Abstract:
A system for thinning a layer on a substrate without damaging a delicate underlying layer in the substrate. The system includes means for mechanically eroding the layer on the substrate, and means for electropolishing the layer on the substrate. In this manner, portions of the layer that cannot be removed by electropolishing can be removed by the mechanical erosion. However, electropolishing can preferentially be used on some portions of the layer so that unnecessary mechanical stresses can be avoided. Thus, the system imparts less mechanical stress to the substrate during the removal of the layer, and the delicate underlying layer receives less damage during the process, and preferably no damage whatsoever.

Description:
FIELD 
   This invention relates to the field of integrated circuit fabrication. More particularly, this invention relates to thinning the layers that are formed during the fabrication of integrated circuits. 
   BACKGROUND 
   As integrated circuits have become increasingly smaller, electrically conductive structures within the integrated circuits are placed increasingly closer together. This situation tends to enhance the inherent problem of parasitic capacitance between adjacent electrically conductive structures. Thus, new electrically insulating materials have been devised for use between electrically conductive structures, to reduce such capacitance problems. The new electrically insulating materials typically have lower dielectric constants, and thus are generally referred to as low k materials. While low k materials help to resolve the capacitance problems described above, they unfortunately tend to introduce new challenges. 
   Low k materials are typically filled with small voids that help reduce the material&#39;s effective dielectric constant. Thus, there is less of the material itself within a given volume, which tends to reduce the structural strength of the material. The resulting porous and brittle nature of such low k materials presents new challenges in both the fabrication and packaging processes. Unless special precautions are taken, the robustness and reliability of an integrated circuit that is fabricated with low k materials may be reduced from that of an integrated circuit that is fabricated with traditional materials, because low k materials differ from traditional materials in properties such as thermal coefficient of expansion, moisture absorption, adhesion to adjacent layers, mechanical strength, and thermal conductivity. 
   Low k materials are typically more brittle and have a lower breaking point than other materials. One reason for this is the porosity of the low k material, where a significant percentage of its physical volume is filled with voids. Thus, integrated circuits containing low k materials are inherently more prone to breaking or cracking during processes where physical contact is made with the integrated circuit surface, such as wire bonding and electrical probing, or processes that cause bending stresses such as mold curing, underfill curing, solder ball reflow, chemical mechanical polishing, or temperature cycling. 
   As integrated circuits have become smaller, they have shrunk not only in the amount of surface area required by the circuit, but also in the thicknesses of the various layers by which they are formed. As the thicknesses of the layers has decreased, it has become increasingly important to planarize a given layer prior to forming a subsequent overlying layer. One of the methods used for such planarization is called chemical mechanical polishing. During chemical mechanical polishing, the surface of the layer to be planarized, thinned, or both is brought into contact with the surface of a polishing pad. The pad and the substrate are rotated and translated relative to each other in the presence of a polishing fluid, which typically contains both physical erosion particles and chemical erosion compounds. 
   Unfortunately, the need to planarize the layers of an integrated circuit using traditional chemical mechanical polishing has become a problem, because the amount of down force and friction required to adequately erode a layer using chemical mechanical polishing has become great enough to crush, shear, or otherwise damage the increasingly delicate underlying low k layers as they are reduced in thickness with the general reduction in the size of integrated circuits. 
   For example, in copper dual damascene processing, there is a step to remove unwanted portions of a deposited copper layer from an upper surface of an integrated circuit. New integrated circuit designs place delicate low k layers somewhere beneath the copper layer to be removed. Traditional chemical mechanical polishing processes tend to be too rough during the removal of the copper layer, and damage the low k layer. Electropolishing is a more gentle method than chemical mechanical polishing, and has also been used to remove electrically conductive layers, such as copper. However, electropolishing tends to be unable to break through the oxidation on the surface of the copper layer, and thus is also inadequate for removing the copper layer. In addition, electropolishing also tends to not be able to remove the barrier layer and seed layer that often underlie the copper layer. 
   There is a need, therefore, for a new system for use in integrated circuit fabrication, which helps to alleviate one or more of the challenges mentioned above, and enables layers within an integrated circuit to be planarized or otherwise removed without damaging delicate underlying layers. 
   SUMMARY 
   The above and other needs are met by a system for thinning a layer on a substrate without damaging a delicate underlying layer in the substrate. The system includes means for mechanically eroding the layer on the substrate, and means for electropolishing the layer on the substrate. 
   In This manner, portions of the layer that cannot be removed by electropolishing can be removed by the mechanical erosion. However, electropolishing can preferentially be used on some portions of the layer so that unnecessary mechanical stresses can be avoided. Thus, the system imparts less mechanical stress to the substrate during the removal of the layer, and the delicate underlying layer receives less damage during the process, and preferably no damage whatsoever. 
   In various embodiments, the means for mechanically eroding the layer and the means for electropolishing the layer are configured to operate simultaneously. Preferably, the means for mechanically eroding the layer includes any one or combination of a rotating polishing pad, a rotating brush, and a spray nozzle adapted to direct a spray of a solution towards the layer. The means for electropolishing the layer preferably includes means for establishing a voltage potential through an electrically conductive liquid between the layer on the substrate and the means for mechanically eroding the layer. 
   According to another aspect of the invention there is described a system for thinning a layer on a substrate without damaging a delicate underlying layer in the substrate. An electropolishing pad mechanically erodes the layer on the substrate. A power supply establishes a voltage potential through a bath of an electrically conductive liquid between the layer on the substrate and the electropolishing pad. 
   In various embodiments of this aspect of the invention, the voltage potential has a range of between about one tenth of one volt and about one hundred volts. In some embodiments the system also includes a brush for mechanically eroding the layer on the substrate, and a spray nozzle adapted to direct a spray of the electrically conductive liquid towards the layer. 
   According to another aspect of the invention there is described a method for thinning a layer on a substrate without damaging a delicate underlying layer in the substrate, where a first portion of the layer is mechanically eroded, and a second portion of the layer is electropolished. 
   In various embodiments of this aspect of the invention, the first portion of the layer is one or both of an overlying oxidized portion of the layer and an underlying portion of the layer that is formed of a material that cannot be removed by electropolishing. The second portion of the layer preferably includes a metal, and is most preferably copper. In one embodiment, the first portion of the layer is electropolished simultaneously with the mechanical erosion, and in another embodiment the second portion of the layer is mechanically eroded simultaneously with the electropolishing. Preferably, the layer includes a first electrically conductive layer, an underlying non electrically conductive barrier layer, and an intervening electrically conductive seed layer. The delicate underlying layer is preferably formed of a low k material. In one embodiment, the first portion of the layer is thinned to a relatively greater extent by mechanical erosion and is thinned to a relatively lesser extent by electropolishing, and the second portion of the layer is thinned to a relatively greater extent by electropolishing and is thinned to a relatively lesser extent by mechanical erosion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
       FIG. 1  is a functional block diagram of a chemical mechanical electropolishing system according to a preferred embodiment of the present invention. 
       FIG. 2  is a cross sectional view of a portion of an integrated circuit on a substrate, depicting the layers to be removed, and the delicate underlying layer. 
       FIG. 3  is a cross sectional view of a portion of an integrated circuit on a substrate, depicting the delicate underlying layer and the structure that is formed after the layers have been removed. 
       FIG. 4  is a flow chart of a first embodiment of a method of processing a substrate with a system according to the present invention. 
       FIG. 5  is a flow chart of a second embodiment of a method of processing a substrate with a system according to the present invention. 
   

   DETAILED DESCRIPTION 
   With reference now to  FIG. 1 , there is depicted a functional block diagram of a chemical mechanical electropolishing system  10  according to a preferred embodiment of the invention. The system  10  differs in many important aspects from either a traditional chemical mechanical polishing system or an electropolishing system, which differing aspects enable the chemical mechanical electropolishing, or CME, system  10  to thin or remove layers, such as a copper layer, without damaging delicate underlying layers, such as low k layers. The system  10  is also capable of removing additional layers, such as barrier layers and seed layers, which often underlie the main layer to be remove. 
   The system  10  is used for processing a substrate  12  on which integrated circuits are formed. The substrate  12  is preferably formed of a semiconducting material, such as of group IV materials like silicon, germanium, or silicon germanium, or group III-V materials such as gallium arsenide. However, in other embodiments the substrate  12  is an insulating substrate, such as alumina, sapphire, or glass.  FIG. 2  is a cross sectional view of a portion of an integrated circuit including the substrate  12 . A structure  44  has been formed in a layer  36  of the substrate  12 , which layer  36  may be a low k layer, or a layer of another material which is delicate and easily damaged, as generally described above. 
   The layer  36 , in the example depicted in  FIG. 2 , is overlaid with a barrier layer  38 , a seed layer  40 , and a conductive layer  42 , such as a copper layer. As can be seen, the barrier layer  38  and the seed layer  40  line the surfaces of the structure  44 , and the conductive layer  42  fills the structure  44 . However, it is desired to remove the layers  38 ,  40 , and  42  from the upper surfaces of the layer  36 , to produce the structure  44  as depicted in FIG.  3 . It is this process of removing those upper portions of the layers  38 ,  40 , and  42  where prior processing methods have proven to be inadequate, either by not completely removing the layers, or by damaging the delicate layer  36  in the process of such removal. The system  10  as depicted in  FIG. 1  is adapted to remove the layers  38 ,  40 , and  42 , while reducing and preferably eliminating these problems.  FIGS. 2 and 3  depict a single damascene structure. However, it is appreciated that the embodiments of the invention as described herein are equally applicable to dual damascene and other structures. 
   The substrate  12  is preferably retained by a carrier  16 , which most preferably provides a rigid support across the entire back surface of the substrate  12 . Thus, the front surface of the substrate  12 , or in other words the surface of the substrate  12  on which the layers  38 ,  40 , and  42  are formed as depicted in  FIG. 2 , is presented for processing by the system  10 . A method for making an electrical contact with the front surface of the substrate  12  is established but not shown. This contact is necessary for the electropolishing process to occur. The front surface of the substrate  12  is preferably applied against an electropolishing pad  14  during at least a portion of the processing. The electropolishing pad  14  is preferably different in many respects from a standard polishing pad that is used in tradition chemical mechanical polishing. 
   For example, the electropolishing pad  14  is preferably formed of a material that is similar to a standard polishing pad, with a conductive filler added. By reducing down force, less friction is developed between the electropolishing pad  14  and the substrate  12 . By reducing the friction between the electropolishing pad  14  and the substrate  12  in this manner, there is less shearing force developed in the delicate layer  36 , which tends to reduce the amount of damage sustained by the layer  36  during processing. 
   Most preferably, the substrate  12  is applied against the electropolishing pad  14  with a force that is reduced from that which is traditionally used for chemical mechanical polishing. By reducing the down force applied between the substrate  12  and the electropolishing pad  14 , two benefits are realized. First, the friction is reduced between the substrate  12  and the electropolishing pad  14 , which reduces the shearing force in the layer  36 , and thereby reduces the amount of damage to the layer  36 , as described above. Second, the crushing force applied to the layer  36  is also reduced, which further reduces the amount of damage sustained by the layer  36  during the process. In addition, reducing the amount of down force used during processing of the substrate  12  tends to reduce the amount of dishing and erosion that occurs within the structure  44 . 
   In a standard chemical mechanical polishing process, the amount of down force applied between the polishing pad and the substrate is between about four pounds per square inch and about nine pounds per square inch. In the preferred embodiments of the present invention, the down force between the electropolishing pad  14  and the substrate  12  is reduced to be less than about four pounds per square inch, and in a most preferred embodiment is about one and one half pounds per square inch. 
   In addition, the electropolishing pad  14  is preferably electrically conductive. In this manner, an electrical potential can be applied through the electropolishing pad  14 , such as by using the electropolishing pad  14  as an electrode, in a manner that is described in more detail hereafter. Further, in one embodiment of the invention, the electropolishing pad  14  is fabricated to have a presented surface area that is smaller than the surface area of the substrate  12  that is presented for processing. One example of this is an electropolishing pad  14  that is circular, and which has a smaller diameter than the generally circular substrate  12  with which it is used. In some embodiments the processing surface area of the electropolishing pad  14  is between about twenty percent and about fifty percent of the processing surface area of the substrate  12 . However, a standard size electropolishing pad  14  could also be used. A typical chemical mechanical polishing pad has a processing surface area that ranges from about twenty-five percent larger than the processed surface area of the substrate  12 , to about fifteen times the surface area of the substrate  12 . Thus, a typical chemical mechanical polishing pad is usually much larger than the surface of the substrate  12  that it is used to process. 
   However, by reducing the surface area of the electropolishing pad  14  to be less than the surface area of the substrate  12  which it is used to process, the total amount of friction generated between the electropolishing pad  14  and the substrate  12  is reduced. As described above, this further reduction in the amount of friction generated between the electropolishing pad  14  and the substrate  12  tends to reduce the amount of shearing force that is generated within the layer  36 , and thus tends to reduce the amount of damage that is sustained by the layer  36  during processing in the system  10 . 
   The electropolishing pad  14  is preferably mechanically connected to a motion controller  24 , such as by a spindle  22  or other means. In this manner the motion controller  24  enables the electropolishing pad  14  to be moved in a variety of ways. For example, the electropolishing pad  14  can be oscillated, such as in an X or Y direction, or a combination of the two, or along other nonrectilinear axes. Further, the electropolishing pad  14  can be rotated, such as around the spindle  22 . In addition, the entire electropolishing pad  14  can be moved in an orbital motion, such as by translating the spindle  22  around the circumference of a circle, or along an irregular path, or along paths that change according to either a regular or a pseudorandom pattern. The electropolishing pad  14  can also be caused to vibrate, such as with an ultrasonic motion or other high speed motion. In this manner, the electropolishing pad  14  is preferably moved across the surface of the substrate  12  in an even manner, so that the removal of the layers  38 ,  40 , and  42  is accomplished uniformly across the surface of the substrate  12 . 
   The substrate  12  is also preferably moved relative to the electropolishing pad  14 , such as by engagement with a spindle  18  between the carrier  16  and a motion controller  20 . The substrate  12  can preferably be moved in all of the same ways as those described above in regard to the electropolishing pad  14 . For example, the substrate  12  can preferably be oscillated, such as in an X or Y direction, or a combination of the two, or along other nonrectilinear axes. Further, the substrate  12  can be rotated, such as around the spindle  18 . In addition, the entire substrate  12  can be moved in an orbital motion, such as by translating the spindle  18  around the circumference of a circle, or along an irregular path, or along paths that change according to either a regular or a pseudorandom pattern. The substrate  12  can also be caused to vibrate, such as with an ultrasonic motion or other high speed motion. 
   Most preferably there is some amount of relative motion that is produced by the substrate  12 &#39;s motion controller  20 , and some amount of relative motion that is produced by the electropolishing pad  14 &#39;s motion controller  24 . However, it is appreciated that in various embodiments it is possible to produce the relative motion using only one of the motion controller  20  and the motion controller  24 , in which case the other motion controller could be omitted from the system  10  design. In a most preferred embodiment, a different motion set is produced by each of the motion controllers  20  and  24 . For example, the motion controller  20  could cause the substrate  12  to rotate around the axis of the spindle  18  or other connection means, while the motional controller  24  causes the electropolishing pad  14  to rotate about the spindle  22  and orbit across the entire surface area of the substrate  12 . Other such combinations of relative motion are also comprehended herein. 
   In a most preferred embodiment, at least one component of the relative motion between the substrate  12  and electropolishing pad  14  is at a speed that is dramatically greater from that which is traditionally used for chemical mechanical polishing. One purpose for this is to increase the rate at which material is removed from the surface of the substrate  12 . Without being bound by theory, the rate of material removal is generally proportional to the force exerted or the friction generated between the substrate  12  and electropolishing pad  14 , and the relative speed of motion between the surfaces of the substrate  12  and the electropolishing pad  14 . As the force and friction between the substrate  12  and the electropolishing pad  14  are generally reduced when processed on the system  10  as described herein, the rate of material removal is preferably enhanced or otherwise compensated for by increasing the speed of relative motion. Most preferably, the electropolishing pad  14  is rotated at a speed of between about one hundred rotations per minute and about six hundred rotations per minute. Smaller diameter electropolishing pads  14  are most preferably rotated at the higher speed and larger diameter electropolishing pads  14  are most preferably rotated at the lower speed. 
   The substrate  12  and the electropolishing pad  14  are preferably brought into contact in the presence of an abrasive electrolyte  26  that is held by the system  10 , such as within a bath  28 . In other embodiments the abrasive electrolyte  26  may also be introduced by a spray or stream, as described in more detail hereafter. The abrasive electrolyte  26  is different from a standard chemical mechanical polishing solution or rouge in a variety of important respects. For example, the abrasive electrolyte  26  is designed to be both electrically conductive and mechanically abrasive. The abrasive electrolyte  26  may also be chemically abrasive to some degree. 
   Although some chemical mechanical polishing solutions may be water based, or based on some other electrically conductive fluid, the abrasive electrolyte  26  is different from these solutions, in that it does not contain impurities which prohibit or otherwise inhibit or degrade an electrolytic oxidation or other removal of the electrically conductive layer  42 , which is most preferably copper. Typical polishing solutions are filled with materials that would tend to plate out or otherwise degrade such a reaction. However, the abrasive electrolyte  26  is preferably free of such materials, and other materials which would tend to oxidize, reduce, or otherwise react at the voltage potentials desired for the oxidation reaction that can be used to help remove the conductive layer  42 . 
   Further, the abrasive electrolyte  26  preferably includes abrasive particles. The abrasive particles are preferably inert to the other reactions, both electrical and chemical, which may be occurring within the bath  28 . Most preferably, the abrasive particles have a size of between about fifty nanometers and about two hundred and fifty nanometers in average diameter. Thus, the abrasive particles within the abrasive electrolyte  26  are preferably similar to the abrasive particles found within a slurry used for chemical mechanical polishing. 
   Further, in a preferred embodiment, both the substrate  12  and the electropolishing pad  14  are entirely contained within the bath  28  of the abrasive electrolyte  26 . In this manner an electrical potential can preferably be established between the substrate  12 , such as by way of the carrier  16 , and the electropolishing pad  14 , such as by way of the spindle  22  or other backing element. Thus, the substrate  12  and the electropolishing pad  14  are preferably used as electrodes during at least a portion of the processing of the substrate  12 , and the abrasive electrolyte  26  acts as the current carrying medium between the electrode substrate  26  and the electrode electropolishing pad  14 . 
   It is appreciated that the electrical potential applied between the substrate  12  and the electropolishing pad  14  can be sustained without there being a complete bath  28  of the abrasive electrolyte  26 . Thus, in other embodiments there is some amount of the abrasive electrolyte  26  introduced between the substrate  12  and the electropolishing pad  14 , but not an amount sufficient to immerse both the substrate  12  and the electropolishing pad  14 . However, in the most preferred embodiment the substrate  12  and the electropolishing pad  14  are both substantially immersed in the abrasive electrolyte  26  during at least a portion of the processing, such as when an electrical potential is applied between the two. 
   The entire operation of the system  10  is preferably controlled by a controller  30 , which may be remotely located, but is preferably local to the rest of the system  10 . The controller  30  preferably controls parameters such as, but not limited to, the pressure or down force between the substrate  12  and either the brush  46  or the electropolishing pad  14 , the pressure of the spray  48 , the speed and type of the relative motion between the substrate  12  and any one of the electropolishing pad  14 , the brush  46 , and the spray  48 , the electrical potential between the substrate  12  and either the electropolishing pad  14  or the brush  46 , and which of the electropolishing pad  14 , brush  46 , and spray  48  to use at any given time, if any, and for how long. 
   Input such as for the programming of the system  10  is preferably received through an input  32 , which may include such devices as a keyboard, a pointing device such as a mouse or joystick, and a network interface such as can be used for receiving programming and other instructions across a computer network. Most preferably the system  10  also includes a display  34  of some type, upon which information in regard to the programming, processing, and progress of the system  10  can be presented. 
   There are many modes in which the system  10  can operate, which modes preferably depend at least in part upon the materials, thicknesses, and other properties of the layers such as  38 ,  40 , and  42  that are to be removed from the surface of the substrate  12 , and the nature of the underlying delicate layers, such as  36 . Thus, any specific embodiments described herein are not intended to be limitations on all possible embodiments of the system  10  or its use. 
   For example, in the case where the conductive layer  42  is a copper layer, and the underlying layer  36  is a delicate low k layer, there are many challenges to be overcome, as described above. The system  10  overcomes these challenges by way of its unique capabilities. For example, to remove the oxide that tends to form on the surface of the copper layer  42 , and which tends to inhibit the use of electropolishing, the electropolishing pad  14  can be brought into contact with the surface of the substrate  12  for a period of time and with a down force that is just sufficient to remove the oxidation. At that point in time, the down force between the substrate  12  and the electropolishing pad  14  can be reduced, or the contact between the substrate  12  and the electropolishing pad  14  can be removed altogether. 
   Then a potential can be applied between the substrate  12  and the electropolishing pad  14 , so that the copper conductive layer  42  is removed by an oxidation or other reaction, such as etching by an acidic abrasive electrolyte. When the copper conductive layer  42  is substantially removed, the electropolishing pad  14  can again be brought in to contact with the substrate  12 , or the down force between the electropolishing pad  14  and the substrate  12  can be increased. In this manner, any remaining portions of the seed layer  40 , and the barrier layer  38 , which is typically formed of a nonconductive material, can be removed, yielding the structure  44  as depicted in FIG.  3 . 
   It is appreciated that there are many permutations and combinations of steps such as those described in the specific example above, which can be used to planarize or otherwise remove various layers from the surface of the substrate  12  while reducing or eliminating the damage to the delicate underlying layers, such as layer  36 . The system  10  tends to reduce such damage by reducing the amount of down force that is required for processing, and reducing the friction between the substrate  12  and the electropolishing pad  14 . Further, the system  10  makes use of electrochemical processing to erode the electrically conductive layers, thus further reducing or eliminating the need for contact between the substrate  12  and the electropolishing pad  14 , which further preserves the integrity of the delicate layers such as layer  36 . 
   In alternate embodiments of the system  10 , a brush  46  is used either in addition to or in place of the electropolishing pad  14 . For example, the brush  46  may replace the electropolishing pad  14 . Alternately, either the electropolishing pad  14  can be moved away from the substrate  12  to allow room for the brush  46  to be used, or the substrate  12  can be moved away from the electropolishing pad  14  to be adjacent the brush  46 . The brush  46  may be able to better remove specific layers, or better remove layers from different structures of the integrated circuit than the electropolishing pad  14 . For example, a brush  46 , because of its generally reduced amount of surface contact, relative to the electropolishing pad  14 , will tend to induce lesser forces within the substrate  12 . The brush  46  may be one or more of a rolling brush or a rotating brush, or may have some other type of relative motion, produced by a motion controller  50  for example, such as is described above in regard to the motion of the substrate  12  and the electropolishing pad  14 . 
   Similarly, a spray  48  may also be used, either in some combination with the electropolishing pad  14  and the brush  46 , or as a replace for one or both of the electropolishing pad  14  and the brush  46 . For example, the electropolishing pad  14  or the brush  46  can be moved away from the substrate  12  to allow room for the spray  48  to be used, or the substrate  12  can be moved away from the electropolishing pad  14  or the brush  46  to be adjacent the spray  48 . The spray  48  preferably sprays the abrasive electrolyte  26  against the surface of the substrate  12 . In preferred embodiments, the level of the bath  28  is reduced when the spray  48  is used, so that the bath  28  of the abrasive electrolyte  26  does not impede the force of the spray  48 . 
   The spray  48  may also take one or more of a variety of different forms. For example, the spray  48  may be pulsated, such as with an ultrasonic or other frequency. Further, the spray  48  may be oscillated, spun, or otherwise moved relative to the surface of the substrate  12 , such as with one or more of the motions described above in regard to the substrate  12  and the electropolishing pad  14 . In addition, the spray  48  may be a single jet or multiple jets, and may in different embodiments be directed from a single angle toward the substrate  12 , an adjustable or varying angle, or from a variety of simultaneous angles. The spray  48  may also have some other type of relative motion, produced by a motion controller  52  for example, such as is described above. 
   In some embodiments, the use of the spray  48  or the brush  46  may be preferred over the use of the electropolishing pad  14  at different points during the processing of the substrate  12 . For example, the spray  48  or brush  46  could be used during removal of a surface oxidation from the conductive layer  42 , or during the removal of one or both of the seed layer  40  and the barrier layer  38 , or even to increase the rate of material removal during the electropolishing of the conductive layer  42 , in a manner that is more gentle than the application of the electropolishing pad  14 . 
   In other embodiments, all three of the electropolishing pad  14 , the brush  46 , and the spray  48  are used during the processing of the substrate  12 . For example, the spray  48  may be used simultaneously with either the electropolishing pad  14  or the brush  46 . Alternately, the electropolishing pad  14 , the brush  46 , and the spray  48  can be separately used at different points in the processing of the substrate  12 , such as when the particular attributes of a given one of the electropolishing pad  14 , the brush  46 , and the spray  48  are most suitable for removal of a given portion of the layers  38 ,  40 , and  42 , such as removing an oxide from the surface, removing the conductive layer  42 , removing one or both of the seed layer  40  and the barrier layer  38 , or cleaning off the surface of the layer  36  to ensure than no remaining traces of the removed materials are left behind. In this embodiment, all three of the electropolishing pad  14 , the brush  46 , and the spray  48  are present in the system  10 . 
     FIGS. 4 and 5  depict flow charts for two additional possible processing flows  60  and  80 , which are presented by way of example. In  FIG. 4 , process  60  starts when a substrate  12  is presented for processing on the system  10 , as given in block  62 . The substrate  12  is initially processed with the electropolishing pad  14  and with the potential applied, as given in block  64 . The substrate  12  may be inspected periodically, as given in block  66 , to determine whether the desired amount of processing has been performed. If not, then processing of the substrate  12  is continued as given in block  64 . If so, then processing of the substrate  12  is completed by one or more of the other methods, such as given in block  68 . The completed substrate  12  is delivered for further processing, as given in block  70 , when all of the processing on system  10  has been completed. 
   Similarly, in  FIG. 5 , process  80  starts when a substrate  12  is presented for processing on the system  10 , as given in block  82 . The substrate  12  is initially processed with the electrolytic reaction between the substrate  12  and some other electrode, such as either the brush  46  or the electropolishing pad  14 , as given in block  84 , in which the abrasive electrolyte  26  is used as the conducting medium. The substrate  12  may be inspected periodically, as given in block  86 , to determine whether the desired amount of processing has been performed. If not, then processing of the substrate  12  is continued as given in block  84 . If so, then processing of the substrate  12  is completed by one or more of the other methods, such as given in block  88 . The completed substrate  12  is delivered for further processing, as given in block  90 , when all of the processing on system  10  has been completed. 
   The foregoing description of preferred embodiments for this invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.