Abstract:
A process for removing a metallized surface from a workpiece is provided. A kinetic removal mechanism for removal of the metallized surface is characterized by a formation step for formation of a removable surface film and an abrasive step for removal of the film. The process includes causing the workpiece to contact a polishing surface while effecting relative motion between the workpiece and the polishing surface. The process also includes causing a polishing solution having less than 1 wt % of a polishing abrasive to be distributed at a contact area between the workpiece and the polishing surface so that the abrasive step is a rate-determining step of the removal mechanism.

Description:
TECHNICAL FIELD 
     The present invention relates, generally, to systems for polishing or planarizing workpieces, such as semiconductor wafers. More particularly, it relates to an improved method for planarizing a metallized surface on a workpiece. 
     BACKGROUND 
     The production of integrated circuits begins with the creation of high-quality semiconductor wafers. During the wafer fabrication process, the wafers may undergo multiple masking, etching, and dielectric and conductor deposition processes. In addition, metallization, which generally refers to the materials, methods and processes of wiring together or interconnecting the component parts of an integrated circuit located on the surface of a wafer, is critical to the operation of a semiconductor device. Typically, the “wiring” of an integrated circuit involves etching trenches and “vias” in a planar dielectric (insulator) layer and filling the trenches and vias with a metal. 
     In the past, aluminum was used extensively as a metallization material in semiconductor fabrication due to the leakage and adhesion problems experienced with the use of gold. Other metallization materials have included Ni, Ta, Ti, W, Ag, Cu/Al, TaN, TiN, CoWP, NiP and CoP. As the size of integrated circuit devices becomes smaller, architectural feature restrictions, such as line isolation and material resistivity, may limit performance of such devices. To meet the demands of small feature devices, the semiconductor industry is migrating to new materials and architectures. For example, the semiconductor industry has been moving to the use of copper for metallization due to the alloying and electromigration problems that are seen with aluminum. In addition, single and dual damascene architectures are being used to enhance electrical isolation of conducting wires. These architectures continue to evolve, and may be used in structures having less than 0.18 micron minimum feature dimensions. Further, to enhance performance speed possible with these new device architectures and smaller device features, lower dielectric constant materials (i.e., k&lt;2.6) are being used to isolate conducting wires. However, such low dielectric constant materials exhibit characteristic porosity which reduces their mechanical strength, making them relatively fragile materials susceptible to shearing and crushing. 
     Because of the high degree of precision required in the production of integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to optimize the fabrication process, as well as to ensure proper accuracy and performance of the microelectronic structures created on the wafer surface. As the size of copper damascene structures continues to decrease, such as to minimum feature dimensions no greater than 0.18 microns, non-uniformity due to density variations across a die must be minimized. Therefore, between each processing step, it is usually necessary to polish or planarize the surface of the wafer to obtain the flattest surface possible. 
     Chemical Mechanical Polishing (“CMP”) machines have been developed to polish or planarize semiconductor wafer surfaces to the flat condition desired for integrated circuit components and the like. For examples of conventional CMP processes and machines, see U.S. Pat. No. 4,805,348, issued Feb. 21, 1989 to Arai et al.; U.S. Pat. No. 4,811,522, issued Mar. 14, 1989 to Gill; U.S. Pat. No. 5,099,614, issued Mar. 31, 1992 to Arai et al.; U.S. Pat. No. 5,329,732, issued Jul. 19, 1994 to Karlsrud et al.; U.S. Pat. No. 5,498,196, issued Mar. 12, 1996 to Karlsrud et al.; U.S. Pat. No. 5,498,199, issued Mar. 12, 1996 to Karlsrud et al.; U.S. Pat. No. 5,558,568, issued Sep. 24, 1996 to Talieh et al.; and U.S. Pat. No. 5,584,751, issued Dec. 17, 1996 to Kobayashi et al. 
     Typically, as illustrated in  FIG. 1 , a CMP machine  10  includes a wafer carrier  12  configured to hold, rotate, and transport a wafer  14  during the process of polishing or planarizing the wafer. The wafer carrier is rotated to cause relative lateral motion between the polishing surface and the wafer to produce a substantially uniform thickness. In general, the polishing surface includes a horizontal polishing pad  16 , 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  16  is attached to a platen  18  which rotates, orbits, and/or dithers. During a polishing operation, the wafer is pressed against the polishing surface with a desired amount of “down force” such that the polishing surface exerts a desired amount of pressure against the surface of the wafer. The carrier and the polishing pad are rotated or orbited, typically at different velocities, to cause relative lateral motion between the polishing pad and the wafer to promote uniform polishing. 
     An abrasive slurry typically is applied to a top surface  20  of the polishing surface through a conduit  22  during polishing of the wafer. The abrasive slurry acts to chemically weaken the molecular bonds at the wafer surface so that the mechanical action of the polishing surface can remove the undesired material from the wafer surface. For example, slurries used for the CMP of a copper-alloy metallized surface typically comprise a solid abrasive and an oxidizing agent. The oxidizing agent acts to oxidize the metallized surface while the solid abrasive mechanically removes the metal oxide, which tends to be “softer” than the metallized surface, from the surface of the wafer. 
     The kinetic mechanism for the removal of a metallized surface of a wafer includes the formation of a removable surface film containing the metal and the removal of the film by an abrasive or “rubbing” action. The overall rate of removal of the metallized surface from a wafer is characterized by the rate of formation (k f ) of the removable surface film and the rate of abrasion (k a ) of the film. If the rate of formation is slower than the rate of abrasion, the formation of the surface film is the rate-determining step and removal of the metallized surface can proceed no faster than the formation of the surface film. If the rate of abrasion of the metallized surface is slower than the rate of formation of the surface film, abrasion of the surface film is the rate-determining step and removal of the metallized surface can proceed no faster than the abrasion. The rate of formation (k f ) is proportional to the volume and/or concentration of oxidizing agent that is available to the metallized surface for polishing and to the temperature of the system. Thus, if the distribution of polishing solution available to the metallized surface is increased, the rate of formation is increased. Similarly, if the temperature of the system is modified, for example, by suitably increasing or decreasing the temperature of the polishing solution, the rate of formation may be increased. The rate of abrasion (k a ) is dependent on various factors, such as, for example, the pressure applied to the metallized surface from the polishing surface, the velocity of the wafer relative to the polishing surface, and the size and shape of the abrasives contained in the polishing solution. If any one or more of these factors is changed, the rate of abrasion will change accordingly. 
     Typically for CMP using conventional abrasive slurries, the rate of removal of the metallized surface from the wafer at steady state may be characterized by Preston&#39;s Law:
         RR=k*Pressure*Velocity
 
for a given polishing solution, where “RR” is the rate of removal of the metallized surface, “Pressure” is the pressure applied to the metallized surface by the polishing surface, “Velocity” is the velocity at which the wafer moves relative to the polishing surface and “k” is a constant. Thus, as illustrated in  FIG. 2 , if the polishing solution composition and distribution and the velocity remain constant, rate of removal will be approximately proportional to the pressure across a range of pressures.
       

     CMP may pose challenges when used for planarizing small device structures. For example, for devices having small feature dual damascene structures, CMP may remove large areas of copper residues but also result in the over-removal of small features. In addition, CMP may result in shearing and crushing of low dielectric constant materials. Capping films formed of materials tolerant to the CMP process are often adhered to the surface of low dielectric constant materials to protect such materials. However, the CMP process may cause cracks and loss of adhesion at the interface between the capping material and the low dielectric constant material. Further, abrasive slurries used in CMP may result in scratching of the wafer surface, oxide erosion, dishing and the creation of defects. The latter is particularly problematic for small structures, as a small defect will significantly jeopardize the performance of an even smaller device feature. 
     In addition, CMP may cause “edge effects” that reduce the die harvest from a wafer. As the wafer is pressed against the polishing pad, the pad deforms around the edge of the wafer, resulting in greater planarization at the wafer edge relative to the rest of the wafer. These edge effects are problematic as the semiconductor industry migrates from 200 mm wafers to 300 mm wafers. With more die around the edge of a, 300 mm wafer, edge effects will result in damage to a proportionately higher number of die of the 300 mm wafer compared to a 200 mm wafer. 
     To avoid at least some of these disadvantages, CMP may be performed at low down force pressures, that is, the wafer carrier exerts a relatively low down force when pressing the wafer against the polishing pad such that the wafer experiences a “low down force” pressure against the polishing pad. Typically, a “low down force” pressure range includes pressures of from about 0.10 psi to about 3.0 psi, and preferably includes pressures of from about 0.10 psi to about 1.0 psi. 
     In addition, abrasive-free, or relatively abrasive-free, polishing solutions have been used to planarize metallized surfaces on semiconductor wafers. Such polishing solutions typically have less than 1 wt % of polishing abrasives and are formed of oxidizers, such as hydrogen peroxide, which react with the metallized surface to form a removable surface film. Abrasive-free polishing solutions also are formed of agents that render the removable surface film water-soluble. An example of such a polishing solution is disclosed in U.S. Pat. No. 6,117,775, issued to Kondo et al. on Sep. 12, 2000, which patent is herein incorporated by reference. Polishing solutions having less than 1 wt % polishing abrasives have been shown to reduce scratching, dishing and oxide erosion. For convenience, abrasive-free and relatively abrasive-free polishing solutions, such as those having less than 1 wt % polishing abrasives, shall be collectively referred to herein as “abrasive-free polishing solutions.” 
     While exhibiting distinct advantages, abrasive-free polishing solutions may fail to provide adequate rate of removal using conventional polishing pads and delivery mechanisms. Referring again to  FIG. 1 , a conventional polishing apparatus typically includes a polishing pad  16  with a uniform top surface  20  upon which a polishing solution is delivered via a conduit  22 . While this conventional design may achieve acceptable rates of removal of the metal surface using an abrasive slurry, because of the chemically-reactive nature of abrasive-free polishing solutions, this conventional design does not provide for uniform distribution of the abrasive-free solution to the contact area between the wafer and the polishing pad. The wafer typically acts like a “squeegee” preventing even distribution of fresh slurry across the wafer. Thus, the rate of formation of the removable surface film is the rate-determining step of the planarization mechanism. 
     The disadvantage is particularly problematic for CMP processes that require a low down force pressure of the wafer against the polishing pad. The relationship between the rate of removal and pressure applied to the wafer by the polishing pad for conventional CMP apparatus using abrasive-free polishing solutions is illustrated in FIG.  3 . As illustrated in  FIG. 3 , a “critical down force” point, shown as point A, of non-Prestonian behavior exists, below which rates of removal are not satisfactorily proportional to the applied pressure. At low down force pressure ranges, as depicted between pressure P 1  and pressure P 2 , rates of removal are unacceptably low. Accordingly, for devices requiring low down force CMP processing, such as those formed of low dielectric materials, throughput is decreased as a result of the increase in processing time required to remove the metallized surface. In addition, low down force pressures may result in within-die nonuniformity. Further, because the polishing solution is not uniformly distributed over the surface of the wafer, non-uniform planarization results. 
     A need therefore exists for a process and an apparatus for improving planarization of metallized surfaces of workpieces using abrasive-free polishing solutions. A need further exists for a process and an apparatus for improving planarization of metallized surfaces using abrasive-free polishing solutions wherein the rate-determining step of the metal removal mechanism of the planarization process is the abrasion of the metallized surface. In addition, a need exists for a process and any apparatus for improving the planarization of copper surfaces wherein the rate of removal of copper from a copper surface of the workpiece is approximately proportional to the pressure at which the workpiece contacts the polishing surface, where the pressure is within a low down force pressure range. 
     SUMMARY OF INVENTION 
     These and other aspects of the present invention will become more apparent to those skilled in the art from the following non-limiting detailed description of preferred embodiments of the invention taken with reference to the accompanying figures. 
     In accordance with an exemplary embodiment of the present invention, a process of removing a metallized surface from a workpiece is provided. A kinetic removal mechanism for removal of the metallized surface is characterized by a formation step for formation of a removable surface film and an abrasive step for removal of the surface film. The process includes causing the workpiece to contact a polishing surface while effecting relative motion between the workpiece and the polishing surface. The process also includes causing a polishing solution having less than 1 wt % of a polishing abrasive to be distributed at a contact area between the workpiece and the polishing surface so that the abrasive step is a rate-determining step of the removal mechanism. 
     In another exemplary embodiment, the process includes establishing a temperature at a contact area between the workpiece and the polishing surface so that the abrasive step is the rate-determining step of the removal mechanism. 
     In accordance with a further exemplary embodiment, an apparatus for removing a metallized surface from a workpiece is provided. A kinetic removal mechanism for removal of the metallized surface is characterized by a formation step for formation of a removable surface film and an abrasive step for removal of the surface film. The abrasive step is the rate-determining step of the removal mechanism. The apparatus includes a source of a polishing solution having less than 1 wt % of a polishing abrasive and a polishing member. A polishing solution delivery assembly is configured to deliver the polishing solution to the polishing member. A workpiece carrier is configured to carry the workpiece and press the workpiece against the polishing member. A drive assembly is configured to effect relative motion between the workpiece and the polishing member. 
     In accordance with another exemplary embodiment, a process for removing a copper surface from a workpiece having single and/or dual damascene structures is provided, wherein the workpiece contacts a polishing member at a contact pressure. The process includes causing a polishing solution to be distributed at a contact area between the workpiece and the polishing member so that a rate of removal of the copper surface is approximately proportional to the contact pressure within a range of contact pressures, wherein the range of contact pressures comprises a low down force pressure. 
     In a further exemplary embodiment, a process for removing a copper surface from a workpiece having single and/or dual damascene structures is provided. The workpiece contacts a polishing member at a contact pressure. The process includes causing a polishing solution having less than 1 wt % of a polishing abrasive to be distributed at a contact area between the workpiece and the polishing member so that a rate of removal of the copper surface is approximately proportional to the contact pressure within a range of contact pressures, wherein the range of the contact pressures includes a low down force pressure. 
     In accordance with yet another exemplary embodiment, an apparatus for removing a copper surface from a workpiece having single and/or dual damascene structures is provided. The apparatus includes a source of a polishing solution, a polishing member and a workpiece carrier configured to carry the workpiece and to press the workpiece against the polishing member at a contact pressure. A drive assembly is configured to effect relative motion between the workpiece and the polishing member. A polishing solution distribution assembly is configured to distribute the polishing solution at a contact area between the workpiece and the polishing member so that a rate of removal of the copper surface is approximately proportional to the contact pressure along a range of contact pressures, wherein the range of contact pressures comprises a low down force pressure. 
     In accordance with yet a further exemplary embodiment, an apparatus for removing a copper surface from a workpiece having single and/or dual damascene structures is provided. The apparatus includes a source of a polishing solution having less than 1 wt % of a polishing abrasive and a polishing member. A workpiece carrier is configured to carry the workpiece and to press the workpiece against the polishing member at a contact pressure. A drive assembly is configured to effect relative motion between the workpiece and the polishing pad. A polishing solution distribution assembly is configured to distribute the polishing solution at a contact area between the workpiece and the polishing member so that a rate of removal of the copper surface is approximately proportional to the contact pressure along a range of contact pressures, wherein the range of contact pressures comprises a low down force pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will hereafter be described in conjunction with the appended drawing figures, wherein like designations denote like elements, and: 
         FIG. 1  is a cross-sectional view of a polishing pad and platen known in the art; 
         FIG. 2  is a graphical illustration of the change of the rate of removal of a metallized surface on a wafer with the change in relative pressure between the wafer and a polishing surface in a conventional chemical mechanical planarization process. 
         FIG. 3  is a graphical illustration of the change of the rate of removal of a metallized surface on a wafer with the change in relative pressure between the wafer and a polishing surface in a chemical mechanical planarization process in which an abrasive-free polishing solution is used. 
         FIG. 4  is a cross-sectional view of a polishing station which utilizes an abrasive-free polishing solution, in accordance with an exemplary embodiment of the present invention; 
         FIG. 5  is a top view of a platen of the polishing station of  FIG. 4 ; 
         FIG. 6  is a top view of a polishing pad used in a polishing station which utilizes an abrasive-free polishing solution, in accordance with another exemplary embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of a polishing station which utilizes an abrasive-free polishing solution, in accordance with another exemplary embodiment of the present invention; 
         FIG. 8  is an exploded perspective view of a platen in accordance with another exemplary embodiment of the present invention; 
         FIG. 9  is a cross-sectional view of a polishing station which utilizes an abrasive-free polishing solution, in accordance with another exemplary embodiment of the present invention; and 
         FIG. 10  is a top view of a polishing surface of the polishing station illustrated in FIG.  9 . 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. 
     A schematic representation of an exemplary embodiment of a polishing station  100  of the present invention is shown in  FIGS. 4 and 5 . As herein described, polishing station  100  is configured to provide uniform and adequate distribution of an abrasive-free polishing solution so that the metallized surface of a subject workpiece readily forms a removable surface film, thereby make the abrasion step of the planarization mechanism the rate-determining step. Polishing station  100  is suitable for planarizing workpieces having metallized surfaces and is particularly suitable for planarizing workpieces having copper metallization. Such workpieces include those having single and dual damascene structures, such as, for example, those having minimum feature dimensions no greater than 0.18 microns. In addition, polishing station  100  is suitable for planarizing workpieces formed of low dielectric constant materials, such as, for example, those materials having a dielectric constant less than or equal to 2.6. 
     Polishing station  100  includes a polishing platen  102 . A polishing pad  104  with a polishing surface  106  is mounted to the platen  102 . A wafer carrier  126  holds a workpiece  128 , such as a semiconductor wafer, which has a metallized surface. Wafer carrier  126  is configured to press the workpiece against polishing surface  106  while relative motion between workpiece  128  and polishing surface  106  is effected. In one embodiment, wafer carrier  126  may rotate workpiece  128  about an axis  130 . In another embodiment, wafer carrier  126  may move workpiece  128  linearly or orbitally relative to polishing surface  106 . Workpiece  126  may press workpiece  128  against polishing surface  106  with a predetermined down force so that workpiece  126  experiences a down force pressure against the polishing surface. When workpiece  126  is formed of low dielectric constant materials, it may be desirable to limit this pressure to a “low down force” pressure range. This “low down force” pressure range may include pressures within the range of from about 0.10 psi to about 3.0 psi, but preferably within a range of from about 0.10 psi to about 1.0 psi. 
     In one embodiment of the invention, an abrasive-free polishing solution is delivered to polishing surface  106  of pad  104  by a manifold apparatus  108 . A pump  110  may distribute the solution through a fluid line  112  and through distribution manifold  108  to one or more conduits  116  formed within platen  102  in the direction indicated by arrows A 114 . Conduits  116  allow for easy transportation of the abrasive-free polishing solution through platen  102 . The abrasive-free polishing solution may then suitably flow from conduits  116  through one or more bores  118  in the direction of arrows A 122 . Platen  102  is connected to a shaft  122  that is connected to a drive assembly (not shown) to rotate platen  102  and pad  104  around axis  124 . Polishing station  100  may employ suitable rotary unions (not shown), rotary couplings (not shown) and the like to permit rotation around axis  124 . Alternatively, it will be appreciated that the drive assembly may be operative to move platen  102  and polishing pad  104  in an orbital, linear or oscillatory pattern or any combination of orbital, linear, oscillatory and rotary patterns. Referring again to  FIG. 4 , polishing pad  104  similarly has one or more channels  120  that permit the abrasive-free polishing solution to flow from bores  118  of platen  102  to the pad surface. Channels  120  may be molded into pad  104  when originally fabricated or may be machined into pad  104 . Through bores  118  and channels  120 , the polishing solution may flow from conduits  116  to the surface  106  of pad  104 . 
     In another embodiment, as illustrated in  FIG. 6 , polishing pad  104  as referenced in  FIG. 4 , may also be scored with grooves running in the “x” and “y” directions to form a grid with parallel x-direction grooves  302  and crossing perpendicular grooves  304 . Grooves  302  and  304  may intersect channels  120  of pad  104 . Grooves  302  and  304  assist in the distribution of the abrasive-free polishing solution during planarization. As the workpiece is pressed against the polishing pad during planarization, grooves  302  and  304  permit the abrasive-free fluid to flow across the surface of the wafer and serve to reduce or eliminate the “squeegee” effect that conventional polishing pads experience during planarization. While grooves  302  and  304  are shown in a perpendicular relationship, it will be appreciated that polishing pad  104  may comprise grooves of any suitable pattern that is configured to facilitate uniform distribution of fresh polishing solution. 
     In an alternative embodiment, a polishing station  200  utilizes a porous polishing pad  202 . Referring to  FIG. 7 , an abrasive-free polishing solution may be delivered to a polishing surface  204  of a polishing pad  202  from a manifold apparatus  208  formed in a rotating platen  206 . The abrasive-free polishing solution is delivered under pressure through a fluid line  212  connected to a solution source (not shown) to manifold apparatus  208  having one or more conduits  210  formed within platen  206 . The abrasive-free polishing solution may then suitably flow from conduits  210  through one or more bores  220  in the direction of arrows A 214 . The abrasive-free polishing solution then flows through the pores of pad  202  under pressure so as to be evenly distributed to polishing surface  204 . 
     In a further embodiment, polishing pad  202  may be scored with grooves running in the “x” and “y” directions to form a grid with parallel x-direction grooves (not shown) and crossing perpendicular y-direction grooves (not shown). These grooves facilitate uniform distribution across the surface of polishing pad  202  of the abrasive-free polishing solution that flows through the pores of the pad. Alternatively, the grooves may be formed in any suitable pattern that facilitates distribution of fresh polishing solution. 
     It will be appreciated that the above described grooved polishing pads may also be used in CMP apparatus with conventional slurry delivery systems wherein the polishing slurry is deposited on the top surface of the polishing pad, rather than through the polishing pad as described above. When the slurry is deposited on the top surface of the polishing pad, the grooves serve to uniformly distribute the slurry on the top of the pad to facilitate planarization. 
     A method for planarization using one embodiment of the invention will now be described. Referring again to  FIG. 4 , wafer carrier  126  urges wafer  128  against polishing pad  104  such that wafer  128  engages polishing pad  104  at a desired pressure. The pressure exerted by wafer carrier  126  may be any pressure suitable for planarizing a workpiece and may comprise a “low-down force” pressure suitable for planarizing workpieces formed of fragile low dielectric-constant materials. An abrasive-free polishing solution is pumped by pump  110  through fluid line  112  to distribution manifold  108 . From distribution manifold  108 , the abrasive-free polishing solution flows through conduits  116  and bores  118  of platen  102  and channels  120  of polishing pad  104  to the polishing surface  106 . Using this method, fresh abrasive-free polishing solution is distributed uniformly to the metallized surface of workpiece  128 . Wafer carrier  126  and workpiece  128  may rotate about axis  130  while platen  102  and polishing pad  104  move in a rotational, orbital or linear pattern. In addition, wafer carrier  126  and workpiece  128  may oscillate relative to polishing pad  104 . As the abrasive-free polishing solution uniformly contacts workpiece  128 , a removable surface film containing the metal is formed on the metallized surface. The removable surface film is subsequently uniformly removed by the mechanical abrasive action of polishing surface  106  of polishing pad  104 . In this manner, the rate of formation of the removable surface film on the metallized surface by the polishing solution is increased, making abrasion the rate-determining step of the metal removal mechanism. Accordingly, the rate of removal of the metallized surface is approximately proportional to the pressure experienced by the wafer from the polishing surface, even when the pressure is a low down force pressure. 
     In another embodiment, removable surface film formation may be facilitated by modifying the temperature during planarization. In an exemplary embodiment of the present invention, the abrasive-free polishing solution may be heated before being delivered to the manifold apparatus. In another embodiment, the temperature of the planarization process may be increased by providing a heated fluid to the backside of the workpiece. Apparatus for exposing a heat exchange fluid to the backside of a wafer are well known in the art. For an example of an apparatus configured to regulate the polishing rate of a wafer by backside fluid exposure, see U.S. Pat. No. 5,606,488, issued to Ohashi et al. on Feb. 25, 1997, which patent is herein incorporated by reference. Similarly, planarization may be facilitated by decreasing the temperature of the system. For example, the abrasive-free polishing solution may be cooled before being delivered to the manifold apparatus. In another embodiment, the temperature of the planarization process may be decreased by providing a cooled fluid to the backside of the workpiece. 
     The temperature of the planarization process may also be regulated by providing a heat conductivity platen configured to be temperature controlled by a heat exchange fluid circulating therethrough. Although there are a number of methods to fabricate such a platen, only one of those methods is illustrated herein. Referring to  FIG. 8 , in accordance with one embodiment of the invention, a platen  400  is fabricated from a material having a high thermal conduction coefficient to facilitate control of the processing temperature. Platen  400  may be constructed in three pieces that are connected together by belts, rivets, or, preferably, by brazing to form a unitary platen. Platen  400 , in this embodiment, is formed from a substantially circular cover plate  410  that has a substantially planar upper surface  420  to which a polishing pad can be attached, for example, with an adhesive. In this embodiment, platen  400  further includes a channel section  430  that includes channel grooves  440 . Preferably, channel grooves  440  are configured in a serpentine pattern. A heat exchange fluid flows from inlets  450  near the center or axis of platen  400  to a location near the periphery  460  of the platen and then, in a serpentine pattern to exits  480  again located near the center or axis of platen  400 . Platen  400  is completed by a bottom section  490  that includes on its bottom surface (not shown) a configuration for the attachment of the platen to a platen shaft. 
     In an alternative method (not illustrated) for fabricating platen  400 , the channel groove could be formed in the underside of the cover plate. The channel groove then could be sealed by attaching a circular disk having a planar top surface to the underside of the cover plate. The bottom section could then be attached to the circular disk, or, alternatively, the function of the circular disk and the bottom section could be combined. In either this method or the illustrated method, a channel groove through which a heat exchange fluid can be circulated is formed beneath the substantially planar surface of the platen assembly. 
     Cover plate  410 , channel section  430  and bottom section  490  each have a first set of bores  500 , similar to bores  118  as referenced in  FIG. 4 , through which an abrasive-free polishing solution may flow. Bores  500  in cover plate  410  are colinear with bores  500  in channel section  430 , which in turn are colinear with bores  500  in bottom section  490 . A manifold apparatus (not shown) may be connected to bottom section  490  to deliver the polishing solution through bores  500  of the bottom section, channel section and cover plate to the polishing pad. 
       FIG. 9  illustrates another polishing station  600  that is configured to provide uniform and adequate distribution of an abrasive-free polishing solution. An endless belt  602  is provided with at least one side of belt  602  having a polishing surface  604 . Belt  602  rotates about rollers  612  and  614 , which rollers are driven by a drive motor assembly (not shown) so that the rotational motion of rollers  612  and  614  cause belt  602  to be driven in a linear motion, as shown by arrow A 620 , with respect to a workpiece  616  held by a wafer carrier  618 . Belt  602  preferably has a smooth opposite surface  606  that may be laid across and supported by a supporting surface  608 . The minimum width of the belt  602  is dependent on the size of a workpiece  616  to be planarized. An abrasive-free polishing solution may be applied through a conduit  610  via a fluid pump (not shown). During planarization, workpiece carrier  618  presses workpiece  616  against polishing surface  604  with a desired pressure, while rotating workpiece  616  about an axis  622 . 
     In an exemplary embodiment of the present invention, the polishing surface  604  may be scored with grooves to facilitate distribution of fresh polishing solution to the surface of the workpiece so that abrasion of metal oxide on a metallized surface of workpiece  616  is the rate-determining step of the removal mechanism. As illustrated in  FIG. 10 , the grooves may be scored in the “x” and “y” directions to form a grid with x-direction grooves  624  and crossing perpendicular y-direction grooves  626 . While grooves  624  and  626  are shown in  FIG. 10  as perpendicular “x”- and “y”-direction grooves, it will be appreciated that the grooves may be formed in any suitable pattern that facilitates distribution of the abrasive-free polishing solution. 
     Linear polishing station  600  also may use a temperature control mechanism to increase or decrease the temperature of the planarization process so that abrasion, and not removable surface film formation, is the rate-determining step of the removal mechanism. In one embodiment the abrasive-free polishing solution may be heated before being delivered to conduit  610 . In another embodiment, as described above, the temperature of the planarization process may be changed by providing a heated fluid to the backside of the wafer. 
     Using the above various embodiments, the rate of removal of a metallized surface during a planarization process using an abrasive-free polishing solution is facilitated. By using the above embodiments, the metallized surface of a workpiece may be readily formed to a removable surface film by the polishing solution so that abrasion of the metallized surface is the rate-determining step of the planarization process. Further, the rate of removal of the metal from the workpiece is approximately proportional to the pressure exerted against the workpiece by the polishing surface, even within low down force pressure ranges. Thus, expeditious and uniform planarization of the workpiece is achieved, even when the workpiece is pressed against the polishing pad at low pressures. 
     While the above-described embodiments are directed to planarization of a metallized surface using an abrasive-free slurry, it will be appreciated that one or more of the embodiments may also be incorporated in CMP apparatus that utilize abrasive slurries. By working in conjunction with the abrasive particles of the abrasive slurry, the embodiments may be useful in facilitating the rate of removal of the metallized surface. 
     In the foregoing specification, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. 
     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be constructed as critical, required, or essential features or elements of any or all of the claims. As used herein, the terms “comprises,” “comprising” and any other variation thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article or apparatus.