 , as shown in  FIG. 4 . The rotation of conditioner head  22  will assist in moving the effluent outward through vacuum outlets  35  into an evacuation channel  36 . The effluent is then pulled, by vacuum force, through vacuum exit port  37  on conditioner head  22 , providing an efficient cleaning of polishing pad surface  18 . In the particular embodiment as illustrated in  FIG. 4 , conditioning brush  30  further comprises a channel system  32  coupled to apertures  34  to allow for the introduction of conditioning fluids, if desired, via inlet port  39  of conditioner head  22 .  
         [0027]      FIG. 5  illustrates, in a simplified view, the relationship between pad  14 , conditioner head  22  and bristles  40 . As mentioned above, bristles  40  are formed to stand off a predetermined distance below conditioner head  22 , allowing for bristles  40  to enter the deep, soft-walled pores of polishing pad  14  during conditioning, while maintaining the integrity of the vacuum connection or seal between pad  14  and conditioner head  22 . As shown, bristles  40  extend deep enough into vertically-oriented open pores P of pad  14  so that the accumulated debris may be dislodged as conditioning brush  30  sweeps across the pad surface. The length of bristles  40  is controlled, however, so that sidewalls  22 W of conditioner head  22  maintain contact with surface  18  of polishing pad  14 . It is to be understood that the particular dimensions of the bristles will be a function of parameters such as, but not limited to, the depth of the pores of the fibrous polishing material, the pad material itself, the downforce applied by the conditioner head to the polishing pad, and the applied vacuum force. The contact between surface  18  and conditioner head sidewalls  22 W is required so that the vacuum force/leakage is controllable and the debris will continue to be evacuated from pad surface  18 , through conditioning brush  30  and exit from vacuum outlet port  37  of conditioner head  22 . Bristles  40  comprise an inert material, such as nylon, that will not react with any of the chemicals that may be present at the pad surface, such as polishing slurry, conditioning liquids, wafer debris material and the like. In a specific embodiment, bristles  40  may be formed of an abrasive-filled composite material that will provide an even greater amount of cleaning energy to surface  18  of conditioning pad  14 .  
         [0028]      FIG. 6  is a top view of an alternative conditioning brush  60 , where in this particular embodiment, bristles  40  are disposed in V-like patterns  62  across surface  61  of brush  60 . For the sake of clarity, only a portion of bristles  40  are shown in position in  FIG. 6 .  FIG. 7  is a top view of conditioning brush  60  with a complete set of bristles  40  in place. Referring back to  FIG. 6 , a set of apertures  34 , is shown as disposed between each V pattern  62  of bristles. Apertures  34  function in the manner discussed above to dispense conditioning liquids and evacuate effluent from surface  18  of polishing pad  14 .  
         [0029]      FIG. 8  contains a top view of yet another embodiment of an apertured conditioning brush formed in accordance with the present invention. In this arrangement, a conditioning brush  70  comprises bristles  40  arranged in a set of spiral arms  72  emanating from a central area  74  of brush  70 . Apertures  34  are similarly arranged in a spiral arm configuration, with a separate set of apertures  34  disposed between adjacent sets of bristles  40 . As with the arrangement described above in association with  FIG. 4 , bristles  40  and apertures  34  of brush  70  are designed so as to channel the debris toward the outer periphery for efficient removal through evacuation.  
         [0030]     It is to be understood that the apertured conditioning brush of the present invention can be used in association with any type of polishing pad, or polishing felt, but is preferably intended for use with the fibrous polishing and/or buffing pads as discussed above that consist of deep, soft-walled, vertically-oriented pores conducive to the creation of recirculating eddy currents deep within the pad that trap the debris and spent slurry. The apertured conditioning brush of the present invention may also be utilized with conventional (i.e., relatively “hard”) polishing pads, where abrasive bristles provide sufficient surface abrasion, with lower pad wear rates, than traditional abrasive conditioning disks. Moreover, the arrangement of the bristles and apertures across the surface of the conditioning brush may be modified, as need be, to suit the needs of the particular CMP system. Indeed, the subject matter of the present invention is intended to be limited only by the scope of the claims appended hereto.