Abstract:
A method and apparatus for conditioning polishing pads that utilize an apertured conditioning disk for introducing operation-specific slurries, without the need for additional tooling, platens, and materials handling. The method and apparatus utilize a vacuum capability to pull waste material out of the conditioning pad and through the apertured conditioning disk to evacuate the apparatus through an outlet port, the apparatus may also include self-contained flushing means and a piezo-electric device for vibrating the pad conditioning apparatus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. Ser. No. 10/819,754, filed Apr. 7, 2004 and allowed Apr. 19, 2007, which is a continuation-in-part of U.S. Pat. No. 7,052,371 issued May 30, 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to the fields of semiconductor fabrication, microelectromechanical systems (MEMS) fabrication, and precision polishing; and specifically to a method for the removal of waste products from the polishing process, and for the introduction of multiple, different slurries during Chemical Mechanical Polishing (CMP) and planarization.  
         [0004]     2. Description of Related Art with Respect to Semiconductor Fabrication  
         [0005]     An integrated circuit generally consists of a silicon wafer substrate typically produced or fabricated as a disc with a diameter of 100 to 300 millimeters and a thickness of 16 to 40 mils. Metallic, dielectric and insulator depositions forming interconnected circuits are created on a wafer by a series of processes, such as lithography, vapor deposition, and oxidation, that produce the desired electrical circuitry. An electrical insulating layer, up to one-micron in thickness, is then deposited over the electrical circuit layer. With each layer, a multiplicity of undesired irregularities occur on the surface. These irregularities are on the order of 0.05 to 0.5 microns. It is critically important that these irregularities be planarized, so that new layers of circuitry can be developed without loss of focus in lithography, whereby accurate interconnections can be formed between layers.  
         [0006]     Various techniques have been developed and used to effect the removal of these irregularities. Chemical Mechanical Polishing (CMP) (planarity) has become a key technology to remove irregularities and achieve required planarity, layer and line width geometries of microelectronic devices. A CMP system generally consists of the following components: 1) a polishing pad mounted on a rotating or orbital platen or belt; 2) a stream of polishing slurry (oxidizer and abrasive) whose chemistry and abrasive media is important to polishing performance; 3) large amounts of ultra pure water (UPW) used as a lubricant or flushing medium/agent; 4) slurry components and flushing agents. Additionally, to adjust chemistry or fluid properties during processing; 5) a diamond end effector which controls the surface condition and asperity profile of the polishing pad; and 6) the wafer to be polished mounted in a carrier on a rotating head which supplies the polishing pressure.  
         [0007]     The introduction of slurry under the wafer, and the removal of waste products from the polishing and conditioning process, are dependent on the centrifugal force of the rotating pad, the action of the end effector, and the flow of slurry plus UPW.  
         [0008]     Irregularities on the wafer are removed with a slurry of oxidating chemicals and very fine abrasive particles continually presented to its surface. Polishing or planarity is generally accomplished with the wafer placed face down on the polishing pad that is rotating beneath the wafer that is itself rotating around a central axis. Linear and orbital methods are also utilized and this invention is applicable to those processes and tools.  
         [0009]     Current polishing tools and processes consist of a single operation step per platen because of operation with specific slurries. Additional tools, platens, and materials handling are required to support multi-step polishing operations such as that required for copper CMP.  
         [0010]     There currently exists no means of using different chemicals, and abrasives of different materials or particle sizes, without separate equipment or extensive changeover and/or manual cleaning of the polishing equipment.  
         [0011]     Polishing pads are generally made of a plastic (urethane) material. The removal rate of wafer irregularities is affected by the pressure applied to the wafer against the polishing pad, the relative speed of the slurry on the wafer, the amount of fresh slurry presented to the surface of the polishing pad, and the circuit pattern of the wafer. The introduction of slurry under the wafer, and the removal of waste products from the polishing process, are dependent on centrifugal force of the rotating pad, the action of the end effector, and the flow of slurry and components and UPW. This type of flushing does not always remove the waste. Large settled abrasive particles from the slurry, and agglomerated slurry and wastes, form in the pored and grooves of the pad, and between diamond particles on the conditioners. Commercial applications have large volumes of UPW used in production and significant amounts of wastewater that must be treated.  
         [0012]     The rate of wafer polishing depends upon the pressure applied to the wafer, the slurry, and the diamond head on the end effector arm to roughen or condition the polishing pad, to provide a consistent asperity profile. In cross-section, the pad has regions of peaks and valleys which both carry slurry and provide pressure to the abrasive particles therein. The pad generally consists of a hard or soft urethane material with pores and/or fibers dispersed throughout the active layer. The fibers and/or urethane give the pad rigidity, provide pressure to the abrasive/wafer interface, and aid in the removal of material from the surface of the wafer. The pores act as a reservoir for the slurry facilitating the chemical contact and interaction with the wafer surface. The chemical interaction is an important ‘accelerator’ over an abrasive-only polishing situation, and therefore is critical to overall process performance and control.  
         [0013]     The diamond end effector generally consists of diamond particles embedded in a metal matrix in the form of a rotating disk. The disk is principally used to texture the polishing pad so that a sustainable rate of planarization can occur on the wafer and wafer to wafer. It is also used to remove used slurry and debris from the pad. The used slurry and debris often occurs as large hard agglomerations which consist of silicon dioxide (SiO 2 ), dielectric and metals that become embedded in the polishing pad. These materials reduce removal or polishing rates and repeatability, and can produce defects in the form of scratches that damage the wafer surface and device performance (opens, shorts). Data from the semiconductor industry reveal that 60% of chip loss is due to contamination. The CMP process has been reported to be a major source of this contamination.  
         [0014]     The uncontrolled delivery and removal (flushing) of process fluids can also cause polishing waste to build-up on many surfaces within the tooling. When dislodged, these dried/agglomerated compounds can lead to additional defects. Slurry has proven to be “unstable”, prone to agglomeration due to shear forces in delivery systems, heat, and age effects. There is also potential for diamond particles to fracture or be torn from the metal matrix of the end effector disk and scratch the wafer surface. Within typical polishing times, from 60 to 600 seconds, there is significant causal mechanisms for scratching and more control of the process is required.  
         [0015]     Presently this debris is removed from the pad with copious flushing of the pad with UPW and/or slurry. This method relies on centrifugal force, or other pad movement dynamics, on the liquid to carry off the waste and agglomerates. This is a very uncontrolled method of removal because the flushing cannot break-up the static layer of slurry on the pad surface, nor is it able to dislodge the slurry in the holes of the pad. This could lead to additional agglomerates of slurry becoming deposited in holes and recesses of the pad. This slurry can become dislodged, at a later time, and damage subsequent wafers. The reliance of these “rotational forces” to present new slurry to the wafer/pad interface is also less controlled or repeatable than required, causing variation in removal rates and uniformity.  
         [0016]     Polishing pad surfaces, which typically contain pores, holes or grooves for channeling the slurry between the wafer and the pad, require conditioning to create a consistent polishing interface. Slurry and debris from the wafer must be removed by continually “abrading” or “conditioning” the pad surface. Additionally, oxidizing slurries sometimes used in this process contribute to the contamination of the pad by interacting with device layer metals forming harder oxide compounds; or layer delaminations, causing potential contamination and scratching of the wafer.  
         [0017]     One apparatus that attempts to solve the problems defined above is described in U.S. Pat. No. 6,508,697, incorporated herein by reference, in which a system for conditioning rotatable polishing pads used to planarize and polish surfaces of thin integrated circuits deposited on semiconductor wafer substrates, microelectronic and optical systems, is disclosed. The system is comprised of a pad conditioning apparatus, process fluids, and a vacuum capability to pull waste material out of the conditioning pad, self-contained flushing means, and a means for imparting a vibratory motion to the pad conditioning abrasive or fluids. The pad conditioning apparatus is comprised of an outer chamber in a generally circular configuration with an inlet port for introducing process fluids and/or UPW and an outlet port for supplying negative pressure.  
         [0018]     Considering the prior art conditioning apparatus described above, it is an object of the present invention to provide a method, using such a system, for conditioning polishing pads with a self-contained cleansing means for removing debris and loose slurry, as it is dislodged during the conditioning process.  
         [0019]     It is also an objective to provide means for the introduction of different (multi-step) operations with specific slurries or additives without additional tools, platens, and materials handling.  
         [0020]     Another objective is to allow for neutralization of slurry chemistry between steps.  
         [0021]     A further objective is to allow for the introduction of alternative/additional slurry or chemical feeds.  
         [0022]     Yet another objective is to allow for multi-step polishing on each platen.  
         [0023]     A still further objective is to increase through-put by allowing a more aggressive first polishing step, and subsequent, finer abrasive/chemical selectivity near the planarization endpoint.  
         [0024]     Another objective is to eliminate intermediate material handling and to allow for single platen processing of copper and barrier metal films.  
         [0025]     Yet another objective is to extend utility/life of single and double head polishing tools.  
         [0026]     Yet another objective is to reduce defectivity through more selective endpoint control via slurry change (chemistry or abrasive).  
         [0027]     Yet another objective is to improve uniformity by reducing handling/alignment/fixture variations seen by wafer.  
       BRIEF SUMMARY OF THE INVENTION  
       [0028]     The pad conditioning system used in the present invention, as set forth in U.S. Pat. 6,508,697 referred to above, utilizes abrasive disks that have an open structure to collect debris or swarf as it is being abraded off of the substrate surface. The system has a pad conditioning apparatus, process fluids, a vacuum self-contained flushing means, and a piezo-electric device for vibrating the pad conditioning abrasive. The debris, s it is being created, is pulled through the holes of the abrasive and magnetic support, into a chamber behind the support, and into a conduit to a disposal system. Jets of water, other cleaning, or neutralizing chemicals are sprayed through the abrasive in conjunction with the waste removal. This flushing/abrading/vacuum cleaning thoroughly cleans the polishing pad surface, enabling alternative materials to be introduced without cross contamination. All of these elements combine in operation to provide a unique and effective system for conditioning and cleaning polishing pads. They also allow for the introduction into the conditioning, cleaning and polishing processes operation-specific slurries or other chemicals, without the need for extensive retooling, platen change-out, and additional material handling.  
         [0029]     The pad conditioning apparatus has an outer chamber in a generally circular configuration with an inlet port for introducing process fluids and/or UPW, and an outlet port for attaching negative pressure. The outer chamber houses a rotating impeller shaft. The shaft of the impeller assembly protrudes through an opening in the top surface of the outer chamber and is attached to the equipment&#39;s end effector assembly. A support disk, a magnetic disk or mechanical fastening means, and an abrasive conditioning disk, are attached to the impeller in a stacked configuration. As described in U.S. Pat. No. 4,222,204, incorporated herein by reference, the abrasive disk is held in place magnetically or mechanically, offering full support of the disk, because it pulls the disk flat to the support disk. The assembly is constructed with aligned holes that allow debris on the polishing pad to be vacuumed up through these holes.  
         [0030]     In operation, the outside chamber is held stationary with an attached hose connected to a vacuum facility. The water or slurry is introduced either from an inlet port on the outer chamber, or from the center of the impeller through a water collar.  
         [0031]     A series of pressurized water holes radiating out from the center of the impeller disk allows full coverage of the abrasive disk and aids in the break up of the static layers in the pores of the polishing pad. The vacuum action pulls the water and debris immediately up through the aligned holes in the support, magnetic, and abrasive disks, and the rotating impeller blades sweep the water and debris into the vacuum pickup outlet and into the disposal system. The aligned holes, or “open structure”, in the stacked disks allows collection of debris or swarf, as it is being dislodged from the surface of the pad, allowing continuous conditioning and cleaning without interference of the debris between the abrasive disk and the surface of the wafer, The magnetic fastening structure allows for rapid changeover and provides controlled flatness for the abrasive. A mechanical method can also be used which would be gimbaled for alignment and cushioning. Vacuum pulls the wastes from the process, and lifts the polishing pad asperities into an uncompressed position. Select holes also introduce process fluids, such as cleaning chemicals, slurry, passivating agents, complexing agents, surfactants, and UPW, and even cleaning gasses, to the pad in a much more controlled (pressure, location, sequence, and pad/wafer surface conditions, for instance) fashion.  
         [0032]     A self-contained flushing system provides water to loosen and flush the debris up the disks holes into the impeller chamber and on through to the disposal system, A sealed bearing at the top of the outer chamber prevents water or process fluids from escaping. This flushing method also reduces the amount of UPW that is presently needed to flush the polishing pad. This saves on costly slurry, the volume of UPW, and the expensive waste disposal.  
         [0033]     The impeller provides firm backing for the magnetic disk or mechanical fastening and abrasive disk. The magnet is secured to the support disk mechanically or by an adhesive. The abrasive disk is either magnetically or mechanically secured to the support disk. This system allows for periodic cleaning of the pad conditioning apparatus, as well as periodic replacement of the magnet and abrasive disks, without the need to disassemble the entire outer chamber and inner impeller assembly, which would incur extensive down time.  
         [0034]     A piezoelectric transducer is provided near the free end of the end effector arm or fluid stream. When excited with a high frequency voltage, transducer imparts a low amplitude vibration to the pad conditioning apparatus, further enhancing the breakup and removal of the static layer of slurry on the polishing pad surface. A small vertical force imparted by the end effector arm on the polishing pad also aids in breaking up glazing of the slurry, and aids in dislodging particles wedged in the polishing pad surface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]      FIGS. 1 through 5  illustrate the prior art system of U.S. Pat. No. 6,508,697.  
         [0036]      FIG. 1  is a perspective view of the major elements of the Chemical Mechanical Polishing (CMP) system used in the present invention with the wafer holder removed.  
         [0037]      FIG. 2  is a top schematic view of the constituent components used in the present invention.  
         [0038]      FIG. 3  is a view of the outer chamber taken along line  6 - 6  of  FIG. 2 .  
         [0039]      FIG. 4  is a section view of the conditioning apparatus used in the present invention taken along line  7 - 7  of  FIG. 2 .  
         [0040]      FIG. 5  is an exploded view of the constituent components of the conditioning apparatus used in the present invention showing the outer chamber and impeller assembly.  
         [0041]      FIG. 6  is a block diagram showing the method of the present invention.  
         [0042]      FIG. 7  is an exploded view of an inventive impeller arrangement formed in accordance with the present invention.  
         [0043]      FIG. 8  is a cut-away side view of the impeller arrangement of  FIG. 7 .  
         [0044]      FIG. 9  is an isometric bottom view of the impeller arrangement of  FIG. 7 .  
         [0045]      FIG. 10  illustrates an alternative impeller assembly of the present invention, including at least one vacuum port in an impeller blade.  
         [0046]      FIG. 11  illustrates an alternative impeller element configuration, using cylindrical members instead of impeller blades.  
         [0047]      FIG. 12  is a side view of the arrangement of  FIG. 11   
         [0048]      FIG. 13  illustrates an alternative arrangement of the cylindrical impeller elements as shown in  FIGS. 11 and 12 .  
         [0049]      FIG. 14  is a graph illustrating improved polishing pad removal rate when using the polishing pad conditioning system of the present invention.  
         [0050]      FIG. 15  is a graph illustrating improved polishing slurry activity as a function of the vacuum force applied during the conditioning process.  
         [0051]     FIGS.  16 ( a ) and ( b ) contain photographs of the pressure gradient across the surface of an abrasive conditioning disk,  FIG. 16 ( a ) associated with the prior art and  FIG. 16 ( b ) associated with an embodiment of the present invention.  
         [0052]      FIG. 17  is a simplified top view of a CMP apparatus illustrating the location of an abrasive conditioning disk torque measuring apparatus, used in accordance with the present invention to determine physical parameters of the polishing pad. 
     
    
     DETAILED DESCRIPTION  
       [0053]     The present invention relates to a method of conditioning polishing pads used in Chemical Mechanical Polishing or Planarizing (CMP) Systems for removing irregularities on semiconductor wafer substrates. The specific details of the preferred embodiment provide a thorough understanding of the invention; however, some CMP system elements which operate in conjunction with the present invention have not been elaborated on because they are well known and may tend to obscure other aspects that are unique to this invention. It will be obvious to one skilled in the art that the present invention may be practiced without these other system elements.  
         [0054]     Referring to  FIG. 1 , a perspective view of a typical CMP system  10  is illustrated generally comprising a polishing head (not shown) that applies pressure to wafer  11  against a polishing pad  12  through a wafer carrier and support arm (not shown), and a polishing pad conditioning apparatus  15 . Wafer  11  is rotated on polishing pad  12  that is secured to rotating, orbital or linear platen  13 . (The wafer carrier, support arm and motor are not shown). A stream of polishing slurry  14  generally containing an oxidizer, abrasive and/or ultra-pure water (UPW) is poured on the polishing pad surface  12   a  and in cooperation with the rotating motion of wafer  11  acts to remove a few tenths of microns of surface uneveness on the wafer  11  after each layer of integrated circuit fabrication. Pad conditioning apparatus  15  operates to restore and maintain polishing pad surface  12   a  as it is changed by the polishing action. Motor  17 , as seen in  FIG. 2 , pivots end effector arm  16  in an arc about fixed shaft  18  while simultaneously providing rotational motion and a downward force  40  to pad conditioning apparatus  15 . Debris from the polishing operation is removed through outlet  41 .  
         [0055]     A pad conditioning apparatus  15  used in the present invention is shown in the top view of  FIG. 5  and is configured to mechanically and electrically interface with end effector arm  16 . Pad conditioning apparatus  15  is designed to automatically dispense chemicals, slurry and/or UPW, so as to condition polishing pad surface  12   a , and vacuum out debris formed by the polishing process, without interfering with the polishing process or incurring excessive down time. Hose  21 , which is attached to vacuum outlet port  22  on the periphery of conditioning holder  20 , pulls debris into a vacuum facility (not shown). Hose  23 , which is attached to inlet port  19 , projects through the top center of conditioning holder  20  and provides a stream of abrasive slurry for consistent coverage of the pad surface  12   a , and/or provides neutralizers, UPW, or cleaning agents, for flushing and lubrication. To enhance debris removal, piezo-electric device  24 , when excited with a high frequency voltage through electrical connection  25 , imparts a low amplitude vibratory impulse to conditioning apparatus  15 , thereby agitating debris particles on conditioning pad surface  12   a , causing the debris particles to become dislodged for easier removal.  
         [0056]     Outer chamber  30  of conditioning holder  20  shown in  FIG. 3  is a view taken along line  6 - 6  of  FIG. 2 . Outer chamber  30  of the current embodiment, is approximately four inches in diameter and three inches high. It will be obvious to one skilled in the art that the present invention may be practice with dimensional characteristics other than those described, up to and inclusive of the entire working surface of the pad.  
         [0057]      FIG. 4  is a sectional view taken along line  7 - 7  of  FIG. 2 , and shows the impeller assembly  32  with support disk  34 , magnetic disk  35 , and abrasive disk  36 , attached to impeller blades  33 . Holes  37  in each of the disks are aligned, such that debris is pulled from polishing disk  12  to vacuum outlet  22 . Process fluid is taken in through hose  23  and evenly distributed through outlets  38  in impeller disk  39 , to polishing pad  12 , through holes  37 . Seal  31  between outer chamber  30  and impeller shaft  19  prevents process fluid from escaping. An annular channel  40 , in outer chamber  30 , can provide a secondary means of introducing process and flushing fluids to polishing pad  12 .  
         [0058]      FIG. 5  is an exploded view that more clearly shows the constituent parts of conditioning apparatus  15  with screw attachment holes  41  securing support disk  34  to impeller blades  33 . Although only four impeller blades  33  are shown in this view, other impeller blade configurations, including non-rotating “BAR”/chamber configurations, will provide the same function as that described in this embodiment.  
         [0059]      FIG. 7  illustrates, in an exploded view, an improved impeller arrangement  80  formed in accordance with the present invention. As shown, impeller arrangement  80  comprises an outer chamber  82 , an impeller assembly  84 , a magnetic disk  86  and a conditioning disk  88 . It is to be understood that the use of a magnetic disk (or, in general, any type of “support” for conditioning disk  88 ) is considered optional, where in the alternative a (thicker) conditioning disk  88  would be coupled to impeller assembly  84  without an intervening support member. Further, the use of an outer vacuum chamber  82  is considered as only one exemplary embodiment of a vacuum supply system. Alternatives coupled directly to the impeller assembly without the need to encase the entire arrangement are possible and considered to fall within the spirit and scope of the present invention.  
         [0060]     As with the arrangements described above, conditioning disk  88  includes a fine diamond grit for mechanically removing waste material from a polishing pad (not shown). An improvement associated with arrangement  80  of the present invention is the use of an innovative impeller assembly  84  for the application of one or more conditioning agent(s) to a polishing pad. Impeller assembly  84  serves to provide spraying apertures for the application of conditioning agent(s) and channels or sections for waste material removal. In accordance with the present invention, the conditioning agent(s) may comprise a slurry of a specific chemistry (to assist in removing contaminants from the polishing pad via a chemical reaction), ultra-pure water (UPW) or air to “flush” contaminants from the conditioning pad, any other suitable fluid or gaseous agent, or any combination thereof.  
         [0061]     Referring to  FIG. 7 , a plurality of impeller blades  90 - 1  through  90 - 6  are shown as attached to an upper holding member  92  of impeller assembly  84 . It is to be understood that this configuration is exemplary only and, in fact, an impeller arrangement of this embodiment of the present invention may include only a single impeller blade. An exemplary impeller blade  90 -n is shown as including a plurality of apertures  94  along its bottom surface  91 , through which the conditioning agent(s) is/are introduced to the system. In the most general case, a single aperture  94  may be formed on bottom surface  91 , where a plurality of such apertures  94  is considered to be preferred for most embodiments. In systems that include a plurality of impeller blades, one or more of the blades may include these apertures  94 . With respect to  FIG. 7 , impeller blade  90 -n includes a channel system  93  formed within impeller blade  90 -n and terminating at each aperture  94 . As discussed above, conditioning agent(s) is/are introduced through an inlet port  83  of outer housing  82 . The conditioning agent then passes through an opening in center member  97  of impeller assembly  84  and is then introduced to each channel system  93 , as shown in  FIG. 7 . The conditioning agent flows along channel  93  and exits impeller assembly  84  at each aperture  94 , for example, as a “spray” of liquid material. The conditioning agent will then pass through apertures  96  in magnetic disk  86 , and apertures  98  in conditioning disk  88  so as to be dispersed across the surface of the polishing pad.  FIG. 8  is a cross-sectional view of the inventive impeller assembly  80 , illustrating in particular the interaction of the various components discussed above to provide for the application of a conditioning agent to a polishing pad. It is an advantage of the present invention that the use of a plurality of apertures  94  on at least one impeller blade  90 -n, coupled with the rotational movement of impeller assembly  84  (as indicated by the arrows in  FIG. 7 ), provides for improved coverage of the conditioning agent on the polishing pad surface, thereby allowing for more contaminant to be removed and for the conditioning process to be more efficient. This rotational movement of impeller assembly  84  is controlled by an abrasive conditioning disk drive motor  81 , as shown. As will be discussed hereinbelow, a torque measurement instrument may be used in conjunction with drive motor  81  to analyze the applied rotational torque and determine parameters such as, but not limited to, the thickness of the polishing pad (i.e., an aging measurement). In one embodiment of the present invention, the temperature of the conditioning agent may be controlled as desired. For example, the temperature of a conditioning slurry may be controlled so as to control the rate of chemical reaction between the polishing pad and the conditioning slurry. Alternatively, the temperature of the conditioning agent may be controlled to reduce the heat created by the conditioning process itself.  
         [0062]     In accordance with one embodiment of the present invention, spent conditioning agent(s), polishing slurry, contaminants, debris, etc. (hereinafter referred to as “effluent”) may be removed using a vacuum process. A plurality of vacuum ports  102  are illustrated in  FIG. 7  as formed around the inner periphery of outer housing  82 . A vacuum coupling  104  is formed on the outer surface of outer housing  82  and coupled to a vacuum source (not shown). Housing  82  includes a vacuum channel  106  within its walls that is coupled to vacuum ports  102  so that as a vacuum is applied at outer port  104 , a vacuum will start to draw through ports  102 , and then through apertures  96  and  98  of magnetic disk  86  and conditioning disk  88 , respectively. Advantageously, the use of the apertured disks  86  and  88  allows for a significant portion of the effluent to be efficiently evacuated through the relatively large number of aligned openings formed in the combination of disks  86 ,  88 . In the particular embodiment as shown in  FIG. 7 , a set of six vacuum regions are formed, with impeller blades  90 - 1  through  90 - 6  serving as barriers between adjacent vacuum regions.  FIG. 9  is a bottom, isometric view of an exemplary conditioning system of the present invention, particularly illustrating the formation of the different vacuum segments, where  FIG. 8  illustrates the path the effluent will traverse above magnetic disk  86 , through vacuum ports  102 , into vacuum channel  106  and thereafter exiting through outer vacuum port  104 .  
         [0063]     In an alternative embodiment, as illustrated in  FIG. 10 , impeller assembly  84  may be configured to include at least one vacuum port  100  formed on bottom surface  91  of at least one blade  90 -n, where in the alternative a plurality of such vacuum ports are included on at least one blade  90 -n. In order to easily remove larger particles of debris and contaminant, vacuum port  100  may have a larger opening than apertures  94  formed on the same blade  90 -n. Referring to  FIG. 10 , vacuum ports  100  are illustrated as coupled to a vacuum channel  101  along the top interior portion of impeller blade  90 -n, such that the effluent from the pad surface may be pulled out through vacuum ports  100 , pass through channel  101 , and thereafter be directed to the same or similar outer vacuum port  104  (as shown in  FIG. 7 ). In accordance with the present invention, the rotation of impeller assembly  84 , coupled with the application of a vacuum through a number of different vacuum ports  100 , allows for a significant amount of effluent to be removed quickly and efficiently.  
         [0064]     It is to be understood that there may be occasions where an impeller arrangement of the present invention is configured only to apply a conditioning agent to a polishing pad (i.e., does not include any vacuum ports or vacuum evacuation system), or configured only to evacuate effluent from the polishing pad surface through the inventive apertured conditioning disk (using any other technique to apply conditioning agents to the polishing pad surface). In either instance, an impeller arrangement of the present invention is configured to include the appropriate apertures/vacuum ports to be used as discussed above.  
         [0065]     Another advantage of the improved impeller arrangement  80  of the present invention is the use of a central locating key  110  for properly aligning magnetic disk  86  and conditioning pad  88  (or only pad  88  in systems without a support disk) with impeller assembly  84 . In the arrangement as illustrated in  FIG. 7 , a central locating key  110  is configured to fit through a central aperture  112  in conditioning disk  88  and then through a central aperture  114  in magnetic disk  86 . Locating key  110  is properly designed such that the disks will be aligned with each other upon joining. In the particular example as illustrated in  FIG. 7 , a hexagonal key is used as the locating key, where the hexagonal shape will prevent the movement of conditioning disk  88  with respect to magnetic disk  86 . The joined components are then attached to the underside of impeller assembly  84 , where a central locking element  116  of impeller assembly  84  functions to align the apertures  96 ,  98  of magnetic disk  86  and conditioning pad  88  with apertures  94  and/or vacuum ports  100  of each impeller blade  90 -n. By virtue of the large number of apertures formed within magnetic disk  86  and conditioning disk  88 , the ease of alignment between the apertures of these components with apertures  94  and/or vacuum ports  100  is enhanced. Referring to  FIG. 7 , a pair of locking pins  120 ,  122  of central locking element  116  extend through the assembled components and are then inserted in mating openings  124 ,  126  formed in central locating key  110 . A screw or other attachment means may be inserted through central opening  130  of central locating key  110  to central locking element  116  to mechanically secure the arrangement.  FIG. 9  also contains a view of this locking arrangement as seen from the bottom of the arrangement. Although a hexagonal locating shape is illustrated in  FIG. 7 , it is to be understood that other geometries may be used in the formation of central locating key  110 , for the purpose of creating a mechanical attachment, properly aligning the tooling of the system and providing for transfer of the drive/rotational force to the conditioning assembly. Moreover, the locking mechanical attachment has been found to prevent misalignment of conditioning disk  88  with respect to gimbaled impeller assembly  84 , thus maintaining an essentially parallel relationship that limits uneven polishing pad wear.  
         [0066]     In one embodiment of the present invention, a pressurized source  128  is coupled to impeller arrangement  80  and used to impart an impulse function to the streams of slurry/conditioning agent being applied to the polishing pad. The use of a megasonic stream will advantageously dislodge contaminants that have become embedded in the top surface, fibers and/or pores of the polishing pad being conditioned. The presence of the vacuum then allows for these dislodged contaminants to be quickly and efficiently removed from the surface of the polishing pad. There exist various arrangements that may be used to provide for the megasonic streams, such as the use of a separate pressurizing element for each impeller blade. Referring to  FIG. 7 , a piezo-electric driver  99  may be included within impeller blade  90 -n to provide sonic energy and excite the flow of the conditioning agent. Alternatively, one pressurizing source (such as element  128 ) may be used to impart an impulse pressurized force for the stream of conditioning agent(s) introduced through the inlet port.  
         [0067]      FIG. 11  illustrates, in a bottom view, an alternative embodiment of impeller assembly  84  of the present invention.  FIG. 12  is a cut-away side view of this embodiment, taken along line  12 - 12  of  FIG. 11 . In this case, impeller blades  90  are replaced by a plurality of separate impeller elements  160 , each element being cylindrical in form (see  FIG. 12 ), including a central aperture  164  for dispensing the conditioning agent(s) surrounded by a cylindrical encasement  166 . As with the embodiments described above, the precise location and size of each impeller element  160  is at the discretion of the system designer. In the embodiment of  FIG. 11 , the plurality of impeller elements  160  are arranged as a set of “spokes”  162 . That is, separate sets of impeller elements  160  are disposed in linear fashion, extending outward from center member  97 , forming spokes  162 - 1  through  162 - 6 . With particular reference to  FIG. 12 , a channel  168  may be formed within upper holding member  92  to provide a path for the conditioning agent(s) to flow and be dispensed through apertures  164  of impeller elements  160 . Therefore, similar to the blade embodiment described above, this arrangement of impeller elements  160  forms a set of six separate segments that will allow for efficient application of the conditioning agent(s) and/or vacuum removal of the effluent. It is to be presumed that the arrangement of impeller elements  160  is controlled to the extent that central apertures  164  will align with apertures  96  and  98  of magnetic disk  86  and conditioning disk  88 , respectively.  
         [0068]      FIG. 13  illustrates an alternative embodiment of impeller assembly  84  that comprises a plurality of separate impeller elements  160  disposed in a more random pattern across the surface of upper holding member  92 . In this case, a different channel configuration would be required to ensure that each impeller element  160  desired to be used to dispense conditioning agent(s) is in contact with a channel. In the particular embodiment of  FIG. 13 , a first set of impeller elements  160 -V may be disposed around the perimeter of upper holding member  92  and coupled to a vacuum channel (similar to channel  101  discussed in association with  FIG. 10 ) to evacuate effluent from the surface of a polishing pad. The remainder of the impeller elements, designated as  160 -C, would then be used to dispense the conditioning agent(s).  
         [0069]     It is to be understood that the various embodiments of the impeller assembly discussed hereinabove are exemplary only, and it is to be understood that various other arrangements for dispensing conditioning agent(s) and/or evacuating effluent are considered to fall within the spirit and scope of the present invention.  
         [0070]     In comparison to prior art conditioning processes and systems, the arrangement of the present invention provides for the conditioning and associated polishing processes to be considerably more efficient. In particular, the inventive arrangement uses significantly less materials (e.g., polishing slurry, cleaning/rinsing agents) to perform the polishing and conditioning operations. Typical wafer polishing processes require the dispensing of anywhere from about 140-250 ml/minute of polishing slurry to provide stable polishing, since a portion of the reacted slurry remains in the sponge-like pores of the pad after each rotation. Using the conditioning arrangement of the present invention, the pores of the polishing pad are thoroughly cleaned of reacted slurry, presenting the pad as a “fresh”, dry sponge for the introduction of the next dispensing of polishing slurry. As a result of the absence of reacted and “new” slurry within the pores of the polishing pad, less slurry is required to perform the same amount of polishing. For example, a polishing flow on the order of 75-100 ml/min has been found acceptable for systems formed in accordance with the present invention. It is to be understood that similar reductions in the amounts and flow rates of various conditioning agents can also be expected.  
         [0071]     The improvement of using a “recharged”, clean pad during each polishing operation may also be analyzed in terms of the amount of material actually removed during the polishing operation (defined as the removal rate and measured in Å/min).  FIG. 14  contains a graph comparing the average thermal oxide removal rate for a conventional prior art conditioning system vs. the conditioning system of the present invention, the graph based on an extended polishing run utilizing a flow rate for the polishing slurry of 100 ml/min. As shown, the average removal rate for the prior art was about 1944 Å/min, compared to a removal rate of 2183 Å/min for an arrangement formed in accordance with the present invention.  FIG. 15  contains a graph of the removal rate (in this case, thermal oxide polishing), as a function of the vacuum level applied to the pad during the conditioning process. In this particular case, a 5-7% increase in removal rate was found for a vacuum in the range of 6″-9″ Hg. Further, the consumption of conditioning agents and/or rinsing water is also reduced, for the same reasons, particularly with respect to the use of a vacuum to draw the effluent through the apertures. Other results, of course, could be possible in other systems.  
         [0072]     As a result of the need to use less conditioning agent and/or rinse agent, and because the effluent is captured from the pad surface and not diluted with other machine wastes, the amount of polished film material (for example, copper) present in the evacuated material is much more concentrated. Therefore, the waste material may preferably be segregated and processed, allowing for a significant amount of the polished film material (i.e., copper) to be reclaimed. Additionally, a chemical analyzer may be included as part of the waste removal system and used to provide in situ determination of the end point of the polishing process. That is, by monitoring the concentration of various components of film material present in the waste stream, the point where a wafer substrate is reached, or where a bulk film layer has been completely removed, can be determined.  
         [0073]     Yet another feature of impeller arrangement  80  of the present invention is the possibility of modifying sealing surface  131  of outer chamber  82  to provide for a dynamic seal between the conditioning apparatus and the polishing pad surface. In this case, outer chamber  82  is attached as a “floating” member to an end effector arm supporting the conditioning apparatus (such as end effector arm  16  of  FIG. 1 ). In one embodiment the “floating” outer chamber may include a solid sealing surface, particularly well-suited for use with grooved polishing pads. When used with perforated polishing pads, this sealing surface may be textured. Advantageously, the use of a vacuum system to remove spent conditioning agent and contaminants allows for a vacuum seal to be created between outer chamber  82  and the polishing pad. This vacuum force, in the embodiment where it is applied in the vacuum regions between adjacent impeller blades, maintains an essentially co-planar interface between conditioning disk  88  and the surface of the polishing pad, where improved co-planarity will allow for improved uniformity of the abrasive pressure and orientation of conditioning disk  88  (e.g., flatness/diamond furrow density/surface profile) and improved uniformity with respect to removal of contaminants from the polishing pad. Moreover, the use of vacuum seal between outer chamber  82  and the polishing pad will reduce the amount of “plowing” that occurs in conventional systems when the gimbaled conditioning apparatus rotates or tilts slightly toward the leading edge in response to sliding contact/friction with the surface of the polishing pad. FIGS.  16 ( a ) and ( b ) contain illustrations of the contact pressure between a conditioning disk and polishing pad surface, where  FIG. 16 ( a ) is associated with a prior art conditioning system and  FIG. 16 ( b ) is associated with a conditioning system formed in accordance with the present invention. These pictures were obtained using a Tekscan force measurement array. A conventional conditioner was mounted on an IPEC 372M CMP tool, and contact force measurements were taken over increasing loads.  FIG. 16 ( a ) clearly illustrates a localized high pressure zone A (i.e., “plowing”) that is associated with the leading radius of the conditioner. The vacuum enhanced conditioning system of the present invention was similarly tested, with a constant mechanical downforce, and increasing vacuum “loads”. The resultant force plot of  FIG. 16 ( b ) clearly illustrates uniform loads (denoted as area “B”) over the entire abrasive surface.  
         [0074]     Additionally, the controlled application of a bi-directional force (i.e., upward force through the effector arm on the conditioning system and downward vacuum applied force), in accordance with the present invention, allows for better control of the resultant force (this resultant force being maintained, for example, between 0 and 50 pounds). In particular, by dynamically controlling the “negative pressure” of the vacuum force, the actual vacuum can be modified as desired to provide for more efficient contaminant removal, as noted above, without creating excessive or additional force on the abrasive that would then lead to undesirable higher polishing pad removal rates.  
         [0075]     In general, the use and control of the bi-directional force allows for closed loop control of the polishing pad removal rate via parameters such as torque, speed, displacement, force, “z” and “x/y” position, etc. The conditioning arm may further include, as part of this closed loop control system, multi-axis force instrumentation that provides for high resolution and dynamic resultant downforce and torsional moment measurements, all used as feedback information to the closed loop system.  FIG. 17  contains a simplified diagram illustrating the use of abrasive torque instrumentation  200 , used to measure the rotational torque of abrasive conditioning disk drive motor  81  as conditioning system  80  is pivoted across the platen radius of a CMP tool, where changes in rotational torque can be directly correlated to changes in polishing pad thickness. The abrasive torque measurement and conditioning pad wear measurement systems may be included in the closed loop system to monitor the “lifetime” of the polishing pad and provide data regarding end of life detection. Typically, polishing pad life is specified/controlled in terms of number of wafers processed. This is often a conservative approximation and does not account for variations such as, for example, break-in, interruptions, abrasive sharpness, wafer film variations, etc. By measuring the actual surface profile and remaining thickness of the polishing pad in situ, a much more accurate end of life control mechanism is obtained. In particular, the torque of the abrasive conditioning disk drive motor  81  may be measured and analyzed with respect to vertical displacement/abrasive wear, resultant downforce (i.e., combination of vacuum-generated force and mechanically-supplied force), rotational speed, and pad sweep position (radius) to determine the Preston constant (K). This measurement of rotational torque on abrasive drive motor  81  is a unique distinction in comparison to the prior art, where the torque measurements are made at the pivot arm (the pivot arm measurements considered as being a less accurate indication of the actual attributes of the abrasive conditioning disk). This analysis of the motor torque then yields the ability to control downforces and speeds in different radial positions across the polishing pad so as to better manage removal rate and overall polishing pad surface planarity.  
         [0076]     The method of providing operation specific slurries  50  of the present invention is shown in the block diagram of  FIG. 6 . Cleaning the polishing pad  51  in process is comprised of at least five operations run in parallel, sequentially or any combination. This operation can be run in-situ or ex-situ, and can support dynamic in-process pH adjustments to control removal rate and/or endpoint selectivity. The polishing pad  12  is subjected to a vibratory motion  52  to remove processing debris of loose slurry, fluids, and gasses  52 A. The static layer that may remain is destabilized  53  with vacuum, water and other chemicals  53 A. The polishing pad surface, pores, and grooves  54  are then cleaned with vacuum, water and chemicals  54 A. A further step involves neutralizing the slurry  55  residue on the pad surface with water and other chemicals  55 A. The final step is flushing  56  to remove cleansing fluids and any remaining debris  56 A. With the conditioning apparatus thoroughly cleaned, other operation specific slurries  57 A,  57 B, and  57 C may be introduced to the process via slurry feed system or at  57  to the conditioning apparatus  10 .