Abstract:
The present invention provides a novel system, apparatus, and method to deposit conductive films on a workpiece. A system for electroplating a surface of a workpiece using a process solution is disclosed. The system comprises a solution housing configured to house an electrode and to contain the process solution, a filter element disposed in the solution housing configured to partition the solution housing into a lower chamber and an upper chamber, and an upper inlet port coupled to the solution housing configured to deliver the process solution to the upper chamber of the solution housing to fill the upper chamber and the lower chamber immersing the electrode in the lower chamber.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority to Provisional Application Ser. No. 60/429,083 filed Nov. 26, 2002. This application is a continuation in part of: U.S. patent application Ser. No. 09/845,262, filed May 1, 2001 which is a continuation in part of U.S. Pat. No. 6,478,936; and U.S. application Ser. No. 09/760,757, filed Jan. 17, 2001, all incorporated herein by reference. 
     
    
     FIELD  
       [0002]     This invention relates to an apparatus and a method to deposit conductive films on a workpiece, or to electropolish such conductive films off such a workpiece.  
       BACKGROUND  
       [0003]     Multi-level integrated circuit manufacturing involves metal and insulator film depositions followed by photoresist patterning and material removal steps, all carried out on a workpiece surface such as a wafer surface. Photolithography and etching steps provide many features on the wafer surface such as vias, lines and bond pads. In order to form the interconnect structure, these features need to be filled with a conductive material such as copper. Next, the excess copper, also called overburden, needs to be removed by a technique such as chemical mechanical polishing or electropolishing. These techniques, after the excess material removal step, need to provide a planar wafer surface topography, making it ready again for the next level of processing, which again may involve deposition, photolithographic step and a material removal step. It is most preferred that the substrate surface be flat before the photolithographic step so that proper focusing and level-to-level registration or alignment can be achieved. Therefore, after each deposition step that yields a non-planar surface on the wafer, there is often a step of surface planarization.  
         [0004]     Electrodeposition is a widely accepted technique used in IC manufacturing for the deposition of a highly conductive material such as copper (Cu) into the features such as vias and channels opened in an insulating layer on the semiconductor wafer surface. Electrodeposition is commonly carried out cathodically in a specially formulated electrolyte solution containing copper ions as well as additives such as accelerators, suppressors and levelers. These additives along with others such as Cl −  ions control the texture, morphology and plating behavior of the copper layer. A proper electrical contact is made to the seed layer on the wafer surface, typically along the circumference of the round wafer. A consumable Cu or inert anode plate is placed in the electrolyte solution. Deposition of Cu on the wafer surface can then be initiated when a cathodic potential is applied to the wafer surface with respect to an anode, i.e., when a negative voltage is applied to the wafer surface with respect to an anode plate.  
         [0005]     Standard plating techniques provide bottom-up material growth in submicron size features and to some extent in features with widths up to about 2-3 microns. For larger features standard electroplating yields conformal deposits. Therefore, the resulting copper layer surface display the same topography as the wafer surface at locations where the feature widths are larger than a few microns. Standard plating approaches also deposit large overburden copper that later needs to be removed by techniques such as CMP.  
         [0006]     The importance of overcoming the various deficiencies of the conventional electrodeposition techniques is evidenced by technological developments directed to the deposition of planar copper layers. For example, U.S. Pat. No. 6,176,992, entitled Method and Apparatus for Electrochemical Mechanical Deposition, commonly owned by the assignee of the present invention, describes in one aspect an electrochemical mechanical deposition technique (ECMD) that achieves deposition of the conductive material into the cavities on the substrate surface while minimizing deposition on the field regions by polishing the field regions with a pad, as the conductive material is deposited, thus yielding planar copper deposits. U.S. Pat. No. 6,482,307 entitled Method and Apparatus for Making Electrical Contact to Wafer Surface for Full-Face Electroplating or Electropolishing, filed on Dec. 14, 2000, describes in one aspect a technique for providing full-face electroplating or electropolishing. U.S. application Ser. No. 09/760,757, entitled Method and Apparatus for Electrodeposition of Uniform Film with Minimal Edge Exclusion on Substrate, filed on Jan. 17, 2001, describes in one aspect a technique for forming a flat conductive layer on a semiconductor wafer surface without losing space on the surface for electrical contacts.  
         [0007]     In such above-mentioned processes, a pad or a mask, which may also be collectively referred to as workpiece surface influencing devices, can be used during at least a portion of the electrodeposition process when there is physical contact between the workpiece surface and the pad or the mask. The physical contact or the external influence by the pad or the mask affects the growth of the metal by reducing the growth rate on the top surface while effectively increasing the growth rate within the features. This aspect is described in U.S. patent application Ser. No. 09/740,701, entitled Plating Method and Apparatus that creates a Differential Between Additive Disposed on a Top Surface and Cavity Surface of a Work Piece Using an External Influence, filed Dec. 18, 2000.  
         [0008]     A general depiction of a plating apparatus in which improved anode assemblies such as those of the present invention can be used is shown in  FIG. 2 . The carrier head  10  holds a round semiconductor wafer  16  and, at the same time, provides rotation and lateral motion to the wafer. Electrical contacts  7  are made to the conductive lower surface of the wafer. The head can be rotated about a first axis  10   b . The head can also be moved in the x direction represented in  FIG. 2 . An arrangement, which provides movement in the z direction is also provided for the head.  
         [0009]     A pad  8  is provided on top of an anode assembly  9  across from the wafer surface. The pad  8  may have designs or structures such as those forming the subject matter of U.S. Pat. No. 6,413,388, entitled Pad Designs and Structures for a Versatile Materials Processing Apparatus. U.S. Pat. No. 6,413,403 entitled Pad Designs and Structures with Improved Fluid Distribution. Further, U.S. Application with Ser. No. 09/960,236 filed on Sep. 20, 2001, entitled Mask Plate Design, discloses various WSID embodiments. Further, U.S. Application with Ser. No. 10/155,828 filed on May 23, 2002, entitled Low Force Electrochemical Mechanical Deposition Method and Apparatus, discloses a WSID structure having a flexible and abrasive top layer attached on a highly compressible layer. Both applications are assigned to the assignee of the present invention.  
         [0010]     In a metal deposition process using a soluble anode, it is necessary to minimize contamination of the deposited metal with anode sludge or anode fines. Typically, an anode bag is wrapped around the soluble anode to minimize this sort of contamination. In a conventional copper electrodeposition process, as shown in  FIG. 1 , an anode bag or filter  150  is wrapped around an anode  152 . A suitable space separates the anode  152  from the cathode  154  in the deposition cell  156 . Agitation, re-circulation or even filtration of the electrolyte solution  160  may be provided. During routine plating operations, anode sludge builds up in the anode sludge cavity  158  formed by the space between the anode  152  and the bag  150 . In the case of Cu plating, excessive anode sludge build-up affects the quality of the deposited metal on the cathode  154  in an adverse manner. In particular, the uniformity of the deposited metal becomes poorer because of changes in the electric field distribution. In addition, the plating voltage increases because of anode polarization. The copper ions are unable to diffuse fast enough through the sludge layer to meet the requirements of the cathode. Moreover, the resulting loss in plating efficiency may cause hydrogen to be plated, or evolve at the cathode. For routine maintenance, the anode  152  is removed from the deposition cell  156  and cleaned or de-sludged before replacement.  
         [0011]     Another concern in electrodeposition of electronic materials such as copper deposition for interconnects is the cost. The copper deposition electrolytes such as the sulfate based solutions marketed by companies such as SHIPLEY and ENTHONE need to contain organic additives for best results on wafers. These additives are costly and their depletion from the electrolyte bath needs to be minimized. Accelerators are especially prone to breakdown, although suppressors and levelers also get consumed. There are various mechanisms for organic additive consumption or breakdown in a plating system. The first mechanism is idle flow. In other words, additives may breakdown by just flowing or re-circulating within the system, especially if they are allowed to make physical contact with active surfaces. Active surfaces include but are not limited to metallic surfaces, and even the copper anode itself. Typically, plating systems have a solution tank that has some dosing means for the additives. The additives are dosed into the solution in the solution tank and the dosed solution with additives is pumped into filters and then to the electrodeposition module or modules for processing wafers. Solution from the processing modules is then sent back into the tank, also usually after filtering. This way the solution is continually re-circulated and filtered. During the circulation, additives may break down even if no wafer plating takes place in the process modules.  
         [0012]     Another mechanism of additive consumption or breakdown takes place during plating when voltage is applied between the Cu electrode and the wafer surface and there is a plating current passing through the plating circuit. Taking into account the two mechanisms described above we can generally state that additive consumption is a function of the solution flow rate and the charge passed through the solution although there may be other dependences such as temperature and concentration effects.  
         [0013]     Reduction of additive consumption is of utmost importance in the interconnect technology not only because these materials are costly, but also because their breakdown products accumulate in the solution and eventually start affecting the quality of the plated copper in a negative way, e.g. start to negatively impact gap-fill capability of the solution. To replenish the bath with fresh solution and to keep the concentration of additive breakdown products under control, a bleed-and-feed approach is commonly used. During bleed-and-feed, some used solution is bled or discarded and approximately the same amount of fresh solution is fed into the tank. The bled solution may optionally be cleaned and re-used later. In any case, using bleed-and-feed keeps accumulation of additive breakdown products under control. During bleed-and-feed, five to twenty percent of the total solution may have to be replaced on a daily basis. It should be appreciated that if the breakdown rate of additives could be minimized, not only the additive usage would be reduced but also the amount of fresh solution used for bleed-and-feed would be minimized. Either way, sizable cost savings and more stable process results can be achieved if additive consumption is minimized.  
         [0014]     Several designs of anode assemblies have been disclosed. U.S. Pat. No. 6,261,433 describes an anode for copper plating, where copper electrolyte is pumped through copper particles, which are encased in a porous enclosure. U.S. Pat. No. 6,365,017 describes a plating apparatus comprising an ion exchange film or neutral porous diaphragm dividing the plating bath into a substrate region and anode region. Circulation means are provided to circulate the solution in both regions. U.S. Pat. No. 6,126,798 provides an anode including an anode cup, a filter and ion source material, the anode cup and filter forming an enclosure in which the ion source material is located. U.S. patent application Ser. No. 09/845,262, entitled, Anode Designs for Planar Metal Deposits with Enhanced Electrolyte Solution Blending and Process of Supplying Electrolyte Solution Using Such Designs, filed May 1, 2001 discloses a design that includes two filter elements defining an anode chamber containing the anode, and a blending chamber. The solution emanating from the anode chamber through a primary anode filter mixes with the solution delivered directly to the blending chamber. The mixed solution is then delivered to the substrate surface through a secondary filter.  
         [0015]     There is still a need for improved anode assembly designs that provide low additive consumption, avoid anode polarization and at the same time provide high flow of particulate-free electrolyte to the workpiece surface.  
       SUMMARY OF THE INVENTION  
       [0016]     The present invention provides a novel system, apparatus, and method to deposit conductive films on a workpiece. A system for electroplating a surface of a workpiece using a process solution is disclosed. The system comprises a solution housing configured to house an electrode and to contain the process solution, a filter element disposed in the solution housing configured to partition the solution housing into a lower chamber and an upper chamber, and an upper inlet port coupled to the solution housing configured to deliver the process solution to the upper chamber of the solution housing to fill the upper chamber and the lower chamber immersing the electrode in the lower chamber.  
         [0017]     According to an aspect of the invention, a discharge port is coupled to the lower chamber configured to discharge process solution from the lower chamber of the solution housing.  
         [0018]     According to another aspect of the invention, a lower inlet port is coupled to the lower chamber configured to deliver process solution to fill the lower chamber of the solution housing with the process solution.  
         [0019]     According to another aspect of the invention, the filter element includes a first section having a first pore size and a second section having a second pore size. The filter can be configured to be graded.  
         [0020]     According to another embodiment of the invention, another filter element is disposed between the lower chamber and the upper chamber to define an intermediate chamber. The another filter element includes a pore size that is smaller than the filter element.  
         [0021]     According to an aspect of the invention, the upper inlet port is configured to deliver the process solution to fill the intermediate chamber.  
         [0022]     According to yet another aspect of the invention, an intermediate inlet port is coupled to the intermediate chamber configured to deliver process solution to fill the intermediate chamber with process solution. The intermediate inlet port can be configured to deliver process solution to fill the upper chamber.  
         [0023]     Advantages of the invention include improved anode assembly designs that provide low additive consumption, avoid anode polarization and at the same time provide high flow of particulate-free electrolyte to the workpiece surface to improve device consistency and yield. 
     
    
     DRAWINGS  
       [0024]     The invention is described in detail with reference to the drawings, in which:  
         [0025]      FIG. 1  shows a conventional copper electrodeposition process;  
         [0026]      FIG. 2  shows a general depiction of a plating apparatus applicable to the present invention;  
         [0027]      FIG. 3  shows an anode assembly with multiple filters and vertically configured primary and secondary fluid delivery channels in accordance with an embodiment of the present invention;  
         [0028]      FIG. 4  shows secondary flow to a lower anode chamber tapped from primary flow channel orifices in accordance with an embodiment of the present invention;  
         [0029]      FIG. 5  shows an anode sludge drain in accordance with an embodiment of the present invention;  
         [0030]      FIG. 6  shows an embodiment having an external filter disposed below an upper anode housing;  
         [0031]      FIG. 7A  shows an electrochemical processing system using reverse solution flow in an anode housing in accordance with an embodiment of the present invention;  
         [0032]      FIG. 7B  shows an alternative embodiment of a lower portion of an electrochemical processing system in accordance with the present invention;  
         [0033]      FIGS. 8A-8C  shows alternative embodiments of filter designs in accordance with the present invention;  
         [0034]      FIG. 9A  shows an electrochemical processing system using reverse solution flow with multiple filters in an anode housing in accordance with an embodiment of the present invention;  
         [0035]      FIG. 9B  shows a partial sidewall view of a first and second supply ports connected to a common supply line in accordance with an embodiment of the present invention;  
         [0036]      FIG. 10  shows different size filters in supply ports to regulate solution flow in accordance with an embodiment of the present invention;  
         [0037]      FIG. 11  shows an exemplary Electrochemical Mechanical Processing (ECMPR) system using reverse solution flow in an anode housing in accordance with an embodiment of the present invention; and  
         [0038]      FIG. 12  shows a side view along a longer lateral dimension of the anode housing of  FIG. 11 . 
     
    
     DETAILED DESCRIPTION  
       [0039]     For clarity, the electrode assemblies will be referred to as “anode assemblies” and cathodic electroplating will be used as an example in the following description. It should be understood that the same electrode designs are applicable to cathode assemblies that may be used for electropolishing processes Each of the anode assemblies discussed below is particularly adapted to be used with a soluble, i.e. consumable, anode. However, it is contemplated that the anode assemblies could utilize or be utilized as inert anodes and that the assemblies could be used in electroetching or electropolishing applications as well as metal deposition applications.  
         [0040]     According to the invention, multiple anode filters, disposed at several locations within the anode housing, are used. Filters with different pore sizes are provided. Filters can also be laminated between two porous sheets.  FIG. 3  shows an anode assembly with multiple filters and vertically configured primary and secondary fluid delivery channels. In this anode configuration, a primary anode filter  162  is disposed, by way of a filter mount  163 , within the anode chamber and essentially isolates the anode  164  from the rest of the anode chamber. The primary anode filter  162  may, for example, consist of one or multiple layers of napped polypropylene cloth, or a polyethylene, polysulfone, hydrophilic PVDF, or PFTE filter, with a particle or pore size of less than 1.0 micron, average, in diameter. The filter  162  entombs anode sludge around the anode  164 . Disposed away from the primary anode filter  162  is an upper anode filter  166 . The pore size of the upper anode filter  166  is preferably between 30 microns and 0.1 micron in diameter. The upper anode filter  166  is secured in place in such a way that it is effective in filtering the electrolyte solution or fluid that communicates with the cathode.  
         [0041]     A cavity A, within the anode housing  168 , separates the primary anode filter element or elements  162  and the upper or secondary anode filter  166 . The cavity or chamber A may be referred to as an inter-filter blending chamber. In this chamber A, the solution emanating from a lower anode chamber B blends or is mixed with solution from at least one primary flow channel  170 . Together, the chambers A and B form an internal housing volume into which the electrolyte solution can flow. The filter  162  thus divides the internal housing volume into the lower anode chamber B and the inter-filter blending chamber A, which is located between the lower anode chamber and a top anode plate  174 . In the embodiment illustrated in  FIG. 3 , and in each of the embodiments shown in  FIGS. 4-6  which will be described, the blending of electrolyte solution in the chamber A and the higher velocity, or rate of flow, of the solution flowing from the primary flow channel enhance the migration of copper or other metal ions from the lower anode chamber B into the blending chamber A. This enhanced ion migration, in other words, is provided by the blending which occurs in the chamber A and because a flow of the electrolyte solution into the blending chamber A occurs at a higher rate than a flow of the solution into the anode chamber B. The dynamic mixing and migration reduce the copper ion concentration difference between the lower anode chamber B and the upper inter-filter blending chamber A, thus reducing cell polarization due to any large ion concentration differences in the cell.  
         [0042]     The primary flow channel may be a vertical channel providing for electrolyte solution or fluid communication and can be incorporated into the anode housing. The primary and secondary flow channels can both be formed as apertures within the wall of the cell, as shown in  FIG. 3 . The primary flow channels  170  transfer the bulk of the solution, more than 60%, directly into the inter-filter blending chamber A. The solution is then filtered by the very fine upper anode filter  166 , which has apertures that, typically, are less than 10.0 micron, and preferably 0.02-0.5 micron, in average diameter. The filtered solution then is transferred to the cathode via channels  172  in the anode top plate  174  and channels  176  in a pad or pad assembly  178 . The top anode plate  174  forms a closure for the internal housing volume and is secured to a flange  175  defined at an upper end of the anode housing in any appropriate way such as, for example, by bolts. The solution can thus be discharged from the internal housing volume towards the surface of a semiconductor substrate through the channels  172  in the top plate  174  and through the channels  176  in the pad or pad assembly. An O-ring seal  182  may be provided between an underside of the top anode plate  174  and the flange  175  to prevent leakage of plating or plating/planarization solution. The O-ring may be omitted to allow for controlled fluid leakage between the flanges. Controlled leakage may be used to remove bubbles in the mixing chamber. The top anode plate  174  may have essentially the same construction as the pad support plate  22  of U.S. Pat. No. 6,478,936 mentioned earlier, while the pad or pad assembly  178  may have essentially the same structure as the pad  8  of the same earlier mentioned application.  
         [0043]     The secondary flow channels  180  convey the balance of the electrolyte into the lower anode chamber or space B surrounding the anode  164 . The solution emanating from the lower anode chamber B is filtered by the primary anode filter  162  before entering and mixing with the solution in the inter-filter blending chamber A. Preferably, the electrolyte flow through the secondary flow channels  180  is controlled using valves  181 . During the electrochemical process, the valves  181  are turned on to allow electrolyte flow into the lower anode chamber. However, between the processes, electrolyte solution flow through the valves  181  is turned off to prevent idle flow so that the additive consumption occurring during the idle flow is advantageously averted. In other cell configurations, another, external, filter, or a set of additional external filtering elements, may be provided.  FIG. 6  shows one such cell configuration, in which an external filter  472  is disposed below an upper anode housing  468 . This external or “inter-bowl” filter  472  may be used to pre-filter the electrolyte solution flowing in from a fluid inlet  474 . The cell configuration of  FIG. 6  also includes an anode  464  disposed in a lower anode chamber B which is separated from an inter-filter blending chamber A by a primary anode filter  462 . As in the embodiment shown in  FIG. 3 , the primary anode filter  462  may consist of one or multiple layers of filters or a filter cartridge assembly with a particle or pore size between 1 and 5 microns in diameter. The primary anode filter  462  entombs anode sludge around the anode  464 .  
         [0044]     An upper anode filter (not shown in  FIG. 6 ) is disposed away from the primary anode filter  462 , and it is to be understood that a top anode plate (not shown in  FIG. 6 ) is mounted to a flange  475  of upper anode bowl or housing  468 , similar to the way in which the top anode plate  174  is mounted to the flange  175  in the embodiment shown in  FIG. 3 , thereby forming the inter-filter blending chamber A.  
         [0045]     The upper anode bowl  468  includes primary flow channels  470  and secondary flow channels  480  having the same configurations and functions as the primary and secondary flow channels  170  and  180  shown in  FIG. 3 . As mentioned above, the external or inter-bowl filter  472  is disposed below the upper anode housing  468 . This external filter can be mounted, e.g. by an appropriate filter mount, to a lower anode housing or bowl  495 , and pre-filters the solution before it passes into the chambers A and B. The lower anode housing or bowl  495  defines a flange  497  which is connected, e.g. by bolts, to the flange  475  of the upper anode bowl or housing  468 . An additional o-ring seal  492  can be disposed between facing surfaces of the flanges  475  and  497  to provide sealing. In all other aspects, the anode configuration of  FIG. 6  is constructed in the same way as that shown in  FIG. 3 .  
         [0046]      FIG. 5  illustrates the incorporation of an anode sludge drain  376  into another anode configuration. Anode sludge is drained, at routine intervals or as needed, through the opening provided by the anode sludge drain. Any practical device may be used to suck or evacuate the lower anode chamber B during routine wafer or workpiece processing or at any other suitable time. Thus, it is not necessary to disassemble the anode housing  368  and remove the primary anode filter  362  to de-sludge or clean the anode chamber B, as is typical in prior art operations. The in-situ anode drain  376  improves plating cell utilization, because the need for routine anode service is eliminated. The in-situ de-sludge operations also enhance the life of the lower anode filter.  
         [0047]     In all other aspects, the anode configuration of  FIG. 5  is constructed in the same way as that shown in  FIG. 3 .  
         [0048]     In other arrangements, the secondary flow to the lower anode chamber B may be tapped from the primary flow channel orifices as shown in  FIG. 4 . Here, apertures narrower than those of the primary flow channels  270  form the secondary flow channels  280  and are used to partition or divert a portion of the fluid in the primary channels  270  into the lower anode chamber B of the housing  268  surrounding the anode  264 . In all other aspects, the anode configuration of  FIG. 4  is constructed in the same way as that shown in  FIG. 3 .  
         [0049]     Besides the flow channels described above, an additional small orifice (b), as indicated in  FIGS. 3 and 4 , or multiple additional orifices (not shown) may be provided to allow the electrolyte to leak out from the lower anode chamber B to the outside of the anode housing  168 ,  268 ,  368 , or  468 . At least one of these orifices is preferably provided to remove any bubbles that may be trapped between the anode upper surface and the primary anode filter. Similar air bleeder holes (a), as indicated in  FIG. 3 , may be incorporated in the top anode plate or in the upper walls of the anode housing. When the bleeder holes are absent, a de-gassing filtering element (not shown) may be used to de-gas the solution before the solution is transferred to the plating cell. For effective bubble removal, it is imperative that the filters  162 ,  262 ,  166 ,  462  and  362  be slanted or disposed at angles in the range of 1 to 30 degrees with respect to the horizon with the bleed hole disposed at the highest regions just below the filter.  
         [0050]     In other operations, the lower anode chamber B may also be activated as needed to remove any large bubbles that may be trapped below the primary anode filter  162 ,  262 ,  362 , or  462 . The solution can be drained, filtered, and returned to the solution reservoir.  
         [0051]     A similar draining arrangement may be incorporated in upper regions of the anode housing  168 ,  268 ,  368 , or  468 . This will be used to remove any large trapped air bubbles in chamber A, just beneath the upper anode filter.  
         [0052]     As described above, the anode housing is divided into an anode chamber or a lower chamber including the anode and an upper chamber or a blending chamber. A filter element separates the blending chamber from the anode chamber which is disposed beneath the blending chamber. The process solution from the anode chamber flows through the filter and blends with the process solution that is supplied into the upper chamber.  
         [0053]     In the following embodiments, a reverse flow system is used so that the process solution is preferably delivered substantially to the upper chamber, and through the filter element, the solution is introduced from the upper chamber into the lower chamber. The reverse flow of the process solution keeps the filter element clean, avoiding clogging, and at the same time introduces enough solution to the lower chamber to prevent anode polarization. In one aspect of the present invention, restricted flow into the lower chamber also minimizes additive consumption.  
         [0054]     In another embodiment, the filter element may have very small pore size. During the process, due to the relatively small pore size of the filter element, only a small percentage of the solution flows down to the lower chamber, the balance of the solution is kept in the upper chamber. This construction allows less process solution to flow into the lower anode chamber and as a consequence minimizes consumption of additives by the anode. Accordingly, in both reverse flow embodiments, by appropriately increasing the height of the upper chamber with respect to the height of the lower chamber, adequate reverse process solution flow from the upper chamber to the lower anode chamber is provided to keep the filter element clean and also avoid the problem of anode polarization. The above systems may be constructed using more than one filter element and this approach is also within the scope of the present invention.  
         [0055]      FIG. 7A  shows an electrochemical processing system  500  using the reverse solution flow of the present invention in anode housing  502 . Surface  504  of a workpiece  506  is placed on a top opening  508  of the anode housing during an electrochemical process. In the following embodiments the workpiece is a semiconductor wafer, preferably a silicon wafer. The surface of the wafer includes a thin conductive layer, preferably a copper seed layer formed on a typical barrier layer. A process solution  510  fills the anode housing  502  up to the opening  508  and contacts both the surface of the wafer and an anode  512  which is placed on the bottom of the anode housing. The process solution can be a plating solution. The anode  512  is kept submerged in the plating solution that fills the anode housing. The wafer is held and moved by a workpiece carrier head  516 .  
         [0056]     A filter element  518  divides the housing  502  into an anode chamber  520  (or lower chamber) and a supply chamber  522  (or upper chamber). The pore size of the filter may be approximately in the range of 0.02 to 1.0 microns. It should be noted that unlike prior art approaches reverse flow design of the present invention may use filters with larger pore size because the sub-micron size particles generated in the lower chamber are always pushed down by the reverse flow and they do not get the chance to go through the filter  518  into the upper chamber. In this embodiment, the filter  518  is attached to sidewall  524  of the anode housing in a slanted manner. In the anode chamber, a bleeding port  526  is placed adjacent an upper end of the filter  518  for establishing a solution flow in the lower chamber, and also for removing any gas bubbles from the lower chamber. As shown in  FIGS. 8A-8C , the filter  518  may have a slanted, concave or V-shape designs. In each design, however, one or more bleeding ports  526  is placed adjacent upper end of the filter  518  to remove bubbles. The plating solution that leaves the anode housing along with the bubbles and particulates generated in the lower chamber is collected by a plating solution recycling circuit (not shown) and filtered and recycled to be used again.  
         [0057]     Referring back to  FIG. 7A , the plating solution  510  is supplied to the supply chamber  522  through a supply port  528  on the sidewall  524  of the anode housing. There may be one or several supply ports. Most of the solution supplied into the upper chamber moves up towards the workpiece surface. This is indicated with the large arrows in  FIG. 7A . Some solution, however goes to the lower chamber. Flow of plating solution to the anode chamber takes place through the filter  518 , as shown with small arrows. The solution flows to anode chamber and leaves the anode chamber through the bleeding port  526 . Such reverse flow of the process solution avoids clogging up of the filter with particulates since it continually cleans the filter. Solution coming from the upper chamber, impurities from the anode sludge and any bubbles that may be present leave the anode chamber through the bleeding port  526 . At the beginning of the plating process, the anode chamber may have to be pre-filled with the solution rapidly. For this, an auxiliary inlet valve may be used. The auxiliary inlet valve  530  may be positioned in the sidewall  524  and next to a lower edge of the filter. Once the anode chamber is full, the auxiliary inlet valve is closed and process commences. It should be noted that auxiliary inlet to the anode chamber is optional.  
         [0058]      FIG. 7B  shows a redesigned lower portion of the system  500 . In this embodiment, the auxiliary inlet is removed from the system, and a composite filter element  519  replaces the filter element  518 . The composite filter element may comprise filters with more than one pore size. As exemplified in  FIG. 7B , a first section  521   a  may have a larger pore size than a second section  521   b . As a result, solution flow per unit area through the first section  521   a  down to the anode chamber is larger than solution flow per unit area through the second section  521   b . This way, the anode chamber may be filled fast at the beginning of the process and a well-regulated solution flow is established in the anode chamber that flows over the anode from left to right and exits the anode chamber through the bleed holes.  
         [0059]     It should be noted that the amount of solution flowing from the supply chamber  522  to the anode chamber  520  depends on various factors such as the pore size of the filter element, size of the bleed holes and the hydraulic pressure of the solution in the supply chamber  522  over the filter element. Generally, as the height of the upper chamber increases, the pressure generated by the solution on the filter increases increasing the flow going into the lower chamber. Similarly, as the pore size of the filter element increases, the pressure drop across the filter element decreases and the solution flow from the supply chamber  522  to the anode chamber  520  increases, on condition that the bleed hole size does not restrict this flow. It is understood however that such variables can be easily changed in the design of the processing chamber to obtain best results.  
         [0060]     An upper filter  532  may optionally be placed adjacent the opening  508  of the housing to regulate flow and to filter the solution one more time, as the solution is flowed through the supply chamber against the surface of the wafer. This filter may be coarser than the filter  518 , i.e., it may have larger pore size. Solution that is flowing out the opening  508  is collected by the recycling circuitry (not shown) to replenish and feed back the solution to the anode housing  502 .  
         [0061]      FIG. 9A  shows an electrochemical processing system  600  using the reverse solution flow of the present invention with multiple filters in an anode housing  602 . Surface  604  of a wafer  606  is placed on a top opening  608  of the anode housing during an electrochemical process using the system  600 . A plating solution  610  fills the anode housing  602  up to the opening  608  and contacts both the surface of the wafer and an anode  612  which is placed on bottom wall  614  of the anode housing. The anode  612  is kept submerged in the plating solution that fills the anode housing  602 . The wafer is held and moved by a workpiece carrier head  616 .  
         [0062]     A first filter element  618   a  separates an anode chamber  620  (or lower chamber) from a first supply chamber  622  (or intermediate chamber). The pore size of the first filter may preferably in the range of 0.2 to 10 microns. It may even have larger pore size or it may be a composite filter such as the one shown in  FIG. 7   b . Further, a second filter  618   b  separates the first supply chamber from the second supply chamber  623  (upper chamber). The pore size of the second filter may be very small such as in the range of 0.01 to 0.1 microns, typically 0.05 microns. In this embodiment, the filters  618   a  and  618   b  are preferably attached to sidewall  624  of the anode housing in a slanted manner. The filters  618   a  and  618   b  may be placed parallel to one another or they may be slanted in different directions. In the anode chamber, at least one, preferably multiple bleeding ports  626   a  are-placed adjacent an upper end of the filter  618   a  for removing solution, gas bubbles and particles generated in the lower chamber. The plating solution that leaves the anode housing  602  is collected by a plating solution recycling circuit (not shown) and filtered and recycled to use it again.  
         [0063]     The plating solution  610  is supplied to the first supply chamber  622  through a first supply port  628   a  and to the second supply chamber through a second supply port  628   b . The first and second supply ports may be connected to separate solution supply lines, or as shown in  FIG. 9B , to a common supply line  627  which delivers plating solution to both ports  628   a  and  628   b .  FIG. 9B , shows a partial view of sidewall  624 , with alternative solution delivery scheme including the common supply line  627 .  
         [0064]     Delivery of plating solution to the anode chamber takes place through the filter  618   a . The plating solution flows into first supply chamber  622  and then into the anode chamber  620  and leaves the anode chamber through the bleed port  626   a . As mentioned above, the reverse flow of the process solution keeps the filter  618   a  clean and, also, prevents anode polarization. As in the previous embodiment, impurities and bubbles leave the anode chamber through the bleed port  626   a . The plating solution from the second supply port fills the supply chamber  623  and reaches the surface  604  of the wafer. Due to the small pore size of the second filter, and the pressure built in the first supply chamber  622 , almost no solution flow from the second supply chamber to the first supply chamber occurs. Use of the second filter  618   b  which has very fine pores advantageously transports an important fraction of the supplied process solution from a supply tank to the surface of the wafer while less process solution flows into the anode chamber through filter  618   a . As a result, consumption of additives by the anode is minimized, and additionally, none of the particles generated by the anode can diffuse across the filter  618   a . Even if some particles could diffuse through the filter  618   a  and into the chamber  622 , the extremely fine filter  618   b  assures that they do not get into the top chamber where they can find their way onto the substrate. It should be noted that the bleed hole  626   b  is optional, but preferable, since any gas bubbles trapped in chamber  622  may be eliminated through the bleed hole  626   b . In this embodiment, the supply ports  628   a ,  628   b  and bleed ports  626   a ,  626   b  may be controlled by valves for the purposes of controlling the amount of solution delivered and kept in the housing. Alternately, sizes of these orifices are selected such that the amount of solution flow through them is pre-determined. Size of the bleed holes also affects the pressure build up in chambers  620  and  622 . Pressure build-up in chambers, in turn, affects the amount of solution flow down into chamber  620  from chamber  622 . Solution that is flowing out the opening  608  is collected by the recycling circuitry to replenish and feed back to anode housing. Optionally, an upper filter  632  is placed adjacent the opening  608  of the housing. Solution that is flowing out the opening  608  along with the solution from the bleed ports  626   a ,  626   b  is collected by the recycling circuitry to replenish and feed back to anode housing.  
         [0065]      FIG. 10  shows a design where different size filters in supply ports are used to regulate flow. The electrochemical processing system  800  uses the reverse solution flow of the present invention in anode housing  802 . Surface  804  of a wafer  806  is placed on a top opening  808  of the anode housing during an electrochemical process. A plating solution  810  fills the anode housing  802  up to the opening  808  and contacts both the surface of the wafer and an anode  812  which is placed on bottom wall  814  of the anode housing. The solution is delivered to the anode housing through a cavity  815  of a solution container  816  encasing the anode housing  802 . The anode  812  is kept submerged in the plating solution that fills the anode housing. The wafer is held and moved by a workpiece carrier head  817 .  
         [0066]     A first filter  818   a  separates an anode chamber  820  (or lower chamber) from a first supply chamber  822  (or intermediate chamber). The pore size of the first filter may be course. Further, a second filter  818   b  separates the first supply chamber from the second supply chamber  823  (upper chamber). As in the system  600  above, the pore size of the second filter may be very small. In the anode chamber, a bleeding port  828   a  is placed adjacent an upper end of the filter  818   a  for removing gas bubbles, solution and impurities. The plating solution  810  is supplied to the first supply chamber  822  through a first supply port  828   a  and to the second supply chamber through a second supply port  828   b . The supply ports may include a first supply filter  829   a  and a second supply filter  829   b  respectively.  
         [0067]     Selection of the total area of the supply ports and the porosity or pressure drop of filters  829   a  and  829   b  are important factors to determine solution flow. It is preferable that the solution pressure drop in filter  829   a  be larger than that of filter  829   b . In this way, during processing when there is high plating solution flow, a larger portion of the solution flows into second supply chamber  823  and reaches the surface of the wafer. Restricted flow into the first supply chamber  822  and thus into the anode chamber advantageously reduces additive consumption. During idle flow, on the other hand the total solution flow through the supply ports  828   a  and  828   b  may be reduced. When this is done, since the pressure drop across filter element  829   a  is larger than that of across the filter element  829   b , even a larger portion of the restricted flow is expected to go to the second supply chamber. Thus during idle flow, solution flow into the anode chamber is further reduced and additive consumption is further reduced.  
         [0068]     As is understood from the foregoing, additive consumption in an electrochemical process chamber can be reduced by reducing or totally shutting down the solution flowing into the anode chamber where a copper electrode (or any other electrode) resides. This can be achieved automatically in some designs, such as the design shown in  FIG. 10 . In designs that bring the plating solution to the anode chamber through a separate supply line, a control valve on this supply line may be used to reduce or shut down the flow to the anode chamber, especially during idle flow. During the process, this flow cannot be totally shut down since such flow may cause anode polarization.  
         [0069]      FIG. 11  illustrates, in perspective view, an exemplary Electrochemical Mechanical Processing (ECMPR) system  900  using the reverse solution flow of the present invention in anode housing  902 . In this embodiment, the housing may have a rectangular shape having one lateral dimension which is shorter than the other lateral dimension. For example,  FIG. 12  shows a side view along the longer lateral dimension of the housing  902 . One such rectangular anode housing design is exemplified in U.S. application Ser. No. 09/760,757, entitled, Method and Apparatus For Electrodeposition of Uniform Film on Substrate, filed Jan. 17, 2001 and commonly owned by the assignee of the present invention. Referring to  FIGS. 11 and 12 , surface  904  of a wafer  906  is placed in proximity of top surface  907  of a workpiece surface influencing device  908  of the system  900 . The workpiece surface influencing device (WSID)  908  has a rectangular shape and encloses the top opening  909  of the housing. This rectangular design of the WSID and the housing allow electrical contacts  913  to touch the edge of the wafer. During the plating process, a potential difference between the anode and the electrical contacts is established using a power supply  915 . A plating solution  910  fills the housing  902  and flows through channels  911  while contacting both the surface of the wafer and an anode  912  which is placed on bottom wall  914  of the housing  902 . The anode  912  is kept submerged in the plating solution that fills the anode housing. The anode  912  has a rectangular shape corresponding to the shape of the WSID  908  to establish deposition uniformity over the entire surface of the WSID. During the process wafer is held and moved, i.e., rotated and laterally moved by a workpiece carrier head  917 .  
         [0070]     A filter  918  divides the housing  902  into an anode chamber  920  and a supply chamber  922 . In the anode chamber, at least one bleeding port  926  is placed adjacent an upper end of the filter  918  for removing gas bubbles. The plating solution  910  is supplied to the supply chamber  922  through a supply port  928  of the sidewall  924  of the housing  902 . Flow of plating solution  910  to the anode chamber  920  takes place through the filter  918 . As in the system  500  above, the solution flows to anode chamber  920  and leaves the anode chamber  920  through the bleed port  926 . At the beginning of the plating process, an auxiliary inlet valve  930  may be used to supply plating solution  910  into the anode chamber  920 . The auxiliary inlet valve may be positioned in the sidewall  914  of the housing  902 . Optionally, an upper filter  932  is placed adjacent the opening  908  and under the WSID  908  to filter the solution flowed through the supply chamber  922  against the surface of the surface of the wafer. Solution that is flowing through the WSID  908  and the bleed port  926  is collected by the recycling circuitry (not shown) to replenish and feed back to the housing  902 .  
         [0071]     It should be noted that when ECMD process is carried out using the system of  FIGS. 11 and 12 , the wafer surface is brought down onto the surface  907  of the WSID  908 . This causes a pressure increase in the supply chamber  922  and the flow of solution into the anode chamber  920 , via the filter  918 , increases. During idle flow, the wafer is not placed on the WSID  908  and pressure in the supply chamber  922  is low and, as a result, solution flow into the anode chamber  920  is also low. This self-regulation advantageously reduces additive consumption during idle flow and causes the solution flow over the anode to increase during the process when such solution flow is possible.  
         [0072]     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.