Abstract:
Chemical mechanical planarization apparatuses with polishing assemblies that provide for the passive removal of slurry are provided. In accordance with an embodiment, a work piece polishing assembly comprises a polishing pad comprising a polishing surface and an exhaust aperture that extends through the polishing pad from the polishing surface and is configured to receive a slurry from the polishing surface. An underlying member is disposed underlying the polishing pad and comprises a peripheral surface. The underlying member comprises a channel that is in fluid communication with the aperture and that opens at the peripheral surface of the underlying member.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to apparatuses for polishing a surface of a work piece. More particularly, the invention relates to chemical-mechanical planarization apparatuses with polishing assemblies that provide for the passive removal of slurry from a polishing surface. 
     BACKGROUND OF THE INVENTION 
     The manufacture of many types of work pieces requires the substantial planarization or polishing of at least one surface of the work piece. Examples of such work pieces that require a planar surface include semiconductor wafers, optical blanks, memory disks, and the like. One commonly used technique for planarizing the surface of a work piece is the chemical mechanical planarization (CMP) process. The terms “planarization” and “polishing,” or other forms of these words, although having different connotations, are often used interchangeably by those of skill in the art with the intended meaning conveyed by the context in which the term is used. For ease of description such common usage will be followed and the term “chemical mechanical planarization” will generally be used herein with that term and “CMP” conveying either “chemical mechanical planarization” or “chemical mechanical polishing.” The terms “planarize” and “polish” will also be used interchangeably. 
     The CMP method typically requires the work piece to be loaded into and mounted precisely on a carrier head in a manner such that the surface to be planarized is exposed. The exposed side of the work piece is then held against a polishing pad and relative motion is initiated between the work piece surface and the polishing pad in the presence of a polishing slurry. The mechanical abrasion of the surface caused by the relative motion of the work piece with respect to the polishing pad combined with the chemical interaction of the slurry with the material on the work piece surface ideally produces a planar surface. 
     The polishing slurry can be applied to the surface of the polishing pad by deposition of the slurry directly onto the polishing surface of the polishing pad or, alternatively, the slurry can be delivered from a manifold assembly underlying the polishing pad through supply apertures or “through-holes” within the polishing pad. Spent slurry, that is, slurry that has reacted with the work piece surface and contains by-products from the polishing process then is removed from the surface of the polishing pad so that it can be replaced by fresh slurry for uniform planarization. 
     As an alternative to traditional CMP, electrochemical mechanical planarization (ECMP) can be used for polishing the work piece. ECMP involves removal of material from the surface of the work piece through the action of an electrolyte solution, electricity, and relative motion between the work piece and the surface of the polishing pad. The ECMP slurry, or electrolyte, also needs to be removed from the surface of the polish pad as does traditional CMP slurry. 
     Various methods have been used to remove the spent slurry from the polishing pad. One method utilizes polishing pads having grooves within the surface of the polishing pad that permit the spent slurry to flow out from the center of the polishing pad to be exhausted from a peripheral edge of the pad. While wide grooves would permit the slurry to flow freely, the width of the grooves is limited because wider grooves result in less polishing pad available for contact with the work piece. Accordingly, with narrow grooves, the flow of the slurry may be restricted and the residence time of the spent slurry on the surface of the pad may be longer than desired. As a result, a pressure gradient forms across the polishing pad from the center to the peripheral edge. This slurry build-up also may cause the work piece to hydroplane on the polishing pad, decreasing the polishing rate. Moreover, as the polishing pad wears, the depth of the grooves becomes even smaller, thus further reducing the volume of slurry the grooves can carry and compounding the above problems. 
     Another method for removing slurry from the surface of a polishing pad includes exhaust ports that extend through the polishing pad and the underlying polishing assembly. The polishing assembly can include one or more polishing sub-pads, such as a backing pad, a platen that is configured to support the polishing pad, and a manifold assembly that distributes the slurry to the surface of the polishing pad. The exhaust ports may use the force of gravity to exhaust the slurry or may be connected to a pump that pumps the slurry from the polishing pad. Accordingly, the exhaust ports are configured to extend, not only through the polishing pad, but also any polishing sub-pads, the platen and the manifold assembly. Because the polishing sub-pads, platen, and manifold assembly are manufactured separately, the exit ports add a high degree of complexity to the designing and manufacturing of the polishing pad assemblies. 
     Accordingly, it is desirable to provide work piece polishing assemblies that provide for the efficient and passive removal of slurry from the surface of a polishing pad of a CMP apparatus. In addition, it is desirable to CMP apparatuses that utilize such work piece polishing assemblies. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with an exemplary embodiment of the present invention, a work piece polishing assembly comprises a polishing pad comprising a polishing surface and an exhaust aperture that extends through the polishing pad from the polishing surface and is configured to receive a slurry from the polishing surface. An underlying member is disposed underlying the polishing pad and comprising a peripheral surface. The underlying member comprises a channel that is in fluid communication with the exhaust aperture and that opens at the peripheral surface of the underlying member. 
     In accordance with another exemplary embodiment of the present invention, a chemical mechanical planarization apparatus comprises a work piece carrier configured to hold a work piece horizontally and a polishing assembly. The polishing assembly comprises a polishing pad disposed parallel to the work piece and an underlying member underlying the polishing pad. The underlying member comprises a channel configured to receive a slurry from the polishing pad and to permit the slurry to be exhausted from a peripheral surface of the underlying member. 
     In accordance with a further exemplary embodiment of the present invention, a work piece polishing assembly comprises a polishing means for polishing a work piece during planarization using a slurry and an underlying member underlying the polishing means. The polishing means has an aperture that extends therethrough. The underlying means comprises a removal means for receiving slurry from the polishing means and permitting the slurry to be exhausted from a peripheral surface of the underlying member. The removal means comprises a portion that has a cross-sectional area perpendicular to the direction of slurry flow through the portion that is greater than a cross-sectional area of the aperture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a side view of a chemical mechanical planarization apparatus that utilizes a work piece polishing assembly in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is an exploded isometric view of the work piece polishing assembly of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the work piece polishing assembly of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of the work piece polishing assembly of  FIG. 3  taken along the  4 - 4  plane; 
         FIG. 5  is a cross-sectional view of a work piece polishing assembly in accordance with an exemplary embodiment of the present invention; 
         FIG. 6  is a top view of the work piece polishing assembly of  FIG. 5  taken along the  6 - 6  plane; and 
         FIG. 7  is a cross-sectional view of a work piece polishing assembly in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
       FIG. 1  is a side view of a CMP apparatus  50  in accordance with an exemplary embodiment of the present invention. CMP apparatus comprises a work piece carrier  52  and a polishing assembly  54 . The work piece carrier  52  holds in a substantially horizontal plane a work piece  58  during the process of polishing or planarizing the work piece. The work piece carrier  52  is configured to press the work piece against a polishing surface, described below, while relative motion between the work piece and the polishing surface is effected. In one embodiment, the wafer carrier  52  rotates work piece  58  about an axis  66 . In another embodiment, wafer carrier  52  moves the work piece  58  linearly or orbitally relative to a polishing surface. Polishing assembly  54  comprises a horizontal polishing pad  56 , the hardness and density of which depend on the material that is to be polished and the degree of precision required in the polishing process. Polishing pad  56  may be comprised of a top-pad configured to contact the surface of the work-piece as well as one or more sub-pads. The hardness and density of the top-pad and each sub-pad may differ from each other. Polishing pad  56  is supported by and attached to a platen  60 , which in turn overlies a manifold assembly  64 . Manifold assembly  64  may comprise one or more layers that are pressed together to form the assembly. Polishing assembly  54  is configured to rotate, orbit, and/or dither by a motor (not shown) that is coupled thereto. 
     During a polishing operation, the work piece  58  is pressed against a polishing surface  62  of the polishing pad  56  with a desired amount of “down force” such that the polishing surface  62  exerts a desired amount of pressure against the surface of the work piece. When the work piece  58  comprises a low dielectric constant material, it may be desirable to limit this pressure to a reduced pressure range, which typically includes the pressure range of from about 0.10 psi to about 3.0 psi. Relative lateral motion is induced between the carrier  52  and the polishing pad  56  to promote polishing. A slurry, which can be abrasive or non-abrasive, is applied to the polishing surface  62  of the polishing pad  56 . Spent slurry then is passively removed from the polishing surface  62 . 
       FIG. 2  is an exploded isometric view and  FIG. 3  is a cross-sectional view of polishing assembly  54 , in accordance with an exemplary embodiment of the invention, that delivers fresh polishing slurry to polishing surface  62  of polishing pad  56  and allows for the removal of spent slurry from the polishing pad via a peripheral surface of the polishing assembly. Polishing assembly  54  comprises a distribution manifold  68  disposed within the manifold assembly  64 . A pump  70  forces the slurry through a fluid line  72  and through distribution manifold  68  to one or more supply conduits  74  formed within platen  60 . The slurry then may suitably flow from supply conduits  74  through one or more supply holes  76  within polishing pad  56 . Polishing assembly  54  is connected to a drive assembly  78  that is operative to move polishing assembly  54  in an orbital pattern. Alternatively, it will be appreciated that the drive assembly  78  may be operative to move polishing assembly  54  in a rotary, linear or oscillatory pattern or any combination of orbital, linear, oscillatory, and rotary patterns. 
     As illustrated in  FIG. 3 , polishing pad  56  has one or more grooves  80  that permit the slurry to flow from supply holes  76  over the polishing surface  62 . The grooves  80  may be molded into the polishing pad  56  when originally fabricated or may be machined into the pad after fabrication. In one exemplary embodiment, relative to a coordinate system  130 , the grooves may run in the “x” and “y” directions to form a grid with parallel x-direction grooves  82  and crossing perpendicular y-direction grooves  84 . In another exemplary embodiment, x-direction grooves  80  may comprise major x-direction grooves  86  and minor x-direction grooves  88  and y-direction grooves  84  may comprise major y-direction grooves  90  and minor y-direction grooves  92 . The major grooves have a larger cross-sectional area perpendicular to the direction of slurry flow than the minor grooves. The area perpendicular to the direction of slurry flow is defined as the width of the groove  80  or  84  in the x- or y-direction, respectively, multiplied by the depth of the groove in the z-direction. Minor x-direction grooves  88  and minor y-direction grooves  92  intersect at supply holes  76 , causing slurry to flow from supply holes  76  to major grooves  86  and  90 . The minor grooves  88  and  92  and the major grooves  86  and  90  assist in the distribution of the slurry across polishing pad  56  during planarization. While polishing pad  56  is illustrated with minor grooves and major grooves in a perpendicular relationship, it will be appreciated that grooves  80  can be of any cross-sectional size and can be configured in any suitable pattern that is configured to facilitate distribution of slurry. For example, polishing pad  56  may comprise only major grooves or may comprise only minor grooves. Alternatively, polishing pad  56  may comprise grooves of a uniform cross-sectional area that are in a hexagonal or other pattern. 
     Referring again to  FIGS. 2 and 3 , in addition to supply holes  76  for delivery of the slurry to the polishing surface  62 , polishing pad  56  also comprises one or more exhaust apertures  94  through which spent slurry may flow away from polishing surface  62 . Exhaust apertures  94  have an inlet end  96  through which spent slurry enters at polishing surface  62  and an exit end  98 . The apertures  94  are in fluid communication with channels of an underlying member  110  of the polishing assembly, such as, for example, a polishing sub-pad (not shown), or the manifold apparatus. In one exemplary embodiment, the underlying member  110  is platen  60 , which comprises one or more channels  100  that extend horizontally through platen  60 . In one embodiment, channels  100  are disposed and open at a surface  102  of platen  60 , as illustrated. In another embodiment, channels  100  are disposed wholly within platen  60  and are in fluid communication with exhaust apertures  94  via conduits (not shown) within the platen. The exit end  98  of each exhaust aperture  94  opens to one of the channels  100 . The channels have at least one end  140  that extends to a peripheral surface  104  of platen  60 . As used herein, the term “peripheral surface” refers to an outer surface of a structure that is substantially perpendicular to a horizontal surface of the structure. In one exemplary embodiment, the channels  100  have a cross-sectional area  126  perpendicular to the direction of flow that is greater than a cross sectional area  124  of the exhaust apertures  94 . In this embodiment, the term “cross-sectional area  126 ” of channels  100  is the cross-sectional area of the channels  100  that is perpendicular to the direction of slurry flow and is defined as a width  138  of the channel  100  that is perpendicular to the direction of flow, multiplied by the depth  142  of the channel in the z-direction. As illustrated in  FIG. 2 , channels  100  may comprise channels  200  that extend in the x-direction and perpendicular channels  202  that extend in the y-direction. Thus, the cross-sectional area  126  of channels  200  is defined as a width of the channel in the y-direction multiplied by the depth  142  of the channel in the z-direction. Similarly, the cross-sectional area  126  of channels  202  is defined as a width of the channel in the x-direction multiplied by the depth  142  of the channel in the z-direction. In the vertical exhaust apertures  94 , the term “cross-sectional area  124 ” of the exhaust apertures  94  is the cross-sectional area perpendicular to the direction of slurry flow and is defined as a width  136  in the x-direction multiplied by the width (not shown) in the y-direction. In this regard, because the channels open to atmospheric pressure at the peripheral surface of the platen, and because the channels have a cross-sectional area  126  that is greater than the cross-sectional area  124  of the exhaust apertures, the spent slurry within the exhaust apertures and the channels is at atmospheric pressure so that the slurry flows passively from the polishing surface  62  of polishing pad  56  through exhaust apertures  94 , as illustrated by arrows  115 , and is exhausted at the peripheral surface  104  of the platen. Accordingly, there is minimal or no backup of the slurry in the channels  100  or exhaust apertures  94  that may increase the likelihood of hydroplaning of the work piece on the polishing surface  62 . In addition, because the channels  100  are not in the polishing pad  56 , exhaust flow of the slurry is not affected by wear of the polishing pad. 
     In one exemplary embodiment of the invention, the channels  100  are not uniform in size, cross-sectional area or pattern. For example, the cross-sectional areas  126  of the channels may be greater near the periphery of the platen than at the center. In another embodiment, the cross-sectional area of the channels may vary based on the location of the exhaust apertures with which they are in fluid communication, as described in more detail below. In yet another example, the channels do not lie in an x-y perpendicular pattern but, rather, lie in any other pattern that permits exhausting of the spent slurry to the periphery of the platen. 
     In one exemplary embodiment of the present invention, the channels  100  are disposed underlying the grooves  80  of polishing pad  56  and the pattern of the channels  100  mimics at least a portion of the pattern of the grooves  80  in the polishing pad  56 . In this regard, regions of the polishing pad that contact the work piece (“land areas”)  122  are fully supported by the platen  60  so that the polishing pad  56  maintains sufficient contact with the work piece during planarization. In an exemplary embodiment, the width  138  of the channels is substantially equal to the width  136  of apertures  94  so that the “land areas”  122  of the polishing pad are fully supported by platen  60 . In another exemplary embodiment of the invention, the width  138  of the channels is greater than the width  136  of exhaust apertures  94 . 
     Referring to  FIG. 4 , in one embodiment of the invention, polishing pad  56  has a plurality of supply holes  76  and a plurality of exhaust apertures  94 , with at least one exhaust aperture disposed proximate to a supply hole  76 . For example, in an exemplary embodiment of the present invention for the polishing of 300 mm work pieces, an exhaust aperture  94  is within about 0.25 inches to about 1 inch of a supply hole  76 . In another exemplary embodiment, an exhaust aperture  94  is within 0.5 to about 0.7 inches of a supply hole  76 . However, it will be appreciated that the exhaust apertures  94  can be any suitable distance from the supply holes  76  so that the configuration of supply holes and exhaust apertures minimizes the residence time of the spent slurry at the polishing surface  62 . As fresh slurry flows from the supply holes  76  to the polishing surface  62 , it reacts with the work piece surface. Because the exhaust apertures  94  are close to the supply holes  76 , the spent slurry can immediately drain from the polishing surface  62  so that spent slurry does not significantly dilute fresh slurry across the polishing surface. 
     Referring to  FIGS. 5 and 6 , in accordance with another exemplary embodiment of the present invention, one or more channels  100  are disposed wholly within platen  60  and are configured as one or more reservoirs  116  that have a width, indicated by double-headed arrow  132 , that is greater than width  136  of the exhaust apertures  94  of polishing pad  56 . The reservoir  116  has at least one end  128  that is open to the peripheral surface  104  of platen  60 . In one embodiment, due to the width of reservoir  116 , one or more supply tubes  108  extend from a surface  160  of platen  60  through the reservoir  116  to supply conduits  74  within platen  60 , which are in axial alignment and fluid communication with supply tubes  108 . Supply tubes  108  may be formed of flexible material, such as a polymer, or a rigid material, such as a thermoset polymer, a ceramic, or a metal. Exhaust apertures  94  are coupled to the reservoir(s)  116  via exhaust conduits  106  that extend through a portion of platen  60 . Accordingly, during the planarization process, spent slurry can flow from the polishing surface  62  through exhaust apertures  94  and exhaust conduits  106  to reservoir(s)  116 , where it flows horizontally, as illustrated by arrows  120 , under atmospheric pressure, around supply tubes  108  to exhaust at peripheral surface  104  of platen  60 . 
     As noted above, the underlying member  110  of a polishing assembly also can be a polishing sub-pad. Referring to  FIG. 7 , a polishing assembly  150  in accordance with another exemplary embodiment of the present invention comprises polishing top-pad  56  having supply holes  76  and exhaust apertures  94 , platen  60  having supply conduits  74 , and manifold assembly  64  disposed thereunder. A polishing sub-pad  152  is interposed between the top-pad  56  and the platen  60 . Polishing sub-pad  152  may comprise a polishing pad backing layer, an insulating layer, a diaphragm, or the like. Polishing sub-pad  152  may comprise one or more channels  100  disposed horizontally on a surface  154  of polishing sub-pad  152  or within polishing sub-pad  152 . The exit end  98  of each exhaust aperture  94  opens to one of the channels  100 . The channels have at least one end  140  that extends to the peripheral surface  104  of polishing sub-pad  152 . As described above, in one exemplary embodiment, the channels  100  have a cross-sectional area  126  that is greater than a cross sectional area  124  of the apertures  94 . Accordingly, because the channels open to atmospheric pressure at the peripheral surface of the polishing sub-pad, and because the channels have a cross-sectional area that is greater than the cross-sectional area of the exhaust apertures, the spent slurry within the apertures and the channels is at atmospheric pressure so that the slurry flows passively from the polishing surface  62  of top-pad  56  through exhaust apertures  94  and then flows horizontally, as illustrated by arrows  125 , to be exhausted at the peripheral surface  104  of the polishing sub-pad. 
     It will be appreciated that, while the above embodiments describe a CMP apparatus with a polishing assembly that is configured for the supply delivery of slurry through the polishing assembly via a distribution manifold, any other suitable means can be used to deliver the slurry to the polishing surface  62  of the polishing pad  56 . For example, the slurry can be deposited directly onto the polishing surface  62  of the polishing pad. Accordingly, during planarization, the slurry will be distributed across the polishing pad by the motion of the work piece and the polishing assembly and, if present, via grooves  80 . The slurry can then be passively removed from polishing surface  62  through exhaust apertures  94  and channels  100 . 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.