Patent Publication Number: US-2005130566-A1

Title: Slurry distributor for chemical mechanical polishing apparatus and method of using the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a divisional of and claims the benefit of priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 10/234,780 filed 3 Sep. 2002 and entitled Slurry Distributor For Chemical Mechanical Polishing Apparatus And Method Of Using The Same, which application claimed priority from U.S. Provisional Patent Application Ser. No. 60/323,117, filed Sep. 10, 2001, each of which applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      This invention pertains generally to systems, devices, and methods for polishing and planarizing substrates, and more particularly to an apparatus and method for distributing slurry on a polishing surface of a chemical mechanical polishing (CMP) apparatus.  
     BACKGROUND OF THE INVENTION  
      As feature size decreases, density increases, and the size of semiconductor wafers or substrates increase, Chemical Mechanical Planarization (CMP) process requirements become more stringent. Substrate to substrate process uniformity as well as intra-substrate planarization uniformity are important issues from the standpoint of producing semiconductor products at a low cost. As the size of dies increases a flaw in one small area increasing results in rejection of a relatively large circuit so that even small flaws have relatively large economic consequences in the semiconductor industry.  
      Many factors are known in the art to contribute to uniformity problems. These include distribution of a slurry between a surface of the substrate and polishing surface during the polishing operation when there is relative motion between a polishing head on which the substrate is held and the polishing surface during the polishing operation. Slurry is a, usually, chemically active liquid having an abrasive material suspended therein that is used to enhance the rate at which material is removed from the substrate surface.  
      One problem with slurry distribution in a conventional CMP apparatus a non-uniform distribution of slurry on a polishing surface.  FIG. 1  is a top plan view of a platen and a slurry dispenser in a conventional CMP apparatus illustrating a non-uniform distribution of slurry on a polishing surface. Referring to  FIG. 1 , it is seen that distribution of a slurry  10  across a polishing surface  12  is primarily dependent on the location and orientation of an opening or nozzle  14  of a tube  16  dispensing slurry onto the polishing surface, and on the movement or rotation of a platen (not shown) on which the polishing surface  10  is supported. The speed of movement of the platen is generally determined based on a desired polishing rate, that is a rate at which material is removed from a substrate (not shown) being polished. Thus, traditional approaches to providing an adequate and uniform distribution of slurry between a substrate and a polishing head  18  on which the substrate is held have focused on the location and orientation of the nozzle  14  relative to the polishing head.  
      As illustrated in  FIG. 1 , if the nozzle  14  dispenses the slurry too far in radially from an edge  20  of the polishing surface  10  or platen, a portion of the polishing surface beneath the polishing head  18  that is nearest to a center  22  of the polishing surface receives the greatest amount of slurry. As a result, the surface of the substrate near an outer circumferential edge of the polishing head  18  has a higher removal rate than the surface near the center. This pattern is further exacerbated by deformation of the polishing surface  10  by the polishing head  18 , which causes the slurry near the edge of the polishing head to be deflected or redirected towards away from the polishing head as shown in  FIG. 1 .  
      One prior art approach attempting to provide a more uniform distribution of slurry is described in U.S. Pat. No. 5,709,573, to Guthrie et al. (GUTHRIE). GUTHRIE discloses a radially positioned flexible member in contact with the polishing surface to sweep the slurry across the polishing surface. While an improvement over conventional slurry dispensers, this approach is not wholly satisfactory for a number of reasons.  
      One problem with the approach taught in GUTHRIE is that the constant contact between the flexible member and the polishing surface during polishing operations causes rapid wear of the flexible member. This in turn leads to the need to frequently replace the flexible member. In addition to the cost of replacement parts, this results in excessive down time or loss of availability or the apparatus for processing due to the time needed to replace the flexible member and the time need to re-characterize the polishing process or apparatus. Moreover, prior to replacement, as the flexible member wears the amount and distribution of slurry across the polishing surface can vary introducing a new source of non-uniformity. This is particularly a problem with polishing surfaces comprising a pattern of features, such as indentations in a porous polishing surface or concentric grooves, for aiding in slurry distribution. These features cause the flexible member to wear unevenly across the surface in contact with the polishing surface, resulting in a non-uniform distribution of slurry across the polishing surface.  
      Another problem with conventional CMP apparatuses and methods, related to the problem with non-uniform distribution described above, is the inefficient use and wastage of slurry. Because the slurry is dispensed onto the polishing surface ahead of the polishing head, an excess of slurry must typically be dispensed to ensure that when it flows across the polishing surface it will cover the entire area between the substrate and the surface. Because of strict requirements concerning the purity of the slurry and in particular the size of the abrasive particles suspended therein, slurry tends to be expensive. Moreover, because materials used in fabricating semiconductors are often hazardous to people and to the environment, used slurry, which can contain significant amounts of material removed from the substrates, must be disposed of as hazardous waste. Thus, a significant factor in the cost of operating conventional CMP apparatuses is the cost of supplying and disposing of the slurry.  
      Yet another problem with conventional CMP apparatuses and methods is the buildup of solid polishing byproducts on the polishing surface that can damage or destroy a substrate being polished. These byproducts include material removed from the surface of the substrate and agglomerations of abrasives from old or dried out slurry. This particularly a problem for CMP apparatuses including polishing surfaces with numerous small, shallow grooves for the distribution of slurry, or porous polishing pads or coverings.  
      Accordingly, there is a need for an apparatus and method that provides a controlled or uniform distribution of slurry across the polishing surface to provide improved planarization uniformity. There is a further need for an apparatus and method capable of restricting slurry dispensed on the polishing surface to the portion of the polishing surface over which the polishing head passes during the polishing operation, thereby reducing waste of slurry. There is a yet further need for an apparatus and method capable of removing used slurry and polishing byproducts from the polishing surface thereby eliminating buildup of solid polishing byproducts that can damage the substrate.  
     SUMMARY  
      The present invention relates to an apparatus and method for distributing slurry on a polishing surface of a CMP apparatus that achieves a high-planarization uniformity across a surface of a substrate.  
      According to one aspect of the present invention, a polishing apparatus is provided for removing material from a surface of a substrate. Generally, the polishing apparatus includes: (i) a platen having a polishing surface thereon; (ii) a polishing head adapted to hold the substrate against the polishing surface during a polishing operation; (iii) a drive mechanism to rotate the platen providing a relative motion between the polishing head and the polishing surface during the polishing operation; (iv) a dispenser having a number of nozzles adapted to dispense chemical on the polishing surface; and (v) a spreader or distributor positioned between the nozzles of the dispenser and the polishing head. The distributor mixes and uniformly distributes chemical between the surface of the substrate and the polishing surface during the polishing operation when there is relative motion between the polishing head and the polishing surface. The chemical can be a slurry having, for example, a solid abrasive material suspended in a fluid, or, where the polishing surface includes a fixed abrasive thereon, the chemical can be water.  
      In one embodiment, the distributor is made from a rigid, ceramic, glass or polymeric material, such as one or more of the following polymers: polyesters; polyethylene terephthalate; polyimide; polyphenylene sulfide; polyetherketone; polytetrafluoroethylene; and polybenzimidazole, and is adapted to provide a substantially planar lower surface separated from and in a facing relationship with a portion of the polishing surface. The lower surface of the distributor is separated from the polishing surface by a predetermined amount based on a desired removal or polishing rate and in further consideration of the viscosity of the chemical or slurry used. Preferably, the distributor includes a chamfered edge to facilitate movement or flow of the chemical under the lower surface thereof. More preferably, the distributor is oriented to form a predetermined angle relative to a plane of the polishing surface, the predetermined angle selected to further facilitate movement or flow of the chemical under the lower surface thereof. It has been found suitable predetermined angles for most polishing or planarizing operations used in processing semiconductor substrates are from about 10 to about 80 degrees. More preferably, the predetermined angles are from about 20 to about 40 degrees, and most preferably about 30 degrees.  
      In another embodiment, the distributor further includes one or more guide or spacers on the lower surface thereof, the spacers adapted to contact the polishing surface during a polishing operation and to guide or position the distributor relative to the polishing surface. Preferably, the spacers include an adjustment mechanism to adjust a gap between the lower surface of the distributor and the polishing surface, thereby enabling a rate of removal of material from the substrate to be varied.  
      Optionally, polishing apparatus further includes an actuator for positioning the distributor against or adjacent to the polishing surface. Generally, the actuator can include spring actuators, gravity actuators, hydraulic actuators, pneumatic actuators, or electromagnetic actuators, such as solenoids.  
      The nozzles can be located distal from or proximal to the distributor. In one embodiment, the nozzles are abutting or affixed to a support supporting the distributor in position over the polishing surface. Optionally, one or more of the nozzles are adapted to dispense the chemical at a different rate than the remainder of the nozzles. For example, nozzles near either an inner or outer end of the dispenser can dispense chemical at a lower rate than those more centrally located to more tightly focus or constrain the chemical on that portion of the polishing surface over which the polishing head will pass. Alternatively, the nozzle near the inner end of the dispenser can dispense chemical at a higher rate than the other nozzles to compensate for a lower speed of the portion of the polishing surface near a center of the rotating platen, thereby providing a more uniform removal rate throughout the rotation of the substrate on the polishing head. Typically, each of the nozzles is adapted to dispense from about 20 milliliters (ml) to about 200 ml of chemical per second.  
      Alternatively, the distributor is oriented to form a predetermined angle relative to a radius of the polishing surface. The predetermined angle can be adjusted or selected to direct more or less of the chemical to an inner or outer portion of the polishing surface, thereby altering the removal rate over a portion of the polishing surface or more tightly focusing on the polishing head. Preferably, the predetermined angle selected to uniformly distribute the chemical in the path of the polishing head. It has been found suitable predetermined angles for most polishing or planarizing operations used in processing semiconductor substrates are from about 1 to about 30 degrees. More preferably, the predetermined angles are from about 2 to about 20 degrees, and most preferably less than about 10 degrees.  
      In yet another aspect, the invention is directed to a polishing apparatus including, in addition to a distributor adapted to mix and uniformly distribute a chemical or slurry on a polishing surface, a wiper adapted to remove used chemical and polishing byproducts from the polishing surface after the surface has passed under a polishing head. Generally, the wiper is positioned between the polishing head and the distributor, and is oriented to form an angle relative to a radius of the polishing surface, to direct the used chemical and polishing byproducts off an outer edge of the polishing surface or platen. Preferably, the wiper forms an angle of from about 5 to about 30 degrees relative to a radius of the polishing surface.  
      In one embodiment, the wiper further includes a vacuum port to vacuum used chemical and polishing byproducts from the polishing surface. This is particularly advantageous for use with a polishing surface having features such as grooves or a porous polymer polishing pad.  
      In another embodiment, the polishing apparatus can further include a cleaning fluid dispenser for dispensing a cleaning fluid, such as water, onto the polishing before and/or after the wiper to clean the polishing surface during a cleaning operation. In one version of this embodiment, the cleaning fluid dispenser is adapted to dispense cleaning fluid on the polishing surface ahead or upstream of the wiper during the polishing operation to reduce or substantially eliminate buildup of solid polishing byproducts that can damage the substrate.  
      In yet another aspect, the invention is directed to a method of polishing a substrate having a surface using a polishing apparatus having a polishing surface and a polishing head adapted to hold the substrate during a polishing operation. Generally, the method involves: (i) positioning the substrate on the polishing head; (ii) holding the polishing head so as to press the surface of the substrate against the polishing surface; (iii) dispensing a chemical onto the polishing surface using a dispenser having a number of nozzles through which the chemical is dispensed; and (iv) mixing and uniformly distributing the chemical on the polishing surface using a distributor positioned between the nozzles and the polishing head.  
      Optionally, the method can further include the step of removing used chemical and polishing byproducts from the polishing surface after the chemical has passed under the polishing head using a wiper positioned between the polishing head and the distributor. Preferably, the wiper has a lower surface with a linear edge in contact with a portion of the polishing surface substantially entirely along the length of the linear edge. More preferably, the wiper or the linear edge thereof forms a predetermined angle relative to a radius of the polishing surface, the predetermined angle selected to direct the used chemical and polishing byproducts off an outer edge of the polishing surface or platen.  
      Advantages of the apparatus and method of the present invention include any or all of the following: 
          (i) improved planarization uniformity due to uniform distribution of slurry across the polishing surface;     (ii) improved planarization uniformity of substrates initially having non-planar layers deposited thereon, due to tailored or focused distribution of slurry across the polishing surface;     (iii) reduced wasting of slurry, due to tailored or focused distribution of slurry across the polishing surface; and     (iv) improved yields due to reduction or eliminating of buildup or deposits of solid polishing byproducts that can damage the substrate.       

    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and various other features and advantages of the present invention will be apparent upon reading of the following detailed description in conjunction with the accompanying drawings, where:  
       FIG. 1  (prior art) is a top plan view of a platen and a slurry dispenser in a conventional CMP apparatus illustrating a non-uniform distribution of slurry on a polishing surface;  
       FIG. 2  (prior art) is a diagrammatic illustration showing an exemplary CMP apparatus for which a slurry delivery system and method according to the present invention are particularly useful;  
       FIG. 3  is a top plan view of a platen and a slurry dispenser having multiple nozzles adapted to uniformly distribute slurry on a polishing surface according to an embodiment of the present invention;  
       FIG. 4  is a top plan view of a slurry dispenser and a distributor to mix and uniformly distribute slurry on a polishing surface according to an embodiment of the present invention;  
       FIG. 5  is a top plan view of a slurry dispenser having multiple non-uniformly sized nozzles and a distributor to mix and uniformly distribute slurry on a polishing surface according to an embodiment of the present invention;  
       FIG. 6  is a top plan view of a slurry dispenser having multiple nozzles located proximal to a distributor adapted to mix and uniformly distribute slurry on a polishing surface according to an embodiment of the present invention;  
       FIG. 7  is a partial cross-sectional side view of a distributor and a platen showing a chamfered edge of a lower surface of the distributor, and an actuator for positioning the distributor relative to the polishing surface according to an embodiment of the present invention;  
       FIG. 8  is a partial cross-sectional view of a platen and a side view of a distributor having spacers adapted to position the distributor relative to a polishing surface according to an embodiment of the present invention;  
       FIG. 9  is a partial cross-sectional side view of a distributor and a platen showing a chamfered leading edge, an integral dispenser and a trailing edge with a lower surface adapted to provide a micro-layer or metered amount of slurry on a polishing surface according to an embodiment of the present invention;  
       FIG. 10  is a partial cross-sectional side view of a polishing surface having grooves therein showing the filled with slurry by the distributor of  FIG. 9 ;  
       FIG. 11  is a front view of the distributor of  FIG. 9  showing a trailing edge having a lower surface with a raised center according to an embodiment of the present invention;  
       FIG. 12  is a partial top plan view of a distributor and a platen showing the distributor of  FIG. 9  further including wings to direct recovered slurry back the distributor according to an embodiment of the present invention;  
       FIG. 13  is a partial top plan view of a distributor and a platen showing an angle of the distributor relative to a radius of the platen according to an embodiment of the present invention;  
       FIG. 14  is a top plan view of a slurry dispenser positioned between to a distributor and a wiper on a polishing surface, the wiper adapted to remove used slurry and polishing byproducts from the polishing surface according to an embodiment of the present invention;  
       FIG. 15  is a top plan view of an embodiment of the wiper of  FIG. 14  further including a vacuum to remove used slurry and polishing byproducts from the polishing surface according to an embodiment of the present invention;  
       FIG. 16  is a top plan view of a polishing surface of an apparatus having a wiper and a cleaning fluid dispenser(s) adapted to remove used slurry and polishing byproducts from the polishing surface according to an embodiment of the present invention;  
       FIG. 17  is a top plan view of a polishing surface of an apparatus having a wiper and a cleaning fluid dispenser abutting the wiper according to an embodiment of the present invention; and  
       FIG. 18  is a flowchart showing an embodiment of a process for polishing or planarizing a substrate according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      The inventive structure and method are now described in the context of specific exemplary embodiments illustrated in the figures. Those skilled in the art will appreciate that various changes and modifications can be made while remaining within the scope of the claimed invention. For example, for purposes of clarity the invention is described in context of a Chemical Mechanical Polishing (CMP) system having a single polishing head. However, those skilled in the art will appreciate that the apparatus and method of the invention can also be utilized with CMP systems having multiple polishing heads.  
      Referring to  FIG. 1 , there is shown an embodiment of a chemical mechanical polishing or planarization (CMP) apparatus  100  for polishing substrates  102 . As used here the term “polishing” means either polishing or planarization of substrates  102 , including substrates used in flat panel displays, solar cells and, in particular, semiconductor substrates or wafers onto which electronic circuit elements have been deposited. Semiconductor wafers are typically thin and fragile disks having diameters nominally between 100 mm and 300 mm. Currently 100 mm, 200 mm, and  300  semiconductor wafers are widely used in the industry. The inventive method and apparatus  100  are applicable to semiconductor wafers and other substrates  102  at least up to 300 mm diameter as well as to larger diameter substrates.  
      For purposes of clarity, many of the details of the CMP apparatus  100  that are widely known and are not relevant to the present invention have been omitted. CMP apparatuses  100  are described in more detail in, for example, in commonly assigned, co-pending U.S. patent application Ser. No. 09/570,370, filed 12 May 2000 and entitled System and Method for Pneumatic Diaphragm CMP Head Having Separate Retaining Ring and Multi-Region Wafer Pressure Control; Ser. No. 09/570,369, filed 12 May 2000 and entitled System and Method for CMP Having Multi-Pressure Zone Loading For Improved Edge and Annular Zone Material Removal Control; and Ser. No. 09/854,189, filed 11 May 2001 and entitled System and Method for CMP Having Multi-Pressure Annular Zone Subcarrier Material Removal Control, each of which is incorporated herein by reference in its entirety.  
      The CMP apparatus  100  includes a base  104  rotatably supporting a large rotatable platen  106  with a polishing pad  108  mounted thereto, the polishing pad having a polishing surface  110  on which the substrate  102  is polished. The polishing pad  108  is typically a polyeurethane material, such as that available from RODEL of Newark Del. Additionally, a number of recesses (not shown in  FIG. 1 ), such as grooves or cavities, may be provided in the polishing surface  110  to distribute a chemical or slurry (not shown in  FIG. 1 ) between the polishing surface and a surface of a substrate  102  placed thereon. By slurry it is meant a chemically active liquid having an abrasive material suspended therein that is used to enhance the rate at which material is removed from the substrate surface. Typically, the slurry is chemically active with at least one material on the substrate  102  and has a pH of approximately 4 to 11. For example, one suitable slurry consists of approximately 12% abrasive and 1% oxidizer in a water base, and includes a colloidal silica or alumina having a particle size of approximately 100 nm. Optionally, as an alternative or in addition to the slurry, the polishing surface  110  of the polishing pad  108  can have a fixed abrasive material embedded therein, such as available from Minnesota Mining and Manufacturing Company. In embodiments of CMP apparatuses  100  having a polishing surface  110  with a fixed abrasive, the chemical dispensed onto the polishing surface during polishing operations can be water. The base  104  also supports a bridge  112  that in turn supports a carousel  114  having one or more polishing heads  116  (only one of which is shown) on which substrates  102  are held during a polishing operation. The bridge  112  is designed to permit raising and lowering of the carousel  114  to bring surfaces of substrates  102  held on the polishing heads  116  into contact with the polishing surface  110  during the polishing operation. In this particular CMP design, the polishing head  116  is driven by a motor  118  that drives a chain  120 , which in turn drives the polishing head via a chain and sprocket mechanism  122 . In addition to the rotation of the polishing pad  108  and the polishing head  116 , the carousel  114  can be moved to orbit about a fixed central axis of the polishing platen  106  to provide an orbital motion to the polishing head. Furthermore, the inventive distributor and wiper (not shown in this figure) may be utilized in all manner of CMP apparatuses  100  including machines utilizing a linear or reciprocating motion as are well known in the art.  
      In accordance with the present invention, the CMP apparatus further includes a chemical or slurry dispenser  124  and a distributor  125  which will now be described with reference to FIGS.  3  to  14 .  
       FIG. 3  is a top plan view of a polishing surface  110  and slurry delivery apparatus  123  having a slurry dispenser  124  with multiple nozzles  126 ,  128 , adapted to uniformly distribute a chemical or slurry  129  on the polishing surface  110  according to an embodiment of the present invention. Referring to  FIG. 3 , a first nozzle  126  at a distal end of a delivery tube  130  located near a center  132  of the polishing surface  110  to dispense a stream or flow of slurry  129  onto a portion of the polishing surface that will pass under the polishing head  116  near to the center  132  of the polishing surface  110 . A second nozzle  128  generally located on the delivery tube  130  nearer to an outer circumferential edge  134  of the polishing surface  110  dispenses a stream or flow of slurry  129  onto a portion of the polishing surface  110  that will pass under the polishing head  116  near to the edge  134  of the polishing surface. It will be appreciated that the angle and a rate at which the slurry  129  is dispensed from each nozzle  126 ,  128 , can be altered or varied to achieve a more tailored distribution of slurry. For example, in the embodiment shown in  FIG. 3 , the rate at which slurry  129  is dispensed from the second nozzle  128  can be reduced, or an angle φ at which it is dispensed relative to the delivery tube  130  can be reduced to more tightly focus the slurry on the polishing head  116 , thereby reducing waste of the slurry or chemical.  
      Alternatively, the nozzles  126 ,  128 , of the slurry dispenser  124  shown in  FIG. 3  can be sized, located and oriented to provide a heterogeneous distribution of slurry  129  across the polishing surface  110  to achieve a desired polishing profile. For example, copper layers, which have become increasingly common in high-speed integrated circuits, tend to form a convex layer thicker at the center of the substrate  102  than at the edge. Thus, to provide a higher removal rate near the center of the substrate  102  than at the edge it may be desirable to direct the stream of slurry from both nozzles towards the center of the substrate  102  held on the polishing head.  
      An embodiment of the distributor  125  according to the present invention will now be described with reference to  FIG. 4 .  FIG. 4  is a top plan view of a slurry delivery apparatus  123  having slurry dispenser  124  and a distributor  125  to mix and uniformly distribute slurry on the polishing surface  110  according to an embodiment of the present invention. Referring to  FIG. 4 , the distributor is positioned between the delivery tube  130  and the polishing head  116  to mix and spread or distribute chemical or slurry  129  between the surface of the substrate  102  and the polishing surface  110  during the polishing operation. In the embodiment shown, the distributor  125  is a rigid bar or member having a linear shape that extends across at least a portion of the polishing surface  110 . In this embodiment, the linear distributor  125  has a length that is greater than or substantially equal to the diameter of the polishing head  116  to provide a sufficient amount of slurry  129  between the substrate  102  and the polishing surface.  
      Alternatively, the distributor  125  can include an arc or a curved member, or two or more members intersecting at angles to direct the slurry to provide a desired non-uniform distribution of slurry  129  across the polishing surface  110 . For example, for planarizing copper layers as noted above.  
      Generally, the distributor  125  is adapted to provide a shape having a substantially planar lower surface (not shown in this figure) separated from and in a facing relationship with a portion of the polishing surface  110 . Preferably, to reduce or eliminate potential contamination of the substrate  102  during the polishing operation, the distributor  125  is made from a glass, ceramic, or rigid high purity polymer material. More preferably, the distributor  125  is made from a material commonly used in retaining rings (not shown) disposed about the substrate  102  held on the polishing head  116  in a conventional CMP apparatus. Most preferably, the distributor is made from a polymer thick film (PTF) including one or more of the following polymers: polyesters; polyethylene terephthalate; polyimide; polyphenylene sulfide; polyetherketone; polytetrafluoroethylene; and polybenzimidazole.  
      The lower surface of the distributor  125  is separated from the polishing surface  110  by a predetermined amount or gap based on a thickness of a layer or film of slurry required to provide a desired removal or polishing rate. In addition to the desired polishing rate, the predetermined gap by which the distributor  125  is separated from the polishing surface  110  further depends on a viscosity of the chemical or slurry  129  used.  
      Another embodiment of the slurry delivery apparatus  123  will now be described with reference to  FIG. 5 .  FIG. 5  is a top plan view of a slurry delivery apparatus  123  having a distributor  125  and a slurry dispenser  124  with multiple non-uniformly sized nozzles  126 ,  128 . Referring to  FIG. 5 , positioning a smaller first nozzle  126  having a lower slurry dispensing rate at the distal end of the delivery tube  130  reduces the excess of slurry flowing past the edge of the polishing head  116  near the center  132  of the polishing surface  110 , thereby reducing waste of slurry. It will be appreciated that the slurry dispenser  124  can include any number of nozzles that can be sized, located and oriented to achieve any desired distribution of slurry.  
       FIG. 6  is a top plan view of another embodiment of a slurry delivery apparatus  123  having a distributor  125  integrated or combined with the slurry dispenser  124 . Referring to  FIG. 6 , the slurry dispenser  124  includes a delivery tube  130  having multiple nozzles  136  located near or proximal to the upstream side of the distributor  125  to mix and uniformly distribute slurry  129  on the polishing surface  110 . The delivery tube  130  and the distributor  125  are supported in position over the polishing surface by a support  138 . Optionally, the delivery tube  130  and the distributor  125  can be attached to pivot or rotate about the support  138  to provide unobstructed access to the polishing surface  110  and/or platen  106 . Slurry  129  or chemical can be coupled to the delivery tube  130  through a rotatable fluid union (not shown) or through flexible tubing (not shown).  
       FIG. 7  is a partial cross-sectional side view of an embodiment of the distributors  125  illustrated in FIGS.  3  to  6 , showing the platen  106 , a polymer polishing pad  108  with a polishing surface  110  thereon, and a distributor having a chamfered edge  140  on a lower surface  142  thereof. Referring to  FIG. 7 , the chamfered edge  140  forms an angle, α, relative to the polishing surface  110  adapted to facilitate flow of the slurry  129  under the distributor  125 , thereby improving the uniformity of distribution across the polishing surface. If the angle is too small, the resultant film or layer  144  of slurry  129  is either too thick or, if the quantity of the slurry is too little, no distribution is achieved. It has also been found that if the angle is too great, the slurry  129  will accumulate behind the distributor  125 , eventually flowing radially inward and outward along ends thereof, again resulting in a non-uniform distribution or layer  144  of undesired thickness. Suitable predetermined angles for most polishing or planarizing operations used in processing semiconductor substrates are from about 10 to about 80 degrees. More preferably, the predetermined angles are from about 20 to about 40 degrees, and most preferably about 30 degrees.  
       FIG. 7  also illustrates an embodiment of the distributor  125  further including an actuator  146  for positioning the distributor above or against the polishing surface  110 . In accordance with the present invention, the actuator  146  can apply a force urging or pushing the chamfered edge  140  of the distributor  125  towards the polishing surface  110  and rely on the hydraulic force or pressure of the slurry  129  or chemical on the moving polishing surface to lift the chamfered edge so that it glides or flies over the polishing surface. Alternatively, the actuator  146  can be adapted to move the chamfered edge  140  of the distributor  125  by a predetermined limited distance to provide the desired predetermined gap by which it is separated from the polishing surface  110 . In one version of this embodiment, movement of the chamfered edge  140  by the actuator  146  is limited by a stop (not shown), which can be adjusted to provide layers  144  having different thicknesses for different polishing recipes.  
      Generally, the actuator  146  is selected from a group consisting of: gravity actuators; hydraulic actuators; pneumatic actuators; and electromagnetic actuators or solenoids. In the embodiment shown the actuator  146  includes a piston  148  slidably fitted into a chamber  150  into which a hydraulic or pnematic fluid is introduced, or from which it is withdrawn, to re-position the chamfered edge  140  of the distributor  125 . It should be noted that the piston  148  and the chamber  150  can include one or more cylindrical pistons and chambers spaced apart along the length of the distributor  125 , or a rectangular piston and chamber that extend substantially the entire length of the distributor. In a preferred embodiment, the actuator  146  includes a single hydraulic or pneumatic piston and cylinder, or a single solenoid joining or coupling the distributor  125  to the support  138  (not shown in this figure).  
      In another embodiment, the distributor  125  further includes one or more guides or spacers  152  on the lower surface  142  thereof, the spacers adapted to contact the polishing surface  110  during a polishing operation and to guide or position the distributor relative to the polishing surface.  FIG. 8  is a partial cross-sectional side view of the platen  106 , a polymer polishing pad  108  having a polishing surface  110  thereon, and a distributor  125  having spacers  152  adapted to position the distributor relative to the polishing surface. Referring to  FIG. 8 , in one embodiment the distributor  125  is adapted to be lowered by the actuator  146  joining it to the support  138  until the spacers  152  contact the polishing surface. The spacers  152  can be integrally formed with the rest of the distributor  125  or can be separate components attached to the lower surface  142  thereof. Because the spacers  152  can be formed separately from the rest of the distributor  125 , they need not be made of the same material. Thus, the spacers  152  can be made from a material selected to provide properties including enhanced wear resistance. Moreover, because the spacers  152  can be located to contact the polishing surface  110  only in an area outside of the portion of the polishing surface in contact with the polishing head  116 , the possibility of contamination of the substrate  102  by material from the spacers is reduced, thereby further eliminating constraints on choice of material for the spacers. In one preferred embodiment, the height of the spacer  152  can be adjusted or varied by an adjustment mechanism (not shown), such as a threaded rod or screw, or shims, thereby enabling the height of the distributor  125  over the polishing surface  110  to be adjusted for different polishing recipes or to compensate for wear of the spacers or other CMP apparatus  100  components.  
      A preferred embodiment of a distributor according to the present invention will now be described with reference to FIGS.  9  to  12 .  FIG. 9  shows a distributor  125  having a chamfered leading edge  154 , an integral dispenser  156  and a trailing edge  158  with a lower surface  160  adapted to provide a micro-layer  162  or metered amount of slurry on a polishing surface  110 . Referring to  FIG. 9 , a chemical or slurry  129  sprayed or dispensed from integral dispenser  156  causes slurry to accumulate behind the leading, angled surface of chamfered leading edge  154 . The slurry  129  accumulating behind the chamfered leading edge  154  is forced against the polishing surface  110  by the chamfered leading edge substantially entirely fills numerous concentric grooves  164  in the polishing pad  108  (shown in  FIG. 10 ). After the slurry  129  accumulating behind the chamfered leading edge  154  grows or builds-up to a sufficient level, it passes through one or more ports  166  extending through the chamfered leading edge into metering chamber  168 . Slurry  129  or chemical in the metering chamber  168  in combination with the trailing edge  158  forms micro-layer  162  on the polishing surface  110  as the polishing surface continues to move under the distributor  125 .  
      Optionally, where the used slurry  129  is not removed from the polishing surface  110  after it has passed under the polishing head  116 , the chamfered leading edge  154  further serves to recover this used slurry.  
      The ability of the distributor  125  of  FIG. 9  to substantially completely fill the grooves  164  in the polishing surface  110  and to provide a uniform micro-layer  162  thereon is illustrated in  FIG. 10 . The substantially completely filled grooves  164  provide a source of slurry  129  the polishing surface  110  under a central portion of the polishing head  116 , thereby providing unparalleled polishing uniformity.  
       FIG. 11  is a front view of the distributor of  FIG. 9  showing an alternative embodiment in which the lower surface  160  of the trailing edge  158  has a raised center portion  170  to provide a region of the polishing surface  110  having thicker layer of slurry  129  thereon. As noted above, for certain substrates  102  or processes, for example, planarizing copper layers, it is desirable to provide a higher removal rate near the center of the substrate  102  than at the edge. Optionally, the lower surface  160  of the trailing edge  158  can further include spacers  152  to position or assist in positioning the distributor  125  relative to the polishing surface during a polishing operation.  
      In yet another embodiment shown in  FIG. 12 , the distributor further includes wings  172 ,  174 , to direct residual slurry remaining on the polishing surface back to the distributor.  FIG. 12  is a partial top plan view of the distributor of  FIG. 9  showing a distributor  125  further including wings. Referring to  FIG. 12 , the wings  172 ,  174 , can be separate independently fabricated elements or components which are attached to the distributor  125 , or can be integrally form one or more components of the distributor including the chamfered leading edge  154  and the trailing edge  158 . The wings  172 ,  174 , can be attached to sides  176 ,  178 , of the distributor  125  or to the chamfered leading edge  154 . Generally, the wings  172 ,  174 , which with the chamfered leading edge  154  contact the polishing surface  110  are made from the same material as the chamfered leading edge.  
       FIG. 13  is a partial top plan view of the distributor  125  showing an angle of the distributor relative to a radius of the platen  106  according to an embodiment of the present invention. Referring to  FIG. 13 , it has been found that angling the distributor relative to a radius of the platen  106  or polishing surface  110  can redirect slurry  129  on the polishing surface tailoring polishing rates, and focus or limit the stream or flow of slurry  129  onto only the portion of the polishing surface  110  that will pass under the polishing head  116 , thereby reducing waste of slurry. In the embodiment, shown the angling of the distributor  125  relative to a radius of the polishing surface  110  is used in combination with a slurry dispenser  124  have multiple differently sized nozzles to substantially focus or limit the slurry to the portion of the polishing surface  110  that will pass under the polishing head  116 . It will be appreciated that angling the distributor  125  so that the inside end precedes the outer end will result in the slurry being re-directed toward the edge  134  of the polishing surface  110 . Angling the distributor  125  so that the outer end precedes the inside end will result in the slurry being re-directed toward the center  132  of the polishing surface  110 . Increasing or larger angles, μ, increase the degree or amount by which the slurry is re-directed.  
      In another aspect, the invention is directed to a CMP apparatus  100  including, in addition to the distributor  125 , a wiper  180  adapted to remove used chemical or slurry  129  and polishing byproducts from the polishing surface  110  after it has passed under a polishing head  116 .  FIG. 14  is a top plan view of a wiper  180  on the polishing surface  110 . Referring to  FIG. 14 , the wiper  180  is positioned between the polishing head  116  and the distributor  125 , and is oriented to form an angle, γ, relative to a radius of the polishing surface  110 , to direct the used slurry  129  and polishing byproducts off the edge  134  of the polishing surface or platen  106 . The wiper  180  is angled so that the inside end precedes the outer end to re-direct the slurry toward the edge  134  of the polishing surface  110 . Preferably, the wiper forms an angle of from about 5 to about 30 degrees relative to a radius of the polishing surface. Generally, the wiper  180 , which is in contact with the polishing surface  110  is made from the same or similar material as that of the distributor  125 .  
      In one embodiment, shown in  FIG. 15 , the wiper  180  further includes a vacuum port (not shown) coupled via a vacuum line  182  to a vacuum pump  184  to vacuum used chemical and polishing byproducts from the polishing surface. This embodiment is particularly advantageous for use with a polishing surface  110  having features such as grooves  164  or a porous polymer polishing pad  108 .  
      In another embodiment, shown in  FIG. 16 , the CMP apparatus  100  can further include a cleaning fluid dispenser  186  for dispensing a cleaning fluid, such as water, onto the polishing surface  110  before and/or after the wiper  180  to clean the polishing surface during a cleaning operation. In one version of this embodiment, the cleaning fluid dispenser  186  is adapted to dispense cleaning fluid onto the polishing surface  110  ahead or upstream of the wiper  180  during the polishing operation to reduce or substantially eliminate buildup of solid polishing byproducts that can damage the substrate  102 .  
      As with the distributor  125 , the wiper  180  can be joined to a support (not shown) via an actuator  188  that is capable of raising and lowering the wiper into position in contact with the polishing surface  110 . The actuator  188  can include a spring actuators, gravity actuators, hydraulic actuators, pneumatic actuators, or electromagnetic actuators, such as solenoids.  
       FIG. 17  is yet another embodiment of the CMP apparatus  100  according to present invention having a cleaning fluid dispenser  186  integrally formed with or abutting the wiper  180 .  
      A method of operating a CMP apparatus  100  according to the present invention will now be described with reference to  FIG. 18 .  FIG. 18  is a flowchart showing an embodiment of a process for polishing or planarizing a substrate  102  according to an embodiment of the present invention. Generally, the method involves: (i) positioning the substrate  102  on the polishing head  116  (step  200 ); (ii) holding the polishing head  116  so as to press the surface of the substrate  102  against the polishing surface  110  (step  202 ); (iii) dispensing a chemical or slurry  129  onto the polishing surface  110  using a dispenser  124  having a number of nozzles  126 ,  128 , through which the chemical is dispensed (step  204 ); and (iv) mixing and uniformly distributing the chemical on the polishing surface  110  using a distributor  125  positioned between the nozzles  126 ,  128 , and the polishing head  116  (step  206 ).  
      Optionally, the method can further include the step of removing used chemical or slurry and polishing byproducts from the polishing surface  110  after the chemical has passed under the polishing head  116  using a wiper  180  positioned between the polishing head  116  and the distributor  125  (step  208 ). Preferably, the method further includes the step of dispensing a cleaning fluid on the polishing surface  110  upstream from the wiper  180  to substantially eliminate buildup of polishing byproducts (step  210 ).  
      The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best use the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.