WO2008008711A2

WO2008008711A2 - Ion exchange treatment of chemical mechanical polishing slurry

Info

Publication number: WO2008008711A2
Application number: PCT/US2007/072970
Authority: WO
Inventors: Peter Porshnev; Benjamin R. Roberts; Michael Smith
Original assignee: Applied Materials Inc; Edwards Vacuum LLC
Current assignee: Applied Materials Inc; Edwards Vacuum LLC
Priority date: 2006-07-10
Filing date: 2007-07-06
Publication date: 2008-01-17
Anticipated expiration: 2009-01-10
Also published as: WO2008008711A3

Abstract

A CMP slurry (408) is treated by ion exchange (82) in a CMP slurry treatment apparatus (100) which can accept slurries containing particles of metals and other abrasion byproducts. The apparatus comprises an ion exchange column (82) comprising a tank which contains a resin bed of resin beads that extract the hazardous materials, such as metals like copper, from the CMP slurry passed through the tank.

Description

ION EXCHANGE TREATMENT OF CHEMICAL MECHANICAL POLISHING SLURRY

BACKGROUND OF THE INVENTION Field of the Invention

[0001] Embodiments of the present invention generally relate to methods and apparatuses for treating waste slurry generated by chemical mechanical polishing.

Description of the Related Art

[0002] In the fabrication of integrated circuits and displays, semiconducting, dielectric, and conducting features are formed on a substrate in a substrate processing apparatus. For example, a dielectric such as silicon oxide or silicon nitride can be formed to insulate electrical interconnects, and the interconnects themselves can be formed with metal conductor, such as aluminum or copper. At different stages, chemical mechanical polishing (CMP) processes are performed to planarize the substrate surface and remove surface defects such as scratches, roughness and contaminants. In a typical CMP process, a substrate is polished with an CMP slurry containing abrasive particles suspending in an aqueous medium containing chemical etchant. The CMP process generates a slurry containing, for example, abrasive particles, abraded substrate material, reagents and byproducts, suspension liquid, and solvents. The abrasive particles can be made from aluminum oxide, silicon oxide, silicon carbide, titanium oxide, zirconium oxide, or other abrasives commonly used in grinding and polishing slurries; of which silicon oxide is preferred because the substrate is typically made from silicon element or silicon oxide. The abrasive particles are typically sized, for example, from about 10 to about 500 nm. The abraded substrate material can include dielectric materials such as silicon oxide, silicon nitride, and aluminum oxide; and conducting materials such as aluminum, copper, nickel, tantalum, titanium, and tungsten. The slurry also often contains organic and inorganic compounds, including oxidizers, chelating agents, surfactants, and corrosion inhibitors. These compounds originate from the CMP polishing solution and can include etchants and solvents, such as for example: (1) oxidizers, such as hydroxylamine, KMnθ4, KIO₄, H₂O₂, and NO₃ ^"; (2) acids, such as HF, HNO₃, H₃BO₃, NH₄ ⁺, poly(acrylic) acid, oxalic acid, citric acid, acetic acid and peroxy acids; (3) dispersants and surfactants such as polyacrylic acid, quaternary ammonium salts, alkyl sulfates; (4) corrosion inhibitors such as benzotriazole, and alkyl amines; and (5) metal complexing agents such as ethanol amines, oxalic acids, and citric acids. The exemplary CMP slurry is provided only to illustrate a CMP process and should not be used to limit the scope of the present invention.

[0003] The hazardous materials of the CMP slurry need to be removed from the slurry prior to its disposal. As one example, certain CMP slurries contain copper ions, copper compounds, and copper particles because copper is used to form electrical interconnects on the substrates. Abraded copper is considered a hazardous material and Environmental Protection Agency (EPA) regulations require the concentration of copper in the disposed of slurry to be less than typically 0.4 parts/million. To meet these stringent requirements, the copper present in the CMP slurry needs to be almost completely removed from the slurry. Filtration methods have been used to remove copper from the slurry by introducing a reagent that reacts with metal ions in the slurry to form a precipitate which can be removed by filtering. However, extraction and treatment of the precipitate and the frequent replacement of the filters makes this a costly technique.

[0004] Another method of treating CMP slurry uses an ion exchange process to exchange non-hazardous ions for the hazardous metal ions in the slurry. Such an ion exchange process is, for example, disclosed in U.S. Patent Publication no. 2003/0044335 A1 , which is incorporated herein by reference in its entirety. Such ion exchange processes techniques do not require cleaning filters and the ion exchange waste contains concentrated amounts of copper which can be more easily removed, thereby avoiding the high costs associated with the extraction and treatment of precipitates by conventional filtration methods. However, it is difficult to extract metals by ion exchange treatment of a CMP slurry containing particles of metal or metal compound. [0005] One problem is that the slurry contains metal material present in chemical states, such as chemical complexes or insoluble compounds, which do not allow easy replacement by ion exchange methods. Removal of metals by ion exchange is also difficult because the CMP slurry often contains a wide range of compounds, including oxidizers, chelating agents, surfactants, and corrosion inhibitors, which preferentially exchange ions with the ion exchange material to lower the ion exchange capacity of the resin. Also, compounds such as oxidizers can chemically attack the cross-linked structure of ion exchange resins to degrade the structure. Removal of oxidizers by activated carbon filters often results in plugging up of the activated carbon by the particulates. These problems are further exacerbated by the lack of precise knowledge of the chemical compositions and reactions occurring in the CMP slurry.

[0006] The particles present in the CMP slurry present further problems as they often block or otherwise impede the flow of the CMP slurry through the ion exchange column. The solid particles are normally suspended in the liquid but deposit onto the ion exchange resin media in an ion exchange column. Thus, after only a short time of flowing treated slurry into an ion exchange column, the particles in the slurry clog up the ion exchange column causing the fluid pressure in the column to rapidly increase and impeding its operation. It is desirable to limit or prevent such pressure buildup in the ion exchange column.

[0007] Furthermore, the organic and inorganic compounds in the slurry, such as the aforementioned oxidizers, chelating agents, surfactants, and corrosion inhibitors, accelerate deposition of solids, and lower the exchange capacity of the resin by "blinding" active sites in the resin structure. Thus, the resins have to be periodically regenerated to restore the metal exchange capacity of the resin. However, conventional acid regenerant of the resin is also often ineffective because the ion exchange capacity can degrade to a point where the resin bed is no longer useful and must be replaced. Filtering or microfiltering of the solid particles from the waste prior to ion exchange treatment requires additional steps of filtering and disposal of the filtered materials. [0008] Another problem arises because ion exchange resins typically exchange metal ions only if the pH of the slurry is within a pH operating range for the resin material. As such, so many metal removal systems based on ion-exchange can include simple pH adjustment modules which adjust the pH of the slurry before filtration and/or ion-exchange. As one example, U. S patent no. 6,203,705 which is incorporated by reference herein in its entirety, discloses pH adjustment of copper CMP waste streams prior to treatment using ion exchange, and also includes other treatment steps, including hydrogen peroxide destruction and carbon bed treatment. As another example, pH adjustment is discussed in U.S. patent no. 6,346,195, which is incorporated by reference herein in its entirety, to improve ion exchange performance in CMP waste treatment. Furthermore, U.S. patent Publication no. 2003/0044335, entitled "Method and apparatus for Metal Removal Ion Exchange" filed on 01/03/2001 , which is also incorporated by reference herein in its entirety, describes a method of removing copper from a slurry in the presence of an oxidizer without pre-filtration of solid particles or removal of the oxidizer and the slurry having a pH range of from 2 to 5. At the lower end of pH range, the ion-exchange rate is slow, and the exchange direction may reverse, resulting in the elution of trapped copper. At higher pH values, copper typically forms insoluble compounds, such as hydroxides and oxides, and hence it is not available for ion exchange.

[0009] Therefore a need exists for a process for the treatment of CMP slurry which will be robust and effective at treating a wide range of CMP slurry compositions. It is further desirable for the treatment process to be able to use ion exchange processes to extract the metal ions from a wide range of pH levels of the CMP slurry. It also desirable to reduce the content of metallic materials, such as copper, to acceptable EPA standards prior to releasing the treated CMP effluent.

SUMMARY OF THE INVENTION

[0010] Embodiments of the invention generally provide apparatus and methods for treatment of a waste CMP slurry using an ion exchange method for removing metal from the waste CMP slurry. [0011] In one embodiment, a CMP slurry treatment apparatus comprises two or more ion exchange columns, each column comprising a main tank and a polisher tank in fluid communication, and each main tank and polisher tank comprising resin beads capable of treating a slurry having a pH of between about 2 and about 6. The apparatus further comprises a controller adapted to control operation of the ion exchange columns, and one or more detectors adapted to monitor the CMP slurry.

[0012] In another embodiment, an ion exchange column for removing metal ions from the slurry of a CMP polisher is provided, the ion exchange column comprising one or more tanks fluidly connected, and each tank (for example, a main tank or polisher tank) comprising an enclosed volume including a top wall and a bottom wall and the volume comprising a first volume and a second volume, resin beads which fill the first volume which is disposed below the second volume, a lower port disposed at the bottom wall to receive slurry which flows through the tank from bottom to top during ion exchange, an upper port disposed at the top wall to exit the treated slurry, and a diffuser disposed at the upper port.

[0013] The slurry treatment apparatus may further comprise a pretreatment system which adjusts the pH of the slurry in a two step process prior to ion exchange processing. The pH of the slurry may be adjusted to improve the efficiency of the ion exchange process. In one embodiment, the pH may transformed to a value of between about 1.5 to about 5 during a first step to transform metal compounds in the slurry into metal ions, and then further adjusted in a second step to a value of between about 2 to about 5 before the slurry is sent to an ion exchange column. The pretreatment apparatus may include two separate tanks for the two step process, or, in another embodiment, a single tank with baffles which separates a pH transformation zone from a pH adjustment zone.

[0014] The slurry treatment apparatus also provides a method to improve the up time for slurry treatment by using two or more ion exchange columns so that a first column may be treating slurry while a second column is being regenerated.

[0015] In one embodiment, an ion exchange column is regenerated using a mult- step process which begins by flowing deionized water upwards through the column to loosen any solid particles which may be trapped between resin beads, followed by a downflow of acidic solution to exchange metal ions from the resin material with other ions and thereby regenerate the resin material, and then flowing deionized water upwards through the column again to flush out the acidic solution from the column. In another aspect of the invention, a basic solution is flowed upwards through the column to dissolve silica and other organic deposits, followed by another upflow of deionized water to flush out the basic solution prior to flowing the acidic solution.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0017] Figure 1 is a schematic side view of an one embodiment of a CMP slurry treatment apparatus which includes an ion exchange column capable of treating CMP slurry;

[0018] Figure 2A is a detailed schematic top view of an exemplary embodiment of a diffuser basket for a top diffuser used in Figure 3;

[0019] Figure 2B shows a detailed schematic top view of an exemplary embodiment of a top diffuser having slots supported by the basket of Figure 2A;

[0020] Figure 3 is a schematic diagram of another embodiment a CMP slurry treatment apparatus;

[0021] Figure 4A is a graph showing the change in upstream pressure of the CMP slurry as it is passed through the ion exchange column with ion exchange processing time; [0022] Figure 4B is a graph showing the change in pH of the treated CMP slurry over ion exchange processing time;

[0023] Figure 5 is a graph showing the flow rate through the ion column as line (a), and the pressure upstream of the column as line (b), as a function of the pump pressure;

[0024] Figure 6 is a graph of the flow rate or pressure over time in an ion exchange column, for a conventional diffuser over the area (d), and for a diffuser having larger slots as in the areas (e) and (f);

[0025] Figure 7 A is a schematic side view of an exemplary embodiment of an ion exchange column comprising a tank with a layer of filler beads overlying the resin bed in which a down flow of regenerant solution is passed through the tank during regeneration of the resin beads;

[0026] Figure 7B is a schematic side view of an exemplary embodiment of an ion exchange column comprising a tank with a layer of filler beads overlying the resin bed during ion exchange in which an upflow of CMP slurry is passed through the tank;

[0027] Figures 8A is a graph of the flow (a) or pressure (b) over time as distilled water is passed through an ion exchange column having filler beads;

[0028] Figures 8B is a graph of the flow (a) or pressure (b) over time as slurry is passed through an ion exchange column having filler beads;

[0029] Figure 9 is a graph showing the variation in flow and pressure over time with multiple backwash cycles;

[0030] Figure 10 is a schematic diagram of another version of a CMP slurry treatment apparatus comprising a pre-treatment apparatus;

[0031] Figure 11 is a potential-pH graph (Pourbaix diagram) for a Cu-H₂O solution without chelating agents that shows equilibrium concentrations as a function of pH and electrode potential; [0032] Figure 12 is a schematic diagram of yet another version of a CMP slurry treatment apparatus comprising a pre-treatment apparatus;

[0033] Figure 13 is a schematic perspective view of a CMP polisher; and

[0034] Figure 14 is a cross-sectional view of the tabletop and platen of Figure 13 showing a conduit to pass slurry to a CMP slurry treatment apparatus.

DETAILED DESCRIPTION

[0035] CMP slurry is treated prior to disposal in a CMP slurry treatment apparatus which can accept slurries containing metallic ions and solid particles, solvents, and suspension medium. Figure 1 is a schematic side view of one embodiment of a CMP slurry treatment apparatus 100 which includes an ion exchange column 82 capable of treating slurry 108 from a CMP polisher. The ion exchange column 82 comprises a tank 83 that contains a resin bed 88 of resin beads 87 that extract the hazardous materials, such as metals like copper, from a slurry 108 passed through the tank 83. In the treatment cycle, the slurry 108 enters the tank 83 through a lower port 86 and flows upward through the resin beads 87 of the resin bed 88 in the tank 83 in an up-flow direction, as shown by the arrow 111. The upflow of slurry 108 through the resin bed 88 allows particles in the slurry 108 to separate out and flow downwards due to gravity. The treated slurry 112 exits the tank 83 through an upper port 90. In one version, the fluid volume of the tank is from about 4 ft³ to about 8 ft³.

[0036] In the ion exchange column 82, a bottom diffuser 85 is positioned at the lower port 86 which is at the bottom of the tank 83 and a top diffuser 89 at the upper port 90 which is at the top of the tank 83. The bottom and top diffusers 85, 89, hold back the resin beads 87 in the ion exchange column 82 when pressurized slurry 108 is passed through the tank 83. Each bottom and top diffuser 85, 89 has diffuser slots 84, 81 , respectively, that prevent the flow of the resin beads 87 through the bottom and top diffusers 85, 89. The bottom diffuser 85 can have the same design or a different design as the top diffuser 89. [0037] As the slurry 108 passes through the tank 83, the undesirable ions present in the slurry 108 are extracted by the resin beads 87 to become entrapped in the beads while non-hazardous ions present in the resin beads 87 are substituted for the extracted ions. The ion exchange material of the resin beads 87 exchanges pre-selected ions for the metal ions in the slurry to produce a treated slurry 112 which has a second concentration of metal ions that is lower than the first concentration of metal ions in the untreated slurry 108. In one version, the second concentration of metals is at least about 80% lower, and even about 90% lower than the first concentration. For example, when the first concentration of metal ions in the untreated slurry 108 is from about 1 one part per million (ppm) to about 50 ppm; the second concentration of metal ions in the treated slurry 112 is less than 0.2 ppm, or even less than 0.005 ppm.

[0038] After the ion exchange cycle, the resin beads 106 are regenerated by a regenerant cycle which uses a reverse ion exchange process. In the regenerant cycle, a regenerant 124 is introduced into the tank 83 to regenerate the resin beads 87. The regenerant 124 extracts the metal and other ions entrapped in the resin beads 106 to rejuvenate the ion exchange material of the resin beads 87 for further ion extraction. The regenerant 124 can be an acid or base solution capable of extracting the metal ions from the resin beads 87 to form a salt of the metal ions. In one method, the regenerant is passed into the tank 83 through the upper port 90 and passes through the resin bed 88 in a down-flow direction as shown by the arrow 125. This counter current allows the top of the resin bed which should be the cleanest part to be cleaned first by the virgin regenerant liquid and then allows regenerant to clean the other more contaminated lower portions of the resin beads 87. The regenerant waste 128 exits the tank 83 through the lower port 86.

[0039] The regenerant waste from the tank 83 can be stored in a storage facility, sent to a recycling facility, or treated further. Optionally, the regenerant waste 128 can be passed to a conventional metal ion or compound removal system which removes the concentrated metal ions. One such process or removal is electrowinning. Other metal ion removal processes which can also be used include, for example, precipitation of the metals, nanofiltration and other methods. [0040] The resin beads 87 in the tank 83 comprise an ion exchange resin material that is selected based on the composition of the slurry 108. For example, the resin beads 87 can comprise ion exchange material selected to have properties that can enhance or impede the removal of particular ions from the slurry 108, for example, ions such as copper, cobalt, tungsten, and other metals. In one version, the resin beads 87 contain strong acid cation functional groups. It is desirable for the resin beads 87 to have an ion exchange capacity per cycle of from about 0.1 to 5 kg of an extracted metal such as copper.

[0041] The resin beads 87 can also be selected to provide resistance to chemical attack by the oxidizers present in the CMP waste. For example, the oxidizers present in the slurry 108 typically comprise compounds such as hydroxylamine, KMnO₄, KIO₄, H₂O₂, and NO₃ ^". These oxidizers attack the cross-linked structure of the resin beads 106 and progressively degrade the resins. Resin beads 87 capable of withstanding such oxidation attack include, for example, divinylbenzene resins from strong acid cation functional groups. Resin beads 87 having such characteristics are available from many ion-exchange manufacturers, such as Rohm and Haas, Philadelphia, PA or Purolite Company, BaIa Cynwyd, PA.

[0042] The resin beads 87 can also be selected to be resistant to the entry of solid particles from the slurry 108 into the structure of the resin beads 87. For example, the slurry particles can include metal and dielectric particles abraded away from the substrate being polished as well as abrasion particulates used in the CMP polishing solution. However, the structure of the resins beads 87 should allow permeation of solutes into and through the resin structure. These conflicting goals are accomplished by using as resin beads 87 comprising a gel and sulfonic polymeric catalyst in a crosslinked di-vinyl-benzene structure.

[0043] The resin beads 87 should comprise ion exchange material that enhances the ability of their functional groups to selectively exchange metal ions onto the ion exchange material of the resin beads 87. For example, suitable ion exchange materials include those listed in U.S. patent Publication no. 2003/0044335, entitled "Method and apparatus for Metal Removal Ion, filed on 01/03/2001 , assigned to BOC Edwards and incorporated by reference herein in its entirety. The ion exchange functional groups should also overcome the effect of chelating agents (e.g., EDTA, citric acid) that form complexes with the metal ions so that the metal ions can exchange with ions from the resin beads 87. The functional groups should further exchange metal ions for slurries having wide pH ranges from about 2 to about 6.

[0044] In one version, resin beads 87 capable of meeting these diverse properties comprise a crosslinked divinylbenzene structure. Vinylpyridine resin structures provide superior resistant to oxidization by oxidizing agents present in the solution than conventional resins cross-linked by divinylbenzene. As another example, the resin beam ion exchange material can also be a poly-4-vinylpyridine resin and its derivatives thereof. The poly-4-vinylpyridine resins and their derivatives selectively and preferentially exchange transition and heavy metals, which is advantageous when the slurry contains aluminum or aluminum oxides, and it is desirable to remove the copper ions from the slurry without losing ion exchange capacity by removal of aluminum. A suitable resin is styrene divinylbenzene copolymer, available from aforementioned Rohm and Haas. In another example, resins such as Reillex 402 and Reillex 425, available from Reilly Industries, Inc, Indianapolis, Indiana, are also suitable. Yet other resins are, for example, described in U.S. patent nos. 5,582,737; 5,449,462; and 5,539,003; all to Horowitz et al., which describe phosphonic acid based ion exchange resins; all of which are all incorporated herein by reference in their entireties. The resin is selected to provide hazardous material removal efficiency, for example, copper removal efficiency, of at least about 95%. In one version, the resin can be used with resin bead size of from about 0.1 mm to about 1 mm, and even from about 0.5 mm to about 0.7 mm.

[0045] Figure 2A is a detailed schematic top view of an exemplary embodiment of a top diffuser 120a used in the CMP slurry treatment apparatus 100 shown Figure 3. Figure 2B shows a detailed schematic top view of an exemplary embodiment of top diffuser 120a having a plurality of slots 132 supported by the basket 121 of Figure 2A. The top diffuser 120a comprises a basket 121 (as shown in Figure 2A) which has a hollow support cylinder 122 with an elongated slit 123 that extends the length of the cylinder 122. The terminus 129 of the basket 121 screws into a receiving socket (not shown) in the tank 104 to serve as a fluid inlet or outlet. A plurality of outwardly extending circular ledges 126 are spaced apart from one another along the length of the cylinder 122. The circular ledges 126 number from about 2 to about 10. Each circular ledge 126 is sized to hold a cylindrical diffuser section 127 having a plurality of slots 132. In one version, the slots 132 have a gap width of at least about .1 mm, for example, about .2 mm.

[0046] Figure 3 is a schematic diagram of another embodiment of a CMP slurry treatment apparatus 100. The CMP slurry treatment apparatus 100 comprises a plurality of the ion exchange columns 102a, 102b, which can be used to provide a point-of-use (POU) waste treatment system for treating slurry 108, which can be located directly at the point of use location of a CMP polisher 20 (see Figure 13). The CMP slurry treatment apparatus 100 receives slurry 108 from the output of the CMP polisher 20 and holds the slurry in a slurry tank 140. The CMP slurry treatment apparatus 100 employs a fully redundant "lead-lag" configuration, in which a plurality of ion exchange columns 102a, 102b, typically from 2 to 6 columns, is used to provide substantially continuous CMP waste treatment without too much shut-down time for maintenance. In the version shown, the CMP slurry treatment apparatus 100 has two ion exchange columns 102a, 102b. Ion exchange column 102a comprises a main tank 104a and a polisher tank 104b. Ion exchange column 102b comprises a main tank 104c and a polisher tank 104d. When referring to components of the ion exchange columns 102a and 102b as a group, the components will be designated by a common name and hyphenated number henceforth. For example, tanks 104a-d refer to main tanks 104a, 104c and polisher tanks 104b, 104d. Each tank 104a-d has a lower port 110a-d with a bottom diffuser 118a-d and upper port 114a-d with a top diffuser 120a-d, respectively. In one embodiment, each of the top diff users 120a-d may be identical. In another embodiment, each of the top diffusers 120a-d may be slightly different. However, the basic features, such as slots 132 for example, as shown in Figures 2A, 2B for top diffuser 120a are representative of all top diffusers 120a-d. Additionally, the bottom diffusers 118a-d may differ in design from the top diffusers 120a-d. In another embodiment, the bottom diffusers 118a-d may be identical to the top diffυsers 120a-d. The tanks 104a-d each contain an ion exchange resin bed 105a-d comprising resin beads 106a-d capable of exchanging non-hazardous ions for metal or other hazardous ions in the slurry 108. In the main tanks 104a and 104c, the lower ports 110a, 110c and bottom diffusers 118a, 118c are in tubes 142a, 142c, respectively, which extend into the tanks.

[0047] In each of the ion exchange columns 102a, 102b, the tanks 104a and 104c serve as main tanks, and the tanks 104b and 104d serve as polisher tanks. The polisher tanks 104b, 104d are located downstream of, and fluidly connected to, the main tanks 104a, 104c via the conduits 134a, 134b, respectively. In this system, slurry 108 from a CMP polisher is passed through a first ion exchange column 102a for treatment while the second ion exchange column 102b is being regenerated and vice versa. In each ion exchange column 102a, 102b, the main tanks 104a, 104c remove the bulk of the metal or other undesirable ions, and the polisher tanks 104b, 104d further reduce the metal ion concentration in the slurry 108 outputted from the main tanks 104a, 104c by more than an order of magnitude while also removing trace elements present in the slurry 108. The tanks 104a-d all contain the same resin beads 106a-d as previously described for resin beads 87 in Figure 1 , which can be, for example, crosslinked styrene divinylbenzene copolymer. The columns 102a, 102b with the combined system of polisher tanks 104b, 104d and main tanks 104a, 104c provide a copper concentration in the treated slurry 112 of less than about 0.5 ppm, and even less than about 0.2 ppm, and typically from about 0.1 to about 0.2 ppm. The capacity per cycle of each ion exchange column 102a, 102b ranges from 0.1 to 5 kg of extracted copper, depending on the chemistry of the incoming slurry 108 and the ion exchange capacity of the ion exchange columns 102a, 102b.

[0048] The CMP slurry treatment apparatus 100 further comprises a controller 144 that may be remotely located in a control panel or control room and controlled with remote actuators. The controller 144 may be a microcontroller, microprocessor, general-purpose computer, or any other known applicable type of computer. The controller 144 typically comprises a suitable configuration of hardware and software to operate the components of the CMP slurry treatment apparatus 100. For example, the controller 144 may comprise a central processing unit (CPU) that is connected to a memory and other components. The CPU comprises a microprocessor capable of executing a computer-readable program. The memory may comprise a computer-readable medium such as hard disks, optical compact disc, floppy disk, random access memory, and/or other types of memory. An interface between a human operator and the controller 144 can be, for example, via a display 145, such as a monitor, and an input device 149, such as a keyboard. The controller 144 may also include drive electronics such as analog and digital input/output boards, linear motor driver boards, or stepper motor controller boards (not shown). The application and integration of controllers 144 is well known and will not be further detailed herein.

[0049] During an ion exchange cycle, the controller 144 operates either one of the pumps 146a, 146b to pass an upflow of slurry 108 through either one of the ion exchange columns a,b to exchange non-hazardous ions for metal or other hazardous ions from the slurry 108. For example, in an ion exchange cycle, the controller 144 can operate the pump 146a to pump slurry 108 from the slurry tank 140 to the ion exchange column 102a. The ion exchange column 102a receives the slurry 108 through the tube 142a, and the slurry 108 passes through the bottom diffuser 118a to exit the lower port 110a into the main tank 104a. The slurry 108 passes across the main tank 104a as an upflow (in an upward flow direction opposing gravity, as indicated by the up arrow for slurry 108 ) through the resin beads 106a of the resin bed 105a, exits the upper port 114a through the top diffuser 120a, and then passes through the conduit 134a to the polisher tank 104b. The upflow is provided at a flow rate sufficient to fluidize the resin bed 105a to assist in the interaction of metal ions and the ion exchange surface of the resin beads 106a while allowing resin beads flow downwards in the tank 104a due to gravity. Most of the metal in the slurry 108 is extracted by the resin beads in the tanks 104c, 104d at this stage.

[0050] After treatment in the main tank 104a, the slurry 108 is passed to its associated downstream polisher tank 104b which removes residual traces of undesirable ions and compounds. The slurry 108 enters the polisher tank 104b through the lower port 110b via the bottom diffuser 118b, upflows through the resin beads 106b of the resin bed 105b and exits the upper port 114b through the top diffuser 120b to the drain conduit 136 which takes treated slurry to drain 138. By having two different ion exchange columns 102a, 102b, each comprising a main tank 104a, 104c and a polisher tank 104b, 104d, when ion exchange column 102a needs to be regenerated, ion exchange column 102b is used for ion exchange and vice versa. Operation of ion exchange column 102b is the same as operation of ion exchange column 102a.

[0051] As one example, slurry 108 containing copper ions was treated in ion exchange columns 102a, 102b. The copper removal efficiency of the main tanks 104a, 104c was found to be typically above 95%, and the polisher tanks 104b, 104d installed downstream of the main tanks 104a, 104c further reduce the copper concentration by more than an order of magnitude, resulting in an overall copper concentration in the treated slurry of less than from about 0.2 ppm, or even less than from about 0.1 ppm. The ion exchange capacity per cycle allows removal of from about 100 gram to 5 kg of copper, depending on the chemistry of the slurry 108 and the capacity of the tanks 104a-d. In one version, the main tanks 104a, 104b reduce the pH level of the slurry 108 being treated by at least about 0.3, and more typically from about 0.4 to about 0.7. The lower pH level of the slurry passed into the polisher tanks 104b, 104d, allow the resin beads 106 in the polisher tanks 104b, 104d to more efficiently extract ions from the slurry 108 as the lower reduced pH level improves the ion exchange capacity of the resin beads 106. In this way the entire ion exchange column 102a or 102b functions more efficiently with two tanks.

[0052] The controller 144 switches operation from ion exchange treatment to regeneration of ion exchange columns 102a,b automatically upon receiving a signal from the detectors 148a, 148b which indicate detection of high levels of the metal, such as copper, in the treated or partially treated slurry 108. The detectors 148a, 148b can be a pH level detectors to detect when the treated slurries emanating from one of the tanks 104a-d has an excessively high pH level. The detectors 148a, 148b can also be metal concentration detectors to detect an excessively high level of metal, such as copper, in the treated slurry. In one version, the detectors 148a, 148b are located between the main tanks 104a, 104c and the polisher tanks 104b, 104d so that exhaustion of the resin beads 106a, 106c in the main tanks 104a, 104c can be detected prior to the exhaustion of the resin beads 106b, 106d in the polisher tanks 104b, 104d. This provides the further advantage of reducing the chances of metal ion breakthrough in which CMP slurry containing excessively high levels of metal is released into the external environment. A suitable detector 148a, 148b to detect copper levels in the treated slurry comprises a colorometric copper analyzer, for example, a dual cell Tytronics model manufactured by Galvanic Applied Sciences Lowell, MA.

[0053] In one example, the controller 144 switches to regenerant when it detects a steep increase in copper concentration measured in the treated slurry emanating from the upper port 114a of the main tank 104a, for example, an increase of about 10 times the concentration of copper in the treated slurry per 100 gallons of slurry flowing through the main tank 104a, which is an increase of an order of magnitude. At this time, the main tank 104a is switched over to regenerant mode to regenerate the ion exchange capability of the resin beads 106a in the main tank 104a, and the slurry 108 is passed through the main tank 104c of the second ion exchange column 102b for ion exchange. Thus, the controller 144 switches flow of the slurry from the first ion exchange column 102a to the second ion exchange column 102b upon detecting a 10 fold increase in copper concentration per 100 gallons of slurry flow in the treated waste emanating from the upper port 114a of the first ion exchange column 102a. The controller 144 can also be programmed to switch flow of the slurry from the first ion exchange column 102a to the second ion exchange column 102b upon detecting a change in pH level of the slurry of less than 0.5 after the slurry exits the main ion-exchange tank of the first ion exchange column 102a.

[0054] In the regenerant mode, the metal ions, for example, copper ions entrapped in the resin beads 106a are stripped off the resin when the pH of regenerant 109 solution is in the range of from about 0.6 to about 0.8. During the regeneration cycles, the controller 144 controls the pump 146c to pass regenerant 124 through the resins in the main tanks 104a, 104c and polisher tanks 104b, 104d in a downflow direction to regenerate the resin beads 106a-d. The CMP slurry treatment apparatus 100 can also have a regenerant tank 150 which contains a regenerant 124 such as a dilute acid solution, for example, sulfuric acid diluted with water, which is passed through the resin beads 106a-d in the tanks 104a-d. The dilute sulfuric acid is used to generate a low pH solution for resin regenerant. As one example, the regenerant 124 flow rate is set at about 1 gallon per minute (gpm) to provide enough time for the resin beads 106a-d to exchange metal ions for protons. Upon the completion of the regenerant cycle, the tanks 104a-d can be flushed with distilled water to remove residual acid remaining in the resin beads 106a-d. The regenerant tank 150 can have a volume of from about 10 to about 118 gallons.

[0055] Resin selection can be further problematic when the slurry 108 contains complex and unpredictable composition of particles, chelating agents, organic and inorganic surfactants and oxidizers, which when passed into the ion exchange column 82, for example, undesirably affect the resin beads 87 and the fluid dynamics of the ion exchange column 82. For example, Figure 4A is a graph showing the change in upstream pressure of the slurry 108 from a CMP polisher as it is passed through the ion exchange column 82 with ion exchange processing time. The graph shows the rapid increase in slurry liquid pressure upstream of the ion exchange column 82 which reduces flow rates through the column. The pressure build-up is seen by the rise at a time of approximately 12:26 hours and again in the time of approximately 20:00 hours. Figure 4B is a graph showing the change in pH of the treated CMP slurry over ion exchange processing time. Analysis of the two graphs in Figures 4A and 4B indicated that a rapid slurry fluid pressure build occurred when a CMP slurry having a low pH was passed into the ion exchange column 82. When the pressure in the ion exchange column 82 exceeded 35 psi, at 20:00, the ion exchange process was stopped, and examination of the ion exchange column 82 revealed that the top diffuser 89 was clogged with its slots 81 plugged with resin beads 87 and with no visual evidence of silica gel formation.

[0056] The cause of this pressure buildup is not fully understood but it is believed that the ion exchange column 82 changes the pH of the slurry 108 as it passes through the resin beads 87 to lower the pH level to about 3 to about 4, which is enough to cause gelling and agglomeration of solid particles in the slurry, due to pH shock. Thus, an ion exchange slurry chemistry specifically used to extract copper from the slurry can cause gellation and agglomeration of particles in the slurry. This gellation is further exacerbated by binding agents present in the slurry which glue together the resin beads 87. Furthermore, the turbidity between the input slurry 108 and output treated slurry 112 did not significantly change, indicating that the pressure buildup was not a result of particles being trapped in the resin beads 87 and ion exchange column 82 of the CMP slurry treatment apparatus 100. However, it was observed that the slots 81 of the top diffuser 89 of the ion exchange column 82 became plugged by solids each time the pressure buildup occurred, the plugging solids being an agglomeration of resin bead fines and fragments, CMP polishing pad and substrate debris, and slurry particles. The entrapped agglomerates in the slots 81 of the top diffuser 89 contributed to the pressure buildup problem. Based on these experimental results and observations, a process was developed to reduce pressure build-ups in the ion exchange of copper from the slurry 108.

[0057] Initially, a top diffuser 89 having narrower slots 81 sized less than 0.2 mm was used. While this diffuser worked well for some slurries 108, the passage of other types of slurries through the slots 81 resulted in extensive entrapment of agglomerated solids in the slots. It was determined that the entrapped agglomerates in the slots 81 could not be easily dislodged even by pulsing the flow of the slurry 108 in forward (or upward) and reverse (or downward) flow directions. The slot 81 plugging appeared to be a "self- filtration" phenomena in which trapped materials further reduced the remaining open flow paths causing more of the agglomerated solids to further plug up the slots 81. The variation of slurry 108 flow rate over time caused by a pump duty cycle of 50%, resulted in flow fluctuations which further enhanced the migration of protected fines and debris through the resin bed 88 and into the slots 81 of the top diffuser 89. Furthermore, some treated slurry streams contained relatively large particulates, such as polishing pad debris, abrasive particles, or other large particulates resulting from abrasion of the substrate. These large particulates caused "bridging" of gaps between resin beads 87 in the slots 81 of the top diffuser 89 leading to the formation of mats and occluding the slots 81. Higher concentration slugs of slurry solids which occurred during tool dumps or intensive polishing steps, also caused rapid accumulation of these particulates on the top diffuser 81 and in the resin bed 88, resulting in undesirable pressure buildup.

[0058] Using fluidized bed experiments, it was determined that the slurry flux, that is the flow rate per unit area, produced higher local velocities about the slots 81 of the top diffuser 89 which more rapidly entrapped the agglomerated particles. The higher flux rate also resulted in the volume of the resin bed 88 increasing and causing the resin beads 87 to be forced against the slots 81 resulting in a further increase in pressure of the slurry 108 in the ion exchange column 82. It is also determined that higher flux rates of the slurry 108 flushed out particles which had settled in the resin bed 88 and which subsequently contributed to the agglomerated particles entrapped in the slots 81 of the top diffusers 89. Thus, in one version, the slurry flow rate into the ion exchange column 82 was reduced to the lowest stable rate that provided continuous operation without pressure buildup. The ion exchange column 82 was operated at the lower flow rates to determine if they actually increased the volume of slurry that could be processed between required top diffuser 89 cleanings. If a higher total volume of slurry 108 could be processed between cleaning cycles, it would allow more efficient use of the ion exchange column 82 even though a lower flow rate of slurry is being processed. This is because the diffuser cleaning cycles result in downtime during which no slurry 108 is processed which is undesirable.

[0059] Figure 5 is a graph showing the flow rate (line (a)) through a ion exchange column 82 and the pressure upstream (line (b)) of the ion exchange column 82 as a function of the CDA pressure of the pump used to pump slurry through the ion exchange column 82. In this experiment, the CMP slurry treatment apparatus 100 was used to process the slurry 108 originating from a CMP polisher 20 (see Figure 13) which provided a slurry flow rate of from about 1 to about 2 g/min. The CMP slurry treatment apparatus 100 had a pump with a pumping capacity of 4 g/min which was operated at about 40% to about 50% of its duty cycle to avoid the overfilling the tank 83. In operation, the instantaneous flow rate through the ion exchange column 82 was 4 g/min, while the average flow rate was 2 g/min to match the flow rate of the incoming slurry 108. It was determined that by reducing the driving CDA pump pressure, the instantaneous flow rate was reduced from about 16 to about 18 l/min down to from about 7 to about 8 l/min. At a CDA pump pressure of about 30 psi, the slurry flow rate through the ion exchange column 82 was reduced to about 10 l/min. Pressures below 30 psi were found to generate pump instabilities and cause stalling of the pump. At these lower instantaneous flow rates, the pump duty cycle approached 100%. After operating the ion exchange column 82 at reduced slurry flow rates for 15 days, the average pump pressure was found to be about 13.2 psi with an average flow rate of 10.1 l/min, compared with an average pressure of 35.2 psi and flow rate of 13.7 l/min for the initial conditions. Less than 4 pressure build-up spikes were observed compared to 8 to 10 build-up spikes observed for the same period of time under conventional higher flow rates. This demonstrates that reducing instantaneous flow rates to levels of less than 10 l/min, and even from about 7 to about 8 l/min, substantially reduces pressure build-ups.

[0060] The top and bottom diffusers 89, 85, which are currently used have slots 81 , 84, respectively, that are sized at widths of about 0.2 mm. These slots 81 , 84 are at least 50% bigger in width than the slots 81 , 84 of the initial top and bottom diffusers 89, 85 and were^xfound to reduce pressure build-up by about 5-10 psi. Figure 6 is a graph of the flow (dotted line) or pressure (solid line) over time for a top diffuser 89 having smaller slots 81 as shown by the area (d) versus a top diffuser 89 with bigger slots 81 as shown in areas (e) and (f), which were placed in an ion exchange column 82. It is seen that the top diffuser 89 with bigger slots 81 provided a steady flow rate with reduced pressure fluctuations as compared to the conventional top diffuser 89 with smaller slots 81. The average pressure level also dropped considerably to provide higher overall flow rates when using the top diffuser 89 having larger slots 81. In one embodiment, larger slots 81 , 84 sized at widths of about .2 mm or larger for top and bottom diffusers 89, 85 may be used for ion exchange column 82. Additionally, slots 81 may also refer to slots 132 for all top diffusers 120a-d used in ion exchange columns 102a, 102b, and the slots 132 may be sized at widths of about .2 mm or larger.

[0061] In another solution, a polisher tank 104b, 104d having a larger diameter was used to further reduce the plugging and pressure build-up problems. In this example, a polisher tank 104b, 104d having a diameter of 88 mm (12 in) was used compared to a previously used polisher tank 104b,d having a diameter of 200 mm (8 in). The larger polisher tank 104b, 104d was made of polyester and provided by Pentair, Golden Valley, MN.

[0062] In yet another solution to the plugging problem, which can be used in combination with the aforementioned top diffusers 120a-d with larger slots 132, or separately, the volume of the resin beds 105b, 105d of a polisher tank 104b, 104d is set such that a top gap region 152b, 152d (see Figure 3) of each polisher tank 104b, 104d has a volume (also referred to as empty gap volume) of from about 20% to about 60%, or even about 40%, of the volume of each resin bed 105b, 105d. The ratio of the volume of each resin bed 105b, 105d to the empty gap volume is at least about 50%, or even from about 60% to about 80%. The total volume of the polisher tanks 104b, 104d is typically at least about 2 ft³, and more typically from about 1 ft³ to about 4 ft³.

[0063] Figures 7A and 7B show another solution to the plugging problem. Filler beads 154 are added to tank 83 (which can be main tank 104a, 104c and/or polisher tank 104b, 104d in ion exchange columns 102a,b) so that the top diffuser 89 is protectively covered by the filler beads 154 during upflow of slurry 108 through the tank 83 of ion exchange column 82 as shown in Figures 7A and 7B. The filler beads 154 occupy a volume in the tank 83 and separate the resin beads 87 from the top diffuser 89. The filler beads 154 cover the resin beads 87 to fill a second volume of the tank 83 which is on top of a first volume of resin beads 87, and there is further a gap between the filler beads 154 and the top of the tank 83. In the example shown, the filler beads 154 were placed overlying the resin bed 88 of resin beads 87 in tank 83 to reduce penetration of resin beads 87 into the slots 81 of the top diffuser 89 during a pressurized upflow of slurry 108, as shown in Figure 7B. In one version, the filler beads 154 occupy a total volume of about 60% of volume of the tank 83. In this version, the ratio of the volume of the filler beads 154 to the volume of resin beads 87 is from about 10% to about 40%, and the ratio of the volume of the gap to the combined volume of the filler beads and ion exchange beads is from about 30% to about 40%.

[0064] During regenerantion of the resin beads 87 in which a downflow of regenerant 124 is passed through tank 83, the resin beads 87 and filler beads 154 are compressed down toward the bottom diffuser 85 as shown in Figure 7A. For a tank 83 having a volume of 6 ft³, a suitable volume of filler beads 154 is at least about 0.8 ft³; however, when the resin beads 87 are used in the tank, the inert filler volume is 0.4 ft³. For a tank 83 having a length of 53 inches, this was equal to filling about 7 inches of the tank 83. At least one plug/manual clean cycle is run to determine if filler beads 154 increase volume processed between cleanings. For example, Figure 8A is a graph of the flow (a) or pressure (b) over time of distilled water passed through an ion exchange column 82 having filler beads 154, and Figure 8B shows the flow (a) or pressure (b) over time when a slurry 108 is passed through the same ion exchange column 82. The pressure and flow rates remained constant, at about 4-5 psi and 15 l/min in both cases, indicating that the filler beads 154 completely prevented blockage of the slots 81 of the top diffuser 89 by the resin beads 87. In one version, the filler beads 154 comprise a non-reactive material such as polypropylene.

[0065] A filter 147 (see Figure 3) which is capable of extracting particles sized 118 micron or less can be positioned at the slurry pumps 146a, 146b to further reduce resin bead 106a-d and agglomerate build-up on the top diffuser 120a-d. The filter 147 can be located at the inlet side of the slurry pumps 146a, 146b. A suitable filter 147 can be a filter disc having perforations with a micron rating of from about 100 microns to about 300 microns, which corresponds to a mechanical grit size of about 60.

[0066] A process step of "backwashing" the resin beads 87 in the tank 83 (which can be main tank 104a, 104c and/or polisher tank 104b, 104d) can also be used during the ion exchange process to flush out the solid particulates coagulated in the tank 83 and on the resin beads 87. During the backwash step, a high flow rate of distilled water is flushed through the ion exchange column 82 in the reverse direction for a short period of time of about 60 to about 90 seconds. Figure 9 is a graph of the flow or pressure over time using a top diffuser 89 having slots 81 with widths sized about .2 mm and with backwash cycles. Periodic backwashes were conducted every 2 hours and included a first backwash (1^st BW)₁ second backwash (2^nd BW), and third backwash (3^rd BW). Thus, it is seen that pressure build-up is reduced after each backwash cycle, and periodic backwashes have the effect of limiting pressure fluctuations and increasing slurry flow rates. Figure 9 shows that flow rates of between 16 l/min and 18 l/min were maintained when using periodic backwashing.

[0067] One regeneration method maximizes the life of the resin bed 88 of the tank 83 (which can be main tank 104a, 104c and/or polisher tank 104b, 104d) used to remove metals from a CMP waste stream. Initially, prior to performing a regenerant cycle, a first upflow of deionized water is pumped through the tank 83 through lower port 86. The upflow expands the volume occupied by the resin beads 87 in the tank 83 to loosen particles entrapped between the resin beads 87 which become entrapped because of compressive forces exerted by the pressure of the slurry 108 flowed through the tank 83. The loosened particulate solids pass upwards through the top diffuser 89 to exit the tank 83 via the upper port 90. The upflow of deionized water can be provided at a flow rate of about the same as the flow rate used to pass the slurry 108 through the ion exchange column 82. In one version, the deionized water is passed through the tank 83 in an upflow at a flow rate of from about 4 to about 6 g/min for a tank 83 having a volume of from about 4 to about 8 ft³. For example, a flow rate of from about 7 to about 10 l/min can be used for a tank 83 having a volume of 6 ft³. The upflow is continued until the volume of water passed through the tank 83 is approximately equal to at least about 1 times the fluid volume of the tank 83, or even about 2 times the tank 83 volume.

[0068] Once the particles have been loosened and partially removed, in an optional step, a basic solution is passed through the tank 83 to dissolve silica and other inorganic deposits on the resin bed 88 and flush the now mobilized waste particles remaining in the tank 83 out of the resin bed 88. The basic solution comprises dilute NaOH, NH₄OH or KOH. For example, the basic solution comprises NaOH in molar concentration of from about 0.5 to about 1. The basic solution can be made with 2% NaOH. The flow rate through the resin bed 88 in the upflow direction is from about 0.25 to about 0.5 times the slurry treatment flow rate, which is the flow rate of the slurry through the tank 83 during treatment of the slurry. A suitable flow rate is at least about 2 l/min, or even from about 3 to about 6 l/min. In this step, a total volume of basic solution of at least about 2, and more typically 3 times, the tank 83 fluid volume is passed in an upflow direction though the tank 83.

[0069] After the basic solution flow, a second upflow of deionized water can be passed in an upflow direction through the tank 83 to rinse out the basic solution from the resin bed 88 and remove any remaining particulates. The deionized water is passed at a total volume of from about 1 to about 2 times the fluid volume of the tank 83.

[0070] Thereafter, a regenerant 124 comprising an acidic solution is introduced into the tank 83 in a downflow direction via the upper port 90 to regenerate the resin beads 87. The acidic solution reacts with the copper ions captured by the resin beads 87 and removes the copper from the resin bed 88. The acidic regenerant step also replaces the exchanged metals on the resin functional groups with protons to regenerate the ion exchange capacity of the resin beads 87. A suitable acidic solution comprises dilute H₂SO₄ at concentration of from about 2 wt% to about 6 wt%, or even about 4 wt%. The regenerant waste 128 passes through the resin bed 88 and exits through the lower port 86 through the bottom diffuser 85. Because the regenerant waste 128 is substantially free of solid particulates, the wear on the bottom diffuser 85 is reduced. The flow rate of the acidic solution in the downflow direction is at least about 0.25, and more preferably at least about 0.5 times, the slurry treatment flow rate. For example, the acidic solution flow rate can be at least about 1 l/min, or even from about 3 to about 6 l/min, to provide enough fluid for the resin beads 87 to exchange metal ions out of the resin beads 87. [0071] After the regenerant step is completed, a third upflow of deionized water is flushed though the tank 83 via the lower port 86 in an upflow direction indicated by arrow 111 to flush out the acidic solution from the ion exchange column 82 and adjust the pH of the resin beads 87 back to their operating levels. The deionized water also serves to push out any resin beads 87 that may be trapped in the slots 84 of the bottom diffuser 85 back into the tank 83. The deionized water is passed at a flow rate of from about 7 l/min to about 10 l/min, and in a total volume which is 1 to 2 times the fluid volume of the tank 83.

[0072] It should be noted that the concentration levels of basic or acidic solution, and the selection of a particular base or acid can vary with the type of resin beads 87 being used and the type of ions removed from the slurry 108. Also, the previous upflow of the basic solution can be performed at a different frequency than the regenerant frequency and is typically lower. In some applications, the upflow cleaning step is performed once per month, while the regenerant process is performed weekly. Thus, the present regenerant and cleaning process should not be limited to the examples provided herein to illustrate the process, and include other variants of the process or other chemicals as would be apparent to those of ordinary skill in the art.

[0073] In yet another version of the CMP slurry treatment apparatus 100, a pretreatment apparatus is used to implement a pH transformation protocol to adjust the pH level of a slurry 108 prior to ion exchange. In this version, the slurry 108 comprises metal compounds, as well as metal complexes and chelating agents, and is treated using a two-stage treatment process. An exemplary embodiment of an CMP slurry treatment apparatus 100 comprising a pretreatment apparatus 401 , as shown in Figure 10, comprises a pH transformation tank 402, pH adjustment tank 404, valves 420-424, conduits 430-433, and a controller 440 for controlling the valves 420-424. The CMP slurry treatment apparatus 100 is integrated with the CMP polisher 20 by, for example, being disposed underneath a tabletop of the CMP polisher 20, or it can be a stand-alone unit remotely located from the CMP polisher 20. [0074] The pH transformation tank 402 comprises a vessel having an inlet connected to the CMP polisher 20 and an outlet connected to an inlet of the pH adjustment tank 404 via a conduit 430. The conduit 430 can include a pump 452 and/or a valve 421 disposed along its length to control the flow of the slurry 108 from the pH transformation tank 402 to the pH adjustment tank 404. The pH transformation tank 402 and pH adjustment tank 404 may both be made of a corrosion resistance material, such as for example, polyvinylchloride (PVC).

[0075] The pretreatment apparatus 401 is in fluid communication with an ion exchange column 82 (which can be ion exchange column 102a or 102b) via the conduit 431. In another embodiment, the pretreatment apparatus 401 may be in fluid communication with a plurality of ion exchange columns via additional conduits. The conduit 431 can also include a pump 450 and/or a valve 424 disposed along its length to control the flow of the slurry from the pretreatment apparatus 401 to the ion exchange column 82. The CMP slurry treatment apparatus 100 also includes a conduit 433 disposed to an inlet of the pH adjustment tank 404, which is connected to a base supply 412 to deliver a base to the pH adjustment tank 404. The conduit 433 may include a pump (not shown) and/or a valve 423 disposed along its length to control the flow of the base from the base supply 412 to the pH adjustment tank 404. The CMP slurry treatment apparatus 100 further includes at least one pH monitor 408 disposed in the pH transformation tank 402 and/or pH adjustment tank 404, which is in communication with the controller 440. A suitable pH monitor 408 comprises, for example, a pH electrode and meter readout available from Honeywell, New York, NY. The controller 440 controls the overall operation of the CMP slurry treatment apparatus 100 including the flow rate of the slurry, the operating pressure of the system, and the sequencing of the valves 420-424.

[0076] In operation, slurry 108 flows from the CMP polisher 20 to the pH transformation tank 402 where copper compounds and copper complexes in the slurry 108 are chemically transformed into elemental copper ions. To operate the CMP slurry treatment apparatus 100, the chemistry of the slurry 108 is evaluated to ensure proper transformation of metal compounds into metal ions in a reasonable time period. For example, when the slurry 108 contains a chelating agent, such as ammonia, the chelating agent chemically reacts with abraded metal polished off from the substrate, such as copper, to form soluble metal complexes that compete with the metal ions for extraction by the ion exchange resin. A chelating agent is an organic compound that is capable of forming coordinate bonds with metals through two or more atoms of the organic compound, and the compound formed by a chelating agent and a metal is called a chelate.

[0077] The pH level desirable to be attained by the slurry 108 before passing it to the ion exchange column 82 depends upon the chemical form that a metal takes on at particular pH levels. A Pourbaix diagram provides the thermodynamically most stable, and thus most abundant, form of a metal at a given potential and pH condition. The Pourbaix diagram for a copper-water system at a constant temperature is shown in Figure 11. In this diagram, vertical lines separate species in acid-base equilibrium, horizontal lines separate species in redox equilibria not involving hydrogen or hydroxide ions, and diagonal boundaries separate species in redox eqilibria in which hydroxide or hydrogen ions are involved. Dashed lines enclose the practical region of stability of the water solvent to oxidation or reduction. As shown in the diagram, at pH levels higher than about 6, copper exists predominantly in the form of CuO and Cuθ₂, which are insoluble copper compounds in water. At pH levels lower than about 6, copper predominantly exists in the form of copper ions in water. Note that the Pourbaix diagram provides equilibrium conditions but does not indicate the time to reach equilibrium. While the Pourbaix diagram is specifically directed to a copper-water system, it should be noted that other element systems, such as those comprising nickel, titanium and aluminum, will produce corresponding Pourbaix diagrams, and the present process and apparatus also covers these systems.

[0078] Thus, referring to the Pourbaix diagram, an ion exchange method to extract copper from slurry 108 requires the pH level of the slurry to be less than about 6 so that the copper in the system remains in a soluble ionic form that can be exchanged with other non-hazardous ions. Thus, a pH transformation process is used to adjust the pH level of the slurry 108 to the levels required by the ion exchange method. Generally, the pH transformation process comprises adding an acidic or basic solution to the slurry 108 to adjust the pH level to a desired pH range. However, simply adjusting the pH level of the slurry 108 to conform to the pH level required by the ion exchange process can be inadequate because of the chemical complexity of the slurry. For example, it has been observed that the pH level to trigger a chemical transformation from a copper compound to copper ions depends on the type of chelating agent present in the slurry 108. The presence of chelating agents, such as ammonia or EDTA, have been found to lead to the formation of soluble copper complexes which compete with the metal or copper ions in the slurry 108 in the ion exchange process. Thus, simply adjusting the pH level of the slurry 108 by treating the slurry to obtain a pH value between 3 and 6, as suggested by the Pourbaix diagram, may not necessarily obtain the proper pH range for metal extraction from the slurry 108.

[0079] In one version of the present solution, the original slurry 108 has a basic pH level of from about 5 to about 11 , due at least in part to the high concentrations of copper compounds in the waste. A pH transformation process suitable for such a slurry 108 comprises collecting the slurry in the pH transformation tank 402, and adding an acidic solution from an acid supply 410 to the pH transformation tank 402 to lower the pH level of the slurry 108 to a intermediate transformation pH level. Typically, the acidic solution comprises sulfuric acid, but can also comprise other acids well known in the art. The transformation pH level is selected to be the lowest pH level that triggers the chemical transformation. For copper, the transformation pH level is selected to be from about 1.5 to about 5. The pH monitor 408 monitors the pH level in the pH transformation tank 402 and relays that information to the controller 440, which then controls the flow of the acid from the acid supply 410 to the pH transformation tank 402 via the valve 420. In the pH transformation step, the original pH level of the slurry is adjusted to a pH level of from about 1.5 to about 5 to transform the metal compound to metal ions.

[0080] During the transformation, the copper compounds and complexes dissolve and form elemental copper ions. Depending on the pH level, the time required to complete the transformation varies. It has been observed that when maintained at a transformation pH level of between about 1.5 to about 5, the time required to complete the transformation of metal compounds to metal ions can be from about 1 to about 10 minutes. In one version, the transformation time is approximately about 20 minutes. Accordingly, the size of the pH transformation tank 402 should, for a given slurry flow rate, be selected to ensure that the slurry 108 is retained in the pH transformation tank 402 for a sufficient time period to complete the transformation. In one version, the slurry is collected in a tank sized sufficiently large to collect substantially the entire volume of slurry produced by a CMP polisher during the transformation time taken to chemically transform the metal compound to metal ions. For example, for a slurry flow rate of from about 2 to about 3.5 g/min, the pH transformation tank comprises a volume of from about 20 to about 35 gallons. As another example, for a slurry flow rate of between about 1 and about 3 g/min, the pH transformation tank 402 should have a volume of at least 50 gallons in order to retain the slurry 108 for a sufficient time to allow transformation of all the slurry.

[0081] After the desired pH level is attained in the pH transformation tank 402, the pH transformed slurry 108 is transferred from the pH transformation tank 402 to the pH adjustment tank 404 using valve 421 and pump 452. In the pH adjustment tank 404, the pH level of the slurry 108 is further adjusted to a metal removal pH level which is suitable for efficient metal removal utilizing ion exchange techniques. For example, the ion exchange column 82 is most efficient for slurries having a pH level of between about 2 and about 5, and even from about 3 to about 4.5. If the pH level is too low, the ion exchange process is too slow and can in fact reverse resulting in the elution of trapped copper. If the pH level is too high, copper ions are not available for exchange. Accordingly, in the pH adjustment step, the pH level of the slurry is adjusted to a pH level of from about 2 to about 5, or even from about 3 to 4.5 to all the metal ions to be efficiently exchanged onto the ion exchange resins. In the pH adjustment tank 404, a base from the base supply 412 is added to the slurry 108 to increase the pH level of the slurry 108 from the transformation pH level to the metal removal pH level. Typically, the base comprises potassium hydroxide, sodium hydroxide, or other basic solutions. The pH monitor 408 monitors the pH level in the pH adjustment tank 404 and relays that information to the controller 440 by sending a pH level signal to the controller 440, and in response the controller 440 adjusts the amount of base (or acid as described below) passed to the tank by controlling the flow of the base from the base supply 412 to the pH adjustment tank 404 via the valve 423.

[0082] Once the pH level of the slurry 108 has been adjusted to the metal removal pH level suitable for ion exchange in the ion exchange column 82, the adjusted slurry 108 is passed to the ion exchange column 82 using pump 450 and valve 424. There, the metal ions in the slurry 108 are removed and the treated slurry 112 is metal-free and can be sent to a drain 138 for disposal or further processed. The metal ions trapped by the CMP slurry treatment apparatus 100 can be retrieved through a regenerant process. During regeneration, an acid solution from the acid supply 410 is passed through the resin beds 105a,b of the ion exchange column 82 to disassociate the metal ions from the resin material. The regenerant waste 128 comprising metal ions is passed to a metal removal system for disposal or further processing of the metal residues.

[0083] A slurry 108 having acidic pH levels can also be transformed to optimal pH levels. Acidic slurry often has pH levels ranging from about 2.5 to about 4.5. In this version, the reverse steps are performed, and a basic solution is added to the pH transformation tank 402 to lower the pH level of the slurry 108 to a transformation pH level. Typically, the basic solution comprises sodium hydroxide, but can also comprise other bases. Again, the transformation pH level is selected to be about the highest pH level that triggers the chemical transformation. The pH monitor 408 monitors the pH level in the pH transformation tank 402 and relays that information to the controller 440, which then controls the flow of the base from a base supply that substitutes the acid supply 410, to the pH transformation tank 402. Once the transformation is completed, i.e., the copper compounds and complexes have dissolved to transform the pH of slurry 108, the transformed slurry 108 is passed to the pH adjustment tank 404. In the pH adjustment tank 404, the pH level of the slurry 108 is adjusted to a metal removal pH level suitable for the CMP slurry treatment apparatus 100 to efficiently remove copper ions, by the addition of an acidic solution, such as sulfuric acid. [0084] In the version shown in Figure 12, the pretreatment apparatus 501 comprises a single collection tank 503 that includes a plurality of baffles 508 that separate a pH transformation zone 502 and a pH adjustment zone 504. This version requires fewer components, e.g., one collection tank 503 and one less pump 452, than the previously described version. The CMP slurry treatment apparatus 100 includes a conduit 434 disposed to an inlet of the pH transformation zone 502 which is connected to an acid supply 410 (or base supply) to deliver acid (or base) to the pH transformation zone 502. The conduit 434 may include a pump (not shown) and a valve 420 disposed along its length to control the flow of the acid from the acid supply 410 to the pH transformation zone 502. The CMP slurry treatment apparatus 100 also comprises a controller 440 and a pH monitor 408 which is disposed in each of the pH transformation and pH adjustment zones 502, 504, respectively. The pH monitor 408 is in communication with the controller 440 which controls the overall operation of the slurry treatment apparatus 501 including the flow rate of the slurry, the operating pressure of the system, and the sequencing of the valves 420-424.

[0085] In operation, slurry 108 flows from the CMP polisher 20 to the pH transformation zone 502 where copper compounds and copper complexes in the slurry are chemically transformed into elemental copper ions. The pH monitor 408 monitors the pH level in the transformation zone 502 and relays that information to the controller 440, which then controls the flow of the acid from the acid supply 410 to the transformation zone 502 via the valve 420. During transformation, the baffles 508 impede the flow of slurry from the pH transformation zone 502 to the pH adjustment zone 504 and also create turbulence that accelerates pH transformation. The pH chemical transformation is completed by the time the slurry 108 reaches the pH adjustment zone 504. Depending on the pH level, the time required to complete the pH transformation varies. Accordingly, the size of the pH transformation zone 502 should, for a given slurry flow rate, ensure that the slurry is retained in the pH transformation zone 502 for a sufficient time period to complete the pH transformation. For example, for a typical slurry flow rate of between about 1 and about 3 gallons per minute, the pH transformation zone 502 should hold at least 50 gallons in order to retain the slurry for approximately 15 minutes. In the pH adjustment zone 504, the pH level of the slurry 108 is adjusted to a metal removal pH level suitable for the CMP slurry treatment apparatus 100 to efficiently remove copper ions, for example, by the addition of controlled amounts of a base to the pH adjustment zone 504.

[0086] An exemplary CMP polisher 20 which can be used to planarize a surface of a substrate to, for example, remove a thickness of a surface layer on the substrate, expose underlying features, flatten the substrate, or remove surface defects, is shown in Figures 13 and 14. The exemplary embodiment of a CMP polisher 20 is provided to illustrate the present invention; however, the present invention should not be limited to this exemplary embodiment and other CMP polishers as apparent to those of ordinary skill are within the scope of the present invention.

[0087] Figure 13 is a schematic perspective view of a CMP polisher. Generally, the CMP polisher 20 comprises a lower machine base 22 having a tabletop 28 that supports one or more polishing stations, including for example, a first polishing station 25a, a second polishing station 25b, a final polishing station 25c, and a transfer station 27. The transfer station 27 serves multiple functions, including receiving individual substrates 10 from a loading apparatus (not shown), washing the substrates, loading the substrates into carrier heads 80, receiving the substrates 10 from the carrier heads 80, washing the substrates 10 again, and transferring the substrates 10 back to the loading apparatus. One polishing system that is used to perform CMP is the Mirra® CMP System available from Applied Materials, Inc., located in Santa Clara, California.

[0088] Each polishing station 25a-25c includes a rotatable platen 30 having a polishing pad 92 disposed thereon. Each platen 30 may be a rotatable aluminum or stainless steel plate connected to a platen drive motor (not shown). In a typical arrangement, the first and second stations 25a and 25b may include a polishing pad comprising a fixed-abrasive pad, and the final polishing station 25c may include a polishing pad 92 comprising a non-abrasive pad. The polishing stations 25a-25c also include a pad conditioner apparatus 40 which has a rotatable arm 42 holding an independently rotating conditioner head 44 and an associated washing basin 46. The pad conditioner apparatus 40 maintains the condition of the polishing pad so that it will effectively polish the substrates. The polishing stations 25a and 25b having fixed-abrasive pads disposed thereon do not require the pad conditioner apparatus since fixed-abrasive pads generally do not require conditioning. However, as illustrated, each polishing station may include a conditioning station if the CMP polisher is used with other pad configurations.

[0089] The polishing stations 25a-25c also have a polishing solution arm 52 that includes two or more supply tubes to provide the polishing solution and/or water to the surface of the polishing pad. The polishing solution arm 52 delivers the polishing solution in an amount sufficient to cover and wet the entire polishing pad. Each polishing solution arm 52 also includes several spray nozzles (not shown) that can provide a high-pressure fluid rinse of the polishing pad at the end of each polishing and conditioning cycle. Furthermore, two or more intermediate washing stations 55a, 55b, and 55c containing washing fluid are positioned between adjacent polishing stations 25a, 25b, and 25c to allow cleaning of a substrate as it passes from one station to another.

[0090] A rotatable multi-head carousel 60 is positioned above the lower machine base 22. The carousel 60 includes four carrier head systems 70a, 70b, 70c, and 7Od. Three of the carrier head systems receive or hold the substrates 10 by pressing them against the polishing pads 92 disposed on the polishing stations 25a- 25c. One of the carrier head systems 70a-70d receives a substrate from and delivers a substrate 10 to the transfer station 27. The carousel 60 is supported by a center post 62 and is rotated about a carousel axis 64 by a motor assembly (not shown) located within the lower machine base 22. The center post 62 also supports a carousel support plate 66 and a cover 68.

[0091] The four carrier head systems 70a-70d are mounted on the carousel support plate 66 at equal angular intervals about the carousel axis 64. The center post 62 allows the carousel motor to rotate the carousel support plate 66 and orbit the carrier head systems 70a-70d about the carousel axis 64. Each carrier head system 70a-70d includes one carrier head 80. A carrier drive shaft 78 connects a carrier head rotation motor 76 (shown by the removal of one quarter of the cover 68) to the carrier head 80 so that the carrier head 80 can independently rotate about its own axis. There is one carrier drive shaft 74 and motor 76 for each head 80. In addition, each carrier head 80 independently oscillates laterally in a radial slot 72 formed in the carousel support plate 66. The carrier head 80 holds the substrate 10 against the polishing pad 92, evenly distributes a downward pressure across the back surface of the substrate 10, transfers torque from the carrier drive shaft 78 to the substrate 10, and ensures that the substrate 10 does not slip out from beneath the carrier head 80 during polishing operations.

[0092] Figure 14 is a cross-sectional view of the tabletop 28 and platen 30 of Figure 13 showing a conduit to pass slurry to a CMP slurry treatment apparatus. A circular fence 210 surrounds the rotating platen 30 and captures polishing slurry 108 centrifugally expelled from the platen 30. The slurry 108 stream from the platen 30 flows down to a trough 220 formed in the tabletop 28 and then flows into the drain channel 240. The drain channel 240 comprises a channel 242 in communication with a drain pipe 244 connected to the tabletop 28 by screws 246 passing through a flange 248 of the drain pipe 244 and threaded into the bottom of the tabletop 28. The slurry 108 from the platen 30 flows under gravity through the drain channel 240 and through the drain pipe 244 to the CMP slurry treatment apparatus 100.

[0093] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

In the Claims:

1. A slurry treatment apparatus for removing metal from a slurry of a CMP polisher, the apparatus comprising: two or more ion exchange columns, each column comprising: a main tank comprising: a lower port to receive and pass therethrough an upflow of slurry; resin beads capable of treating slurry having a pH of between about 2 and about 6; an upper port to release the treated slurry; a polisher tank fluidly connected to the upper port of the main tank, and the polisher tank comprising: a lower port to receive and pass therethrough an upflow of slurry; resin beads capable of treating slurry having a pH of between about 2 and about 6; and an upper port to release the treated slurry; a controller adapted to control operation of the ion exchange columns; and one or more detectors in communication with the controller, and wherein each detector is adapted to monitor the slurry.

2. The apparatus according to claim 1 , further comprising a pretreatment apparatus to chemically transform insoluble metal compounds in the slurry to metal ions prior to delivery of the slurry to the ion exchange columns.

3. The apparatus according to claim 1 , further comprising a regenerant tank comprising regenerant to regenerate the resin beads.

4. An ion exchange column for removing metal ions from the slurry of a CMP polisher, the ion exchange column comprising one or more tanks fluidly connected, each tank comprising: an enclosed volume including a top wall and a bottom wall, wherein the volume comprises a first volume and a second volume; resin beads which fill the first volume which is disposed below the second volume; a lower port disposed at the bottom wall to receive slurry which flows through the tank from bottom to top during ion exchange; an upper port disposed at the top wall to exit the treated slurry; and a diffuser disposed at the upper port.

5. The ion exchange column of claim 4, wherein the second volume of the tank comprises an empty gap volume, and wherein the ratio of the first volume comprising resin beads to the empty gap volume ranges from about 50% to 80%.

6. The ion exchange column of claim 4, wherein the second volume of the tank further comprises filler beads which fill the second volume and a gap between the second volume and top wall of the tank.

7. The ion exchange column of claim 6, wherein the filler beads comprise polypropylene.

8. The ion exchange column of claim 6, wherein the ratio of the volume of the gap to the combined volume of the filler beads and resin beads is from about 30% to about 40%.

9. The ion exchange column of claim 4, wherein the resin beads comprise a styrene divinylbenzene copolymer..

10. A slurry treatment apparatus for removing metal compounds from the slurry of a CMP polisher, the apparatus comprising: a base supply source; an acid supply source; ⁾ a pretreatment apparatus comprising: a pH transformation tank comprising: an inlet to receive a slurry having an original pH level; a vessel to hold the slurry; an acid inlet to receive an acid solution from an acid supply source in an amount sufficient to adjust the original pH level of the slurry to a transformation pH level of from about 1.5 to about 5 thereby forming a transformed slurry comprising metal ions; a pH adjustment tank comprising: an inlet to receive the transformed slurry; a vessel to hold the slurry; a base inlet to receive a base solution from a base supply source in an amount sufficient to adjust the pH level of the slurry to a metal removal pH level of from about 2 to about 5, thereby forming a pH adjusted slurry which allows removal of the metal ions by ion exchange material; a controller adapted to control valves that regulate fluid flow from the acid and base supply sources and between the pH transformation and adjustment tanks; one or more pH monitors adapted to monitor the pH of the slurry in the pH transformation and/or pH adjustment tanks, and wherein each monitor is in communication with the controller; and one or more ion exchange columns in fluid communication with the pretreatment apparatus and which extract metal ions from the pH adjusted slurry.

11. A slurry treatment apparatus for removing metal compounds from the slurry of a CMP polisher, the apparatus comprising: a base supply source; an acid supply source; a pretreatment apparatus comprising: a collection tank comprising: a slurry inlet to receive a slurry having an original pH; a pH transformation zone comprising an acid inlet to receive an acid from an acid supply source in an amount sufficient to adjust the original pH level of the slurry to a pH level of from about 1.5 to about 5 during passage of the slurry through the pH transformation zone, thereby forming a slurry comprising metal ions; a pH adjustment zone to receive the transformed slurry after the transformation process, and comprising a base inlet to receive base from a base supply source in an amount sufficient to adjust the pH level of the slurry to a metal removal pH level of from about 2 to about 5 during passage of the slurry through the pH adjustment zone, thereby forming a pH adjusted slurry which allows removal of the metal ions by ion exchange material; and a plurality of baffles which separate a pH transformation zone and a pH adjustment zone a controller adapted to control valves that regulate fluid flow from the acid and base supply sources; one or more pH monitors adapted to monitor the pH of the slurry in the pH transformation and/or pH adjustment zones, and wherein each monitor is in communication with the controller; and one or more ion exchange columns in fluid communication with the pretreatment apparatus and which extract metal ions from the pH adjusted slurry.

12. A method of treating a CMP slurry by ion exchange, the method comprising: receiving a slurry having an original pH level, the slurry comprising metal compounds; a pH transformation step, comprising: monitoring the pH level of the slurry; controlling one or more valves to flow an acid solution to the slurry; flowing an acid solution to the slurry to adjust the pH of the slurry; adjusting the original pH level of the slurry to a transformation pH level, whereby the metal compounds are transformed to metal ions; flowing the pH transformed slurry to another zone or vessel for pH level adjustment; a pH adjustment step, comprising: monitoring the pH level of the slurry; controlling one or more valves to flow a base solution to the slurry; flowing a base solution to the transformed slurry to adjust the pH of the slurry; adjusting the pH level of the slurry to an adjustment pH level, whereby the metal ions can be efficiently exchanged onto the ion exchange resins; controlling on or more valves to flow the pH adjusted slurry to an ion exchange material; an ion exchange step, comprising: flowing slurry upwards through an ion exchange column comprising a main tank, and said tank comprising resin beads ; exposing the slurry to an ionic exchange resin to remove metal ions from the slurry; a regeneration step, comprising: monitoring slurry treatment condition following ion exchange for a first ion exchange column; detecting a regeneration condition for a first ion exchange column; switching slurry flow to a second ion exchange column; and regenerating the first ion exchange column while treating slurry in the second column.

13. The method of claim 12, wherein the transformation pH level is from about 1.5 to about 5, and the adjustment pH level is from about 2 to about 5.

14. A method of regenerating an ion exchange column comprising one or more exchange tanks, the method comprising: flowing deionized water upwards through the ion exchange column, whereby solid particles entrapped between the resin beads are loosened and removed from the column; flowing an acidic solution downwards through the ion exchange column whereby metal ions entrapped in the resin beads are exchanged with non- hazardous ions to regenerate the resin beads, and flowing deionized water upwards through the ion exchange column, whereby the acidic solution is flushed out of the column.

15. The method of claim 14, further comprising a step after flowing deionized water and before flowing an acidic solution, the step comprising: flowing a basic solution upwards through the ion exchange column to dissolve silica and other inorganic deposits; and flowing deionized water upwards through the ion exchange column, whereby the basic solution is flushed out of the column.

16. The method of claim 15, wherein the basic solution comprises a dilute solution of one of the following: NaOH, NH₄OH, and KOH.

17. The method according to claim 14, wherein the acidic solution comprises H₂SO₄ at a concentration of about 2 wt% to about 6 wt%.

18. A method of treating a CMP slurry by ion exchange, the method comprising: receiving a slurry having an original pH level, the slurry comprising metal compounds; an ion exchange step, comprising: flowing slurry upwards through an ion exchange column comprising a main tank, and said tank comprising resin beads; exposing the slurry to an ionic exchange resin to remove metal ions from the slurry; a regeneration step, comprising: monitoring slurry treatment condition following ion exchange for a first ion exchange column; detecting a regeneration condition for a first ion exchange column; switching slurry flow to a second ion exchange column; and regenerating the first ion exchange column while treating slurry in the second column.

19. The method of claim 18, wherein the regeneration condition comprises a 10 fold increase in copper concentration per 100 gallons of slurry flow through the column.

20. The method of claim 18, wherein the ion exchange step further comprises flowing slurry across filler beads in an ion exchange column.